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 as we do, but a 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 although a mustard plant might not respond the first time it encounters a hungry caterpillar, the next time it will boost 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, the scientists 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; the playing of wind noises or insects’ mating calls did not trigger the same chemical boost. A deeper investigation could lead to advances in agriculture and natural crop resistance — as opposed to spraying pesticides.
“We can imagine applications of this where plants could be treated with sound or genetically engineered to respond to certain sounds that would be useful for agriculture,” said biologist Heidi Appel, author of the study published online in the journal Oecologia.
Despite not having brains or nervous systems in the traditional sense, plants are surprisingly sophisticated. They can communicate with one another and signal impending danger to their neighbors by releasing chemicals into the air. Plants constantly react to their environment — not only light and temperature changes, but also physical stimuli. Two famous examples are the Venus’ flytrap, which snaps shut when an unsuspecting bug contacts one of its trigger hairs, and the touch-me-not plant (Mimosa pudica), which shrinks and closes its leaves upon even a slight touch.
“Plants certainly have the capacity to feel mechanical loads,” plant biologist Frank Telewski said. “They can respond to gravity, wind, ice or an abundance of fruit.”
But what would be the advantage of responding to such stimuli? One argument against plants perceiving sound is that being able to pick up on Beethoven has no bearing on a plant’s well-being — but the leaf-chomping of a nearby insect certainly does.
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.