XVI International Botanical Congess

To date, 240 members of the P450 gene superfamily have been cloned in plants. The A. thaliana sequencing project indicates that a single plant may contain over 300 P450 isoforms. P450s are involved in the oxidation of hundreds of physiological substrates and probably a greater number of xenobiotics. This wide spectrum of 'physiological' P450s rather than the existence of specialized broad substrate range isoforms accounts for their role in the transformation of environmental chemicals. There is evidence that the emergence of cross-resistance to unrelated herbicides in weed species is based on enhanced metabolism of these pesticides by P450s and GSTs. We show that 1) the same P450 is capable of oxidizing unrelated xenobiotics in addition to its natural substrate and 2) that the same herbicide is metabolized by different P450 isoforms in a same plant.