Abstract
Multiple isoenzymes of glutathione transferase (GST), purified from the shoots of wheat seedlings treated with the herbicide safener fenchlorazole-ethyl, could be resolved into polar and hydrophobic types using hydrophobic interaction chromatography. Both types of GSTs could also be resolved based on their affinities forS-hexyl-glutathione-agarose. A minor proportion of the GSTs could be eluted from the column with a salt wash and this loosely bound fraction contained polypeptides which were recognized by an antiserum raised against the theta-type maize GSTZmGST I–II. The major proportion could only be recovered usingS-hexyl-glutathione and these GSTs were characterized in detail. These isoenzymes catalyzed the glutathione conjugation of xenobiotics, including herbicides, and showed additional activities as glutathione peroxidases. Each GST was composed of two subunits, with four distinct classes of subunit being determined. A 25-kDa polypeptide, termedTriticum aestivumGST 1 (TaGST 1), was the most abundant subunit and could be resolved into two variants,TaGST 1a andTaGST 1b by reversed-phase HPLC. This GST subunit was recognised by an antiserum raised against the maize GSTZmGST V–VI, which is a tau-type GST. In addition toTaGST 1, two 26-kDa polypeptides,TaGST 2 andTaGST 3, and a 24-kDa polypeptide,TaGST 4, could be resolved by a combination of hydrophobic interaction chromatography, SDS-PAGE, and reversed-phase HPLC. In the shoots of untreated wheat seedlings the major isoenzyme wasTaGST 1a–1b, while in the shoots of fenchlorazole-ethyl-treated plants the heterodimersTaGST 1–2,TaGST 1–3, andTaGST 1–4 also accumulated. Significantly, only the safener-inducibleTaGST 1–2,TaGST 1–3, andTaGST 1–4 isoenzymes catalyzed the detoxification of fenoxaprop-ethyl and this may help to explain why fenchlorazole-ethyl enhances the glutathione-mediated metabolism and also the tolerance of wheat toward this herbicide. All isoenzymes were active in detoxifying the herbicides metolachlor and fluorodifen, but onlyTaGST 1–2 andTaGST 1–3 showed any activity toward atrazine.
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