title: Differential sensitivity of five cyanobacterial strains to ammonium toxicity and its inhibitory mechanism on the photosynthesis of rice-field cyanobacterium Ge-Xian-Mi (Nostoc).
abstract: Effects of two fertilizers, NH(4)Cl and KCl, on the growth of the edible cyanobacterium Ge-Xian-Mi (Nostoc) and four other cyanobacterial strains were compared at pH 8.3+/-0.2 and 25 degrees C. Their growth was decreased by at least 65% at 10 mmol L(-1) NH(4)Cl but no inhibitory effect was observed at the same level of KCl. Meanwhile, the strains exhibited a great variation of sensitivity to NH(4)(+) toxicity in the order: Ge-Xian-Mi>Anabaena azotica FACHB 118>Microcystis aeruginosa FACHB 905>M. aeruginosa FACHB 315>Synechococcus FACHB 805. The 96-h EC(50) value for relative growth rate with regard to NH(4)(+) for Ge-Xian-Mi was 1.105 mmol L(-1), which was much less than the NH(4)(+) concentration in many agricultural soils (2-20 mmol L(-1)). This indicated that the use of ammonium as nitrogen fertilizer was responsible for the reduced resource of Ge-Xian-Mi in the paddy field. After 96 h exposure to 1 mmol L(-1) NH(4)Cl, the photosynthetic rate, F(v)/F(m) value, saturating irradiance for photosynthesis and PSII activity of Ge-Xian-Mi colonies were remarkably decreased. The chlorophyll synthesis of Ge-Xian-Mi was more sensitive to NH(4)(+) toxicity than phycobiliproteins. Thus, the functional absorption cross section of Ge-Xian-Mi PSII was increased markedly at NH(4)Cl levels >or=1 mmol L(-1) and the electron transport on the acceptor side of PSII was significantly accelerated by NH(4)Cl addition >or=3 mmol L(-1). Dark respiration of Ge-Xian-Mi was significantly increased by 246% and 384% at 5 and 10 mmol L(-1) NH(4)Cl, respectively. The rapid fluorescence rise kinetics indicated that the oxygen-evolving complex of PSII was the inhibitory site of NH(4)(+).
authors.affiliation: College of Life Sciences, Central China Normal University, Wuhan 430079, Hubei, PR China.
authors.forename: Guozheng
authors.initials: G
authors.lastname: Dai
authors.forename: Charles P
authors.initials: CP
authors.lastname: Deblois
authors.forename: Shuwen
authors.initials: S
authors.lastname: Liu
authors.forename: Philippe
authors.initials: P
authors.lastname: Juneau
authors.forename: Baosheng
authors.initials: B
authors.lastname: Qiu
mesh_terms: D000643:Ammonium Chloride / Q000633:toxicity*; D000458:Cyanobacteria / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D004579:Electron Transport; D005308:Fertilizers / Q000633:toxicity*; D046937:Nostoc / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D012275:Oryza / Q000254:growth & development*; D010101:Oxygen Consumption / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects*; D010860:Pigments, Biological / Q000096:biosynthesis; D013045:Species Specificity
chemical_list: D005308:Fertilizers; D010860:Pigments, Biological; D000643:Ammonium Chloride