title: Conversion of photosystem II dimer to monomers during photoinhibition is tightly coupled with decrease in oxygen-evolving activity in the diatom Chaetoceros gracilis.
abstract: The rapid turnover of photosystem II (PSII) in diatoms is thought to be at an exceptionally high rate compared with other oxyphototrophs; however, its molecular mechanisms are largely unknown. In this study, we examined the photodamage and repair processes of PSII in the marine centric diatom Chaetoceros gracilis incubated at 30 or 300 μmol photons m-2s-1in the presence of a de novo protein-synthesis inhibitor. When de novo protein synthesis was blocked by chloramphenicol (Cm), oxygen-evolving activity gradually decreased even at 30 μmol photons m-2s-1and could not be detected at 12 h. PSII inactivation was enhanced by higher illumination. Using Cm-treated cells, the conversion of PSII dimer to monomers was observed by blue native PAGE. The rate of PSII monomerization was very similar to that of the decrease in oxygen-evolving activity under both light conditions. Immunological detection of D1 protein in the Cm-treated cells showed that the rate of D1 degradation was slower than that of the former two events, although it was more rapid than that observed in other oxyphototrophs. Thus, the three accelerated events, especially PSII monomerization, appear to cause the unusually high rate of PSII turnover in diatoms.
authors: Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan. nagao@bio.phys.nagoya-u.ac.jp.
authors: Ryo
authors: R
authors: Nagao
authors: Department of Biology, Faculty of Science, Tokyo University of Science, Kagurazaka 1-3, Shinjuku-ku, Tokyo, 162-8601, Japan.|Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
authors: Tatsuya
authors: T
authors: Tomo
authors: Department of Biological Science, Faculty of Science, Shizuoka University, Ohya, Suruga-ku, Shizuoka, 422-8529, Japan.
authors: Rei
authors: R
authors: Narikawa
authors: Department of Biology, Faculty of Science, Tokyo University of Science, Kagurazaka 1-3, Shinjuku-ku, Tokyo, 162-8601, Japan.
authors: Isao
authors: I
authors: Enami
authors: Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, 153-8902, Japan.
authors: Masahiko
authors: M
authors: Ikeuchi
mesh_terms: D002701:Chloramphenicol / Q000494:pharmacology; D017377:Diatoms / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D004591:Electrophoresis, Polyacrylamide Gel; D008027:Light; D010100:Oxygen / Q000378:metabolism; D017785:Photons; D045332:Photosystem II Protein Complex / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D045332:Photosystem II Protein Complex; D002701:Chloramphenicol; D010100:Oxygen
keywords: D1 degradation; Diatom; Oxygen-evolving activity; PSII monomerization; Photodamage and repair