SEARCH · PubMed Health

Results for “GIBBERELLINS”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources

PubMed1993

Germination and Dormancy of Abscisic Acid- and Gibberellin-Deficient Mutant Tomato (Lycopersicon esculentum) Seeds (Sensitivity of Germination to Abscisic Acid, Gibberellin, and Water Potential).

Germination responses of wild-type (MM), abscisic acid (ABA)-deficient (sitw), and gibberellin (GA)-deficient (gib-1) mutant tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds to ABA, GA4+7, reduced water potential ([psi]), and their combinations were analyzed using a population-based threshold model (B.R. Ni and K.J. Bradford [1992] Plant Physiol 98: 1057-1068). Among the three genotypes, sitw seeds germinated rapidly and completely in water, MM seeds germinated more slowly and were partially dormant, and gib-1 seeds did not germinate without exogenous GA4+7. Times to germination were inversely proportional to the differences between the external osmoticum, ABA, or GA4+7 concentrations and the corresponding threshold levels that would either prevent ([psi]b, log[ABAb]) or promote (log[GAb]) germination. The sensitivity of germination to ABA, GA4+7, and [psi] varied widely among individual seeds in the population, resulting in a distribution of germination times. The rapid germination rate of sitw seeds was attributable to their low mean [psi]b (-1.17 MPa). Postharvest dormancy in MM seeds was due to a high mean [psi]b (-0.35 MPa) and a distribution of [psi]b among seeds such that some seeds were unable to germinate even on water. GA4+7 (100 [mu]M) stimulated germination of MM and gib-1 seeds by lowering the mean [psi]b to -0.75 MPa, whereas ABA inhibited germination of MM and sitw seeds by increasing the mean [psi]b. The changes in [psi]b were not due to changes in embryo osmotic potential. Rather, hormonal effects on endosperm weakening opposite the radicle tip apparently determine the threshold [psi] for germination. The analysis demonstrates that ABA- and GA-dependent changes in seed dormancy and germination rates, whether due to endogenous or exogenous growth regulators, are based primarily upon corresponding shifts in the [psi] thresholds for radicle emergence. The [psi] thresholds, in turn, determine both the rate and final extent of germination within the seed population.

Journal Article↗

PubMed1993

Thermoinductive Regulation of Gibberellin Metabolism in Thlaspi arvense L. (II. Cold Induction of Enzymes in Gibberellin Biosynthesis).

Vernalization of Thlaspi arvense L. results in the alteration of gibberellin (GA) metabolism such that the metabolism and turnover of the GA precursor ent-kaur-16-en-19-oic acid (kaurenoic acid) is dramatically increased. This cold-induced change in GA metabolism is restricted to the shoot tip, the site of perception of cold in this species (J.P. Hazebroek, J.D. Metzger [1990] Plant Physiol 94: 157-165). In the present report additional biochemical information about the nature of this low-temperature-regulated process is provided. The endogenous levels of kaurenoic acid in leaves and shoot tips of plants were estimated by combined gas chromatography-chemical ionization mass spectrometry at various times after 4 weeks of vernalization at 6[deg]C. The endogenous levels in shoot tips declined 10-fold by 2 d after the plants were returned to 21[deg]C; this decline continued such that there was nearly 50-fold less kaurenoic acid by 10 d after the end of vernalization. No effect of vernalization on the endogenous levels of kaurenoic acid in leaves was observed. An in vitro enzyme assay was developed to monitor changes in the ability of tissues to convert kaurenoic acid to ent-7[alpha]-hydroxykaur-16-en-19-oic acid (7-OH kaurenoic acid). The activity of this enzyme rapidly increased in microsomal extracts from shoot tips following the end of vernalization. No thermoinduced increase in activity was observed in leaves. The enzymic oxidation of ent-kaurene to ent-kaurenol was also induced in shoot tips by vernalization. However, this reaction does not appear to be rate limiting for GA biosynthesis, because substantial amounts of kaurenoic acid accumulated in noninduced shoot tips. These results corroborate our hypothesis that the conversion of kaurenoic acid to 7-OH kaurenoic acid is the primary step in GA metabolism regulated by vernalization in Thlaspi shoot tips.

Journal Article↗

PubMed1995

Vernalization and Gibberellin Physiology of Winter Canola (Endogenous Gibberellin (GA) Content and Metabolism of [3H]GA1 and [3H]GA20.

