Excitation energy transfer between photosystems in the cyanobacterium Synechocystis 6803

In cyanobacteria, the light-harvesting complex phycobilisomes (PBS) can transfer the harvested energy to photosystem II (PSII) and photosystem I (PSI) and from PSII to PSI. The efficiency of energy transfer from PBS to PSII or PSI, as probed by the ratio of the fluorescence yield of PBS to that of PSII or PSI, was similar in static and aerated cultures of a cyanobacterium Synechocystis sp. strain PCC 6803. In contrast, the fluorescence yield for PSII was notably high while that for PSI was remarkably low in static cultures when compared to that in aerated cultures. Additionally, the level of the efficiency of excitation energy capture by open PSII reaction center was markedly decreased in static cultures in comparison to that in aerated cultures. Thus, the energy transfer from PSII to PSI, but not from PBS to PSII and PSI, was inhibited in static cultures and was most likely caused by the reduction of PSII activity.