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At least 865 records · Page 48Linked to original sources
PubMed1993

Gibberellin (GA3) enhances cell wall invertase activity and mRNA levels in elongating dwarf pea (Pisum sativum) shoots.

The invertase (EC 3.2.1.26) purified from cell walls of dwarf pea stems to homogeneity has a molecular mass of 64 kilodaltons (kD). Poly(A)+RNA was isolated from shoots of dwarf pea plants, and a cDNA library was constructed using lambda gt11 as an expression vector. The expression cDNA library was screened with polyclonal antibodies against pea cell wall invertase. One invertase cDNA clone was characterized as a full-length cDNA with 1,863 base pairs. Compared with other known invertases, one homologous region in the amino acid sequence was found. The conserved motif, Asn-Asp-Pro-Asn-Gly, is located near the N-terminal end of invertase. Northern blot analysis showed that the amount of invertase mRNA (1.86 kb) was rapidly induced to a maximal level 4 h after GA3 treatment, then gradually decreased to the control level. The mRNA level at 4 h in GA3-treated peas was fivefold higher than that of the control group. The maximal increase in activity of pea cell wall invertase elicited by GA3 occcured at 8 h after GA3 treatment. This invertase isoform was shown immunocytochemically to be localized in the cell walls, where a 10-fold higher accumulation occurred in GA3-treated tissue compared with control tissue. This study indicates that the expression of the pea shoot cell-wall invertase gene could be regulated by GA3 at transcriptional and/or translational levels.

Amino Acid Sequence↗
PubMed2004

Abscisic acid in the thermoinhibition of lettuce seed germination and enhancement of its catabolism by gibberellin.

Germination of lettuce (Lactuca sativa L. cv. 'Grand Rapids') seeds was inhibited at high temperatures (thermoinhibition). Thermoinhibition at 28 degrees C was prevented by the application of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis. At 33 degrees C, the sensitivity of the seeds to ABA increased, and fluridone on its own was no longer effective. However, a combined application of fluridone and gibberellic acid (GA3) was able to restore the germination. Exogenous GA3 lowered endogenous ABA content in the seeds, enhancing catabolism of ABA and export of the catabolites from the intact seeds. The fluridone application also decreased the ABA content. Consequently, the combined application of fluridone and GA3 decreased the ABA content to a sufficiently low level to allow germination at 33 degrees C. There was no significant temperature-dependent change in endogenous GA1 contents. It is concluded that ABA is an important factor in the regulation of thermoinhibition of lettuce seed germination, and that GA affects the temperature responsiveness of the seeds through ABA metabolism.

Abscisic Acid↗
PubMed1997

Gibberellin A3 causes a decrease in the accumulation of mRNA for ACC oxidase and in the activity of the enzyme in azuki bean (Vigna angularis) epicotyls.

Differential screening, aimed at the isolation of cDNA clones of mRNAs whose accumulation is influenced by GA3, resulted in the isolation of a cDNA clone of an mRNA whose level was decreased by GA3 in segments of epicotyls of Vigna angularis. The putative protein encoded by this cDNA resembled the 1-aminocyclopropane-1-carboxylate oxidases (ACC oxidases) identified in other plant species (about 80% homology at the amino acid level). Thus, the corresponding gene was designated AB-ACO1 (azuki bean ACC oxidase). GA3 also decreased the activity of ACC oxidase in azuki bean epicotyls, but it did not decrease the rate of ethylene evolution. In fact, GA3 increased the rate of ethylene evolution and the level of ACC. Thus, GA3 seemed to increase the production of ethylene by promoting the synthesis of ACC.

Amino Acid Oxidoreductases↗
PubMed2000

Involvement of ethylene and gibberellin signalings in chromosaponin I-induced cell division and cell elongation in the roots of Arabidopsis seedlings.

