Journal Article

Physiological Significance of the Regulation of Photosystem Stoichiometry upon High Light Acclimation of <i>Synechocystis</i> sp. PCC 6803

Kintake Sonoike, Yukako Hihara and Masahiko Ikeuchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 4, pages 379-384
Published in print April 2001 | ISSN: 0032-0781
Published online April 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce046
Physiological Significance of the Regulation of Photosystem
Stoichiometry upon High Light Acclimation of Synechocystis sp. PCC
6803

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We characterized the photosynthetic properties of the pmgA mutant of Synechocystis PCC 6803, which cannot change its photosystem stoichiometry under a high-light condition (200 µmol m–2 s–1), in order to clarify the physiological significance of the regulation of photosystem stoichiometry. We found that (1) PSII activity was inhibited more in wild-type cells on the first day under the high-light conditions than in mutant cells. (2) The growth of the mutants following the initial imposition of high light was faster than that of wild-type cells. (3) However, growth was severely inhibited in the mutants after the third day of exposure to high light. (4) The growth inhibition in the mutants under the extended high-light conditions was reversed by the addition of sublethal concentrations of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), which seemed to mimic photoinhibition of PSII. These results suggest that the main role of adjusting the photosystem stoichiometry with respect to light intensity is not to maintain efficient photosynthesis, but to down regulate electron transfer. Failure to down regulate electron flow leads to cell death under prolonged exposure to high light in this cyanobacterium.

Keywords: Key words: Excitation pressure — Light acclimation — Non-photochemical quenching — Photosystem stoichiometry — State transition — Synechocystis PCC 6803.; Abbreviations: Fo, Fm, Fv, minimal, maximal and variable level of Chl a fluorescence; Fo′, Fm′, Fv′, minimal, maximal and variable level of Chl a fluorescence under excitation light; PFD, photon flux density; qP, qN, photochemical and non-photochemical quenching of Chl a fluorescence; ϕII, effective quantum yield of electron transfer through PSII.

Journal Article.  3887 words.  Illustrated.

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

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