Plants can sense and react to temperature changes, harsh winds, and even human touch. But can they hear?
They have no specialized structure to perceive sound like we do, but a new study has found that plants can discern the sound of predators through tiny vibrations of their leaves — and beef up their defenses in response.
It is similar to how our own immune systems work — an initial experience with insects or bacteria can help plants defend themselves better in future attacks by the same predator. So while a mustard plant might not respond the first time it encounters a hungry caterpillar, the next time it will up the concentration of defense chemicals in its system that turn its once-delicious leaves into an unsavory, toxic meal.
Now, biologists from the University of Missouri have found that this readying process, called “priming,” can be triggered by sound alone. For one group of plants, they carefully mimicked what a plant would “hear” in a real attack by vibrating a single leaf with the sound of a caterpillar chewing. The other group was left in silence.
When later faced with a real caterpillar, the plants that heard chewing noises produced a greater amount of insecticide-like chemicals than the silence group. They also seemed able to pick out those vibrations signaling danger; playing wind noises or insect mating calls did not trigger the same chemical boost. . . .
Although it has not been proved, the suspicion is that plants can perceive sound through proteins that respond to pressure found within their cell membranes. Sound waves cause their leaves to vibrate ever so slightly, causing the plant to respond accordingly.
Because chewing insects produce high-amplitude vibrations that travel rapidly to other parts of a plant, the researchers were able to record the fine movement of a leaf during a caterpillar feeding episode using a laser tracking system. They then played back the recording to a group of 22 Arabidopsis plants, related to mustard and cabbage, that had not been exposed to caterpillars before.
Appel then placed real caterpillars on the leaves of the group to feed. After waiting a day or two for the plants to mount their defenses, she measured the chemistry of their leaves for insecticide-like chemicals called glucosinolates — the same substance that gives mustard its kick. If eaten in large doses, however, it becomes toxic.
Not only was the concentration of glucosinolates higher than a control group, but there was also a correlation between concentration and how strong the vibrations were. If the leaf moved a greater amount during playback, they saw more of the chemical being produced by the plant.
To see if a plant would react to any type of sound, the researchers tried playing a leafhopper mating call or blowing wind. In response to these, it did not appear to put up extra defenses.
The published study is here.
So maybe playing music and talking to plants does something after all!
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