ISOLATION AND CHARACTERIZATION OF 2 DCMU-RESISTANT MUTANTS OF THE BLUE-GREEN-ALGA APHANOCAPSA-6714

Two mutant strains (denoted as DCMUr-I and DCMUr-II) of the blue-green alga, Aphanocapsa 6714, capable of growing in the presence of 10-5 M DCMU (an inhibitor of electron transport on the acceptor side of photosystem II), were isolated. The DCMU sensitivity of growth rates and of 2 photosystem II activities, O2 emission and fluorescence, was investigated in the mutant cells and compared with that of the wild-type. The DCMU sensitivity of isolated thylakoids was also studied. The sensitivity of the mutant cells to other DCMU-type inhibitors (o-phenanthroline and atrazine) was tested. Strain DCMUr-I resistance could be due to the acquisition of a cellular permeability barrier to DCMU, expressed only after an adaptation phase in the presence of the inhibitor. DCMUr-II resistance seems to be due primarily to an alteration of the thylakoid membranes of the photosynthetic apparatus itself.