Influence of the Redox Potential of the Primary Quinone Electron Acceptor on Photoinhibition in Photosystem II

Christian Fufezan,Christine M Gross,Martin Sjödin,A William Rutherford,Anja Krieger-Liszkay,Diana Kirilovsky

doi:10.1074/jbc.m610951200

Abstract

We report the characterization of the effects of the A249S mutation located within the binding pocket of the primary quinone electron acceptor, Q(A), in the D2 subunit of photosystem II in Thermosynechococcus elongatus. This mutation shifts the redox potential of Q(A) by approximately -60 mV. This mutant provides an opportunity to test the hypothesis, proposed earlier from herbicide-induced redox effects, that photoinhibition (light-induced damage of the photosynthetic apparatus) is modulated by the potential of Q(A). Thus the influence of the redox potential of Q(A) on photoinhibition was investigated in vivo and in vitro. Compared with the wild-type, the A249S mutant showed an accelerated photoinhibition and an increase in singlet oxygen production. Measurements of thermoluminescence and of the fluorescence yield decay kinetics indicated that the charge-separated state involving Q(A) was destabilized in the A249S mutant. These findings support the hypothesis that a decrease in the redox potential of Q(A) causes an increase in singlet oxygen-mediated photoinhibition by favoring the back-reaction route that involves formation of the reaction center chlorophyll triplet. The kinetics of charge recombination are interpreted in terms of a dynamic structural heterogeneity in photosystem II that results in high and low potential forms of Q(A). The effect of the A249S mutation seems to reflect a shift in the structural equilibrium favoring the low potential form.

Highlights

On the electron acceptor side, electron transfer involves two plastoquinones, the primary and secondary quinone acceptors (QA and QB)
We report the characterization of the effects of the A249S mutation located within the binding pocket of the primary quinone electron acceptor, QA, in the D2 subunit of photosystem II in Thermosynechococcus elongatus
The D2-A249S mutant was created in photosystem II of Thermosynechococcus (T.) elongatus

Summary

Introduction

On the electron acceptor side, electron transfer involves two plastoquinones, the primary and secondary quinone acceptors (QA and QB). To measure the thermoluminescence originating from the S2QA- recombination (Q-Band), the dark-adapted samples were flashed once and incubated with either 20 !M DCMU or 100 !M bromoxynil or without any additions at 40 °C for 3 min.

Results

Conclusion