Gibberellin A(3) Is Biosynthesized from Gibberellin A(20) via Gibberellin A(5) in Shoots of Zea mays L

Production of Gibberellins via a Non-Natural Pathway Using Steviol as a Substrate

Gibberellins (GAs) are plant hormones widely used in agriculture. At present, GAs are produced by fermentation of the fungus Fusarium fujikuroi. However, fungal growth is too slow, resulting in slow fungal fermentation and a low yield. Here, to develop an alternative production source of GAs, an artificial pathway was engineered in Escherichia coli. By selecting and combining enzymes derived from plants and bacteria, a novel 4-enzyme pathway was successfully constructed to produce GAs using steviol, a readily available and less valuable byproduct during enzymatic refining of rebaudioside A, as a feedstock. Whole-cell biotransformation with E. coli strain expressing the novel pathway produced 71.17 ± 2.00 mg/L GA1 and a trace amount of GA3 from steviol in 48 h. This report presents a significant advancement in the fast production of GAs and establishes a method for the metabolism of terpenoids to produce target products in microbial hosts.

The Current Status of Research on Gibberellin Biosynthesis

Gibberellins are produced by all vascular plants and several fungal and bacterial species that associate with plants as pathogens or symbionts. In the 60 years since the first experiments on the biosynthesis of gibberellic acid in the fungus Fusarium fujikuroi, research on gibberellin biosynthesis has advanced to provide detailed information on the pathways, biosynthetic enzymes and their genes in all three kingdoms, in which the production of the hormones evolved independently. Gibberellins function as hormones in plants, affecting growth and differentiation in organs in which their concentration is very tightly regulated. Current research in plants is focused particularly on the regulation of gibberellin biosynthesis and inactivation by developmental and environmental cues, and there is now considerable information on the molecular mechanisms involved in these processes. There have also been recent advances in understanding gibberellin transport and distribution and their relevance to plant development. This review describes our current understanding of gibberellin metabolism and its regulation, highlighting the more recent advances in this field.

StGA2ox1 is induced prior to stolon swelling and controls GA levels during potato tuber development

The formation and growth of a potato (Solanum tuberosum) tuber is a complex process regulated by different environmental signals and plant hormones. In particular, the action of gibberellins (GAs) has been implicated in different aspects of potato tuber formation. Here we report on the isolation and functional analysis of a potato GA 2-oxidase gene (StGA2ox1) and its role in tuber formation. StGA2ox1 is upregulated during the early stages of potato tuber development prior to visible swelling and is predominantly expressed in the subapical region of the stolon and growing tuber. 35S-over-expression transformants exhibit a dwarf phenotype, reduced stolon growth and earlier in vitro tuberization. Transgenic plants with reduced expression levels of StGA2ox1 showed normal plant growth, an altered stolon swelling phenotype and delayed in vitro tuberization. Tubers of the StGA2ox1 suppression clones contain increased levels of GA20, indicating altered GA metabolism. We propose a role for StGA2ox1 in early tuber initiation by modifying GA levels in the subapical stolon region at the onset of tuberization, thereby facilitating normal tuber development and growth.

16,17-dihydro gibberellin A5 competitively inhibits a recombinant Arabidopsis GA 3beta-hydroxylase encoded by the GA4 gene

Ring D-modified gibberellin (GA) A5 and A20 derivatives are structurally similar to GA20 and GA9 (the precursors to growth-active GA1 and GA4) and, when applied to higher plants, especially grasses, can reduce shoot growth with concomitant reductions in levels of growth-active GAs and increases in levels of their immediate 3-deoxy precursors. The recombinant Arabidopsis GA 3beta-hydroxylase (AtGA3ox1) protein was used in vitro to test a number of ring D-modified GA structures as possible inhibitors of AtGA3ox1. This fusion protein was able to 3beta-hydroxylate the 3-deoxy GAs, GA9 and GA20, to GA4 and GA1, respectively, and convert the 2,3-didehydro GA, GA5, to its 2,3-epoxide, GA6. Michaelis-Menten constant (Km) values of 1.25 and 10 microM, respectively, were obtained for the GA9 and GA20 conversions. We utilized the enzyme's ability to convert GA20 to GA1 in order to test the efficacy of GA5, 16,17-dihydro GA5 (dihydro GA5), and a number of other ring D-modified GAs as inhibitors of AtGA3ox activity. For the exo-isomer of dihydro GA5, inhibition increased with the dose of dihydro GA5, with Lineweaver-Burk plots showing that dihydro GA5 changed only the Km of the enzyme reaction, not the V(max), giving a dissociation constant of the enzyme-inhibitor complex (Ki) of 70 microM. Other ring D-modified GA derivatives showed similar inhibitory effects on GA1 production, with 16,17-dihydro GA20-13-acetate being the most effective inhibitor. This behavior is consistent with dihydro GA5, at least, functioning as a competitive substrate inhibitor of AtGA3ox1. Finally, the recombinant AtGA3ox1 fusion protein may be a useful screening tool for other effective 3beta-hydroxylase inhibitors, including naturally occurring ones.

