Biochemical characterization of Synechococcus mutants selected against the bleaching herbicide norflurazon

Mutants from the cyanobacterium Synechococcus PCC 7942 have been generated by treatment with ethyl methanesulfonate and selected against the bleaching herbicide norflurazon. Several strains with different degrees of norflurazon resistance have been obtained and assayed. Biochemical characterization of norflurazon interaction with phytoene desaturation showed similar inhibition properties of carotene biosynthesis in vivo and in vitro using four different mutants. This result indicates that in the mutants assayed the affinities for binding of norflurazon to phytoene desaturase are decreased. Concurrently with norflurazon resistance, decreased rates of the phytoenedesaturase reaction and lower carotenoid concentrations in the mutants are found. Strain NFZ 49 also exhibited resistance against fluorochloridone. The other three mutants assayed did not show cross-resistance against various phytoene-desaturase inhibitors.