Fractionation of gibberellins in plant extracts by reverse phase high performance liquid chromatography

Quantitative determination of gibberellins by high performance liquid chromatography from various gibberellins producing Fusarium strains

High performance liquid chromatographic (HPLC) method was developed for analysis of seven gibberellins, i.e., GA3, GA4, GA7, GA3 methyl ester, GA7 methyl ester 3,13 diacetate, GA7 methyl ester, and fusaric acid, using an isocratic system. Method was used for estimation of gibberellins from different Fusarium strains. Gibberellins were extracted from 28 strains of Fusarium, out of which six strains of Fusarium were isolated from soil of different parts of India and 22 strains were procured from the Indian Type Culture Collection, Indian Agricultural Research Institute, New Delhi. Extracts were analyzed for qualitative and quantitative estimation of gibberellins by thin layer chromatography and HPLC, respectively. On the basis of quantitative analysis of produced gibberellins by HPLC, they were categorized as low, moderate, and high gibberellin producing strain. For the first time, Fusarium solani was also reported as high GA3 producing strain.

Quantitation of gibberellins A1, A 3, A 4, A 9 and an A 9-conjugate in good- and poor-flowering clones of Sitka spruce (Picea sitchensis) during the period of flower-bud differentiation

The levels of endogenous gibberellin A1 (GA1), GA3, GA4, GA9 and a cellulase-hydrolysable GA9-conjugate in needles and shoot stems of Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts with different coning or flowering histories were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated GA3, GA4 and GA9 as internal standards. The samples were taken at the approximate time of the start of flower-bud differentiation, i.e. when the shoots had elongated approx. 95% of the final length. The needles of the good-flowering clones contained 11-12 ng per g fresh weight (FW) and 15-28 ng· (g FW) (-1) of GA9-conjugate and GA9, respectively. The shoot stems of the same material contained no detectable amounts of GA9-conjugate and 11-15 ng-(g FW)(-1) of GA9. The amounts of GA9-conjugate and GA9 were apparently lower in the poor-flowering clones, the needles containing 4-9 ng-(g FW)(-1) and 7-17 ng·(g FW)(-1), respectively. Also in this material the shoot stems contained no detectable amounts of GA9-conjugate. The amounts of GA4 were very small in both materials, ranging from 1-1.6 ng-(g FW)(-1). The good-flowering clones contained no detectable amounts of the more polar gibberellins, GA1 and GA3. The poor-flowering clones, on the other hand, contained high levels of GA15 17-19ng·(gFW)(-1) in the needles and 10-13 ng·(g FW) (-1) in the shoot stems, and also smaller amounts of GA3, 2-3 ng·(g FW)(-1) in the needles and approx. 1 ng·(g FW)(-1) in the shoot stems. The results demonstrate differences in GA-metabolism between the poor- and the good-flowering clones. The higher amounts of GA9-conjugate and GA9 might indicate a higher capacity for synthesizing GA4 in the good-flowering material. This synthesis does not, however, result in a build-up of the GA4-pool, maybe because of a high rate of turnover. Gibberellin A4 was apparently neither hydroxylated to GA1 nor converted to GA3 in the goodflowering material, as was the case in the poor-flowering material. This might indicate that gibberellin metabolism in the poor-flowering material is directed towards GA1 and GA3, GAs preferentially used in vegetative growth.

Identification of Gibberellins in Norway Spruce (Picea abies [L.] Karst.) by Combined Gas Chromatography-Mass Spectrometry

Gibberellins A(1) (GA(1)), A(3) and A(9) were identified from extracts of shoots of 6-month old Norway spruce (Picea abies) seedlings by the use of sequential reverse and normal phase high performance liquid chromatography (HPLC), bioassay, radioimmunoassay (RIA) and combined gas chromatography-mass spectrometry (GC-MS). The bioassay and RIA were used after fractionation by HPLC to detect the GA-containing fractions, which were then examined by GC-MS. The GAs identified are considered to be endogenous.

