Plant growth inhibitors (Proanthocyanidins) from Prunus armeniaca

Biochemical Systematics and Ecology 26 (1998) 13—23

Plant growth inhibitors (Proanthocyanidins)from Prunus armeniaca

Mohan S.M. Rawat*, Geeta Pant, Devi Prasad, Rakesh K. Joshi,Chandra B. Pande

Department of Chemistry, H.N.B. Garhwal University, Srinagar (Garhwal)-246 174 U.P., India

Received 17 April 1997; accepted 15 May 1997

Abstract

A field survey in Prunus armeniaca growing areas of Garhwal Himalaya was conducted withreference to the germination and growth of some companion crops at various sites of differentsoil fertility. Retardation in germination, growth and yield were noted in nearby ¹riticumaestivum plants, particularly on those sites where the percentage of soil organic matter was low.It was also observed that the magnitude of interference gradually decreased as the distance fromthe tree increased. Aqueous and organic solvent extracts of the aerial parts of Prunus armeniacawere made and their residues were tested, after proper dilution, for their phytotoxic effect ongermination and growth of the test crop. Residues of light petroleum and ethyl acetate extractsshowed maximum inhibition in growth and germination of the test species. The isolatedcompounds were identified with the help of spectroscopic techniques and bioassays. b-Sito-sterol, 2,6-dihydroxy-4-methoxyacetophenone and kaempferol were isolated from a petroleumextract whereas aromadendrin, quercetin, b-sitosterol-b-D-glucoside, pleoside and tannins (fourproanthocyanidins — A-type) were characterized from an ethyl acetate extract. Of these,proanthocyanidins showed maximum inhibition, whereas quercetin, aromadendrin, kaempferoland genin of pleoside inhibited to a lesser extent. ( 1998 Elsevier Science Ltd. All rightsreserved.

Keywords: allelopathy; bioassay; ¹riticum aestivum; Prunus armeniaca

1. Introduction

Prunus armeniaca is an important social- and agro-forestry tree, generally grown ingardens, crop fields and is also traditionally planted in the boundary of agricultural

*Corresponding author.

0305-1978/98/$19.00 ( 1998 Elsevier Science Ltd. All rights reserved.PII: S0305-1978(97)00080-X

fields. The impact of Prunus sp. on surrounding plant species has been noted byseveral workers (Jensen, 1907; Schreiner and Reed, 1907; Manareshi, 1953; Vogel andWeber, 1931; Horsely, 1979). The possibility of biochemical interactions betweenintercrop and crop plants has been suggested in many instances by several workersbased on their practical experience or experimental results (Horsely, 1991; Larcher,1995; Rice, 1984). Manareshi (1953) observed the depressed growth of Prunus cerasuswhen planted in Prunus armeniaca fields. So, the present investigation was carried outto determine the impact of Prunus armeniaca on surrounding crop species and toisolate the responsible allelopathic compounds.

2. Materials and methods

Field studies were conducted in the areas where Prunus armeniaca trees were foundgrowing in the vicinity of crops, namely wheat, barley, lantil and fingermillet. Thefertility ingredients of the soil of different sites, namely percentage of organic matter,available phosphorus and potassium, were determined by the rapid Purdue test(Jackson, 1973). The ¹riticum aestivum (wheat) crop was found to be more affected byPrunus armeniaca in different sites. Therefore, further observations regarding growthand development of ¹riticum aestivum was made at a distance of 3 m from the trees toeliminate a direct shading effect. The observations of plant germination, height andyield were recorded by making four quadrates of 1 m2 each, i.e. 3—4, 4—5, 5—6 and6—7 m from Prunus armeniaca. The fifth quadrate 7 m from the tree was considered asnormal, where the interference was considered zero (Narwal and Sarmah, 1992). Fourdifferent fields of almost the same height and fertility ingredients were taken for theobservational studies. The percentage reduction in germination was calculated bycounting the seedlings in each quadrate after 5 weeks of sowing and comparing themwith the population of a normal quadrate where germination was considered as100%. Data regarding height and yield were recorded after maturity of the crop, fromthe average of 20 healthy plants in each quadrate and compared with the average ofthe same number of healthy plants from the normal quadrate where the height andyield were considered as 100%. Finally the average of germination, height and yield offour different fields was calculated (Fig. 1).

