Abstract
Among the variety of chlorophyll species, 3-mono-vinyl (MV) chlorophyll (Chl) a is most commonly used for the photochemistry in photosynthetic organisms. The exceptions to this is a group of marine cyanobacteria, Prochlorococcus spp., which use 3,8-di-vinyl (DV) Chl a for their photochemistry. In the transgenic mutant of a cyanobacterium Synechocystis sp. PCC 6803 whose enzyme in chlorophyll synthesis, i.e. DV reductase, is blocked, it accumulates DV-Chl a instead of MV-Chl a. This transgenic species was sensitive to high light, and isolated photosystem II complexes with DV-Chl a (DV-PS II) were bleached much faster than PS II with MV-Chl a (MV-PS II). Furthermore, the acceptor-side inhibition was observed on the basis of degradation products of the D1 protein. To identify the reasons for this inhibition in DV-PS II, we measured the yield of singlet oxygen at near infrared region in DV-Chl a solution and DV-PS II, because the singlet oxygen plays a key role of acceptor side photoinhibition. We found MV-Chl a in solution was effective on formation and quenching of singlet oxygen than DV-Chl a. Possible implications of the results will be discussed.
