Studies on Mode of Action and Selectivity Mechanism of Herbicides

Abstract

The studies during these 15 years in the 6th Laboratory of Plant Physiology, National Institute of Agricultural Sciences, to which the author belonged until the end of 1977, were summarized.Tolerance mechanism of rice plants to propanil was genetically clarified by finding out an artificial rice mutant which is susceptible to the herbicide and can not hydrolyze it. This mutant also showed high susceptibility to another herbicide swep and the same tolerance mechanism of rice plants was supposed in the case of swep. Organophosphorus insecticides inhibit the propanil hydrolyzing enzyme of rice plants and the phosphate type was more active in the inhibition than the phosphorothioate type as like as in the case of cholinesterase inhibition.Diphenylethers with ortho-substituent(s), such as nitrofen, CNP, fluorodifen, or chlomethoxynil, require for light to kill weeds, and at least one of light acceptor was found to be xanthophyll with chlorophyll deficient rice mutants. This mode of action is different from that of paraquat, because of inability of the Hill reaction inhibitors and susceptibility of yellow mutant in the case of diphenylethers. These diphenylether herbicides, along with oxadiazon, phenopylate or MK-129 having quite different chemical structures from the formers, may form a new herbicide group with the common mode of action, the utility in transplanted rice culture and the low toxicity to mammalia and fish.Slow herbicidal effect of bentazon was explained by the inhibition of photosynthesis of weeds and the tolerant mechanism of graminaceous plants was found to be mainly the detoxification by hydroxylation and following conjugation with glucose at 6-position.The mode of action of such herbicides as PCP, benthiocarb, 5-chloro-4-methyl-2-propionamide thiazole, ethyl-N-(2, 4, 5-trichlorophenyl)carbamate, or lauryl DL-valinate HCl, was also proposed.