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PubMed1972

Two effects of prolonged far red light on the response of lettuce seeds to exogenous gibberellin.

Prolonged far red irradiation of imbibed lettuce seeds (Lactuca sativa L. cv. Grand Rapids) makes them unresponsive to subsequent treatment with gibberellin. It has been found that this effect is overcome by supplying gibberellin buffered at a low pH. On the basis of this and other evidence it is suggested that an extended far-red exposure causes a loss of gibberellin sensitivity through an effect on the permeability of the endosperm. In seeds treated simultaneously with gibberellin and far red light, the hormone is taken up at the beginning of the irradiation, but its action is suspended until the seeds are placed in the dark.

Journal Article↗

PubMed1974

Physiology of the Yellow-Green 6 Gene in Tomato: A Possible Interrelationship between the Phenotypic Expressions of the Yellow-Green 6 Gene Mutation and the Gibberellins.

The yellow-green 6 (yg(6)) mutation in tomato (Lycopersicon esculentum Mill.) is controlled by a single recessive gene with pleiotropic effects. The syndrome of characters associated with the mutation are enhanced stem elongation, reduced chlorophyll content and absence of detectable anthocyanins. We now have shown that the mutant also has fewer lateral roots than the wild type and higher l-phenylalanine ammonia-lyase (E.C. 4.3.1.5) activity than the normal tomato. These traits of the mutant closely resemble those induced in many plants by the application of gibberellic acid which suggests that the phenotypic expressions of the mutation might in some manner be related to the endogenous level or activity of the gibberellins. In support of this premise, data are presented which show that the characters of the mutant can be induced in the wild type tomato by application of gibberellic acid. Conversely, several traits of the wild type can be induced in the mutant by an inhibitor of gibberellin hiosynthesis, Phosfon. In addition, an embryoless barley half-seed bioassay for the gibberellins and gas-liquid chromatography indicated that the mutant contained at least three times as much total gibberellin as the wild type plant.

Journal Article↗

PubMed1976

Effects of Ancymidol (a Growth Retardant) and Triarimol (a Fungicide) on the Growth, Sterols, and Gibberellins of Phaseolus vulgaris (L.).

The effect of the two substituted pyrimidines, ancymidol (a growth retardant) and triarimol (a fungicide) on Phaseolus vulgaris was studied. Both compounds retarded shoot and root elongation as well as increases in fresh weight. Both compounds caused production of ethylene-like responses when given in high dosages or when applied shortly after germination. As growth retardation was shown to occur in the absence of net increase in sterol levels, neither ancymidol nor triarimol apparently retards growth by inhibiting sterol synthesis.Both ancymidol and triarimol treatment drastically reduced the amount of extractable gibberellin-like activity in beans. Ancymidol also either induced or enhanced the production of a compound which gave a negative response in the bioassay plant Oryza sativa var. Tan-ginbozu. The addition of gibberellin completely relieved the dwarfing effects of both ancymidol and triarimol in dark-grown beans. It is concluded that ancymidol and triarimol affect a gibberellin-induced growth response, probably by inhibiting gibberellin biosynthesis.

Journal Article↗

PubMed1978

Role of Indole-3-acetic Acid and Gibberellin in the Control of Internodal Elongation in Avena Stem Segments: Long Term Growth Kinetics.

Exogenous application of indoleacetic acid results in a significant suppression of the linear growth that is promoted by exogenous gibberellic acid in Avena stem segments in a fashion similar to that previously noted in Avena leaf base segments (van Overbeek and Dowding, 1961, Fourth International Conference Plant Growth Regulation). Treatment with the auxin transport inhibitors, methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate (CFM) or 2,3,5-triiodobenzoic acid (TIBA), alone promotes elongation growth of the stem segments over that of control growth. This effect is interpreted as being due to the interference in the transport of native indoleacetic acid by CFM and TIBA, thus removing the inhibitory effect of native indoleacetic acid on gibberellin-promoted growth in the internodal intercalary meristem. This results in a greater promotion of internodal growth by native gibberellins. In the presence of (2-chloroethyl) trimethylammonium chloride (CCC), the growth-promoting effects of CFM and TIBA are decreased, and the antiauxin, PCIB (4-chloro-phenoxyisobutyric acid), has no growth-promoting effects whatsoever. These results indicate that the CFM and TIBA-promoted growth require the continuous presence of gibberellins. They further support the view that native indoleacetic acid acts as a growth suppressor hormone in its regulation of gibberellin-promoted internodal extension in Avena shoots.

