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PubMed1968

Role of gibberellins in stem elongation and flowering in radish.

The relationship among gibberellins, CCC, vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA(3) had no additional effect. Gibberellin A(3) (60 mug total) was not able to induce flowering in nonvernalized plants grown on 8-hour days, but it did increase the percentage of nonvernalized plants that flowered under long days from 60 to 100.Gibberellin content of vernalized seedlings increased within the first 24 hours after seedlings were transferred to the greenhouse. Content reached a peak in the first 4 days after transfer and thereafter remained constant. Essentially no gibberellin was found in 2 day-old non-vernalized (control) seedlings of comparable size to the vernalized ones. Gibberellin content in the controls reached a peak on the fourth day of growth in the greenhouse; thereafter, it decreased steadily.Bolting was inhibited slightly by CCC when applied during vernalization; it was almost completely inhibited when CCC was applied after seed vernalization. Extraction experiments revealed that CCC actually reduced the gibberellin content when applied during or after vernalization. The dwarfing agent, however, had essentially no effect on flowering. We concluded that gibberellins likely play a direct role in bolting of ;Miyashige-sofuto' radish, but probably are not directly functional in initiating flowering.

Journal Article↗

PubMed1970

Endogenous gibberellins and inhibitors in relation to flower induction and inflorescence development in the olive.

Comparative analyses of reproductive and vegetative tissues of the olive (Olea europaea L. cv. Manzanillo) for endogenous hormones, particularly inhibitors and gibberellin like substances, were made to study the relation between such hormones and thermoinduction of flowering. Qualitative and quantitative changes in gibberellin-like subtance(s) were observed in lateral buds (potential flower buds) but not in leaves or terminal buds (potential vegetative buds) sampled from orchard trees at intervals during the winter and spring. At least two types of gibberellin-like substances were found in extracts of lateral buds; their levels increased progressively during the low temperature induction period, reaching a maximum shortly before floral initiation. Two types of inhibitors were extracted from buds and leaves. A nonacidic type did not change during the induction stage but decreased considerably during the initiation period. An acidic inhibitor, which was identified as an abscisic acid-like substance, was present at a relatively lower level in lateral (flower) buds than in terminal (vegetative) buds during the induction period.It was concluded that winter chilling induces flowering in the olive possibly by altering a balance between endogenous gibberellins and inhibitors, including abscisic acid.Inflorescence development following the winter chilling period was associated with an increase in the level of endogenous inhibitors and gibberellins. Shoot growth, however, was correlated with a decrease in the inhibitor(s) level. A rise in gibberellin-like activity is believed to be a result, not a cause, of shoot growth.

Journal Article↗

PubMed1981

Differences in Endogenous Levels of Gibberellin-Like Substances in Nodules of Phaseolus lunatus L. Plants Inoculated with Two Rhizobium Strains.

Lima bean plants (Phaseolus lunatus L.) inoculated with Rhizobium sp. strain 127E14, which lacks constitutive nitrate reductase activity, were significantly taller after 4 weeks of age than plants inoculated with strain 127E15, which contains constitutive nitrate reductase activity. Plants inoculated with either strain responded to application of 5 micrograms gibberellic acid per plant with rapid internode elongation; plants inoculated with strain 127E15 became less responsive to gibberellic acid from 3 to 5 weeks of age, while plants inoculated with strain 127E14 did not. The height of plants inoculated with strain 127E14 was reduced by 20% with application of gibberellin biosynthesis inhibitors to the roots, while height of plants inoculated with strain 127E15 was unaffected.Plants inoculated with strain 127E14 developed nodules containing 4 to 50 times greater quantities of extractable gibberellin-like substances than the nodules of plants inoculated with strain 127E15. Plants inoculated with strain 127E14 had nodules containing larger quantities of gibberellin-like substances in both the acidic and basic ethyl acetate fractions, and these differences were observed before the onset of rapid growth responsible for the difference in plant height.The internode elongation in plants infected with strain 127E14, its reversal by gibberellin biosynthesis inhibitors, and the accumulation of large quantities of gibberellin-like substances in nodules infected with strain 127E14 support the hypothesis that root nodules may contribute gibberellins to the host.

