Effect of a substituted pyridazinone on the decrease of lipoxygenase activity in soybean cotyledons

Application of San 9785 (4-chloro-5-dimethylamino-2-phenyl-3 (2H) pyridazinone) to soybean and peanut plants results in a significant reduction of lipoxygenase activity in the corresponding seeds. The present study of the effect of San 9785 on the decrease of lipoxygenase activity was conducted on soybean (Glycine max L. Merr., cv. Century) cotyledons developing in vitro. Lipoxygenase 2 3 activity was more reduced by San 9785 than lipoxygenase 1 activity in the cotyledons cultured in the presence of 100 μM San 9785. Immunoblotting of cotyledon proteins with lipoxygenase antisera revealed that San 9785 accelerated the appearance of possible lipoxygenase degradation products in the treated cotyledons. The incorporation of [³⁵S]methionine into lipoxygenase was also reduced in the cotyledons incubated with San 9785, but the levels and translational activity of lipoxygenase RNA in these tissues were not affected. This study indicates that the treatment of soybean cotyledons with San 9785 probably causes an increased post-translational degradation of lipoxygenase.