Reduction of linolenate content in soybean cotyledons by a substituted pyridazinone

The effect of a substituted pyridazinone, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (San 9785), on the reduction of linolenate content was examined in the cotyledons of the soybean cv. Century and a low linolenate mutant of soybeans, C1640, cultured in vitro. No apparent changes in dry matter and total fatty acid accumulation were observed in the cotyledons developing in the presence of San 9785. However, a significant reduction of linolenate content with a corresponding increase in linoleate resulted from growth of the cotyledons in culture medium containing San 9785. San 9785 had a greater effect on decreasing the linolenate content in cotyledons excised in early developmental phases than later stages from both the wild type and mutant soybeans. This result supports other observations that the biosynthesis oflinolenate relative to the other major fatty acids of soybean cotyledons declines in later developmental stages. The compound becomes progressively less effective in reducing the content of linolenate during seed development in the mutant than in the wild type. Both San 9785 and the mutation result in changes in phosphatidylcholine molecular species which indicates the presence of a number oflinolenate desaturation systems in developing soybean cotyledons. The possible biochemical nature of the mutation is discussed.