Journal Article↗

PubMed1988

Chemical structure of the cell walls of dwarf maize and changes mediated by gibberellin.

Dwarf maize (Zea mays L.), a mutant deficient in gibberellin synthesis, provides an excellent model to study the influence of gibberellin on biochemical processes related to plant development. Alterations in the chemical structure of the cell wall mediated by gibberellin were examined in seedlings of this mutant. The composition of the walls of roots, mesocotyl, coleoptile, and primary leaves of dwarf maize was similar to that of normal maize and other cereal grasses. Glucuronoarabinoxylans constituted the principal hemicelluloses, but walls also contained substantial amounts of xyloglucan and mixed-linkage beta-d-glucan. Root growth in dwarf maize was essentially normal, but growth of mesocotyl and primary leaves was severely retarded. Injection of the gibberellin into the cavity of the coleoptile resulted in a marked increase in elongation of the primary leaves. This elongation was accompanied by increases in total wall mass, but the proportion of beta-d-glucan decreased from 20% to 15% of the hemicellulosic polysaccharide. During leaf expansion, the proportion decreased further to only 10%. Through 4 days incubation, the proportion of beta-d-glucan in leaves of control seedlings without gibberellin was nearly constant. Extraction of exo- and endo-beta-d-glucan hydrolases from purified cell walls and assay against a purified oat bran beta-d-glucan demonstrated that gibberellin increased the activity of the endo-beta-d-glucan hydrolase. These and other data support the hypothesis that beta-d-glucan metabolism is central to control of cell expansion in cereal grasses.

Journal Article↗

PubMed1991

Gibberellins and Carotenoids in the Wild Type and Mutants of Gibberella fujikuroi.

A new screening procedure was used to isolate 14 gib mutants of Gibberella fujikuroi with modifications in the production of gibberellins. The production of carotenoids and gibberellins was investigated in the gib mutants and in representative car mutants with various modifications of carotenoid biosynthesis. The determinations of gibberellins were carried out with a simplified fluorescence method. One of the mutants lacked both gibberellins and carotenoids. In many mutants the two pathways compensated each other: an increase in the production of one group of compounds was accompanied by a decrease in the production of the other. Under certain conditions the compensation was quantitative when the output of the two pathways was measured in moles of the common precursor, geranylgeranyl pyrophosphate. alpha-Picoline, an inhibitor of lycopene cyclase in G. fujikuroi, inhibits gibberellin biosynthesis. Other agents that affect the accumulation of carotenoids have no noticeable effect on the accumulation of gibberellins; such is the case with diphenylamine and beta-ionone, two inhibitors of phytoene dehydrogenation, and visible light, which stimulates carotenogenesis.

Journal Article↗

PubMed1998

Gibberellin: inhibitor of an inhibitor of...?

Gibberellin is an endogenous plant growth regulator. Here, we describe our present understanding of how gibberellin regulates plant growth, using recent results gained from studies of gibberellin-signalling mutants of Arabidopsis. These results show that a signalling pathway represses plant growth and that gibberellin releases this repression. In consequence, the well-known growth-promoting properties of gibberellin are due to its activity as an "inhibitor of an inhibitor" [Brian Pw. Sym Soc. Exp Bio 1957; 11:166-182 (Ref. 1)] of plant growth.

Arabidopsis↗

PubMed1990

New monoclonal antibodies to 3 beta-hydroxy-gibberellins.

Two new monoclonal antibodies to 3 beta-hydroxy-gibberellins are described. Monoclonal antibodies GA1-1 and GA1-2 were derived from immunizations with the hapten-protein conjugate gibberellin A1-17-KLH. Cross-reactivities with a panel of 43 gibberellins and gibberellin derivatives are compared with those of other anti-gibberellin monoclonal antibodies.

