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PubMed1982

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).

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PubMed1982

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).

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PubMed1982

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.

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PubMed1983

Inhibition of Abscisic Acid Biosynthesis in Cercospora rosicola by Inhibitors of Gibberellin Biosynthesis and Plant Growth Retardants.

The fungus Cercospora rosicola produces abscisic acid (ABA) as a secondary metabolite. We developed a convenient system using this fungus to determine the effects of compounds on the biosynthesis of ABA. Inasmuch as ABA and the gibberellins (GAs) both arise via the isoprenoid pathway, it was of interest to determine if inhibitors of GA biosynthesis affect ABA biosynthesis. All five putative inhibitors of GA biosynthesis tested inhibited ABA biosynthesis. Several plant growth retardants with poorly understood actions in plants were also tested; of these, six inhibited ABA biosynthesis to varying degrees and two had no effect. Effects of plant growth retardants on various branches of the isoprenoid biosynthetic pathway may help to explain some of the diverse and unexpected results reported for these compounds. Knowledge that certain inhibitors of GA biosynthesis also have the ability to inhibit ABA biosynthesis in C. rosicola indicates the need for further studies in plants on the mode of action of these compounds.

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PubMed1983

Metabolism of Tritiated Gibberellins A(4) and A(9) in Norway Spruce, Picea abies (L.) Karst. : Effects of a Cultural Treatment Known to Enhance Flowering.

Shoots of mature grafted propagules of Picea abies (L.) Karst. metabolized [(3)H]gibberellin A(4) (GA(4)) to at least 14 acidic substances, two of which were tentatively identified by gas-liquid radiochromatography as GA(2) (possibly an artifact) and GA(34). [(3)H]GA(9) was converted into a number of metabolites, one of which was chromatographically similar to, but not identical with, GA(4). Metabolism was maximally 61 and 57% over 48 hours for GA(4) and GA(9), respectively, and was correlated with the rate of change (i.e. increase followed by decrease) in endogenous GA-like substances as shoot elongation progressed. Propagules covered with a clear plastic film, a treatment which promotes flowering, metabolized [(3)H]GA(4) more slowly than did control plants in the open. Inasmuch as a GA(4/7) mixture can also promote flowering in P. abies, the retarded metabolism of [(3)H]GA(4) may reflect the manner in which trees under plastic metabolize endogenous GA-like substances. If so, then the stimulating effect of this cultural treatment on flowering may come about through an increased level of endogenous, less polar GA-like substances.

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PubMed1983

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).

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PubMed1983

Reversible conjugation of gibberellins in situ in maize.

Gibberellins [(3)H]GA(4) (1.33 Curies per millimole) and [(3)H]GA(20) (2.36 Curies per millimole) were injected into the shanks of maize (Zea mays L.) cobs during rapid grain filling and mature seeds were subsequently harvested. Extracts of mature, dry seeds from 1980 feeds yielded only 20 to 30% of the (3)H radioactivity in acidic, ethyl acetate-soluble form, and this was principally associated with the precursor, with lesser amounts of the major metabolite, [(3)H]GA(1) (putative identification based on sequential SiO(2) partition, and gradient-eluted reverse-phase C(18) high performance liquid chromatography [HPLC]). Most of the radioactivity in the dry seeds was associated with compounds having partition characteristics of, and co-chromatographing on, sequential SiO(2) partition and reverse-phase HPLC with glucosyl conjugates of the precursors (GA(4) or GA(20)) and their probable major metabolite (GA(1)). The majority of conjugate associated with the precursor GA(4) eluted coincidental with GA(4) glucoside. Subsequent acid or enzymic hydrolysis (beta-glucosidase or cellulase) yielded the free GAs, putative identification being based on isocratic HPLC of each (3)H-labeled conjugate --> hydrolysis --> isocratic HPLC of the (3)H-labeled hydrolysate. Upon imbibition of the seeds, radioactivity associated with the conjugate fraction decreased; concomitantly, statistically significant increases in levels of free [(3)H]GA-like compounds were observed. Although the specific ratios of GA-like and GA-glucosyl conjugate-like substances varied substantially across years, hybrids, and even, in different plants from the same hybrid, this ;reversible conjugation' (i.e. apparent conjugation during seed maturation followed by release of the GA moiety during germination), was reproducible for [(3)H]GA(20) in seed from two maize hybrids produced over 2 years.

