The Rote of Plant and Microbial Hydrolytic Enzymes in Pesticide Metabolism

esters with carbonyl, phosphoryl, and thionyl linkages, are subject to enzymatic hydrolysis. Pesticide hydrolysis by esterases and amidases from plants and microorganlsms can serve as a deloxification or activation mechanism that can govern pesticide sel€ctivity or resistance, and initiate or determine the rate of pesticide biodegradation in the environment. Substrate specificity of esterases and amidases varies dramatically among species and biotypes of plants and microorganisms. The constitutive or induJible nature of these enzymes, as well as production of isozymes, is also important in the expression of these mechanisms' For example,'increased aryl acylamidase activity has been reported as the mechanism of evolved resistance to the hedicide Propanil in two Echinochloq weed species fiunglerice, E. colona (L.) Link; barnyardgrass, E. crus-Balli (L.) Beauv.l. Other acylamidases, such as a linuron-inducible enzyme produced by Bacillus sphaericus' have broad substrate specificities including action on acylanilide' phenylcarbamate, and substituted phenylurea herbicides. Many rnicrobial hydrolytic enzymes are exfiacellular, thus hydrolysis can occur without uptake. Advances in molecular biology have led to an increased understanding of hydrolytic enzyme actiYe sites, especially those conferring selective specificity' This knowledge will create opportunities for engineering novel resistance mechanisms in plants and biosynthetic and/or degradative enzymes