Animals↗

PubMedDate not supplied

Alteration of gibberellin response in transgenic tobacco plants which express a human Lewis fucosyltransferase.

In plants, Lewisa type N-glycans may be involved in cell-to-cell communication and recognition. N-glycoproteins harboring Lewisa glycotopes are mainly found in plasma membranes and cell walls. Some can be also involved in cell wall synthesis or the loosening process, and subsequently in cell elongation. In order to determine the potential role(s) of the alpha4-fucosylation during vegetative development, transgenic tobacco plants overexpressing a human Lewis fucosyltransferase (hFUT3), which transfers a fucose residue in a alpha(1,4)-linkage on complex glycans, have been developed. The heterologous enzyme hFUT3 was strongly expressed and fully functional in transgenic tobacco. Transgenic plants showed a delay in growth linked to a reduction of internode length. Furthermore, transgenic seedling roots were significantly shorter than wild-type roots and the length of their epidermis cells was reduced. Strikingly, root growth was completely and specifically restored following gibberellin treatment. Etiolated hypocotyls of hFUT3 overexpressors were also more sensitive to exogenous gibberellin. Furthermore, paclobutrazol, an inhibitor of gibberellin synthesis, induced a similar effect on control and transgenic dark-grown hypocotyls suggesting that gibberellin biosynthesis was probably not altered in seedlings overexpressing hFUT3. Thus, alpha4-fucosylation could act as a possible modulator of conformation and/or functioning of N-glycoproteins involved in the gibberellin-dependent elongation process.

Aging↗

PubMed1997

Inhibition of gibberellin biosynthesis by nitrate in Gibberella fujikuroi.

Gibberellin production in Gibberella fujikuroi starts upon exhaustion of the nitrogen source. To determine the role of nitrate and ammonium in the regulation of gibberellin biosynthesis we have isolated mutants that cannot use nitrate as a nitrogen source. Nitrate inhibited partially the production of gibberellins in mutants devoid of nitrate reductase activity. The inhibition occurred whether nitrate was added before or after the onset of gibberellin production. Addition of tungstate to the wild type mimicked the results with nitrate reductase mutants. We conclude that nitrate inhibits gibberellin biosynthesis by itself, independently of the intracellular signal that conveys nitrogen availability.

Cell Division↗

PubMed2002

Cytokinins and gibberellins in sap exudate of the oil palm.

Exudates were collected from stumps of pre-anthesis inflorescences of oil palm and analysed for cytokinin and gibberellin content using combined HPLC-ELISA techniques. Three antisera, for zeatin-type, dihydrozeatin-type and isopentenyladenine-type cytokinins, were used in ELISAs to identify members of these three groups of cytokinins. Ribotides, 9-glucosides, free bases and ribosides were detected for each of the groups with zeatin riboside the most abundant cytokinin identified in the exudate. Isopentenyladenine-type and dihydrozeatin-type cytokinins were also identified but at lower levels. In addition, two monoclonal antibodies were used in the development of novel ELISAs for members of the 13-hydroxylated and non-13-hydroxylated families of gibberellins. The new ELISAs allow the determination of gibberellins in smaller amounts of tissue than are required for GC-MS. The most abundant gibberellins identified in exudates were GA19 and GA44, as well as other members of the early 13-hydroxylation pathway. Gibberellins were confirmed by GC-MS. The presence of these types of growth regulators in exudate supplying immature inflorescences suggest they have a role in growth and development of these structures.

Arecaceae↗

PubMed2003

A serine carboxypeptidase gene (PsCP), expressed in early steps of reproductive and vegetative development in Pisum sativum, is induced by gibberellins.

