title: Sulfite-stress induced functional and structural changes in the complexes of photosystems I and II in a cyanobacterium, Synechococcus elongatus PCC 7942.
abstract: Excess sulfite is well known to have toxic effects on photosynthetic activities and growth in plants, however, so far, the behavior of the photosynthetic apparatus during sulfite-stress has not been characterized as to the responsible proteins or genes. Here, the effects of sulfite on photosystem complexes were investigated in a cyanobacterium, Synechococcus elongatus PCC 7942, a possible model organism of chloroplasts. Culturing of the cells for 24 h in the presence of 10 mM sulfite retarded cell growth of the wild type, concomitantly with synthesis of Chl and phycobilisome repressed. The excess sulfite simultaneously repressed photosynthesis by more than 90%, owing largely to structural destabilization and resultant inactivation of the PSII complex, which seemed to consequently retard the cell growth. Notably, the PsbO protein, one of the subunits that construct the water-splitting system of PSII, was retained at a considerable level, and disruption of the psbO gene led to higher sensitivity of photosynthesis and growth to sulfite. Meanwhile, the PSI complex showed monomerization of its trimeric configuration with little effect on the activity. The structural alterations of these PS complexes depended on light. Our data provide evidence for quantitative decreases in the photosystem complex(es) including their antenna(e), structural alterations of the PSI and PSII complexes that would modulate their functions, and a crucial role of psbO in PSII protection, in Synechococcus cells during sulfite-stress. We suggest that the reconstruction of the photosystem complexes is beneficial to cell survival.
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Horinouchi 1432-1, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Kobayashi
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Horinouchi 1432-1, Hachioji, Tokyo 192-0392, Japan JST, CREST, Chiyoda-ku, Tokyo, 102-0075, Japan.
authors.forename: Mikio
authors.initials: M
authors.lastname: Tsuzuki
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Horinouchi 1432-1, Hachioji, Tokyo 192-0392, Japan JST, CREST, Chiyoda-ku, Tokyo, 102-0075, Japan nsato@ls.toyaku.ac.jp.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Sato
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002734:Chlorophyll / Q000378:metabolism; D008027:Light; D010788:Photosynthesis / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D045524:Phycobilisomes / Q000187:drug effects; D013312:Stress, Physiological; D013447:Sulfites / Q000633:toxicity*; D046940:Synechococcus / Q000187:drug effects / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D020524:Thylakoids / Q000187:drug effects
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; D013447:Sulfites; D002734:Chlorophyll
keywords: Synechococcus; photosynthesis; photosystem I; photosystem II; psbO; sulfite stress