Journal Article↗

PubMed1985

Sites of gibberellin biosynthesis in pea seedlings.

Potential sites of gibberellin biosynthesis in 10-day-old ;Alaska' pea (Pisum sativum L.) seedlings were investigated using a cell-free ezyme system capable of incorporating [(14)C]-mevalonic acid into ent-kaurene. In peas, ent-kaurene is assumed to be a committed intermediate in the gibberellin biosynthetic pathway. Comparative results from enzyme assays using extracts from shoot tips, leaf blades, internodes, and root tips indicate that the highest capacity for ent-kaurene (and presumably gibberellin) synthesis is in those tissues with the greatest potential for growth. The highest rates were obtained with extracts prepared from the fifth (youngest) internode, the fourth (youngest) expanded leaf, and the shoot tip itself. This report represents the first direct evidence that the enzymes responsible for early stages in gibberellin biosynthesis occur in internode tissues with potential for rapid elongation.

Journal Article↗

PubMed1990

Detection of endogenous gibberellins and their relationship to hypocotyl elongation in soybean seedlings.

Four gibberellins, GA(53), GA(19), GA(20), and GA(1), were detected by bioassay, chromatography in two HPLC systems, and combined gas chromatography-mass spectroscopy-selected ion monitoring (GC-MS-SIM) in etiolated soybean (Glycine max [L.] Merr.) hypocotyls. GC-MS-SIM employed [(2)H(2)]-labeled standards for each endogenous gibberellin detected, and quantities estimated from bioassays and GC-MS-SIM were similar. This result plus the tentative detection of GA(44) and GA(8) (standards not available) indicates that the early-C-13-hydroxylation pathway for gibberellin biosynthesis predominates in soybean hypocotyls. Other gibberellins were not detected. Growth rates decreased after transfer to low water potential (psi(w)) vermiculite and were completely arrested 24 hours after transfer. The GA(1) content in the elongating region of hypocotyls had declined to 38% of the 0 time value at 24 hours after transfer to low psi(w) vermiculite, a level which was only 13% of the GA(1) content in control seedlings at the same time (24 hours posttransfer). Rewatering seedlings following 24 hours growth in low psi(w) vermiculite resulted in a complete recovery in elongation rate, an increase in GA(1) (20% at 2 hours, two-fold at 8 hours, eightfold at 24 hours), and a decrease in ABA levels (tenfold at 2 hours). Treatment of well-watered seedlings with the GA-synthesis inhibitor tetcyclacis (TCY) resulted in lowered GA(1) levels and increased ABA levels. When seedlings grown 24 hours in low psi(w) vermiculite were rewatered with TCY, recovery of the elongation rate was delayed and reduced, and the decline in ABA levels was slowed. Addition of GA(3) restored the elongation rate inhibited by TCY. Seedlings were growth responsive to exogenous GA(3), and this GA(3)-promoted growth was inhibited by exogenous ABA. The data are consistent with the hypothesis that changes in GA(1) and ABA levels play a role in adjusting hypocotyl elongation rates. However, the changes observed are not of sufficient magnitude nor do they occur rapidly enough to suggest they are the primary regulators of elongation rate responses to rapidly changing plant water status.

Journal Article↗

PubMed1992

Aleurone nuclear proteins bind to similar elements in the promoter regions of two gibberellin-regulated alpha-amylase genes.

