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PubMed1978

Endogenous gibberellin and abscisic Acid content as related to senescence of detached lettuce leaves.

Levels of gibberillins (GAs) and of abscisic acid (ABA) in attached leaves of romaine lettuce (Lactuca sativa L.) declined as the leaf became older. The time course of changes in hormone levels, determined in detached lettuce leaves kept in darkness, revealed that a sharp decline in GAs accompanied by a moderate rise in ABA occurred before the onset of chlorophyll degradation. As senescence advanced, no GAs could be detected and a considerable rise of ABA was observed. A similar sequence of hormonal modifications, but more pronounced, was observed in the course of accelerated senescence induced by either Ethephon or water stress. When kinetin or GA(3) was applied to detached leaves, the loss of chlorophyll and the rise in ABA were reduced. Bound GAs were detected in senescent leaves. They were not found in the kinetin-treated leaves, which contained a relatively high level of free GAs. The results suggest that senescence in detached romaine lettuce leaves is connected with a depletion of free GAs and cytokinins, which is thereafter followed by a great surge in ABA.

Journal Article↗
PubMed1979

Role of auxin and gibberellin in differentiation of primary Phloem fibers.

The hypothesis that auxin and gibberellic acid (GA(3)) control the differentiation of primary phloem fibers is confirmed for the stem of Coleus blumei Benth. Indoleacetic acid (IAA) alone sufficed to cause the differentiation of a few primary phloem fibers. In long term experiments auxin induced a considerable number of fibers in mature internodes. GA(3) by itself did not exert any effect on fiber differentiation. Combinatiosn of IAA with GA(3) completely replaced the role of the leaves in primary phloem fiber differentiation qualitatively and quantitatively. Although the combined effect of the two growth hormones diminished considerably with increasing distance from the source of induction, auxin with GA(3) or IAA alone induced fibers in a few internodes below the application site. When various combinations of both hormones were applied, high concentrations of IAA stimulated rapid differentiation of fibers with thick secondary walls, while high levels of GA(3) resulted in long fibers with thin walls. The size of the primary phloem fibers correlated with the dimensions of the differentiating internode, thereby providing evidence that both growth regulators figure in the control of stem extension. High IAA/low GA(3) concentrations have an inhibitory effect on internode elongation, whereas low IAA/high GA(3) concentrations promote maximal stem elongation.

Journal Article↗
PubMed1986

Translocation of paclobutrazol, a gibberellin biosynthesis inhibitor, in apple seedlings.

The [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1- yl)-pentan-3-ol] (paclobutrazol, PP333) measured in apple seedlings (;York Imperial' Malus domestica Borkh) was confirmed by gas chromatography-mass spectrometry. Data showed that paclobutrazol was taken up through roots and transported primarily in the xylem through the stems and accumulated in leaves. No detectable basipetal movement of paclobutrazol in apple seedlings was found.

Journal Article↗
PubMed1986

The influence of dwarfing interstocks on the distribution and metabolism of xylem-applied [h]gibberellin a(4) in apple.

The influence of an interstock of the dwarfing cultivar M9 and the nondwarfing cultivar MM115 on the distribution and metabolism of labeled gibberellic acid A(4) ([(3)H]GA(4)) of high specific radioactivity (5.18 x 10(10) becquerel per millimole) applied to the xylem of the rootstock in grafted apple (Malus x domestica Borkh.) trees was compared. Free [(3)H] GA-like metabolites of [(3)H]GA(4), including putative GA(1), GA(2), GA(3), and GA(34), as well as various (3)H-putative GA glucosyl conjugates were detected in stem segments from both cultivars. M9 interstocks reduced the total uptake of [(3)H]GA(4) and decreased the proportion of (3)H metabolites transported to the shoots and leaves of scions. The M9 interstock tissue and adjacent rootstock and scion tissue retained a much greater amount and a higher proportion of the label than did comparable tissue of the nondwarfing MM115 interstock. In addition, the amount and proportion of free [(3)H]GAs was higher, and the proportion of putative [(3)H]GA glucosyl conjugates lower, in M9 interstocks compared to MM115. These effects of the dwarfing interstock on GA distribution and metabolism indicate a significant role for GAs in any satisfactory explanation of the dwarfing mechanism in apple.

Journal Article↗
PubMed1988

Synthesis and biological activity of an azido derivative of paclobutrazol, an inhibitor of gibberellin biosynthesis.

