The effect of the Cyt b6-f redox state on the PSI formation was examined with the cyanophyte Synechocystis PCC 6714 by using a Q-cycle inhibitor, HQNO (2-n-heptyl-4-hydroxyquinoline N-oxide). HQNO inhibited the rapid reduction of flash-oxidized Cyt f, the reaction correlating with the stimulation of PSI formation, on one hand, and accumulated reduced Cyt b6, on the other, indicating that the electron flow in the Q-cycle correlates with regulation of PSI synthesis. HQNO also inhibited the stimulation of PSI formation under PSII light, resulting in a low PSI/PSII ratio even under PSII light, while the PSI formation under PSI light was not suppressed by HQNO. Simultaneous inhibition of Cyt b6 oxidation through the Q-cycle and the stimulated PSI formation by HQNO suggests that an HQNO-sensitive Cyt b6 oxidation is involved in the mechanism of monitoring the state of electron transport system for regulation of PSI formation.
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Murakami et al. (1993) studied this question.