Mobilization of seed reserves and environmental control of seed germination

4 Mobilization of Seed Reserves and Environmental Control of

Seed Germination Rakesh Pandey Vijay Paul and Malavika Dadlani

I 1 INTRODUCTION The development of embryo and associated tissues depends upon assimilates supplied by the mother plant up to maturation of seeds Later the vascular connecti on between the mother plant and seeds are severed and the desiccation occurs Dry seed with moisture content of 10-15 per cent has a remarkably low metabolism However the seed is equipped with all those structures substances and information that can help in its proper establishment in the new surroundings The new develo pmental cycle begins with imbibition and resumption of metabolic activity During seed germination the embryo is heterotrophic ie it primarily depends upon the seed reserves Thi s phase when plan t is establishin g and still dependent on reserves can be called as seedling phase Seedling establishment occurs with the gain in photosynthetic competence and switch from heterotrophic to photoautotrophic growth

The mobilization of seed reserves depends on suitable environment and has implications for success of natural vege tation agriculture and industry It is an imp ortant development event and involves three major processes-breakdown of seed reserves transport of breakdown products to the em bryo and synthesis of new materials from the breakdown products (Srivastava 2000) The present chapter will highlight these processes during germi nation its regulation and environmental factors affecting seed germination

I

I Mobilization of Seed Reserves and Environmental Control of Seed Germination 85

2 SEED GERMINATION AND ITS TYPES

Germination can be defined as the emergence and development from the seed embryo of the essential structures that indic ate the seeds ability to produce a normal plant under favorable conditions (AOSA 2000) The process of germination leads to emergence of the growing parts of the seed or the seed itself from the ground Based on this the seed germination has been cla ssified into two type s-s-epigeal and hypogeal (Fig 1)

Cotyledons

s Hypogeal Epigeal germination germination

Fig 1 Types of seed germination-epigeal and hypogeal

In epigeal germination the cotyledons arc raised out of the soil by elongation of the hypocotyl and often become green and photosynthetic In hypogeal ger mination the hypocotyl remains short and compact but the epicotyl elongates tp raise the first leaves out of the soil while the cotyledons remain beneath the soil Some examples are given in Table I

TABLE 1 List of some crop seeds with_epigeal and hypogeal germination

Epigeal germination Hypogeal germination

Onion (Allium cepa) Whe at (Triticum aestivum ) ~c

nt French bean tPha seolus vulgaris) Maize (Zea lIIays)

Groundnut (Arachis hypogea ) Pea tPisum sativumi ~ r

s Cucumber (Cucurbita pepo) Broad bean (Vida faba )

iC Barley (Hordeum vulgare)

g lA J COMPOSITION OF SEEDS

The seeds consi st of four major storage reserves as related to the provision of energy du ring h germination These are starch proteins fats and mine rals located in the storage tissues - ie

endosperm or cotyl edons The composition of some seeds is presented in Table 2 r The seed carbohydrates predominantly occu r in the form of starch Monocots are the major

starch accumulating seeds (eg rice wheat maize etc) Starch is a polymer of glucose which may be linear as in amylose or branched as in amyl opectin Amylose con sists of a 1-4 linked glucose molecul es and amylopectin has side chains attached with a 1-6 linkag e About 50-75 per cent of starch in cereals is in the form of amylopectin and 20-25 per cent in the form of amylose

86 Seed Science and Technology

Reserve starch is located in di fferent tissues eg endosperm in cereal and cotyledo ns in legume In the endos perm of cereal the starch granules are embedded in a matrix of storage protein and surrounded by the wall s of the dead cells In the living cotyled on cells of legumes the membranes or amyloplasts get di sintegrated at seed maturity and the granules are exposed di rectly to the cytoplasm or cell s Other fo rms of carbohydrate s are structural in nature es cell wa ll ga lactomannans and hcmicclluloses whi ch have to be broken dow n for radi cle emergence duri nlt

bull b gcrmmauon

TABLE 2 Types of food reserves and the major storage structures in some crop seeds

Species Average composition ( dry wt) Major storage tissue

Protein

Maize (Zea lIla ys )

Wheat (Tri ticum aestivuni i

Barley tH ordcum vul gare)

Rice tO rvia sativa

Field pea (Pisuni sat ivuni )

Peanut (A rachis hypogea)

Soybean (Glycine lIl ax )

Rapeseed iBrassica WPllS )

II

12

12

10

24

31

37

21

Fat

5

2

3

2

6

48 17

48

Starch

75 Endosperm

75 Endo sperm

76 Endosp erm

80 Endosperm

56 Co tyledon

12 Cotyledo n

26 Cotyledon

19 Cotyled on

Source Bewley and Black ( 1978)

Storage o il is sy nthes ized in the form of tria cyl gly cerol (TAG) duri ng the growth o r I

e mbryos of o ilsccds Triacylg lycero ls are fatty acid esters of glycerol and are synthesized wit hin the unit membrane bila yers of endo plas mic reticulum (ER) Th e lipids are e nc losed in half me mbrane and subseque ntly bud off fro m the ER These organell es arc ca lled oil bodies or o lcoso rncs Oi l bodi es con sist of a ph osph oli pid monolayer e mbedded with prote ins cal led o lcosins which prev ent the se organel les fro m coales cing There fo re formation of large oil bodi es is prevented and a high surface-to-volu me ratio is maintained Some impor tant fatt y acids present in the TAGs ca n be sa turated (stearic acid ) or unsaturated types (o le ic ac id linoleic acid linolenic acid) (Table 3)

TABLE 3 Fatty acid composition of TAGs in some oilseeds

Crop Fatty acids ( of total)

Stearic acid Oleic acid Linoleic acid Linolenic acid

Soybean

Groundnut

Sunfl ower

Brassica

6

2

4

I

23

50

26

6 1

52

31

64

20

8

0

0

10

Plants accumulate protein reserves in dev eloping seeds The proteins are stored in spherica l organ e lles called protein bo dies In ma ture d ry seeds storage prote ins are prese nt in the

chnology Mobilization of Seed Reserve s and Environmental Control of Seed Germination 87

I legume e mbryo ax is as we ll as in the storage tissues suc h as e ndospe rm Th e protein bodies arc large

orcin and (2- 10 urn in diam eter) sphe rica l orga ne lles bound by a sing le membrane Th ey arc o nly formed

embrancs duri ng seed developm ent in spe cifi c storage tissues (eg endosperm or cotyledo n mes ophyll)

Iy to the Most of th e conte nt of the protein bodi es can be ac co unted fo r by the rese rve pro tein s howe ver

e ll w all these organ elles a lso co nta in phytin lect ins and certa in acid hyd rol ases T he seed sto rage proteins

ec durin g have been c lass if ied by Osb orne ( 1924) based on their so lu bil ity (Ta ble 4 j D icot seed s predomina ntly acc umulate globulins and in ce rea ls prolamins acc umulate duri ng the mi ddle and late maturati on stag es

reds TAB LE 4

tge tissu e Compos iti on of storage protein in some seed s

Types of seed storag e Solubility of seed protein protein

Wheat Maize PeaIm

Im Albumins Watcr 9 4 40 Im Globulins Sa il 1 2 60 Im Glutclins Dilute acidicalkaline sol 46 39 0 lIJ Prolamins Alcohol 40 55 0 HI

n Th e seeds are also rich in min er al nutri ent s suc h as phosphoru s magn esium calciu m iron man ganese pot assium etc Phosph oru s is pre sent as part o f ph ytin in the protein bodies which is anionic in na ture and hence rem ain s ass ociated wit h catio ns suc h as magnesium calcium iron ma nganese pot assium

row th of S~~~JCv) xl within 4MOBILIZATION of SEED STORAGE RESERVES AND THEIR UTILIZATION J in half DURING GERMI NATION iodics or

The switchi ng of nutri tion al dependence of seed from internal to external so urces and a transition IS called

to the autot rop hic phase of li fe cycle is a gradua l proc ess Due to the ready availability andil bodies util ization of energy rich reserves stored in the see d the seedling phase sh ows a hyper-exponentials present re lative gro wth rate (RGR) ie rate of dry matte r increase per unit initi al dry matter Aftercic ac id seedli ng phase the RGR tapers o ff (Hunt et al 1993) Thu s the seedling phase ha s a maximum re lati ve growth (RGRmax) and never ag ain in the life cyc le o f p lant such higher RGR values are ob se rved (F ig 2) A mthor ( 1989) also repor ted tha t it is dur ing seed ge rmination that the specific respiration rates (C0 2 re leased per gra m dry mass per hour ) reach their highest values in the enti rel ife cycle Th is ma y be an adapt ive fea ture of plan ts for proper establishment under varied environmenta l conditions so as to maintain a substantial plant population and species survival in

ic acid nature These high RGRs may he mechani stically ana logous to the launch of a space-shuttle which sho uld move up wards with an enorm ous thrust by burn ing many tons of fuels (02 and H2)

per second to overco me Earth s gravitationa l pu ll

The end poi nt o f seedling phase depends on the dep iction of see d reserves and it has been observed in pea and su nflower seeds (Hanley et al 2004) that the timing of RGRmax coincides with the exhaustion of coty led on reserves and the attainme nt of independen ce from cotyledons

pherical It highlights the role o f mobilization o f see d reserves for sustai ning the plant during early stages t in the Th ere fore the timi ng of RG Rmax ca n be used as the end of see dl irig phase


Crop Maturity

Seedling phase

Time (days) Fig 2 Maximum RGR reaches during seedling phase in plant life cycle (Hunt et el 1993)

The major mobilization of seed reserves takes place during the third phase of imbibition afte r the ge rmina tio n sensu stricto ie radi cle eme rgence Th er efore mobilization of food reserves is not strictly a co mpo nent of germination but a uniquely associated aspect

Ch an ges in different part s of see ds and their compositi on during ge rmination in many species have indicated the turnover of seed reserves (Fig 3) which indicates mobi lization

fro m the co ty ledo ns to the rapidly gro wing hypocotyl and othe r parts ie plumule radi cle and

e mb ryo

Protein Phytin Starch Fats Seed Reserves

Catabolism

Proteinases Phytase Amylases Lipase Enzy mes

1 1 1 1 Amino Inositol P0 - Glucose Fatty acids + Glyce rol Products Acids Ca2+ Mg2+

