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PubMed1966

Auxin and gibberellin effects on cell growth and starch during abscission in cotton.

An increase in starch content of cells in the abscission zone of the cotton explant appeared correlated with an increase in number of cells. A large increase in the number of cells in the abscission zone, concomitant with an increase in starch content, followed treatment with gibberellin as compared to auxin. In the final stages of abscission starch was hydrolyzed in the cells of the separation layer. Some starch remained after the petiole abscised.A positive phloroglucinol-hydrochloric acid reaction in the cells of the petiole distal to the line of separation indicated the presence, not of lignin, but of soluble sugars and uronic acids. This reaction was especially intense following gibberellic acid treatment.It was concluded that gibberellin in accelerating abscission leads to (1) an increase in cell number and starch content in the abscission zone, (2) the hydrolysis of starch in the separation layer just before abscission, and (3) the breakdown of polysaccharides and the release of soluble sugars and uronic acids. Auxin, an abscission retardant, either delays or prevents these events.

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PubMed1967

Barley Endosperm Bioassay for Gibberellins. II. Application of the Method.

The use of the modified endosperm bioassay in conjunction with techniques for extracting and paper chromatographing extracts, and the application of statistical analyses to the results, is reported. The modified procedure has not altered the relative response to different gibberellins, though an analysis of many standard curves indicates that at least 1 feature of the bioassay system is still uncontrolled. A comparison of this bioassay with 15 others indicates that the endosperm response may have wide applicability in explorations of the physiological effects of gibberellins.

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PubMed1968

Contents and recovery of gibberellins in monoecious and gynoecious cucumber plants.

Diffusates from seedlings and root exudates from 6-week-old plants of a monoecious line of cucumber, Cucumis sativus L., contained considerably higher levels of gibberellin-(GA-) like substances than did those from plants of an isogenic gynoecious line. Most of the GA-like activity was found in a chromatogram region typical of GA(1) and GA(3); some activity, particularly in root exudates, appeared also at an R(F) similar to that of GA(4) and GA(7).When seedlings were treated with (3)H-labeled GA(1), more radioactivity was found in the diffusates from monoecious seedlings than from gynoecious ones. The same was true of biological activity in root diffusates from older plants which had been treated with gibberellin A(4+7).In conjunction with evidence present in literature, these results support the idea that endogenous GAs play a part in the regulation of sex expression in cucumber, relatively high levels favoring the formation of staminate flowers.

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PubMed1969

Gibberellin and CCC Effects on Flowering and Growth in the Long-day Plant Lemna gibba G3.

The application of gibberellic acid (GA(3)) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA(3) concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A(7) was used instead of GA(3).The addition of the plant growth retardant CCC [(2-chloroethyl) trimethylammonium chloride] to the culture medium on long days resulted in almost complete inhibition of flowering at 10(-3) M. Vegetative growth was also inhibited to some extent. With CCC at 10(-3) M the simultaneous addition of GA(3) resulted in partial reversal of flower inhibition with 0.3 mg/l GA(3) being optimal. The inhibition of vegetative growth as measured by fresh and dry weight was also partially reversed by GA(3), but the threshold concentration for reversal of flower inhibition was at least 10 times lower than that for inhibition of vegetative growth.These results are interpreted as indicating that gibberellins are important for flowering in the non-rosette long-day plant L. gibba G3, but apparently are present in non-limiting concentrations on short days.

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PubMed1970

Radioactive gibberellin a(5) and its metabolism in dwarf peas.

Radioactive gibberellin A(5) ((3)H-GA(5)) was synthesized from gibberellic acid. When it was applied to dwarf peas grown in the dark, an average of 3% was converted to another acid gibberellin within 48 hours. The biological activity of the metabolite did not account for the response to applied GA(5). GA(5) is therefore assumed to be biologically active per se.(3)H-GA(5) did not appear to form a stable complex with a macromolecule in pea shoots. When injected into dwarf pea pods, (3)H-GA(5) was readily metabolized by maturing seed to more water-soluble substances and to two other acidic compounds. This metabolism continued even throughout germination of the seed without reconversion of the metabolites to GA(5). It is concluded that "bound" GA(5) plays no part in the germination of dwarf pea seeds.

