Variability of glutathione S-transferase levels and dimethenamid tolerance in safener-treated wheat and wheat relatives

Glutathione S-transferase (GST) levels were quantified in shoots of wheat and wheat relatives to determine if variation existed for GST levels, with or without treatment with herbicide safeners, and if GST levels could be used as an accurate biochemical marker for wheat seedling tolerance to the herbicide dimethenamid. Wheat lines and relatives were either unsafened or treated with the safeners fluxofenim (CGA-133205) or cloquintocet-mexyl (CGA-185072). GST levels were assayed using an enzyme-linked immunosorbent assay utilizing a maize GST antibody (GST-ELISA) and an enzyme activity assay using dimethenamid as a substrate (GST-D). In general the GST-ELISA indicated that significant GST was present constitutively (in untreated plants) and that the two safeners increased GST levels to a similar extent. In contrast to the GST-ELISA, the GST-D assay generally detected little or no constitutive GST-D activity; fluxofenim increased GST-D activity more than cloquintocet-mexyl. Tolerance to dimethenamid in fluxofenim-safened wheat seedlings in the greenhouse was correlated with GST-D activity (r² = 0.51) but not with GST-ELISA (r² = 0.03). These data suggest that screening wheat and wheat relatives for safener-increased GST-D activity can be used as a biochemical marker to predict and select for increased wheat seedling tolerance to dimethenamid.