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PubMed1983

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.

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PubMed1983

Endogenous Gibberellin-Like Substances in Somatic Embryos of Grape (Vitis vinifera x Vitis rupestris) in Relation to Embryogenesis and the Chilling Requirement for Subsequent Development of Mature Embryos.

Endogenous gibberellin (GA)-like substances were examined in suspension cultures of somatic embryos of a hybrid grape (Vitis vinifera x Vitis rupestris) during embryogenesis, and in mature embryos chilled at 4 degrees C, and subsequently incubated at 26 degrees C with and without abscisic acid (ABA). The extract was separated into a nonpolar fraction (would contain GA-precursors); a fraction that would contain free GAs; and a highly H(2)O-soluble fraction (would contain GA glucosyl conjugates and very polar free GAs). Quantitation after SiO(2) partition chromatography was accomplished by microdrop and immersion dwarf rice bioassays. As embryogenesis developed, the free and highly H(2)O-soluble GA-like substances, expressed on a dry weight basis, decreased (however, they increased on a per embryo basis). Chilling at 4 degrees C for 1 week greatly increased activity of free GA-like substances (per g dry weight and per embryo), it then declined over the next three weeks of chilling. Activity (per g dry weight and per embryo) in the H(2)O-soluble fraction declined throughout chilling. Activity in the GA-precursor fraction, however, increased steadily with chilling (per g dry weight and per embryo). Incubation at 26 degrees C after chilling enhanced activity in the free GA and H(2)O-soluble fractions (per g dry weight and per embryo), but activity in the GA-precursor fraction dropped dramatically. Incubation at 26 degrees C with (+/-) ABA after chilling prevented germination and maintained high activity for GA precursors and less polar free GAs and low activity in the polar free GA and H(2)O-soluble fractions.Kaurene and kaurenoic acid were characterized in the GA-precursor fraction of chilled embryos by gas-liquid chromatography-mass spectrometry (GLC-MS). The existence of GA(4) and GA(9) in ABA-treated, chilled embryos was also confirmed by GLC-MS.

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PubMed1984

Changes in Cytokinins and Gibberellin-Like Substances in Pinus radiata Buds during Lateral Shoot Initiation and the Characterization of Ribosyl Zeatin and a Novel Ribosyl Zeatin Glycoside.

Based on detection and quantitation by bioassay, endogenous gibberellin-like substances (GAs) and cytokinins (CKs) in Pinus radiata D. Don buds during sequential shoot initiation shift from less polar to more polar forms (GAs) and from conjugated to free forms (CKs). As the terminal bud moves from the production of "short shoots" (needle fascicles) to "long shoots" (lateral branches or female conebuds), a more polar GA appears while a glucoside-conjugate of zeatin riboside is reduced, and zeatin riboside levels increase markedly.Permethyl derivatives of the two highly active CK fractions were examined by capillary gas chromatography-mass spectrometry after separation by C(18) reverse phase high performance liquid chromatography. The mass spectra indicated the presence of: 9-beta-d-ribofuranosyl-6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin riboside) and 9-[hexosyl(probably glucosyl)-beta-d-ribofuranosyl]-6-(4-hydroxy-3-methyl-but-2- enylamino)purine (a glycoside of zeatin riboside in which the glycosyl moiety is attached directly to the ribosyl moiety at an unknown position).

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PubMed1984

Transport of Benzyladenine and Gibberellin A(1) from Roots in Relation to the Dominance between the Axillary Buds of Pea (Pisum sativum L.) Cotyledons.

