Plant and Cell Physiology Advance Access originally published online on October 3, 2007
Plant and Cell Physiology 2007 48(10):1462-1471; doi:10.1093/pcp/pcm116
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A Balanced PGR5 Level is Required for Chloroplast Development and Optimum Operation of Cyclic Electron Transport Around Photosystem I
1Graduate School of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka, 812-8581 Japan
2Department of Genetics, University of Georgia, Athens, GA 30602, USA
3Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0101 Japan and
4Warnell School of Forestry and Natural Resources, University of Georgia. Athens, GA 30602-2152, USA
*Correspondence author: E-mail, shikanai{at}agr.kyushu-u.ac.jp; Fax, +81-92-642-2882.
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Abstract |
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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
Abbreviations: AL, actinic light; ETR, electron transport rate; Fd, ferredoxin; FR, far-red; FQR, ferredoxin-plastoquinone reductase; ML, measuring light; NDH, NAD(P)H dehydrogenase; NPQ, non-photochemical quenching; PAM, pulse amplitude modulation; PGR5, PROTON GRADIENT REGULATION 5; PQ, plastoquinone; qE, energization-dependent quenching.
5Present address: Department of Biology, Duke University, Durham, NC 27708, USA.
(Received July 5, 2007; Accepted August 23, 2007)
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