Effect of Sethoxydim and Haloxyfop on Acetyl-Coenzyme a Carboxylase Activity inFestucaSpecies

Abstract

In greenhouse studies, the calculated I50(herbicide application resulting in 50% inhibition of shoot regrowth) in tall fescue was approximately 0.004 kg/ha for both sethoxydim and haloxyfop. In red fescue, the I50for sethoxydim and haloxyfop was 9.4 kg/ha and 0.04 kg/ha, respectively. As measured in crude cell extracts of tall fescue, incorporation of14C-acetyl-coenzyme A into fatty acids was inhibited 62 and 71% by 10 μM sethoxydim and 10 μM haloxyfop, respectively. In red fescue, 10 μM haloxyfop inhibited14C-acetyl-CoA incorporation into fatty acids by 29%, whereas 10 μM sethoxydim had no effect. The I50for inhibition of acetyl-coenzyme A carboxylase activity in tall fescue with sethoxydim and haloxyfop was 6.9 and 5.8 μM, respectively. In red fescue the I50for haloxyfop was 118 μM. Sethoxydim concentrations as high as 1 mM had little effect on acetyl-coenzyme A carboxylase activity in red fescue. These results suggest that acetyl-coenzyme A carboxylase is a sensitive site of action for sethoxydim and haloxyfop in tall fescue, and that tolerance to these herbicides in red fescue is due to the presence of a more tolerant form of the enzyme.