The plant material (aerial parts) was collected from mature fruiting trees andwas shade dried and ground. Aqueous extracts were prepared from 40 g materialsuspended in 1000 ml double distilled water for 48 h at room temperature (Anaya etal., 1987; Jimenez-Osornio and Gliessman, 1987) and tested for bacterial growth,which was not observed in the extract (Theroux et al., 1992). The extract was vacuumfiltered through Whatman filter paper No. 1 and dried in vacuum under reducedpressure.

For the bioassay of solvent extracts and characterization of allelochemicals, 1 kg ofdried and powdered plant material was extracted with ethanol. After evaporationunder reduced pressure, the residue was successively extracted in a Soxhlet apparatuswith light petroleum (60—80° BDH), chloroform (BDH), ethyl acetate (BDH) andmethanol (BDH). All extracts were dried in vacuum under reduced pressure.

14 M.S.M. Rawat et al./Biochemical Systematics and Ecology 26 (1998) 13—23

Fig. 1. Effect of Prunus armeniaca on ¹riticum aestivum at varying distances.

The bioassay of different organic solvent extracts and the aqueous extract (400 ppmconcentration) was carried out using ¹riticum aestivum as the test crop. Fifty milli-grams of water and each organic solvent residue, were dissolved separately in 50 ml ofthe solvent in which they were extracted and 2 ml of this solution was poured on toWhatman filter paper No. 1 in Petri-dishes (9 cm diameter). In controls only 2 ml ofthe respective solvents were used. After evaporation of the solvent, 5 ml doubledistilled water was added and 10 seeds of the test crop were set in each Petri-dish andcovered with another filter paper. Each extract and control treatments were replicatedfour times. All the Petri-dishes were kept in an incubator at 25$1°C for approxim-ately 72 h. The percentage inhibition in terms of roots, shoot length and germinationwas calculated by considering the control as zero.

For characterization of allelochemicals the residues of the light petroleum extractand the ethyl acetate extract were subjected to column chromatography over silica gel(Merck). The residue of the light petroleum extract on gradient elution with benzene(BDH):ethyl acetate afforded compounds A, B and C whereas the ethyl acetate extracton elution with chloroform followed by gradient elution with chloroform:methanol,afforded compounds D, E, F, G and a mixture of four compounds (fraction H).Fraction H was further separated by HPLC using the ODS-C

18column,

MeOH—H2O solvent system (22:78, v/v), UV detector (j

.!9254 nm), at the temper-

ature 40$1°C and 6 ml min~1 flow rate, to afford compounds I-1, I-2, I-3 and I-4.Melting points were determined on a Boetius micro-melting point apparatus and

are uncorrected. Optical rotations were measured by a JASCO DIP-SL automatic

M.S.M. Rawat et al./Biochemical Systematics and Ecology 26 (1998) 13—23 15

polarimeter (cell length 0.5 dm). Electron impact (EI) and fast atom bombardment(FAB) mass spectra were recorded using JEOL D-300 and JEOL SX-102 massspectrometers. CD data were obtained in ethanol on JASCO J-20 spectrometer.1H and 13C NMR spectra (d values) were recorded using JEOL EX-270 and GSXa-500 spectrometers, using TMS as the internal standard.

2.1.1. Light petroleum extractCompound A. b-Sitosterol; colourless needles (MeOH), m.p. 135—143°C, [a]

D!35°

(CHCl3; C"1.0). EI-MS m/z: 414 [M]`, 1H NMR (CDCl

3): 0.68 (s, 3H), 0.78 (s, 3H),

0.88 (s, 3H), 0.97 (d, 6H), 1.0 (s, 3H), 3.7 (m, 3H), 4.5 (s, 1H).Compound B. 2,6-Dihydroxy-4-methoxyacetophenone; colourless crystals, m.p.

140°C; EI-MS m/z: 182 [M]`, 1H NMR (CDCl3#DMSO): 11.70 (s, 2H, 2-OH and

6-OH), 5.90 (s, 2H, H-3 and H-5), 3.75 (s, 3H, —OCH3), 2.60 (s, 3H, O"C—CH

3;

13C NMR (CDCl3#DMSO): 163.4 (C-4), 164.3 (C-2 and C-6), 93.2 (C-3 and C-5),

105.3 (C-1), 55.2 (—OCH3), 32.6 (O"C—CH

3) and 203.4 (C"O).

Compound C. Kaempferol; light yellow needles (MeOH), m.p. 274—275°C.13C NMR (CDCl

3): 146.2 (C-2), 134.2 (C-3), 176.9 (C-4), 160.7 (C-5), 98.8 (C-6), 161.6

(C-7), 93.6 (C-8), 157.7 (C-9), 144.9 (C-10), 120.5 (C-1@), 130.5 (C-2@ and C-6@), 115.9 (C-3@and C-5@), and 160.1 (C-4@).

