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PubMed1970

Gibberellins in Relation to Flowering and Stem Elongation in the Long Day Plant Silene armeria.

Two long days induced some flowering and 4 or more long days caused 100% flowering in Silene armeria. On long days microscopically detectable flower primordia were first seen after 6 days, which is at least 1 day before the start of stem elongation. Both gibberellin A(3) and A(7) caused flowering on short days, but the results were variable and flowering was never 100%. Three different gibberellins were detected in Silene extracts. The pattern of gibberellins extracted from plants on short and long days was qualitatively the same, but on long days gibberellin content was up to 100% higher than on short days. Only small amounts of diffusible gibberellins were obtained from Silene shoot tips (including very young leaves) on short days. However, on long days the diffusible gibberellins increased by as much as 10-fold after 4 to 6 long days but then declined somewhat after 10 long days. The gibberellins extracted from the shoot tips at the completion of the diffusion period also increased under long days, although the increase was not as large as for the diffusible gibberellins. An A(5)-like gibberellin present in extracts was not detected in diffusates.Treatment with AMO 1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride) completely inhibited stem elongation on long days but had no effect on flowering. In addition, treatment with AMO 1618 caused at least an 80% decrease in the level of extractable gibberellin, while the diffusible gibberellin was reduced below the limits of detection in the d5 corn bioassay. When endogenous gibberellin levels were suppressed by pretreatment with AMO 1618 on short days, gibberellin A(3) caused more stem elongation in plants moved to long days than in plants left on short days. Thus the sensitivity of Silene plants to gibberellin with respect to stem growth is affected by photoperiod. It is concluded that in Silene endogenous gibberellins are a controlling factor for stem elongation but apparently are not required for flower formation.

Journal Article↗
PubMed1974

Selective binding of (3H)gibberellin A1 by protein fractions from dwarf pea epicotyls.

A homogenate from dwarf pea seedlings that had been treated with [(3)H]gibberellin A(1) was separated by Sephadex G-200 into two protein fractions, of high and intermediate molecular weight, with affinity for [(3)H]gibberellin A(1). Neither fraction bound [(3)H]gibberellin A(8), the only metabolite of [(3)H]gibberellin A(1) detected in significant quantity in extracts of pea seedlings. These proteinhormone complexes were noncovalently bound, as evidenced by their rapid disruption in ethanol. Approximate molecular weights of the fractions were 500,000 and 60,000. In experiments designed to detect competition for the binding proteins between [(3)H]gibberellin A(1) and closely related [(3)H]gibberellin molecules, [(3)H]gibberellin A(8) and pseudo [(3)H]gibberellin A(1) were inactive, but keto [(3)H]gibberellin competed favorably. Equilibrium dialysis experiments revealed that both high-molecular-weight and intermediate-molecular-weight protein-hormone complexes could undergo hormone exchange with nonlabeled gibberellin A(1).

Chromatography, Gel↗
PubMed2005

EUI1, encoding a putative cytochrome P450 monooxygenase, regulates internode elongation by modulating gibberellin responses in rice.

Elongation of rice internodes is one of the most important agronomic traits, which determines the plant height and underlies the grain yield. It has been shown that the elongation of internodes is under genetic control, and various factors are implicated in the process. Here, we report a detailed characterization of an elongated uppermost internode1 (eui1) mutant, which has been used in hybrid rice breeding. In the eui1-2 mutant, the cell lengths in the uppermost internodes are significantly longer than that of wild type and thus give rise to the elongated uppermost internode. It was found that the level of active gibberellin was elevated in the mutant, whereas its growth in response to gibberellin is similar to that of the wild type, suggesting that the higher level accumulation of gibberellin in the eui1 mutant causes the abnormal elongation of the uppermost internode. Consistently, the expression levels of several genes which encode gibberellin biosynthesis enzymes were altered. We cloned the EUI1 gene, which encodes a putative cytochrome P450 monooxygenase, by map-based cloning and found that EUI1 was weakly expressed in most tissues, but preferentially in young panicles. To confirm its function, transgenic experiments with different constructs of EUI1 were conducted. Overexpression of EUI1 gave rise to the gibberellin-deficient-like phenotypes, which could be partially reversed by supplementation with gibberellin. Furthermore, apart from the alteration of expression levels of the gibberellin biosynthesis genes, accumulation of SLR1 protein was found in the overexpressing transgenic plants, indicating that the expression level of EUI1 is implicated in both gibberellin-mediated SLR1 destruction and a feedback regulation in gibberellin biosynthesis. Therefore, we proposed that EUI1 plays a negative role in gibberellin-mediated regulation of cell elongation in the uppermost internode of rice.

