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LECTURE 3:INTRODUCTION TO

LIGHT RESPONSE

http://smtom.lecture.ub.ac.id/Password:

LECTURE FLOW1. INTRODUCTION

1. Definition2. Other Tropism

2. TYPES OF LIGHT EFFECTS1. Several Types of Light Effects2. Potato Case

3. PHOTOMORPHOGENESIS4. CASES OF PLANT RESPONSES

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LECTURE OUTCOMEAfter the completion of this lecture and masteringthe lecture materials, students should be able to1. explain the meaning of photomorphogenesis,

phototropism, photoperiodism, and geotropism2. explain various types of light effects on plant

growth and developmeny3. explain the mechanism adaptation of mangrove

to salinity4. explain some changes in plants due to

breeding program

1. INTRODUCTION1. Definition Plants show many different responses or reactions

to light and most of which can be classified into fourtypes; photosynthesis, photomorphogenesis,phototropism and photoperiodism- Photomorphogenesis is the regulatory effect of

light on the growth, development and differentiationof plant cells, tissues and organs.

- Phototropism is the growth response of a plant inresponse to light direction. Different parts of a plantexhibit different reactions to light. Stems exhibitpositive phototropism while most roots exhibitnegative phototropism.

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Phototropism is one way a plant can maximize itsexposure to sunlight.

This is also an important survival tactic becauseplants need sunlight to make food.

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http://leavingbio.net/plant%20responses.htm

2. Other Tropisms A tropism (from Greek τρόπος, tropos, "a

turning") is a biological phenomenon, indicatinggrowth or turning movement of a biologicalorganism, usually a plant, in response to anenvironmental stimulus.

Geotropism is the growth response ofa plant in response to gravity. Rootsexhibit positive geotropism while stemsand leaves exhibit negative geotropism.

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Hydrotropism is the growth response of a plant to water.Roots exhibit positive hydrotropism.

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Thigmotropism is the growth response of a plant to physical contact(touch). Plants that cling to physical structures such as walls exhibitpositive thigmotropism.

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Unfolding manner of common beech leaves: (a) a bud, (b) budsjust after opening, (c) an early stage of unfolding, and (d)corrugated leaves.

Nastic movement, Thigmotropism or Circadian response

2. TYPES OF LIGHT EFFECT1. Several Types of Light Effects

1. Inhibition of the elongation of the hypocotyls2. Inhibition of translocation from the cotyledons3. Increase of the surface area of the cotyledons4. Unfolding of the cotyledons’ lamina5. Development of hairs at the hypocotyls6. Opening of the hypocotyls’ hook7. Development of the primary leaves8. Development of mature leaf primordia9. Increase in the negative geotropic reaction of the

hypocotyls10. Development of xylem elements synthesis

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11. Differentiation of the stomata within the epidermis ofthe cotyledons.

12. Development of super-etioplasts in the cotyledons’mesophyll.

13. Changes in the intensity of the cell respiration.14. Synthesis of anthocyanin in the cotyledons and the

hypocotyls.15. Increase in the synthesis of carotenoids.16. Increase in the capacity of the chlorophyll synthesis.17. Increase in the RNA synthesis within cotyledons.18. Increase in the protein synthesis within cotyledons.19. Intensification of the storage fat breakdown.20. Intensification of the Storage protein breakdown.21. Increase in the synthesis of ethylene.

22. Acceleration of the Shibata-shift within thecotyledons

23. Determination of the cotyledons’ capacity tophotophosphorylate

24. Modulation of the cotyledons’ enzyme synthesis

Inhibition of arabidopsis hypocotyl elongation byjasmonates is enhanced under red light inphytochrome B-dependent manner.

MeJA action still remained in the coi1 mutant, and(+)-7-iso-JA-L-Ile, a well-known active form ofjasmonate, had a weaker effect than MeJA underthe red light condition,

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Inhibition of arabidopsis hypocotyl elongation by jasmonates isenhanced under red light in phytochrome B dependent manner

a Hypocotyl lengths of 6-day-old Col seedlings with 0, 1, 10, 30, 50, or100 μM MeJA on MS medium (with 1 % sucrose) under 50–60 μmol m−2 s−1

Rc, 2–5 μmol m−2 s−1 Bc or 0.02–0.05 μmol m−2 s−1 FRc. b Photograph of 6-day-old Col and coi1-16s seedlings grown on MS medium (with 1 %sucrose) with different concentrations of MeJA under 30–50 μmol m−2 s−1

Rc. c Hypocotyl lengths of 6-day-old Col and coi1-16s mutant seedlings with0, 1, 10, 30, 50, or 100 μM MeJA treatment on MS medium (with 1 %sucrose) under 30–50 μmol m−2 s−1 Rc. For a and c data are the mean ± SD(n = 20 seedlings per genotype). Chen et al. (2013)

Methyl jasmonate (MeJA), red light (Rc), blue light (Bc), far red light (FRc)

RcBc

2. Potato Case A potato left growing in darkness produces

shoots that look unhealthy and lacks elongatedroots.

