Showing papers on "Gibberellic acid published in 1986"
TL;DR: It is concluded that in response to gibberellic acid, barley aleurone tissue secretes a nuclease having ribonuclease, deoxyribonucleasing, and 3'-nucleotidase activities.
Abstract: Incubation of barley (Hordeum vulgare L. cv Himalaya) half-seeds with gibberellic acid enhances the secretion of ribonuclease and deoxyribonuclease from aleurone tissue (MJ Chrispeels, JE Varner 1967 Plant Physiol 42: 398-406; L Taiz, JE Starks 1977 Plant Physiol 60: 182-189). These activities were over 50-fold greater in medium of half-seeds incubated with gibberellic acid than in control medium. Ribonuclease and deoxyribonuclease activities initially appeared in the medium 24 to 48 hours after hormone induction and increased for up to 96 hours. Both activities had a pH optimum of 6.0 and a temperature optimum of 55°C. When the medium from gibberellic acid-treated half-seeds was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, the major ribonuclease and deoxyribonuclease activity bands comigrated. The two enzyme activities remained associated throughout a 2,700-fold purification employing ammonium sulfate fractionation, Heparin-Agarose affinity chromatography, and Reactive Blue 2-Agarose affinity chromatography. Also accompanying the ribonuclease and deoxyribonuclease activities throughout purification was the ability to hydrolyze the 3′-phosphoester linkage of 3′-AMP. The purified protein was composed of a single polypeptide with an apparent molecular weight of 36 kilodaltons as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It is concluded that in response to gibberellic acid, barley aleurone tissue secretes a nuclease having ribonuclease, deoxyribonuclease, and 3′-nucleotidase activities.
116 citations
TL;DR: The patterns of isoenzyme secretion are suggestive of tissue-specific differences in expression of the genes which code for (1-->3,1-->4)-beta-glucanase isoenzymes, which were obtained with barley cultivars harvested in Australia and North America.
Abstract: An immunological assay has been used to investigate the synthesis of (1→3,1→4)-β-glucanase (EC 3.2.1.73) isoenzymes from isolated barley aleurone layers and scutella. Enzyme release from both tissues is enhanced by 1 micromolar gibberellic acid and 10 millimolar Ca2+, although increases induced by gibberellic acid are observed only in the presence of Ca2+. Isoenzyme I is synthesized predominantly in the scutellum, while isoenzyme II is synthesized exclusively in the aleurone. A third, putative isoenzyme III has been detected in significant proportions in scutellar secretions and may also be secreted from aleurone layers. Both gibberellic acid and Ca2+ appear to preferentially enhance isoenzyme II secretion from the aleurone and isoenzyme III secretion from scutella. The patterns of isoenzyme secretion are suggestive of tissue-specific differences in expression of the genes which code for (1→3,1→4)-β-glucanase isoenzymes. Qualitatively similar results were obtained with barley cultivars harvested in Australia and North America.
93 citations
TL;DR: Of nine plant growth regulators tested, only 6-benzylaminopurine and abscisic acid affected C-photosynthate unloading from excised seed coats of Phaseolus vulgaris L.
Abstract: Of nine plant growth regulators (indoleacetic acid, 1-naphthalene acetic acid, gibberellic acid, giberellin 4/7, 6-benzylaminopurine, 6-furfurylaminopurine, abscisic acid, and 1-aminocyclopropane carboxylic acid) tested, only 6-benzylaminopurine and abscisic acid affected 14C-photosynthate unloading from excised seed coats of Phaseolus vulgaris L. Unloading, in the presence of KCl, was stimulated by 25 to 40%. Stimulation occurred immediately for 6-benzylaminopurine and for abscisic acid within 10 to 12 minutes of application.
81 citations
TL;DR: It is concluded that some step leading to flowering and which determines the differences in sensitivity of the buds to this growth regulator has taken place already at this early date.
