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Plant and Cell Physiology Advance Access published online on October 3, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm116
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Balanced PGR5 level is required for chloroplast development and optimum operation of cyclic electron flow around photosystem I

Yuki Okegawa1, Terri A. Long2,§, Megumi Iwano3, Seiji Takayama3, Yoshichika Kobayashi1, Sarah F. Covert4 and Toshiharu Shikanai1

1Graduate School of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka, Japan 812-8581
2Department of Genetics, University of Georgia, Athens GA 30602 USA
3Graduate School of Biological Sciences, Nara institute of Science and Technology, Ikoma, Nara, Japan 630-0101
4Warnell School of Forestry and Natural Resources, University of Georgia. Athens, GA 30602-2152 USA

Corresponding author, Toshiharu Shikanai, Graduate School of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka, Japan 812-8581, E-mail shikanai{at}agr.kyushu-u.ac.jp; TEL&FAX +81-92-642-2882


  Abstract

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 over-accumulating PGR5 in the thylakoid membrane, chloroplast development was delayed, especially in the cotyledons. Although photosynthetic electron transport was not affected during steady-state photosynthesis, 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 over-accumulation 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 regulated also by other factors during steady-state photosynthesis.

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

§Present address: Department of Biology, Duke University, Durham, NC 27708


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