Inhibition of growth of microcultured Hancornia speciosa shoots by 3beta-hydroxylated gibberellins and one of their C-3 deoxy precursors.

Gibberellins (GAs) A(1), A(3), A(4) and A(7), all 3beta-hydroxylated, growth-active GAs, significantly inhibited shoot elongation and the formation of nodes in in vitro-grown Hancornia speciosa, as did GA(20), a 3-deoxy precursor of GA(1). Ancymidol, an early-stage inhibitor of GA biosynthesis, significantly retarded shoot elongation without affecting the formation of nodes. Co-application of ancymidol and GA(1 )did not overcome the ancymidol-induced growth retardation. Trinexapac-ethyl, which can inhibit 3beta-hydroxylation (GA activation) and 2beta-hydroxylation (GA inactivation), gave no significant response on either shoot elongation or node formation, while two isomers of 16,17-dihydro GA(5), also inhibitors of GA 3beta-hydroxylation, significantly inhibited both shoot growth and the formation of nodes. These unusual results may indicate a unique metabolism for GAs in microcultured shoots of H. speciosa.

Bioactivity of 25-hydroxy-, 26-hydroxy, 25,26-dihydroxy- and 25,26-epoxybrassinolide.

The bioactivity of 25-hydroxybrassinolide, (25S)- and (25R)-26-hydroxybrassinolide, (25S)- and (25R)-25,26-dihydroxybrassinolide, and of (25R)-25,26-epoxybrassinolide was tested in the rice leaf lamina inclination assay. The 25- and (25S)-26-hydroxy derivatives are known metabolites of the naturally-occurring phytohormone brassinolide, whereas the other compounds are novel, but closely related, congeners. When tested alone, all showed either no activity or only weak activity at relatively high doses. When coapplied with indole-3-acetic acid (IAA), an auxin that synergizes the effects of brassinosteroids, enhanced bioactivity was observed for each compound. However, even when applied together with IAA, none of the compounds proved more bioactive than brassinolide with or without IAA. We conclude from these results that enzymatic hydroxylation of endogenous brassinolide at C-25 and/or C-26 does not enhance brassinosteroid activity, and so does not comprise an activation pathway in brassinolide biosynthesis. Instead, these hydroxylations result in modest to appreciable metabolic deactivation.

Design, synthesis, and bioactivity of the first nonsteroidal mimetics of brassinolide.

Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics.

Reduced de-etiolation of hypocotyl growth in a tomato mutant is associated with hypersensitivity to, and high endogenous levels of, abscisic acid.

A recessive single gene mutant, 7B-1, in tomato was originally selected for its photoperiod-dependent male sterility. The 7B-1 mutant also has some pleiotropic effects including reduced light-induced inhibition, i.e. de-etiolation, of the hypocotyl in long days (LD), increased seed size and weight, and reduced transpiration rate. These traits led us to investigate the sensitivity of 7B-1 to exogenous hormones and the interaction of these responses with daylength. In LD, but not in short days (SD), 7B-1 was more sensitive than wild-type (WT) to exogenous abscisic acid (ABA) for inhibition of seed germination, root elongation and transpiration rate. 7B-1 mutant also exhibited reduced responses to exogenous gibberellin (GA(3)) for hypocotyl elongation, and to inhibitors of GA biosynthesis for seed germination and root and hypocotyl elongation. 7B-1 hypocotyls contained a higher level of endogenous ABA than WT in both photoperiods, although ABA levels were higher in LD than in SD. In contrast, growth-active GAs, i.e. GA(1), GA(3) and GA(4), and IAA were low in the mutant hypocotyls. The 7B-1 mutant appears to be an ABA-overproducer, and the photoperiod-regulated ABA levels may be responsible for the hypersensitivity of the mutant to exogenous ABA.

Endogenous gibberellins in immature seeds of Prunus persica L.: identification of GA(118), GA(119), GA(120), GA(121), GA(122) and GA(126).

