26] Analysis of herbicide metabolism by monocot microsomal cytochrome P450

Abstract

Publisher Summary This chapter illustrates the essential steps for preparing microsomes from a variety of monocot plants and shows the assay of this material for chlorsulfuron-5-hydroxylase activity. The level of activity is high and the high-performance liquid chromatography (HPLC)-based assay is sensitive enough that radiolabeled material is unnecessary. The role of P450s in selectivity is simple: plants that are able to rapidly metabolize the active compound to one that is nonphytotoxic survive the treatment, while those that cannot, are killed. This is the basis for the use of many compounds on monocot crop species. Wheat ( Triticum aestivum ) and many of the cereal grains have nearly identical resistance to many herbicides because these plants have a very similar capacity to metabolize these compounds. The two other major monocot crop species, rice ( Oryza sativa ) and corn ( Zea mays ), have slightly different xenobiotic metabolizing capabilities, but also rely on cytochrome P450-dependent mechanisms for resistance to a variety of herbicidal compounds. While the P450-mediated hydroxylation of herbicides is an important step in metabolism-based resistance, it often does not alter the phytotoxicity of the compound and is not directly observable in vivo .