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Plant turns predator to ward off attackers

When an insect blunders into the sticky tentacles of the carnivorous sundew plant, the leaf curls up into a kind of outer stomach in which the plant digests its catch. This is no mere reflex but a complex chemical system of capturing and devouring live prey, a new study suggests. Working with the South African cape sundew, researchers analyzed the chemicals produced by plants given a meal of live fruit flies. As the leaf engulfed the fly, the plant produced compounds called jasmonates that increased along with the degree of curl, the team reported in the Proceedings of the Royal Society B.

The leaves also curled up when the investigators touched them with a liquid preparation of jasmonate. But small stones or gentle strokes with a brush had no effect, indicating that the curling response is not just a reaction to contact or movement. Nor did dead flies evoke any response. But crushed dead flies caused the leaves to curl up – suggesting that chemicals released by trapped prey may trigger the production of jasmonates, which turn the leaf into a stomach. Many plants produce jasmonates in defense against munching insects. But that wasn’t the case here; fruit flies, which eat rotting fruits and vegetables, have soft mouthparts that don’t damage a sturdy, living plant. The researchers suspect that the sundew has adapted a system meant to defend against predators into one that allows the plant to become a predator itself.

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