Electron paramagnetic resonance study of the electron transfer reactions in photosystem II membrane preparations from...

Arabidopsis thaliana is widely used as a model organism in plant biology as its genome has been sequenced and transformation is known to be efficient. A large number of mutant lines and genomic resources are available for Arabidopsis. All this makes Arabidopsis a useful tool for studies of photosynthetic reactions in higher plants. In this study, photosystem II (PSII) enriched membranes were successfully isolated from thylakoids of Arabidopsis plants and for the first time the electron transfer cofactors in PSII were systematically studied using electron paramagnetic resonance (EPR) spectroscopy. EPR signals from both of the donor and acceptor sides of PSII, as well as from auxiliary electron donors were recorded. From the acceptor side of PSII, EPR signals from Q(A)- Fe²(+) and Phe- Q(A)- Fe²(+) as well as from the free Phe- radical were observed. The multiline EPR signals from the S₀- and S₂-states of CaMn₄O(x)-cluster in the water oxidation complex were characterized. Moreover, split EPR signals, the interaction signals from Y(Z) and CaMn₄O(x)-cluster in the S₀-, S₁-, S₂-, and the S₃-state were induced by illumination of the PSII membranes at 5K and characterized. In addition, EPR signals from auxiliary donors Y(D), Chl(+) and cytochrome b₅₅₉ were observed. In total, we were able to detect about 20 different EPR signals covering all electron transfer components in PSII. Use of this spectroscopic platform opens a possibility to study PSII reactions in the library of mutants available in Arabidopsis.