Auxin from the developing inflorescence is required for the biosynthesis of active gibberellins in barley stems

Multiple gibberellins (GAs) were quantified in the stems of intact, decapitated, and decapitated auxin-treated barley (Hordeum vulgare) plants. Removal of the developing inflorescence reduced the endogenous levels of indole-3-acetic acid (IAA), GA(1), and GA(3) and increased the level of GA(29) in internodal and nodal tissues below the site of excision. Application of IAA to the excised stump restored GA levels to normal in almost all cases. The conversion of [(14)C]GA(20) to bioactive [(14)C]GA(1) and of [(14)C]GA(5) to bioactive [(14)C]GA(3) was reduced by decapitation, and IAA application was able to restore conversion rates back to the levels found in intact plants. The amount of mRNA for the principal vegetative 3-oxidase (converting GA(20) to GA(1), and GA(5) to GA(3)) was decreased in decapitated plants and restored by IAA application. The results indicate that the inflorescence of barley is a source of IAA that is transported basipetally into the internodes and nodes where bioactive GA(1) and GA(3) are biosynthesized. Thus, IAA is required for normal GA biosynthesis in stems, acting at multiple steps in the latter part of the pathway.

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.

Azospirillum spp. metabolize [17,17-2H2]gibberellin A20 to [17,17-2H2]gibberellin A1 in vivo in dy rice mutant seedlings

Azospirillum spp. are endophytic bacteria with beneficial effects on cereals--effects partially attributed to gibberellin production by the microorganisms. Azospirillum lipoferum and Azospirillum brasilense inoculated to rice dy mutant reversed dwarfism in seedlings incubated with [17,17-2H2]GA20 with formation of [17,17-2H2]GA1, showing the in vivo capacity to perform the 3beta-hydroxylation. When prohexadione-Ca, an inhibitor of late steps in gibberellin biosynthesis, was added to the culture medium, no complementation was observed and no [17,17-2H2]GA1 was produced. The latter suggests that the bacterial operating enzyme may be a 2-oxoglutarate-dependent dioxygenase, similar to those of plants.

Role of gibberellins in parthenocarpic fruit development induced by the genetic system pat-3/pat-4 in tomato

The role of gibberellins (GAs) in the induction of parthenocarpic fruit-set and growth by the pat-3/pat-4 genetic system in tomato (Lycopersicon esculentum Mill.) was investigated using wild type (WT; Cuarenteno) and a near-isogenic line derived from the German line RP75/59 (the source of pat-3/pat-4 parthenocarpy). Unpollinated WT ovaries degenerated but GA3 application induced parthenocarpic fruit growth. On the contrary, parthenocarpic growth of pat-3/pat-4 fruits, which occurs in the absence of pollination and hormone treatment, was not affected by applied GA3. Unpollinated pat-3/pat-4 fruit growth was negated by paclobutrazol, an inhibitor of ent-kaurene oxidase, and this inhibitory effect was negated by GA3. The quantification of the main GAs of the early 13-hydroxylation pathway (GA1, GA8, GA19, GA20, GA29 and GA44) in unpollinated ovaries at 3 developmental stages (flower bud, FB; pre-anthesis, PR; and anthesis, AN), by gas chromatography-selected ion monitoring, showed that the concentration of most of them was higher in pat-3/pat-4 than in WT ovaries at PR and AN stages. The concentration of GA1, suggested previously to be the active GA in tomate, was 2-4 times higher. Unpollinated pat-3/pat-4 ovaries at FB, PR and AN stages also contained relatively high amounts (5-12 ng g-1) of GA3, a GA found at less than 0.5 ng g-1 in WT ovaries. It is concluded that the mutations pat-3/pat-4 may induce natural facultative parthenocarpy capacity in tomato by increasing the concentration of GA1 and GA3 in the ovaries before pollination.

Identification of endogenous gibberellins in strawberry, including the novel gibberellins GA123, GA124 and GA125

Extracts of carboxylic acids from immature fruits of strawberry (Fragaria x ananassa Duch. cv. Elsanta) were analysed for gibberellins by combined gas chromatography-mass spectrometry. The following previously characterised gibberellins were identified by comparison of their mass spectra and Kovats retention indices (KRIs) with those of standards or published data: GA1, GA3, GA5, GA8, GA12, GA17, GA19, GA20, GA29, GA44, GA48, GA49, GA53, GA77, GA97, GA111 and GA112. Evidence for endogenous 1-epi GA61 (GA119) and 11alpha-OH-GA12 was also obtained. In addition, a number of putative GAs were detected. Of these, three were shown to be 12alpha-hydroxy-GA53, 12alpha-hydroxy-GA44, and 12alpha-hydroxy-GA19 by comparison with authentic compounds prepared by rational synthesis, and have been allocated the descriptors GA123, GA124 and GA125, respectively.