2.1.2. Ethyl acetate extractCompound D. Aromadendrin; colourless needles (MeOH), m.p. 236°C, EI-MS m/z:

288 [M]`, 1H NMR (CDCl3): 4.95 (d, 1H, H-2), 4.45 (d, 1H, H-3), 6.00 (d, 2H, H-6 and

H-8), 7.35 (d, 2H, H-2@ and H-6@), and 6.85 (d, 2H, H-3@ and H-5@). 13C NMR (CDCl3):

82.7 (C-2), 71.3 (C-3), 197.7 (C-4), 163.2 (C-5), 95.9 (C-6), 166.7 (C-7), 94.8 (C-8), 162.4(C-9), 100.3 (C-10), 128.3 (C-1@), 129.3 (C-2@ and C-6@), 114.7 (C-3@ and C-5@) and 157.6(C-4@).

Compound E. Quercetin; yellow needles (MeOH), m.p. 312—313°C, EI-MS m/z: 302,1H NMR (DMSO): 6.12 (d, 1H, J"1.9 Hz, H-6), 6.50 (d, 1H, J"1.9 Hz, H-8), 7.51 (d,1H, J"1.6, H-2@), 7.53 (dd, 1H, J"1.6, 8.2 Hz, H-6@), 6.81 (d, 1H, J"8.2 Hz, H-5@),13C NMR (DMSO): 146.7 (C-2), 135.6 (C-3), 176.0 (C-4), 160.8 (C-5), 92.4 (C-6), 164.1(C-7), 93.5 (C-8), 156.2 (C-9), 103.2 (C-10), 122.2 (C-1@), 115.3 (C-2@), 145.2 (C-3@), 147.9(C-4@), 115.7 (C-5@), 120.7 (C-6).

Compound F. b-Sitosterol-b-D-glucoside; white crystals (MeOH), m.p. 295—298°C,EI-MS m/z: 576 [M]`. On acid hydrolysis (5% methanolic HCl) an aglycone b-sitosterol (compound A) and D-glucose were obtained.

Compound G. Pleoside (Domesticoside; 2-O-glucosyl-6-hydroxy-4- methoxy-acetophenone); white crystals (MeOH), m.p. 200—203°C, [a]

D!41.6° (C

5H

5N,

C"3.2), FAB-MS#ve m/z: 345 [M#H]`, 1H NMR (CD3COCD

3#DMSO#

CDCl3): 6.4 (d, 1H, H-3), 6.1 (d, 1H, H-5) 3.9 (s, 3H, —OCH

3), 2.7 (s, 3H, O"C—CH

3),

13.8 (s, 1H, 6-OH), 5.1 (d, 1H, H-1@), 3.5 (sugar multiplet); 13C NMR: 106.8 (C-1), 162.0(C-2), 95.9 (C-3), 166.9 (C-4), 94.3 (C-5), 167.4 (C-6), 56.0 (—OCH

3), 33.5 (O"C—CH

3),

204.5 (C"O), 102.0 (C-1@), 74.3 (C-2@), 78.2 (C-3@), 71.0 (C-4@), 79.2 (C-5@), 62.3 (C-6@).Acid hydrolysis of G; compound G (20 mg) was refluxed with 5% methanolic HCl for


1 h. The aglycone was extracted with EtOH (5 ml) and crystallized from MeOH. Itwas identified as 2,6-dihydroxy-4-methoxyacetophenone (compound B) by compari-son of spectral data with that of an authentic sample. The neutralized hydrolysatecontained D-glucose only (PC, BuOH:HOAc:H

2O, 4:1:5, v/v), authentic glucose run in

parallel.Compound I-1. Mahuannin A; colourless amorphous powder, m.p. '360°C, FAB-

MS #ve m/z: 545 [M#H]`, 1H NMR (CD3COCD

3): 4.41, d (J"3.5 Hz, 1H, H-3),

4.78, d (J"3.5 Hz, 1H, H-4), 5.99, d (J"2.0 Hz, 1H, H-6), 6.08, d (J"2.0 Hz, 1H,H-8), 7.46, d (J"8.1 Hz, 2H, H-12, 16), 6.81, d (J"8.1 Hz, 2H, H-13, 15), 5.10, brs(1H, H-2@), 4.27, dd (J"2.7, 3.9 Hz, 1H, H-3@), 2.93, brdd (J"3.9, 16.2 Hz, 1H, H-4@a),2.86, brdd (J"2.7, 16.2 Hz, 1H, H-4@b), 6.11, s (1H, H-6@), 7.48, d (J"8.1 Hz, 2H,H-12@, 16@), 6.84, d (J"8.1 Hz, 2H, H-13@, 15@); 13C NMR (CD