Amino Acid Sequence↗
PubMed1966

Organs of gibberellin synthesis in light-grown sunflower plants.

The sites of gibberellin (GA) synthesis in light grown sunflower plants were studied. The results of organ excision and the exogenous application of indole acetic acid and gibberellic acid indicated that gibberellin synthesis occurred in the young leaves of the apical bud. This was substantiated using a combination of diffusion and extraction techniques. Diffusion of sunflower apical buds on agar for 20 hours revealed a level of gibberellin greater than that obtained by solvent extraction of a similar number of apices, indicating that synthesis of gibberellin was occurring in those apices during the diffusion period. The gibberellin level of apices extracted following a 20 hour diffusion period was the same as that obtained from buds extracted immediately following excision from the plant, again suggesting that apical buds are sites of gibberellin synthesis. A similar experiment was conducted with young internodal sections, the results indicating that they were not sites of gibberellin synthesis.The ability of various parts of sunflower plants to produce gibberellin as measured by the agar diffusion technique was correlated to internode elongation, the region of maximum gibberellin production being associated with the region of maximum extension growth.Root tips were also shown to be sites of gibberellin synthesis, this ability being confined to the apical 3 to 4 mm region of the root.

Journal Article↗
PubMed1971

Effects of photoperiod on growth rate and endogenous gibberellins in the long-day rosette plant spinach.

The earliest visible responses of spinach plants (Spinacia oleracea L., cv. Savoy Hybrid 612) transferred from short to long days (8 hours of high intensity light supplemented with 16 hours of low intensity illumination from incandescent lamps) were upright leaf orientation and increased elongation of the petioles. The effect of long days on growth rate was direct; i.e., there was no after-effect if the plants were transferred to short days. Gibberellin A(3) applied to plants under short days had an effect similar to that of long days, whereas application of the growth retardant AMO-1618 [2'-isopropyl-4'-(trimethylammonium chloride)-5'-methylphenyl piperidinel-carboxylate] under long days caused a growth habit typical of short-day conditions. Gibberellin A(3) caused more stem growth in plants under long days in which the endogenous gibberellin content had been reduced by AMO-1618 than in plants under short days not treated with the growth retardant.Three gibberellin-like substances, called I, II, and III in order of increasing R(F) value, were present in acidic extracts of spinach under short days. After transfer to long days, II increased, whereas I and III decreased, the latter below the level of detection in the d5 corn assay. Following application of AMO-1618 the gibberellin content of plants under long days fell off more rapidly than in those under short days, indicating that gibberellin turnover was markedly higher under long days. This increased rate of gibberellin metabolism was established after 2 long days. When plants were returned to short days, the turnover of gibberellins declined. It is suggested that a higher rate of gibberellin biosynthesis combined with increased sensitivity to gibberellin is responsible for the observed growth responses in spinach under long days.

Journal Article↗
PubMed2005

Contribution of gibberellins to the formation of Arabidopsis seed coat through starch degradation.