The endogenous gibberellins in immature seeds of Prunus persica were analyzed by gas chromatography-mass spectrometry. Eleven known gibberellins, GA(3), GA(9), GA(17), GA(19), GA(30), GA(44), GA(61), GA(63), GA(87), GA(95) and GA(97) were identified. Additionally, several hitherto unknown gibberellins were detected and their putative structures were verified by synthesis of the authentic gibberellins. These gibberellins were then assigned trivial numbers, e.g. 1alpha-hydroxy GA(20) (GA(118)), 1alpha-hydroxy GA(9) (GA(119)), 1,2-didehydro GA(9) (GA(120)), 1,2-didehydro GA(70) (GA(121)), 1,2-didehydro GA(69) (GA(122)) and 1,2-didehydro GA(77) (GA(126)). GA(118) and GA(119) were the first 1alpha-hydroxy gibberellins identified from higher plants. The above profile of 1,2-didehydro gibberellins suggests that 1,2-dehydrogenation might occur prior to 3beta-hydroxylation in biosynthesis of GA(3), GA(30) and GA(87) in immature seeds of P. persica.

Role of ethylene in cotyledon development of microspore-derived embryos of Brassica napus.

Ethylene production during seed development in Brassica napus occurs first at 20 d after pollination (DAP), while a second greater peak occurs at 35 DAP. Because of the inaccessible location of the embryo within the maternal tissue, microspore-derived embryos (MDEs) of B. napus were used as a model for studying the role of ethylene during embryo development. The MDEs also produced a peak in ethylene evolution at 20 DAC (i.e. the early cotyledonary stage), dropping to minimal levels by 25-30 DAC. At 20 DAC the excised cotyledon evolved 85% of the ethylene found in the whole MDE. To determine the role of ethylene, MDEs were treated with aminoethoxyvinylglycine (AVG, an inhibitor of ethylene biosynthesis), CoCl(2) (an inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase), and silver thiosulphate (STS, an inhibitor of ethylene action). An inhibition in ethylene production or action at 20 DAC resulted in diminished lateral cotyledon expansion, due to a reduction in the lateral expansion of cells within the cotyledon. Recovery to 'control-type' levels of cotyledon cell expansion was achieved by application of ACC (the metabolic precursor of ethylene) to AVG-treated MDEs. Thus, ethylene production at 20 DAP likely controls cotyledon expansion during embryo development.

Synthesis and bioactivity of 6alpha- and 6beta-hydroxy analogues of castasterone.

The reduction of castasterone with sodium in ethanol produced chiefly the known 6alpha-hydroxy stereoisomer, whereas reduction with sodium orohydride in methanol afforded mainly the novel 6beta-epimer. Both compounds showed variable bioactivity through four separate assays via the rice leaf lamina inclination bioassay. However, when treated with an appropriate statistical program to remove outliers, the averaged results clearly indicated that the two 6-hydroxy epimers possess comparable and significant bioactivity, which is, however, lower than that of castasterone or brassinolide. When applied together with 1000 ng of the auxin, indole-3-acetic acid (IAA), the activity of both the 6alpha and 6beta hydroxy epimers was enhanced by ca. one order of magnitude across a wide range of doses.

Effect of chain length and ring size of alkyl and cycloalkyl side-chain substituents upon the biological activity of brassinosteroids. Preparation of novel analogues with activity exceeding that of brassinolide.

A series of brassinosteroids with different alkyl or cycloalkyl substituents in place of the isopropyl group at C-24 of brassinolide (1) were prepared by the CuCN-catalyzed addition of Grignard reagents to (threo-2R,3S,5alpha,22R,23R,24S)-23,24-epoxy-6, 6-(ethylenedioxy)-2,3-(isopropylidenedioxy)-26, 27-dinorcholestan-22-ol (9), followed by deketalization and Baeyer-Villiger oxidation. Compound 9 was employed as part of a 70:30 threo/erythro mixture of epoxides 9 and 10, from which the erythro-epoxide 10 was recovered intact after the Grignard additions. Thus, the corresponding n-dodecyl, n-hexyl, n-propyl, tert-butyl, cyclohexyl, cyclopentyl, cyclobutyl, and cyclopropyl analogues of brassinolide were obtained. A rearrangement byproduct was observed during the preparation of the cyclopropyl-substituted brassinosteroid when ether was used as the solvent in the Grignard reaction, but could be avoided by the use of THF. A method for recycling the undesired erythro-epoxide 10 was developed on the basis of deoxygenation with tellurium and lithium triethylborohydride. The rice leaf lamina inclination assay was then used to measure the bioactivity of the products. In general, increasing activity was observed as the length or ring size of the C-24 hydrocarbon substituent decreased. The novel cyclobutyl- and cyclopropyl-substituted analogues of brassinolide (1) were ca. 5-7 times as active as 1 and thus appear to be the most potent brassinosteroids reported to date. Further enhancement of the bioactivity of all of the above brassinosteroids, except that of the inactive n-dodecyl derivative, was observed when the brassinosteroid was applied together with an auxin, indole-3-acetic acid (IAA). The synergy between the brassinosteroids and IAA thus increased the bioactivity of the brassinosteroids, including the cyclopropyl and cyclobutyl derivatives, by ca. 1-2 orders of magnitude.

