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Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons Abstract Changes in the levels of cytosolic and chloroplastic isoforms of glutamine synthetase were examined in senescing radish (Raphanus sativus L. cv Comet) cotyledons by immunoblotting analysis using antibodies raised separately against maize glutamine synthetase isoforms. Translatable mRNAs for these isoforms were also examined by analyzing translation products from poly(A)+ RNA in a wheat germ system with the antibodies. The relative content of cytosolic isoform (GS1) increased twofold in the cotyledons that were placed in the dark for 72 hours to accelerate senescence, while that of chloroplastic isoform (GS2) declined to half of its initial level. The dark-treatment also increased the relative level of translatable mRNA for GS1 sevenfold after 72 hours, and decreased rapidly that for GS2 and for other nuclear-coded chloroplast proteins as well. Cotyledons also accumulated GS1 mRNA when they became senescent after a lengthy growth period under continuous light. These observations suggested that GS1 genes were activated, while those for GS2 were repressed, and eventually the population of the enzyme was altered in senescent cotyledonary cells. The role of increased cytosolic enzyme is discussed in relation to the nitrogen metabolism in senescent leaves. 2 Present address: Kihara Institute for Biological Research, Yokohama City University, Mutsukawa, Minami-ku, Yokohama 232, Japan. 1 Supported by a grant (Original and Creative Research Project on Biotechnology) from the Research Council, Ministry of Agriculture, Forestry and Fisheries, and also in part from a Grant-in-Aid for Scientific Research on Priority Areas (Molecular Basis of Totipotency of Plant Cells) from the Ministry of Education, Science and Culture of Japan. This content is only available as a PDF. © 1988 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Plant Physiology Oxford University Press

Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Kawakami, Naoto; Watanabe, Akira
Plant Physiology , Volume 88 (4) – Dec 1, 1988
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References (27)

Publisher
Oxford University Press
Copyright
Copyright © 2021 American Society of Plant Biologists
ISSN
0032-0889
eISSN
1532-2548
DOI
10.1104/pp.88.4.1430
Publisher site
See Article on Publisher Site

Abstract

Abstract Changes in the levels of cytosolic and chloroplastic isoforms of glutamine synthetase were examined in senescing radish (Raphanus sativus L. cv Comet) cotyledons by immunoblotting analysis using antibodies raised separately against maize glutamine synthetase isoforms. Translatable mRNAs for these isoforms were also examined by analyzing translation products from poly(A)+ RNA in a wheat germ system with the antibodies. The relative content of cytosolic isoform (GS1) increased twofold in the cotyledons that were placed in the dark for 72 hours to accelerate senescence, while that of chloroplastic isoform (GS2) declined to half of its initial level. The dark-treatment also increased the relative level of translatable mRNA for GS1 sevenfold after 72 hours, and decreased rapidly that for GS2 and for other nuclear-coded chloroplast proteins as well. Cotyledons also accumulated GS1 mRNA when they became senescent after a lengthy growth period under continuous light. These observations suggested that GS1 genes were activated, while those for GS2 were repressed, and eventually the population of the enzyme was altered in senescent cotyledonary cells. The role of increased cytosolic enzyme is discussed in relation to the nitrogen metabolism in senescent leaves. 2 Present address: Kihara Institute for Biological Research, Yokohama City University, Mutsukawa, Minami-ku, Yokohama 232, Japan. 1 Supported by a grant (Original and Creative Research Project on Biotechnology) from the Research Council, Ministry of Agriculture, Forestry and Fisheries, and also in part from a Grant-in-Aid for Scientific Research on Priority Areas (Molecular Basis of Totipotency of Plant Cells) from the Ministry of Education, Science and Culture of Japan. This content is only available as a PDF. © 1988 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Journal

Plant Physiology – Oxford University Press

Published: Dec 1, 1988

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