PARTIAL CHARACTERIZATION OF GLUTATHIONE S-TRANSFERASES FROM WHEAT (TRITICUM SPP) AND PURIFICATION OF A SAFENER-INDUCED GLUTATHIONE-S-TRANSFERASE FROM TRITICUM-TAUSCHII

Hexaploid wheat (Triticum aestivum L.) has very low constitutive gluta thione S-transferase (GST) activity when assayed with the chloroacetam ide herbicide dimethenamid as a substrate, which may account for its l ow tolerance to dimethenamid in the field. Treatment of seeds with the herbicide safener fluxofenim increased the total GST activity extract ed from T. aestivum shoots 9-fold when assayed with dimethenamid as a substrate, but had no effect on glutathione levels. Total GST activity in crude protein extracts from T. aestivum, Triticum durum, and Triti cum tauschii was separated into several component GST activities by an ion-exchange fast-protein liquid chromatography. These activities (iso zymes) differed with respect to their activities toward dimethenamid o r 1-chloro-2,4-dinitrobenzene as substrates and in their levels of ind uction by safener treatment. A safener-induced GST isozyme was subsequ ently purified by anion-exchange and affinity chromatography from etio lated shoots of the diploid wheat species T. tauschii (a progenitor of hexaploid wheat) treated with the herbicide safener cloquintocet-mexy l. The isozyme bound to a dimethenamid-affinity column and had a subun it molecular mass of 26 kD based on sodium dodecyl sulfate-polyacrylam ide gel electrophoresis. The purified enzyme (designated GST TSI-1) wa s recognized by an antiserum raised against a mixture of maize (Zea ma ys) GSTs. Amino acid sequences obtained from protease-digested GST TSI -1 had significant homology with the safener-inducible maize GST V and two auxin-regulated tobacco (Nicotiana tabacum) GST isozymes.