Screening the foods of an endangered parrot, the kakapo (Strigops habroptilus), for oestrogenic activity using a recombinant yeast bioassay.

In recent years the possibility of environmental oestrogens affecting the reproduction of vertebrates has become an issue of both public and scientific interest. Although the significance of such chemicals remains controversial there is clear evidence that, in some contexts, environmental oestrogens can influence the fertility of vertebrates. Highly endangered species represent a situation in which even modest reductions in the fertility of key individuals may have implications for the survival of the entire species. This paper reports the screening of both natural and supplementary foods of the kakapo (Strigops habroptilus), a critically endangered New Zealand nocturnal parrot, for oestrogenic activity using a recombinant yeast based bioassay. Low levels of oestrogenic activity were detected in one of the 'chick-raising' foods, but no oestrogenic activity was detected in the adult supplementary foods. The oestrogenicity of a range of phytochemicals possibly associated with the kakapo natural diet was also examined. Two such phytochemicals, podocarpic acid and its reduced derivative podocarpinol, showed weak oestrogenic activity (approximately 10(-6) and 10(-4) of the activity of 17-beta-oestradiol, respectively).

Rhizobium leguminosarum as a plant growth-promoting rhizobacterium: direct growth promotion of canola and lettuce.

Early seedling root growth of the nonlegumes canola (Brassica campestris cv. Tobin, Brassica napus cv. Westar) and lettuce (Lactuca sativa cv. Grand Rapids) was significantly promoted by inoculation of seeds with certain strains of Rhizobium leguminosarum, including nitrogen- and nonnitrogen-fixing derivatives under gnotobiotic conditions. The growth-promotive effect appears to be direct, with possible involvement of the plant growth regulators indole-3-acetic acid and cytokinin. Auxotrophic Rhizobium mutants requiring tryptophan or adenosine (precursors for indole-3-acetic acid and demonstrate a new facet of the Rhizobium-plant relationship and that Rhizobium leguminosarum can be considered a plant growth-promoting rhizobacterium (PGPR).

Identification of a Novel Gibberellin (GA85) in Very Young Seedlings of Brassica campestris cv. Tobin.

A new gibberellin (GA) was identified from extracts of cotyledons of 7 day-old canola seedlings (Brassica campestris cv. Tobin). This GA is 12α-hydroxy-GA1 and has been assigned the trivial name of GA85. Isolation was monitored by the Tan-ginbozu dwarf rice micro-drop assay after each high-performance liquid chromatography (HPLC) step. Identification was based on Kovats retention index (KRI) and the mass spectrum of the methyl ester, trimethylsilyl ether (MeTMSi) derivative after analysis by gas chromatography-mass spectrometry (GC-MS) in comparison with an authentic sample of 12α-hydroxy-GA1. Based on quantitation by the dwarf rice micro-drop assay, GA85 is one of the major biologically active GAs in cotyledons of young canola seedlings.

Ethylene-Mediated Regulation of Gibberellin Content and Growth in Helianthus annuus L.

Elongation of hypocotyls of sunflower can be promoted by gibberellins (GAs) and inhibited by ethylene. The role of these hormones in regulating elongation was investigated by measuring changes in both endogenous GAs and in the metabolism of exogenous [(3)H]- and [(2)H(2)]GA(20) in the hypocotyis of sunflower (Helianthus annuus L. cv Delgren 131) seedlings exposed to ethylene. The major biologically active GAs identified by gas chromatography-mass spectrometry were GA(1), GA(19), GA(20), and GA(44). In hypocotyls of seedlings exposed to ethylene, the concentration of GA(1), known to be directly active in regulating shoot elongation in a number of species, was reduced. Ethylene treatment reduced the metabolism of [(3)H]GA(20) and less [(2)H(2)]GA(1) was found in the hypocotyls of those seedlings exposed to the higher ethylene concentrations. However, it is not known if the effect of ethylene on GA(20) metabolism was direct or indirect. In seedlings treated with exogenous GA(1) or GA(3), the hypocotyls elongated faster than those of controls, but the GA treatment only partially overcame the inhibitory effect of ethylene on elongation. We conclude that GA content is a factor which may limit elongation in hypocotyls of sunflower, and that while exposure to ethylene results in reduced concentration of GA(1) this is not sufficient per se to account for the inhibition of elongation caused by ethylene.