Gibberellin metabolism in cell-free extracts from spinach leaves in relation to photoperiod

Cell-free extracts capable of converting [(14)C]-labeled gibberellins (GAs) were prepared from spinach (Spinacia oleracea L.) leaves. [(14)C]-labeled GAs, prepared enzymically from [(14)C]mevalonic acid, were incubated with these extracts, and products were identified by gas chromatography-mass spectrometry. The following pathway was found to operate in extracts from spinach leaves grown under long day (LD) conditions: GA(12) --> GA(53) --> GA(44) --> GA(19) --> GA(20). The pH optima for the enzymic conversions of [(14)C]GA(53), [(14)C]GA(44) and [(14)C]GA(19) were approximately 7.0, 8.0, and 6.5, respectively. These three enzyme activities required Fe(2+), alpha-ketoglutarate and O(2) for activity, and ascorbate stimulated the conversion of [(14)C]GA(53) and [(14)C]GA(19). Extracts from plants given LD or short days (SD) were examined, and enzymic activities were measured as a function of exposure to LD, as well as to darkness following 8 LD. The results indicate that the activities of the enzymes oxidizing GA(53) and GA(19) are increased in LD and decreased in SD or darkness, but that the enzyme activity oxidizing GA(44) remains high irrespective of light or dark treatment. This photoperiodic control of enzyme activity is not due to the presence of an inhibitor in plants grown in SD. These observations offer an explanation for the higher GA(20) content of spinach plants in LD than in SD.

Identification of endogenous gibberellins from sorghum

Gibberellins (GA) A(1), A(19), and A(20) were identified in shoot cylinders containing the apical meristems from sorghum (Sorghum bicolor L.). Extracts were purified by sequential SiO(2) partition chromatography and reversed-phase C(18) high performance liquid chromatography and biologically active (dwarf rice cv Tan-ginbozu microdrop assay) fractions were subjected to gas chromatography-selected ion monitoring. Based on the use of [(3)H]GA and [(2)H](d(2))GA internal standards, amounts of GA(1), GA(19), and GA(20) were estimated to be 0.7, 8.8, and 1.5 namograms per gram dry weight of tissue, respectively.

Identification of Endogenous Gibberellins in the Winter Annual Weed Thlaspi arvense L

Eleven endogenous gibberellins (GAs) were identified by combined gas chromatography-mass spectrometry in purified extracts from shoots of field pennycress (Thlaspi arvense L.): GA(1,9,12,15,19,20,24,29,44,51,53). Traces of GA(8) and GA(25) were tentatively indicated by combined gas chromatography-mass spectrometry-selected ion monitoring. Comparison of the total ion current traces indicated that GA(19) and GA(44) were most abundant, while GA(12,15,20,24,29,53) occurred in lesser amounts. Only small amounts of GA(1,9,51) were present. The levels of GA(8) and GA(25) were barely detectable. Consideration of hydroxylation patterns of the ent-gibberellane ring structure indicates two families of GAs: one with a C-13 hydroxyl group (GA(1,8,19,20,29,44,53)) and another whose members are either nonhydroxylated (GA(9,12,15,24,25)) or lack a C-13 hydroxyl group (GA(51)). This suggests that in field pennycress there are two parallel pathways for GA metabolism with an early branch point from GA(12): an early C-13 hydroxylation pathway, leading ultimately to GA(1) and GA(8) and a C-13 deoxy pathway culminating in the formation of GA(9) and GA(51).

Internode length in Pisum sativum L. The kinetics of growth and [(3)H]gibberellin A 20 metabolism in genotype na Le