~ -Ox id ati on Glyoxylate pathway Gluconeogenesis 1 -

42

1 Utiliza tion and respiration Sucrose

Fig 3 Utilization of seed reserves during seed germination

41 Mobilizat ion of Seed Carbohydrates

411 Starch In en dosper m of cerea ls starc h degrad at ion takes place in a nonliving tissue-effectively in an acid ic apoplast ic env iro nme nt in wh ich no intracellular or intercell ular co mpartmcntation exists

v

I

Mob ilization of Seed Reserves and Environmental Con trol of Seed Germ ination 89

Both the amyloplast envelope and the plasma membrane disintegrate Degradation of starch granule is catalyzed by a-amylase Due to this the granules have abundant channels leading from pores on the surface to the interior During degradation-both in vitro and in the germinating cndosperm-they become deeply pitted with loss of internal material surrounding the channels before much of the surface has been attacked indicating an endoamylolytic attack The ashyglucosidase from cereal endosperm can also attack cereal starch granules and this enzyme and a-amylase interact synergistically to promote degradation of granules In cereal endosperm the

t degradation of glucans released from starch granules probably proceeds via limit dextrinase fJshyand a-amylase and a-glucosidase to maltose and glucose which can enter the embryo (Fig 4) These enzymes are either synthesized within surrounding cell layers or mobilized within the endosperm as degradation proceeds The synthesis of a-amylase enzyme takes place in the scutellum and is released to starchy endosperm The dissolution of endosperm generally commences adjacent to the scutellum and progresses as a front moving away from the scutellar face towards the distal end of the grain At later stage a-amylase is synthesized in the aleurone layer and secreted into the endosperm GA is synthesized by the embryo during germination and diffuses to the aleurone layer The enzyme fJ-amylase is not de novo synthesised and becomes activated after initial digestion of the starch by a-amylase Complete hydrolysis of amylose can be achieved by fJ-amylase and the limit dextrinases The dextrinases in barley are de novo synthesized whereas in rice they are synthesized during seed maturation and activated during germination Maltose is a major product of starch hydrolysis and is further broken to glucose by a-glycosidase (maltase) enzyme present in the embryo and aleurone layer Study of a knockout mutant of maize shows

Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase

Glucose-1-P i---- - ------- -------- --- shyUTP UDP-GlucoseI

--- ~ Pyrophosphorylase

UDP-Glucose + ppi (Pyrophosphate)

Fruetose -----lsucrose synthetase ---------------l~ Sucrose + UDP

Fig 4 Breakdown of starch in cereals

90 Seed Science and Techn f

that limit dextrinase is necessary for normal rates of starch degradation in the endosperm durin10

the early stages of germination (up to seven days) but not thereafter (Dinges et al 2003)

In monocot seeds the scutellum is a modified single cotyledon located between the endosperm and the embryo and plays important role during germination The epithelial cells of scutell um facilitate exchange between the embryo and the endosperm Glucose is absorbed from the endosperm and converted to ~uc ro se in the scutellum and transported to the em bryo

In legumes the hydrolysis of cotyledonary reserves commences after emergence and elongation of the radicle Starch degradation takes place within living cells of the cotyledons but probably not within the plastid in which the starch was synthesized The plastid envelope is believed to disintegrate prior to germination so that degradation occurs within the cytosol The initial slow phase is associated with activity of starch phosphorylase Then the more rapid degradation phase coincides with a and p-amylase activity There is a very substantial increases in a-amylase activity during the first few days of germination of starch-storing legume seeds and it is consistent with the idea that here too it is responsible for the attack on the starch granule Changes in the properties of starch during degradation in germinating pea seeds also point to an endoamylolytic attack However starch in cotyledons is extensively phosphorylated In mung bean seeds also the level of phosphate in the starch is comparable with that in leaves This imp lies a possible role for a recently discovered enzyme glucan water dikinase (GWD) in controlling starch degradation iri legumes (Ritte et al 2002) The starch of most cereal endosperms contains almost undetectably low levels of phosphate and here the GWD enzyme may not play role The enzyme GWD adds the P-phosphate group of ATP to either the 3- or the 6-carhon of a glucosyl residue of amylopectin

GWD

Amylose amp Starch PhosphorylaseAmylopectin -------------~~ Glucose-1-P + Limit dextrin (pea seeds)

UDP-Glucose UTP Pyrophosphoryla se

1 UDPGlc + Ppi (Pyrophosphate)

Fructose 1Su~rose Synthetase

Sucrose + UDP

Fig 5 Breakdown of starch in dicots (eg pea seeds)

The degradation of glucans produced from starch in germinating pea embryos is proposed to proceed via limit dextrinase and glu ean phosphorylase in the cytosol (Fig 5) Glucan pho sphorylase or starch phosphorylase enzym e catalyzes the conv ersion of the terminal glucosyl unit at the nonreducing end of glucan chains to glucose I-phosphate using inorganic phosphate It cannot pass o- L 6 linkages Activity of a cytosolic isoform of glucan phosphorylase is also low during seed development and then increases dramatically during the first fivedays of ge rmin ation

Mob ilization of Seed Reserves and Environmental Control of Seed Germination 91

r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I

Starch [shyt-------AY~P~(j

Sucrose

t Glucose

1 Glucan ---shy - -- Maltose

I________________________________ J Gluean shy - - - - - - Gluc-1 -(P)

(A) (B)

Fig 6 Pattern of starch mobilization in (A) cereal and (8) legume seeds (- - - - - indicate loss of membrane)The precise roles and importance of a-amylase and other starchshydegrading enzymes in metabolizing soluble glucans are still not clear (Adapted from Smithet al 2005)

The amyloplast membrane disintegrates so that starch degradation is catalyzed by cytosolic enzymes (Fig 6B) Sucrose synthesized from starch is exported from the starch-st oringcells to the growing root and shoot of the seedling

412 Degradatio n of cell walls complex carbohydrates and weakening of covering s tructures

The degradation of the cell walls of endosperm is required for starch mobilization The complex carbohydrates may be present as storage reserves or as structural features These consist of mannans and galactomannans Mannans consist of linear chains of (I ~4) p-Iinked mannosyl residues whereas galactomanns consist of linear chains of (1~4) p-linked mannosyl residues with single a-glalactosyl residues joined by (I ~6) linkages at intervals along the ch ain Som e legume seeds have storage carbohydrates in the form of glactomannan (eg endospermic legumes such as fenugreek)

In many seeds eg Arabidopsis tobacco tNicotiana tabacumi and tomato (Lycopersicon esculentum y the cell walls of the seed coat and endosperm act as mechanical barriers to radicle emergence The major cell wall components of the endosperm that surround the em bryo in seeds o f tom ato are galac tom annans Their influence on seed germinahility may co nfer do rmant state to the seeds In these seeds the radicle protrusion during germination requires weakening of the testa andor the endosperm covering the embryo Enzymes released from endosperm or radic le can fac ilitate the weakeni ng of these structural impediments for radicle pro trusion These enzymes ma y be re leased by the endosperm andor the radic le This localized weakeni ng of enclosing tissues may amhiguously e ither he considered as dormancy loss or part of ger mination The tissue dissolution increases the growth potential of emerging radicle Recent evidences have favoured the hatchi ng hy pothesis as postulated by Ikuma and Thiman (1963 ) that production of an enzyme enables the tip of the radicle to penetrate through the coat Evide nces for these hatching enzyme include the contribution of various cell-wall-modifying proteins and the hydrolytic enzymes sec reted by the endosperm eg 13-1 3-glucanase cndo -Bvl 4- mannases po lygalacturonase and exp ansin isoforrns (Leubncr-Metzgcr 2003 Nonagaki and Morohashi 1996 Chen and Bradford 2000 Nonogaki 2006)

Seed Science and Technolofll

In monocot seeds the intermediate layer between the absorptive epithilium of the scutelIum and the starchy endosperm consists of hemic elluloses (glucans containing -I 3 and P-I 4 links) This layer first undergoes digestion by enzyme endo-Bvglucanases and therefore makes the epithilium to come in contact with the starchy endosperm The endosperm cell walls which contain arabinoxylans P-l 3 and P-l 4 glucans are digested with the help of arabinoxylanases and glucanases The degradation of p-glucan can provide upto 18 per cent of the total glucose released during endosperm mobili zation in barley (Hordeum vulgare) (Fincher 1989) In this way the degradation of p-glucans can provide significant energy for seed germination

413 Regulation of storage starch mobilization

Regulation of storage starch mobilization has been precisely investigated in germinating cereal seeds In these plants the product of starch degradation (glucose) regulates expression of gibberellin genes-phytohormones controlling amylase enzyme synthesis (Thomas and Rodriquez 1994) These are further discussed in a later section (Section 51)

42 Mobilizat io n of Seed Storage Lip ids

The pathways and enzymatic activities of mobilization of the storage oil-were first elucidated in detail in castor bean Recent studies on biochemical genetics in the model oilseed species Arabidopsis have also provided insight in this aspect (Graham 2008) During seed germination mobilization of storage oil takes place from oil bodies (oleosomes) It involves p-oxidation the glyoxylate cycle partial tricarboxylic acid (TCA) cycle and gluconeogenesis These reactions take place in different sub cellular entities eg oil bodies glyoxysomes mitochondria and cytosol Electron micrographic studies also indicate physical association of oil bodies glyoxysomes and mitochondria during germination Glyoxysomes follow two kinds of fate in the lipid storing seeds In one type (eg castor bean endosperm) they disintegrate with reserve mobilization and in other (eg cotton and cucumber) they become photosynthetic

The first step in oil breakdown is catalyzed by lipases which hydrolyze TAG to produce free fatty acids (FAs) and glycerol The FAs then enter glyoxysomes where p-oxidation and part of the glyoxylate cycle occursThese 4-carbon compounds are then transported to the mitochondria where they can either be converted to malate and transported to the cytosol for gluconeogenesis or used as substrates for respiration (Fig 7) The pathway can be subdivided as foIlowsshy

