Characterization of Strains of Scenedesmus Resistant to the Herbicide DCMU , ( 3 - ( 3 , 4 - dichloropheny

approved: Redacted for Privacy (Norman I. Bishop) Three DCMU resistant mutants of the green alga Scenedesmus obliquus D3 are characterized. The mutants exhibit a ten fold greater resistance to DCMU than the wild type strain; this is comparable to the level of DCMU resistance detected in other DCMU resistant algae. In whole cell reactions, as well as isolated chloroplast reactions, the resistance is maintained. Altered cell wall permeability is shown not to be the cause of resistance. In the presence of increasing concentrations of DCMU the wild type shows a large and rapid increase in fluorescence while the resistant mutants show a slow continual rise. The wild type and the resistant mutants show a comparable susceptibility to atrazine. Polypeptide analysis demonstrates that during chloroplast development and in fully matured cells the polypeptide patterns of the wild type and the resistant mutant thylakoids are the same. Two dimensional thin layer chromatograms of thylakoid lipids of the wild type and resistant strains are qualitatively comparable. A notable difference is detected in the unsaturation ratio of fatty acids found in the wild type versus the resistant mutants; the wild type contains proportionately less unsaturated fatty acids than the mutants. The DCMU resistant mutants characterized in this study exhibit a ten fold increase in resistance to DCMU. Atrazine resistant higher plants exhibit a significantly larger magnitude of resistance; because of this large difference it is probable that the resistance phenomena observed in Scenedesmus mutants is not the same as that occurring in atrazine resistant higher plants. The results of this study indicate that lipid composition influences the binding of the herbicide DCMU in thylakoid membranes of DCMU resistant mutants of Scenedesmus obliquus. Characterization of Strains of Scenedesmus Resistant to the Herbicide DCMU, (3-(3,4-dichloropheny1)-1,1-dimethylurea)