Safeners detoxification

The basis of selectivity of foramsulfuron in the presence of the safener isoxadifen-ethyl is a more rapid rate of metabolic detoxification in maize compared with target weeds, in which little or no degradation of the parent sulfonylurea occurs [51]. Three main routes of metabolism have been established in maize - a hydrolytic cleavage of the sulfonylurea bridge, a deformylation of the amino group and oxidative metabolism of the dimethoxypyrimidine ring. 

Fig. 5.2. Examples of herbicide detoxification reactions stimulated by the safener mefenpyr-diethyl. (A) Conjugation reaction of fenoxaprop with glutathione (GSH). (B) Oxidative demethylation of mesosulfuron-methyl.

Herbicide selectivity in crops may involve a three-step process of detoxification, conjugation and transport into the vacuole. These three processes can be induced in a coordinated fashion by safeners. The major detoxifying enzymes occur in large gene families, which results in considerable variation in selectivity patterns. Our understanding of these enzymes and their regulation has been greatly assisted by new molecular techniques. 

Until our GST localization studies in Triticum tauschii (50), it was unclear as to why a safener could induce a detoxification system that effectively... 

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