A cDNA clone encoding a serine carboxypeptidase (PsCP), isolated from young fruits of Pisum sativum L., was used to study the temporal and spatial expression and hormonal regulation of serine carboxypeptidase during reproductive and vegetative development. In unpollinated pea ovaries PsCP transcript levels decreased during senescence. However, during early fruit development, PsCP transcript were accumulated in both pericarp and seeds, preferentially in the nucellus, with a polar distribution at the chalazal region of the embryo sac, suggesting a role in seed development. PsCP transcript levels increased also when fruit set was induced in unpollinated ovaries by gibberellins, although the distribution was uniform. PsCP expression was also induced by auxins but not cytokinins, indicating a selective hormonal regulation of PsCP transcription. Localization of PsCP transcript after pollination parallel reported changes in gibberellin distribution, suggesting that PsCP transcription in developing fruits and seeds is induced by gibberellins. PsCP is also expressed in developing seedlings but not in cotyledons, suggesting that it is not involved in the mobilization of storage materials. PsCP transcripts were suppressed by treatment of seedlings with paclobutrazol and restored by gibberellic acid (GA3) treatment. In addition, PsCP transcript levels decreased in etiolated pea seedlings when they were exposed to continuous light but not when exposed to light in the presence of GA3. These results indicate that PsCP transcript accumulation is induced by gibberellins in developing seedlings. This is the first report of a serine carboxypeptidase-like gene induced by gibberellins in reproductive and vegetative developing tissues in dicotyledoneous plants.

Blotting, Northern↗

PubMed1994

Carcinogenic effect of gibberellin A3 in Swiss albino mice.

Gibberellin A3 is a plant growth regulator used in many countries, including Egypt, to increase the growth of fruits and vegetables. The carcinogenic effect of gibberellin A3 was investigated in this study with Swiss albino mice. Administration of gibberellin A3 by gavage for 22 months induced a significant increase in their body weights. Tumors were induced in 18% of the males and 36% of the females and were located in the skin of the axillary region (sebaceous adenomas), breast (adenocarcinomas), and lung (adenocarcinomas and secondary metastatic deposits from breast tumors). Bronchocentric granulomas were induced in animals exposed to gibberellin A3 for 14 months. These results indicate that gibberellin A3 was carcinogenic in mice.

Animals↗

PubMed1994

The cis-acting gibberellin response complex in high pI alpha-amylase gene promoters. Requirement of a coupling element for high-level transcription.

In cereal alpha-amylase gene promoters the cis-acting gibberellin response element (GARE) is required for increased transcription in the presence of gibberellin. In low-isoelectric point (pI) alpha-amylase gene promoters a second type of cis element, termed a coupling element, must also be present in a specific position near the GARE; otherwise, the level of transcription in the presence of gibberellin is only a few percent of maximum. The coupling element may help determine where and when in development high-level, hormonally regulated transcription will occur. Such coupling elements have not yet been shown to be necessary for high-level transcription from high-pI alpha-amylase gene promoters. Here we use quantitative transient expression assays to show that a high-pI promoter truncated to -300 is a weak promoter due to the absence of a functional coupling element in the vicinity of the GARE. Gibberellin-induced transcription increases substantially when coupling element function is provided, either by appending upstream regions normally attached to the promoter or by inserting a defined coupling element from a low-pI promoter. Thus, in a second type of gibberellin-regulated promoter coupling element function was found to be crucial for hormone regulation to result in high-level transcription.

Amino Acid Sequence↗

PubMed1975

Production of gibberellin-like substances by fungi isolated from mycorrhizae of pine (Pinus silvestris/L.).

Gibberellin-like substances were found to be produced by fungi isolated from mycorrhizae of pine. Among the isolates studied gibberellin-like substances producers were most numerous among the Basidiomycetes forming ectotrophic mycorrhiza and among non-sporulating fungi forming no mycorrhiza. In most strains the gibberellin-like subtances were elaborated after 10--20 days of incubation. The Rf values of the gibberellin-like compounds were different in various strains, but in most of them substances showing gibberellin activity appeared on the chromatograms run with benzene, acetic acid (10:3 v/v) at Rf 0.2--0.6.