These are morphological adaptations forgrowing in darkness, collectively calledetiolation.

After exposure to light, a potato undergoeschanges called de-etiolation, in which shootsand roots grow normally.

A potato’s response to light is an example ofcell-signal processing.

The stages are reception, transduction, andresponse.

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(a) Before exposure to light (b) After a week’s exposure tonatural daylight(a) Before exposure to light (b) After a week’s exposure to

natural daylight

1. Typically, photomorphogenic responses are mostobvious in germinating seedlings, but light affectsplant development in many ways throughout allstages of development.

Photomorphogenesisis the process bywhich plantdevelopment iscontrolled by light

3. PHOTOMORPHOGENESIS

Next

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Process: Seed Germination2. Gibberelic Acid

- Arrives at aleurone cells- Activates certain genes

3. TranscriptionTransportationTranslationamylase

3. Amylase accelerates hydrolysis of starch

Phytochromes, pigments containing protein functioning asphotoreceptor, is involved in some response of plants tolight

Phytochromesare located incytoplasm forthe unactivatedform, and in thenucleus for theactivated form

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What is the type ofphytochromes actually inhibitoryfor seed germination?

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Pr form is firstsynthesized and,after exposed tored, converted toPfr form whichthen entersnucleus andbinds to DNAprotein to inhibitor activatespecific genes

What is the first event in germination?

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The case of Mougeotia An example of Photomorphogenesis is the rotation

of chloroplast observed in Mougeotia- Mougeotia is a filamentous green alga whose cells contain

a single ribbonlike chloroplast nestled between two largevacuoles and surrounded by a layer of cytoplasm.

Phytochrome is implicated in the rotation responseof Mougeotia chloroplast because the system ismost sensitive to red light, and the red light effectcan be reversed by far-red light.- Using microbeams of red and far-red light, Wolfgang

Haupt and his coworkers in Germany showed that inMougeotia, phytochrome is localized near the periphery ofthe cytoplasm in the vicinity of the plasma membrane.

The perpendicularorientation isreferred to as"face position."

- When a microbeam of red light was directed at the cellsurface under a microscope, the edge of the chloroplastadjacent to the microbeam rotated 90°, even though thechloroplast itself was not illuminated.

- The chloroplast can rotate about its long axis and canrespond to light by orienting perpendicularly to thedirection of light

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Haupt and his coworkers discovered that theability of plane-polarized red light to causechloroplast rotation depends on the plane ofpolarization relative to the long axis of the cell. This phenomenon is depicted in the experiment when half of a

cell was illuminated over the entire surface with polarized redlight (R) vibrating perpendicular to the cell axis; the other halfwas illuminated with light vibrating parallel to the cell axis.

The chloroplast rotated from theprofile to the face position only inresponse to red light vibrating inthe perpendicular direction,producing a twist in the chloroplast.On the basis of these experiments,it was concluded that phytochromemolecules have a definedorientation (Haupt 1982).

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4. CASES OF PLANTRESPONSES

1. Response to drought stress

Like all otherhalophilous plants(plants that grow onsaline soil or soilthat affected by saltwater), mangrovescan tolerate higherinternal salinity.

2. Mangrove Adaptation to Salinity

Mangroves balance the osmosis throughaccumulating carbohydrates of small molecularweights inside their bodies instead of proline, anamino acid that most halophilous plantsaccumulate for the balance

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Salt Excretion. Some mangrove plants are saltsecretors. The common salt concentration in the sapis high at about one-tenth that of sea water. Salt ispartially excluded by the roots and the salt is excretedby the salt glands by the plant expending energy

Salt crystals on theleaves of Acanthusilicifolius

Examples: Api-api (Avicennia species), Jeruju (Acanthus species) orKacang-kacang (Aegiceras corniculata)

The concentrated salt solutionevaporates near the gland,becomes crystals which areremoved by wind or rain. Onecan taste the salt by licking theleaves of these species toconfirm this!

Salt gland from the mangroveswamp species Aegicerascorniculatum. (a) Secretorycells surrounded by cuticle andepidermal cells [after W. P.Anderson (ed.), Ion Transportin Plants, Academic Press,New York, 1973].

