CHARACTERIZATION OF THE SAFENER-INDUCED GLUTATHIONE-S-TRANSFERASE ISOFORM-II FROM MAIZE

The safener-induced maize (Zea mays L.) glutathione S-transferase, GST II (EC 2.5.1.18) and another predominant isoform, GST I, were purifie d from extracts of maize roots treated with the safeners R-25788 (N,N- diallyl-2-dichloroacetamide) or R-29148 3-dichloroacetyl-2,2,5-trimeth yl-1,3-oxazolidone). The isoforms GST I and GST II are respectively a homodimer of 29-kDa (GST-29) subunits and a heterodimer of 29- and 27- kDa (GST-27) subunits, while GST I is twice as active with 1-chloro-2, 4-dinitrobenzene as GST II, GST II is about seven times more active ag ainst the herbicide, alachlor. Western blotting using antisera raised against GST-29 and GST-27 showed that GST-29 is present throughout the maize plant prior to safener treatment. In contrast, GST-27 is only p resent in roots of untreated plants but is induced in all the major ae rial organs of maize after root-drenching with safener. The amino-acid sequences of proteolytic fragments of GST-27 show that it is related to GST-29 and identical to the 27-kDa subunit of GST IV.