In etiolated, 5-day-old pea (Pisum sativum L.) seedlings a significantly more intensive growth of buds situated in the axil of the excised cotyledons was observed as early as 4 hours after decapitation and excision of one cotyledon of each pair. If [8-(14)C]benzyladenine ([(14)C]BA) was applied to roots of intact plants 10 hours prior to such decapitation and excision, significantly higher both total and specific (14)C activities were observed in buds situated on the side of the excised cotyledons as early as 4 hours after decapitation and excision. Although the removal of a substantial part of the root system carried out simultaneously with decapitation and excision of one cotyledon resulted in a decrease in total (14)C activity of buds, nevertheless a higher accumulation of (14)C activity was maintained in buds situated on the side of excised cotyledon. If [(14)C]BA was applied to roots of seedlings after they were decapitated and deprived of one cotyledon, both total and specific (14)C activities of buds situated on the side of excised cotyledons were significantly higher as early as the end of uptake of [(14)C]BA by roots, i.e. after 10 hours. On the other hand, [1,2-(3)H]gibberellin A(1) applied to roots of intact and/or decapitated and one-cotyledon-deprived seedlings in the same way as [(14)C]BA did not appear in the buds until very much later and only in negligible amounts (i.e.(3)H activity). This indicates that the release of buds from apical dominance represents an active and selective process which can result from the ability of buds to utilize and/or synthesize only certain growth substances within a certain time interval.

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PubMed1984

Gibberellin A(4/7) and the Promotion of Flowering in Pinus radiata: Effects on Partitioning of Photoassimilate within the Bud during Primordia Diferentiation.

Gibberellin A(4/7) mixture (GA(4/7)), a highly effective promoter of early and enhanced flowering in the Pinaceae, caused a significant reallocation of dry matter and (14)C-photosynthate within terminal buds of Pinus radiata D. Don within 8 days of hormone treatment. Treatment with GA(4/7) to terminal shoots of vigorous, potentially flowering mature grafted propagules reduced the flow of photoassimilated (14)C and dry matter into the terminal bud as a whole, but significantly increased the dry matter and (14)C allocated within the bud to developing long-shoot primordia (potential seed-cone buds). This was accomplished at the expense of the structural tissues, the apical dome region, and the vegetative branch buds. Although GA(3) caused a similar reallocation of dry matter within the terminal bud, it was significantly less effective than GA(4/7) thus appears to have, in addition to any nutrient diversion abilities, a distinct morphogenic function in sexual differentiation.

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PubMed1985

Role of Gibberellins in the Environmental Control of Stem Growth in Thlaspi arvense L.

Field pennycress (Thlaspi arvense L.) is a winter annual that requires a cold treatment for the induction of stem elongation. An inbred line was selected in which no stem elongation was observed in plants grown for 6 months at 21 degrees C regardless of the prevailing photoperiod. Increased exposure time of plants grown initially at 21 degrees C to cold (2 degrees C) induced a greater rate of stem elongation when the plants were returned to 21 degrees C. Moreover, longer cold treatments resulted in a greater maximum stem height and reduced the lag period for the onset of measurable internode elongation. The optimal temperature range for thermoinduced stem growth was broad: rates of stem growth in plants maintained for 4 weeks at either 2 degrees or 10 degrees C were virtually identical. However, a 4-week thermoinductive treatment at 15 degrees C resulted in a greater lag period for the initiation of stem elongation and a decreased growth rate. The rate of cold-induced stem elongation was greater in plants subjected to long days than for plants subjected to short days following the cold treatment. Thus, photoperiod does not control the induction of stem elongation, but does regulate stem elongation in progress. Exogenous gibberellin A(3) (GA(3)) was able to substitute for the cold requirement, but elicited a greater response in plants maintained under long days than short days. This indicates that photoperiod influences the plant's sensitivity to GAs. The GA biosynthesis inhibitor, 2-chloroethyltrimethyl ammonium chloride, inhibited low temperature-induced stem elongation, and this inhibition was completely reversed by exogenous GA(3). These results suggest that cold-induced stem elongation in field pennycress is mediated by some change in the endogenous GA status.

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PubMed1985

Identification of Gibberellins A(1), A(5), A(29), and A(32) from Immature Seeds of Apricot (Prunus armeniaca L.).

