Journal Article

Cyclic Electron Flow within PSII Protects PSII from its Photoinhibition in Thylakoid Membranes from Spinach Chloroplasts

Chikahiro Miyake and Mitsutaka Okamura

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 4, pages 457-462
Published in print April 2003 | ISSN: 0032-0781
Published online April 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg053
Cyclic Electron Flow within PSII Protects PSII from its Photoinhibition in Thylakoid Membranes from Spinach Chloroplasts

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Cyclic electron flow within PSII (CEF-PSII) was proven to alleviate the photoinhibition of PSII. We set the conditions where CEF-PSII functioned or did not, by adding nigericin to the reaction mixture for the dissipation of ΔpH across thylakoid membranes, and then the thylakoids were illuminated. When CEF-PSII did not function and the activity of linear electron flow (LEF) was low, light-treated thylakoid membranes largely lost the activity of LEF. The inactivation of LEF was due to the loss of the activity of PSII, but not that of PSI. The inactivation of PSII was suppressed, when CEF-PSII functioned or LEF was enhanced. These results imply that CEF-PSII contributes to the protection of PSII from its photoinhibition with LEF, as an electron sink.

Keywords: Keywords: Alternative electron flow — Chloroplasts — Cyclic electron flow — Photoinhibition — PSII – Thylakoid membranes.; Abbreviations: AEF, alternative electron flow; CEF-PSII, cyclic electron flow within PSII; ΔpH, a gradient in pH across thylakoid membranes; Φ(PSII), the quantum yield of the electron flux in PSII, defined as (Fm′–Fs)/Fm′; Fm, maximum yield of Chl fluorescence after dark adaptation; Fm′, Fm after illumination; Fs, yield of steady-state Chl fluorescence; LEF, linear electron flow; NPQ, non-photochemical quenching coefficient of Chl fluorescence, defined as (Fm–Fm′)/Fm′; PFD, photosynthetically active photon flux density; V(O2), the rate of O2 uptake; WWC, the water–water cycle.

Journal Article.  4011 words.  Illustrated.

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

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