Abstract: In the Satsuma mandarin (Citrus unshiu Marc.) the presence of the fruit results in a gradual inhibition of flowering and of bud sprouting. This inhibitory effect starts several months before the onset of the winter rest period and lasts until the end of the accumulation of carotenoids in the fruit peel, more than one month after the completion of fruit growth. During all this time and until natural bud sprouting, flowering and bud sprouting are inhibited by exogenous gibberellic acid. Peak responses to this growth regulator coincide with periods of maximal rates of flowering inhibition by the fruit. Kinetin and abscisic acid, applied at the time of peak response to gibberellic acid, inhibited flowering and reduced the number of shoots developed through the reduction of the number of shoots formed per sprouted node, but failed to reduce the number of nodes which sprouted. The same pattern of sprouting was obtained in trees treated with gibberellic acid during the winter rest period or several months earlier. It is concluded that some step leading to flowering and which determines the differences in sensitivity of the buds to this growth regulator has taken place already at this early date.
64 citations
TL;DR: In vitro translation using total RNA isolated from ABA-treated aleurone layers indicated that translatable mRNA levels of these proteins essentially paralleled the levels of in vivo synthesized proteins.
Abstract: As part of a continuing effort to elucidate the mode of action of abscisic acid (ABA) in barley (Hordeum vulgare L. cv Himalaya) aleurone layers, we have investigated the induction of several polypeptides by ABA in this tissue. There were nine ABA-induced polypeptides as observed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and considerably more (at least 16 spots) on a two-dimensional gel. These proteins started to show enhanced synthesis 2 to 4 hours after ABA treatment, and their synthesis continued for at least 48 hours. In vitro translation using total RNA isolated from ABA-treated aleurone layers indicated that translatable mRNA levels of these proteins essentially paralleled the levels of in vivo synthesized proteins. The most abundant of the ABA-induced proteins was a 29 kilodalton polypeptide which was also synthesized in tissue incubated without ABA. In vivo synthesis of this protein declined as ABA concentration was decreased, with 1 nanomolar ABA approaching control level. Cell fractionation experiments located the 29 kilodalton major ABA-induced protein in 1,000g and 13,000g pellets; most other induced proteins were in the 80,000g supernatant. The 29 kilodalton protein appeared to be sensitive to degradation by sulfhydryl type proteases. As expected, the induction of these proteins by ABA was suppressed by gibberellic acid. Phaseic acid, the first stable metabolite of ABA, suppressed the gibberellic acid-enhanced α-amylase synthesis but was unable to induce the ABA-induced proteins. None of the ABA-induced proteins were secreted into the incubation medium. A 36 kilodalton ABA-induced protein showed cross-reactivity with antibody against a barley lectin specific for glucosamine, galactosamine, and mannosamine.
57 citations
TL;DR: The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA(3), KIN, and CO(2).
Abstract: Application of exogenous ethylene in combination with gibberellic acid (GA3), kinetin (KIN), and/or CO2 has been reported to induce germination of lettuce seeds at supraoptimal temperatures. However, it is not clear whether endogenous ethylene also plays a mediatory role when germination under these conditions is induced by treatment regimes that do not include ethylene. Therefore, possible involvement of endogenous ethylene during the relief of thermoinhibition of lettuce (Lactuca sativa L. cv Grand Rapids) seed germination at 32°C was investigated. Combinations of GA3 (0.5 millimolar), KIN (0.05 millimolar), and CO2 (10%) were used to induce germination. Little germination occurred in controls or upon treatment with ethylene, KIN, or CO2. Neither KIN nor CO2 affected the rate of ethylene production by seeds. Both germination and ethylene production were slightly promoted by GA3. Treatments with GA3+CO2, GA3+KIN, or GA3+CO2+KIN resulted in approximately 10-to 40-fold increases in ethylene production and 50 to 100% promotion of germination as compared to controls. Initial ethylene evolution from the treated seeds was greater than from the controls and a major surge in ethylene evolution occurred at the time of visible germination. Application of 1 millimolar 2-aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene synthesis, in combination with any of above three treatments inhibited the ethylene production to below control levels. This was accompanied by a marked decline in germination percentage. Germination was also inhibited by 2,5-norbornadiene (0.25-2 milliliters per liter), a competitive inhibitor of ethylene action. Application of exogenous ethylene (1-100 microliters per liter) overcame the inhibitory effects of AVG and 2,5-norbornadiene on germination. The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA3, KIN, and CO2. It also appears that these treatment combinations do not act exclusively via promotion of ethylene evolution as the application of exogenous ethylene alone did not promote germination.
