Metabolism of Herbicides or Xenobiotics in Plants

This lesson will take an in depth view of how plants handle foreign chemicals (xenobiotics) such as herbicides. It will discuss the three main phases that plants use to handle toxic chemicals, which enzymes are involved in these biochemical conversions, how these processes help protect crops again phytotoxic chemicals and consider the importance of these processes to successful weed management. Overview Herbicide detoxication via metabolism is the primary mechanism of selectivity for most herbicides. Selective weed control using herbicides often relies on the ability of tolerant crop plants to detoxify the herbicide more rapidly than weeds. The same processes used by plants to detoxify herbicides are used for other xenobiotics (foreign chemicals); therefore, these terms will be used interchangeably. In this lesson, we will explore in detail three major phases of herbicide metabolism in plants, the enzymes involved in those processes and the final fate of herbicide metabolites. In addition, how crop injury or weed sensitivity might be altered by synergists, antagonists or other factors that affect metabolism will be described. Involvement of herbicide metabolism in resistance will also be discussed. Objectives At the completion of this lesson, learners will be able to: Understand the importance of herbicide metabolism for crop tolerance (selectivity). Identify the three major phases of xenobiotic metabolism in plants. Explain the major enzyme systems involved during metabolism of xenobiotics in plants. Provide examples of each major phase and understand how metabolism may also lead to herbicide bio-activation. Modules: Lesson home Overview and Objectives Introduction Phase I - Introduction Phase I - Oxidation Reactions Phase I - Reduction Reactions Phase I - Hydrolysis Reactions Phase II - Introduction Phase II - Glutathione Conjugation Phase II - Sugar Conjugation Phase II- Amino Acid Conjugation Phase III Field Considerations Summary Glossar