The relationship between shoot growth and [(3)H]gibberellin A20 (GA20) metabolism was investigated in the GA-deficient genotype of peas, na Le. [17-(13)C, (3)H2]gibberellin A20 was applied to the shoot apex and its metabolic fate examined by gas chromatographic-mass spectrometric analysis of extracts of the shoot and root tissues. As reported before, [(13)C, (3)H2]GA1, [(13)C, (3)H2]GA8 and [(13)C, (3)H2]GA29 constituted the major metabolites of [(13)C, (3)H2]GA20 present in the shoot. None of these GAs showed any dilution by endogenous (12)C-material. [(13)C, (3)H2]GA29-catabolite was also a prominent metabolite in the shoot tissue but showed pronounced isotope dilution probably due to carry-over of endogenous [(12)C]GA29-catabolite from the mature seed. In marked contrast to the shoot tissue, the two major metabolites present in the roots were identified as [(13)C, (3)H2]GA8-catabolite and [(13)C, (3)H2]GA29-catabolite. Both of these compounds showed strong dilution by endogenous (12)C-material. Only low levels of [(13)C, (3)H2]GA1, [(13)C, (3)H2]GA8, [(13)C, (3)H2]GA20 and [(13)C, (3)H2]GA29 accumulated in the roots. It is suggested that compartmentation of GA-catabolism may occur in the root tissue in an analogous manner to that shown in the testa of developing seeds. Changes in the levels of [1β,3α-(3)H2]GA20 metabolites over 10 d following application of the substrate to the shoot apex of genotype na Le confirmed the accumulation of [(3)H]GA-catabolites in the root tissues. No evidence was obtained for catabolic loss of [(3)H]GA20 by complete oxidation or conversion to a methanol-inextractable form. The results indicate that the root system may play an important role in the regulation of biologically active GA levels in the developing shoot of Na genotypes of peas.

Internode length in Zea mays L. : The dwarf-1 mutation controls the 3β-hydroxylation of gibberellin A20 to gibberellin A 1

[(13)C, (3)H]Gibberellin A20 (GA20) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [(13)C, (3)H]Gibberellin A20 was metabolized to [(13)C, (3)H]GA29-catabolite and [(13)C, (3)H]GA1 by the normal, and to [(13)C, (3)H]GA29 and [(13)C, (3)H]GA1 by the dwarf-5 mutant. In the dwarf-1 mutant, [(13)C, (3)H]GA20 was metabolized to [(13)C, (3)H]GA29 and [(13)C, (3)H]GA29-catabolite; no evidence was found for the metabolism of [(13)C, (3)H]GA20 to [(13)C, (3)H]GA1. [(13)C, (3)H]Gibberellin A8 was not found in any of the feeds. In all feeds no dilution of (13)C in recovered [(13)C, (3)H]GA20 was observed. Also in the dwarf-5 mutant, the [(13)C]label in the metabolites was apparently undiluted by endogenous [(13)C]GAs. However, dilution of the [(13)C]label in metabolites from [(13)C, (3)H]GA20 was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA20 to GA1.

Internode length in Pisum : The Le gene controls the 3β-hydroxylation of gibberellin A20 to gibberellin A 1

The influence of the Na and Le genes in peas on gibberellin (GA) levels and metabolism were examined by gas chromatographic-mass spectrometric analysis of extracts from a range of stem-length genotypes fed with [(13)C, (3)H]GA20. The substrate was metabolised to [(13)C, (3)H]GA1, [(13)C, (3)H]GA8 and [(13)C, (3)H]GA29 in the immature, expanding apical tissue of all genotypes carrying Le. In contrast, [(13)C, (3)H]GA29 and, in one line, [(13)C, (3)H]GA29-catabolite, were the only products detected in plants homozygous for the le gene. These results confirm that the Le gene in peas controls the 3β-hydroxylation of GA20 to GA1. Qualitatively the same results were obtained irrespective of the genotype at the Na locus. In all Na lines the [(13)C, (3)H]GA20 metabolites were considerably diluted by endogenous [(12)C]GAs, implying that the metabolism of [(13)C, (3)H]GA20 mirrored that of endogenous [(12)C]GA20. In contrast, the [(13)C, (3)H]GA20 metabolites in na lines showed no dilution with [(12)C]GAs, confirming that the na mutation prevents the production of C19-GAs. Estimates of the levels of endogenous GAs in the apical tissues of Na lines, made from the (12)C:(13)C isotope ratios and the radioactivity recovered in respective metabolites, varied between 7 and 40 ng of each GA per plant in the tissue expanded during the 5 d between treatment with [(13)C, (3)H]GA20 and extraction. No [(12)C]GA1 and only traces of [(12)C]GA8 (in one line) were detected in the two Na le lines examined. These results are discussed in relation to recent observations on dwarfism in rice and maize.