(i) Breakdownof TAGs and import of FAs to glyoxysomes

(ii) p-Oxidation

(iii) Glyoxylate cycle and NADH regeneration and

(iv) Gluconeogenesis

421 Breakdown of TAGs and import to glyoxysomes Triacylglycerols (TAGs) are broken down to free fatty acids (FAs) and glycerol by an interfacial lipase enzyme associated with the oil body membrane The free fatty acids are then imported into glyoxysome via the COMATOSE (CTS) ATP-binding cassette (ABC) transporter protein located in the glyo xysomal membrane Long-chain FAs are activated in the cytosol and transported as acyl-CoA esters across the peroxisomal membrane by ABC transporters (Eastmond 2006 and Graham 2008) Mutation of the CTS locus results in seeds that are blocked in FA breakdown which strongly suggests that CTS is important in the transport of TAG-derived carbon into

Mobilization of Seed Reserves and Environmental Control of Seed Germination 93

peroxisomes The activation of FAs to fatty acyl-CoAs is essential for FA catabolism to proceed through p-oxidation

422 Peroxis omal p-Oxidation

In the glyoxysomes the acyl-CoAs undergo oxidative attack in a series of enzymatic steps at the C-3 or p-carbon position also known as the p-oxidation pathway Studies on endospermic castor

urn ks) theichsesose

bean seeds have provided information on the role of p-oxidation in the mobilization of storagehis oil reserves in oilseeds Completion of each p-oxidation pathway leads to the cleavage of an acetyl-CoA (two carbons C2) from the fatty acyl chain (acyl-CoA Cn) containing n carbon atoms and the remaining acyl-CoA (Cn-2) re-enters the p-oxidation repeatedly till complete degradation of the long-chain acyl-CoAs to C2 acetyl units The core group of p-oxidation enzymes therefore

cal acts on a range of similar substrates varying in chain length ie substrates with diminishing lin carbon chain length with each passage through the p-oxidation spiral This is achieved by two 4) alternative strategies either multiple isoforms with different chain-length specificities or alternatively

enzymes with broad substrate specificity

This core pathway requires enzymes acyl-CoA oxidase (ACX) multifunctional protein

In (MFP) and 3-ketoacyl-CoA thiolase (KAT) to catalyze oxidation hydration and dehydrogenation

es and thiolytic cleavage respectively of acyl-CoA The Multifunctional Protein (MFP) is an unusual

n protein as it contains four domains for distinct catalytic activities 2-trans enoyl-CoA hydratase L-3-hydroxyacyl-CoA dehydrogenase D-3-hydroxyacyl-CoA epimerase and il3 il2-enoyl-CoA isomerase Two of p-oxidation pathway enzymes 2-trans-enoyl-CoA hydratase and 1-3shyhydroxyacyl-CoA dehydrogenase are contained on the MFP These are often referred to as the core activities of the MFP catalyzing the hydration of 2-trans-enoyl-CoA to 3-hydroxyacyl-CoA and the subsequent oxidation of 3-hydroxy acyl-CoA MFP has a complex role in p-oxidation using different combinations of activities for the p-oxidation of saturated and unsaturated fatty acids The acyl-CoA oxidases catalyze the first step of oxidation of acyl-CoA to 2-trans-enoylshyCoA The reaction requires flavin adenine dinucleotide (FAD) as a cofactor to generate FADH2 which is then oxidized by flavoprotein dehydrogenase to produce hydrogen peroxide (HzOz) The dehydrogenase step requires NAD+ and generates NADH so a system is needed within the peroxisome to regenerate NAD+

Some seeds contain large quantities of unsaturated fatty acids particularly linolenic and linoleic acid both of which contain double bonds in the cis configuration at even carbons These require two additional activities of the multifunctional protein D-3-hydroxyacyl-CoA epimerase and the il3 il2-enoyl-CoA isomerase activity before the fatty acid can proceed through core pshyoxidation (Graham and Eastmond 2002)The enzyme 3-ketoacyl-CoA thiolase catalyzes the last step of FA p-oxidation which involves the thiolytic cleavage of 3-ketoacyl-CoA to acyl-CoA (Cn-2) and acetyl-CoA (C2)

The major end products of the peroxisomal p-oxidation spiral are HZ0 2 NADH and acetylshyCoA Hydrogen pero xide is potentially damaging to proteins lipids and DNA The catalase enzyme present in the peroxisomal matrix plays an essential protective role by breaking down HZ02 to molecular oxygen and water Plant peroxisomes also contain an ascorbate-dependent membrane bound electron transfer system that involves the oxidation and reduction of membrane bound ascorbate by ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDAR) respectively which results in the breakdown of H20 2 to water This prevents the HZ0 2 from


c(

ii c z o I U g E

Malate dehydrogenase

) (j) w z w Cl o w z o U J J Cl

- OOC-CH(OH) -H2-COOshy

r Malate

Fumarase

-OOC- CH =CH- COOshyFumarate

i Succinate dehydrogenase

-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome

Glycerol kinase -------------

CHpH I CHOH I CHpH Glycerol

GLYOXYLATE CYCLE

_- - --shy OOC - CH(OH) - CH2- COOshy- Malate

Triacylglycerol

CHi0 COCH2CH2RI CH20COGH2CHiR I CH200CH2CH2R

Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~

Fig 7 Mobilization of lipids during seed germination (Adapted from Graham 2008) MDH = Malate dehydrogenase APX amp MDAR = Ascorbate peroxidase and monodehydroascorbate reductase CTS = COMATOSE ATP-binding cassette transporter enzymes are shown in Italics

e TS Free fatty acid ~ Acyl-CoA synthetase

R - CH2- CH2- CO - S - CoA

ltfAcyl CoA (C) ~ ~02 n Ayl - CoA oxidase I - - H202 R - CH = CH - CO - S - CoA 12-trans-enoyl-CoA Multifunctional protein I HydrataseI

Hydy~~Hl -~~p~o~e middot ~~g dehydrogenase R - CO - CH2- CO - S - CoA

z l~_KetoaCY_COAi ~ 3-Ketoacyl-CoA thiolase

~ CH3-CO-S-CoA Acetyl CoA co - CH2- CH2- CO - S - CoA Acyl-CoA (Cn_2)

- - -~- - - ----- shy ---- shy -- shy -- shy ----- shy -- shy

- OOC-G H2-G(OH)(COO-)- CH(OH)-COOshy

~r Citrate ----- ~

OxaTo--shy y acetate -OO C-CH2-CO-COO-

Oxaloacetate

Isoicitrate shy Acomtasei

Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w

sphate C) 0 w zetone 0

sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase

Mobilization of Seed Reserves and Environmental Control of Seed Germination

escaping beyond the outer surface of the glyoxysomal membrane and causing leth al damage Thus catalase protects constituents of the peroxisomal matrix from oxidative damage and tne APXIMDAR system prevents H20 2 from escaping beyond the outer surface of the peroxisomal membrane and causing lethal oxidative damage during storage oil mobilization (Fig 7)

423 Glyoxylate cycle and NADH regeneration The acetyl-CoA derived from FA 13-oxidation is metabolized via the glyoxylate cycle to produce 4-carbon and 6-carbon compounds and these four-carbon compounds (malate oxaloacetate) may be used as substrates for respiration or transported to the cytosol for synthesis of sugars in a process called gluconeogenesis

Oxidation of the peroxisomal NADH (formed during 13-oxidation) is essential for the continued operation of FA 13-oxidation to regenerate NAD+ and it mu st occur inside the the peroxisomal membrane as it is impermeable to NAD(H) The reoxidation is catalysed by the glyoxysomal malate dehydrogenase (MDH) operating in the reverse direction (ie oxaloacetate to malate transformation) for the continued operation of 13-oxidation but it is not part of Glyoxylate cycle An ascorbate-dependent membrane bound electron transfer system also can oxidize NADH

424 Gluconeogenesis

The -fatty acid metabolism via 13-oxidation and glyoxylate cycle leads to formation of malate The four-carbon compounds eg malate from the glyoxylate cycle can be converted into hexose by gluconeogenesis and subsequently used for cell wall biosynthesis or converted into sucrose for transport to the growing seedling tissue Th is process is important in both endospermic oilseed species such as castor and non-endospermic species such as Arabidopsis whi ch store the bulk of their seed oil reserves in the embryo In many oilseeds also the disappearance of lipids is accompanied by the appearance of carbohydrates However lipids are not always converted to carbohydrates during germination

The major controlling step of gluconeogenesis is the production of phosphoeno l pyruvate (PEP) from oxaloacetate (OAA) and the regutatoryenzyme is phosphoenolpyruvate carboxykinase (PCK) (Penfield et al 2004) Another product of lipo lysis ie glycerol can also enter gluconeogenesis with formation of glycerol-3-phosphate (G-3-P) catalyscd by g lycerol kinase (GK) enzyme

425 Regulation of storage oil breakdown

A number of treatments viz exogenous supply of sugars result in decrease or blockage of storage oil breakdown and mobilization during post germinative seed ling gro wth (Graha m 2008) The nitrogen status of the seedlings also has a major impact on this effect a reduction of nitra te in the media leads to the enhancement of sucrose repression of oil break down Th us the carbon to nitrogen ra tio rat her tha n the carbohydrate status alone plays a predo minant role in the regulation of sto rage oil mobilization (Martin et al 2002)

T he phytohor mone abscisic acid (ABA) blocks see d germination in Arabidopsis bu t docs not completely inhibit lipid breakdown or the expression of genes tha t encode the key enzymes of FA 13 -o xidation or the g lyoxylate cy cle Storage o il mobilizati on is seve rely red uc ed in Arabidopsis mutants disrupted in either lipolysis of TAG transport of FAs into the g lyox yso rn cs act ivatio n of FAs inside the glyoxysome or in any of the co re reactions of 13-oxidati on Knowledge

