Activation of alternative electron transfer in PS II by inhibition of proton transfer at the acceptor side

Abstract

Cd2+, Zn2+ and Cu2+ have expressed effect on QB protonation and reduction in bacterial reaction centers (BRC) (Utschig et al., 2001). This work is dedicated to investigating influence of Cd2+, Pb2+, Hg2+, Zn2+, and Cu2+ at the level of acceptor side of photosystem II (PS II). Light-dependent proton uptake decreased in the presence of 80 μM Cu2+ by 90%, and of 200 μM Zn2+—by 70%. At that, considerable reductions of electron transport rate were not observed. In the concentration range of 50–200 μM Cu2+ and Cd2+ caused an insignificant growth of [PSII-QB-non-reducing]rel, whereas in the presence of Zn2+ and Pb2+ this value grew more than by 25%. At all concentrations of ions of heavy metals the [PSII-QB-non-reducing]rel value did not exceed 60%. By their effect on dark relaxation of variable chlorophyll fluorescence, heavy metals used might be divided in two groups: (1) Cu2+ Hg2+, accelerating the fast and medium components of fluorescence decay; (2) Zn2+, Pb2+ and Cd2+, slowing down medium and fast components. An assumption was made that blocking the reaction of QB protonation by ions of heavy metals activates the alternative acceptor site in PS II.