Induction and inactivation of a cytochrome P450 confering herbicide resistance in wheat seedlings

Abstract

Cytochrome P450-dependent enzymes from wheat catalyze the oxidation of endogenous compounds (lauric and oleic acids) and of several herbicides (diclofop, chlortoluron, bentazon). Treatment of wheat seedlings with the safener, naphthalic anhydride and with phenobarbital increases dramatically several P450-dependent enzyme activities including diclofop and lauric acid hydroxylation. The parallel induction of lauric acid (omega-1)-hydroxylase and diclofop hydroxylase activities suggests that both compounds proceeds from the same or very similar forms of P450. To test whether either one or multiple P450 forms are involved in these oxidations, we have designed selective irreversible inhibitors of lauric acid (omega-1)-hydroxylase. Results of in vivo and in vitro experiments with acetylenic analogs of lauric acid (10- and 11-dodecynoic acids) strongly suggest that a single P450 catalyzes both laurate and diclofop hydroxylation. Treatment of wheat seedlings with these acetylenes results in a strong inhibition of the in vivo metabolism of diclofop although oxidation of chlortoluron and bentazon are not affected. Our results suggest that at least three distinct P450 forms are involved in the detoxification process of the three herbicides. Interestingly, we also demonstrate that herbicides themselves are potent inducers of the amount of total P450 and laurate/diclofop hydroxylase activies. This increased capacity of wheat to detoxify the herbicide through the induction of P450 enzymes seems to be for a large extend the mechanism which confers a tolerance on various herbicides.

Genome‐wide analysis of phenobarbital‐inducible genes in Drosophila melanogaster

“…As well, Cyp6a8 oxidizes the endogenous substrate lauric acid (C12:0), a short‐chain unsaturated fatty acid (Helvig et al ., 2004). PB inducible cytochrome P450s involved in lauric acid metabolism has been identified across a diverse set of species ranging from rats to wheat (Tanaka et al ., 1990; Forthoffer et al ., 2001).…”

Plant cytochrome P450-mediated herbicide metabolism

“…It is important to note, however, that the participation of P450s in the in vivo or in vitro metabolism of a particular herbicidal substrate may not necessarily confer resistance to that (Forthoffer et al 2001;Frear et al 1991;Helvig et al 1996;McFadden et al 1989;Zimmerlin and Durst 1990;Zimmerlin and Durst 1992) NADPH, O 2 dependence; inhibition by anti-P450 reductase antibody, 1-ABT, CO, electron transfer inhibitors, herbicides, lauric acid analogs and TET Imazapic Imidazolinone Arylalkyl hydroxylation Corn microsomes (Davies et al 1998) NADPH dependence; inhibition by 1-ABT Imazethapyr Imidazolinone Arylalkyl hydroxylation Corn microsomes (Baerg et al 1996) Metabolism inhibited by terbufos sulfone…”

Map-based cloning of a novel rice cytochrome P450 gene CYP81A6 that confers resistance to two different classes of herbicides

“…This herbicide disrupts photosynthesis of the target plant by blocking electron transfer in photosystem II (McFadden et al 1990;Leah et al 1991;Burton and Maness 1992;Forthoffer et al 2001). Sulfonylurea, on the other hand, is a different class of herbicides in terms of their translocation ability and mode of action although it has a similar herbicide spectrum to bentazon.…”