55 citations
TL;DR: By culturing portions of lentil shoot meristems and epicotyls on a medium containing kinetin and gibberellic acid, callus tissue was produced which could be induced to regenerate shoots in relatively large numbers, even after several subcultures.
Abstract: Until recently, grain legumes in general have proven recalcitrant at de novo regeneration in vitro. By culturing portions of lentil (Lens culinaris) shoot meristems and epicotyls on a medium containing kinetin and gibberellic acid, callus tissue was produced which could be induced to regenerate shoots in relatively large numbers, even after several subcultures. The shoots could be rooted in a mist chamber to yield whole, fertile plants.
52 citations
TL;DR: Aleurone tissue from freshly harvested immature wheat grains which is normally unresponsive to gibberellic acid can be made responsive by subjecting the tissue to a pre-incubation treatment in a simple buffered medium prior to the addition of the growth substance.
Abstract: Aleurone tissue from freshly harvested immature wheat grains (Triticum aestivum L. cv. Sappo) which is normally unresponsive to gibberellic acid can be made responsive by subjecting the tissue to a pre-incubation treatment in a simple buffered medium prior to the addition of the growth substance. The effectiveness of this treatment is dependent on grain age, with grains less than 15–20 days post anthesis failing to become converted to a responsive state whilst tissue from grains older than this become increasingly susceptible. Tissue from grains of a certain age (approx. 25–28 days post anthesis) produce small amounts of α-amylase following this treatment even in the absence of exogenously applied growth substance. Using different 32-labelled complementary-DNA probes for α-amylase in wheat it was demonstrated that the failure of freshly harvested tissue to produce α-amylase was correlated with the absence of the appropriate mRNA species. Inability to accumulate α-amylase mRNA in response to gibberellic acid was removed by the pre-iccubation treatment and also by enforced drying. The gibberellin-regulated expression of other unidentified genes also responds to pre-incubation or drying. Induction of gibberellin-responsiveness in immature aleurone cells did not extend to the secretion of acid phosphatase, protease and ribonuclease.
48 citations
TL;DR: The fungus Fusarium moniliforme was entrapped in sodium alginate gel to synthesize gibberellic acid from paneer (cheese) whey resulting in comparatively higher yield than free fungal mycelium under optimized conditions.
39 citations
TL;DR: The results show that the release of the initial large polypeptide fragments from hordein proteins is mediated by a protease(s) whose appearance is not dependent on the exogenously added gibberellic acid, and further hydrolysis is, however, mediated by proteases induced in the presence of this growth substance.
Abstract: Soluble products, released by the hydrolysis of hordeins into the media of barley (Hordeum vulgare cv. Perth) half-seeds were analyzed. Large polypeptide fragments (methanol-insoluble) were identified using the Western immunoblot technique with the antibodies prepared against B and C polypeptides of hordein. A number of hordein IgG-reacting bands were noted in the samples from dry kernels. In samples incubated in the absence of gibberellic acid, polypeptide fragments in the size range of 25 to 30 kilodaltons appeared within 24 hours, and those in the size range of 40 kilodaltons became more prominent. In samples incubated in the presence of gibberellic acid, polypeptide fragments in the size range of 45 to 67 kilodaltons were less apparent and those in the size range of less than 15 kilodaltons were more pronounced. The hordein-related polypeptide fragments were present in low amounts after 72 hours in the presence of gibberellic acid. Methanol-soluble peptides were fractionated, on the basis of size, into two broad peaks. In the absence of gibberellic acid, there was no significant change in their profile over a 72 hour incubation period. In the presence of this growth substance, however, there was a decrease in the proportion of large size peptides (50-70 amino acid residues in length), and an increase in the levels of small peptides (15-35 amino acid residues in length) and amino acids. Our interpretation of the results is that the release of the initial large polypeptide fragments from hordein proteins is mediated by a protease(s) whose appearance is not dependent on the exogenously added gibberellic acid. Further hydrolysis is, however, mediated by proteases induced in the presence of this growth substance.
38 citations
TL;DR: It is indicated that GA3 modifies the thermal sensitivity of meristem function in Gramineae in a manner which enhances low-temperature growth.
