Journal Article

Quality Control of PSII: Behavior of PSII in the Highly Crowded Grana Thylakoids Under Excessive Light

Yasusi Yamamoto, Suguru Kai, Atsuki Ohnishi, Nodoka Tsumura, Tomomi Ishikawa, Haruka Hori, Noriko Morita and Yasuo Ishikawa

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 55, issue 7, pages 1206-1215
Published in print July 2014 | ISSN: 0032-0781
Published online March 2014 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcu043

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The grana thylakoids of higher plant chloroplasts are crowded with PSII and the associated light-harvesting complexes (LHCIIs). They constitute supercomplexes, and often form semi-crystalline arrays in the grana. The crowded condition of the grana may be necessary for efficient trapping of excitation energy by LHCII under weak light, but it might hinder proper movement of LHCII necessary for reversible aggregation of LHCII in the energy-dependent quenching of Chl fluorescence under moderate high light. When the thylakoids are illuminated with extreme high light, the reaction center-binding D1 protein of PSII is photodamaged, and the damaged protein migrates to the grana margins for degradation and subsequent repair. In both moderate and extreme high-light conditions, fluidity of the thylakoid membrane is crucial. In this review, we first provide an overview of photoprotective processes, then discuss changes in membrane fluidity and mobility of the protein complexes in the grana under excessive light, which are closely associated with photoprotection of PSII. We hypothesize that reversible aggregation of LHCII, which is necessary to avoid light stress under moderate high light, and swift turnover of the photodamaged D1 protein under extreme high light are threatened by irreversible protein aggregation induced by reactive oxygen species in photochemical reactions.

Keywords: Light stress; Membrane crowdedness; Non-photochemical quenching; Photoinhibition; Photosystem II; Protein aggregation

Journal Article.  5975 words.  Illustrated.

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

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