Acremonium↗

PubMed1971

Hormonal Control of Lecithin Synthesis in Barley Aleurone Cells: Regulation of the CDP-Choline Pathway by Gibberellin.

The enzymes of the cytidine diphosphate-choline pathway, which is involved in lecithin biosynthesis, are present in imbibed barley aleurone cells. The first enzyme, choline kinase (EC 2.7.1.32), is found in the soluble protein fraction. Its activity is not affected by prior treatment of aleurone layers with gibberellin. The second and third enzymes of the pathway, phosphorylcholine-cytidyl (EC 2.7.7.15) and phosphorylcholine-glyceride (EC 2.7.8.2) transferases, are associated with the particulate fractions. Their activities are greatly increased by gibberellin treatment during the lag phase (0-8 hr) of gibberellin-effected alpha-amylase synthesis. The hormonal effects are evident two hours after gibberellin treatment. Inhibitors that block gibberellin-effected alpha-amylase formation also inhibit the stimulation of these membrane-bound enzymes by the hormone.

Journal Article↗

PubMed1992

Gibberellin Is Required for Flowering in Arabidopsis thaliana under Short Days.

Mutants of Arabidopsis thaliana deficient in gibberellin synthesis (ga1-3 and ga1-6), and a gibberellin-insensitive mutant (gai) were compared to the wild-type (WT) Landsberg erecta line for flowering time and leaf number when grown in either short days (SD) or continuous light (CL). The ga1-3 mutant, which is severely defective in ent-kaurene synthesis because it lacks most of the GA1 gene, never flowered in SD unless treated with exogenous gibberellin. After a prolonged period of vegetative growth, this mutant eventually underwent senescence without having produced flower buds. The gai mutant and the "leaky" ga1-6 mutant did flower in SD, but took somewhat longer than WT. All the mutants flowered readily in CL, although the ga1-3 mutant showed some delay. Unlike WT and ga1-3, the gai mutant failed to respond to gibberellin treatment by accelerating flowering in SD. A cold treatment promoted flowering in the WT and gai, but failed to induce flowering in ga1-3. From these results, it appears that gibberellin normally plays a role in initiating flowering of Arabidopsis.

Journal Article↗

PubMed1995

Phenotypic Suppression of the Gibberellin-Insensitive Mutant (gai) of Arabidopsis.

The semidominant gibberellin-insensitive (gai) mutant of Arabidopsis thaliana shows impairment in multiple responses to the plant hormone gibberellin A3, which include effects on seed germination, stem elongation, apical dominance, and rapid flowering in short days. Results presented here show that the gai mutation also interferes with development of fertile flowers in continuous light. Mu-tagenesis of the gai mutant resulted in recovery of 17 independent mutants in which the gibberellin-insensitive phenotype is partially or completely suppressed. Sixteen of the suppressor mutations act semidominantly to restore gibberellin responsiveness. One representative of this class, the gar1 mutation, could not be genetically separated from the gai locus and is proposed to cause inactivation of the gai gene. The exceptional gar2 mutation partially suppresses the gai phenotype, is completely dominant, and is not linked to the gai locus. The gar2 mutation may define a new gene involved in gibberellin signaling. A recessive allele of the spindly (SPY) locus, spy-5, was also found to partially suppress the gai mutant phenotype.

Journal Article↗

PubMed1968

Extractable and Diffusible Gibberellins From Light- and Dark-grown Pea Seedlings.

Gibberellins were obtained from light- and dark-grown peas by solvent extraction and agar diffusion. Both A(5)- and A(1)-like gibberellins were obtained by extraction; however, by diffusion only the A(1)-like gibberellin was found. There was no significant quantitative difference in the levels of diffusible or extractable gibberellin obtained from light- and dark-grown tall and dwarf peas. Several possible explanations for the discrepancy between diffusible and extractable gibberellin were investigated. Of these, only I was supported by experimental evidence, namely, that GA(5) can be converted to GA(1).

Journal Article↗