Binding of nuclear proteins from wild oat aleurone protoplasts to the promoter regions of two gibberellin-regulated wheat alpha-amylase genes (alpha-Amy1/18 and alpha-Amy2/54) has been studied by gel retardation and DNase 1 footprinting. Gel retardation studies using 300-430 bp fragments of the promoters showed similar binding characteristics with nuclear extracts from both gibberellin A1-treated and untreated protoplasts. DNase 1 footprints localised binding of nuclear proteins from gibberellin A1-treated aleurone protoplasts to regions in both promoters. Similar sequence elements in the promoter regions of both genes were protected from digestion although the location and number of footprints in each promoter region were different. Each footprint contained either a sequence similar to the cAMP and/or phorbol ester response elements, or a hyphenated palindrome sequence. The presence of cAMP and/or phorbol ester response element-like sequences in the footprints suggests that transcription factors of the bZIP type may be involved in the expression of alpha-amylase genes in aleurone cells. Footprints containing hyphenated palindrome sequences, found in the promoter regions of both genes, suggest the possible involvement of other classes of transcription factor. The conserved alpha-amylase promoter sequence TAA-CAGA was also shown to bind nuclear protein in the alpha-Amy2/54 promoter. These observations are discussed in relation to alpha-amylase gene expression in aleurone and to functional data concerning these genes.

Base Sequence↗

PubMed1996

Gibberellin-repressible gene expression in the barley aleurone layer.

Gibberellins are noted for their ability to induce expression of genes, such as alpha-amylase, in the aleurone layers of cereals. However, a number of mRNA species in the mature imbibed aleurone cell of barley, such as a storage globulin (Heck et al., Mol Gen Genet 239: 209-218 1993), are simultaneously and specifically repressed by gibberellin. In a continuing effort to understand this effect, we report cloning and characterization of two additional cDNAs from barley designated pHvGS-1 and pcHth3 that have high corresponding mRNA levels in the mature imbibed aleurone but are repressed 10-fold or more within 24 h of treatment with gibberellic acid (GA3). The extent of repression was concentration dependent and maximally effective at 10(-6) M GA3. Repression was also noted in the constitutive gibberellin response mutant, slender, in the absence of exogenous GA3. The antagonistic phytohormone, abscisic acid, had no effect or was weakly inductive of the steady-state levels of these mRNAs. During development of the seed, repressible mRNAs are present to different degrees in the maturing aleurone layer and embryo, but not in the starchy endosperm. Some repressible mRNA persists in the mature dry aleurone layer, but is degraded during imbibition, replenished by de novo transcription, and maintained at high steady-state levels until GA3 is perceived. Preliminary investigation suggests that repression is at least partly due to destabilization of the mRNAs which have estimated half-lives of 12 h or greater in the absence of GA3. pcHth3 encodes a member of the gamma-thionin gene family located on chromosome 7. pHvGS-1 corresponds to a gene on chromosome 3 of unknown function.

Abscisic Acid↗

PubMed2004

Gibberellin production by bacteria and its involvement in plant growth promotion and yield increase.

This review focuses on studies with bacteria for which biosynthesis/production of the plant hormones gibberellins have been demonstrated. Actual data on gibberellin metabolism by bacteria are analyzed in comparison with the biosynthetic pathways known for vascular plants and fungi. The potential involvement of gibberellins produced by symbiotic and soil-endophytic microorganisms in plant growth promotion and yield increase is also discussed.

Bacteria↗

PubMed1983

Multiple molecular forms of the gibberellin-induced alpha-amylase from the aleurone layers of barley seeds.