96 Seed Science and TechnolofX

of the underlying biochemistry and metabolism of the breakdown as well as the synthes is of storage oil is essential for the development of new and improved oilseed crops that not only accumulate high levels of the desired oil but also use it efficiently to support vigorous seedling growth (Graham 2008 )

43 Mobilization of Seed Storage P rotein~

431 Proteases associated with Germination

The hydrolytic cleavage of peptide bonds is catalysed by peptidases (also called pepti de hydrolases or proteases or proteinases) These are further classified into endopeptidases which act on internal peptide linkages of proteins and exopeptidases which act on the carboxyl terminal peptide linkages The classification of endoproteinases is made on the basis of the active site residue The proteolytic reaction involves nucleophilic attack at the carbonyl carbon supported by donation of a proton to the NH group of the peptide bond which is being attacked In serine threonine and cysteine proteases the hydroxyl or sulfhydryl groups of the active-site amino acids act as the nucleophile during catalysis Plant cysteine proteases are major proteolytic enzy mes induced in plants for mobilization of nitrogen from storage proteins during germination These have broad substrate specificity Some specific names given to the germinaton related cysteine proteases are based on their plant origin eg oryzanin vignain legumain etc Papain was the first cysteine protease to be discovered in the latex and fruit of Carica papaya Papain-like enzymes are involved in protein degradation and N-mobilization during seedgermination and leaf senescence Serine carboxypeptidases also function during the mobilization of N-resources during seed germination

Proteolytic activity is a major life supporting function and majority of proteolytic activity takes place in the vacuoles During seed germination and seedling growth the protein storage vacuole is transformed into a lytic vacuole Many proteases are present in the lumen of plant vacuoles (Muntz 2003) Proteinases stored in protein storage vacuoles (PSY) start protein mobilization within a few hours of seed imbibition (Muntz 1996 Muntz et al 200 l Schlereth et al 2001) Cell fraction studies on seeds indicate that 75-80 per cent of the proteolytic activities are associated with the protein body fractions (Van der Wilden et al 1980) The protein degradation begins in radicle tips prevascular strands and in sub epidermal cell layers where growth and differentiation are initiated These reserves are not the major protein reserves and are nearly exhausted by the time of radicle emergence The functional vascular strands are established between axis and storage cotyledons The major seed protein reserves are therefore mob ilized during post germination by de novo synthesis of proteases The emptying protein storage vacuoles merge and transform into a fewor sing le central lytic vacuole

432 Protein mobilization There are at least three possible mechanisms of protein mobilization in germinating seeds as descri bed by Wang et al (2007)

(i) The protease and seed storage proteins are localized in the same vacuoles during seed development With the commencement of germination the stored proteases are activated and proteolysis starts

(ii) Proteases and storage proteins are stored within PSYs which contain three morphologicalIy and functionalIy distinct compartments-crystalIoids matrix and

M

s

97 chnology

uhcsis of not only seedling

peptide hich act terminal ive site nted by

serine 10 acids nzymes These ysteine be fi rst izymes scence seed

ctivity torage

plant rotein lereth olytic otein vhere

dare ished lized roles

s as

iced ited

ree md


globoid The matrix and crystalloid contain storage proteins while the globoids contain phytin and proteins for the lytic vacuole (LV) pathway With the commencement of germination these globoids get broken and there is release of proteases that act on matrix and cry stalloids in PSVs

(iii) The proteases are synthesized de novo during germination and are transported to PSVs through a secretory pathway The de novo synthesized proteases can also be transported from the ER to PSVs or alternatively through prevacuolar compartment (PVC) to the PSV for protein degradation (Toyooka et al 2000 Laval et al 2003)

In cereal grains the reserve proteins are stored in two tissues-majority is present in the starchy endosperm (about 70 per cent) and in the aleurone layers there is about 30 per cent of see d protein The cells of endosperm are non-living and the refo re require proteolytic enzymes either from aleurone layer following de novo synthesis or by activation of enzymes already synthesized in the endosperm during seed maturation The aleurone proteins are degraded by de novo synthesized proteinases and the released amino acids are used for synthesis of mo re hydrolytic enzymes which are released into the non-living starchy endosperm Therefore in the aleurone cells both processes-proteolysis and protein synthesis occur simultaneously These two processes are separated spatially with proteolysis occurring in the protein bodies and protein synthesis occurring in the cytoplasm

In dicots there are two phases of protein breakdown-the initial limited proteolysis phase and the later phase of massive uncontrolled proteolysis The initial limited proteolysis of proteins is mediated by specific cndoproteinases and the resulting peptides are then hydrolysed to free amino acids during uncontrolled proteolytic phase by the action of multiple less specific exopeptidases andor endopeptidases The protein storage tissue cells also undergo change to vacuole during the second phase Therefore limited proteolysi s and complete polypeptide degradation are closely interacting processes The initial limited proteolysis of proteins may have role in making the seed storage proteins more susce ptible to the further uncontrolled proteolysis by opening up the protein conformation andbringing out the susceptible sites Limited proteolysis plays an important role in initiating storage globulin degradation and consequently the amount of liberated amino acids is small The beginning of measurable storage protein degradation can be detected at day s 2-3 after the start of imbibition (DAI) depending on the species under investigation The breakdown of the major amount of storage globulins occur s from 4-8 DAI depending on the plant species and it coincides with the major activity of proteolytic enzymes During the later stages of protein mobilization the living storage tissues eg aleurone cells in cereals and the cotyledon cells in dicots undergo complete disintegration in a reg ulated manner known as Programmed cell death (peD) This helps in complete mobilization and recycling of reserves from and also these cells cease to regulate any other activity related to germination

433 Regulation of protein degradatio n

The protein mobili zation depends on several factors such as-phytohormones fee dback contro l of protease types of proteases preferential degradation of some proteins conformation of proteins membrane boundaries separating stored proteins from proteascs pH values e tc Proteases are coshylocalized inside the pro tein bo dies There are some mechanisms that protect stored proteins against degradation by stored protcascs for example structur al inaccessibili ty of pro teins membrane boundaries separating stored proteins from proreases or pH values that main tain proteascs

Ii

-98 Seed Science and Technology Mol

inactive (Fath et al 2000 Jiang and Rogers 2002 Muntz 2007) The feedback control of protease activi ties is mediated by concentration gradients of amino acids between embryo and storage tissue This allows a fine tuning of amino acid provision from the source according to the demand in the sink represented by the growing embryo

In cereal aleurone cells control is exhibited by the antagonistically acting phytohormones_ gibberellic acid and abscisic acid and mediated mainly by transcription regulation (Bethke et al 2006) This leads to de 1I0VO synthesis of protcascs and other enzymes In dicots the evidence for de novo synthesis of protea ses as regulated by hormones (GA and auxin) is not fully resolved However exogenous application of hormones has positive effect on protease activity GibbereIIins (GA l and GA20) were identified in embryonic axes of V mungo seedlings (Taneyama et al 200 I) Treatment of the seeds with an inhibitor of GA biosynthesis greatly reduced the accumulation of proteases in cotyledons of V mungo and it recovered by exogenous application of GA I and GA20 to the seedlings

Proteolysis of some proteins takes place earlier as compared to the others In seeds containing both the legumins and vicilins (eg lield bean soybean) the degradation of legumins ( I Is globulins) proceeds more slowly (Wilson et al 1986) Similarly the storage protein hreakdow n proceeds much more rapidly in the cotyledons of germ inating Phaseolus vulgaris where 7s globulins predominate than in seeds of Pisum sativum Vicia faba or Glycine max in which nearly 50 per cent or more of storage protein is made of II s globulin

The histochemical analys is of germinating mungbean and soybean cotyledons has revealed that storage protein degradation is initiated only in the subepidermal layers in mungbean or in cells adjacent to the vascular bundles in soybean and further protein breakdown proceeds inwards though the tissue This leaves behind cells with lytic vacuoles free of storage proteins There is a co-incidence of proteinases and corresponding m-RNAs in the cotyledons as observed from the immune-localization of pretenses and in situ m-RNA hybridization techniques Precursors of new proteinases are synthesized at the rough ER and transferred via the pre-vacuolar compartment into the vacuole where they are activated by proteolytic processing

44 Mobilization of Mineral Nutrients

Phytate (rnyo-inositol hcxaphosphatc) is the major phosphate reserve in seeds It is mainly associated with cations such as K+ Mg2+ Ca2+ and called phytin or phytate It is present in the protein bodies and observed as electron dense globoids (eg cereal aleurone layer and cotyledons) In cere al seeds it is already present in protein bodies however in dicots synthesized de novo after imbibition It consititue an important source of macro and micro nutrients to the seeds during germination Rele ase of phosphate groups from phytin takes place due to action of phytase enzyme The phosphate is rapidly incorporated into phospholipids phosphate esters in respiratory pathway and nucleic acids during the metabolism and growth processes associated with germination

Phytase I hiPIiytm ) myo-mosito + p osp late + catio ns

5 CONTROL OF SEED RESERVE MOBILIZATION

51 Role of Embryonic Axis The mobi lization of food reserves and the growth of seedling are eflicientl y synchronized proces ses controlled by em bryonic axis The control by axis is based on two hypotheses First the growing

axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -


axis may act as sink to draw away the products of degradation Second the growing axis may produce the plant growth substance(s) that stimulate the synthesis of hydrolytic enzymes needed for food reserve mobilization in the cotyledons (Bewley and Blac k 1994 Nandi et al 1995)

The source-sink hypothesis assumes the storage reserves as source and the growing embryonic axis as sink The rates of mobilization of seed reserves depend on the demand from axis There is no mobilization if the sink (axis) is removed For example cotyledons isolated fro m seeds before imbibition show no increase in endopeptidase activity and protein degradation Similarly there is a positive effect on the extractable enzyme activities such as a-amylase prote inase lipase etc due to the attached axis The rate of storage protein mob ilization by cystei ne endopeptidase was obse rved to be regu lated by the level of liberated amino acids at the axis by feedback in buckwheat (Dunaevsky and Belozersky 1989) Lipid breakdown in oilseeds also depends on the intact axis However some cotyledonary lipid breakdown may occur even in the absence of the embryonic axis in cucumber seeds and is probably a consequence of the formation of a transi tory starch store which acts as sink (Chapman and Galleschi 1985) The transitory sta rch can not be utilized in the absence of the axis