The gene pat-2, which induces natural parthenocarpy, alters the gibberellin content in unpollinated tomato ovaries

We investigated the role of gibberellins (GAs) in the effect of pat-2, a recessive mutation that induces facultative parthenocarpic fruit development in tomato (Lycopersicon esculentum Mill.) using near-isogenic lines with two different genetic backgrounds. Unpollinated wild-type Madrigal (MA/wt) and Cuarenteno (CU/wt) ovaries degenerated, but GA(3) application induced parthenocarpic fruit growth. On the contrary, parthenocarpic growth of MA/pat-2 and CU/pat-2 fruits, which occurs in the absence of pollination and hormone application, was not affected by GA(3). Pollinated MA/wt and parthenocarpic MA/pat-2 ovary development was negated by paclobutrazol, and this inhibitory effect was counteracted by GA(3). The main GAs of the early-13-hydroxylation pathway (GA(1), GA(3), GA(8), GA(19), GA(20), GA(29), GA(44), GA(53), and, tentatively, GA(81)) and two GAs of the non-13-hydroxylation pathway (GA(9) and GA(34)) were identified in MA/wt ovaries by gas chromatography-selected ion monitoring. GAs were quantified in unpollinated ovaries at flower bud, pre-anthesis, and anthesis. In unpollinated MA/pat-2 and CU/pat-2 ovaries, the GA(20) content was much higher (up to 160 times higher) and the GA(19) content was lower than in the corresponding non-parthenocarpic ovaries. The application of an inhibitor of 2-oxoglutarate-dependent dioxygenases suggested that GA(20) is not active per se. The pat-2 mutation may increase GA 20-oxidase activity in unpollinated ovaries, leading to a higher synthesis of GA(20), the precursor of an active GA.

Gibberellin Biosynthesis in Maize. Metabolic Studies with GA(15), GA(24), GA(25), GA(7), and 2,3-Dehydro-GA(9)

[17-(14)C]-Labeled GA(15), GA(24), GA(25), GA(7), and 2,3-dehydro-GA(9) were separately injected into normal, dwarf-1 (d1), and dwarf-5 (d5) seedlings of maize (Zea mays L.). Purified radioactive metabolites from the plant tissues were identified by full-scan gas chromatography-mass spectrometry and Kovats retention index data. The metabolites from GA(15) were GA(44), GA(19), GA(20), GA(113), and GA(15)-15,16-ene (artifact?). GA(24) was metabolized to GA(19), GA(20), and GA(17). The metabolites from GA(25) were GA(17), GA(25) 16alpha,17-H(2)-17-OH, and HO-GA(25) (hydroxyl position not determined). GA(7) was metabolized to GA(30), GA(3), isoGA(3) (artifact?), and trace amounts of GA(7)-diene-diacid (artifact?). 2,3-Dehydro-GA(9) was metabolized to GA(5), GA(7) (trace amounts), 2,3-dehydro-GA(10) (artifact?), GA(31), and GA(62). Our results provide additional in vivo evidence of a metabolic grid in maize (i.e. pathway convergence). The grid connects members of a putative, non-early 3,13-hydroxylation branch pathway to the corresponding members of the previously documented early 13-hydroxylation branch pathway. The inability to detect the sequence GA(12) --> GA(15) --> GA(24) --> GA(9) indicates that the non-early 3,13-hydroxylation pathway probably plays a minor role in the origin of bioactive gibberellins in maize.

The dwarf-1 (dt) Mutant of Zea mays blocks three steps in the gibberellin-biosynthetic pathway

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA-biosynthetic pathway. They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the D1 gene of maize (Zea mays L.) controls the three biosynthetic steps: GA20 to GA1, Ga20 to GA5, and GA5 to GA3. We also present evidence that three gibberellins, GA1, GA5, and GA3, have per se activity in stimulating shoot elongation in maize. The metabolic evidence comes from the injection of [17-13C,3H]GA20 and [17-13C,3H]GA5 into seedlings of d1 and controls (normal and d5), followed by isolation and identification of the 13C-labeled metabolites by full-scan GC-MS and Kovats retention index. For the controls, GA20 was metabolized to GA1,GA3, and GA5; GA5 was metabolized to GA3. For the d1 mutant, GA20 was not metabolized to GA1, GA3, or to GA5, and GA5 was not metabolized to GA3. The bioassay evidence is based on dosage response curves using d1 seedlings for assay. GA1, GA3, and GA5 had similar bioactivities, and they were 10-times more active than GA20.

