Abstract
State transitions and cyclic electron flow (CEF) around photosystem (PS) I are flexible regulatory mechanisms in photosynthetic machinery. The coupling of State 2 transition and CEF by unknown mechanism has been estimated from their simultaneous activations in a green alga Chlamydomonas reinhardtii. From our recent results, it was revealed that Cyt b6f and some other components in CEF form a supercomplex with PSI during State 2 transition. In this study, CEF activity in isolated PSI supercomplex was evaluated by spectroscopic analyses. By a light excitation of PSI, lumen side and stroma side electron transfer reactions were driven in the presence of mobile electron carriers (plastocyanin and ferredoxin) confirming that the isolated protein supercomplex was a functional CEF complex. We also observed that PSII antenna relocation from PSII to PSI was followed by CEF activation from in vivo analyses. We propose comprehensive regulation model of state transitions and CEF linked by a PSI supercomplex formation.
