Abstract
Light-harvesting complex II (LHCII) of photosystem II (PSII) adjusts light absorption cross section of photosystem I (PSI) and PSII under changing light environments, a process called state transitions. This short-term acclimation mechanism consists of three processes: phosphorylation of LHCIIs, unstacking of thylakoid membranes, and migration of LHCIIs from PSII to PSI. However, detailed mechanism for each process still remains unclear. Here, to investigate the role of unstacking of thylakoid membranes in state transitions, we analyzed 1) fluorescence quenching, 2) phosphorylation of LHCIIs, and 3) observation of thylakoid membranes with electron microscope during dark period using several mutants. The results indicated Δycf9 mutant, which was deficient in a formation of PSI-LHCI/II supercomplex, still showed the decrease in PSII fluorescence, phosphorylation of LHCIIs as well as unstacking of thylakoid membranes. Therefore, we suggest unstacking of thylakoid membranes has an important role for decreasing the excitation energy transfer between PSIIs in state transitions.