Changes after Decapitation in Concentrations of Indole-3-Acetic Acid and Abscisic Acid in the Larger Axillary Bud of Phaseolus vulgaris L. cv Tender Green.

Early changes in the concentrations of indole-3-acetic acid (IAA) and abscisic acid (ABA) were investigated in the larger axillary bud of 2-week-old Phaseolus vulgaris L. cv Tender Green seedlings after removal of the dominant apical bud. Concentrations of these two hormones were measured at 4, 6, 8, 12 and 24 hours following decapitation of the apical bud and its subtending shoot. Quantitations were accomplished using either gas chromatography-mass spectrometry-selected ion monitoring (GS-MS-SIM) with [(13)C(6)]-IAA or [(2)H(6)]-ABA as quantitative internal standards, or by an indirect enzyme-linked immunosorbent assay, validated by GC-MS-SIM. Within 4 hours after decapitation the IAA concentration in the axillary bud had increased fivefold, remaining relatively constant thereafter. The concentration of ABA in axillary buds of decapitated plants was 30 to 70% lower than for buds of intact plants from 4 to 24 hours following decapitation. Fresh weight of buds on decapitated plants had increased by 8 hours after decapitation and this increase was even more prominent by 24 hours. Anatomical assessment of the larger axillary buds at 0, 8, and 24 hours following decapitation showed that most of the growth was due to cell expansion, especially in the intermodal region. Thus, IAA concentration in the axillary bud increases appreciably within a very few hours of decapitation. Coincidental with the rise in IAA concentration is a modest, but significant reduction in ABA concentration in these axillary buds after decapitation.

Effects of jasmonic Acid on embryo-specific processes in brassica and linum oilseeds.

A number of effects on embryogenesis of the putative phytohormone jasmonic acid (JA), and its methyl ester (MeJA), were investigated in two oilseed plants, repeseed (Brassica napus) and flax (Linum usitatissimum). Results from treatments with JA and MeJA were compared with those of a known effector of several aspects of embryogenesis, abscisic acid (ABA). Jasmonic acid was identified by gas chromatography-mass spectrometry as a naturally occurring substance in both plant species during embryo development. Both JA and MeJA can prevent precocious germination of B. napus microspore embryos and of cultured zygotic embryos of both species at an exogenous concentration of >1 micromolar. This dose-response was comparable with results obtained with ABA. Inhibitory effects were also observed on seed germination with all three growth regulators in rapeseed and flax. A number of molecular aspects of embryogenesis were also investigated. Expression of the B. napus storage protein genes (napin and cruciferin) was induced in both microspore embryos and zygotic embryos by the addition of 10 micromolar JA. The level of napin and cruciferin mRNA detected was similar to that observed when 10 micromolar ABA was applied to these embryos. For MeJA only slight increases in napin or cruciferin mRNA were observed at concentrations of 30 micromolar. Several oilbody-associated proteins were found to accumulate when the embryos were incubated with either JA or ABA in both species. The MeJA had little effect on oilbody protein synthesis. The implications of JA acting as a natural regulator of gene expression in zygotic embryogenesis are discussed.

Cytokinins in the Phloem Sap of White Lupin (Lupinus albus L.).

Cytokinin-like activity in samples of xylem and phloem sap collected from field-grown plants of white lupin (Lupinus albus L.) over a period of 9 to 24 weeks after sowing was measured using the soybean hypocotyl callus bioassay following paper chromatographic separation. The phloem sap was collected from shallow incisions made at the base of the stem, the base of the inflorescence (e.g. stem top), the petioles, and the base and tip of the fruit. Xylem sap was collected as root exudate from the stump of plants severed a few centimeters above ground level. Concentration of cytokinin-like substances was highest in phloem sap collected from the base of the inflorescence and showed an increase over the entire sampling period (from week 10 [61 nanogram zeatin equivalents] to week 24 [407 nanogram zeatin equivalents]). Concentrations in the xylem sap and in the other phloem saps were generally lower. Relatively high concentrations of cytokinin-like substances in petiole phloem sap (70 to 130 nanogram zeatin equivalents per milliliter) coincided in time with high concentrations in sap from the base of the inflorescence (see above). Concentrations in sap (phloem or xylem) from the base of the stem were very much lower. This finding is consistent with movement of cytokinins from leaves into the developing inflorescence and fruit, rather than direct input to the fruit from xylem sap. However, an earlier movement of cytokinins from roots into leaves via the xylem cannot be ruled out. Sap collected at an 18-week harvest was additionally separated by sequential C(18) reversed-phase high performance liquid chromatography --> NH(2) normal phase high performance liquid chromatography, bioassayed, and then analyzed by electron impact gas chromatography-mass spectrometry. Identification of zeatin riboside and dihydrozeatin as two of the major cytokinins in combined sap samples was accomplished by gas chromatography-mass spectrometry-selected ion monitoring.