A class of plant growth regulators, gibberellins, induce the synthesis of alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) in the aleurone layers of barley (Hordeum vulgare L. var. Himalaya) seeds. The purified alpha-amylase is composed of multiple isozymic forms with indistinguishable molecular weights, but different net charges. These alpha-amylase isozymes separate on isoelectric focusing gels into two groups, each containing multiple species. One group has an apparent isoelectric point (pI) of approximately 5.8 (the high pI group). The other group's pI values are around 4.5 (the low pI group). On some gels a small amount of protein focuses between the high and low pI isozymes. These proteins comigrate with the low pI isozymes upon reelectrophoresis. The synthesis of these two groups is temporally regulated. The high pI group is the dominant set of isozymes secreted from embryoless half seeds during the first two days of gibberellin administration. After four days, however, the major isozymes are those of the low pI group. This shift in isozyme pattern is due to a shift in their relative rates of synthesis. Peptide analysis of these two groups of isozymes with Staphylococcus aureus V8 protease and cyanogen bromide shows amino acid sequence differences. However, members within the same group have similar peptide patterns. Both groups of isozymes are synthesized in vitro in a wheat germ extract primed with poly(A)+ RNA isolated from gibberellin-treated aleurone layers. This indicates that the synthesis of the two groups of alpha-amylase isozymes is probably directed by two or more different populations of mature mRNA. A model that explains these observations and the available genetic information is that barley aleurone alpha-amylase isozymes are encoded by at least two sets of structural genes.

Amylases↗

PubMed2003

Dispatch. Gibberellin signaling: GRASs growing roots dispatch.

Gibberellins are important endogenous plant growth regulators. A new study has revealed an unexpected role for gibberellin-regulated transcription factors in promoting root growth; this depends on signaling from another plant hormone, auxin, suggesting that auxin promotes root growth by modulating the cellular response to gibberellins.

Gibberellins↗

PubMed2006

Regulation of color break in citrus fruits. Changes in pigment profiling and gene expression induced by gibberellins and nitrate, two ripening retardants.

Citrus clementina fruits were repeatedly treated on-tree from mature green until breaker stages with either nitrate or gibberellin, two retardants of external ripening. The natural color break was characterized by a reduction in chlorophyll concentration, a decrease in beta,epsilon-carotenoids, beta-carotene, neoxanthin, and all-E-violaxanthin, and an increase in beta,beta-xanthophylls [mainly (9Z)-violaxanthin and beta-cryptoxanthin]. The two retardants delayed both chlorophyll depletion and total carotenoid accumulation and in addition altered carotenoid composition. Treated fruits maintained longer the typical carotenoid composition of green fruits and reduced beta,beta-xanthophyll accumulation. Natural degreening was accompanied by a marked decrease in transcript levels of 1-deoxy-d-xylulose 5-phosphate synthase (DXS) and geranylgeranyl reductase (CHL P) while, conversely, pheophorbide a oxygenase (PaO) and phytoene synthase (PSY) gene expression increased. Gibberellin and nitrate delayed the reduction of DXS expression and the induction of PaO and PSY transcript accumulation, while no differences in CHL P were observed. The data indicate that both ripening retardants repressed natural PaO and PSY expression, suggesting a mechanistic basis for the elevated levels of chlorophyll and lower carotenoid concentration resulting from the gibberellin and nitrogen treatments and the consequent color break delay in citrus fruit peels.

Carotenoids↗

PubMed2002

Characterization of gibberellin producing strains of Fusarium moniliforme based on DNA polymorphism.

The gibberellins are one of the major groups of growth promoting hormones and are secondary metabolites of the fungus Fusarium moniliforme (Perfect stage: Gibberella fujikuroi). Sixteen strains of Fusarium from different geographical regions and different hosts were analysed for their ability to produce gibberellins (GA) and for genetic relatedness by random amplified polymorphic DNA (RAPD). Range of gibberellin production varied between 28.9 to 600.0 mg g(-1) dry weight of mycelium in different strains of Fusarium. RAPD analysis showed completely different pattern between high, moderate and low producing strains. High producers formed nearly identical RAPD patterns, whereas the low and moderate producers gave heterologous amplification patterns. Since Fusarium pallidoroseum was in another group, it was possible to distinguish between different species of the genus Fusarium by RAPD. These investigations may find an application in the diagnosis of unknown Fusarium species and in distinguishing isolates of Gibberella fujikuroi within the section of Liseola.

DNA, Fungal↗

PubMed2001

A plastid envelope location of Arabidopsis ent-kaurene oxidase links the plastid and endoplasmic reticulum steps of the gibberellin biosynthesis pathway.