Abstract: High-resolution growth measurements were conducted using a linear variable displacement transformer in conjunction with a temperature-programmed meristem-cooling collar. Chilling and rewarming profiles were determined for a range of Gramineae, in the presence and absence of varying concentrations of gibberellic acid (GA3). In wheat (Triticum aestivum L.) seedlings, the growth-constraining temperature (Pe) was progressively lowered by increasing GA3 concentration, with a difference of-4.8°C between controls and material treated with 10−4 M GA3. Dwarf-5 maize (Zea mays L.) seedlings had a higher Pe than tall segregates and the difference was markedly reduced by exposure to a saturating concentration of GA3. A similar effect was observed with Tanginbozu dwarf rice (Oryza sativa L.). The growth ratetemperature responses of Rht3 gibberellin-insensitive dwarf wheat seedlings were unaffected by GA3 and the Pe values for these segregates were around 5° C higher than for normals. Slender (s1) barley (Hordeum vulgare L.) genotypes had Pe values of-7° C, compared with +4° C for wild-type material, and did not show positive hysteresis for growth rate during the rewarming phase. These studies indicate that GA3 modifies the thermal sensitivity of meristem function in Gramineae in a manner which enhances low-temperature growth.
TL;DR: These treatments overcame secondary dormancy at all times, indicating the presence of only one of the two known blocks to germination that exist during primary dormancy.
Abstract: The induction of secondary dormancy in caryopses of genetically pure dormant lines of Avena fatua L. is described. Seeds harvested from mature plants were after-ripened under controlled conditions (26°C, 25% relative humidity) until fully non-dormant. Secondary dormancy was then induced into these caryopses by incubation on moist filter papers in an aspirated nitrogen atmosphere at 20°C over periods from 3 h to 14 days. These caryopses failed to germinate when returned to an aerobic environment. The dose-response curves for gibberellic acid, sodium azide, sodium nitrite, sodium nitrate and ethanol show that all of these treatments can overcome the induced secondary dormancy. Drying increased the sensitivity of secondary dormant caryopses to these treatments. These treatments overcame secondary dormancy at all times, indicating the presence of only one of the two known blocks to germination that exist during primary dormancy. Similarities between primary and secondary dormancy in A. fatua are discussed.
TL;DR: Inhibition of germination by exogenous applications of all highly active phenols except salicylic acid was alleviated by the application of gibberellic acid and kinetin.
Abstract: Seeds of Atriplex triangularis contained phenols: small seeds had gentisic, salicylic, syringic, and chlorogenic acids and catechol; medium seeds, gentisic and salicylic acids and catechol and protocatechol; large seeds, gentisic, caffeic, and 2-hydroxy-5 methoxy benzoic acids and protocatechol. Small seeds had a lower concentration (0.85 mg g-1 dry weight [DW]) of total phenols than medium (1.58 mg g-1 DW) and large (4.41 mg g-1 DW) seeds. However, the presence of endogenous inhibitors-salicylic, syringic, and chlorogenic acids and catechol-in small seeds, but not in large, could account for germination inhibition in these seeds. Inhibition of germination by exogenous applications of all highly active phenols (10-2 M) except salicylic acid was alleviated by the application of gibberellic acid and kinetin.
TL;DR: Tobacco callus grown under shoot-forming conditions or in the presence of gibberellic acid, which inhibits shoot formation, was incubated in [14C]-sucrose at three different periods in culture and then replanted.
Abstract: Tobacco callus grown under shoot-forming conditions or in the presence of gibberellic acid, which inhibits shoot formation, was incubated in [14C]-sucrose at three different periods in culture and then replanted. Evolution of 14CO2 occurred during the 10 day post-incubation period. Most of the radioactivity was incorporated into the ethanol-soluble fraction, which lost most of its label after 24 h. Starch was the major ethanol-insoluble component and post-incubation synthesis occurred in this fraction for 24 h or longer. Greater net synthesis of starch occurred in shoot-forming tissue and the loss of label from starch began later than in tissue cultured in the presence of gibbe-rellic acid. Newly synthesized starch was not immediately utilised in the organogenic process, but its utilization could be correlated with the shoot-forming process.
Journal Article•
TL;DR: In this article, polyadenylated mRNA has been isolated from barley aleurone layers incubated in the presence and absence of exogenous gibberellic acid and abscisic acid.
