CHARACTERIZATION OF GLUTATHIONE-S-TRANSFERASE ISOFORMS IN 3 MAIZE INBRED LINES EXHIBITING DIFFERENTIAL SENSITIVITY TO ALACHLOR

Glutathione S-transferases (GSTs) are a family of isozymes that cataly ze the conjugation of glutathione to several xenobiotics, including a number of important herbicides. Several GST isoforms have been identif ied in maize (Zea mays L.). In this study we focused on three isoforms , GST I, II, and IV, derived from homo- or heterodimerization of two s ubunits GST-29 and GST-27, which have been shown to be responsible for reactivity to alachlor. The expression of these isoforms was examined in three inbred lines of maize that showed tolerance, susceptibility, and intermediate resistance to alachlor -N-[2,6-diethylphenyl]-N-[met hoxymethyl]acetamide) treatment. The different isoforms were separated by anion-exchange chromatography and subunits were quantified by west ern blot analysis. GST assays were performed against both 1-Cl-2,4-din itrobenzene and alachlor. This analysis showed that the susceptible an d intermediate lines exhibit impaired function in the GST-27 and GST-2 9 subunits, respectively. In addition, this study suggests that GST IV is the principal, detoxifying enzyme for alachlor, although GST I and II are required to achieve tolerance to high rates of the herbicide.