To clarify the role of gibberellins in the seed development of Arabidopsis, we investigated the sites where gibberellins are synthesized and induce alpha-amylase genes. The spatial and temporal expression of the genes encoding gibberellin biosynthetic enzymes and alpha-amylases was examined by reverse transcription-PCR (RT-PCR) and in situ hybridization. The mRNAs of AtGA20ox2, AtGA20ox3 and AtGA3ox4 began to be detectable 5-7 d after pollination. In situ hybridization showed that these genes were expressed almost simultaneously around starch granules in the outer integument, preceding the disappearance of those granules. AtGA20ox2 and AtGA3ox4 but not AtGA20ox3 also showed their signals at the rim of the developing embryo. The alpha-amylase gene, Amy3, which responded to gibberellin, was mainly expressed in the developing seed, spatially overlapping with the expression of AtGA20ox2 and AtGA3ox4. These results suggest that gibberellins function in at least two sites of the seed: the outer integument and part of the embryo. We examined the phenotypes of a T-DNA insertion line of AtGA3ox4 and observed the following: (i) a decrease of alpha-amylase gene transcripts in young siliques; (ii) delay of starch degradation in the outer integument; (iii) disarrangement of the seed surface structure; and (iv) abnormal swelling pattern of polysaccharides after imbibition by the mature seed. These characteristics are phenotypes of plants under gibberellin starvation, because the abnormalities could be almost overcome with applied gibberellin, and the gibberellin-treated mutant was indistinguishable from the wild type. These results strongly suggest that gibberellins in the outer integument would be required for the normal formation of the Arabidopsis seed coat.

Arabidopsis↗
PubMed1970

Inhibitors from Carob (Ceratonia siliqua L.): II. Effect on Growth Induced by Indoleacetic Acid or Gibberellins A(1), A(4), A(5), and A(7).

Two inhibitory fractions (B(1) and C) from extracts of immature fruit of carob were tested for their ability to inhibit the action of indoleacetic acid (IAA) in three bioassays. There was no reduction of IAA-induced reactions in the Avena curvature test, abscission of debladed coleus petioles, or growth of cucumber hypocotyls. The highest ratio of inhibitor to IAA was 10,000 times greater than the ratio necessary to inhibit by 50% the growth caused by an equivalent amount of gibberellin A(3) in pea seedlings. At the highest concentration used, fraction C alone caused curvature of Avena coleoptiles. The inhibitory fractions appeared to enhance the effect of IAA in the cucumber test.Concentrated whole extract and fractions B(1) and C were tested for reduction of growth caused by gibberellins A(1), A(4), A(5), A(7), and a neutral gibberellin-like substance from beans in the dwarf-5 maize bioassay. Each gibberellin was inhibited and required the same amount of inhibitor for a 50% reduction of the induced growth. The inhibiting effect could be completely overcome by increasing the amount of gibberellin while maintaining the same concentration of inhibitor. Fractions B(1) and C were also tested with gibberellins A(2) and A(4) in the cucumber hypocotyl test. Both inhibitory fractions reduced growth but were more effective against gibberellin A(3) than gibberellin A(4) in the assay. The ability to reduce gibberellin-induced growth and not reduce IAA-induced growth indicates that the inhibitors from carob have a greater specificity of action than that previously reported for any inhibitor.

Journal Article↗
PubMed2004

Posttranscriptional regulation of alpha-amylase II-4 expression by gibberellin in germinating rice seeds.

Hormonal regulation of expression of alpha-amylase II-4 that lacks the gibberellin-response cis-element (GARE) in the promoter region of the gene was studied in germinating rice (Oryza sativa L.) seeds. Temporal and spatial expression of alpha-amylase II-4 in the aleurone layer were essentially identical to those of alpha-amylase I-1 whose gene contains GARE, although these were distinguishable in the embryo tissues at the early stage of germination. The gibberellin-responsible expression of alpha-amylase II-4 was also similar to that of alpha-amylase I-1. However, the level of alpha-amylase II-4 mRNA was not increased by gibberellin, indicating that the transcriptional enhancement of alpha-amylase II-4 expression did not occur in the aleurone. Gibberellin stimulated the accumulation of 45Ca2+ into the intracellular secretory membrane system. In addition, several inhibitors for Ca2+ signaling, such as EGTA, neomycin, ruthenium red (RuR), and W-7 prevented the gibberellin-induced expression of alpha-amylase II-4 effectively. While the gibberellin-induced expression of alpha-amylase II-4 occurred normally in the aleurone layer of a rice dwarf mutant d1 which is defective in the alpha subunit of the heterotrimeric G protein. Based on these results, it was concluded that the posttranscriptional regulation of alpha-amylase II-4 expression by gibberellin operates in the aleurone layer of germinating rice seed, which is mediated by Ca2+ but not the G protein.

