Characterization of two acetyl-CoA carboxylase isoforms in diclofop-methyl-resistant and -susceptible biotypes of Alopecurus myosuroides

Previous results indicated that resistance to acetyl-CoA carboxylase;inhibi ting herbicides in ii Spanish diclofop-methyl-resistant biotype of Alopecur us myosuroides could be due in part to the presence of a less sensitive for m of acetyl-CoA carboxylase (ACCase, EC 6.4.1.2). In this study, partial pu rification and separation of two multifunctional acetyl-CoA carboxylase iso forms (ACCase I and ACCase II) did not reveal any differences between resis tant and susceptible biotypes of A. myosuroides in terms of purification, a ctivity, elution profile in a trimethylaminoethyl (TMAE)-anion-exchange col umn, and molecular mass of ACCase subunits. ACCase I and ACCase II eluted f rom a TMAE-anion-exchange column at approximately 280 and 220 mM KCl, respe ctively. Both isoforms were composed by subunits of 200-202 kDa. ACCase I r epresented about 90% of the total activity recovered from the TMAE column a nd was diclofop sensitive, with I-50 values (herbicide concentration result ing in 50% inhibition of ACCase activity) within the range of other suscept ible grasses. ACCase II was diclofop tolerant, with I-50 values 100-fold gr eater than those observed for ACCase I. The differences in susceptibility o bserved between resistant and susceptible crude extracts disappeared in fur ther purification steps, the I-50 values not being significantly different between R and S biotypes after TMAE-anion-exchange chromatography. These re sults indicate that the presence of two distinct, multifunctional ACCase is oforms in grasses (only reported in maize and Lolium multiflorum) is also o bserved in both the resistant and the susceptible biotypes of A. myosuroide s. However, it also confirms that diclofop resistance in the resistant biot ype is not due to a mutation at the target site, which is the predominant A CCase I isoform. (C) 1999 Academic Press.