Gibberellins (GAs) A(1), A(5), and A(29) were identified, and also GA(32) was confirmed, as endogenous GAs of immature seeds (3-4 weeks after anthesis, 0.25-0.5 gram fresh weight) of apricot (Prunus armeniaca L.) based on capillary gas chromatography (GC), retention time (Rt), and selected ion monitoring (SIM), in comparison with authentic standards. Fractions subjected to GC-SIM were purified and separated using sequential solvent partitioning --> paper chromatography --> reverse phase C(18) high performance liquid chromatography (HPLC) --> bioassay on dwarf rice cv Tan-ginbozu. Two other peaks of free GA-like bioactivity (microdrop and immersion dwarf rice assays) were eluted from C(18) HPLC at Rts where GA(4/7) and GA(8) (or other GAs with similar structures) would elute. Also, three unidentified GA glucoside-like compounds (based on bioactivity on the immersion assay, and no bioactivity on the microdrop assay) were noted. There were very high amounts of GA(32) (112 ng of GA(3) equivalents per gram fresh weight), and minor amounts (0.5 ng of GA(3) equivalents) for each of GA(1) and GA(5), respectively, based on the microdrop assay.

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PubMed1985

Identification of Ten Gibberellins from Sporophytes of the Tree fern, Cyathea australis.

Ten gibberellins (GAs) have been identified by Kovats retention indices and full mass spectra from GC-MS analysis of purified extracts of sporophytes of the tree-fern, Cyathea australis. These include the known GA(1), GA(4), GA(9), GA(15), GA(24), GA(35), and GA(58) and three new GAs, 12beta-hydroxyGA(9) (GA(69)), 12alpha-hydroxyGA(9) (GA(70)) and 12beta-hydroxyGA(4) (GA(71)). The structure of GA(71) was established by the preparation and characterization of its methyl ester (as a metabolite of GA(4) methyl ester in a culture of prothallia of Lygodium japonicum).

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PubMed1986

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).

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PubMed1986

Photocontrol of gibberellin metabolism in situ in maize.

Mature maize seeds were labeled with 10 to 100 pg per seed of [(3)H] gibberellins (GA) and [(3)H]GA glucosyl conjugate-like substances by feeding [(3)H]GA(20) of high specific activity (2.3 Curies per millimole) during seed maturation. The dry seeds, which contained 14% [(3)H]GA(20), 7% putative [(3)H]GA(1) and 78% [(3)H]GA glucosyl conjugate-like metabolites, were imbibed and germinated in the dark and under incandescent light. In both light and dark the proportion of [(3)H]GA conjugate-like metabolities declined (relative to that in the mature dry seeds) during imbibition and up to germination at hour 36. This decline was accompanied by increases in the proportions of [(3)H]GA(20) and putative [(3)H]GA(1) thereby indicating hydrolysis, which was greater in the dark than in the light. The proportions of [(3)H]GA conjugate-like substances in light-grown germinants were higher (121 and 141% of dark-grown) at 24 and 48 hour harvests and this statistically significant pattern was sustained up to 120 hours after imbibition. Conversely, the proportions of [(3)H]GA(20) and putative [(3)H]GA(1) were lower in the light-grown seedlings. Thus, during imbibition, hydrolysis (de-conjugation) of [(3)H]GA glucosyl conjugate-like substances apparently occurred, and occurred more rapidly in the dark than in the light. Subsequently, during germination the reformation of [(3)H]GA conjugate-like substances was less rapid in the dark than in the light. The observation that dark-imbibed seeds and dark-grown seedlings have higher proportions of putative free [(3)H]GAs, relative to [(3)H]GA conjugate-like substances, is consistent with the increased shoot elongation (etiolation) that occurs in dark-grown maize seedlings, and may indicate a homeostatic role for GAs and their conjugates in shoot elongation of maize germinants.

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PubMed1986

Transport of gibberellin a(1) in cowpea membrane vesicles.

The permeability properties of gibberellin A(1) (GA(1)) were examined in membrane vesicles isolated from cowpea hypocotyls. The rate of GA(1) uptake was progressively greater as pH decreased, indicating that the neutral molecule is more permeable than anionic GA(1). Membrane vesicles used in this study possessed a tonoplast-type H(+)-translocating ATPase as assayed by MgATP-dependent quenching of acridine orange fluorescence and methylamine uptake. However, GA(1) uptake was not stimulated by MgATP. At concentrations in excess of 1 micromolar, GA(1), GA(5), and GA, collapsed both MgATP-generated and artifically imposed pH gradients, apparently by shuttling H(+) across the membrane as neutral GA. The relatively high permeability of neutral GA and the potentially detrimental effects of GA in uncoupling pH gradients across intracellular membranes supports the view that GA(1) accumulation and compartmentation must occur by conversion of GA(1) to more polar metabolites.

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