TL;DR: Gibberellic acid, not Ca2+, is established as the principal regulator of α-amylase mRNA accumulation in barley aleurone, while Ca2+ controls high pI α-AMylase synthesis at a later step in the biosynthetic pathway.
Abstract: The effect of gibberellic acid and Ca2+ on the accumulation of α-amylase mRNAs in aleurone layers of barley (Hordeum vulgare L. cv Himalaya) was studied using cDNA clones containing sequences of mRNAs for the high and low isoelectric point (pI) α-amylases. There is no significant hybridization between the two α-amylase cDNA clones under the hybridization and washing conditions employed. These clones were therefore used to monitor levels of mRNAs for high and low pI α-amylases. It is shown that although the synthesis of the high pI α-amylase proteins depends on the presence of Ca2+ in the incubation medium, the accumulation of mRNA for this group occurs to the same degree in the presence or the absence of Ca2+. The accumulation of low pI α-amylase mRNA is also not affected by the presence or absence of Ca2+ in the incubation medium. These results establish gibberellic acid, not Ca2+, as the principal regulator of α-amylase mRNA accumulation in barley aleurone, while Ca2+ controls high pI α-amylase synthesis at a later step in the biosynthetic pathway.
TL;DR: Micropropagation of carob is possible from seedlings and mature trees using Murashige and Skoog medium with 5 μM zeatin for shoot multiplication and 10 μM indole-butyric acid for root induction.
TL;DR: Antagonistic action of phenolic compounds towards ABA, and increasing the action of GA when present together with GA and ABA establishes a dual role to this class of compounds; balancing the effect of both growth promoting and growth inhibiting hormones.
Abstract: Abscisic acid, a potent growth inhibitor inhibits hypocotyl growth ofRaphanus sativus seedlings. Phenolic compounds,viz., trans-cinnamic acid, chlorogenic acid, ferulic acid, salicylic acid, tannic acid and quercetin when applied with ABA, antagonize ABA action and restore normal seedling growth. Gibberellic acid promotes hypocotyl growth and on combined application with ABA, the ratio of their concentrations determines the course of the resultant growth. This interaction can be modulated by phenolic compounds. Phenolic compounds in low concentrations when present together with GA and ABA, favour GA-induced growth by antagonizing the inhibitory influence of ABA. The inhibitory action of abscisic acid on a wide range of growth processes is so far known to be reversed only by growth promoting hormones,viz., IAA, GA and cytokinins. Antagonistic action of phenolic compounds towards ABA, and increasing the action of GA when present together with GA and ABA, establishes a dual role to this class of compounds; balancing the effect of both growth promoting and growth inhibiting hormones.
01 Jan 1986
TL;DR: No single medium was adequate to ensure complete development of the fertilized ovules to plantlets, thus necessitating a sequential five step transfer to different media, which confirmed the hybrid nature of the plants.
Abstract: An interspecific hybrid of the sexually incompatible species G. hirsutum cv. Laxmi and G. arboreum cv. Jyoti was obtained through in ovulo embryo culture. Eightto twelve-day-old ovules were excised and cultured on Beasley and Ting's medium supplemented with Indol-3 acetic acid (5×10-6 to 7×10-6 M), Kinetin (5×10-6 to 5×10-8 M), Gibberellic acid (5×10-7 to 5×10-9M), Ammonium chloride (5 to 15mM) and Casein hydrolysate (50 to 200mg/l) added individually and in various combinations along with sucrose. No single medium was adequate to ensure complete development of the fertilized ovules to plantlets, thus necessitating a sequential five step transfer to different media. Cytological studies confirmed the hybrid nature of the plants.
TL;DR: The effect of activated charcoal (AC) on the germination of botanical potato seeds was tested by applying AC to seeds in petri dishes which had been pretreated with gibberellic acid (GA).
Abstract: The effect of activated charcoal (AC) on the germination of botanical potato seeds was tested by applying AC to seeds in petri dishes which had been pretreated with gibberellic acid (GA). A diverse sample of accessions including cultivar and cultivated species germplasm, cultivated species hybrids, wild species, and wild species known for their slow germination was tested. The time required from hydration to75% germination was significantly less for all types of seeds tested when AC was present. Cultivated species hybrids reached75% germination an average of four days sooner, wild species two days sooner, and slow germinating wild species 18 days sooner when AC was present. Only slow germinating wild species’ seeds germinated with significantly more uniformity in the presence of AC.