The dwarf-1 (dt) Mutant of Zea mays blocks three steps in the gibberellin-biosynthetic pathway

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA-biosynthetic pathway. They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the D1 gene of maize (Zea mays L.) controls the three biosynthetic steps: GA20 to GA1, Ga20 to GA5, and GA5 to GA3. We also present evidence that three gibberellins, GA1, GA5, and GA3, have per se activity in stimulating shoot elongation in maize. The metabolic evidence comes from the injection of [17-13C,3H]GA20 and [17-13C,3H]GA5 into seedlings of d1 and controls (normal and d5), followed by isolation and identification of the 13C-labeled metabolites by full-scan GC-MS and Kovats retention index. For the controls, GA20 was metabolized to GA1,GA3, and GA5; GA5 was metabolized to GA3. For the d1 mutant, GA20 was not metabolized to GA1, GA3, or to GA5, and GA5 was not metabolized to GA3. The bioassay evidence is based on dosage response curves using d1 seedlings for assay. GA1, GA3, and GA5 had similar bioactivities, and they were 10-times more active than GA20.

Gibberellin Metabolism in Maize (The Stepwise Conversion of Gibberellin A12-Aldehyde to Gibberellin A20

The stepwise metabolism of gibberellin A12-aldehyde (GA12-aldehyde) to GA20 is demonstrated from seedling shoots of maize (Zea mays L.). The labeled substrates [13C,3H]GA12-aldehyde, [13C,3H]GA12, [14C4]GA53, [14C4/2H2]GA44, and [14C4/2H2]GA19 were fed individually to dwarf-5 vegetative shoots. Both [13C,3H]GA12-aldehyde and [13C,3H]GA12 were also added individually to normal shoots. The labeled metabolites were identified by full-scan gas chromatography-mass spectrometry and Kovats retention indices. GA12-aldehyde was metabolized to GA53-aldehyde, GA12, GA53, GA44, and GA19; GA12 was metabolized to 2[beta]-hydroxy-GA12, GA53, 2[beta]-hydroxyGA53, GA44, 2[beta]-hydroxyGA44, and GA19; GA53 was metabolized to GA44, GA19, GA20, and GA1; GA44 was metabolized to GA19; and GA19 was metabolized to GA20. These results, together with previously published data from this laboratory, document the most completely defined gibberellin pathway for the vegetative tissues of higher plants.

Seed and 4-chloroindole-3-acetic acid regulation of gibberellin metabolism in pea pericarp

In this study, we investigated seed and auxin regulation of gibberellin (GA) biosynthesis in pea (Pisum sativum L.) pericarp tissue in situ, specifically the conversion of [14C]GA19 to [14C]GA20. [14C]GA19 metabolism was monitored in pericarp with seeds, deseeded pericarp, and deseeded pericarp treated with 4-chloroindole-3-acetic acid (4-CI-IAA). Pericarp with seeds and deseeded pericarp treated with 4-CI-IAA continued to convert [14C]GA19 to [14C]GA20 throughout the incubation period (2-24 h). However, seed removal resulted in minimal or no accumulation of [14C]GA20 in pericarp tissue. [14C]GA29 was also identified as a product of [14C]GA19 metabolism in pea pericarp. The ratio of [14C]GA29 to [14C]GA20 was significantly higher in deseeded pericarp (with or without exogenous 4-CI-IAA) than in pericarp with seeds. Therefore, conversion of [14C]GA20 to [14C]GA29 may also be seed regulated in pea fruit. These data support the hypothesis that the conversion of GA19 to GA20 in pea pericarp is seed regulated and that the auxin 4-CI-IAA can substitute for the seeds in the stimulation of pericarp growth and the conversion of GA19 to GA20.

Gibberellins promote vegetative phase change and reproductive maturity in maize

Postembryonic shoot development in maize (Zea mays L.) is divided into a juvenile vegetative phase, an adult vegetative phase, and a reproductive phase that differ in the expression of many morphological traits. A reduction in the endogenous levels of bioactive gibberellins (GAs) conditioned by any one of the dwarf1, dwarf3, dwarf5, or anther ear1 mutations in maize delays the transition from juvenile vegetative to adult vegetative development and from adult vegetative to reproductive development. Mutant plants cease producing juvenile traits (e.g. epicuticular wax) and begin producing adult traits (e.g. epidermal hairs) later than wild-type plants. They also cease producing leaves and begin producing reproductive structures later than wild-type plants. These mutations greatly enhance most aspects of the phenotype of Teopod1 and Teopod2, suggesting that GAs suppress part but not all of the Teopod phenotype. Application of GA<inf>3</inf> to Teopod2 mutants and Teopod1, dwarf3 double mutants confirms this result. We conclude that GAs act in conjunction with several other factors to promote both vegetative and reproductive maturation but affect different developmental phases unequally. Furthermore, the GAs that regulate vegetative and reproductive maturation, like those responsible for stem elongation, are downstream of GA<inf>20</inf> in the GA biosynthetic pathway.