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PubMed1971

Incorporation of C-Kaurene into the Gibberellin of a Higher Plant (Pharbitis nil Chois).

Enzymic formation of (14)C-kaurene from 2-(14)C-mevalonate was carried out with a cell-free system of Cucurbita pepo L. It was shown that either heating of the enzyme system or the addition of the growth retardants (2-chloroethyl)-trimethylammonium chloride and 2'-isopropyl-4' (trimethylammonium chloride)-5'-methylphenyl piperidine-1-carboxylate prevented the synthesis of (14)C-kaurene. Experiments in which (14)C-kaurene was applied to seedlings of Pharbitis nil revealed that the kaurene is converted to at least two compounds present in the acidic ethyl acetate fraction, containing free gibberellins, as well as in the second acidic ethyl acetate fraction, containing the released bound gibberellins. One of the compounds cochromatographed with gibberellic acid; the other compound is possibly a break-down product of gibberellic acid with no biological activity.

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PubMed1974

Response of seedlings of a dwarf and a normal strain of watermelon to gibberellins.

Hypocotyl and root elongation in a dwarf and a normal strain of watermelon (Citrullus lanatus [Thunb.] Matsu.) in the absence or presence of different gibberellins was investigated in seedlings grown under gold fluorescent light or in darkness. The normal strain, "Sugar Baby," responded only slightly to the gibberellic acids employed. At appropriate concentrations all of the gibberellic acids were capable of normalizing growth in the monorecessive dwarf strain, WB-2, in darkness or in light. Gibberellins A(4+7) and A(7) were effective in stimulating hypocotyl elongation at concentrations 10 to 15 times lower than that needed for a response to GA(1) or GA(3). Dark-grown dwarfs responded to about a 3-fold lower concentration of GA(4+7) than those grown in light.In contrast to hypocotyl elongation, root elongation was greater in the dwarf than in the normal strain. Concentrations of gibberellic acids which enhanced hypocotyl elongation of WB-2 plants, inhibited root growth proportionately.Anatomically, the response of the dwarf strain to GA(4+7) was primarily in terms of increased cell division. Dark-enhanced elongation of both SB and WB-2 was due almost solely to increased cell elongation. The results suggest that, at least in some species, a major component of dark-enhanced growth (or light-inhibited growth) is physiologically distinct from gibberellic acid-stimulated elongation.

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PubMed1977

Growth and gibberellin a(1) metabolism in excised lettuce hypocotyls.

Excised lettuce (Lactuca sativa L. cv. Arctic) hypocotyls retain the ability to elongate in response to exogenously supplied gibberellic acid and gibberellin A(1) (GA(1)). We have studied the relationship between metabolism of GA(1) and elongation in this tissue. In 24 hours at 28 C, hypocotyls treated with 3 mum GA(1) double in length while controls elongate less than 45%. After an exogenous hormone supply is removed, hypocotyls continue to grow faster than untreated controls, although as the hormone application time is decreased, the GA(1) concentration required to effect a given length change increases. [(3)H]GA(1) was used to determine rates of hormone uptake, efflux, and metabolism. In the presence of [(3)H]GA(1), hypocotyls accumulate and metabolize lable for at least 24 hours. When the exogenous label is removed, the amount of acidic GA in the hypocotyl declines rapidly to a constant level while ethyl acetate-insoluble metabolites increase rapidly to a constant level. Lable accumulation and metabolism at any time are proportional to the external GA(1) concentration below 50 mum GA(1). Chromatographic analysis of radioactive compounds present in tissue extracts suggests that unaltered GA(1) is the major component of the acidic ethyl acetate-soluble fraction, and gibberellin A(8) is a minor component. The ethyl acetate-insoluble fraction appears to contain an unidentified GA(1) metabolite with chromatographic properties similar to those of GA(1). The strong retention of accumulated GA(1) confirms the possibility of a continuing requirement for GA(1) during the sustained response to a GA(1) "pulse" but raises the question of accessibility of the stored hormone for growth promotion.

