Abstract
This study demonstrated that excess Ca2+ increased the toxicity of Hg2+ to PSII of cyanobacterium Synechocystis sp. using fast rise chlorophyll fluorescence test. Excess Ca2+ increased the inhibitory effect of Hg2+ on O2 evolution. Exposure to Hg2+ 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 (φDo), indicating that some reaction centers were transformed to dissipation sinks under Hg2+ stress. Hg2+ stress slowed down electron transport on both donor side and acceptor side and caused accumulation of P680+. Excess Ca2+ intensified all the Hg2+ 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 Ca2+ concentration.
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