Journal Article

A Balanced PGR5 Level is Required for Chloroplast Development and Optimum Operation of Cyclic Electron Transport Around Photosystem I

Yuki Okegawa, Terri A. Long, Megumi Iwano, Seiji Takayama, Yoshichika Kobayashi, Sarah F. Covert and Toshiharu Shikanai

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 10, pages 1462-1471
Published in print October 2007 | ISSN: 0032-0781
Published online October 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcm116
A Balanced PGR5 Level is Required for Chloroplast Development and Optimum Operation of Cyclic Electron Transport Around Photosystem I

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PSI cyclic electron transport contributes markedly to photosynthesis and photoprotection in flowering plants. Although the thylakoid protein PGR5 (Proton Gradient Regulation 5) has been shown to be essential for the main route of PSI cyclic electron transport, its exact function remains unclear. In transgenic Arabidopsis plants overaccumulating PGR5 in the thylakoid membrane, chloroplast development was delayed, especially in the cotyledons. Although photosynthetic electron transport was not affected during steady-state photosynthesis, a high level of non-photochemical quenching (NPQ) was transiently induced after a shift of light conditions. This phenotype was explained by elevated activity of PSI cyclic electron transport, which was monitored in an in vitro system using ruptured chloroplasts, and also in leaves. The effect of overaccumulation of PGR5 was specific to the antimycin A-sensitive pathway of PSI cyclic electron transport but not to the NAD(P)H dehydrogenase (NDH) pathway. We propose that a balanced PGR5 level is required for efficient regulation of the rate of antimycin A-sensitive PSI cyclic electron transport, although the rate of PSI cyclic electron transport is probably also regulated by other factors during steady-state photosynthesis.

Keywords: Antimycin A; Arabidopsis; Ferredoxin; NPQ; PGR5; PSI cyclic electron transport

Journal Article.  6495 words.  Illustrated.

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

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