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PubMed1980

Fractionation of gibberellins in plant extracts by reverse phase high performance liquid chromatography.

In studies on endogenous plant gibberellins (GAs), reverse phase (Bondapak C(18)) high performance liquid chromatography (HPLC) has proved to be a useful method for the fractionation of plant extracts. The behavior of 18 authentic GAs in such a chromatographic system is described. The main factors determining chromatographic behavior are the degree and the position of hydroxylation of the GA. Generally, dihydroxylated GAs elute before monohydroxylated GAs, whereas 13-hydroxylated GAs elute before 3-hydroxylated GAs. The number of carboxyl groups and the degree of saturation of the A-ring have little effect. For 20-carbon GAs, the oxidation state at C-20 is only relevant insofar as GAs having a methyl group at this position elute later than those with other groups (lactone, aldehyde, or carboxyl).As an illustration of the use of reverse phase HPLC, the endogenous GAs of immature seeds of Pharbitis nil L., strain "Violet," were reinvestigated. The presence of gibberellins A(3), A(5), A(17), A(20), and A(29) was confirmed by gas-liquid chromatography-mass spectrometry. In addition, two other GAs, A(19) and A(44), were also identified in extracts of this material.

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PubMed1980

On the uptake, metabolism and retention of [h] gibberellin a(1) by barley aleurone layers at low temperatures.

Barley (c.v. Himalaya) aleurone layers were incubated in [(3)H]gibberellin A(1) (GA(1)) at low temperatures. At 3 and 4 C, (3)H-activity was steadily accumulated in aleurone layers, and this accumulation was correlated with significant [(3)H]GA(1) metabolism. At 1 and 1.5 C, metabolism could not be detected, and at these temperatures aleurone layers equilibrated with the [(3)H]GA(1) concentration in the incubation medium. At equilibrium, the total amount of (3)H-activity per unit volume in the aleurone layers was higher than in the incubation medium. Aleurone layers incubated at 0.5 C for 72 hours with [(3)H]GA(1) in the presence of saturating levels of carrier GA(1) consistently retained lower levels of (3)H-activity than when incubated in [(3)H]GA(1) alone. The retention of [(3)H]GA(1) was unaffected by saturating levels of carrier GA(8). GA(1) retained by barley aleurone layers that were incubated at 0.5 C for 72 hours was able to induce alpha-amylase synthesis when aleurone layers were subsequently washed and transferred to a gibberellin-free medium at 25 C.

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PubMed1981

Induction of glyconeogenic enzymes by gibberellin a(3) in endosperm of castor bean seedlings.

Seedlings of castor bean (Ricinus communis cv. Hale) were exposed to gibberellin A(3) (GA(3)) (100 micromolar) for periods up to 20 hours. Endosperm homogenates were fractionated on linear sucrose gradients and enzymes in mitochondria, glyoxysome, and cytosol fractions were assayed. Gibberellin treatment resulted in increases in the activities of enzymes in all three compartments. There were also enzymes in all three compartments which were not affected by exogenous applications of GA(3). The isozymes of l-asparate-alpha-ketoglutarate aminotransferase in both mitochondria and glyoxysomes were induced coordinately, whereas the isozymes of citrate synthase and malate dehydrogenase were not. All gluconeogenic enzymes in glyoxysomes are induced by GA(3). With the exception of the mitochondrial malate dehydrogenase isozyme, all enzymes of the tricarboxylic acid cycle believed to participate in glyconeogenesis were increased. The cytosolic enzymes malate dehydrogenase, phosphoenolpyruvate carboxykinase, and fructose bisphosphatase were induced, but the levels of pyruvate kinase and enolase were not affected by GA(3) treatment.

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PubMed1983

Role of Endogenous Plant Growth Regulators in Seed Dormancy of Avena fatua: II. Gibberellins.

