Abstract
State transitions are required for balancing excitation energy between Photosystem I (PSI) and II (PSII) and are regulated by the redox state of cytochrome b6f complex. In state 2, when cytochrome b6f complex is reduced, a part of LHCII is believed to migrate from PSII to PSI to form PSI-LHCI/II supercomplex. We have already demonstrated that monomeric LHCIIs (CP26, CP29 and LhcbM5) reversibly associate with PSI-LHCI supercomplex in state 2. Here we characterized the amount and function of monomeric LHCIIs bound to PSI-LHCI supercomplex in state 2. First, PSI-LHCI/II was dissociated into PSI-LHCI and monomeric LHCIIs and the chlorophyll distribution between these complexes was estimated. In addition, Chls/P700 in PSI-LHCI/II was estimated by measuring light-induced photooxidation of P700. It was concluded that the functional antenna size of PSI-LHCI/II increases 1.2 - 1.4 times more than that of PSI-LHCI by the association of monomeric LHCIIs.