3COCD

3): 100.5 (C-2),

67.2 (C-3), 29.1 (C-4), 156.9 (C-5), 97.6 (C-6), 157.4 (C-7), 96.1 (C-8), 155.1 (C-9), 103.1(C-10), 130.9 (C-11), 129.4 (C-12, 16), 116.1 (C-13, 15), 159.2 (C-14), 80.2 (C-2@), 67.2(C-3@), 29.3 (C-4@), 155.1 (C-5@), 96.3 (C-6@), 158.1 (C-7@), 106.2 (C-8@), 151.3 (C-9@), 105.6(C-10@), 129.9 (C-11@), 129.1 (C-12@, 16@), 115.6 (C-13@, 15@), 156.6 (C-14@); CD:[h]227!111 400, [h]202#86 400, [h]270#9280 and [h]279#11 000.

Compound I-2. Ephedrannin A; colourless amorphous powder, m.p. '360°C,FAB-MS #ve m/z: 557 [M#H]`, 1H NMR (CD

3COCD

3): 4.39, d (J"3.3 Hz, 1H,

H-3), 5.09, d (J"3.3 HZ, 1H, H-4), 6.14, d (J"1.8 Hz, 1H, H-6), 6.08, d (J"1.8 Hz,1H, H-8), 7.92, d (J"8.6 Hz, 2H, H-12, 16), 6.93, d (J"8.6 Hz, 2H, H-13, 15), 6.24,s (1H, H-6@), 8.52, d (J"8.6 Hz, 2H, H-12@, 16@), 6.99, d (J"8.6 Hz, 2H, H-13@, 15@);13C NMR (CD

3COCD

3): 100.7 (C-2), 67.1 (C-3), 29.0 (C-4), 157.4 (C-5), 97.2 (C-6),

158.1 (C-7), 95.9 (C-8), 154.1 (C-9), 103.6 (C-10), 130.8 (C-11), 129.3 (C-12, 16), 115.4(C-13, 15), 160.1 (C-14), 147.6 (C-2@), 136.7 (C-3@), 176.6 (C-4@), 159.3 (C-5@), 98.9 (C-6@),158.7 (C-7@), 107.4 (C-8@), 152.6 (C-9@), 105.2 (C-10@), 123.5 (C-11@), 131.1 (C-12@, 16@),116.1 (C-13@, 15@), 160.2 (C-14@).

Compound I-3. Mahuannin B; colourless amorphous powder, m.p. '360°C, FAB-MS #ve m/z 545 [M#H]`, 1H NMR (CD

3COCD

3): 4.31, d (J"3.3 Hz, 1H, H-3),

4.57, d (J"3.3 Hz, 1H, H-4), 6.06, d (J"2.0 Hz, 1H, H-6), 6.09, d (J"2.0 Hz, 1H,H-8), 7.44, d (J"8.1 Hz, 2H, H-12, 16), 6.79, d (J"8.1 Hz, 2H, H-13, 15), 4.99, brs(1H, H-2@), 4.29, dd (J"2.8, 3.7 Hz, 1H, H-3@), 2.91, brdd (J"3.7, 16.9 Hz, 1H, H-4@a),2.87, brdd (J"2.6, 16.9 Hz, 1H, H-4@b), 6.12, s (1H, H-6@), 7.46, d (J"8.1 Hz, 2H,H-12@, 16@), 6.86, d (J"8.1 Hz, 2H, H-13@, 15@), 13C NMR (CD

3COCD

3): 100.3 (C-2),

66.9 (C-3), 29.0 (C-4), 157.1 (C-5), 97.8 (C-6), 157.3 (C-7), 96.0 (C-8), 155.3 (C-9), 103.4(C-10), 130.8 (C-11), 129.5 (C-12, 16), 116.3 (C-13, 15), 159.4 (C-14), 81.4 (C-2@), 67.9(C-3@), 29.7 (C-4@), 155.3 (C-5@), 96.3 (C-6@), 158.2 (C-7@), 106.5 (C-8@), 151.9 (C-9@), 105.8(C-10@), 130.1 (C-11@), 129.8 (C-12@, 16@), 115.7 (C-13@, 15@), 156.7 (C-14@); CD:[h]222#71 000, [h]203!111 000, [h]270!14 670 and [h]280!8400.