Isolation of the Arabidopsis GA4 locus

Progeny from a transgenic Arabidopsis plant generated by the Agrobacterium root transformation procedure were found to segregate for a gibberellin (GA)-responsive semidwarf phenotype. Complementation analysis with genetically characterized GA-responsive mutants revealed that the transgenic plant has an insertional mutation (ga4-2) that is an allele of the ga4 locus. The semidwarf phenotype of ga4-2 is inherited as a recessive mutation that cosegregates with both the T-DNA insert and the kanamycin resistance trait. DNA gel blot analysis indicated that the insertion site contains a complex T-DNA unit. A genomic library was constructed with DNA from the tagged ga4 mutant; a DNA clone was isolated from the library that flanks the T-DNA insert. The plant sequence isolated from this clone was used to isolate the corresponding full-length genomic and cDNA clones from wild-type libraries. DNA sequence comparison of the clones to the existing data bases suggests that they encode a hydroxylase. This conclusion is in agreement with a biochemical study that indicated that the ga4 mutant is deficient in 3 beta-hydroxylase in the GA biosynthetic pathway of Arabidopsis. RNA gel blot analysis showed that the message is ubiquitously expressed in different tissues of Arabidopsis but most abundantly in the silique. Unexpectedly, a higher level of transcription was detected in the ethyl methanesulfonate-induced ga4 mutant, and this overexpression was repressed by treatment with exogenous GA.

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

The possible involvement of gibberellins (GAs) in the regulation of hypocotyl elongation by phytochrome was examined. Under white light the tall long hypocotyl (lh) cucumber (Cucumis sativus L.) mutant, deficient in a type B-like phytochrome, shows an increased "responsiveness" (defined as response capability) to applied GA4 (the main endogenous active GA) compared to the wild type. Supplementing far-red irradiation results in a similar increase in responsiveness in the wild type. Experiments involving application of the precursor GA9 and of an inhibitor of GA4 inactivation suggest that both the GA4 activation and inactivation steps are phytochrome independent. Endogenous GA levels of whole seedlings were analyzed by combined gas chromatography-mass spectrometry using deuterated internal standards. The levels of GA4 (and those of GA34, the inactivated GA4) were lower in the lh mutant under low-irradiance fluorescent light compared with the wild type, similar to wild type under higher irradiance light during the initial hypocotyl extension phase, and higher during the phase of sustained growth, in which extension involved an increase in the number of cells in the upper region. In all cases, growth of the lh mutant was more rapid than that of the wild type. It is proposed that GA4 and phytochrome control cell elongation primarily through separate mechanisms that interact at a step close to the terminal response.

The Metabolism of Gibberellin A20 to Gibberellin A1 by Tall and Dwarf Mutants of Oryza sativa and Arabidopsis thaliana

The purpose of this study was to demonstrate the metabolism of gibberellin A20 (GA20) to gibberellin A1 (GA1) by tall and mutant shoots of rice (Oryza sativa L.) and Arabidopsis thaliana (L.) Heynh. The data show that the tall and dx mutant of rice and the tall and ga5 mutant of Arabidopsis metabolize GA20 to GA1. The data also show that the dy mutant of rice and the ga4 mutant of Arabidopsis block the metabolism of GA20 to GA1. [17-13C,3H]GA20 was fed to tall and the dwarf mutants, dx and dy, of rice and tall and the dwarf mutants, ga5 and ga4, of Arabidopsis. The metabolites were analyzed by high-performance liquid chromatography and full-scan gas chromatography-mass spectrometry together with Kovats retention index data. For rice, the metabolite [13C]GA, was identified from tall and dx seedlings; [13C]GA1 was not identified from the dy seedlings. [13C]GA29 was identified from tall, dx, and dy seedlings. For Arabidopsis, the metabolite [13C]GA1 was identified from tall, ga5, and ga4 plants. The amount of [13C]GA1 from ga4 plants was less than 15% of that obtained from tall and ga5 plants. [13C]GA29 was identified from tall, ga5, and ga4 plants. [13C]GA5 and [13C]GA3 were not identified from any of the six types of plant material.

Metabolism and Biological Activity of Gibberellin A4 in Vegetative Shoots of Zea mays, Oryza sativa, and Arabidopsis thaliana

[17-13C,3H]Gibberellin A4 (GA4) was injected into the shoots of tall (W23/L317), dwarf-1 (d1), and dwarf-5 (d5) Zea mays L. (maize); tall (cv Nipponbare), dwarf-x (dx), and dwarf-y (dy) Oryza sativa L. (rice); and tall (ecotype Landsberg erecta), ga4, and ga5 Arabidopsis thaliana (L.) Heynh. [13C]GA4 and its metabolites were identified from the shoots by full-scan gas chromatography-mass spectrometry and Kovats retention indices. GA4 was metabolized to GA1 in all nine genotypes. GA4 was also metabolized in some of the genotypes to 3-epi-GA1, GA2, 2[beta]-OH-GA2, 3-epi-GA2, endo-GA4, 16[alpha], 17-H2-16, 17-(OH)2-GA4, GA34, endo-GA34, GA58, 15-epi-GA63, GA71, and 16-epi-GA82. No evidence was found for the metabolism of GA4 to GA7 or of GA4 to GA3. The bioactivities of GA4 and GA1 were determined using the six dwarf mutants for assay. GA4 and GA1 had similar activities for the maize and rice mutants. For the Arabidopsis mutants, GA4 was more active than GA1 at low dosages; GA4 was less active than GA1 at higher dosages.