The phytohormones released by the embryo help in the mobilization process During germination of cereal seeds there is a massive de lOVO synt hesis of a-amylase and also proteases Phytohormones gibb erellic acid and abscisic acid control the synthesis of these enz ymes in cereal aleurone layers which is mediated mainly by transcriptional regulation (Bethke et al 200 6) Similar hormonal regulation in dicots has not been conclusively proved So me of the GA induced enz ymes in cereals are listed in Table 5

TABLE 5 GA induced enzymes synthesized de novo in cereal aleurone tissues

that take part in reserve mobilization

Enzymes Function

a-amylase

a-glucosidase

Cystein pro teinases

( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses

Hydrolysis of starch

Hydro lysis of starch

Hyd rolysis of proteins

Digestion of cell wall


Hyd rolysis of nucle ic acid

Sug ars negatively affect the embryo growth and even at low concentrations inhibit germination (Bas et al 2004 Yuan and Wysoka-Diller 2006) This inh ibition is dist inct from the mann ose inhib ition of ge rmin ation (Pego et al 1999) Under con ditions of suga r deficiency an increased degradat ion of both storage and cytoplasmic proteins occurs The increase in proteolyt ic activ ity may be caused by release of proteo lyt ic enzyme genes from catabolic repression induced by sug ar (Borek and Ratajczak 2002)

52 Gene Expression and Metabolite Pools Associated with Mobilization It was generally assu med earlier that ca tabolic processes normally occur during germination However recent studies have found that init ial events in the mobil izat ion of protein and lipid reserves also occu r during seed maturation There is accumulation of seed storage-protein subunits due to proteolysis and thus protein reserves may be deg raded not only during germination and

100 Seed Science and Technology l

seedling growth but also during the maturation phase (Gallardo et al 2001) Similarly the activities of enzymes involved in triacylglycerol catabolism (catalase aconitase phosphoenq pyruvate carboxykinase and others) andlor mRNA transcripts associated with this process have also been detected in developing oilseeds eg cotton castor bean cucumber and Brassica napus In Brassica napus the seed oil content actually falls during the final stages of seed maturation At least 10 per cent of the major storage product of developing embryos of Brassica napus (L) triacylglycerol is lost during the desiccation phase of seed development (Chia et al 2005) Enzymes of a -oxidation and the glyoxylate cycle and phosphoenolpyruvate carboxykinase were present in embryos during oil accumulation and increased in activity and abundance as the seed s matured and became desiccated However lipid degradation was not associated wit h net gluconeogenic activity during maturation Based on above facts Holdsworth et al (2007) suggested that potential for germination is largely programmed during seed maturation process

Rapid advancement in the techniques such as gene chips containing probes for thousands of genes for functional genomics studies 2-D electrophoresis of proteins followed by MALDIshyTOF analysis-for proteomics studies and Gas Chromatograph Mass Spectrometry- for metabolome analysis have helped in study of thousands of genes proteins and metabolites in the seeds during maturation desiccation and germination This has helped in better understanding of the profiles and dynamics of cellular constituents (Fig 8) For example detailed transcriptome analysis of barley grain from maturation to germination (Sreenivasulu et al 2008) has indic ated that during early germination (24 hours after imbibition) the number of transcripts detected in the embryo fraction increased upto 13050 but remained lower in the endosperm-aleurone fraction in harley (about 10480 transcripts) The genes involved in reserve mobilization were expressed much earlier during germination ie already 24 hours after imbibition before radicle emergence Profiles of some transcripts and associated proteins as related to reserve mobilization (Sreenivasulu et al 2008 Yang et al 2007) is as follows- cell wall bound invertase vacuolar invertase sucrose synthease sucrose-phosphate-synthase ~-oxidation genes phospholipases ce ll wall modification proteins eg expansions and endoxyloglucan-transferase cell wall degradation enzymes eg cellulases and P-I 4-glucanases- cysteine proteases serine carboxipeptidase etc The metabolite pools related to reserve mobilization (Fait et al 2006 ) showed increase in the following-amino acids (aspartate proline threonine) sugars (fructose-6-phosphate glucose-6shyphosphate) and organic acids (dihydroxyacetone glycerate-3-phosphte 2-oxoglutarate cit rate isoc itrate etc)

Cotyledons

i r---- -------------------------------- I

I

Utilization of pre-stored metabolites +

Activation of pre-stored enzymes +

~r_~~a~~~oo~ ~~-=~~~ mRNAs + gt ~ j ~l~jj~~~ ~ ~j~ l~l ~ j~l ~ij l l 1

__~~~~~~~~~_~ i l i 111111111111l1l1 llilllilllllllill~

Fig 8 Summary of information obtained from new biological approaches (genomics proteomics and Metabolomics) in relation to good germination

Mobilization of Seed Reserves and Environmental Con trol of Seed Germination 101

53 Respiratory Activity and Energy Provision for Storage Mobilization

One of the first activities to resume with seed imbibition is respiration The dry seed mitochondri a when hydrated can produce some ATP due to preexi sting enzymes during initial phase of seed germination Initi ally during phase I of water uptak e the glycolytic and oxid ative pentose pho sphate pathways recommence and already present Krebs cycle en zymes are activated (Botha et al 1992) With the progress of imbibition during phase II high er mitochondrial activity is reali zed by two patterns In the starch storing seed s the mitochondrial activity is enhanced by the repair and activ ation of preexisting mitochondria whereas in the oilseeds biogenesis of mitochondria take s place (Ehrenshaft and Bramble 1990 ) Therefore rapid respiratory activity and major stored reserve mobilization takes place during pha se III after radicle emergence

The seed respiration during germination has four stages and shows a peak during the later stages of germination (Fig 9) During phase I there is a sharp rise in resp iration associated with sharp increase in imbibition During phase II there is a lag in respiration and this phase is associ ated with a high activity of alcohol dehydrogenase enzyme and anaerobic respiration During phase III there is second respiration burst and is associated with aerobic respiration and activi ty of newly synthes ized mitochondria and respiratory enzymes Thereafter during phase IV there is a mark ed decline in the CO 2 evolution associated with the disintegration of cotyledons

0 ()

gt ~ ()

N o o

Stage I Stage II Stage III Stage IV bull --------- I(

I I I I I I I I I I I I I I I I I I I I I I I I I I I

Time

Fig 9 The phases of respiration during seed germinatio n (Adapted from Arteca 1997)

Oxygen is required in germination as a terminal electron acceptor in respiration and other oxidative processes The energy is stored as ATP The Adenylate Energy Charge (AEC) indicates the amount of available energy within the adenylate pool and varies from 0 to 1 The extreme values ie 0 indicate an adenylate pool containing only AMP and I indicates presence of only ATP Actively metaboli zing cells have high AEC values of 0 8 or more

AEC = ([ATP] + 0 5[~DP]) ([ATP] + [ADP] + [AMP])

6 ENVIRONMENTAL FACTORS AFFECTING SEED GERMINATION

Dry mature seeds are resting organs with metabolic activity almost at a standstil l They arc able to insulate themselves from adverse environment by process of dormancy The seeds are bestowed with very sensitive receptors and chemicals to perceive the environmental conditions They seem


to wait and watch for suitable environment During and after germination they have to face the vagaries of nature and therefore proper conditions that encourage metabolism are needed eg suitable hydration temperature presence of oxygen light etc The present discussion will be restricted with respect to the effect of environmental factors on seed ge rm ination and their quantilication in non dormant seeds only with respect to hydration temperature air and light

61 Soil

Soil is the medium for germination and plant establishment Therefore seed germinatio n is influenced by the soil environment viz water holding capacity aeration hydraulic conduc tiv ity rate of (low of water to seed soil temperature soil frost water logging soil particle size soil so luti on pH ions salinity seed soil contact tillage operations sowing depth light exposure of soils soil c ru st ing compaction organic matte r ni tra te mulching buri al depth presence of allelochemica ls soil microbes etc Some of the factors eg water availability pH and ae ra tion influence germi nation sensu stricto whereas most other factors exert greater inlluence on post germination growth and hence field emergence and stand establishment

62 Water

Se ed germination is essentially related to water availability Seeds of most plant species at maturity usually have moisture content below ~

15 (on fresh weight basis) These seeds have CIlC

wate r poten tia) in the order of about -100 J

M Pa ie - 1000 bars (Shaykew ich and Williams 1973) T he surface properties of S macromole cu les such as proteins starch and ce ll wall in the seeds lead to imbibition of wate r W hen seeds get in contact with water the re is an initial inrush which is a physica l _ Time

process and co nsidered to be u ncontrolled Fig 10 Effect of wate r potential (yen) on durati on of (Parrish an d Leopold 1977) Within the seed phase II of ge rmina tion yen1 indicates the different tiss ue s and organs hydrate to different highe st re lative wate r pote ntia l (or water extents leading to non-homogeneous wate r ava ilability) an d yen 2 yen3 yen 4 and yen 5 refer to distribution the progress ively decreasing wate r potenshy

tials Therefore the seed s growing in yen 1 T he seed wat er uptake shows a triphasic reache d the phase II sooner as compared

to yen2 yen3 and l4 However a t yen 5the seedspattern The ph ase I is initial rap id uptake co uld not proceed to phase III and germ ishy

foll owed by a plateau phase (ph ase II) A na tion cou ld not occur

further increase in wa ter up take dur ing pha se (II~ ) occou rs as the embryo axi s e lo ngates and brea ks through the covering layer s to co mplete germination In terms of the regulation of ge rmi nation phase II is of primary interest si nce germination in the physiologi cal sense can be considered to be co mpleted when embryo growth is initiated It is the lengt h of phase II that is ge nerally ex tended in dormancy low or high temperatures water defi c it or ab scisic aci d while factor s which promote germi nat ion do so by sh orte ning thi s lag phase (Fig 10) Rad icle protrusion at the completion of seed germi nation depends on em bryo growth dr iven by wa te r uptake In con trast dormant seeds th at do not complete ge rm ination do not enter phase III of water up take


