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PubMed1998

Photoperiod control of gibberellin levels and flowering in sorghum

Regulation of rhythmic peaks in levels of endogenous gibberellins (GAs) by photoperiod was studied in the short-day monocot sorghum (Sorghum bicolor [L.] Moench). Comparisons were made between three maturity (Ma) genotypes: 58M (Ma1Ma1, Ma2Ma2, phyB-1phyB-1, and Ma4Ma4 [a phytochrome B null mutant]); 90M (Ma1Ma1, Ma2Ma2, phyB-2phyB-2, and Ma4Ma4); and 100M (Ma1Ma1, Ma2Ma2, PHYBPHYB, and Ma4Ma4). Plants were grown for 14 d under 10-, 14-, 16-, 18-, and 20-h photoperiods, and GA levels were assayed by gas chromatography-mass spectrometry every 3 h for 24 h. Under inductive 10-h photoperiods, the peak of GA20 and GA1 levels in 90M and 100M was shifted from midday, observed earlier with 12-h photoperiods, to an early morning peak, and flowering was hastened. In addition, the early morning peaks in levels of GA20 and GA1 in 58M under conditions allowing early flowering (10-, 12-, and 14-h photoperiods) were shifted to midday by noninductive (18- and 20-h) photoperiods, and flowering was delayed. These results are consistent with the possibility that the diurnal rhythm of GA levels plays a role in floral initiation and may be one way by which the absence of phytochrome B causes early flowering in 58M under most photoperiods.

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PubMed1998

Gibberellins promote trichome formation by Up-regulating GLABROUS1 in arabidopsis

Trichome development is dependent on gibberellin (GA) signaling in Arabidopsis thaliana. Using the GA-deficient mutant ga1-3, the GA-response mutant spy-5, and uniconazol (a GA-biosynthesis inhibitor), we show that the GA level response correlates positively with both trichome number and trichome branch number. Two genes, GL1 and TTG, are required for trichome initiation. In ga1-3, coexpression of GL1 and R, the maize TTG functional homolog, under control of the constitutive 35S promoter, restored trichome development, whereas overexpression of neither GL1 nor R alone was sufficient to significantly suppress the glabrous phenotype. We next focused on GL1 regulation by GAs. In the double mutant the gl1-1 glabrous phenotype is epistatic to the spy-5 phenotype, suggesting that GL1 acts downstream of the GA signal transduction pathway. The activity of a beta-glucuronidase reporter gene driven by the GL1 promoter was decreased in the wild type grown on uniconazol and showed a clear GA-dependent activation in ga1-3. Finally, quantification of GL1 transcript levels by reverse transcriptase-polymerase chain reaction demonstrated that relative to wild type, ga1-3 plants contained less transcript. These data support the hypothesis that GAs induce trichome development through up-regulation of GL1 and possibly TTG genes.

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PubMed1998

The role of gibberellin, abscisic acid, and sucrose in the regulation of potato tuber formation in vitro

The effects of plant hormones and sucrose (Suc) on potato (Solanum tuberosum L.) tuberization were studied using in vitro cultured single-node cuttings. Tuber-inducing (high Suc) and -noninducing (low Suc or high Suc plus gibberellin [GA]) media were tested. Tuberization frequencies, tuber widths, and stolon lengths were measured during successive stages of development. Endogenous GAs and abscisic acid (ABA) were identified and quantified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Exogenous GA4/7 promoted stolon elongation and inhibited tuber formation, whereas exogenous ABA stimulated tuberization and reduced stolon length. Indoleacetic acid-containing media severely inhibited elongation of stolons and smaller sessile tubers were formed. Exogenous cytokinins did not affect stolon elongation and tuber formation. Endogenous GA1 level was high during stolon elongation and decreased when stolon tips started to swell under inducing conditions, whereas it remained high under noninducing conditions. GA1 levels were negatively correlated with Suc concentration in the medium. We conclude that GA1 is likely to be the active GA during tuber formation. Endogenous ABA levels decreased during stolon and tuber development, and ABA levels were similar under inducing and noninducing conditions. Our results indicate that GA is a dominant regulator in tuber formation: ABA stimulates tuberization by counteracting GA, and Suc regulates tuber formation by influencing GA levels.