Gibberellin biosynthesis from gibberellin A12-aldehyde in a cell-free system from germinating barley (Hordeum vulgare L., cv. Himalaya) embryos

Gibberellin (GA) metabolism from GA12-aldehyde was studied in cell-free systems from 2-d-old germinating embryos of barley. [(14)C]- or [17-(2)H2]Gibberellins were used as substrates and all products were identified by combined gas chromatography-mass spectrometry. Stepwise analysis demonstrated the conversion of GA12-aldehyde via the 13-deoxy pathway to GA51 and via the 13-hydroxylation pathway to GA29, GA1 and GA8. In addition, GA3 was formed from GA20 via GA5. We conclude that the embryo is capable of producing gibberellins that can induce α-amylase production in the aleurone layer. There was no evidence for 12β- or 18-hydroxylation and GA4 was neither synthesised nor metabolised by the system. All metabolically obtained GAs, with the exception of GA3, were also found as endogenous components of the cell-free system in spite of ammonium-sulfate precipitation and desalting steps.

Hydrolysis and reconjugation of gibberellin A20 glucosyl ester by seedlings of Zea mays L

The [6-2H]glucosyl ester of [17-13C,3H]gibberellin A20 (GA20) was injected into light-grown 14-day-old seedlings of normal, dwarf-1, and dwarf-5 maize (Zea mays L.). The plant material was extracted 24 h later, and the extracts were purified by solvent partitioning, column chromatography, and HPLC. 13C-labeled metabolites were identified from the purified extracts by full-scan gas chromatography/mass spectrometry and selected ion current monitoring in conjunction with Kovats retention indices. The metabolites, [13C]GA20, [13C]GA29, [13C]GA20-13-O-glucoside, and [13C]GA29-2-O-glucoside, were identified from normal, dwarf-1, and dwarf-5 seedlings. [13C]GA8 and [13C]GA8-2-O-glucoside were also identified from normal and dwarf-5 seedlings but not from dwarf-1 seedlings. The data provide definitive evidence for the endogenous hydrolysis by the seedlings of the introduced conjugate and its reconjugation to three glucosides.

Seed effects on gibberellin metabolism in pea pericarp

Pea fruit (Pisum sativum L.) is a model system for studying the effect of seeds on fruit growth in order to understand coordination of organ development. The metabolism of (14)C-labeled gibberellin A(12) (GA(12)) by pea pericarp was followed using a method that allows access to the seeds while maintaining pericarp growth in situ. Identification and quantitation of GAs in pea pericarp was accomplished by combined gas chromatography-mass spectrometry following extensive purification of the putative GAs. Here we report for the first time that the metabolism of [(14)C]GA(12) to [(14)C]GA(19) and [(14)C]GA(20) occurs in pericarp of seeded pea fruit. Removal of seeds from the pericarp inhibited the conversion of radiolabeled GA(19) to GA(20) and caused the accumulation of radiolabeled and endogenous GA(19). Deseeded pericarp contained no detectable GA(20), GA(1), or GA(8), whereas pericarp with seeds contained endogenous and radiolabeled GA(20) and endogenous GA(1). These data strongly suggest that seeds are required for normal GA biosynthesis in the pericarp, specifically the conversion of GA(19) to GA(20).

The Distribution of Gibberellins in Vegetative Tissues of Pisum sativum L. : I. Biological and Biochemical Consequences of the le Mutation

The concentrations of endogenous gibberellin (GA) 1, 5, 8, 19, 20, and 29 in the component tissues of maturing tall (Le) and dwarf (le) pea (Pisum sativum) plants have been determined. The following conclusions were drawn from the data obtained: (a) GA(20) and its metabolites accumulate only in the growing regions of Le and le plants; (b) the le mutation is biochemically expressed in all immature tissues of the dwarf plants; (c) the quantitative composition of the GA metabolites in the various immature tissues is variable; (d) the total GA concentration in apical buds, unexpanded leaves, and tendrils is considerably higher than in GA(1)-responsive stem tissue; and (e) there is very little GA accumulation of the inactive 2beta-hydroxylated GAs (GA(8) and GA(29)) in either the mature vegetative tissues or the roots of pea plants.