Chromosaponin I (CSI), a triterpenoid saponin isolated from pea, stimulates the growth of roots in Arabidopsis thaliana seedlings on wetted filter paper in the light for 14 d. The growth rates of roots in Columbia (Col) and Landsberg erecta (Ler) wild-types were 0.92 and 0.26 mm d(-1), respectively, and they were accelerated to 3.46 (Col) and 2.20 (Ler) mm d(-1) by treating with 300 microM CSI. The length of mature epidermal cells was increased by 1.8-fold (Col) and 2.81-fold (Ler) compared with control and the number of epidermal cells was increased by a factor of 1.65 (Col) and 2.12 (Ler). Treatment with 2-aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, also increased cell length but not cell number. The effects of CSI on root growth were not detected in the ethylene-insensitive mutant ein2-1. CSI did not inhibit ethylene production but stimulated the growth of roots in ctr1-1, the constitutive triple response mutant for ethylene, indicating that CSI inhibits ethylene signaling, especially downstream of CTR1. In the GA-insensitive mutant gai and the mutant spy-3, in which the basal level of GA signaling is activated, CSI did not increase cell number, although both CSI and AVG stimulated cell elongation in these mutants. These results suggest that the inhibition of ethylene signaling is the cause of CSI-induced cell elongation. A possible involvement of both GA and ethylene signalings is discussed for the CSI-induced cell division.

Aminobutyrates↗
PubMed2003

Functional dissections between GAMYB and Dof transcription factors suggest a role for protein-protein associations in the gibberellin-mediated expression of the RAmy1A gene in the rice aleurone.

In the germinated cereal aleurone layer, gibberellic acids (GA) induce expression of a number of genes encoding hydrolytic enzymes that participate in the mobilization of stored molecules. Previous analyses suggest that the key events controlling the GA-regulated gene expression in the aleurone are formation of active transcription machinery referred to as the GA responsive complex, followed by recruiting GAMYB. In general, bipartite promoter contexts composed of the GA-responsive element and the pyrimidine box are observed within the regulatory regions of cereal GA-responsive genes. Protein factors that recognize each promoter sequence were identified and distinct effects on the GA-mediated activation of gene expression have been also investigated; however, the connection and intercalation between two promoter motifs remain obscure. In this study, I have evaluated cooperative function of GAMYB and a pyrimidine box-binding protein OsDOF3 that influenced the promoter activity of the most predominant GA-responsive gene (RAmy1A) of rice (Oryza sativa). Transient expression of OsDOF3 in the germinated aleurone prolonged GAMYB function on the reporter expression in the absence of GA. The synergistic effect required a set of DNA bindings of two proteins on the RAmy1A promoter region. The yeast two-hybrid assay showed the physical interaction of GAMYB and OsDOF3 in yeast cells, indicating that the association of GAMYB and OsDOF3 may be a functional unit in transcription regulation. The results showed the accessory function of OsDOF3 responsible for a dosage-dependent mediation of GA signaling that leads to high-level expression of physiological target genes.

Amino Acid Sequence↗
PubMed2003

Possible involvement of leaf gibberellins in the clock-controlled expression of XSP30, a gene encoding a xylem sap lectin, in cucumber roots.

Root-produced organic compounds in xylem sap, such as hormones and amino acids, are known to be important in plant development. Recently, biochemical approaches have revealed the identities of several xylem sap proteins, but the biological functions and the regulation of the production of these proteins are not fully understood. XYLEM SAP PROTEIN 30 kD (XSP30), which is specifically expressed in the roots of cucumber (Cucumis sativus), encodes a lectin and is hypothesized as affecting the development of above-ground organs. In this report, we demonstrate that XSP30 gene expression and the level of XSP30 protein fluctuate in a diurnal rhythm in cucumber roots. The rhythmic gene expression continues for at least two or three cycles, even under continuous light or dark conditions, demonstrating that the expression of this gene is controlled by a circadian clock. Removal of mature leaves or treatment of shoots with uniconazole-P, an inhibitor of gibberellic acid (GA) biosynthesis, dampens the amplitude of the rhythmic expression; the application of GA negates these effects. These results suggest that light signals perceived by above-ground organs, as well as GA that is produced, possibly, in mature leaves, are important for the rhythmic expression of XSP30 in roots. This is the first demonstration of the regulation of the expression of a clock-controlled gene by GA.

Circadian Rhythm↗
PubMed2004

An overview of gibberellin metabolism enzyme genes and their related mutants in rice.

