PLANTS CAN SENSE PERIL
Study finds they detect predators via vibrations then boost defenses
A newstudy says they detect predators by vibrations. »
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 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 howour own immune systems work— an initial experience with insects or bacteria can help plants defend themselves better in future attacks by the same predator. Although a mustard plant might not respond the first time it encoun- ters a 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.
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.
Although the mechanism of how plants discern sounds is not known, a deeper investigation could lead to advances in agriculture and natural crop resistance — as opposed to spraying costly and harmful pesticides.
“We can imagine applications of this where plants could be treated with sound or genetically engineered to respond to certain sounds thatwould be useful for agriculture,” said study author and biologistHeidi Appel.
The study was published online Tuesday 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 neigh- bors by releasing chemicals into the air.
Plants constantly react to their environment — not only to light and temperature changes, but also to physical stimuli. Two famous examples are the Venus’ flytrap, which snaps shut when a 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,” said plant biologist Frank Telewski, who was not involved in the research. “They can respond to gravity, wind, ice or an abundance of fruit.”
But trying to prove that plants can sense sound has been difficult.
“There is a long history of people interested in whether plants could hear sound, and that usually involved sounds that are very salient to us — music or tones of pure sound — just to see if plantswould react,” said study author and biologist Reginald Cocroft.
Even though some people swear that a soothing voice or classi- cal music works wonders for their greenery, the scientific evidence is spotty. Experts think that music in particular is too complex and varied to use in a controlled study.
When pure tones are played, some experiments have seen changes in plant growth, germination or gene expression. For instance, one recent study showed that young roots of corn will grow toward an auditory source playing continuous tones and even responded better to certain frequencies.
But what would be the evolutionary advantage of responding to such stimuli?
One argument against plants perceiving sound is that picking up on the music of Beethoven or a solid note has no bearing on a plant’swell-being— but the leaf-chomping of a nearby insect certainly does.
“None of the sounds used before are things that are ecologically relevant sounds in the plant environment,” Appel said.