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Articles

Activity in Vivo and Redox States in Vitro of Nitro- and Chlorodiphenyl Ether Herbicide Analogs ¹

Department of Botany and Plant Pathology, Colorado State University, Fort Collins, Colorado 80523, Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523

Excised cucumber (Cucumis sativus L. cv 447 Wisconsin SMR 18) cotyledons were sensitive to acifluorfen-methyl (methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate) and MC-15608 (methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-chlorobenzoate). Injury was detected by monitoring efflux of 3-O-methyl-D-[U-¹⁴C]glucose from herbicide-treated tissue after exposure to light. Efflux kinetics of 3-O-methyl-[¹⁴C]glucose from cotyledons treated with either acifluorfen-methyl (AFM) or MC-15608 were similar. Neither herbicide was active in darkness.

Cyclic voltammetry was used to study redox behavior of AFM and MC-15608 in protolytic and aprotic solvents. In protic media reduction of AFM was chemically irreversible. Reduction of MC-15608 in protolytic solvent was not observed. In aprotic solvent, the electrode reaction of AFM was quasireversible. The voltammogram of MC-15608 in aprotic solvent was indicative of a multielectron, completely irreversible electrode reaction.

Although the physiological data indicate that AFM and MC-15608 have similar effects in vivo, the redox behavior of the two compounds is quite different. These results suggest that mechanisms involving direct reduction and reoxidation of the diphenyl ether molecule are probably not the basis for the action of these herbicides.