Photosystem II electron transfer in highly herbicide resistant mutants ofSynechocystis6714

Abstract
Three mutants ofSynechocystis6714 have been selected for their high relative resistance to DCMU and to atrazine (× 300 for DCMU, × 67 for atrazine). Measurements of chlorophyll fluorescence have been used to monitor electron transfer from QA(the primary electron acceptor of photosystem II) to QB(the secondary electron acceptor). The initial electron transfer is not slowed down in the resistant strains; the second phase of the fluorescence decay is somewhat slower. The data are interpreted to indicate that a mutation giving rise to a high level of resistance does not induce a large alteration of the QBbinding site for mutants resistant to atrazine and/or to DCMU.