RESISTANT ACETYL-COA CARBOXYLASE IS A MECHANISM OF HERBICIDE RESISTANCE IN A BIOTYPE OF AVENA-STERILIS SSP LUDOVICIANA

A biotype of Avena sterilis ssp. ludoviciana is highly resistant to a range of herbicides which inhibit a key enzyme in fatty acid synthesis , acetyl-CoA carboxylase (ACCase). Possible mechanisms of herbicide re sistance were investigated in this biotype. Acetyl-CoA carboxylase fro m the resistant biotype is less sensitive to inhibition by herbicides to which resistance is expressed. I,, values for herbicide inhibition of ACCase were 52 to 6 times greater in the resistant biotype than in the susceptible biotype. This was the only major difference found betw een the resistant and susceptible biotypes. The amount of ACCase in th e meristems of the resistant and susceptible is similar during ontogen y and no difference was found in distribution of ACCase between the tw o biotypes. Uptake, translocation and metabolism of [C-14]diclofop-met hyl were not different between the two biotypes. In vivo, ACCase activ ity in the meristems of the susceptible biotype was greatly inhibited by herbicide application whereas only 25% inhibition occurred in the r esistant biotype. Depolarisation of plasma membrane potential by 50 mu M diclofop acid was observed in both biotypes and neither biotype sho wed recovery of the membrane potential following removal of the herbic ide. Hence, a modified form of ACCase appears to be the major determin ant of resistance in this resistant wild oat biotype.