A seed must reach a minimal water content known as the critical hydration level in order the to germinate (Koller and Hadas 1982) At field capacity the soil moisture is near optimum for

middot0 middot 0 seed germination in soil Rice seed begins to germinate when its moisture content reac hes 265 be per cent (fresh weight) corn at 305 per cent sugarbeet at 31 per cent and soybean at 50 per cent cir (Hunter and Erikson 1952) The external water potential (-P) value at or below which seeds shy

t cannot reach their critical hydration level is called its critical water potential The critical water potential for some important crop seeds (Table 6) indicate that corn chickpea and sorghum can germinate at higher moisture stress as compared to rice pea and clover (Hadas 2004)

is y TABLE 6 lil Critical water potential for germination of some seeds (Hadas 2004) of

Crop Critical water potential (MPa) )f

n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120

Similar to the critical water potential of the substratum the water potential of seed is also very important Germination is not possible in most species unles s the water potential of the seed is greater than -15 MPa (Kaufman and Ross 1970) It has emerged that for seed germinati on to occur there is a requirement of min imum seed water potential called the thre shold or base water potential Gummerson (1986) made a seminal contribution in this respe ct by proposing that seed germination responses to water poten tial might be described on a h ydrotime scale analogous to the thermal time The hydrotime is expressed as Mega Pascal days The hydrotime is related to the magnitude of the difference between the seed or environment water potential and the

0)

threshold or ba se water potential for radic le rocr

protrusion I t is based on the assumption that c

total hydro time to radicle emergence is same ~ ~ for all seeds in the population and seeds in a ~ ~

population differ in their base water potential Q3 Jb(g)

for radicle protru sion (Bradford 1996) As lt)

germination rate is linearly rel ated to water 1potential (Fig 11) biol ogic al tim e can be calculated by the amo unt by which wat er (-) J (MPa) (0) potential exceeds the base water potential below Fig 11 Effect of water potential on the seed which germination will not reach completion germination rate so that for any individual seed hyd rotime (8H)

can be expressed as follows -shy


where 8H =hydrotime in MPa-hours or MFa-days

f =ambient water potential

f(g) =minimum water potential for seed germination

tg =time taken to germination

or GR = I tg =SHI(lP - f(graquo)

where GR =germination rate

The value of SH is the total hydrotime (MPa-hours or MFa-days) required for each seed to complete germination The slope of response is lISH

63 Temperature

Temperature is the single most important factor regulating germination of non-dormant seeds in irrigated annual agrocosystems at the beginning of a growth season The response to temperature during germination is influenced by genotype seed quality time from harvest etc The three cardinal points of vital activity for germination are a minimum temperature below no activity occurs an optimum at which the highest germination occurs and a maximum temperature above which no germination takes place (Fig 12) The optimum temperature at which max imum germination percentage is observed within the shortest time is usually within a range of 15-30 DC for most seeds Over a certain range of temperature germination will speed up as temperature increases and slow down as it decreases As temperature decreases below the optimum germination of temperate and tropical species slows at similar rates at about 14 DC however the rate of germination of tropical species declines dramatically and below 10 DC germination ceases (Simon et al 1976)

Q) Cl III C ~ Q) 0 C o ~ c E Qj

C)

Optimum Temperature

Temperature

Fig 12 Cardial temperatures for seed germination

The temperature below which germination does not occur ie base temperature (T) for different seeds is also given in Table 7 The maximum temperature can also be called as ceiling temperature (TeJ

A favourable temperature during the rapid imbibition phase is very important For example imbibition of cotton seeds at 5-15 DC can lead to injury Thi s indic ates a tempera ture sensit ive even t associated with the seed imbibition which most probably is related to membrane repair During this phase there is also leakage of substances from the seeds which is enhanced at the

105 d Technology Mobilization of Seed Reserves and Environmental Control of Seed Germination

limiting temperatures ie lowest and highest temperatures The leakage can be explained due to

each seed to

ant seeds in temperature

The three no activity iture above maximum ~ of 15-30 mperature rmination ie rate of s (Simon

incomplete plasma membrane in the dry seeds With the onset of hydration the membrane lipids are organized to form a bilayer but the temperature during this period should be suitable so that formation of membrane lipid bilayer is improved At lower temperature the lipid bilayers are in gel phase and proper membrane functions can not be maintained The minimum temperature response of different seeds and their geographical distribution is therefore related and is also further controlled by the chemical composition of membranes Some seeds particularly tropical species appear to be irreversibly damaged during the first few hours of imbibition at chilling temperatures The sensitivity to the imbibitional chilling is very high in recalcitrant seeds which can not germinate at chilling temperatures due to cellular disruption eg seeds of tropical plantation crop Coffea arabica

TABLE 7 Cardinal temperatures (OC) for seed germination in some plants

Seeds Minimum or Base Temperature (Tb)

Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5

Optimum Temperature (To)

32-35

30-37

15-31

24

25

30

20

Maximum or Ceiling Temperature (Te)

40-44

40-42

30-43

30

28-30

35

28-30

Temperature primarily influences the germination rate by regulating the duration of the lag phase II of water uptake At increasing sub optimal temperatures the duration of phase II gets shortened as shown in the figure below for seed germination (Fig 13)

) for Time ~i1 i ng Fig 13 Generalized pattern of moisture uptake during different phases in the seed germination as

influenced by temperature There is faster germination at higher temperature eg as comshypared to T bull T and T bull However at the lowest temperature (T ) the seeds could not proceed

2 3 4 5

to phase III and germination did not occur

For understanding the response of seed germination to temperature the combination of temperature and time is a more appropriate unit of measure of development than the time alone This concept is called thermal time and measured as heat units in degree days (Od) Seed germination


has a specific requirement of heat units The thermal time requirement of some crops in degree days (Bierhuizen 1973) is as follows - winter wheat (47) spring wheat (52) peas (90) lentil (67) oat (90) and white mustard (60)

The heat units received by seed after sowing are obtained by summation of mean temperature above the base temperature (T) For example let us suppose a crop requires 100 degree days for seed germination and does not germinate below 5 DC (iebull T =5 DC) If the seeds are sown under mean daily temperature conditions of 25 DC to 27 DC then the requirement of 100 degree days will be met after 5 days Therefore the crop will take five days for germination and the progress of thermal time is given in Table 8

TABLE 8 Daily progress of thermal time (cumulative heat units) from sowing to germination

Days after Daily temperature (C) Mean daily Base Heat units Cum ulative sowing Maximum Mill imum temperature temperature perceived per heat units

(0C) (Th 0C) day (Od) (Od)

I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

The clock time for germination in above example is 5 days and during this period an equivalent biological time or thermal time of 105 degd has accumulated for germination

5 days (clock time) = 105 degree days

However in case of other phenological stages the base temperature may be di fferent and the thermal time be calculated accordingly The information on thermal time for germination as given in above example can be generalized to derive the following formula

Heat unit requirement = (Mean temperature - Base temperature) x (No of da ys)

or 8T(g) =(T - T) tg

where 8T(g) =thermal time for germination T =ambient temperature

T =base temperature - T - T =difference between ambient temperature and base temperature

8T (g) or thermal time is constant for a given seed fraction Therefore time for germination

is same at all suboptimal temperatures when expressed as thermal time middot

and alterna tively tg the time taken for germination (in days) can be calculated as

Days taken for germination =(Heat unit requirement)(Mean temperature - Base temperature)

or tg =(8T(graquo)(T - T)

1 The germination is slower or more time is taken for germination both at the low and high

temperatures Therefore the plot of time taken to germination (rg) and temp erature shows a U shaped curve with sharp increase in tg at the extremes (Fig 14) Thi s curve will be bro ader

107Mobilization of Seed Reserves and Environmental Control of Seed Germination

c 2 m cE --shyQ)0l (9=shy

8 Q) E F

Temperature (0C)

Fig 14 Influence of temperature on time to germination

for seeds with wide optimum temperature range A practical consequence is that early emergence can be achieved relatively cheaply with plastic covers if the soil temperature is near the minimum

The reciprocal of tg can be defined as germination rate (GR) The plot of GR and tem perature shows A (inverted V) shaped curve (Fig 15) At optimum temperature (To) the GR is mos t rapid

GR = Iltg = (T - T)(8T(g))

I The GR increases linearly above T with a slope of 18T(g)

rele vant to agriculture where more weed population is built up by conventional tillage practices

Temperature (oG)

Fig 15 Effect of temperature on germination rate where Tb = base temperature To = optimum

temperature and T = ceiling temperature c

In nature the seeds experience diurnal temperature variations and appear to perform be tter at alte rnat ing tempera ture regimes Some species do not germinate at all at constant temperatures and some species require light along with alternating temperatures (Thompson and Grime 1983) Species that require alternating temperatures are as follow s -Typha latifolia Phragmites australis Sorghum halepense etc In natu re the alternating temperature requirement can help in the imp rovement in the soil seed bank of some spec ies over the others It can also help the seeds in sensing the depth of burial as there is difference in the amp litude of temperature alterations betw een the upper and deeper soil layers (Fenner and Thompson 2005) This may also be

---


as compared to the zero or minimum tillage practices Seeds are grouped based on optimal temperature requirement (Arteca 1997)

(i) Cool temperature tolerant

(ii) Cool temperature requiring but affected at higher temperature (iii) Warm temperature requiring but susceptible to low temperature (iv) Alternating temperature requiring

64 Oxygen

The atmospheric O2 concentration is about 21 and (A) in the soil it is usually at 19 However it can reduce to 1 per cent or less at field cap acity or flooding Germination of most seeds is retarded if the oxygen ~

concentration is reduced substantially below that of c o air Oxygen is primarily required for seed respiration ~

while its utilization also depends on the other ~ environmental factors eg temperature and osmotic 03 opotential of the germination medium (Corbineau and Come 1995) It has been observed that at higher temperatures and osmoticum there is a reduction in the germination even at higher O2 concentrations Oxygen () Alternatively the seed needs higher O2 concentration