A photolabile azido derivative of the kaurene oxidase inhibitor 1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl) pentan-3-ol (paclobutrazol) has been synthesized for use as a photoaffinity labeling agent. The compound was tested as an inhibitor of the oxidation of ent-kaurene catalyzed by cell-free preparations from endosperm of Cucurbita maxima. The I(50) of the azido derivative was 9.5 nanomolar, which compares well with that of paclobutrazol (6.3 nanomolar in our measurements). The azido compound bound to Cytochrome P-450 in microsomes from Cucurbita maxima, and induced a Type II spectral change, with an apparent binding constant of 0.24+/-0.04 micromolar.

Journal Article↗
PubMed1989

Changes in Assimilated C Distribution and Soluble Acid Invertase Activity of Zinnia elegans Induced by Uniconazol, an Inhibitor of Gibberellin Biosynthesis.

The physiological aspects involved in the Uniconazol-induced morphological changes in Zinnia elegans Jacq. cv Red Sun were clarified biochemically by determining the distribution of assimilated (13)C as well as the soluble acid invertase activity. The application of Uniconazol, (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-pentane-3-ol, reduced the growth of stems and leaves without affecting the roots. In addition, the translocation of assimilated (13)C from leaf to other organs was inhibited, with the stem being more restricted than the root. These changes were matched by a corresponding decrease in the specific activity of soluble acid invertase. Subsequent treatment of GA(3) counteracted these effects of Uniconazol. Moreover, the total and reducing sugar content was closely correlated with the soluble acid invertase activity in the stem. It is concluded that the reduction in invertase activity of stem is a biochemical manifestation of the retardation of stem growth induced by Uniconazol.

Journal Article↗
PubMed1990

Partial Purification and Characterization of the Gibberellin A(20) 3beta-Hydroxylase from Seeds of Phaseolus vulgaris.

The GA(20) 3beta-hydroxylase present in immature seeds of Phaseolus vulgaris has been partially purified and characterized. The physical characteristics of the enzyme are similar to those of the GA 2beta-hydroxylases present in mature and immature seeds of Pisum sativum. It is acid-labile, hydrophobic, and of M(r) 45,000. The enzyme catalyzes the synthesis of GA(1), GA(5), and GA(29) from GA(20). Activity is dependent upon the presence of Fe(2+), ascorbate, 2-oxoglutarate, and oxygen. 2-Oxoglutarate does not function as a cosubstrate; in the presence of the enzyme, succinate is not a reaction product.

Journal Article↗
PubMed1990

The Role of Auxin and Gibberellin in Controlling Lignin Formation in Primary Phloem Fibers and in Xylem of Coleus blumei Stems.

The hypothesis that auxin (IAA) and gibberellic acid (GA(3)) control the formation of lignin is confirmed for the primary phloem fibers and for the secondary xylem in the stem of Coleus blumel Benth. Indoleacetic acid alone, or a combination of high IAA/low GA(3) (w/w), induced short phloem fibers with thick secondary walls, that contained lignin rich in syringyl units (high ratio of syringyl/guaiacyl). On the other hand, a combination of high GA(3)/low IAA (w/w), which promoted the differentiation of long phloem fibers with thin walls, decreased the relative content of the syringyl units (low syringyl/guaiacyl ratio). In the secondary xylem, these hormonal treatments yielded only slight changes in the noncondensed monomeric guaiacyl units, confirming the relative stability of the guaiacyl lignification pattern in this tissue. In the xylem, indoleacetic acid alone, or a combination of high IAA/low GA(3) induced lignin poor in syringyl units (low syringyl/guaiacyl ratio). A combination of high GA(3)/low IAA promoted a relatively slight increase in syringyl yield, indicating greater responsiveness of the syringyl lignification pattern to growth regulators. The possible functional and technological significance of our results is discussed.

Journal Article↗
PubMed1991

Genetic Regulation of Development in Sorghum bicolor: V. The ma(3) Allele Results in Gibberellin Enrichment.

