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PubMed1966

Effect of Photoperiodic Floral Induction on the Metabolism of a Gibberellin Precursor, (-)-Kaurene, in Pharbitis nil.

Pharbitis nil seedlings rapidly metabolized (-)-kaurene-17-(14)C administered to the cotyledons. Less than 20% of the radioactivity was recovered by extraction of the cotyledons on the following day. Of this the major metabolite was an unidentified acidic material which did not correspond chromatographically to any of the known gibberellins.Significant differences were observed between the radioactivity found in the buds of a group of seedlings subjected to photoperiodic floral induction and that in a noninduced group. In both cases almost all of this radioactivity was in the neutral fraction, but thin-layer chromatography of these fractions revealed that the induced group contained 2 or more labelled components which were either absent or present in lower concentrations in the noninduced group.

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PubMed1967

Auxin-gibberellin interaction in apical dominance.

Indoleacetic acid and gibberellic acid were added to decapitated light-grown ;Alaska' pea seedlings as substitutes for the intact apex in the control of apical dominance. Of various concentrations and combinations tried, a combination of 1% indoleacetic acid + 1% gibberellic acid was the most inhibiting to side bud growth. The greatest degree of hormonally induced side bud inhibition was achieved when seedlings were deprived of soil nutrients.

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PubMed1968

Far-red Sensitive Dark Processes Essential for Light- and Gibberellin-induced Germination of Lettuce Seed.

The action of prolonged far-red on seed germination was studied in Lactuca sativa L. var. Grand Rapids. Exposure of imbibed seeds to 6 hours far-red before the application of gibberellic acid (GA(3)) and thiourea completely prevented germination. Using GA(3), this far-red was effective after the sixth hour of imbibition. At 6, 12, and 18 hours of imbibition equal durations of far-red had equal effects. The kinetics of far-red action was investigated: it was found that although far-red for several hours, irrespective of the energy level, was needed for maximum inhibition, shorter durations (15 and 30 mins) were also appreciably effective provided they were followed by several hours darkness before the supply of GA(3). This is taken to indicate the existence of labile product(s) of the action of a far-red sensitive pigment. Evidence is provided for the existence of promotive dark processes controlled by this pigment, which are essential for germination whether triggered by GA(3), thiourea or red-light. A model for the operation of the pigment system is proposed and its role in the germination mechanism of this seed is discussed.

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PubMed1968

Effects of Kinetin, IAA, and Gibberellin on Ethylene Production, and Their Interactions in Growth of Seedlings.

Kinetin in concentrations of 10(-8) to 10(-4)m, stimulated ethylene production in 3 and 4-day old etiolated seedlings of Alaska pea (Pisum sativum L. var. Alaska). Seedlings of other species responded similarly. The response to kinetin depended on the age of the seedlings.Kinetin alone did not influence ethylene production in 6-day old stem sections, but it greatly increased the enhancing effect of IAA.Gibberellic acid had no effect on ethylene production by pea seedlings during the first 6 days of growth. Ethylene and gibberellic acid are antagonistic in their effects on growth of the seedlings; ethylene interfered severely with the action of gibberellic acid but did not completely suppress it.The inhibitors cycloheximide, cupferron, and N-ethylmaleimide, caused considerable inhibition of kinetin-induced ethylene production but were much less effective in the endogenous ethylene-forming system.

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PubMed1970

Grafting and gibberellin effects on the growth of tall and dwarf peas.

Tall peas var. Alaska and dwarf peas var. Progress No. 9 were grafted onto their own roots or reciprocally grafted to determine the rootstock effect on the growth of the stem. In all cases the grafted stems grew the same as their ungrafted controls regardless of which rootstock they were grown on. When similarly grafted plants were supplied with gibberellic acid, good graft unions did not inhibit its translocation. This evidence supports the thesis that the mechanism controlling stem growth in peas is located in the stem and that the roots have no direct control over this mechanism.

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PubMed1971

The regulation of cambial division and secondary xylem differentiation in xanthium by auxins and gibberellin.

Cambial division continued in decapitated Xanthium plants without concomitant xylem fiber differentiation. The application of indoleacetic acid to these plants did not affect the production of cambial derivatives or induce xylem fiber differentiation. When naphthaleneacetic acid was applied either to the second internode or to the stump of a lateral shoot, xylem fiber differentiation was induced in the newly formed cambial derivatives on the xylem side of the cambium in the stem. When naphthaleneacetic acid was applied unilaterally, xylem fiber differentiation was restricted to that side of the stem in the first internode and hypocotyl. Naphthaleneacetic acid also enhanced the production of cambial derivatives. Gibberellic acid enhanced cambial derivative production but did not affect the differentiation of xylem fibers. Similar numbers of cambial derivatives were produced in some naphthaleneacetic acid-treated plants in which xylem fiber differentiation was induced and in gibberellic acid-treated plants which did not differentiate xylem. When naphthaleneacetic acid was applied 72 hours after decapitation, the oldest of the cambial derivatives on the xylem side failed to develop into fibers although younger cells did. These results suggest that auxin has its direct effect on the induction of xylem differentiation rather than the induction of divisions prerequisite to differentiation.