We have used fusions of gibberellin biosynthesis enzymes to green fluorescent protein (GFP) to determine the subcellular localization of the early steps of the pathway. Gibberellin biosynthesis from geranylgeranyl diphosphate is catalysed by enzymes of the terpene cyclase, cytochrome P450 mono-oxygenase and 2-oxoglutarate-dependent dioxygenase classes. We show that the N-terminal pre-sequences of the Arabidopsis thaliana terpene cyclases copalyl diphosphate synthase (AtCPS1) and ent-kaurene synthase (AtKS1) direct GFP to chloroplasts in transient assays following microprojectile bombardment of tobacco leaves. The AtKS1-GFP fusion is also imported by isolated pea chloroplasts. The N-terminal portion of the cytochrome P450 protein ent-kaurene oxidase (AtKO1) directs GFP to chloroplasts in tobacco leaf transient assays. Chloroplast import assays with 35S-labelled AtKO1 protein show that it is targeted to the outer face of the chloroplast envelope. The leader sequences of the two ent-kaurenoic acid oxidases (AtKAO1 and AtKAO2) from Arabidopsis direct GFP to the endoplasmic reticulum. These data suggest that the AtKO1 protein links the plastid- and endoplasmic reticulum-located steps of the gibberellin biosynthesis pathway by association with the outer envelope of the plastid.

Arabidopsis↗

PubMed2002

A role for arabinogalactan proteins in gibberellin-induced alpha-amylase production in barley aleurone cells.

Arabinogalactan proteins (AGPs) are plant proteoglycans that have been implicated in plant growth and development. The possible involvement of AGPs in the action of gibberellin (GA), a class of plant hormones, was examined by applying beta-glucosyl Yariv reagent (beta-Glc)3Y, a synthetic phenyl glycoside that interacts selectively with AGPs, to barley aleurone protoplasts. Gibberellin induces transcription and secretion of alpha-amylases in the protoplasts. Induction of alpha-amylase was clearly inhibited by (beta-Glc)3Y but not by (alpha-Gal)3Y, a negative control of the Yariv reagent that does not interact with AGPs. Transfection analysis, using an alpha-amylase promoter-GUS fusion gene in the protoplasts, indicated that the transcriptional activation of the alpha-amylase promoter was inhibited specifically by (beta-Glc)3Y. These observations are the first indication of an involvement of AGPs in a plant hormone function. The inhibitory effect of (beta-Glc)3Y was not observed when aleurone layers or half-seed grains were used. This result, together with the fact that protoplasts do not have cell walls, suggests that the AGPs that function in alpha-amylase induction reside at the plasma membrane. An aleurone-specific AGP was detected by reversed-phase HPLC, and supported the idea that an AGP may play an important role in aleurone-specific events. The possible mechanism of AGP function in gibberellin-induced alpha-amylase production is discussed.

Cell Survival↗

PubMed2002

In vitro bulb development in shallot (Allium cepa L. Aggregatum Group): effects of anti-gibberellins, sucrose and light.

Bulbing was studied in shallot plants cultured in vitro. Bulbing occurred under a 16 h photoperiod with fluorescent + incandescent light and 30-50 g 1(-1) sucrose in the culture medium. Exogenous gibberellin (10 microM GA3) inhibited leaf and root growth and bulbing. When added to the medium at a concentration of 10 microM, three inhibitors of gibberellin biosynthesis (ancymidol, flurprimidol and paclobutrazol) promoted bulb formation and the percentage of bulbing. When ancymidol was used in combination with GA3, it did not reverse the effect of GA3 applied alone. Under treatments with 30-70 g l(-1) sucrose, bulbing ratios greater than those found in control plants were achieved by addition of ancymidol, and bulb fresh weight was increased in the same way. Ancymidol caused a 66% decrease in sucrose content in leaf bases but greatly increased the glucose, fructose and fructan contents. The increase in fructan content by ancymidol could result from the three-fold rise in total [14C]sucrose uptake per plant from the culture medium associated with a marked increase in leaf base labelling at the expense of root labelling. The possible role of ancymidol is discussed and evidence supports a major regulatory role for gibberellins in bulbing.

