A NEW PHENOTYPE FOR A HERBICIDE-RESISTANT MUTANT OF SYNECHOCYSTIS-6714 WITH A HIGH-SENSITIVITY TO PHOTOINHIBITION

In this article, we describe the genotype and phenotype of a double mu tant of Synechocystis PCC 6714 carrying A251V and S264A mutations in t he Q(B) pocket of the D-1 protein. The mutation A251V confers an incre ased sensitivity to high light on the Photosystem II (PS II). The A251 V mutation also results in a modification of electron transfer between Q(A)(-) and Q(B), a destabilization of the S(2)Q(B)(-) State and a de stabilization of the S-1 state due to a better accessibility of the ox ygen evolving complex to cytosolic reductants. The double mutant is mo re sensitive to high light than the simple mutant. The electron transf er between Q(A)(-) and Q(B) is modified in both mutants. In contrast t o the single mutant, in the A251V, S264A mutant, the S(2)Q(B)(-) and t he S(2)Q(A)(-) states are stabilized and there are no modifications on the donor side of the Photosystem II. We conclude that there is no di rect relationship between the S-1 destabilization and the increased se nsitivity to high light. The correlation between the sensitivity of th e PS II to high light and Q(A)(-), Q(B)(-) stabilities is also uncerta in.