Modification of dimethipin action by light

White light reduced the efficacy of dimethipin in inducing both desiccation and abscission in kidney beans (Phaseolus vulgaris L. cv. Black Valentine). Moreover, light reduced the previously reported inhibitory effect of dimethipin on protein synthesis (Metzger and Keng 1984) in a way that paralleled the reduction in dimethipin-induced morphological changes. Therefore the inhibition of protein synthesis by dimethipin was the parameter measured in experiments designed to characterize the light-induced reduction of dimethipin efficacy. The light effect was directly proportional to both the fluence rate and the duration of the light treatment. A similar effect of light was observed in cultured kidney bean cells devoid of chlorophyll, ruling out the participation of a photosynthetic related process. Moreover, light had no effect on either the metabolism of [2,3]-¹⁴C-dimethipin in kidney bean leaves or uptake of dimethipin into cultured kidney bean cells. No evidence was obtained for photochemical decomposition of dimethipin either. Thus, the light effect is possibly the result of direct modification of the biochemical processes associated with the primary mechanism(s) of dimethipin action, or perhaps promotion of the rate of repair of dimethipin-induced cellular damage.Mention of trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.