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PubMed1999

The sensitivity of barley aleurone tissue to gibberellin is heterogeneous and may Be spatially determined

In cereals, gibberellin (GA) enhances the synthesis and secretion of hydrolytic enzymes from aleurone cells. These enzymes then mobilize the endosperm storage reserves that fuel germination. The dose-response curve of aleurone protoplasts to GA extends over a range of concentrations from 10(-11) to more than 10(-6) M. One hypothesis is that subpopulations of cells have different sensitivities to GA, with each cell having a threshold concentration of GA above which it is switched on. The dose-response curve therefore reflects a gradual recruitment of cells to the pool exhibiting a full GA response. Alternatively, all cells may gradually increase their responses as the GA level is increased. In the present study we found that at increasing GA concentrations, increasing numbers of barley (Hordeum vulgare) cells showed the enhanced amylase secretion and vacuolation characteristic of the GA response. We also observed that the region of aleurone tissue closest to the embryo contains the highest proportion of cells activated at the GA concentrations thought to occur naturally in germinating grain. These data indicate that an aleurone layer contains cells of varying sensitivities to GA and that recruitment of these differentially responding pools of cells may explain the broad dose response to GA.

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PubMed1999

Gibberellin dose-response curves and the characterization of dwarf mutants of barley

Dose-response curves relating gibberellin (GA) concentration to the maximal leaf-elongation rate (LERmax) defined three classes of recessive dwarf mutants in the barley (Hordeum vulgare L.) 'Himalaya. ' The first class responded to low (10(-8)-10(-6) M) [GA3] (as did the wild type). These grd (GA-responsive dwarf) mutants are likely to be GA-biosynthesis mutants. The second class of mutant, gse (GA sensitivity), differed principally in GA sensitivity, requiring approximately 100-fold higher [GA3] for both leaf elongation and alpha-amylase production by aleurone. This novel class may have impaired recognition between the components that are involved in GA signaling. The third class of mutant showed no effect of GA3 on the LERmax. When further dwarfed by treatment with a GA-biosynthesis inhibitor, mutants in this class did respond to GA3, although the LERmax never exceeded that of the untreated dwarf. These mutants, called elo (elongation), appeared to be defective in the specific processes that are required for elongation rather than in GA signaling. When sln1 (slender1) was introduced into these different genetic backgrounds, sln was epistatic to grd and gse but hypostatic to elo. Because the rapid leaf elongation typical of sln was observed in the grd and gse backgrounds, we inferred that rapid leaf elongation is the default state and suggest that GA action is mediated through the activity of the product of the Sln gene.

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PubMed1999

Cloning and molecular analyses of a gibberellin 20-oxidase gene expressed specifically in developing seeds of watermelon.

To understand the biosynthesis and functional role of gibberellins (GAs) in developing seeds, we isolated Cv20ox, a cDNA clone from watermelon (Citrullus lanatus) that shows significant amino acid homology with GA 20-oxidases. The complementary DNA clone was expressed in Escherichia coli as a fusion protein, which oxidized GA(12) at C-20 to the C(19) compound GA(9), a precursor of bioactive GAs. RNA-blot analysis showed that the Cv20ox gene was expressed specifically in developing seeds. The gene was strongly expressed in the integument tissues, and it was also expressed weakly in inner seed tissues. In parthenocarpic fruits induced by 1-(2-chloro-4-pyridyl)-3-phenylurea treatment, the expression pattern of Cv20ox did not change, indicating that the GA 20-oxidase gene is expressed primarily in the maternal cells of developing seeds. The promoter of Cv20ox was isolated and fused to the beta-glucuronidase (GUS) gene. In a transient expression system, beta-glucuronidase staining was detectable only in the integument tissues of developing watermelon seeds.

5' Untranslated Regions↗

PubMed1999

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.

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PubMed1999

The SLENDER gene of pea encodes a gibberellin 2-oxidase.

