Glutathione (GSH) plays a key role in detoxification of certain herbicides (e.g. chloroacetanilides, thiocarbamates and s-triazines) in higher plants via the action of glutathione S-transferase(s) (Breaux, 1986; Pickett and Lu, 1989; Rossini et al, 1996; Gronwald and Plaisance, 1998):

X-SG (the glutathione conjugate) can then be transported into and sequestered by the vacuole (Li et al, 1995; Kreuz et al, 1996; Marrs, 1996). Glutathione S-transferases have been shown to be induced by a wide range of chemical agents (Ulmasov et al, 1995), wounding, heavy metals, ethylene, and ozone (Marrs, 1996). These enzymes may have initially evolved to conjugate naturally occurring compounds such as phenylpropanoids (Dean et al, 1995; Alfenito et al, 1998), and naturally occurring endogenous reactive electrophilic compounds (Marrs, 1996), but may have then been recruited to detoxify anthropogenic exogenous xenobiotics (Kreuz et al, 1996; Marrs, 1996). Wheat can be protected from injury from the chloracetamide herbicide dimethanamid through the use of the herbicide safener fluxofenim which induces a dimethenamid-conjugating GST 9-fold (Riechers et al, 1997).

Glutathione S-transferases (GSTs) may also be involved in conjugating electrophiles generated from the reaction of hydroxyl radicals with lipids and DNA, and thus contribute to oxidative stress resistance (Marrs, 1996). Apoplastic GST induction may be mediated by an oxidative signal in soybean (Flury et al, 1996).

In sorghum, 2 isoforms of GST have been characterized extensively; GST A1/A1 is a homodimer, GST B1/B2 is a heterodimer. The two isoenzymes exhibit distinct herbicide substrate specificities. Both are glycosylated, and exhibit GSH peroxidase activity with products of lipid peroxidation (Gronwald and Plaisance, 1998).

Alfenito MR, Souer E, Goodman CD, Buell R, Mol J, Koes R, Walbot V 1998 Functional complementation of anthocyanin sequestration in the vacuole by widely divergent glutathione S-transferases. Plant Cell 10: 1135-1149.

Breaux EJ 1986 Identification of the initial metabolites of acetochlor in corn and soybean seedlings. J. Agric. Food Chem. 34: 884-888.

Dean JV, Devarenne TP, Lee I-S, Orlofsky LE 1995 Properties of a maize glutathione S-transferase that conjugates coumaric acid and other phenylpropanoids. Plant Physiol. 108: 985-994.

Flury T, Wagner E, Kreuz K 1996 An inducible glutathione S-transferase in soybean hypocotyl is localized in the apoplast. Plant Physiol. 112: 1185-1190.

Gronwald JW, Plaisance KL 1998 Isolation and characterization of glutathione S-transferase isoenzymes from sorghum. Plant Physiol. 117: 877-892.

Kreuz K, Tommasini R, Martinoia E 1996 Old enzymes for a new job: Herbicide detoxification in plants. Plant Physiol. 111: 349-353.

Li Z-S, Zhao Y, Rea PA 1995 Magnesium adenosine 5'-triphosphate-energized transport of glutathione-S-conjugates by plant vacuolar membrane vesicles. Plant Physiol. 107: 1257-1268.

Marrs KA 1996 The function and regulation of glutathione S-transferases in plants. Annu. Rev. Plant Physiol. Plant Mol. Biol. 47: 127-158.

Pickett CG, Lu AYH 1989 Glutathione-S-transferases: gene structure, regulation, and biological function. Annu. Rev. Biochem. 58: 743-764.

Riechers DE, Irzyk GP, Jones SS, Fuerst EP 1997 Partial characterization of glutathione S-transferases from wheat (Triticum spp.) and purification of a safener-induced glutathione S-transferase from Triticum tauschii. Plant Physiol. 114: 1461-1470.

Rossini L, Jepson I, Greenland AJ, Gorla MS 1996 Characterization of glutathione S-transferase isoforms in three maize inbred lines exhibiting differential sensitivity to alachlor. Plant Physiol. 112: 1595-1600.

Ulmasov T, Ohmiya A, Hagen G, Guilfoyle T 1995 The soybean GH2/4 gene that encodes a glutathione S-transferase has a promoter that is activated by a wide range of chemical agents. Plant Physiol. 108: 919-927.