Plants Signal Each Other When Attacked

WASHINGTON - Mar 26/04 - SNS -- USDA researchers have demonstrated that corn plants signal one another when attacked by insect pests.

Chemical signals released by plants when attacked not only attract beneficial insects, they stimulate early defense responses in nearby plants, according to published findings from Agricultural Research Service and university scientists.

The results demonstrated the first proof of plant-to-plant warning signals in corn plants.

The warning signals are chemical compounds called green leafy volatiles (GLV). Shortly after coming under attack from pests, corn plants send these volatiles into the air to draw support from the pest's natural enemies. The volatiles, which smell like cut grass, attract caterpillar predators and parasitoids.

When the researchers exposed undamaged corn seedlings to GLV from damaged plants, the seedlings' chemical defenses increased. But an even stronger defensive reaction was triggered when seedlings were exposed to the volatiles, purposely damaged and then treated with a beet armyworm caterpillar substance to imitate insect attack.

Plants used as an experimental control were damaged, but never exposed to GLV. They did not react as strongly, which suggests that the volatile signals help prepare the plants' defensive reaction. Different, night-time volatiles also stimulated a defensive reaction in neighboring plants. Plants that were sensitized to GLV first and then damaged--but not exposed to the caterpillar substance--did not react as strongly as they would have if they had been exposed to the caterpillar substance.

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