M-置換ジフェニルエーテル系化合物TOPEとKC6361の生理的作用特性

Abstract

This study was conducted to examine physiological effects of m-substituted diphenylethers, TOPE (3-methylphenyl-4-nitrophenylether) and KC6361 [3-(N, N′-diethylcarbamoyl)-phenyl-4-nitrophenylether]. Both compounds are p-nitrodiphenylethers, but their A rings are substituted at meta position with methyl and diethylcarbamoyl group, respectively. TOPE was found to exert its herbicidal effect by causing swelling of meristematic regions of treated monocots and wrinkled expansion of cotyledon tissues of dicots, with and subsequent necrosis of the treated tissues. The mechanism of action of TOPE did not appear to be associated with the inhibition of the photosynthetic and mitochondrial electron transport, the porphyrin pathway, or the carotenoid biosynthesis. Rather, TOPE abnormally stimulated nucleic acid biosynthesis. These effects might result in ultimate death of the treated plants. KC6361, applied at preemergence at rates ranging from 0.5 to 1kg/ha, effectively controlled the weeds of amaranth (Amaranthus viridis), flatsedge (Cyperus iria), large crabgrass (Digitaria sanguinalis), and barnyardgrass (Echinochloa crus-galli), following the appearance of white foliage. However, the crops of soybean (Glycine max), rice (Oryza sativa), and corn (Zea mays) were not injured by KC6361 even at a rate of 2kg/ha, showing that KC6361 has a relatively good selectivity between weed and crop species. KC6361, like pyridazinone herbicides such as norflurazon [4-chloro-5-(methylamino)-2-(α, α, α-trifluoro-m-tolyl)-3 (2H)-pyridazinone], enhanced the growth of dwarf rice (O. sativa cv. Tanginbozu) in a certain concentration range. KC6361 increased phytoene and phytofluene levels in treated leaves, but decreased β-carotene level. These results imply that KC6361, similarly to norflurazon, has an inhibitory effect on phytoene and/or phytofluene desaturase in the carotenoid biosynthetic pathway. The effects of both TOPE and KC6361 occurred under light as well as under dark condition. Taken altogether, it can be concluded that physiological activities of the p-nitrodiphenylether compounds in which the A rings are substituted at meta position rather than at ortho and para position are totally distinct from those of the commercialized light-dependent p-nitrodiphenylether herbicides. Furthermore, their physiological activities vary with the substituted group at meta position of A ring.