title: Ammonia triggers photodamage of photosystem II in the cyanobacterium Synechocystis sp. strain PCC 6803.
abstract: Ammonia has long been known to be toxic for many photosynthetic organisms; however, the target for its toxicity remains elusive. Here, we show that in the cyanobacterium Synechocystis sp. strain PCC 6803, ammonia triggers a rapid photodamage of photosystem II (PSII). Whereas wild-type cells can cope with this damage by turning on the FtsH2-dependent PSII repair cycle, the FtsH2-deficient mutant is highly sensitive and loses PSII activity at millimolar concentration of ammonia. Ammonia-triggered PSII destruction is light dependent and occurs already at low photon fluence rates. Experiments with monochromatic light showed that ammonia-promoted PSII photoinhibition is executed by wavebands known to directly destroy the manganese cluster in the PSII oxygen-evolving complex, suggesting that the oxygen-evolving complex may be a direct target for ammonia toxicity.
authors.affiliation: Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Drath
authors.forename: Nicole
authors.initials: N
authors.lastname: Kloft
authors.forename: Alfred
authors.initials: A
authors.lastname: Batschauer
authors.forename: Kay
authors.initials: K
authors.lastname: Marin
authors.forename: Jens
authors.initials: J
authors.lastname: Novak
authors.forename: Karl
authors.initials: K
authors.lastname: Forchhammer
mesh_terms: D000641:Ammonia / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D046939:Synechocystis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D000644:Quaternary Ammonium Compounds; D000641:Ammonia; D009584:Nitrogen