The amount of active gibberellin (GA) in plant tissues is determined in part by its rate of catabolism through oxidation at C-2. In pea (Pisum sativum L.) seeds, GA 2-oxidation is controlled by the SLN (SLENDER) gene, a mutation of which produces seedlings characterized by a slender or hyper-elongated phenotype. We cloned a GA 2-oxidase cDNA from immature pea seeds by screening an expression library for enzyme activity. The clone contained a full-length open reading frame encoding a protein of 327 amino acids. Lysate of bacterial cultures expressing the protein converted the C(19)-GAs, GA(1), GA(4), GA(9), and GA(20) to the corresponding 2beta-hydroxy products. GA(9) and GA(20) were also converted to GA(51) and GA(29) catabolites, respectively. The gene appeared to be one member of a small family of GA 2-oxidases in pea. Transcript was found predominantly in roots, flowers, young fruits, and testae of seeds. The corresponding transcript from sln pea contained a point mutation and did not produce active enzyme when expressed heterologously. RFLP analysis of a seedling population segregating for SLN and sln alleles showed the homozygous mutant allele co-segregating with the characteristic slender phenotype. We conclude that SLN encodes GA 2-oxidase.

Amino Acid Sequence↗

PubMed2001

Expression of a gibberellin 2-oxidase gene around the shoot apex is related to phase transition in rice.

A major catabolic pathway for gibberellin (GA) is initiated by 2beta-hydroxylation, a reaction catalyzed by GA 2-oxidase. We have isolated and characterized a cDNA, designated Oryza sativa GA 2-oxidase 1 (OsGA2ox1) from rice (Oryza sativa L. cv Nipponbare) that encodes a GA 2-oxidase. The encoded protein, produced by heterologous expression in Escherichia coli, converted GA(1), GA(4), GA(9), GA(20), and GA(44) to the corresponding 2beta-hydroxylated products GA(8), GA(34), GA(51), GA(29), and GA(98), respectively. Ectopic expression of the OsGA2ox1 cDNA in transgenic rice inhibited stem elongation and the development of reproductive organs. These transgenic plants were deficient in endogenous GA(1). These results indicate that OsGA2ox1 encodes a GA 2-oxidase, which is functional not only in vitro but also in vivo. OsGA2ox1 was expressed in shoot apex and roots but not in leaves and stems. In situ hybridization analysis revealed that OsGA2ox1 mRNA was localized in a ring at the basal region of leaf primordia and young leaves. This ring-shaped expression around the shoot apex was drastically decreased after the phase transition from vegetative to reproductive growth. It was absent in the floral meristem, but it was still present in the lateral meristem that remained in the vegetative phase. These observations suggest that OsGA2ox1 controls the level of bioactive GAs in the shoot apical meristem; therefore, reduction in its expression may contribute to the early development of the inflorescence meristem.

Amino Acid Sequence↗

PubMed1966

Variations in endogenous gibberellins in developing bean seeds I. Occurrence of neutral and acidic substances.

Activities of separated and chromatographed substances in the nonacidic, acidic ethyl acetate and acidic butanol fractions from bean seeds, Phaseolus vulgaris L., cv. Bountiful and Kentucky Wonder, were measured in the Progress No. 9 dwarf pea bioassay grown under red light. Activity in the nonacidic fraction was shown to be attributable only to neutral substances and was free of acidic gibberellin-like substances. As the seed matures, neutral substances and one of the acidic butanol-soluble substances (B-I) increase in activity. The acidic ethyl acetate substances and butanol-soluble substance (B-II) initially increase and then almost disappear.

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PubMed1966

DNA synthesis in the elongating nondividing cells of the lentil epicotyl and its promotion by gibberellin.