The localization, metabolism and biological activity of gibberellins in maturing and germinating seeds of Pisum sativum cv. Progress No. 9

Gibberellin A20 (GA20), GA29 and GA29-catabolite were quantified in cotyledons, embryonic axes, and testas of Pisum sativum cv. Progress No. 9 throughout the final stages of seed maturation and during germination. Stable isotope-labelled GAs were used as internal standards in conjunction with combined gas chromatography-mass spectrometry. Gibberellin A20 and GA29 were mainly located in the cotyledons of maturing seeds, and GA29-catabolite was predominantly located in the testa. Stable isotope- and radio-labelled GA20 and GA29 were fed to both intact seeds developing in vivo, and to isolated seed parts cultured in vitro. The combined results of in-vivo and in-vitro feeds indicated that GA20 is metabolised to GA29 in the cotyledons, that GA29 is transported from the cotyledons to the testa, and that GA29 is metabolised to GA29-catabolite in the testa. Although the metabolism of GA20 in the cotyledons and of GA29 in the testa has been shown definitively, the mobility of GA29 has not yet been demonstrated directly. During seed desiccation and germination GA29-catabolite and products arising from it are transferred from the testa into the embryo. There is no evidence of a physiological function for GA29-catabolite in germination or early seedling growth. Use of a growth retardant indicates that seedling growth, but not germination, is dependent on de-novo GA biosynthesis.

Purification and separation of plant gibberellins from their precursors and glucosyl conjugates

A procedure using two small preparative columns (in sequence) of C(18) reverse phase Bondapak B material with methanolic extracts of plant tissue (Pisum sativum L., Malus domestica Borkh., Pimpinella anisum L.) yields two fractions: (i) gibberellin (GA) precursors, and (ii) free GA/GA methyl esters (GA-Me)/GA glucosyl conjugates. The discrete separation of (iii) free GA/GA-Me from (iv) GA glucosyl conjugates is then accomplished by a combination of differential solvent solubility and SiO(2) partition chromatography. All fractions are almost pigment free, and appreciable dry weight purification was accomplished for the GA precursor and free GA/GA-Me fractions. Solvent volumes can be kept low, no buffer salts are introduced, and each fraction (i, iii, iv) can be subjected directly to preparative or analytical reverse phase C(18) high performance liquid chromatography without recourse to solvent partitioning, and often without further purification.

Effect of photoperiod on the metabolism of deuterium-labeled gibberellin a(53) in spinach

Application of gibberellin A(53) (GA(53)) to short-day (SD)-grown spinach (Spinacia oleracea L.) plants caused an increase in petiole length and leaf angle similar to that found in plants transferred to long days (LD). [(2)H] GA(53) was fed to plants in SD, LD, and in a SD to LD transition experiment, and the metabolites were identified by gas chromatography with selected ion monitoring. After 2, 4, or 6 SD, [(2)H]GA(53) was converted to [(2)H]GA(19) and [(2)H]GA(44). No other metabolites were detected. After 2 LD, only [(2)H] GA(20) was identified. In the transition experiment in which plants were given 4 SD followed by 2 LD, all three metabolites were found. The results demonstrate unequivocally that GA(19), GA(20), and GA(44) are metabolic products of GA(53), and strongly suggest that photoperiod regulates GA metabolism, in part, by controlling the conversion of GA(19) to GA(20).

Gibberellins and heterosis in maize : I. Endogenous gibberellin-like substances

Under controlled environment and/or field conditions, vegetative growth (height, internode length, leaf area, shoot dry weight, grain yield) was greater in an F(1) maize hybrid than in either parental inbred. Endogenous gibberellin (GA)-like substances in apical meristem cylinders were also higher in the hybrid than in either inbred, both on a per plant and per gram dry weight basis. There were no apparent qualitative differences in GA-like substances, however. Levels of GA-like substances in all genotypes were highest prior to tassel initiation. Chromatographic comparisons of the GA-like substances and authentic standards of GA native to maize on gradient-eluted SiO(2) partition and reverse-phase C(18) high-pressure liquid chromatography columns are described. No consistent differences in abscisic acid levels of the three genotypes were observed. This correlation of heterosis for endogenous GA-like substances with heterosis for growth suggests that amounts of endogenous GA may be related to hybrid vigor in maize.

