The metabolism of propachlor in corn seedlings and in excised leaves of corn, sorghum, sugarcane, and barley is similar during the first 6 to 24 hr following treatment. At least three water-soluble metabolites are produced in each species during this period.Two of these metabolites, compounds I and II, were isolated. Compound I was identified as the glutathione conjugate of propachlor. Compound II appears to be the -glutamylcysteine conjugate of propachlor. In corn seedlings compounds I and II were shown to be transitory metabolites, and they were not detected in significant concentrations 72 hr following treatment. The possibility that N,Ndiallyl-2-chloroacetamide (CDAA) and 4-chloro-2butynyl-m-chlorocarbanilate (barban) might form similar conjugates was considered.Glutathione has been the subject of many biochemical investigations, but its role in biological systems is still not completely understood. Glutathione is a substrate or coenzyme in several enzymatic reactions and is believed to protect thiol groups of proteins. In addition, it plays an important role in the detoxication of exogenous chemicals by formation of glutathione conjugates (Boyland and Chas- seaud, 1969). Mercapturic acids are believed to be formed from the corresponding glutathione conjugates by successive removal of the glutamyl and glycine residues, followed by Nacetylation of the cysteine residue (Boyland and Chasseaud, 1969). The metabolism of organic halides and related compounds to glutathione conjugates or mercapturic acids occurs in mammals (Booth et al., 1961), birds (Wit and Leeuwangh, 1969), and insects (Cohen and Smith, 1964). A similar mode of metabolism was established in plants when 2-chloro-4ethylamino-6-isopropylamino-s-triazine (atrazine) was found to be metabolized to a glutathione conjugate and a -glutamylcysteine conjugate in sorghum (Lamoureux et al., 1970); the process was shown to be enzymatic (Frear and Swanson, 1970). Glutathione transferase activity has been demonstrated in corn, sorghum, sugarcane, Sudan grass, and Johnson grass.The enzyme is capable of catalyzing the formation of glutathione conjugates with a number of herbicidal 2-chloro-s-triazines (Frear and Swanson, 1970). The report that 2-chloro-JV-isopropylacetanilide (propachlor) reacts nonenzymatically in vitro with glutathione (Frear and Swanson, 1970) indicated that glutathione conjugation may be a pathway for metabolism of the -chloroacetamide herbicides in higher plants. This paper reports on the metabolism of propachlor by this route in several species of higher plants.
EXPERIMENTALGeneral Methods. Quantitative amino acid analyses were performed on a Technicon Amino Acid Analyzer using a 140-cm column of Chromobeads Type B and the standard citrate buffer gradient (Technicon Chromatography Corp., 1962). The 14C content of insoluble plant residues was determined by liquid scintillation techniques after the samples were combusted in an oxygen atmosphere (Shimabukuro, 1967). The general methods used for monitoring 14C, preparing silica gel thin-layer pl...
