| Research Abstract |
Light-energy conversion in oxygenic photosynthesis is driven by cooperative actions of PSI and PSII. Thus, the efficiency of energy conversion depends strictly on the balance between the two photoreactions. We have found that the balance is maintained by regulation of PSI/PSII stoichiometry through the control of PSI synthesis induced by the state of thylakoid ETS. Our further study has focused on (i) the relationship between the state of ETS and regulation of PSI synthesis, (ii) the site controlled in the process of PSI synthesis. For the problems (1), examination of ETS state has been done by flah-induced oxidation-reduction of thylakoid components before and after acclimation. For (ii), Chl a synthesis and synthesis of psaA/B polypeptides have been examined under various photosynthetic conditions. Results have indicated that (1) HQNO-sensitive Cyt b_6 oxidation is monitored, (2) greater size of this reaction causes stimulation of PSI synthesis, (3) control of PSI synthesis occurs at least at the terminal step (s) of Chl a synthesis. Regulation of transcription of psaA/B seems not to be involved in this control. Based on these results, a work model for the mechanism of regulation of PSI formation, the signal, the signal transduction and the control site of PSI synthesis, has been proposed.
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