Herbicide safeners and glutathione metabolism

Abstract

Herbicide safeners are chemicals which protect crop plants from injury by certain herbicides, without affecting weed control efficacy of the herbicides. The protective mechanism of herbicide safeners has not yet been fully elucidated, but there is increasing evidence that safeners act by selectively enhancing herbicide detoxification in crop plants. To date, two main detoxification pathways have been related to the mode of action of herbicide safeners. The first includes oxidation and subsequent glucose conjugation, mediated by cytochrome P450‐dependent monooxygenases and UDP‐glucosyltransferases, respectively. This pathway appears to be important predominantly in safener protection to aryloxyphenoxypropionate and sulfonylurea herbicides. The second pathway represents the conjugation of thiocarbamate sulfoxides and chloroacetanilide herbicides with glutathione. This mechanism is accomplished by either elevating the levels of reduced glutathione or the activity of glutathione S‐transferase, or both. Since glutathione has been reported to be involved in several stress situations of plants its function associated with safener‐induced herbicide tolerance will be discussed in more detail in this review.

Glycosyltransferases in secondary plant metabolism: tranquilizers and stimulant controllers

“…For example, enzymes involved in xenobiotic metabolism in the liver of mammals, including glucuronosyltransferases, are known to be induced by xenobiotic agents (Tephly and Burchell 1990). A possible analogy to this may be found in plants, where several enzymes thought to be involved in xenobiotic metabolism are known to be inducible (Farago et al 1994;Robineau et al 1998). Several putative and veri®ed GTencoding genes have been found to be induced by methyl jasmonate (Imanishi et al 1998), SA (Horvath and Chua 1996;Fraissinet-Tachet 1998;Lee and Raskin 1999) and wounding (O'Donnell et al 1998).…”

“…Whether thesē avonoids are sensed directly by proteinaceous receptors, or simply induce nodulation due to indirect consequences following the elicitation of a general defence response would be interesting to know. A similar question should be asked about safener-and xenobioticinducible enzymes, including GTs, which are involved in the detoxi®cation of xenobiotics (Farago et al 1994;Robineau et al 1998). Glycosylation also aects inter plant-to-plant signalling within the same species.…”

Salinity-induced glutathione synthesis in Brassica napus

“…Environmental conditions that stimulate synthesis of GSH will therefore place an increased demand upon S-assimilation into cysteine. Support for this argument comes from reports showing that the demand for increased GSH synthesis in plants treated with cadmium (Chen and Goldsbrough 1994) or herbicide safeners (Hell 1997) was mediated by the activation of c-ECS activity and concomitant with substantial increases in the activities of key enzymes responsible for S-assimilation [ATP sulfurylase (ATP-S), serine acetyl transferase (SAT) and O-acetylserine (thiol)lyase (OAS-TL); Farago et al 1994].…”

Tissue-specific expression and localization of safener-induced glutathione S -transferase proteins in Triticum tauschii

“…Herbicide safeners protect crop plants by increasing herbicide metabolism and detoxification pathways (Fuerst and Gronwald 1986;Hatzios 1991;Farago et al 1994;Riechers et al 1996a; Davies and Caseley 1999). The increase in metabolism results from enhanced activity of herbicide detoxification enzymes, such as GSTs, cytochrome P450-dependent monooxygenases, and glucosyltransferases (Gronwald et al 1987;Cole 1994;Kreuz et al 1996;Brazier et al 2002).…”