Journal Article

Up-Regulation of Mitochondrial Alternative Oxidase Concomitant with Chloroplast Over-Reduction by Excess Light

Keisuke Yoshida, Ichiro Terashima and Ko Noguchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 4, pages 606-614
Published in print April 2007 | ISSN: 0032-0781
Published online April 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcm033
Up-Regulation of Mitochondrial Alternative Oxidase Concomitant with Chloroplast Over-Reduction by Excess Light

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

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Alternative oxidase (AOX), the unique terminal oxidase in plant mitochondria, catalyzes the energy-wasteful cyanide (CN)-resistant respiration. Although it has been suggested that AOX might prevent chloroplast over-reduction through the efficient dissipation of excess reducing equivalents, direct evidence for this in the physiological context has been lacking. In this study, we examined the mitochondrial respiratory properties, especially AOX, connected to the accumulation of reducing equivalents in the chloroplasts and the activities of enzymes needed to transport the reducing equivalents. We used Arabidopsis thaliana mutants defective in cyclic electron flow around PSI, in which the reducing equivalents accumulate in the chloroplast stroma due to an unbalanced ATP/NADPH production ratio. These mutants showed higher activities of the enzymes needed to transport the reducing equivalents even in low-light growth conditions. The amounts of AOX protein and CN-resistant respiration in the mutants were also higher than those in the wild type. After high-light treatment, AOX, even in the wild type, was preferentially up-regulated concomitant with the accumulation of reducing equivalents in the chloroplasts and an increase in the activities of enzymes needed to transport reducing equivalents. These results indicate that AOX can dissipate the excess reducing equivalents, which are transported from the chloroplasts, and serve in efficient photosynthesis.

Keywords: Alternative oxidase; Arabidopsis thaliana; Cyanide-resistant respiration; Cyclic electron flow around PSI; Malate/oxaloacetate shuttle

Journal Article.  4637 words.  Illustrated.

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

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