To enhance our understanding of GA metabolism in rice (Oryza sativa), we intensively screened and identified 29 candidate genes encoding the following GA metabolic enzymes using all available rice DNA databases: ent-copalyl diphosphate synthase (CPS), ent-kaurene synthase (KS), ent-kaurene oxidase (KO), ent-kaurenoic acid oxidase (KAO), GA 20-oxidase (GA20ox), GA 3-oxidase (GA3ox), and GA 2-oxidase (GA2ox). In contrast to the Arabidopsis genome, multiple CPS-like, KS-like, and KO-like genes were identified in the rice genome, most of which are contiguously arranged. We also identified 18 GA-deficient rice mutants at six different loci from rice mutant collections. Based on the mutant and expression analyses, we demonstrated that the enzymes catalyzing the early steps in the GA biosynthetic pathway (i.e. CPS, KS, KO, and KAO) are mainly encoded by single genes, while those for later steps (i.e. GA20ox, GA3ox, and GA2ox) are encoded by gene families. The remaining CPS-like, KS-like, and KO-like genes were likely to be involved in the biosynthesis of diterpene phytoalexins rather than GAs because the expression of two CPS-like and three KS-like genes (OsCPS2, OsCPS4, OsKS4, OsKS7, and OsKS8) were increased by UV irradiation, and four of these genes (OsCPS2, OsCPS4, OsKS4, and OsKS7) were also induced by an elicitor treatment.

Alkyl and Aryl Transferases↗
PubMed2004

A rice WRKY gene encodes a transcriptional repressor of the gibberellin signaling pathway in aleurone cells.

The molecular mechanism by which GA regulates plant growth and development has been a subject of active research. Analyses of the rice (Oryza sativa) genomic sequences identified 77 WRKY genes, among which OsWRKY71 is highly expressed in aleurone cells. Transient expression of OsWRKY71 by particle bombardment specifically represses GA-induced Amy32b alpha-amylase promoter but not abscisic acid-induced HVA22 or HVA1 promoter activity in aleurone cells. Moreover, OsWRKY71 blocks the activation of the Amy32b promoter by the GA-inducible transcriptional activator OsGAMYB. Consistent with its role as a transcriptional repressor, OsWRKY71 is localized to nuclei of aleurone cells and binds specifically to functionally defined TGAC-containing W boxes of the Amy32b promoter in vitro. Mutation of the two W boxes prevents the binding of OsWRKY71 to the mutated promoter, and releases the suppression of the OsGAMYB-activated Amy32b expression by OsWRKY71, suggesting that OsWRKY71 blocks GA signaling by functionally interfering with OsGAMYB. Exogenous GA treatment decreases the steady-state mRNA level of OsWRKY71 and destabilizes the GFP:OsWRKY71 fusion protein. These findings suggest that OsWRKY71 encodes a transcriptional repressor of GA signaling in aleurone cells.

Amino Acid Sequence↗
PubMed2004

Two transcription factors are negative regulators of gibberellin response in the HvSPY-signaling pathway in barley aleurone.

SPINDLY (SPY) protein from barley (Hordeum vulgare L. cv Himalaya; HvSPY) negatively regulated GA responses in aleurone, and genetic analyses of Arabidopsis thaliana predict that SPY functions in a derepressible GA-signaling pathway. Many, if not all, GA-dependent responses require SPY protein, and to improve our understanding of how the SPY signaling pathway operates, a yeast two-hybrid screen was used to identify both upstream and downstream components that might regulate the activity of the HvSPY protein. A number of proteins from diverse classes were identified using HvSPY as bait and barley cDNA libraries as prey. Two of the HvSPY-interacting (HSI) proteins were transcription factors belonging to the myb and NAC gene families, HSImyb and HSINAC. Interaction occurred via the tetratricopeptide repeat domain of HvSPY and specificity was shown both in vivo and in vitro. Messenger RNAs for these proteins were expressed differentially in many parts of the barley plant but at very low levels. Both HSImyb and HSINAC inhibited the GA(3) up-regulation of alpha-amylase expression in aleurone, both were activators of transcription in yeast, and the green fluorescent protein-HSI fusion proteins were localized in the nucleus. These results are consistent with the model that HSI transcription factors act downstream of HvSPY as negative regulators and that they in turn could activate other negative regulators, forming the HvSPY negative regulator-signaling pathway for GA response.

Base Sequence↗
PubMed2004

Interactions between ethylene and gibberellins in phytochrome-mediated shade avoidance responses in tobacco.