Winter canola (Brassica napus cv Crystal) is an oilseed crop that requires vernalization (chilling treatment) for the induction of stem elongation and flowering. To investigate the role of gibberellins (GAs) in vernalization-induced events, endogenous GA content and the metabolism of [3H]GAs were examined in 10-week vernalized and nonvernalized plants. Shoot tips were harvested 0, 8, and 18 d postvernalization (DPV), and GAs were purified and quantified using 2H2-internal standards and gas chromatography-selected ion monitoring. Concentrations of GA1, GA3, GA8, GA19, and GA20 were 3.1-, 2.3-, 7.8-, 12.0-, and 24.5-fold higher, respectively, in the vernalized plants at the end of the vernalization treatment (0 DPV) relative to the nonvernalized plants. Thermoregulation apparently occurs prior to GA19 biosynthesis, since vernalization elevated the concentration of all of the monitored GAs. [3H]GA20 or [3H]GA1 was applied to the shoot tips of vernalized and nonvernalized plants, and after 24 h, plants were harvested at 6, 12, and 15 DPV. Following high-performance liquid chromatography analyses, vernalized plants showed increased conversion of [3H]GA20 to a [3H]GA1-like metabolite and reduced conversion of [3H]GA1 or [3H]GA20 to polar 3H-metabolites, putative glucosyl conjugates. These results demonstrate that vernalization influences GA content and GA metabolism, with GAs serving as probable regulatory intermediaries between chilling treatment and subsequent stem growth.

Journal Article↗

PubMed1999

Regulation of gibberellin 20-oxidase and gibberellin 3beta-hydroxylase transcript accumulation during De-etiolation of pea seedlings.

Gibberellin (GA) 20-oxidase (GA 20-ox) and GA 3beta-hydroxylase (GA 3beta-hy) are enzymes that catalyze the late steps in the formation of active GAs, and are potential control points in the regulation of GA biosynthesis by light. We have investigated the photoregulation of the GA 20-ox and GA 3beta-hy transcript levels in pea (Pisum sativum L.). The GA 20-ox transcript level was higher in light-grown seedlings than in etiolated seedlings, whereas GA 3beta-hy mRNA accumulation was higher in etiolated seedlings. However, transfer of etiolated seedlings to light led to a 5-fold increase in the expression of both transcripts 4 h after transfer. GA 20-ox mRNA accumulation is regulated by both phytochromes A and B. Transfer to light also resulted in a 6-fold decrease in GA(1) levels within 2 h. These results suggest that the light-induced drop in GA(1) level is not achieved through regulation of GA 20-ox and GA 3beta-hy mRNA accumulation. The application of exogenous GA(1) to apical buds of etiolated seedlings prior to light treatments inhibited the light-induced accumulation of both GA 20-ox and GA 3beta-hy mRNA, suggesting that negative feedback regulation is an important mechanism in the regulation of GA 20-ox and GA 3beta-hy mRNA accumulation during de-etiolation of pea seedlings.

Darkness↗

PubMed1975

Metabolism of H-Gibberellin A(1) and H-Gibberellin A(4) by Phaseolus coccineus Seedlings.

[(3)H]-Gibberellin A(1) (GA(1)) and (3)H-GA(4) were applied separately to Phaseolus coccineus seedlings grown under red light. (3)H-GA(1) was converted to a compound with gas-liquid radiochromatography retention times identical to those of GA(8). (3)H-GA(4) underwent conversion to at least three metabolites, none of which corresponded to GA(1-38). The rate of metabolism of (3)H-GA(4) was significantly higher than that of (3)H-GA(1).

Journal Article↗

PubMed1976

Endogenous Gibberellins of Pine Pollen: III. Conversion of 1,2-[H]GA(4) to Gibberellins A(1) and A(34) in Germinating Pollen of Pinus attenuata Lemm.

Gibberellins A(1) and A(34) (possibly A(2)) were found as products of metabolism of 1,2-[(3)H]GA(4) during germination of Pinus attenuata pollen. The conversion from GA(4) to GA(1) and GA(34) occurred as hydroxylations at atoms C-13 and C-2 of the ent-gibberellane skeleton, respectively. Percentage interconversion of the GA(4) absorbed was in the range of 0.15 to 0.43% for GA(1) and 1.54 to 3.22% for GA(34). Identifications were made on a gas-liquid chromatograph with radioactive monitoring by comparison with standards.

Journal Article↗

PubMed1983

Gibberellins and heterosis in maize : I. Endogenous gibberellin-like substances.

