Plants Spooked by Leaf-Munching Sounds Prepare their Defenses

Don't let them fool you. Plants have feelings, too. And a recent study by researchers at the University of Missouri-Columbia found that when they sense fear, they work harder to rid themselves of potential threats.

"Previous research has investigated how plants respond to acoustic energy, including music," said senior researcher Heidi Appel, a scientist in the Division of Plant Sciences in the College of Agriculture, Food and Natural Resources and the Bond Life Sciences Center at University of Missouri-Columbia, in a news release. "However, our work is the first example of how plants respond to an ecologically relevant vibration. We found that feeding vibrations signal changes in the plant cells' metabolism, creating more defensive chemicals that can repel attacks from caterpillars."

Researchers played recordings of caterpillar feeding vibrations and compared them to those who experienced silence. They discovered that plants that were previously exposed to feeding vibrations often fought harder to produce more caterpillar-repellent mustard oils used as a defense mechanism.

This chemical defense was studied in the Arabidopsis plant that's related to both cabbage and mustard.

"What is remarkable is that the plants exposed to different vibrations, including those made by a gentle wind or different insect sounds that share some acoustic features with caterpillar feeding vibrations did not increase their chemical defenses," said Professor  Rex Cocroft of the university. "This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration.

"Plants have many ways to detect insect attack, but feeding vibrations are likely the fastest way for distant parts of the plant to perceive the attack and begin to increase their defenses."

"Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture," Appel concluded. "This research also opens the window of plant behavior a little wider, showing that plants have many of the same responses to outside influences that animals do, even though the responses look different."

More information regarding the findings can be seen via the journal Oecologia.