THE EFFECT OF GIBBERELLIC ACID ON GROWTH AND INDOLE METABOLISM OF DWARF PEA PLANTS.
Item
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Title
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THE EFFECT OF GIBBERELLIC ACID ON GROWTH AND INDOLE METABOLISM OF DWARF PEA PLANTS.
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Identifier
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AAI8708292
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identifier
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8708292
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Creator
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HUSAIN, ZAHEED.
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Contributor
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Jack G. Valdovinos
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Date
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1987
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Plant Physiology
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Abstract
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A study was conducted to describe the pathway of biosynthesis of indole-3-acetic acid (IAA) from tryptophan (TPP) and determine the effect of gibberellic acid (GA(,3)) on this system. Treatment of dwarf peas (Pisum sativum L. var Little Marvel) with 0.8 ug GA(,3)/plant resulted in increase in plant height along with increased auxin level. A cell-free preparation of pea shoot tissue was able to convert D,L-tryptophan-3-('14)C into different indole metabolites. The acidic and neutral fractions obtained after TPP incubation were subjected to thin-layer chromatography. In the neutral fraction, two peaks of radioactivity were found and these matched the Rfs for indole-acetaldehyde (IAAld) and indole-3-ethanol (IEt). One major peak of radioactivity was observed in the radiochromatograms of the acidic fraction and it corresponded with authentic IAA. The IEt observed as a product of tryptophan metabolism was further characterized by TLC in different solvent systems and by color reaction with the Ehrlich and perchloric Salkowski reagents.;The enzymes involved in the conversion of TPP to IAA involved, in the first step, a transaminase (tryptophan aminotransferase, EC 2(.)6(.)1) reaction. The aminotransferase was purified about 82-fold by acetone precipitation and Sephadex G-200 filtration. It had a pH optima of 8.5 and a temperature optima of 40(DEGREES)C. With (alpha)-ketoglutarate a co-substrate, the enzyme transaminated aromatic as well as alphatic amino acids including D,L-tryptophan, D,L-alanine and D,L leucine. D-TPP was found to be more effective than L-TPP as a substrate. GA(,3) treatment to dwarf pea plants results in increase in the specific activity of the enzyme over the observation period. In the second step of TPP conversion, IPyA is decarboxylated by an enzyme to IAAld. In plants treated with GA(,3), the enzyme activity was significantly higher three days after treatment but remained unaffected at all other stages when observations were made. The final step enzyme is a dehydrogenase that can convert IAAld to IAA in the presence of MAD as a co-factor.;Dwarf pea tissue was also found to convert IAAld to IEt by the activity of a reductase enzyme and it was purified about 75-fold. The activity of the enzyme in GA-treated plants was higher than controls up to the third day, declined and then increased again around the sixth day following treatment. The presence of IAA in the enzyme assay, drastically reduced the conversion of IAAld to IEt. It is suggested that IEt itself has a more important regulatory role in plant growth and three different bio-assays showed it to be biologically active. (Abstract shortened with permission of author.).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Biology