Under controlled environment and/or field conditions, vegetative growth (height, internode length, leaf area, shoot dry weight, grain yield) was greater in an F(1) maize hybrid than in either parental inbred. Endogenous gibberellin (GA)-like substances in apical meristem cylinders were also higher in the hybrid than in either inbred, both on a per plant and per gram dry weight basis. There were no apparent qualitative differences in GA-like substances, however. Levels of GA-like substances in all genotypes were highest prior to tassel initiation. Chromatographic comparisons of the GA-like substances and authentic standards of GA native to maize on gradient-eluted SiO(2) partition and reverse-phase C(18) high-pressure liquid chromatography columns are described. No consistent differences in abscisic acid levels of the three genotypes were observed. This correlation of heterosis for endogenous GA-like substances with heterosis for growth suggests that amounts of endogenous GA may be related to hybrid vigor in maize.

Journal Article↗

PubMed1983

Gibberellins and Heterosis in Maize : II. Response to Gibberellic Acid and Metabolism of [H]Gibberellin A(20).

Two maize inbreds, CM7 and CM49, and CM7 x CM49, their F(1) hybrid (which displayed significant heterosis), were examined with regard to response to exogenous gibberellin A(3) (GA(3)), and in their ability to metabolize GA(20), a native GA of maize. The leaf sheath elongation response to GA(3) was far greater for the imbreds than for their hybrid. The inbreds also displayed significant elongation of the leaf blades in response to GA(3), whereas the hybrid was unaffected. Promotion of cell division in the leaf sheath of CM7 and the hybrid was effected by GA(3), but no promotion of cell elongation was observed in CM49, even though significant leaf sheath elongation occurred. Shoot dry weight of both inbreds was significantly increased by GA(3), but response by the hybrid in this parameter was slight and variable. Root dry weight of CM7 was significantly increased by GA(3), but was unchanged in CM49 and the hybrid. Thus, inbred shoot dry weight increases effected by GA(3) were not at the expense of the root system. Rapid metabolism of [2,3-(3)H]GA(20) occurred in all genotypes, although genotypic differences were observed. The hybrid had the highest rates of metabolism to GA glucosyl conjugate-like substances. Oxidative metabolism was also fastest in the hybrid, followed by CM7, and slowest in CM49, the slowest-growing inbred. Thus, rate of GA(20) metabolism is under genetic control in normal (i.e. not dwarfed) maize genotypes. These results, taken together with previous reports that the hybrid has significantly enhanced levels of endogenous GA-like substances, suggest that GA play a role in the expression of heterosis in maize.

Journal Article↗

PubMed1985

Competition for in vitro [h]gibberellin a(4) binding in cucumber by gibberellins and their derivatives.

The gibberellin (GA) binding properties of a cytosol fraction from hypocotyls of cucumber (Cucumis sativus L. cv National Pickling) were examined using a DEAE filter paper assay, [(3)H]GA(4), and over 20 GAs, GA derivatives and other growth regulators. The results demonstrate structural specificity of the binding protein for gamma-lactonic C-19 GAs with a 3 beta-hydroxyl and a C-6 carboxyl group. Additional hydroxylations of the A, C, or D ring of the ent-gibberellane skeleton and methylation of the C-6 carboxyl impede or abolish binding affinity. Bioassay data are generally supported by the in vitro results but significantly GA(9) and GA(36), both considered to be precursors of GA(4) in cucumber, show no affinity for the binding protein. The results are discussed in relation to the active site of the putative GA(4) receptor in cucumber.

Journal Article↗

PubMed1987

Internode Length in Pisum: Gene na May Block Gibberellin Synthesis between ent-7alpha-Hydroxykaurenoic Acid and Gibberellin A(12)-Aldehyde.

The elongation response of the gibberellin (GA) deficient genotypes na, ls, and lh of peas (Pisum sativum L.) to a range of GA-precursors was examined. Plants possessing gene na did not respond to precursors in the GA biosynthetic pathway prior to GA(12)-aldehyde. In contrast, plants possessing lh and ls responded as well as wild-type plants (dwarfed with AMO-1618) to these compounds. The results suggest that GA biosynthesis is blocked prior to ent-kaurene in the lh and ls mutants and between ent-7alpha-hydroxykaurenoic acid and GA(12)-aldehyde in the na mutant. Feeds of ent-[(3)H]kaurenoic acid and [(2)H]GA(12)-aldehyde to a range of genotypes supported the above conclusions. The na line WL1766 was shown by gas chromatography-mass spectrometry (GC-MS) to metabolize [(2)H]GA(12)-aldehyde to a number of[(2)H]C(19)-GAs including GA(1). However, there was no indication in na genotypes for the metabolism of ent-[(3)H]kaurenoic acid to these GAs. In contrast, the expanding shoot tissue of all Na genotypes examined metabolised ent-[(3)H]kaurenoic acid to radioactive compounds that co-chromatographed with GA(1), GA(8), GA(20), and GA(29). However, insufficient material was present for unequivocal identification of the metabolites. The radioactive profiles from HPLC of extracts of the node treated with ent-[(3)H]kaurenoic acid were similar for both Na and na plants and contained ent-16alpha,17-dihydroxykaurenoic acid and ent-6alpha,7alpha,16beta,17-tetrahydroxykaurenoic acid (both characterized by GC-MS), suggesting that the metabolites arose from side branches of the main GA-biosynthetic pathway. Thus, both Na and na plants appear capable of ent-7alpha-hydroxylation.

