Reported September 2007

BACKGROUND: Plants seem like the most peaceful of organisms, but even they have their own form of defense mechanisms. They emit toxins or volatile chemicals in response to plant-eating insects. For the first time, researchers at the U.S. Department of Agriculture's Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla., have identified how plants know when they are under attack. Ultimately, their work could lead to the development and genetic manipulation of plants with improved protection against pests.

THE BEST DEFENSE: Proteins already present in the plants are eaten by the attacking insects. Digesting the proteins, the insects convert this food into a new type of chemical, which is in turn secreted back onto plants in later feedings. The plants recognize these secretions as a type of "SOS" signal and launch their telltale defensive chemistry. Although researchers have long known some plants can distinguish between different insect attackers, they had not been able to fully describe all the potential interactions. There are, after all, at least four million kinds of insects and 230,000 flowering plant species, and the plant defense signals can occur at trace levels too small to easily detect or isolate. Prior research showed bacteria and fungi, for example, can trigger a variety of chemical warning signals in plants, which respond by increasing hormones to regulate defensive responses. But until now, researchers didn't know which chemical signals act as alarms, or how. It turns out the attacking insect's digestive enzymes may interact with the plant, generating a defensive response.

If you would like more information, please contact:

Eric A. Schmelz, PhD
Gainesville, FL
(352) 374-5858
Eric.Schmelz@ars.usda.gov

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