Identification of Gibberellins in Spinach and Effects of Light and Darkness on their Levels

The endogenous gibberellin (GA) content of spinach (Spinacia oleracea) was reinvestigated by combined gas chromatography-mass spectrometry analysis. The 13-hydroxy GAs: GA(53), GA(44), GA(19), GA(17), GA(20), GA(5), GA(1), GA(29), and GA(8); the non-3, 13-hydroxy GAs: GA(12), GA(15), GA(9), and GA(51); and the 3beta-hydroxy GAs: GA(4), GA(7), and GA(34), were identified in spinach extracts by comparing full-scan mass spectra and Kovats retention indices with those of reference GAs. In addition, spinach plants contained GA(7)-isolactone, 16,17-dihydro-17-hydroxy-GA(53), GA(29)-catabolite, 3-epi-GA(1), and 10 uncharacterized GAs with mass spectra indicative of mono- and dihydroxy-GA(12), monohydroxy-GA(25), dihydroxy-GA(24), and dihydroxy-GA(g). The effect of light-dark conditions on the GA levels of the 13-hydroxylation pathway was studied by using labeled internal standards in selected ion monitoring mode. In short day, the GA levels were higher at the end of the light period than at the end of the dark period. Levels of GAs at the end of each short day were relatively constant. During the first supplementary light period of long day treatment, GA(53) and GA(19) declined dramatically, GA(44) and GA(1) decreased slightly, and GA(20) increased. During the subsequent high-intensity light period, the GA(20) level decreased and the levels of GA(53), GA(44), GA(19), and GA(1) increased slightly. Within 7 days after the beginning of long day treatment, similar patterns for GA(53) and GA(19) occurred. Furthermore, when these plants were transferred to darkness, an increase in the levels of GA(53) and GA(19) was observed. These results are compatible with the idea that in spinach, the flow through the GA biosynthetic pathway is much enhanced during the high-intensity light period, although GA turnover occurs also during the supplementary period of long day, both effects being responsible for the increase of GA(20) and GA(1) in long day.

Identification, quantitation and distribution of gibberellins in fruits of Pisum sativum L. cv. Alaska during pod development

In addition to the previously-reported gibberellins: GA1; GA8, GA20 and GA29 (García-Martínez et al., 1987, Planta 170, 130-137), GA3 and GA19 were identified by combined gas chromatography-mass spectrometry in pods and ovules of 4-d-old pollinated pea (Pisum sativum cv. Alaska) ovaries. Pods contained additionally GA17, GA81 (2α-hydroxy GA20) and GA29-catabolite. The concentrations of GA1, GA3, GA8, GA19, GA20 and GA29 were higher in the ovules than in the pod, although, with the exception of GA3, the total content of these GAs in the pod exceeded that in the seeds. About 80% of the GA3 content of the ovary was present in the seeds. The concentrations of GA19 and GA20 in pollinated ovaries remained fairly constant for the first 12 ds after an thesis, after which they increased sharply. In contrast, GA1 and GA3 concentrations were maximal at 7 d and 4-6 d, respectively, after anthesis, at about the time of maximum pod growth rate, and declined thereafter. Emasculated ovaries at anthesis contained GA8, GA19 and GA20 at concentrations comparable with pollinated fruit, but they decreased rapidly. Gibberellins a1 and A3 were present in only trace amounts in emasculated ovaries at any stage. Parthenocarpic fruit, produced by decapitating plants immediately above an emasculated flower, or by treating such flowers with 2,4-dichlorophenoxyacetic acid or GA7, contained GA19 and GA20 at similar concentrations to seeded fruit, but very low amounts of GA1 and GA3 Thus, it appears that the presence of fertilised ovules is necessary for the synthesis of these last two GAs. Mature leaves and leaf diffusates contained GA1, GA8, GA19 and GA20 as determined by combined gas chromatography-mass spectrometry using selected ion monitoring. This provides further evidence that vegetative tissues are a possible alternative source of GAs for fruit-set, particularly in decapitated plants.

Gibberellins and leaf expansion in near-isogenic wheat lines containing Rht1 and Rht3 dwarfing alleles