Sorghum bicolor genotypes, near isogenic with different alleles at the third maturity locus, were compared for development, for responsiveness to GA(3) and a GA synthesis inhibitor, and occurrence and concentrations of endogenous GAs, IAA, and ABA. At 14 days the genotype 58M (ma(3) (R)ma(3) (R)) exhibited 2.5-fold greater culm height, 1.75-fold greater total height, and 1.38-fold greater dry weight than 90M (ma(3)ma(3)) or 100M (Ma(3)Ma(3)). All three genotypes exhibited similar shoot elongation in response to GA(3), and 58M showed GA(3)-mediated hastening of floral initiation when harvested at day 18 or 21. Both 90M and 100M had exhibited hastening of floral initiation by GA(3) previously, at later application dates. Tetcyclacis reduced height, promoted tillering, and delayed flowering of 58M resulting in plants which were near phenocopies of 90M and 100M. Based on bioassay activity, HPLC retention times, cochromatography with (2)H(2)-labeled standards on capillary column GC and matching mass spectrometer fragmentation patterns (ions [m/z] and relative abundances), GA(1), GA(19), GA(20), GA(53), and GA(3) were identified in extracts of all three genotypes. In addition, based on published Kovats retention index values and correspondence in ion masses and relative abundances, GA(44) and GA(17) were detected. Quantitation was based on recovery of coinjected, (2)H(2)-labeled standards. In 14 day-old-plants, total GA-like bioactivity and GA(1) concentrations (nanograms GA/gram dry weight) were two- to six-fold higher in 58M than 90M and 100M in leaf blades, apex samples, and whole plants while concentrations in culms were similar. Similar trends occurred if data were expressed on a per plant basis. GA(1) concentrations for whole plants were about two-fold higher in 58M than 90M and 100M from day 7 to day 14. Concentrations of ABA and IAA did not vary between the genotypes. The results indicate the mutant allele ma(3) (R) causes a two- to six-fold increase in GA(1) concentrations, does not result in a GA-receptor or transduction mutation and is associated with phenotypic characteristics that can be enhanced by GA(3) and reduced by GA synthesis inhibitor. These observations support the hypothesis that the allele ma(3) (R) causes an overproduction of GAs which results in altered leaf morphology, reduced tillering, earlier flowering, and other phenotypic differences between 58M and 90M or 100M.

Journal Article↗
PubMed1996

Flowering as metamorphosis: two sequential signals regulate floral initiation in Lolium temulentum.

We investigated floral initiation in the long-day monocot Lolium temulentum, strain Ceres, by culturing apices explanted from photoperiodically induced plants at various times after one inductive long day onto medium with, and without, gibberellin. Apices cultured on the first day after the inductive long day usually required gibberellin in the medium to initiate floral morphogenesis while apices explanted on the second day after induction did not require gibberellin. Apices explanted on the first day after induction onto medium without gibberellin grew vegetatively for many days but a several-day exposure to culture medium with gibberellin at any time caused most apices to initiate floral morphogenesis. The gibberellin synthesis inhibitor, ancymidol, when applied to plants before apex excision and when present in the culture medium reduced floral initiation by more than 50% in the absence of added gibberellin in the medium, but it was ineffective in the presence of gibberellin. These results indicated that floral initiation in photoperiodically induced plants resulted from two signals acting at the apex. The first signal induced the apex into a florally determined state and then the second signal, gibberellin, elicited expression of the florally determined state. Leaf removal and culture of apices from plants previously treated with gibberellin provided evidence that the leaf-applied gibberellin did not itself act on the apex to cause floral determination or initiation. Rather, the exogenous gibberellin appeared to stimulate the production of a signal in the leaves that then led to floral initiation.

Culture Techniques↗
PubMed2005

Dissection of the phosphorylation of rice DELLA protein, SLENDER RICE1.

DELLA proteins are repressors of gibberellin signaling in plants. Our previous studies have indicated that gibberellin signaling is derepressed by SCF(GID2)-mediated proteolysis of the DELLA protein, SLENDER RICE1 (SLR1), in rice. In addition, the gibberellin-dependent increase of phosphorylated SLR1 in the loss-of-function gid2 mutant suggests that the SCF(GID2)-mediated degradation of SLR1 might be initiated by gibberellin-dependent phosphorylation. To confirm the role of phosphorylation of SLR1 in its gibberellin-dependent degradation, we revealed that SLR1 is phosphorylated on an N-terminal serine residue(s) within the DELLA/TVHYNP and polyS/T/V domain. However, gibberellin-induced phosphorylation in these regions was not observed in the gid2 mutant following the constitutive expression of SLR1 under the control of the rice actin1 promoter. Treatment with gibberellin induced both the phosphorylated and non-phosphorylated forms of SLR1 with similar induction kinetics in gid2 mutant cells. Both the phosphorylated and non-phosphorylated SLR1 proteins were degraded by gibberellin treatment with a similar half-life in the rice callus cells, and both proteins interacted with recombinant glutathione S-transferase (GST)-GID2. These results demonstrate that the phosphorylation of SLR1 is independent of its degradation and is dispensable for the interaction of SLR1 with the GID2/F-box protein.

Chromatography, Ion Exchange↗
PubMed2000

Hormonal interactions in the control of Arabidopsis hypocotyl elongation.