Gibberellin A(1) (GA(1)) was identified by combined gas chromatographymass spectrometry as the major biologically active gibberellin (GA) in seeds of wild oat (Avena fatua L.) regardless of the depth of dormany or stage of imbibition. Both unimbibed dormant and nondromant seeds contained similar amounts of GA(1) as estimated by the d5-maize bioassay. During imbibition, the level of GA(1) declined in both dormant and non-dormant seeds, although the decline was more rapid in dormant seeds. Only in imbibing nondormant seeds did the GA biosynthesis inhibitor, 2-chloroethyltrimethyl ammonium chloride (CCC), cause a reduction in the level of GA(1) from that observed in control seeds. These results are interpreted as an indication that while afterripening does not cause a direct change in the levels of GAs during dry storage, it does induce a greater capacity for GA biosynthesis during imbibition.Nondormant seeds imbibed in the presence of 50 millimolar CCC germinated equally as well as untreated seeds. When wild oat plants were fed CCC throughout the entire life cycle, viable seeds were produced that lacked detectable GA-like substances. These seeds afterripened at a slightly slower rate than the controls. Moreover, completely afterripened (nondormant) seeds from plants fed CCC continuously contained no detectable GA-like substances, and when these seeds germinated, dwarf seedlings were produced, indicating GA biosynthesis was inhibited during and after germination. In total, these results suggest that the increased capacity for GA biosynthesis observed in imbibing nondormant seeds is not a necessary prerequisite for germination. It is therefore possible that GA biosynthesis in imbibing nondormant seeds is one of many coordinated biochemical events that occur during germination rather than an initiator of the processes leading to germination.

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PubMed1984

Role of gibberellin in the growth response of submerged deep water rice.

We have shown previously that ethylene, which accumulates in the air spaces of submerged stem sections of rice (Oryza sativa L. cv "Habiganj Aman II"), is involved in regulating the growth response caused by submergence. The role of gibberellins in the submergence response was studied using tetcyclacis (TCY), a new plant growth retardant, which inhibits gibberellin biosynthesis. Stem sections excised from plants that had been watered with a solution of 1 micromolar TCY for 7 to 10 days did not elongate when submerged in the same solution or when exposed to 1 microliter per liter ethylene in air. Gibberellic acid (GA(3)) at 0.3 micromolar overcame the effect of TCY and restored the rapid internodal elongation in submerged and ethylene-treated sections to the levels observed in control sections that had not been treated with TCY. The effect of 0.01 to 0.2 micromolar GA(3) on internodal elongation was enhanced two- to eight-fold when 1 microliter per liter ethylene was added to the air passing through the chamber in which the sections were incubated. GA(3) and ethylene caused a similar increase in cell division and cell elongation in rice internodes. Thus, ethylene may cause internodal elongation in rice by increasing the activity of endogenous GAs. In internodes from which the leaf sheath had been peeled off, growth in response to submergence, ethylene and GA(3) was severely inhibited by light.

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PubMed1985

Role of polyamines in gibberellin-induced internode growth in peas.

To determine the requirement for polyamines in gibberellin (GA) induced internode growth polyamine content was measured in internodes of peas of various internode phenotypes (slender, tall, dwarf, nana) with and without applied gibberellin (GA(3)) and polyamine synthesis inhibitors. Polyamines were assayed as dansyl derivatives which were separated by reverse phase high performance liquid chromatography and detected by fluorescence spectrophotometry. The amounts of polyamines in the different genetic lines of peas, which differed in internode lengths and extractable GA content, correlated with the extent of internode elongation. High polyamine concentrations were associated with young internodes and decreased with internode expansion. Extremely short internodes of nana plants without GA exhibited equal or higher amine concentrations relative to internodes of other lines of peas and GA-stimulated nana seedlings. The polyamine synthesis inhibitors, alpha-difluoromethylornithine and alpha-difluoromethylarginine, independently or in combination, inhibited polyamine accumulation and internode elongation of tall peas and GA-stimulated nana plants. Agmatine and putrescine restored growth and endogenous polyamine content to variable degrees. However, exogenous polyamines were not effective in promoting growth unless intracellular amines were partially depleted.These results suggest that polyamines do not have a role in cell elongation, but may be required to support cell proliferation. Polyamines do not mediate the entire action of GA in internode growth of peas since GA induction of growth involves both cell division and cell elongation, whereas polyamines appear to affect cell division only.

