Abstract
The inhibitory effect of mercury on photosystem II (PSII) photochemistry was investigated in the green alga Dunaliella tertiolecta. In the presence of 80 μM HgCl 2, oxygen evolution is completely inhibited, whereas 50% of the variable fluorescence still remains. The effect of mercury on the fluorescence yield in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) is reversed when the electron donor to PSII is hydroxylamine instead of water. This result confirms that the inhibition site of mercury in the presence of DCMU is associated with the activity of the water-splitting system. Mercury induces a decrease in the complementary area, indicating that the number of functional PSII primary electron acceptors is decreased. Mercury inhibition results in a decrease in the PSII quantum yield in algal cells. However, the reduction rate of the PSII primary electron acceptor (Q A) is not affected. Therefore, this effect on PSII induces a complete inactivation of the PSII reaction centres associated with the mercury-inhibited water-splitting system.
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