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L Rappaport

Publications and source records attributed to L Rappaport.

At least 127 records · Page 7Linked to original sources
PubMed1971

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VIII. Early Effects of Gibberellin A(3) and Abscisic Acid on Ultrastructure.

Using the electron microscope, we compared the effects of abscisic acid and gibberellin A(3) on excised buds from resting potato (Solanum tuberosum L.) tubers. Cells of abscisic acid-treated buds became progressively more vacuolated during a 12-hour time course study as compared with control (water) and gibberellin A(3)-treated buds. Concentric configurations of endoplasmic reticulum were present in apical cells of freshly excised buds. After about 6 hours these configurations began to open and disperse, and after 12 hours, intact concentric configurations were no longer evident. Both abscisic acid and gibberellin A(3) induced opening and dispersal of the concentric configurations, sometimes as early as 0.5 hour after excision and treatment with hormones.

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PubMed1970

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VII. Effect of Abscisic and Gibberellic Acids on Nucleic Acid Synthesis in Excised Buds.

The effect of gibberellin A(3) (10(-4)m) and abscisic acid (10(-4)m), applied separately and together, on incorporation of (3)H-thymidine and (3)H-uridine into DNA and RNA of buds from freshly harvested potatoes was investigated. In some treatments apical buds in intact tubers were treated three times daily for 3 days with test solution before the buds were excised and treated an additional 12 hours in Petri dishes. In other treatments, untreated buds were excised and treated 12 hours. Irrespective of length of treatment, gibberellin A(3) slightly promoted synthesis of DNA and RNA, and abscisic acid essentially blocked such synthesis, in both the presence and absence of gibberellin A(3).

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PubMed1970

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VI. Biochemical Changes Induced in Excised Potato Buds by Gibberellic Acid.

The rest period of the potato tuber was studied in relation to certain biochemical changes that are induced by gibberellic acid (GA(3)). The concentration of reducing sugars in excised plugs with buds treated with 10(-4)m GA(3) decreased in the first 4 hours after treatment and then rapidly increased up to 70 hours. The pattern in control buds was similar, but the changes occurred more slowly. The response to GA(3) is temperature-dependent and is not limited to any particular tissue of the tuber. The concentration of reducing sugars in excised buds increased proportionally to the log of the concentration of GA(3) in a range from 10(-8) to 10(-4)m. At 10(-3)m, GA(3) slightly inhibited production of reducing sugars. Malonate inhibits the initial decrease and the subsequent increase in reducing sugars in control buds, but not the increase induced by GA(3).Total protein in buds was not influenced by 10(-4)m GA(3) over a period of 40 hours, nor did activity of alpha-amylase increase significantly until 20 hours after beginning of treatment. Invertase activity was present initially and, in the presence of GA(3), increased after 20 hours. GA(3) had no effect on starch phosphorylase activity, which was always present and remained steady over the 20-hour test period.In short term experiments the rate of protein synthesis and synthesis of specific protein fractions were not affected by 10(-4)m GA(3), as measured by the incorporation of l-phenylalanine-U-(14)C or by experiments with (14)C- and (3)H- labeled l-phenylalanine or l-leucine.

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PubMed1968

Role of gibberellins in stem elongation and flowering in radish.

The relationship among gibberellins, CCC, vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA(3) had no additional effect. Gibberellin A(3) (60 mug total) was not able to induce flowering in nonvernalized plants grown on 8-hour days, but it did increase the percentage of nonvernalized plants that flowered under long days from 60 to 100.Gibberellin content of vernalized seedlings increased within the first 24 hours after seedlings were transferred to the greenhouse. Content reached a peak in the first 4 days after transfer and thereafter remained constant. Essentially no gibberellin was found in 2 day-old non-vernalized (control) seedlings of comparable size to the vernalized ones. Gibberellin content in the controls reached a peak on the fourth day of growth in the greenhouse; thereafter, it decreased steadily.Bolting was inhibited slightly by CCC when applied during vernalization; it was almost completely inhibited when CCC was applied after seed vernalization. Extraction experiments revealed that CCC actually reduced the gibberellin content when applied during or after vernalization. The dwarfing agent, however, had essentially no effect on flowering. We concluded that gibberellins likely play a direct role in bolting of ;Miyashige-sofuto' radish, but probably are not directly functional in initiating flowering.