Base Sequence↗
PubMed2001

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.

Gas Chromatography-Mass Spectrometry↗
PubMed1998

Gibberellin signaling.

Recent findings provide insights into the gibberellin signaling system in plants. Genes for gibberellin biosynthetic enzymes have been cloned, and an emerging theme is that gibberellin biosynthesis is negatively regulated by gibberellin responses. Mutants defective in gibberellin signaling have been analyzed, and an important finding is that gibberellin represses growth inhibition. The list of intracellular gibberellin signal-transduction elements has been expanded to include G-proteins and protein kinases.

Arabidopsis↗
PubMed2006

Overexpression of PRE1 and its homologous genes activates Gibberellin-dependent responses in Arabidopsis thaliana.

Gibberellins control various aspects of growth and development. Here, we identified a gene, designated paclobutrazol resistance1 (PRE1), by screening Arabidopsis activation-tagged lines. PRE1 encodes a helix-loop-helix protein and belongs to a small gene family. Physiological and genetic analysis indicated that overexpression of PRE1 altered various aspects of gibberellin-dependent responses such as germination, elongation of hypocotyl/petiole, floral induction and fruit development, and suppressed gibberellin-deficient phenotypes of the ga2 mutant. Expression of some gibberellin-responsive genes was also affected by PRE1. Expression of PRE1 was shown to be early gibberellin inducible in the wild-type plants and under control of SPY and GAI, upstream negative regulators of gibberellin signaling. The shortened hypocotyl length phenotype of the gai-1 mutant was suppressed by PRE1 overexpression. Ectopic overexpression of each of the four PRE1-related genes conferred pleiotropic phenotypes similar to PRE1 overexpression, indicative of overlapping functions among the PRE gene family. Our results of gain-of-function studies suggest that PRE genes may have a regulatory role in gibberellin-dependent development in Arabidopsis thaliana.

Arabidopsis↗
PubMed1989

Mechanism of gibberellin-dependent stem elongation in peas.

Stem elongation in peas (Pisum sativum L.) is under partial control by gibberellins, yet the mechanism of such control is uncertain. In this study, we examined the cellular and physical properties that govern stem elongation, to determine how gibberellins influence pea stem growth. Stem elongation of etiolated seedlings was retarded with uniconozol, a gibberellin synthesis inhibitor, and the growth retardation was reversed by exogenous gibberellin. Using the pressure probe and vapor pressure osmometry, we found little effect of uniconozol and gibberellin on cell turgor pressure or osmotic pressure. In contrast, these treatments had major effects on in vivo stress relaxation, measured by turgor relaxation and pressure-block techniques. Uniconozol-treated plants exhibited reduced wall relaxation (both initial rate and total amount). The results show that growth retardation is effected via a reduction in the wall yield coefficient and an increase in the yield threshold. These effects were largely reversed by exogenous gibberellin. When we measured the mechanical characteristics of the wall by stress/strain (Instron) analysis, we found only minor effects of uniconozol and gibberellin on the plastic compliance. This observation indicates that these agents did not alter wall expansion through effects on the mechanical (viscoelastic) properties of the wall. Our results suggest that wall expansion in peas is better viewed as a chemorheological, rather than a viscoelastic, process.

Cell Wall↗