The sound a caterpillar makes when it chews on a leaf sets off a plant’s alarm system. In response, researchers say, the plant launches its defenses.
“Previous research has investigated how plants respond to acoustic energy, including music,” says Heidi Appel, a senior research scientist at the University of Missouri. “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.”
To study the effect, researchers placed caterpillars on Arabidopsis, a small flowering plant related to cabbage and mustard. Using a laser and a tiny piece of reflective material on the leaf of the plant, they were able to measure the movement of the leaf in response to the chewing caterpillar.
Appel and Rex Cocroft, a professor in the Division of Biological Sciences, then played back recordings of caterpillar feeding vibrations to one set of plants, but played back only silence to the other set of plants.
When caterpillars later fed on both sets of plants, the researchers found that the plants previously exposed to feeding vibrations produced more mustard oils, a chemical that is unappealing to many caterpillars.
“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,” Cocroft says. “This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration.”
Appel and Cocroft say future research will focus on how vibrations are sensed by the plants, what features of the complex vibrational signal are important, and how the mechanical vibrations interact with other forms of plant information to generate protective responses to pests.
“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,” Cocroft says.
“Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture,” Appel says. “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.”
The National Science Foundation funded the study, which was published in Oecologia.
Source: University of Missouri