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PubMed1966

Isolation, Crystallization, and Partial Identification of Potato Factor II from Potato Tubers.

The isolation, crystallization, and partial identification of potato factor II, a stimulator from the chemically neutral fraction of potato extract, is described. The compound was originally found to stimulate elongation of dwarf peas grown under red light, a gibberellin bioassay. It melts between 137 degrees and 139 degrees . In paper chromatography it migrates to R(F) 0.62 in isopropyl alcohol: ammonium hydroxide: H(2)O (10:1:1, v/v). Based on infrared and NMR data, it does not contain a lactone ring and possibly possesses an amide radical and an OH(-) group, as well as many methylene radicals. Potato factor II may be similar to certain of the fatty acid derivatives previously reported to stimulate growth of excised sections, but it is unique in that it stimulates growth of intact plants. This effect points to the need for completely separating neutral from acid gibberellin-like substances when the latter are assayed on dwarf peas.

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PubMed1966

Variations in endogenous gibberellins in developing bean seeds I. Occurrence of neutral and acidic substances.

Activities of separated and chromatographed substances in the nonacidic, acidic ethyl acetate and acidic butanol fractions from bean seeds, Phaseolus vulgaris L., cv. Bountiful and Kentucky Wonder, were measured in the Progress No. 9 dwarf pea bioassay grown under red light. Activity in the nonacidic fraction was shown to be attributable only to neutral substances and was free of acidic gibberellin-like substances. As the seed matures, neutral substances and one of the acidic butanol-soluble substances (B-I) increase in activity. The acidic ethyl acetate substances and butanol-soluble substance (B-II) initially increase and then almost disappear.

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PubMed1966

Variations in Endogenous Gibberellins in Developing Bean Seeds II. Changes Induced in Acidic and Neutral Fractions by GA(1).

Immature (8-mm), medium mature (11-mm), and mature green (16- and 17-mm) bean seeds (Phaseolus vulgaris L. cv. Kentucky Wonder and Bountiful) were incubated in gibberellin A(1) solutions for 24 hours at 20 degrees . Extracts from the seeds were separated into nonacidic, acidic ethyl acetate, and acidic butanol fractions. These were chromatographed. The eluates of the chromatograms were tested on Progress No. 9 dwarf peas grown under red light. The level of neutral gibberellin-like substances remained unchanged in immature seed, but they increased markedly in mature green seeds. Coincident with increased levels of the neutral substances, there were significant decreases in acidic ethyl acetate-soluble gibberellin-like substances, including applied GA(1), and in 1 acidic butanol-soluble gibberellin-like substance. Seed incubation in GA(1) brought about increased activity of substance B-II in immature and medium mature seeds. The level of butanol-soluble gibberellin-like substance B-I in seeds of any size was not affected by incubation in GA(1). Considering the marked increases in activity induced in the neutral fraction and the decreases in activity of certain eluates from the chromatograms of the acidic fractions, it was concluded that the neutral fraction may serve as a reserve form of gibberellins in the dry seed. The acidic ethyl acetate substances and substance B-II may be required for normal development of the bean seed.

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PubMed1966

Ethylene as a factor regulating the growth of pea epicotyls subjected to physical stress.

Pea epicotyls (Pisum sativum, cv. Alaska) were enclosed in chambers in which their elongation was restricted by means of a foam neoprene stopper or by a medium of glass beads. These treatments increased evolution of ethylene and resulted in reduced length and increased diameter of both the internodes and the cells of the internodes. These responses increased with increasing degrees of restriction. A time-sequence study of the emergence of epicotyls through 90 mm of glass beads showed that an accelerated evolution of ethylene preceded a reduction in elongation. As the epicotyls elongated through the glass bead medium and less resistance was encountered, evolution of ethylene declined and rapid elongation was resumed. The morphological and anatomical effects of a 120-mm column of glass beads were duplicated by applied ethylene concentrations of 0.2 ppm or less. Evolution of CO(2) was inhibited slightly by the ethylene treatments. The data indicate that production of ethylene by pea epicotyls is increased by nonwounding physical stress, and that the ethylene acts as an endogenous growth regulator, decreasing elongation and increasing diameter in response to increasing increments of stress.

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