Abstract
It is known that photosynthetic activity of plants is lowered under strong light and this is mainly caused by photodamage of photosystem II (PSII). However, the detailed process of the PSII photodamage remains to be clarified. In this study, we investigated the molecular mechanism of PSII photodamage utilizing the effects of herbicides. PSII membranes from spinach and those in the presence of DCMU and bromoxynil were illuminated with strong light (2000 μE m-2 s-1) and the activities of the Mn cluster, QA, and P680 were estimated by Fourier transform infrared (FTIR) spectroscopy. The results showed that (1) the signals of QA and the Mn cluster decreased by illumination at the same rate in all three samples, (2) the decay of the P680 signal was always slower than that of the QA signal, (3) the signal decays were faster and slower with bromoxynil and DCMU, respectively, than those of the control sample. These results indicate that the destruction of the Mn cluster is not a determinant of PSII photodamage and that the QA release by double reduction triggers the P680 damage. The present results provide experimental evidence for the acceptor-side mechanism of PSII photodamage.