Identification of Two Brassinosteroids from the Cambial Region of Scots Pine (Pinus silverstris) by Gas Chromatography-Mass Spectrometry, after Detection Using a Dwarf Rice Lamina Inclination Bioassay.

A simple and improved dwarf rice (Oryza sativa var Tan-ginbozu) lamina inclination bioassay for brassinosteroids (BRs) was developed based on a previously published method (K Takeno, RP Pharis [1982] Plant Cell Physiol 23: 1275-1281). The assay used 3-day-old intact seedlings, and detection of BR was made more sensitive by synergizing the response to BR with indole-3-acetic acid (IAA). The minimum detectable amount of BR was less than 0.1 nanogram/rice plant (brassinolide equivalents). Purification steps for isolation of BR from tissue scrapings taken from the cambial region of Scots pine (Pinus silverstris) harvested during the period of rapid wood production were guided by this assay. After column chromatography (silica gel and PrepPak C(18)) and reversed phase C(18) high performance liquid chromatography, the biologically active fractions were analyzed by gas chromatography-mass spectrometry (GC-MS) and/or GC-MS-selected ion monitoring. Two BRs, castasterone (major) and brassinolide (minor) were identified. This is the first identification of BR from the cambial region of a conifer.

Effects of Abscisic Acid and High Osmoticum on Storage Protein Gene Expression in Microspore Embryos of Brassica napus.

Storage protein gene expression, characteristic of mid- to late embryogenesis, was investigated in microspore embryos of rapeseed (Brassica napus). These embryos, derived from the immature male gametophyte, accumulate little or no detectable napin or cruciferin mRNA when cultured on hormone-free medium containing 13% sucrose. The addition of abscisic acid (ABA) to the medium results in an increase in detectable transcripts encoding both these polypeptides. Storage protein mRNA is induced at 1 micromolar ABA with maximum stimulation occurring between 5 and 50 micromolar. This hormone induction results in a level of storage protein mRNA that is comparable to that observed in zygotic embryos of an equivalent morphological stage. Effects similar to that of ABA are noted when 12.5% sorbitol is added to the microspore embryo medium (osmotic potential = 25.5 bars). Time course experiments, to study the induction of napin and cruciferin gene expression demonstrated that the ABA effect occurred much more rapidly than the high osmoticum effect, although after 48 hours, the levels of napin or cruciferin mRNA detected were similar in both treatments. This difference in the rates of induction is consistent with the idea that the osmotic effect may be mediated by ABA which is synthesized in response to the reduced water potential. Measurements of ABA (by gas chromatography-mass spectrometry using [(2)H(6)]ABA as an internal standard) present in microspore embryos during sorbitol treatment and in embryos treated with 10 micromolar ABA were performed to investigate this possibility. Within 2 hours of culture on high osmoticum the level of ABA increased substantially and significantly above control and reached a maximum concentration within 24 hours. This elevated concentration was maintained for 48 hours after culturing and represents a sixfold increase over control embryos. The ABA-treated embryos accumulated the hormone very quickly, but ABA concentrations returned to basal levels within 72 hours after treatment. The possibility that embryo-synthesized ABA may be a mediator of effects of osmotic stress on gene expression in Brassica embryos is discussed.

A mutant gene that increases gibberellin production in brassica.