TL;DR: The results showed that in 0.2-mm embryos virtually all protein synthesis was dependent on an attached suspensor, and embryos of 0.5-mm did not appear to be differentially responsive to various gibberellin concentrations.
TL;DR: Evidence is provided that ABA modulates the synthesis of V. faba storage proteins by stimulating the accumulation of vicilin and legumin polypeptides and reversing the inhibition of fluridone by ABA.
TL;DR: Mature endosperm tissue excised from germinated seeds grew and proliferated on White's basal medium supplemented with two cytokinins, an auxin and gibberellic acid and showed triploid number of chromosomes (3n=21).
Abstract: Mature endosperm tissue excised from germinated seeds (2–4 days after radicle emergence) of Annona squamosa grew and proliferated on White's basal medium supplemented with two cytokinins, an auxin and gibberellic acid. The callus obtained could be periodically subcultured. Shoot differentiation and root induction were obtained from callus on media of different compositions. Analyses of the root and young leaf tips showed triploid number of chromosomes (3n=21).
TL;DR: In this paper, the effects of indoleacetic acid, gibberellic acid, and abscisic acid on the activity of the enzyme were investigated in source leaves of mature sugar beets.
Abstract: The initial step in carbon allocation occurs in leaves and is the chemical partitioning of carbon between sucrose and starch. Sucorse phosphate synthase is one of the enzymes belived to regulate rate of sucrose synthesis. In this study, the effects of indoleacetic acid, gibberellic acid, and abscisic acid on the activity of this enzyme were investigated in source leaves of mature sugar beets. Preliminary evidence is presented that, concurrent with a modification of sucrose uptake rates, i.e., phloem loading, these plant growth substances modify the activity of sucrose phosphate synthase resulting in altered partitioning of carbon between sucrose and starch.
TL;DR: Results indicate that pods, at an early stage of development, have a limited capacity for the biosynthesis of certain factor(s) but that seed development is not similarly affected.
TL;DR: The GA(3) treatment significantly reduced the starch content of cuttings during the rooting period, but did not significantly change the content of ethanol soluble carbohydrates.
Abstract: Seedlings of Pinus sylvestris L. were grown at three different irradiances (12, 30, or 60 W m(-2)) under a 17 h photoperiod. After six weeks, cuttings were excised and rooted at 30 W m(-2). Gibberellic acid (GA(3), 5 microl of 2 x 10(-4) or 2 x 10(-3) M) was applied to each cutting immediately after excision. Cuttings from stock plants grown at the low irradiance rooted most quickly, whereas the highest number of roots per cutting was obtained in cuttings from stock plants grown at 30 W m(-2). Gibberellic acid delayed rooting and reduced the number of roots in cuttings from stock plants grown at 12, 30, or 60 W m(-2). The initial carbohydrate content of cuttings increased with stock plant irradiance. For all carbohydrates, except myoinositol and an unknown inositol derivative, the content per cutting increased during the first 28 days of rooting. The GA(3) treatment significantly reduced the starch content of cuttings during the rooting period, but did not significantly change the content of ethanol soluble carbohydrates.
TL;DR: A foliar application of gibberellic acid 5 weeks after emergence increased the shoot/storage root ratios and significantly reduced the amount of secondary phloem produced in the storage root of 9 cultivars representing a range of types of carrot.
Abstract: A foliar application of gibberellic acid (GA) (100 mg/l) 5 weeks after emergence increased the shoot/storage root ratios, measured 4 weeks later, of 9 cultivars representing a range of types of carrot. Chlormequat chloride (CCC) (2000 mg/l) decreased the ratio for seven of the cultivars. Assessment 8 weeks after treatment showed fewer significant effects of both growth regulators.
TL;DR: Auxins such as indoleacetic acid, indolebutyric acid, naphthaleneACetic acid and 2,4,5-trichlorophenoxyacetic Acid were found to be potent inhibitors of nomilin biosynthesis in young seedlings of Citrus limon.