Two-day-old lentil seedlings, (Lens culinaris Med.) were incubated for a 48-hour period with and without gibberellin (GA) in the presence and absence of 5-fluorodeoxyuridine (FUDR). The number of cells per epicotyl did not increase during this period. Growth of the epicotyl was thus due to cell elongation alone.The elongating cells of this tissue synthesized DNA. GA promoted and FUDR inhibited cell elongation, DNA synthesis, and RNA synthesis in the tissue.FUDR promoted uptake of thymidine and thymidine incorporation into cellular DNA, presumably by inhibiting synthesis of endogenous thymidine. Presence of GA promoted thymidine incorporation into cellular DNA and uridine incorporation into cellular RNA. In either case, there was no effect on the uptake of the precursor into the tissue.Fractionation of thymidine-labeled nucleic acids on a MAK column showed that thymidine was exclusively incorporated into the DNA fraction. Presence of GA promoted thymidine incorporation into this fraction and also increased the amount of ribosomal RNA.The data provide direct evidence for the conclusion that DNA synthesis is necessary for elongation of certain plant cells.

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PubMed1969

Temperature Regulation of Endogenous Gibberellin Activity and Development of Tulipa gesneriana L.

The changes in the contents of free and bound gibberellin-like activity (GA) of Tulipa gesneriana L. cv. Ralph during development under 2 temperature conditions were studied. The results show that the content of free GA of bulbs grown at 18 degrees increased by 67% over the initial level during development. The bound GA showed a slight initial increase and was followed by a rapid decrease. In contrast, bulbs treated at 13 degrees showed a marked decline in free GA and a 2-fold increase in the content of bound GA. However, after the transfer of these bulbs from 13 degrees to 18 degrees the free GA increased to the initial level while the bound GA decreased to a low level.The rate of floral shoot and root development and time of flowering were accelerated at 18 degrees as compared to 13 degrees .From the data obtained, it was suggested that a temperature-sensitive interconversion mechanism between free and bound GA exists in tulip bulbs and that there is apparent synthesis or transformation of these phytohormones during development of the bulbs.

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PubMed1972

Gibberellin Substitution for the Requirement of the Cotyledons in Stem Elongation in Pisum sativum Seedlings.

The removal of the cotyledons from 8-day-old light-grown Pisum sativum cv. Alaska seedlings caused a reduction in the rate of stem elongation to 50% of the intact control value. Gibberellic acid restored the stem elongation rate of decotylized plants to the level of the intact controls. The effect of decotylization was to lower both the rate of node formation and the rate of internode elongation. The steady state rate of internode elongation was reduced to 50% of the control rate by decotylization. Applied gibberellic acid did not restore the normal rate of node formation nor the lag in internode elongation caused by decotylization, but gibberellic acid did restore the normal steady state rate of internode elongation. Analysis of variance demonstrated an interaction between the cotyledons and applied gibberellic acid. 2-Isopropyl-4-dimethylamino-5-methyl phenyl-1-piperidine carboxylate methyl chloride inhibited internode elongation to the same extent in both intact and decotylized plants. The results indicate that the cotyledons are an effective source of gibberellin for the young pea seedling.

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PubMed1973

Embryoless Wheat Grain: A Natural System for the Study of Gibberellin-induced Enzyme Formation.

Yorkstar wheat, grown in New York State, has a high percentage (10-11) of grains without embryos. The embryoless grains have viable aleurone layers and show no sign of injury. These grains are able to support alpha-amylase synthesis only in the presence of gibberellin A(3) (GA(3)). In the absence of GA(3) some protein synthesis occurs in embryoless grains during the early hours of soaking, indicating that such activity occurs prior to and independent of GA(3) induction of alpha-amylase. The level of beta-amylase on a dry weight basis is the same in embryoless and normal grains and decreases with time of soaking. In the presence of GA(3), beta-amylase decreases at a slower rate. Isoenzymes of alpha-amylase from GA(3)-treated embryoless and normal grains show quantitative as well as qualitative differences. Cycloheximide (60 mug/ml) completely inhibits the synthesis of alpha-amylase by embryoless grains. Of the RNA synthesis inhibitors, actinomycin D (60 mug/ml) was ineffective while 6-methylpurine (60 mug/ml) gave 65% inhibition without decreasing the number of isoenzymes.

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PubMed1973

Effect of Abscisic Acid on Uptake and Metabolism of [H]Gibberellin A(1) and [H]Pseudogibberellin A(1) by Barley Half-seeds.