Compound I-4. 13@-Hydroxy mahuannin A; white amorphous powder, m.p. '360°C,FAB-MS #ve m/z 561 [M#H]`, 1H NMR (CD

3COCD

3): 4.12, d (J"3.4 Hz, 1H,

H-3), 4.40, d (J"3.4 Hz, 1H, H-4), 5.92, d (J"2.2 Hz, 1H, H-6), 6.01, d (J"2.2 Hz,1H, H-8), 7.44, d (J"8.6 Hz, 2H, H-12, 16), 6.83, d (J"8.6 Hz, 2H, H-13, 15), 4.89,brs (1H, H-2@), 4.10, dd (J"4.0, 3.1 Hz, 1H, H-3@), 2.77, brdd (J"4.0, 16.3 Hz, 1H,H-4@a), 2.63, brdd (J"3.1, 16.3 Hz, 1H, H-4@b), 6.05, s (1H, H-6@), 7.12, d (J"1.4 Hz,


1H, H-12@), 6.81, d (J"8.7 Hz, 1H, H-15@), 6.89, dd (J"8.7, 1.4 Hz, 1H, H-16@).13C NMR (CD

3COCD

3): 99.1 (C-2), 66.0 (C-3), 27.9 (C-4), 155.8 (C-5), 96.5 (C-6), 156.4

(C-7), 94.7 (C-8), 152.7 (C-9), 102.9 (C-10), 130.1 (C-11), 127.7 (C-12, 16), 115.0 (C-13,15), 157.5 (C-14), 78.9 (C-2@), 64.5 (C-3@), 28.6 (C-4@), 154.9 (C-5@), 94.9 (C-6@), 150.3 (C-7@),105.7 (C-8@), 150.1 (C-9@), 100.9 (C-10@), 130.2 (C-11@), 114.7 (C-12@), 144.7 (C-13@), 144.6(C-14@), 115.2 (C-15@), 117.9 (C-16@); CD: [h]227!65 000, [h]203#3400.

The bioassays of isolated compounds were carried out with 40 ppm concentrationof their respective solutions. A similar procedure to that described previously wasused.

3. Results and discussion

Light petroleum and ethyl acetate extracts showed more inhibition than otherextracts, with respect to parameters observed in the bioassays (Fig. 2), namely inhibi-tion in germination, root length and shoot length indicated the presence of ac-tive/toxic compounds in higher concentrations.

Therefore, light petroleum and ethyl acetate extracts were subjected to repeatedcolumn chromatography on silica gel to afford compounds A to G and I-1 to I-4.

Compounds A—E were shown to be b-sitosterol (Austin et al., 1969), 2,6-dihydroxy-4-methoxyacetophenone (Hikino et al., 1969), kaempferol (Markham et al., 1978;

Fig. 2. Effect of aerial part extracts (400 ppm) of Prunus armeniaca on ¹riticum aestivum seedling biossays.


Mabry et al., 1970), aromadendrin (Manez et al., 1988) and quercetin (Markham et al.,1978; Mabry et al., 1970) by comparison with authentic samples and spectral data.Compound F was identified to be b-sitosterol-b-D-glucoside (Austin et al., 1969) byco-TLC, co-IR and MMP with an authentic sample. On acid hydrolysis, F yieldedcompound A and glucose. Compound G was identified as pleoside (domesticoside;2-O-glucosyl-6-hydroxy-4-methoxyacetophenone) (Hikino et al., 1969; Pande, 1995).The 1H NMR spectrum of G, showed a doublet (J"7.4 Hz) for an anomeric protonof b-linked glucose at 5.1. The two aromatic protons recorded at 6.4 and 6.1, wereassigned to H-3 and H-4, respectively. Acidic hydrolysis of G afforded compoundB and glucose. The sugar moiety was identified by paper chromatography (PC). Theaglycone was identified by comparing its spectral data with compound B.

Compounds I-1 to I-4 were characterized as A-type proanthocyanidins. The 1H-NMR spectra of these compounds displayed characteristic AB doublets(J"3.3—3.5 Hz) of A-type proanthocyanidins (Balde et al., 1991) in the heterocyclicregion, which is supported by the typical ketal carbon resonance at 100.5, 100.7, 100.3and 99.1 for I-1, I-2, I-3 and I-4, respectively.