Metabolism of tritiated gibberellin a(20) in maize

After the application of 2.36 Curies per millimole [2,3-(3)H]gibberellin A(20) (GA(20)) to 21-day-old maize (Zea mays L., hybrid CM7 x CM49) plants, etiolated maize seedlings, or maturing maize cobs, a number of (3)H-metabolites were observed. The principal acidic (pH 3.0), ethyl acetate-soluble metabolite was identified as [(3)H]GA(1) on the basis of co-chromatography with standard [(3)H]GA(1) on SiO(2) partition, high resolution isocratic elution reverse phase C(18) high performance liquid chromatography and gas-liquid chromatography radiocounting. Two other acidic metabolites were identified similarly as [(3)H]GA(8) and C/D ring-rearranged [(3)H]GA(20), although gas-liquid chromatography radiocounting was not performed on these metabolites. Numerous acidic, butanol-soluble (e.g. ethyl acetate-insoluble) metabolites were observed with retention times on C(18) high performance liquid chromatography radiocounting similar to those of authentic glucosyl conjugates of GA(1) and GA(8), or with retention times where conjugates of GA(20) would be expected to elute. Conversion to [(3)H]GA(1) was greatest (23% of methanol extractable radioactivity) in 21-day-old maize plants. In etiolated maize seedlings, the C/D ring-rearranged [(3)H]GA(20)-like metabolite was the major acidic product, while conversion to [(3)H]GA(1) was low.

Effect of Photoperiod on Metabolism of [H] Gibberellins A(1), 3-epi-A(1), and A(20) in Agrostemma githago L

To determine whether daylength influences the rate of metabolism of gibberellins (GAs) in the long-day (LD) rosette plant Agrostemma githago L., [(3)H]GA(20) and [(3)H]GA(1) were applied under short day (SD) and LD. Both were metabolized faster under LD than under SD. [(3)H]GA(20) was metabolized to a compound chromatographically identical to 3-epi-GA(1). [(3)H]GA(1) was metabolized to two acidic compounds, the major metabolite having chromatographic properties similar to, but not identical with GA(8). [(3)H]3-epi-GA(1) applied to plants under LD was metabolized much more slowly than was [(3)H]GA(1), and formed a very polar metabolite which did not partition into ethyl acetate at pH 2.5. Very polar metabolites were also formed after the feeds of [(3)H]GA(20) and [(3)H]GA(1). It was not possible to characterize these very polar compounds further because of their apparent instability. The results obtained suggest that in Agrostemma GA(20) is the precursor of 3-epi-GA(1), but there is at present no evidence indicating the precursor of GA(1).

Photoperiodic control of gibberellin metabolism in spinach

[(3)H]GA(20) applied to spinach plants (Spinacia oleracea L.) was metabolized to several products. Two of these were identified by combined gasliquid chromatography-radio counting as [(3)H]GA(29) and [(3)H]3-epi-GA(1). Inasmuch as both GA(20) and GA(29) are endogenous gibberellins in spinach (Metzger, Zeevaart 1980 Plant Physiol 65: 623-626), it was concluded that the conversion of GA(20) to GA(29) is a natural process. However, 3-epi-GA(1) was not detected in extracts of spinach shoots analyzed by combined gas chromatography-mass spectrometry. This indicates that the conversion of exogenous [(3)H]GA(20) to [(3)H]3-epi-GA(1) may be an artifact.Long-day pretreatment of spinach shoots caused a 2-fold increase in the rate of [(3)H]GA(20) metabolism over the rate of metabolism in plants maintained under short-day conditions. Furthermore, [(3)H]GA(29) accumulated more rapidly under long than under short days, whereas photoperiodic treatment had no effect on the accumulation of [(3)H]3-epi-GA(1). Thus, the long-day-induced increase in the level of endogenous GA(29) in spinach shoots (Metzger, Zeevaart 1980 Plant Physiol 66: 844-846) appears to be the result of an increased capability to convert GA(20) to GA(29).

