Functional Analyses of the Plant Photosystem I–Light-Harvesting Complex II Supercomplex Reveal That Light-Harvesting Complex II Loosely Bound to Photosystem II Is a Very Efficient Antenna for Photosystem I in State II

摘要

State transitions are an important photosynthetic short-term response that allows energy distribution balancing between photosystems I () and II (). In plants when is preferentially excited compared with (State II), part of the major light-harvesting complex migrates to to form a - supercomplex. So far, little is known about this complex, mainly due to purification problems. Here, a stable - supercomplex is purified from Arabidopsis thaliana and maize (Zea mays) plants. It is demonstrated that loosely bound to in State I are the trimers mainly involved in state transitions and become strongly bound to in State II. Specific Lhcb1-3 isoforms are differently represented in the mobile compared with S and M trimers. Fluorescence analyses indicate that excitation energy migration from mobile to is rapid and efficient, and the quantum yield of photochemical conversion of href="#def1" rid="def1" class=" def">PSI-href="#def9" rid="def9" class=" def">LHCII is substantially unaffected with respect to href="#def1" rid="def1" class=" def">PSI, despite a sizable increase of the antenna size. An updated href="#def1" rid="def1" class=" def">PSI-href="#def9" rid="def9" class=" def">LHCII structural model suggests that the low-energy chlorophylls 611 and 612 in href="#def9" rid="def9" class=" def">LHCII interact with the chlorophyll 11145 at the interface of href="#def1" rid="def1" class=" def">PSI. In contrast with the common opinion, we suggest that the mobile pool of href="#def9" rid="def9" class=" def">LHCII may be considered an intimate part of the href="#def1" rid="def1" class=" def">PSI antenna system that is displaced to href="#def2" rid="def2" class=" def">PSII in State I.