title: Quality control of PSII: behavior of PSII in the highly crowded grana thylakoids under excessive light.
abstract: 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.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan yasusiya@cc.okayama-u.ac.jp.
authors.forename: Yasusi
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Suguru
authors.initials: S
authors.lastname: Kai
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Atsuki
authors.initials: A
authors.lastname: Ohnishi
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Nodoka
authors.initials: N
authors.lastname: Tsumura
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Hori
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Morita
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ishikawa
mesh_terms: D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D010944:Plants / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D066329:Protein Aggregates; D017382:Reactive Oxygen Species / Q000378:metabolism; D013312:Stress, Physiological; D020524:Thylakoids / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D066329:Protein Aggregates; D017382:Reactive Oxygen Species
keywords: Light stress; Membrane crowdedness; Non-photochemical quenching; Photoinhibition; Photosystem II; Protein aggregation