A single gene mutant (elongated internode [ein/ein]) with accelerated shoot elongation was identified from a rapid cycling line of Brassica rapa. Relative to normal plants, mutant plants had slightly accelerated floral development, greater stem dry weights, and particularly, increased internode and inflorescence elongation. The application of the triazole plant growth retardant, paclobutrazol, inhibited shoot elongation, returning ein to a more normal phenotype. Conversely, exogenous gibberellin A(3) (GA(3)) can convert normal genotypes to a phenotype resembling ein. The content of endogenous GA(1) and GA(3) were estimated by gas chromatography-selected ion monitoring using [(2)H]GA(1), as a quantitative internal standard and at day 14 were 1.5- and 12.1-fold higher per stem, respectively, in ein than in normal plants, although GA concentrations were more similar. The endogenous levels of GA(20) and GA(1), and the rate of GA(19) metabolism were simultaneously analyzed at day 7 by feeding [(2)H(2)]GA(19) and measuring metabolites [(2)H(2)]GA(20) and [(2)H(2)]GA(1) and endogenous GA(20) and GA(1), with [(2)H(5)]GA(20) and [(2)H(5)]GA(1) as quantitative internal standards. Levels of GA(1) and GA(20) were 4.6- and 12.9-fold higher, respectively, and conversions to GA(20) and GA(1) were 8.3 and 1.3 times faster in ein than normal plants. Confirming the enhanced rate of GA(1) biosynthesis in ein, the conversion of [(3)H]GA(20) to [(3)H]GA(1) was also faster in ein than in the normal genotype. Thus, the ein allele results in accelerated GA(1) biosynthesis and an elevated content of endogenous GAs, including the dihydroxylated GAs A(1) and A(3). The enhanced GA production probably underlies the accelerated shoot growth and development, and particularly, the increased shoot elongation.

Dormancy in Peach (Prunus persica L.) Flower Buds : I. Floral Morphogenesis and Endogenous Gibberellins at the End of the Dormancy Period.

Flower buds of peach (Prunus persica L.) trees, cv Novedad de Cordoba (Argentina), were collected near the end of the dormant period and immediately before anthesis. After removal of scale leaves, morphological observations of representative buds, made on transverse and longitudinal microtome sections, showed that all verticils making up the flower are present in an undifferentiated form during the dormant period (June). Flower buds collected at the end of dormant period (August) showed additional growth and differentiation, at which time formation of two ovules was beginning in the unicarpelar gynoecium. Dehiscence of anthers had not yet occurred 10 days before full bloom, and the ovules were still developing. Free endogenous gibberellin (GA)-like substances were quantified by bioassay (Tan-ginbozu dwarf rice microdrop) after SiO(2) partition column chromatography, reversed phase C18-high performance liquid chromatography, and finally Nucleosil [N(CH(3))(2)]high performance liquid chromatography. Bioactive fractions were then subjected to capillary gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM). Gibberellins A(1), A(3), and A(8) were tentatively identified in peach flower buds using GC-SIM and Kovat's retention indices, and relative amounts approximated by GC-SIM (2:8:6 for GA(1), GA(3), and GA(8), respectively). The highest concentration (330 nanograms per gram dry weight) of free GA(1)/GA(3) was found in dormant buds (June) and diminished thereafter. The concentration free of GA(1)/GA(3) did not increase immediately prior to bud break. However, high GA(1)/GA(3) concentrations occurred during stages where rate of growth and cellular differentiation of (mainly fertile) verticils can be influenced.

Gibberellin structure and florigenic activity in Lolium temulentum, a long-day plant.

Structural requirements for florigenic activity among gibberellins (GAs) and GA derivatives, including several new ones, applied once to leaves of Lolium temulentum, were examined. The compounds were applied to plants kept either in non-inductive short days (SD) or exposed to one inductive long day (LD). Inflorescence initiation and stem-elongation responses were assessed three weeks later. Among the GAs used, the range in effective dose for inflorescence initiation was more than 1000-fold, but substantially less for stem elongation. Some GAs promoted both stem elongation and inflorescence initiation, some promoted one without the other, and some affected neither. The structural features enhancing florigenic activity were often different from those enhancing stem elongation. Except in the case of 2,2-dimethyl GA4, a double bond in the A ring at either C-1,2 or C-2,3 was essential for high florigenic activity, though not for stem elongation. A free carboxy group was needed for both. Inflorescence initiation in Lolium was enhanced by hydroxylation at C-12, -13 and -15, whereas hydroxylation at C-3 reduced the effect on inflorescence initiation but increased that on stem elongation. A 12ß-hydroxyl was more effective than the α epimer for inflorescence initiation whereas the reverse was true for stem elongation. Although such differential effectiveness of GAs for inflorescence initiation and for stem elongation could reflect differences in uptake, transport or metabolism, we suggest that it is indicative of specific structural requirements for inflorescence initiation.