Hormones key to drought resistance.

A team of University of Missouri plant physiologists has discovered how key plant hormones help plants deal with drought. That information will be valuable to plant breeders seeking varieties that will perform well under drought stress. Researcher Robert Sharp discovered that the hormone abscisic acid (ABA) encourages root growth in drought-affected plants, which is critical to sustain water uptake, and maintains shoot growth as well. Bill Spollen, a postdoctorate in Sharp's laboratory, found that ABA apparently functions to restrict the production of another hormone, ethylene, the same gas that causes bananas to ripen, apples to soften, and tomatoes to turn from green to red.

"When we make a root ABA-deficient, the roots produce more ethylene, so the roots grow short and fat," Sharp explains. "We can restore root elongation by adding ABA or by using chemical inhibitors to restrict the plant's production of ethylene or its sensitivity to ethylene." Preliminary studies show the same thing happens in the shoot. Again, ABA can play a protective role by prohibiting excess production of ethylene under drought conditions. However, it appears that the ABA levels in shoots are insufficient to overcome the effects of ethylene fully, and so the shoots grow more slowly...