Plant-tastic Chemical Signals

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During this time of year, I often find boxes and boxes of fruits and vegetables on the kitchen counter as I come home from school. My parents are both avid gardeners, and I often hear them discussing methods in which they can improve their garden. They have attempted everything from hanging CDs on the peach tree to scare off birds, to wrapping plastic around the bases of young trees to protect them from animals. Unfortunately, my parents are often unable to protect them from their greatest threat: insects. (Dun dun dun…)

Plants, however, may be able to fortify themselves against insects to an extent. An interesting article in Scientific American suggests that a plant is able to “warn” its neighbors when that plant has been infested with harmful insects. One study involved testing caterpillar preference on several willow trees. Researchers observed that caterpillars were less likely to feed on the leaves of willow trees that were near trees already infested with caterpillars. I was surprised by this, as the trees nearby should be the next nearest food source. Since the trees were not physically connected or related in any way, it was proposed that they emitted some sort of signal. Later findings suggested that the damaged plant releases a gas to unharmed plants, which results in an increased defense against dangers.

For the past few years, Martin Heil and his research team at the Center for Research and Advanced Studies have been studying the behavior of lima bean plants. When lima bean leaves are being eaten by beetles, the plant releases both a chemical signal and produces nectar that attracts other beetle-eating insects. In order to observe the chemical signals more closely, the researchers devised an experiment in which infested lima bean plants interacted with lima bean plants. After choosing specific leaves to monitor, they used gas chromatography and mass spectrometry techniques that allowed them to identify the chemicals in the released into the air. The researchers found that the healthy and half-eaten leaves of the same plant produced the same chemical, while the control, a leaf from a plant isolated in the experiment, had no scent. Strangely enough, the leaves of the healthy plant also produced the same chemicals, and were less likely to be eaten by the beetles!

Are plants “selfless” enough to warn other plants against attack? Or is the chemical signal produced by an “injured” leaf meant for the remaining leaves of the same plant, and this signal just happens to be picked up by a neighboring plant? This was the question that researchers hoped to answer in a second experiment, one in which the leaves were isolated from one another in plastic bags. This time, only the attacked leaf produced the scent. When the scent was blown towards the other leaves on the plant, those leaves began producing the scent as well. The results demonstrated that the chemical signals were meant for the other leaves of the same plant, not other plants. However, nearby plants take advantage of this warning to maintain their own wellbeing.

Even if my parents find a new way to solve the insect problem, our garden will still be filled with a variety of plants, insects, animals, and microorganisms. In this way, our garden is like a community, a mini-ecosystem in which all of these organisms can coexist. As we learned in our reading, this interdependency is what enables each species to survive. Insects and animals depend on plants, just as plants depend on insects and animals. Plants also depend on other plants, and this article made me realize the extent to which they can communicate.

About Mr. Mohn

Biology Teacher

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