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

Two mutant strains (denoted as DCMU^r-I and DCMU^r-II) of theblue-green alga Aphanocapsa 6714, capable of growing in thepresence of 10^–5 M DCMU (an inhibitor of electron transporton the acceptor side of photosystem II), were isolated. The DCMU sensitivity of growth rates and of two photosystemII activities, O₂ emission and fluorescence, was investigatedin 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 bedue to the acquisition of a cellular permeability barrier toDCMU, expressed only after an adaptation phase in the presenceof the inhibitor. DCMU^r-II resistance seems to be due primarilyto an alteration of the thylakoid membranes of the photosyntheticapparatus itself. (Received June 4, 1979; )