Fig 16 Generalized response of tomatoat higher temperatures and osmoticum as depicted in seed germination to O supply at

the following Fig 16 2

normal and higher temperatures Most species require oxygen however some and osmoticum (A) 15 DC or in

higher water potential (0 MPa) (8) species show better germination in hypoxic conditions 30 DC or lower water potential (-05 (eg Cynodon dactylon) Under such conditions MPa) (Adapted from Corbineau and

ethanol production takes place by anaerobic respiration Come 1995) Rice seeds can also germinate under anaerobic conditions but subsequent growth is greatly affected by lack of oxygen supply Some species can even germinate under anoxia eg Echinocloa and Erythrina caffra Based on the germination at low O2 pressure the seeds have been classified into two groups (AI-Ani et al 1985)

Group I In the oil seeds the germination is completely inhibited when O2 reaches 2 eg sunflower soybean flax radish and lettuce Their adenylate energy charge values go below 04 under anoxia and therefore it limits energy provision for germination

Group II In the starchy seeds the germination can occur in O2 concentrations less than 1 eg rice wheat maize sorghum pea etc Their adenylate energy charge remains high (06-075) and therefore energy provision for germination is sustained under anoxia

During the early stages of imbi bition the mitochondria are not fully functional and the re is limited oxygen demand During this phase anaerobic respiratory metabolism (glycolysis and fermentation pathways) synthesizes ATP from stored metabolites The activity of alcohol dehydrogenase enzyme is high Proteomics study of early germination process in rice and other cereal seeds also indicate that the energy demand seems to be fulfilled mainly by glycolysis (Yang et al 2007) Even under well aerated conditions the oxygen concentration inside the

109


y

imbibed seed near embryo may be quite low because of the lower diffusion of oxyg en and uptake

of oxygen by the coat and endosperm Under these conditions as expected the mRNA levels of enzymes of glycolytic pathway-glyceraldehyde-3-phosphate dehydrogenase aldolase enzyme and alcohol dehydrogenase increased significantly at 24 h after seed imbibition indicating anaerobic metabolism The TCA cycle enzyme succinate dehydrogenase mRNA levels increased to less extent during this period (Fait et al 2006) in Arabidopsis seeds Recent metabolomic studies also show that there is a large change in the metabolite profiles associated with aerobic respiration in Arabidopsis seeds after keeping for I day under germinative conditions (Fait et al 2006) After the repair and activation of mitochondria the oxygen consumption rapidly increases and during this phase of seed germination oxygen is utilized for oxidative phosphorylation and ATP synthesis After the activation of oxidative metabolism there is a rapid oxid ative burst of ene rgy and it probably help s to initiate- storage mobilization

Another recently observed role of oxygen during germination relates to the massive oxygenation of proteins also called protein carbonylation (Job et al 2005) although its role is not clear At this time the defense mechanisms (antioxidants) in the seeds should also be intact or there should be a build up of antioxidants (eg dehydroascorbate formation) This oxidative burst may be essential for seeds to germinate but poor germination occurs if the defense is weak as in the mutants lacking vitamin E and also may be in aged seeds

65 Light

Light has an inductive effect on seed germination and in many plant species is promoted or suppressed by light Seeds of cultivated plants usually germinate both in light or dark conditions whereas the wild plants have specific light requirements for proper germination Also the sensitivity towards light depends on imbibition Seeds which germinate only in the dark are called negatively photoblastic seeds whereas the species for which light is essential for germination are called positively photosblastic seeds (Table 9)

TABLE 9 Some examp les of photoblastic seeds

Positively photoblastic seeds Negatively photoblastic seeds

Adonis vemais Gladiolus communis

Nastertium officinale Mirabilis jalapa

Salvia pratense Phacelia tenacetifolia

Fagus silvatica Nemophila insignis

Veronica arvensis Avena fatua

Raphanus sativus

Light consist of different spectral zones such as UV blue green red far-red infrared etc having different effects on germination For example red light usually promotes germination whereas blue and far red light inhibits Canopy shade has a low redfar red ratio as compared to direct sunlight The detection of light environment by the seeds occurs with the help of light absorbing molecules known as phytochromes Phytochromes are conjugated proteins consisting of an apoprotein and chromophore made of an open-chain tetrapyrrole (Fig 17)


Protein

0

Pr

cooshy coo-

R ed Fa~ed1 jLight Light

Protein

S

0 + NH

~ P fr

coo-coo-Fig 17 The red light-induced structural change in phytochrome from PI to Pfr form is due to photoshy

isomerization from cis to trans configuration at the 15 16 double bond Far red light reverses the Pfr form to PI form

There are five known phytochrome types-phy A phy B phy C phy D and phy E The phy A exists in 10-50 times higher concentration than other types in the dark grow n seedli ngs The gene regulation mediated by phytochrome occurs due to movement of phytochrome to the nucleus as visualized with the help of green fluorescent protein marker tech nique (Yamaguchi et al 1999) In dark-grown seedlings the most abundant phytochrome isoform is phytochro me A (Phy A) which is present in red light absorbing from PI (Quail 199 1) Prote in deg radation in add ition to the transcriptional regulation plays an important role in determining the level of the photoreceptor phytochrome in developing seedlings upon exposure to light

The effect of light on germination depends on total energy or lluence which depe nds on tluence rate and the du ration of illumination The llue nce rate denotes the number of photons per unit area per unit time (mo l photons m-2 s)

Total energy or Fluence = (Fluence rate) x (Duration)

Based on the response of seed germination to light there are three types as follows- C) Low Iluence respon ses (LFR) (ii) Very low tlue nce responses (VLFR) and (iii) H igh irradiance respons es

111 Mobilization of Seed Reserves and Environmental Control of Seed Germination

(HIR) These responses include the effect on dormancy as well as the germination of nonshydormant seeds

Low flu ence responses (LFR) The LFR are mostly caused by a short phase of light at fluencc ranging from 1-1000 Jl mol m-2 LFR show RJFR reversibility and the effects are positively photoblastic type It obeys reciprocity law ie an equal value of fluence obtained from different fluence rates and times gives an equal response This response is the most known response to light and is related to breaking of dormancy of lettuce seeds (cv Grand Rapids) by red light

Very low fluence responses (VLFR) VLFR is one to ten thousand times more sensitive than LFR and occurs in the fluence range of 10-4 to I Jl mol m-2 and the effects are related to phytochrome As compared to LFR the FR does not nullify the VLFR caused by a red pulse Therefore a VLFR pulse of FR also promotes germination or germination induction and serves as a criterion to distinguish VLFR from LFR VLFR has a great importance under natural conditions where different temperature and light regimes can reduce the sensitivity of seeds to a great extent

High irrad iance responses (HIR) High irradiance response (HIR) is caused by irradiation of a long duration ranging from several hours to a few days It does not obey the reciprocity law and does not show R1FR reversibility

I A study of germination response of the negatively

photoblastic non-dormant seeds of Nemophila insignis g ~to light (Bewley and Black 1978 1994) showed that c

light exposure to these seeds for 4 hours lead to 80 Qiii

per cent germination Further increasing the light c middotEduration to 24 hours resulted in only 20 per cent Cl)

germination Light exposure also increased the time lt9 Cl)

taken for germination This process is called photo gt ~

inhibition of germination and it comes u1der HIR (jj

This response docs not occur with short light exposure 0

of seconds to minutes and at least 3 hours of light is required to inhibit germination Therefore photo inhibition is time dependent and reciprocity does not hold in HIR The Far red light illumination in HIR is both time and fluence rate dependent and therefore differs from the operation of phytochrome in low energy mode (Fig 18) The peak of photo inhibition occurred between 710 and 720 nm and subshypeak between 460 and 480 nm The blue peaks however do not coincide with the absorption spectrum of phytochrome The phase of germination most inhibited in Nemophila insignis seeds corresponds to the 20-40 hours time after imbibition when radicle emergence is taking place (he seed germination is goo d in dark but there is interaction with temperature also as it is inhibited even in dark above 21degC

In the low energy mode the FR can inhibit seed germinatio n if provided within the escape I time of the effect of red light If FR is given for short pulse after the escape time then the effect

of red light will not be reversed However if FR is given for longer period (eg 4 to 256 hours) there will be a reduction in germination Further higher lluence rate inhibited the seed germination increasingly It has been again observed that FR was maximal inhibitory when radicles began to elongate Similarly prolonged blue light exposure also leads to inhib ition of seed germination in

Total incident light

Fig 18 Inhibition of seed germination in Nemophia insignis seeds as observed in high ir radia nce response of Far red light


Nemophila insignis and is strongly fluence rate dependent The action spectra for both red and blue light regions indicated peaks at 470-480 nm and at 720 nm The blue peak do not cor respond to phytochrome and possibly are related to another pigment called cryptochrome

Therefore light can affect the germination of non-dormant seeds to various extents depending on the intensity duration (continuous or periodic) and quality (wavelength) The interaction of seed with light also depends upon the stage of germination temperature regime photoperiod

effect water content genotype etc Same conditions may be promotive or inhibitory to the same seed at different phases of germination In nature several factors can interact simultaneously and the responses are still not properly understood

66 Modelling of Germination Responses to Environment

It is of prime importance to explain and predict the control of germination by the environmental factors for better crop management In this respect models provide a logical framework for quantification of the progress of germination The models use biological time in which germination progresses at different rates according to the ambient conditions The biological time ie the rmal time and hydrotime is different from the clock time When other environmental factors are non limiting biological time can be quantified by thermal time iebull the amount by which temperature exceeds a minimum temperature for germination (T - Th) When the temperature remains constant but water is suboptimal progress towards the completion of germination can be quantified by hydrotime where progress is a function of water potential above the threshold water potential (f - fb(graquo) These models are based on a threshold value (base) below which germination is not completed and therefore are called threshold models

