Isolation and characterization of two DCMU-resistant mutants of the blue-green alga Aphanocapsa 6714

Abstract

Two mutant strains (denoted as DCMU^r-I and DCMU^r-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 two 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. The results suggest that strain DCMU^r-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. DCMU^r-II resistance seems to be due primarily to an alteration of the thylakoid membranes of the photosynthetic apparatus itself.