title: Excess Ca(2+) does not alleviate but increases the toxicity of Hg(2+) to photosystem II in Synechocystis sp. (Cyanophyta).
abstract: This study demonstrated that excess Ca(2+) increased the toxicity of Hg(2+) to PSII of cyanobacterium Synechocystis sp. using fast rise chlorophyll fluorescence test. Excess Ca(2+) increased the inhibitory effect of Hg(2+) on O2 evolution. Exposure to Hg(2+) caused increase in functional antenna size (ABS/RC), trapping rate of reaction center (TR0/RC), dissipated energy flux per reaction center (DI0/RC) and maximum quantum yield of non-photochemical deexcitation ( [Formula: see text] ), indicating that some reaction centers were transformed to dissipation sinks under Hg(2+) stress. Hg(2+) stress slowed down electron transport on both donor side and acceptor side and caused accumulation of P680(+). Excess Ca(2+) intensified all the Hg(2+) toxic effects on PSII function and led to dysfunction of PSII. The number of reaction centers that were transformed into dissipation sinks increased with increasing Ca(2+) concentration.
authors: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, China.
authors: Daoyong
authors: D
authors: Zhang
authors: Chunnuan
authors: C
authors: Deng
authors: Xiangliang
authors: X
authors: Pan
mesh_terms: D002118:Calcium / Q000633:toxicity*; D004579:Electron Transport / Q000187:drug effects; D008628:Mercury / Q000633:toxicity*; D010788:Photosynthesis / Q000187:drug effects; D045332:Photosystem II Protein Complex / Q000187:drug effects*; D046939:Synechocystis / Q000187:drug effects*
chemical_list: D045332:Photosystem II Protein Complex; D008628:Mercury; D002118:Calcium
keywords: Calcium; Chlorophyll fluorescence; Mercury; Photosystem II; Toxicity