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PubMed1971

Gibberellin-induced Fertility in the Fern Ceratopteris thalictroides (L.) Brongn.

Treatment of the homosporous fern Ceratopteris thalictroides L. sporophyte with gibberellic acid results in fertile fronds appearing 3 to 5 weeks after treatment. The hetero-blastic leaf sequence is markedly reduced, and the entire life cycle can be completed in 3 months on defined medium. Treatment with gibberellic acid also stimulates the accumulation of starch in mature leaves.

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PubMed1975

Gibberellin response in lettuce hypocotyl sections.

Excised lettuce (Lactuca sativa L.) hypocotyl sections retain the ability to elongate in response to gibberellic acid (GA(3)) addition. In 48 hr at 30 C a GA(3)-treated segment more than doubles while a control segment elongates less than 50%. Auxin has no detectable effect on this system. Sensitivity to GA(3) is not decreased by apex or root removal. Of the experimental variables tested, temperature, sucrose, and preincubation in water affect growth both with and without GA(3). Blue and far red light inhibit growth without GA(3); this inhibition is reversed by GA(3). Potassium chloride stimulates growth of illuminated sections treated with GA(3) but has no effect on control growth. When sections are incubated in the dark, KCl has a promotive effect on elongation.

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PubMed1976

Transport and metabolism of h-gibberellin a(1) in dioecious cucumber seedlings.

The transport of (3)H-GA(1) through hypocotyl segments of cucumber (Cucumis sativus L.) was found to be nonpolar. The transport of (3)H-GA(1) was increased by pretreatment with relatively high concentrations of either IAA or Ethephon (2-chloroethylphosphonic acid). Hypocotyl segments from plants of a gynoecious genotype transported more (3)H-GA(1) than those of an androecious. The metabolism of (3)H-GA(1) in hypocotyl segments was neither related to the sex genotype of the cucumber plant nor influenced by pretreatment with Ethephon. The primary metabolite of GA(1) was suggested to be GA(8). Two other suspected metabolites were not identified. Differences in the endogenous GA of gynoecious and androecious plants could not be accounted for by transport differences.

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PubMed1977

Tannins as gibberellin antagonists in the synthesis of alpha-amylase and Acid phosphatase by barley seeds.

The tannins chebulinic acid or tara tannin were added to an incubation system in which GA(3) induces enzyme synthesis in endosperm half seeds of barley (Hordeum vulgare L.). The activity of amylase and acid phosphatase in the incubation medium was reduced compared to the activity in the medium after incubation with GA(3) alone. When embryo half seeds of barley were incubated with chebulinic acid or tara tannin in the absence of added GA(3), the enzyme activity of the incubation medium was also reduced. The activity of preformed enzymes obtained from endosperm half seeds previously induced with GA(3) was not reduced by the addition of tannin. Comparisons were made of the amount of enzyme activity from breis of aleurone layers incubated with GA(3) in the presence and absence of tannins. The amounts of activity were relatively small and approximately equal in both cases, indicating that secretion from the aleurone was not blocked by the tannins. The reduction of enzyme activity caused by tannins in both endosperm and embryo half seeds could be completely reversed by the addition of GA(3).

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PubMed1977

Dormancy in Dioscorea: Gibberellin-Induced Inhibition or Promotion in Seed Germination of D. tokoro and D. tenuipes in Relation to Light Quality.

Effects of light and gibberellic acid (GA(3)) application on the germination of Dioscorea tokoro Makino and Dioscorea tenuipes Franch. et Savat. were observed. For complete germination, seeds of both species required prechilling in moist condition before incubation at a higher temperature. Red light irradiation during the incubation after the prechilling promoted germination; blue, green, or far red light markedly inhibited the germination of both species.Application of GA(3) induced complicated changes in the germination of both species in relation to light quality. In the germination of D. tokoro, GA(3) inhibited in the dark and red; however, it promoted germination in blue and far red light. GA(3) promoted germination of D. tenuipes in the dark and in blue, green, or far red light. These phenomena are explainable by assuming two counteractive reactions (germination-promoting and germination-inhibiting) which are both activated by applied GA(3).

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