Effect of Photoperiod on the Levels of Endogenous Gibberellins in Spinach as Measured by Combined Gas Chromatography-selected Ion Current Monitoring

The changes in the levels of five endogenous gibberellins (GAs) in spinach in relation to photoperiodic treatment have been examined by combined gas chromatography-selected ion current monitoring. Long-day treatment caused a 5-fold decline in the level of GA(19) while the levels of GA(20) and GA(29) increased dramatically during the same period. In absolute terms, the level of GA(20) increased from 0.8 microgram per 100 grams dry weight in short days to 5.5 micrograms per 100 grams dry weight after 14 long days. The levels of GA(17) and GA(44) did not change significantly with long-day treatment. These results are consistent with the hypothesis that GA(19) is converted to GA(20) and that this conversion is under photoperiodic control. Since stem growth in spinach is correlated with an increase in the level of GA(20), one major aspect of photoperiodic control of stem growth might be the availability of GA(20) through regulation of the conversion of GA(19) to GA(20).

Changes of Endogenous Gibberellin-like Substances with Sex Reversal of the Apical Inflorescence of Corn

In developing apical meristems of corn, the level of acidic, ethyl acetate-soluble gibberellin (GA)-like substances increased to a maximum of 108 micrograms GA(3)-equivalents per kilogram dry weight of tissue at inflorescence initiation, and then fell rapidly. At anthesis, only a trace (0.2 microgram per kilogram) of GA-like activity remained in the apical (male) inflorescences, whereas moderate activity (32 micrograms per kilogram), mostly of a nonpolar nature, was present in lateral, female, inflorescences.A sex reversal of the apical inflorescence, from male to female, was elicited by reducing the ambient light intensity. Higher levels of GA-like substances, particularly those eluting from a SiO(2) partition column in the nonpolar region, were observed at all harvests in the reverting meristems; levels increased to 180 micrograms per kilogram at inflorescence initiation, then dropped to 122 micrograms per kilogram in the apical (female), reverted meristems. This increase in endogenous GA-like activity with reversion to the female inflorescence is consistent with observations that (a) reversion can be obtained with exogenous application of GA(3) and (b) maleness is enhanced in GA-deficient mutants of maize. Endogenous GAs may thus play a key role in the control of sexuality of corn.

Comparison of the levels of six endogenous gibberellins in roots and shoots of spinach in relation to photoperiod

This communication describes the distribution of gibberellins (GAs) in roots and shoots of spinach in relation to photoperiod. From previous work (Metzger, Zeevaart 1980 Plant Physiol 65: 623-626) shoots were known to contain GA(53), GA(44), GA(19), GA(17), GA(20), and GA(29). We now show by combined gas chromatography-mass spectrometry that roots contain GA(44), GA(19), and GA(29). Trace amounts of GA(53) were detected by combined gas chromatography-selected ion current monitoring. Neither GA(17) nor GA(20) were detected in root extracts. Analysis by the d-5 corn bioassay also showed no effect of photoperiodic treatment on the levels of GA-like substances in root extracts. Both phloem and xylem exudates had patterns of GA-like activity similar to those found in shoots and roots, respectively. Moreover, foliar application of [(3)H]GA(20) resulted in the transport of label from the shoot to the roots. Over half of the label in the roots represented unmetabolized [(3)H]GA(20), indicating that part of the GA(20) in the phloem is transported to the roots. Consequently, if GA(20) is made in, or transported to the roots, it is rapidly metabolized in that organ. This is a clear indication that regulation of GA metabolism is greatly different in roots and shoots.