The models related to thermal time (Garcia-Huidobro et al 1982) and hydrotime (Bradford 1990) describe the effects of temperature or water potential on the germination rate The combined effect of suboptimal temperatures and reduced water potentials on germination was proposed by Gummerson (1986) as hydrothermal time When both temperature and water potential vary thermal time and hydrotime can be combined into jiydrothermal time (8HT) In the 8HT model the germination time of a given seed is quantified by the extent to which the water potential (f) and suboptimal temperature (T) of each seed exceed thresholds The 8HT based model assumes that fb(g) is constant and independent of temperature and TJ is independent of fJ(g) The hydrothermal time (8 HT) requirement can be quantified as

8HT = (T - TJ) (f - fb(Iraquo) tg

A seed lot consists of a population where the germination rates may vary to different extents Following general aspects have emerged from the study of seed fractions (Finch-Savage and Leubner Metzger 2006 Allen et al 2007)

(i) Variation in germination characteristics shows normal distribution

(ii) The responses have threshold minimum and maximum values which set the sensitivity limits for responses to various environmental factors The difference from threshold also determines progress towards germination

(iii) The sensitivity threshold distributions shift to higher or lower mean values in response to ge rmination stimulating factors

The above discussed threshold models and the variations in population characteristics have been integrated into more powerful models and have been termed as population based threshold


models For these models it is assumed that variation or spre ad in germination times among individual seeds is accounted for by the variation in thermal time requirements for different seed fracti ons and it is affected by the variations in the ceiling temperature Similarly I(g) varies among individual seeds and approximates a normal or Gaussian distribution that can be defined by its mean Ib(50) and standard gt deviation (c) 8HT is assumed to be constant ~

and in many cases the base temperature (T) J0shy~

is constant for all seeds whereas the base IJ

water potential varies between seeds The ~ seeds which have highest I have least ~ difference in I - p value and therefore they a accumulate hydrotime slowly and are the slow germinating ones with respect to clock time Therefore distribution of the germination times of individual seeds within the population is determined by the two parameters base water potential (I) and ceiling temperature

I (T ) (Fig 19)

The population based threshold models make it possible to describe the response of the whole seed population in a single equation by incorporation of these relationships and normal distribution (Finch-Savage 2004)

Probit (G) = ([I - 8HT(T - T) tg] - I(50)cryen

where Probit (G) =Probit of the germination fraction

I(50) =the median P crI =standard deviation of I

Ib (MPa) or Tc (oG)

Fig 19 The base water potential (1) and ceiling temperature (T ) are normally distributed in ca seed population

These models have the potential to provide a common framework or universal approach for quantifying the array of ecophysiological responses-of a seed population It helps in managing a timely fast and uniform seed germination and emergence which are crucial for a successful crop stand and maximization of yield

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nation Vol I Springer

n Plant Responses to

ization in germinating

m during germ ination

iol 94 840-849

ions for experimental nistry and Molecular

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m weakening during

elopment of Brassica

ironment In J Kigel p 397-424

ase type deb ranching i6-80

tidase in breakdown

that initiates sto rage

~ embryos of maize

)006) Arabidopsis hes Plant Physiol

in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis

ion of pearlmillet I

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j

I I

I

I Mobilization of Seed Reserves and Environmental Control of Seed Germination 85

2 SEED GERMINATION AND ITS TYPES

Germination can be defined as the emergence and development from the seed embryo of the essential structures that indic ate the seeds ability to produce a normal plant under favorable conditions (AOSA 2000) The process of germination leads to emergence of the growing parts of the seed or the seed itself from the ground Based on this the seed germination has been cla ssified into two type s-s-epigeal and hypogeal (Fig 1)

Cotyledons

s Hypogeal Epigeal germination germination

Fig 1 Types of seed germination-epigeal and hypogeal

In epigeal germination the cotyledons arc raised out of the soil by elongation of the hypocotyl and often become green and photosynthetic In hypogeal ger mination the hypocotyl remains short and compact but the epicotyl elongates tp raise the first leaves out of the soil while the cotyledons remain beneath the soil Some examples are given in Table I

TABLE 1 List of some crop seeds with_epigeal and hypogeal germination

Epigeal germination Hypogeal germination

Onion (Allium cepa) Whe at (Triticum aestivum ) ~c

nt French bean tPha seolus vulgaris) Maize (Zea lIIays)

Groundnut (Arachis hypogea ) Pea tPisum sativumi ~ r

s Cucumber (Cucurbita pepo) Broad bean (Vida faba )

iC Barley (Hordeum vulgare)

g lA J COMPOSITION OF SEEDS

The seeds consi st of four major storage reserves as related to the provision of energy du ring h germination These are starch proteins fats and mine rals located in the storage tissues - ie

endosperm or cotyl edons The composition of some seeds is presented in Table 2 r The seed carbohydrates predominantly occu r in the form of starch Monocots are the major

starch accumulating seeds (eg rice wheat maize etc) Starch is a polymer of glucose which may be linear as in amylose or branched as in amyl opectin Amylose con sists of a 1-4 linked glucose molecul es and amylopectin has side chains attached with a 1-6 linkag e About 50-75 per cent of starch in cereals is in the form of amylopectin and 20-25 per cent in the form of amylose



bull b gcrmmauon



Protein




Rice tO rvia sativa





II

12

12

10

24

31

37

21

Fat

5

2

3

2

6

48 17

48

Starch

75 Endosperm

75 Endo sperm

76 Endosp erm

80 Endosperm

56 Co tyledon

12 Cotyledo n

26 Cotyledon

19 Cotyled on







Soybean

Groundnut

Sunfl ower

Brassica

6

2

4

I

23

50

26

6 1

52

31

64

20

8

0

0

10









reds TAB LE 4



Wheat Maize PeaIm











Crop Maturity

Seedling phase





e mb ryo


Catabolism




42





v

I




Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase











GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I



bull b gcrmmauon



Protein




Rice tO rvia sativa





II

12

12

10

24

31

37

21

Fat

5

2

3

2

6

48 17

48

Starch

75 Endosperm

75 Endo sperm

76 Endosp erm

80 Endosperm

56 Co tyledon

12 Cotyledo n

26 Cotyledon

19 Cotyled on







Soybean

Groundnut

Sunfl ower

Brassica

6

2

4

I

23

50

26

6 1

52

31

64

20

8

0

0

10









reds TAB LE 4



Wheat Maize PeaIm











Crop Maturity

Seedling phase





e mb ryo


Catabolism




42





v

I




Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase











GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I








reds TAB LE 4



Wheat Maize PeaIm











Crop Maturity

Seedling phase





e mb ryo


Catabolism




42





v

I




Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase











GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I


Crop Maturity

Seedling phase





e mb ryo


Catabolism




42





v

I




Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase











GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

v

I




Amylose

a-amYlay

Glucose + Maltose

1 a-glucosidase

Glucose

1 a-glucosidase











GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I






GWD





Sucrose + UDP




r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I


r-------------------------------shy~--- - - - - - ----------

Starch I I

l-T---AY~it-)

Sucrose

t Glucose

r

---------------- shy - - I I


Sucrose

t Glucose



(A) (B)














(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I









(ii) p-Oxidation



















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I
















c(

ii c z o I U g E




r Malate

Fumarase



-OOC-CH2-GH2-GOOshy

Succinate

Catalase

Glyoxysome



GLYOXYLATE CYCLE


Triacylglycerol


Lipases

R - CH2- CH2- COOH

~ Free fatty acid

j MDH

Malate ~










~r Citrate ----- ~


Oxaloacetate


Citrate shy

+

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

95 Technology

tase

~se

utese

omerase

hate In iii w z w


sphate o J~ J

sphate C)

osphate 1genase te

nese

utase E CIl ltJ c 0

-2 IshygtshyU

laquouvete Ise

~a la te

itase





424 Gluconeogenesis















M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I










M

s

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

97 chnology




ctivity torage



s as

iced ited

ree md








Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

Ii











axil

p~

for

axi IS

~~~ wa budl

int 1

em stal

1uu l

be l

1 Si 1en

Ell

cc- a C) ( I middot

X~

R

(~

in d m

s

5 I H

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

- - - - - - - -- - --- -







Enzymes Function

a-amylase

a-glucosidase


( 1-3 1-4)- I3 -g1ucanases

Xylana ses

RNA ses












Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I




Cotyledons

i r---- -------------------------------- I

I










0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I





0 ()

gt ~ ()

N o o



Time








61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I



61 Soil


62 Water
















n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I







n t

Corn

Rice

Pea

Clover

Sorghum

Cotton

Chickpea

- 125

-079

-066

-035 - 152

- 070

- 120


0)
















63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I









63 Temperature



C)

Optimum Temperature

Temperature






each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I



each seed to






Zea mays

Oryza sativa

Triticum sativum

Nicotiana tabacum

Beta vulgaris

Pisum sativum

Hordeum vulgare

8-10

10-12

3-5

10

4-5

1-2

3-5


32-35

30-37

15-31

24

25

30

20


40-44

40-42

30-43

30

28-30

35

28-30




2 3 4 5









I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I







I 35 15 25 5 25 - 5 = 20 20 2 36 16 26 5 26 - 5 = 21 41

3 35 15 25 5 25 - 5 = 20 61 4 37 17 27 5 27 - 5 = 22 83

5 36 18 27 5 27 - 5 = 22 105

















8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I



8 Q) E F

Temperature (0C)




GR = Iltg = (T - T)(8T(g))



Temperature (oG)




---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

---





64 Oxygen












109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I

109


y




65 Light









Raphanus sativus



Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I


Protein

0

Pr

cooshy coo-


Protein

S

0 + NH

~ P fr











































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I





































I (T ) (Fig 19)





Ib (MPa) or Tc (oG)




































ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I



























ce and Technology


num Press New York





iol 94 840-849



m weakening during




tidase in breakdown


~ embryos of maize


in cereal aleurone

p 250

ge rminating cereal

New Phytol 171

Proteomic analysis


























abolism in higher






















j

I I






















j

I I

Mobilization of seed reserves and environmental control of seed germination

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Transcript of Mobilization of seed reserves and environmental control of seed germination