Absorption, translocation and metabolism of 3, 3'-dimethyl-4-methoxybenzophenone (NK-049) applied to rice and barnyardgrass were examined to elucidate its selective herbicidal action between the two plants. Marked differences were observed in the rates and amounts of absorption and translocation between the rice (tolerant) and barnyardgrass (susceptible) plants. When applied on leaf surface, NK-049 readily penetrated into the leaf of barnyardgrass, while in rice, the chemical was slowly

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... . Translocation both upward and downward from the treated zone through leaf veins were slight in both plants. When applied to roots by dipping the roots in NK-049 solution, the chemical was absorbed much more by barnyardgrass as compared with by rice and readily translocated to aerial parts. When apaplied to intact seeds, NK-049 was absorbed more rapidly by barynardgrass on seed weight basis, while on seed number basis rice seeds absorbed much more NK--049 than barnyardgrass seeds. Radioactivity once absorbed by seeds was translocated to the first leaves in the seedlings of both rice and barnyardgrass, but the amount of translocated radioactivity was much greater in barnyardgrass than in rice. No appreciable difference was found in the metabolism of NK-049 between the two plants. It was suggested that one of the main factors for the selective action of NK-049 is the differences in the rate and amount of absorption and translocation of the chemical between rice and barnyardgrass. Carotenoid formation in barnyardgrass was strongly inhibited by NK-049, whereas that in rice was not affected at all. It was suggested that the susceptibility of the carotenoid-biosynthesis systems of the two plants to NK-049 were greatly different from each other and this difference contributes to the selective herbicidal action of the chemical.