Plants respond to proximate neighbors with a suite of responses that comprise the shade avoidance syndrome. These phytochrome-mediated responses include hyponasty (i.e. a more vertical orientation of leaves) and enhanced stem and petiole elongation. We showed recently that ethylene-insensitive tobacco (Nicotiana tabacum) plants (Tetr) have reduced responses to neighbors, showing an important role for this gaseous plant hormone in shade avoidance. Here, we investigate interactions between phytochrome signaling and ethylene action in shade avoidance responses. Furthermore, we investigate if ethylene acts in these responses through an interaction with the GA class of hormones. Low red to far-red light ratios (R:FR) enhanced ethylene production in wild-type tobacco, resulting in shade avoidance responses, whereas ethylene-insensitive plants showed reduced shade avoidance responses. Plants with inhibited GA production showed hardly any shade avoidance responses at all to either a low R:FR or increased ethylene concentrations. Furthermore, low R:FR enhanced the responsiveness of hyponasty and stem elongation in both wild-type and Tetr plants to applied GA(3), with the stem elongation process being more responsive to GA(3) in the wild type than in Tetr. We conclude that phytochrome-mediated shade avoidance responses involve ethylene action, at least partly by modulating GA action.

Darkness↗
PubMed2005

A gibberellin-regulated calcineurin B in rice localizes to the tonoplast and is implicated in vacuole function.

Many developmental and environmental signals are transduced through changes in intracellular calcium concentrations, yet only a few calcium-binding proteins have been identified in plants. Calcineurin B-like (CBL) proteins are calcium-binding proteins that are thought to function as plant signal transduction elements. RNA profiling using a rice (Oryza sativa cv Nipponbare) oligonucleotide microarray was used to monitor gene expression in de-embryonated rice grains. This analysis showed that a putative rice CBL gene responded to gibberellic acid, but not abscisic acid, treatment. The CBL gene family in rice contains at least 10 genes and these have extensive similarity to the CBLs of Arabidopsis (Arabidopsis thaliana). In yeast (Saccharomyces cerevisiae) two-hybrid assays, rice CBLs interact with the kinase partners of Arabidopsis CBLs. Only one rice CBL gene, OsCBL2, is up-regulated by GA in the aleurone layer. A homolog with 91% sequence identity to OsCBL2 was cloned from barley (Hordeum vulgare cv Himalaya), and designated HvCBL2. We examined the localization and function of OsCBL2 and HvCBL2 in rice and barley aleurone because changes in cytosolic calcium have been implicated in the response of the aleurone cell to GA. Green fluorescent protein translational fusions of OsCBL2 and OsCBL3 were localized to the tonoplast of aleurone cell protein storage vacuoles and OsCBL4-green fluorescent protein was localized to the plasma membrane. Data from experiments using antisense expression of OsCBL2 and HvCBL2 are consistent with a role for OsCBL2 in promoting vacuolation of barley aleurone cells following treatment with GA.

Amino Acid Sequence↗
PubMed2001

Release of reactive oxygen intermediates (superoxide radicals, hydrogen peroxide, and hydroxyl radicals) and peroxidase in germinating radish seeds controlled by light, gibberellin, and abscisic acid.

Germination of radish (Raphanus sativus cv Eterna) seeds can be inhibited by far-red light (high-irradiance reaction of phytochrome) or abscisic acid (ABA). Gibberellic acid (GA3) restores full germination under far-red light. This experimental system was used to investigate the release of reactive oxygen intermediates (ROI) by seed coats and embryos during germination, utilizing the apoplastic oxidation of 2',7'-dichlorofluorescin to fluorescent 2',7'-dichlorofluorescein as an in vivo assay. Germination in darkness is accompanied by a steep rise in ROI release originating from the seed coat (living aleurone layer) as well as the embryo. At the same time as the inhibition of germination, far-red light and ABA inhibit ROI release in both seed parts and GA3 reverses this inhibition when initiating germination under far-red light. During the later stage of germination the seed coat also releases peroxidase with a time course affected by far-red light, ABA, and GA3. The participation of superoxide radicals, hydrogen peroxide, and hydroxyl radicals in ROI metabolism was demonstrated with specific in vivo assays. ROI production by germinating seeds represents an active, developmentally controlled physiological function, presumably for protecting the emerging seedling against attack by pathogens.

Abscisic Acid↗