The 1H- and 13C-NMR data of I-1 and I-3 were identical. The only difference wasthe sign of Cotton effect. I-1 showed (!)-ve couplet at (h)227!114 100 while I-3showed (#)-ve couplet at (h)222#71 000, which suggested that I-1 has a 2S-3S-4Sand I-3 has a 2R-3R-4R configuration (Barrett et al., 1979). The spectral data of I-1and I-3 were in close agreement with the data reported for mahuannin A andB (Hikino et al., 1982a,b). Therefore, I-1 and I-3 were characterized as ent-epiaf-zelechin-(2aP7, 4aP8)- epiafzelechin and epiafzelechin-(2bP7, 4bP8)-epiaf-zelechin, respectively.

The 1H- and 13C-NMR data of I-4 were also similar to those of I-1 and I-3. Theonly significant difference observed being the presence of an AMX type spectrum inthe aromatic region (6.81—7.12), due to E-ring protons of lower flavane moiety. Thesedata indicate that the lower flavane moiety was substituted at the 13@ and 14@ positionsby OH function, which is substantiated by 13C chemical shifts of C-13@ at 144.7 andC-14@ at 144.6. CD measurements of I-4 showed a (!)-ve Cotton effect at 227 nmwhich suggested the 2a, 4a linkages in I-4 as found in I-1. On the basis of theseobservations, I-4 is identified as 13@-hydroxy mahuannin A; ent-epiafzelechin-(2aP7,4aP8)-epicatechin (Pant et al., 1992).

The 1H-NMR spectrum of I-2 displayed only two doublets (J"3.3 Hz) in theheterocyclic region at 4.39 and 5.09, assigned for H-3 and H-4 of upper flavane moiety.The 13C-NMR spectrum of I-2 displayed the presence of a carbonyl function at 176.6which indicated the presence of a keampferol unit in I-4. This is further substantiatedby 13C chemical shifts of C-2@ at 147.6, C-3@ at 136.7, C-12@, 16@ at 131.1 and C-13@, 15@at 116.1 which coincided with carbon signals of B- and C-ring of kaempferol (Mar-kham et al., 1978). On the basis of these observations, I-2 was characterized asephedrannin A; ent-epiafzelechin-(2aP7, 4aP8)-kaempferol (Fig. 3d) (Hikino et al.,1982a,b).

The bioassay of isolated compounds revealed that proanthocyanidins and kaem-pferol showed maximum inhibition to germination and growth of ¹riticum aestivumseedlings, whereas 2,6-dihydroxy-4-methoxyacetophenone, pleoside, aromadendrin


Fig. 3. Structures of A-type Proanthocyanidins.

and quercetin affected mainly the growth of the test crop (Fig. 4) at the concentrationof 40 ppm. Among tannins (proanthocyanidins), the order of inhibition was found tobe 13@-hydroxy mahuannin'ephedrannin A'mahuannin A'mahuannin B.

Field observations (Fig. 1), bioassays with extracts (Fig. 2) and bioassays withisolated compounds (Fig. 4) led to the conclusion that the inhibition in germinationand growth and reduction in yield might be due to an allelopathic effect. In fieldstudies, the percentage reduction in germination, growth and yield decreased as thedistance from the tree increased, which suggests that the allelochemicals released fromthe tree inhibit germination as well as growth and yield of the test crop, and in turnaffect the yield of the crop. The tannins possibly interfere with the growth of nitrifyingbacteria (Rice and Pancholy, 1973) and inactivate plant b-glucosidases (Spencer,1987), which may cause inhibition in the growth and germination of the test crop. Thisresult substantiates that tannins (proanthocyanidin A-type) are more inhibitory whencompared to other compounds at a concentration of 40 ppm. Some of these isolatedcompounds are reported to affect various metabolic processes of plants. For example,kaempferol is inhibitory to the synthesis of ATP and acts as an energy transferinhibitor and also inhibits the phosphorylation mechanism (Arntzen et al., 1974;Koeppe and Miller, 1974).


Fig. 4. Effect of isolated compounds (40 ppm) from Prunus armeniaca on ¹riticum aestivum seedlinggrowth.

Acknowledgements

The authors wish to thank Professor A. N. Purohit, FNA, Director, HAPPRC,H.N.B. Garhwal University for many valuable suggestions and G.B. Pant, Institute ofHimalayan Environment and Development, Kosi-Katarmal, Almora for financialsupport.


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Plant growth inhibitors (Proanthocyanidins) from Prunus armeniaca

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