Allium↗

PubMed2005

Influence of the gibberellin-sensitive Rht8 dwarfing gene on leaf epidermal cell dimensions and early vigour in wheat (Triticum aestivum L.).

BACKGROUND AND AIMS: The gibberellin-insensitive Rht-B1b and Rht-D1b dwarfing genes are known to reduce the size of cells in culms, leaves and coleoptiles of wheat. Resulting leaf area development of gibberellin-insensitive wheats is poor compared to standard height (Rht-B1a and Rht-D1a) genotypes. Alternative dwarfing genes to Rht-B1b and Rht-D1b are available that reduce plant height, such as the gibberellin-responsive Rht8 gene. This study aims to investigate if Rht8 has a similar dwarfing effect on the size of leaf cells to reduce leaf area. METHODS: The effect of Rht8 on cell size and leaf area was assessed in four types of epidermal cells (interstomatal, long, sister and bulliform) measured on leaf 2 of standard height (rht8) and semi-dwarf (Rht8) doubled-haploid lines (DHLs). The DHLs were derived from a cross between very vigorous, standard height (rht8) ('Vigour18') and less vigorous, semi-dwarf (Rht8) ('Chuan-Mai 18') parents. KEY RESULTS: Large differences were observed in seedling vigour between the parents, where 'Vigour18' had a much greater plant leaf area than 'Chuan-Mai 18'. Accordingly, 'Vigour18' had on average longer, wider and more epidermal cells and cell files than 'Chuan-Mai 18'. Although there was correspondingly large genotypic variation among DHLs for these traits, the contrast between semi-dwarf Rht8 and tall rht8 DHLs revealed no difference in the size of leaf 2 or average cell characteristics. Hence, these traits were independent of plant height and therefore Rht8 in the DHLs. Correlations for leaf and average cell size across DHLs revealed a strong and positive relationship between leaf width and cell files, while the relationships between leaf and cell width, and leaf and cell length were not statistically different. The relative contribution of the four cell types (long, sister, interstomatal and bulliform) to leaf size in the parents, comparative controls and DHLs is discussed. CONCLUSIONS: Despite a large range in early vigour among the DHLs, none of the DHLs attained the leaf area or epidermal cell size and numbers of the vigorous rht8 parent. Nonetheless, the potential exists to increase the early vigour of semi-dwarf wheats by using GA-sensitive dwarfing genes such as Rht8.

Genes, Plant↗

PubMed2002

Positional cloning of rice semidwarfing gene, sd-1: rice "green revolution gene" encodes a mutant enzyme involved in gibberellin synthesis.

A rice semidwarfing gene, sd-1, known as the "green revolution gene," was isolated by positional cloning and revealed to encode gibberellin 20-oxidase, the key enzyme in the gibberellin biosynthesis pathway. Analysis of 3477 segregants using several PCR-based marker technologies, including cleaved amplified polymorphic sequence, derived-CAPS, and single nucleotide polymorphisms revealed 1 ORF in a 6-kb candidate interval. Normal-type rice cultivars have an identical sequence in this region, consisting of 3 exons (558, 318, and 291 bp) and 2 introns (105 and 1471 bp). Dee-Geo-Woo-Gen-type sd-1 mutants have a 383-bp deletion from the genome (278-bp deletion from the expressed sequence), from the middle of exon 1 to upstream of exon 2, including a 105-bp intron, resulting in a frame-shift that produces a termination codon after the deletion site. The radiation-induced sd-1 mutant Calrose 76 has a 1-bp substitution in exon 2, causing an amino acid substitution (Leu [CTC] to Phe [TTC]). Expression analysis suggests the existence of at least one more locus of gibberellin 20-oxidase which may prevent severe dwarfism from developing in sd-1 mutants.

Amino Acid Sequence↗