title: Ammonium tolerance in the cyanobacterium Synechocystis sp. strain PCC 6803 and the role of the psbA multigene family.
abstract: Ammonium is one of the major nutrients for plants, and a ubiquitous intermediate in plant metabolism, but it is also known to be toxic to many organisms, in particular to plants and oxygenic photosynthetic microorganisms. Although previous studies revealed a link between ammonium toxicity and photodamage in cyanobacteria under in vivo conditions, ammonium-induced photodamage of photosystem II (PSII) has not yet been investigated with isolated thylakoid membranes. We show here that ammonium directly accelerated photodamage of PSII in Synechocystis sp. strain PCC6803, rather than affecting the repair of photodamaged PSII. Using isolated thylakoid membranes, it could be demonstrated that ammonium-induced photodamage of PSII primarily occurred at the oxygen evolution complex, which has a known binding site for ammonium. Wild-type Synechocystis PCC6803 cells can tolerate relatively high concentrations of ammonium because of efficient PSII repair. Ammonium tolerance requires all three psbA genes since mutants of any of the three single psbA genes are more sensitive to ammonium than wild-type cells. Even the poorly expressed psbA1 gene, whose expression was studied in some detail, plays a detectable role in ammonium tolerance.
authors.affiliation: Interfaculty Institute for Microbiology and Infection Medicine, Division Organismic Interactions, University of Tübingen, Auf der Morgenstelle 28, D-72076, Tübingen, Germany; College of Life Sciences, Central China Normal University, 430079, Wuhan, Hubei, China; Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, 430079, Wuhan, Hubei, China.
authors.forename: Guo-Zheng
authors.initials: GZ
authors.lastname: Dai
authors.forename: Bao-Sheng
authors.initials: BS
authors.lastname: Qiu
authors.forename: Karl
authors.initials: K
authors.lastname: Forchhammer
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D064751:Ammonium Compounds / Q000633:toxicity*; D005798:Genes, Bacterial; D008027:Light; D005810:Multigene Family; D009154:Mutation / Q000235:genetics; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000166:cytology / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D013997:Time Factors
chemical_list: D064751:Ammonium Compounds; D045332:Photosystem II Protein Complex; D012333:RNA, Messenger; C422369:photosystem II, psbA subunit; D010100:Oxygen
keywords: ammonium toxicity; oxygen evolution complex; photoinhibition; photosystem II