The Arabidopsis hypocotyl, together with hormone mutants and chemical inhibitors, was used to study the role of auxin in cell elongation and its possible interactions with ethylene and gibberellin. When wild-type Arabidopsis seedlings were grown on media containing a range of auxin concentrations, hypocotyl growth was inhibited. However, when axr1-12 and 35S-iaaL (which have reduced auxin response and levels, respectively) were grown in the same conditions, auxin was able to promote hypocotyl growth. In contrast, auxin does not promote hypocotyl growth of axr3-1, which has phenotypes that suggest an enhanced auxin response. These results are consistent with the hypothesis that auxin levels in the wild-type hypocotyl are optimal for elongation and that additional auxin is inhibitory. When ethylene responses were reduced using either the ethylene-resistant mutant etr1 or aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, auxin responses were unchanged, indicating that auxin does not inhibit hypocotyl elongation through ethylene. To test for interactions between auxin and gibberellin, auxin mutants were grown on media containing gibberellin and gibberellin mutants were grown on media containing auxin. The responses were found to be the same as wild-type Arabidopsis seedlings in all cases. In addition, 1 microM of the auxin transport inhibitor 1-naphthylphthalmic acid does not alter the response of wild-type seedlings to gibberellin. Double mutants were made between gibberellin and auxin mutants and the phenotypes of these appear additive. These results indicate that auxin and gibberellin are acting independently in hypocotyl elongation. Thus auxin, ethylene, and gibberellin each regulate hypocotyl elongation independently.

Arabidopsis↗
PubMed1969

Induction of fern spore germination.

Light-induced germination of Anemia spores can be inhibited by AMO-1618, a selective inhibitor of gibberellin biosynthesis. The inhibitor has no effect on gibberellin-induced dark germination and its inhibition of light-induced germination can be reversed by supplying gibberellin. Barley-endosperm bioassay of concentrates of medium in which spores are imbibed in light reveals the presence of substances with gibberellin-like activity; assay of medium from dark-imbibed spores does not. Simultaneous exposure of spores to sub-optimal levels of light and gibberellin leads to additivity of effect on germination level. Uptake of labeled gibberellin by spores in light is similar to that in darkness. The implications of these findings for the light-dependent synthesis of a gibberellin-like germination substance are discussed. The bearing of the observations upon understanding the interaction of light and gibberellins in seeds of higher plants is considered.

Journal Article↗
PubMed2000

Possible involvement of phosphoinositide-Ca2+ signaling in the regulation of alpha-amylase expression and germination of rice seed (Oryza sativa L.).

We have studied the effects of neomycin, a potent inhibitor of inositol phospholipid-specific phospholipase C (PLC), on the germination of rice seed and the gibberellin-induced expression of alpha-amylase in the aleurone layer and the scutellar tissues. It was shown that, in the absence of exogenous Ca2+, neomycin markedly reduced the germination speed and seedling growth of rice seeds and inhibited the gibberellin-induced expression of alpha-amylase in both secretory tissues. In addition, neomycin decreased the formation of inositol 1,4,5-trisphosphate (IP3) in the gibberellin-treated aleurone layer and the scutellar tissues. However, the inhibitory effects on the germination speed and the expression of alpha-amylase activity were overcome by supplementation of Ca2+. In addition, gibberellin elevated the level of IP3, and ABA prevented the gibberellin-induced formation of IP3, although ABA alone did not alter the IP3 level. The expression of a membrane-bound PLC molecule in rice aleurone layer was shown to be induced by gibberellin, and the gibberellin-induced expression of PLC was markedly delayed by treatment with ABA. These results strongly suggest that the phosphoinositide-Ca2+ signal transduction pathway may play an important role in the gibberellin-induced expression of alpha-amylase molecules closely related to the germination processes of rice seed.

Calcium Signaling↗
PubMed1999

Expression of a functional single-chain antibody against GA24/19 in transgenic tobacco.

An anti-gibberellin A24/19 single-chain Fv gene was constructed from gamma and kappa genes cloned from a hybridoma cell line producing monoclonal antibody against gibberellin A24/19, biosynthetic precursors of gibberellin A4/1 which are biologically active per se. The single-chain Fv gene was introduced into tobacco plants after the binding activity of the single-chain Fv expressed in Escherichia coli was confirmed. When the single-chain Fv expression is targeted to endoplasmic reticulum, the plants could accumulate the single-chain Fv protein with the antigen binding activity up to 3.6% of the total soluble protein. On the other hand, when the expression is targeted to cytosol, accumulation of the single-chain Fv protein was not detected at all. The dwarf phenotype of the transgenic plants expressing the single-chain Fv protein, together with the preliminary analytical data indicating a decreased level of gibberellin A1 in the dwarf transgenics, suggested that the single-chain Fv decreased the concentration of bioactive gibberellins by trapping and inhibiting the metabolism of gibberellin A24 and/or A19 to gibberellin A4 and/or A1.

Antibodies, Monoclonal↗