Changes in the Levels of Abscisic Acid and Its Metabolites in Excised Leaf Blades of Xanthium strumarium during and after Water Stress

The time course of abscisic acid (ABA) accumulation during water stress and of degradation following rehydration was investigated by analyzing the levels of ABA and its metabolites phaseic acid (PA) and alkalihydrolyzable conjugated ABA in excised leaf blades of Xanthium strumarium. Initial purification was by reverse-phase, preparative, high performance liquid chromatography (HPLC) which did not require prior partitioning. ABA and PA were purified further by analytical HPLC with a muBondapak-NH(2) column, and quantified by GLC with an electron capture detector.The ABA content of stressed leaves increased for 4 to 5 hours and then leveled off due to a balance between synthesis and degradation. Since PA accumulated at a constant rate throughout the wilting period, it was concluded that the rate of ABA synthesis decreased after the first 4 to 5 hours stress. Conjugated ABA increased at a low rate during stress. This is interpreted to indicate that free ABA was converted to the conjugated form, rather than the reverse.Following rehydration of wilted leaves, the ABA level immediately ceased increasing; it remained constant for 1 hour and then declined rapidly to the prestress level over a 2- to 3-hour period with a concomitant rise in the PA level. In contrast to the rapid disappearance of ABA after relief of stress, the high PA content of rehydrated leaves declined only slowly. The level of conjugated ABA did not change following rehydration, indicating that conjugation of ABA was irreversible.Detached Xanthium leaves that were subjected to a wilting-recovery-rewilting cycle in darkness, responded to the second wilting period by formation of the same amount of ABA as accumulated after the first stress period.

The effect of photoperiod on the levels of seven endogenous gibberellins in the long-day plant Agrostemma githago L

The following seven gibberellins (GAs) have been identified by gas chromatography-mass spectrometry in shoots and leaves of the long-day plant Agrostemma githago: GA53, GA44, GA19, GA17, GA20, GA1, and 3-epi-GA1. The levels of these compounds were measured, using selected ion monitoring, during photoperiodic induction. The levels of GA44, GA19, GA17, and GA20 all increased to a peak at eight long days (LD), followed by a decline, while the levels of GA1 and 3-epi-GA1 did not reach a peak until 12 LD. The level of GA53 remained steady over the first 10-12 LD. Later in the LD treatment the levels of GA53, GA44, GA19, and GA17 increased again. The rate of metabolism of all GAs except GA53 was higher after 12-16 LD than under short days. These data thus provide indirect evidence for an effect of photoperiodic induction on GA turnover in A. githago.

Gibberellins and the photoperiodic control of stem elongation in the long-day plant Agrostemma githago L

Agrostemma githago is a long-day rosette plant in which transfer from short days (SD) to long days (LD) results in rapid stem elongation, following a lag phase of 7-8 d. Application of gibberellin A20 (GA20) stimulated stem elongation in plants under SD, while 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618, an inhibitor of GA biosynthesis) inhibited stem elongation in plants exposed to LD. This inhibition of stem elongation by AMO-1618 was overcome by simultaneous application of GA20, indicating that GAs play a role in the photoperiodic control of stem elongation in this species. Endogenous GA-like substances were analyzed using reverse-phase high-performance liquid chromatography and the d-5 corn (Zea mays L.) assay. Three zones with GA-like activity were detected and designated, in order of decreasing polarity, as A, B, and C. A transient, 10-fold increase in the activity of zone B occurred after 8-10 LD, coincident with the transition from lag phase to the phase of rapid stem elongation. After 16 LD the activity in this zone had returned to a level similar to that under SD, even though the plants were elongating rapidly by this time. However, when AMO-1618 was applied to plants after 11 LD, there was a rapid reduction in the rate of stem elongation, indicating that continued GA biosynthesis was necessary following the transient increase in activity of zone B, if stem elongation was to continue under LD. It was concluded that control of stem elongation in A. githago involves more than a simple qualitative or quantitative change in the levels of endogenous GAs, and that photoperiodic induction alters both the sensitivity to GAs and the rate of turnover of endogenous GAs.

Identification of six endogenous gibberellins in spinach shoots

Analysis of highly purified extracts from spinach shoots by combined gas chromatography-mass spectrometry has demonstrated the presence of six 13-C-hydroxylated gibberellins (GAs): GA(53), GA(44), GA(19), GA(17), GA(20), and GA(29). The major GAs were GA(17), GA(19), and GA(20), whereas the other three GAs occurred in trace amounts. Structural considerations suggest that the six GAs identified in spinach are related in the following metabolic sequence: GA(53) --> GA(44) --> GA(19) --> GA(17) --> GA(20) --> GA(29).