Electron transfer between QA and QB in photosystem II is thermodynamically perturbed in phototolerant mutants of Synechocystis sp. PCC 6803

NDFS and I6, two phototolerant mutants, were examined by thermoluminescence measurements to track the thermodynamics of redox equivalents contained on the donor receptor and acceptor sides of photosystem II. The expression mechanisms of phototolerance and the nonphotobleaching phenotype of these mutants are also analyzed. Implications of the results, such as decreased equilibrium constants for sharing an electron between the primary, QA, and secondary acceptor plastoquinones, QB, are also discussed.