Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 2 - Advanced -Overview and Objectives

The selective control of broadleaf weeds in cereal grain crops by auxinic herbicides has made this group of herbicides one of the most widespread and important herbicide families in use. These herbicides are thought to act as hormone mimics. This lesson will detail how these herbicides are related structurally and physiologically to the natural plant hormone, auxin (indole-3-acetic acid; IAA) and explain the biochemical mechanisms which may be involved in their action. The mechanism of cell to cell transport and cellular uptake of auxins will be reviewed as well as how they cause cell elongation and induce ethylene biosynthesis. Receptors, signal transduction pathways and changes in gene expression for the natural hormone, IAA, will be described and related to auxinic herbicide activity.

At the completion of this lesson, students will be able to:

1. Explain the importance of the plant hormone, auxin, in plant growth and development and describe how auxinic herbicides mimic auxin.
2. Describe mechanisms of auxin transport across cell membranes and from cell to cell.
3. Explain auxin-induced cell elongation or the Acid Growth Hypothesis.
4. Understand the probable sequence of receptor recognition and signal transduction involved in auxin and auxinic herbicide activity.
5. Describe the changes in gene expression induced by auxins and the species-specific role of ethylene and hydrogen cyanide in auxinic herbicide damage.