Differential Effects of the Substituted Pyridazinone Herbicide Sandoz 9785 on Lipid Composition and Biosynthesis in Photosynthetic and Non-Photosynthetic Marine Microalgae

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A comparison was made of the effects of the substituted pyridazinone herbicide, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H) pyridazinone (Sandoz 9785; BASF 13–338) on the growth rate and lipid class synthesis of two species of photosynthetic (Chroomanas salina and Nannochloropsis oculata), and one species of non-photosynthetic (Crypthecodinium cohnil), marine microalgae. The growth rate, but not the total lipid content, of all three species was reduced by the herbicide. The percentage distribution of radioactivity incorporated by C. cohnii into lipid classes generally resembled the relative abundance of the classes and the presence of Sandoz 9785 resulted in only small changes in lipid class proportions or in the distribution of radioactivity. In C. salina, the proportion of radioactivity located in monogalactosyldiacylglycerol (MGDG) increased from 9.2% to 20.3%, and that in digalactosyldiacylglycerol (DGDG) from 6.3% to 12.7%, in the presence of the herbicide. In N. oculata the proportion of radioactivity recovered in DGDG, but not MGDG, was increased significantly by the presence of Sandoz 9785. The results suggest that Sandoz 9785 alters galactolipid metabolism in photosynthetic microalgae but has no great effect on lipid synthesis in non-photosynthetic species.