In near-isogenic lines of winter wheat (Triticum aestivum L. cv. Maris Huntsman) grown at 20° C under long days the reduced-height genes, Rht1 (semi-dwarf) and Rht3 (dwarf) reduced the rate of extension of leaf 2 by 12% and 52%, respectively, compared with corresponding rht (tall) lines. Lowering the growing temperature from 20° to 10° C reduced the rate of linear extension of leaf 2 by 2.5-fold (60% reduction) in the rht3 line but by only 1.6-fold (36% reduction) in the Rht3 line. For both genotypes, the duration of leaf expansion was greater at the lower temperature so that final leaf length was reduced by only 35% in the rht3 line and was similar in the Rht3 line at both temperatures. Seedlings of the rht3 (tall) line growing at 20° C responded positively to root-applied gibberellin A1 (GA1) in the range 1-10 μM GA1; there was a linear increase in sheath length of leaf 1 whereas the Rht3 (dwarf) line remained unresponsive. Gibberellins A1, 3, 4, 8, 19, 20, 29, 34, 44 and 53 were identified by full-scan gas chromatography-mass spectrometry in aseptically grown 4-d-old shoots of the Rht3 line. In 12-d-old seedlings grown at 20° C, there were fourfold and 24-fold increases in the concentration of GA1 in the leaf expansion zone of Rht1 and Rht3 lines, respectively, compared with corresponding rht lines. Although GA3 was present at a similar level to GA1 in the rht3 (tall) line it accumulated only fivefold in the Rht3 (dwarf) line. The steady-state pool sizes of endogenous GAs were GA19 ≫ GA20 = GA1 in the GA-responsive rht3 line whereas in the GA non-responsive Rht3 line the content of GA19≈ GA20 ⋘ GA1. It is proposed that one of the consequences of GA1 action is suppression of GA19-oxidase activity such that the conversion of GA19 to GA20 becomes a rate-limiting step on the pathway to GA1 in GA-responsive lines. In the GA-non-responsive Rht lines it is suggested that GA19 oxidase is not downregulated to the same extent and GA1 accumulates before the next rate-limiting step on the pathway, its 2β-hydroxylation to GA8. The steady-state pool sizes of GA19, 20, 1, 3 and 8 were similar in developmentally equivalent tissues of the rht3 (tall) line growing at 10° C and 20° C despite a 2.5-fold difference in the rate of leaf expansion. In contrast, in the Rht3 (dwarf) line, the extent of accumulation of GA1 reflected the severity of the phenotype at the two temperatures with slower growing tissues accumulating less, not more, GA1. These results are interpreted as supporting the proposed model of regulation of the GA-biosynthetic pathway rather than previous suggestions that GA1 accumulates in GA-insensitive dwarfs as a consequence of reduced growth rates.

Partial Purification and Characterization of the Gibberellin A(20) 3beta-Hydroxylase from Seeds of Phaseolus vulgaris

The GA(20) 3beta-hydroxylase present in immature seeds of Phaseolus vulgaris has been partially purified and characterized. The physical characteristics of the enzyme are similar to those of the GA 2beta-hydroxylases present in mature and immature seeds of Pisum sativum. It is acid-labile, hydrophobic, and of M(r) 45,000. The enzyme catalyzes the synthesis of GA(1), GA(5), and GA(29) from GA(20). Activity is dependent upon the presence of Fe(2+), ascorbate, 2-oxoglutarate, and oxygen. 2-Oxoglutarate does not function as a cosubstrate; in the presence of the enzyme, succinate is not a reaction product.

Biosynthetic Origin of Gibberellins A(3) and A(7) in Cell-Free Preparations from Seeds of Marah macrocarpus and Malus domestica

Cell-free preparations from seeds of Marah macrocarpus L. and Malus domestica L. catalyzed the conversion of gibberellin A(9) (GA(9)) and 2,3-dehydroGA(9) to GA(7); GA(9) was also metabolized to GA(4) in a branch pathway. The preparation from Marah seeds also metabolized GA(5) to GA(3) in high yield; GA(6) was a minor product and was not metabolized to GA(3). Using substrates stereospecifically labeled with deuterium, it was shown that the metabolism of GA(5) to GA(3) and of 2,3-dehydroGA(9) to GA(7) occurs with the loss of the 1beta-hydrogen. In cultures of Gibberella fujikuroi, mutant B1-41a, [1beta,2beta-(2)H(2)]GA(4), was metabolized to [1,2-(2)H(2)]GA(3) with the loss of the 1alpha- and 2alpha-hydrogens. These results provide further evidence that the biosynthetic origin of GA(3) and GA(7) in higher plants is different from that in the fungus Gibberella fujikuroi.

Comparison of gibberellins in normal and slender barley seedlings

Gibberellins A(1), A(3), A(8), A(19), A(20), and A(29) were identified by full scan gas chromatography-mass spectrometry in leaf sheath segments of 7-day-old barley (Hordeum vulgare L. cv Golden Promise) seedlings grown at 20 degrees C under long days. In a segregating population of barley, cv Herta (Cb 3014), containing the recessive slender allele, (sln 1) the concentration of GA(1) and GA(3) was reduced by 10-fold and 6-fold, respectively, in rapidly growing homozygous slender, compared with normal, leaf sheath segments. However, the concentration of the C(20) precursor, GA(19), was nearly 2-fold greater in slender than in normal seedlings. There was little difference in the ABA content of sheath segments between the two genotypes. The gibberellin biosynthesis inhibitor, paclobutrazol, reduced the final sheath length of normal segregants (50% inhibition at 15 micromolar) but had no effect on the growth of slender seedlings at concentrations below 100 micromolar. There was a 15-fold and 4-fold reduction in GA(1) and GA(3), respectively, in sheath segments of 8-day-old normal seedlings following application of 10 micromolar paclobutrazol. The same treatment also reduced the already low concentrations of these gibberellins in slender segregants. The results show that the pool sizes of gibberellins A(1) and A(3) are small in slender barley and that leaf sheath extension in this genotype appears to be gibberellin-independent. The relationship between gibberellin status and tissue growth-rate in slender barley is contrasted with other gibberellin nonresponsive, but dwarf, mutants of wheat (Triticum aestivum) and maize (Zea mays).