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PubMed1985

Identification of Endogenous Gibberellins from Salix pentandra.

Gibberellins A(1), A(19), A(20), and A(29) have been identified by sequential high-performance liquid chromatography retention time (Rt) and combined gas chromatography-mass spectrometry (Rt and characteristic mass spectra) from elongating shoots of Salix pentandra L. Gibberellins A(1) and A(19) were also detected in purified extracts from male and female flowers (catkins) of S. pentandra.

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PubMed1987

Physiological Studies of a Synthetic Gibberellin-Like Bioregulator: II. Effect of Site of Application on Biological Activity.

The biological activity of the synthetic gibberellin agonist AC-94,377 (1-[3-chlorophthalimido]-cyclohexanecarboxamide) in certain plants is strictly dependent on the site of application. Root application of AC-94,377 at concentrations greater than or equal to 1 micromolar to seedlings of dwarf corn (Zea mays L. var d(5)), dwarf rice (Oryza sativa L. cv Tan-ginbozu), and sunflower (Helianthus annuus L. cv NK265) seedlings resulted in readily measurable gibberellin-like biological activity. Application of up to 10 micrograms of AC-94,377 to the shoots of these same species had no effect. AC-94,377 was metabolized to more polar products in both dwarf corn and sunflower seedlings. After 4 days of continuous root treatment with [(14)C]AC-94,377, greater than 70% of the recovered (14)C was found in the form of unmetabolized AC-94,377. In contrast, only 30 to 40% of the recovered (14)C was unmetabolized 4 days after shoot treatment. Translocation studies demonstrated that the movement of [(14)C]AC-94,377 was limited and occurred almost exclusively in an apoplastic fashion. Four days after leaf treatment, less than 1.5% (corn) or 4% (sunflower) of the recovered radioactivity had moved away from the treated area. It was concluded that the lack of biological activity of AC-94,377 following shoot treatment resulted principally from limited phloem mobility and to a lesser extent from accelerated metabolic breakdown.

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PubMed1988

Dual Effect of Light on the Gibberellin- and Nitrate-Stimulated Seed Germination of Sisymbrium officinale and Arabidopsis thaliana.

Red light (R) has a dual effect on the seed germination of the two related species Arabidopsis thaliana and Sisymbrium officinale. The two species provide different means to separate the light-effects. In S. officinale, stimulation of germination by R depends on the stimultaneous presence of nitrate (light-effect I). The effect of both factors is completely blocked by tetcyclacis, an inhibitor of gibberellin (GA)-biosynthesis. Addition of a mixture of gibberellins A(4) and A(7) (GA(4+7)) antagonizes the inhibition. In the absence of nitrate, R shifts germination to lower GA-requirement (light-effect II). In A. thaliana a similar second light-effect is seen on the GA-requirement of GA-deficient ga-1 mutant seeds. R stimulates germination of wild type seeds in water (light-effect I). For both species, light-effect I shows a fluence threshold value of approximately 10(-5) moles per square meter, which is independent of the nitrate concentration. Increasing nitrate concentrations narrow the fluence-range required for maximal germination whereby the product of nitrate concentration and fluence value determines the germination level, indicating a multiplicative interaction between R and nitrate. Fluence-response curves for light-effect II are similar for both species. Germination occurs in the range of 10(-6) to 10(-2) moles per square meter fluence. The maximal level of germination is determined by the level of dark-germination and light-effect II. Increasing GA(4+7) concentrations induce a shift to lower fluence values. It is shown that in the second effect the co-action of R and exogenous GA(4+7) is clearly additive. It is concluded that light-effect I induces a chain of events leading to GA biosynthesis. Light-effect II seems to enhance the sensitivity of the seeds to GAs.

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