Journal Article↗

PubMed1989

Competition for in vitro [h]gibberellin a(4) binding in cucumber by substituted phthalimides: comparison with in vivo gibberellin-like activity.

Certain N-substituted phthalimides (NSPs) have gibberellin (GA)-like activity in a number of GA bioassays. The interaction between representative NSPs and a protein fraction from cucumber (Cucumis sativus L.) hypocotyls that has GA-binding characteristics consistent with those expected of GA receptors was studied. Analysis of in vitro equilibrium saturation data indicated the presence of only one class of high affinity [(3)H]GA(4) binding sites (K(d) approximately 30 nanomolar, n = 0.25 picomole per milligram of protein). In the presence of 6 or 60 micromolar 1-[3-chlorophthalimido]-cyclohexanecarboximide (AC-94,377), the K(d) for [(3)H]GA(4) increased, whereas the maximum number of saturable [(3)H]GA(4) binding sites did not change significantly. The dissociation of [(3)H]GA(4) from its binding sites was complex and was best described by a bi-exponential equation. AC-94,377 did not affect the rates of [(3)H]GA(4) dissociation from its binding sites. These results implied that AC-94,377 and [(3)H]GA(4) compete for binding to the same sites. A correlation was observed between the activity of over 20 NSPs in the cucumber hypocotyl bioassay and their in vitro affinity for the GA binding sites. Our observations lend further support to the notion that certain GA binding proteins in cucumber cytosol are GA receptors and also provide a molecular explanation for the GA-like in vivo activity of some NSPs.

Journal Article↗

PubMed2004

Gibberellin structure and function: biological activity and competitive inhibition of gibberellin 2- and 3-oxidases.

Some gibberellin (GA) analogues, especially with C-16,17 modifications of GA(5), can inhibit growth of plants apparently by acting as competitors with the endogenous substrate of GA biosynthetic enzymes. Here, we directly confirm the competitive action of GA derivatives but also show that some analogues may retain significant bioactivity. A recombinant 3-oxidase from pea, which converts GA(20) to bioactive GA(1), was inhibited by GA(5), and 16,17-dihydro-GA(5) derivatives, especially if the C-17 alkyl chain length was increased by up to three carbons or if the C-13 hydroxyl was acetylated. Genetic confirmation that GA(5) analogues target 3-oxidases in vivo was provided by comparing the growth response of a WT (LE) pea with a 3-oxidase mutant (le-1). Two pea 2-oxidases that inactivate bioactive GAs, were inhibited by GA(1) and GA(3) but were generally insensitive to GA(5) analogues. alpha-Amylase production by barley half-seeds in response to GA analogues provided a method to study their action when effects on GA biosynthesis were excluded. This bioactivity assay showed that 16,17-dihydro GA(5) analogues have some inherent activity but mostly less than for GA(5) (5-50-fold), which in turn was 100-fold less active than GA(1) and GA(3). However, although C-17 alkyl derivatives with one or two added carbons showed little bioactivity and were purely 3-oxidase inhibitors, adding a third carbon (the 17-n-propyl-16,17-dihydro GA(5) analogue) restored bioactivity to that of GA(5). Furthermore, this analogue has lost its capacity to inhibit stem elongation of Lolium temulentum (Mander et al., Phytochemistry 49:1509-1515, 1998a), although it strongly inhibits the 3-oxidase. Thus, the effectiveness of a GA derivative as a growth retardant will reflect the balance between its bioactivity and its capacity to inhibit the terminal enzyme of GA biosynthesis. The weaker growth inhibition in dicots including pea (approximately 10%) than in monocots such as L. temulentum (>35%) is suggestive of taxonomic differences in the bioactivity of GAs and/or their effects on GA biosynthesis.

Journal Article↗

PubMed1965