Journal Article

Are Isocitrate Lyase and Phospho<i>enol</i>pyruvate Carboxykinase Involved in Gluconeogenesis during Senescence of Barley Leaves and Cucumber Cotyledons?

Zhi-Hui Chen, Robert P. Walker, Richard M. Acheson, László I. Técsi, Astrid Wingler, Peter J. Lea and Richard C. Leegood

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 41, issue 8, pages 960-967
Published in print August 2000 | ISSN: 0032-0781
Published online August 2000 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcd021
Are Isocitrate Lyase and Phosphoenolpyruvate Carboxykinase Involved in Gluconeogenesis during Senescence of Barley Leaves and Cucumber Cotyledons?

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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The aim of this study was to investigate whether gluconeogenesis catalysed by phosphoenolpyruvate carboxykinase (PEPCK) occurs during leaf senescence. This was addressed by determining changes in the abundance and intercellular location of enzymes necessary for gluconeogenesis during the senescence of barley leaves and cucumber cotyledons. PEPCK was never present in barley leaves, despite the presence of large amounts of isocitrate lyase (ICL), a key enzyme of the glyoxylate cycle, and of its product, glyoxylate. Although PEPCK was present in non-senescent cucumber cotyledons, its abundance declined during senescence. Throughout senescence, PEPCK was only present in the trichomes and vasculature, whereas ICL was located in mesophyll cells. Pyruvate,Pi dikinase (PPDK) which, in concert with NAD(P)-malic enzyme, is also capable of catalysing gluconeogenesis, was present in non-senescent barley leaves and cucumber cotyledons, but in both plants its abundance decreased greatly during senescence. The abundance of ICL was greatly reduced in senescing detached barley leaves by either illumination or by co-incubation with sucrose, and greatly increased in darkened attached barley leaves. These results argue against the large-scale occurrence of gluconeogenesis during senescence catalysed either by PEPCK or PPDK. In cucumber cotyledons, PEPCK may play a role in metabolic processes linked to the export of amino acids, a role in which phosphoenolpyruvate carboxylase may also be involved. The amount of ICL was increased by starvation and during senescence may function in the conversion of lipids to organic acids, which are then utilised in the mobilisation of amino acids from leaf protein.

Keywords: Key words: Senescence — Barley — Cucumber — Gluconeogenesis — Immunolocalisation — Isocitrate lyase — Phosphoenolpyruvate carboxykinase — Pyruvate,Pi dikinase.; Abbreviations: ICL, isocitrate lyase; PEPC, phosphoenolpyruvate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; PPDK, pyruvate,phosphate dikinase; Rubisco, ribulose 1,5-bisphosphate carboxylase-oxygenase.

Journal Article.  5173 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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