O-glucosyltransferase activities toward phenolic natural products and xenobiotics in wheat and herbicide-resistant and herbicide-susceptible black-grass (Alopecurus myosuroides)

Herbicide safeners manipulate herbicide selectivity by enhancing the activities of detoxifying enzymes, such as glutathione transferases (GSTs) and cytochrome P450 mono-oxygenases (CYPs) in cereal crops. As part of a study examining the importance of O-glucosyltransferases (OGTs) in pesticide metabolism in hexaploid bread wheat (Triticum aestivum L.), seedlings were grown in the presence of dichlormid, a safener used in maize and cloquintocet mexyl, a wheat safener. The efficacy of the treatments was confirmed by monitoring changes in the abundance of phi and tau class GSTs. OGT activities in the root and shoot tissue were assayed using phenolics of natural and xenobiotic origin to determine if they were enhanced by safeners. Cloquintocet mexyl selectively increased OGT activities toward xenobiotics (4-nitrophenol and 2,4,5-trichlorophenol) and flavonoids, (quercetin, luteolin, genistein and coumestrol) in both the roots and shoots. However, OGT activity towards simple phenols and phenylpropanoids was not enhanced by cloquintocet mexyl. Dichlormid was a much weaker enhancer of OGT activity, with the same subset of OGT activities increased as determined with cloquintocet mexyl, but with the effect being largely restricted to the roots. OGT activities were also determined in black-grass (Alopecurus myosuroides L.), an agronomically important weed in wheat. Two populations of black-grass differing in their sensitivity to herbicides were analysed. The population Peldon, which is resistant to multiple classes of herbicides due in part to the elevated expression of CYPs and GSTs active in herbicide detoxification, contained higher OGT activities than herbicide sensitive black-grass. Unlike wheat, treatment with cloquintocet mexyl or dichlormid, had no effect on OGT activities in either black-grass population. (C) 2002 Elsevier Science Ltd. All rights reserved.