Influence of the redox state of QA on phycobilisome mobility in the cyanobacterium Synechocystis sp. strain PCC 6803

In a unicellular cyanobacterium, the mobile fraction of phycobilisome (PBS) was found to be maximum at a particular redox value of QA (i.e., 0.52). An upward or downward shift in the redox value leads to a decrease in this mobile fraction of PBS. Furthermore, the regulatory effect of the redox state of QA on PBS mobility was found to be independent of the effect exerted by the plastoquinone pool. These findings indicate for the first time that PBS mobility is regulated by the QA redox state in cyanobacteria. A possible working mechanism underlying this control is discussed.