We hear a frightening noise and naturally feel the need to defend ourselves. The noise is registered in our ears as a series of vibrations traveling through a medium, and we are instantly alert. A new study shows that plants-yes, plants-can do something very similar.
Researchers recorded the sounds, or vibrations, made by caterpillars when they feed on a plant and then presented the vibrations to other plants. They set up a control, or a separate group of plants, that were not exposed to the vibrations. At the end of the study, the researchers found that the plants subjected to the feeding vibrations produced more mustard oil, a chemical that caterpillars find unappetizing.
This chemical defense was seen in the Arabidopsis plant, which is related to cabbage and mustard. Heidi Appel, a scientist in the Division of Plant Sciences in the College of Agriculture, Food and Natural Resources at the University of Missouri, collaborated with Professor Rex Cocroft to study this complex vibration sensing mechanism in plants.
When the plants were exposed to similar vibrations, such as those produced on the leaves during wind or in response to touch, the chemical defense was not observed. Appel suggests that the Arabidopsis has a highly complex mechanism to specify which vibrations are feeding vibrations, and therefore threatening, and which vibrations are merely environmental and harmless. The change seen in response to the distinguished feeding vibrations is considered to be a remarkable sort of metabolic change in the plant cells.
Appel and Cocroft do not know exactly how the plants sense the feeding vibrations, nor do they understand what features of a vibration signal conveys the level of threat to the plants. But they remain hopeful that, with future research, these questions will be answered. For the answers, Appel says, could be a key agricultural tool.
"Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture," says Appel. "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."
