Metabolism of Herbicides

Abstract

Herbicide metabolism in plants and microorganisms is a major factor in the dissipation of these compounds in the environment. Metabolic degradation of herbicides by plant enzymes is the main mechanism of plant resistance to such phytotoxic chemicals. Alternatively, some plant enzymes can metabolize certain nonphytotoxic chemicals (termed proherbicides) to yield active herbicides within the plant. Generally, metabolism of pesticides can be categorized into three separate phases: phase I (enzymatic conversion of a herbicide to a less active compound), phase II (enzymatic conjugation of the parent compound or metabolites generated from phase I), and phase III (conversion of phase II metabolites into secondary conjugates of bound residues). These categories are discussed generally and specifically using typical herbicides as examples. The metabolic divergences and similarities of plant and microbial metabolism are discussed in general, and selected compounds from various herbicide families are used to illustrate metabolic routes of herbicides in plants and microorganisms.