NONENZYMATIC CONJUGATION OF FENOXAPROP-ETHYL WITH GLUTATHIONE AND CYSTEINE IN SEVERAL GRASS SPECIES

Laboratory studies have shown that the amounts of glutathione (GSH) an d cysteine are higher in grass species that are moderately tolerant, s uch as wheat(Triticum aestivum L., cv. Fredrick), and moderately susce ptible, such as barley (Hordeum vulgare L., cv. Leger) and triticale ( cv. OAC Trillium), to fenoxaprop-ethyl (FE) than in species that are v ery susceptible to the herbicide, such as oat (Avena sativa L., cv. OA C Woodstock), wild oat (Avena fatua L.), yellow foxtail (Setaria glauc a (L.) Beauv.), large crabgrass (Digitaria Sanguinalis (L.) Scop.) and barnyard grass (Echinochloa crus-galli (L.) P.B.). The safener, fench lorazole-ethyl (FCE) was found to increase and decrease, respectively, the amounts of GSH and cysteine in the moderately tolerant and modera tely susceptible species but had no effect on the susceptible species. It is suggested that in the moderately tolerant and moderately suscep tible species, especially following FCE treatment, more GSH is availab le to detoxify the herbicide. Glutathione-S-tranferase activity (GST) for FE was found to be very low in all of the species tested. In vitro experiments at physio-logical pH, demonstrated that FE may conjugate with GSH nonenzymatically. Therefore, it is suggested that nonenzymati c conjugation of fenoxaprop-ethyl with glutathione may be an important mechanism for tolerance of some grasses to this herbicide.