(b) Section through thegland.

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Salt Exclusion. Other mangrove plants can preventsalt from entering xylem of the roots and stop saltbeing transported to tissues through ultrafiltration.

However, even with this,exclusion is not complete. Somesalt is lost by transpirationthrough the leaf surface oraccumulates in some cells of theleaf.

Species deposit a good part of the excess salts in theold leaves which are shed

Examples: Bruguiera, Lumnitzera, Rhizophora orSonneratia

Shedding of plant parts. They store salt inside thevacuoles or fix it in the leaves in the form of crystals.Salt are expelled by the mother plant when the leavesfall. Some species of mangroves can regulate salinityinside their bodies by a mix of the aforementionedmethods.Examples: Many-petaled Mangrove, Milky Mangrove

Xeromorphic Characters. Mangroves arexeromorphic plants, therefore they must preserve ahigh density of water to minimise absorption of seawater, which has a high salinity. To adapt this uniquehabitat, mangroves develop some special features:- Succulence—some species of mangroves contain water

storing tissues in the leaves- Thick cuticle—ceraceous cuticle and periderm

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- Sunken stomata—concave breathing pores at the back of theleaves

- Buttress root—thick roots to absorb water on the soil surface- Tiny hair—Some leaves possess hair-like trichomes to reduce

water loss

Active growth and increase in succulence ofcells. Mangroves can grow rapidly and have high cellsucculence. These increase their salt storing capacity andweaken the effect of high salinity.

Reduction of transpiration rate. Reduce transpirationon leaf surface can minimise salt intake.

3. Breeding Program In the last few decades, the breeding of

agricultural crops for higher yields has been verysuccessful.

Breeders usually select for high-yieldinggenotypes empirically, without particular attentionto specific plant traits that might be conducive tohigher yields.

However, comparing old, low-yielding lines of anycrop with advanced, high-yielding lines showsclearly that many morphological, physiological,and biochemical traits have been altered by theintense selection pressures for higher yields

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historical series of Pima cotton grown in Arizona. Theabbreviations P32 and PS-1 through PS-7 designatesuccessive commercial releases between 1949 and1996. (From Lu et al. 1998.)

• Stomatal conductance.Stomatal conductancehas increased in parallelwith agronomic yields inirrigated Pima cotton(Gossypium barbadense)selected for higher yieldsat a high temperature.

• The figure shows therelationship between lintyield and stomatalconductance in a

Frequency distribution of stomatal conductance in parental populations of thehigh-yielding Pima cotton line (P73), the old Pima line (P32), and their F1 andF2 progeny.

(A) Nonoverlappingdistribution of stomatalconductance in the twoparental populations.

(B) Distribution of stomatalconductance in an F1population from a crossbetween the two parents.

(C)Distribution of stomatalconductance in an F2population derived fromF1 parents. (After Percyet al. 1996.)

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The relationshipbetween grain yield andstomatal conductance ina historical series ofsemidwarf bread wheatgrown in CiudadObregón, Mexico.

The abbreviations H1 through H8 designate successivecommercial lines released by the International Maize andWheat Improvement Center between 1962 and 1988. (FromLu et al. 1998.)

The importance of membrane lipids for tolerance tolow temperatures

How changes in relative levels of cis-unsaturated molecularspecies of phosphatidylglycerol (PG) in thylakoid membranes of(A) tobacco and (B) Arabidopsis affect sensitivity to chilling.(After Nishida and Murata 1996.)

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Ice Formation in Higher-Plant Cells

(A–B) Supercooling. (B–C) Release of heat during freezing incell walls and intercellular spaces. (C–D) Supercooling. (D–E)Small heat spikes released during intracellular freezing ofindividual protoplasts. (After Brown et al. 1974.)

Temperature ofparenchyma cells incucumber (Cucumissativus) fruit duringfreezing. Thetemperature wasrecorded with anelectronic device, athermistor, insertedinto a 5 × 20 mmcylinder of tissue andimmersed in a coolantat –5.8°C.

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http://leavingbio.net/TheStructureandFunctionsofFlowers%5B1%5D.htm

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The right hand illustration shows the change in chloroplast structureand diagrams the progress of light signals through two receptorsystems, cryptochrome and phytochrome. Adapted from Biochemistryand Molecular Biology of Plants, (c) American Society of PlantBiologists, with permission. Source: Shinkle (?).http://photobiology.info/Shinkle.html

Photomorphogenesis asa morphological and as acellular process.The left photos show thechange in form of anArabidopsis thalianaseedling grown indarkness (top) or in whitelight.