Uptake and metabolism of 1,2-[(3)H]gibberellin A(1) ([(3)H]GA(1), I) and its 3-hydroxy epimer ([(3)H]pseudoGA(1), II) by barley (Hordeum vulgare L.) half-seeds were measured after 24 hours of incubation, in the presence or absence of abscisic acid in the media. Uptake of both compounds was enhanced by abscisic acid, and abscisic acid enhanced the extent of metabolism of [(3)H]GA(1). However, [(3)H]pseudoGA(1) was not metabolized, even in the presence of abscisic acid. The significance of the stereo-chemistry of the 3-hydroxyl position is discussed.

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PubMed1974

Metabolism of Tritiated Gibberellin A(9) by Shoots of Dark-grown Dwarf Pea, cv. Meteor.

Tritium-labeled gibberellin A(9) ((3)H-GA(9)) was metabolized by etiolated shoots of dwarf pea (Pisum sativum cv. Meteor) to GA(20), GA(10), 2,3-dihydro-GA(31), and a number of highly polar, acidic GA-like substances. Identifications were made by gasliquid radiochromatography and combined gas chromatography-mass spectrometry. Kinetic studies showed that GA(30) and 2,3-dihydro-GA(31) were produced within 5 hours following (3)H-GA(9) application to pea shoots. The polar GA-like substances were produced between 5 and 10 hours after (3)H-GA(9) application. Levels of GA(10) increased with time, and since no GA(10) was produced during the purification procedures, GA(10) was, in all probability, produced from (3)H-GA(9) within the plant tissue. The radioactive interconversion products produced by pea from (3)H-GA(9) have chromatographic properties similar to biologically active GA-like substances present in etiolated shoots of dwarf pea. Large scale applications of (3)H-GA(9) with very low specific activity to etiolated pea shoots showed that the radioactivity of the interconversion products was correlated exactly with biological activity as assayed by dwarf rice (Oryza sativa cv. Tan-ginbozu).

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PubMed1974

An amphoteric conjugate of [h]gibberellin a(1) from barley aleurone layers.

The major metabolite produced during incubation of [(3)H]gibberellin A(1) ([(3)H]GA(1)) with barley aleurone layers is an amphoteric, water-soluble compound tentatively called [(3)H]ampho GA(1). Formation of [(3)H]ampho GA(1) in barley aleurones begins after a period of 2.5 hours. As judged by degradation studies as well as Sephadex column chromatography, GA(1) appears to be linked to a peptide; positions C-3 and C-7 were ruled out as conjugation sites.

Journal Article↗

PubMed1975

Metabolism of Tritiated Gibberellins in d-5 Dwarf Maize: I. In Excised Tissues and Intact Dwarf and Normal Plants.

Metabolism of [(3)H]gibberellin A(1) ([(3)H]GA(1)) was followed in intact seedlings and excised apices and leaf tissue of both dwarf and normal (tall) plants of d-5 maize (Zea mays L.). The three metabolites produced were tentatively identified as [(3)H]GA(s), [(3)H]GA(s)-glucoside ([(3)H]GA(s)-glu), and [(3)H]GA(1)-X, an unknown.In 3-hour, pulse-labeling experiments with tissues of incubated, expanding leaves, more than 70% of the [(3)H]GA(1) taken up was metabolized to the three products within 12 to 15 hours. [(3)H]GA(1) fed to the roots of 7-day-old seedlings was readily translocated to the leaves, and all three metabolites were found in both roots and leaves. [(3)H]GA(1)-X was the major metabolite in roots, whereas in leaves the major metabolite was [(3)H]GA(s)-glu. There were no consistent differences in [(3)H]GA(1) metabolism between dwarf and normal plants, indicating that dwarfism in d-5 maize is not associated with modified GA(1) metabolism.In excised, mature leaf tissue, [(3)H]GA(1) metabolism was slower than in excised, young leaf tissue. Mature leaf tissues produced [(3)H]GA(s)-glu as by far the major metabolite, with [(3)H]GA(s) and [(3)H]GA(1)-X as minor metabolites. In contrast, in young leaves the three metabolites appeared sequentially in significant proportions: [(3)H]GA(8) first, followed by [(3)H]GA(s)-glu and, finally, [(3)H]GA(1)-X.

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