Plants hear and respond to perceived threats, say researchers

Previous research as well as folklore have suggested that plants react to sound. There are competing theories about which music helps or harms plant life. However, plants have evolved over millions of years and for most of that time there was no music, rock, classical or otherwise, for plants to react to. So if plants have “hearing” or something like it, why did they develop it?

New research from Heidi Appel, senior research scientist in the Division of Plant Sciences at Missouri University, may provide an answer.

“Previous research has investigated how plants respond to acoustic energy, including music. 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,” said Appel in a statement.

In collaboration with Rex Cocroft, professor in the Division of Biological Sciences at MU, Appel placed caterpillars on Arabidopsis, a small flowering plant. With the aid of a laser and a small piece of reflective material, the researchers were able to measure the movement of the leaf in response to the caterpillar.

Cocroft and Appel then played back recordings of caterpillar feeding vibrations to a set of plans while playing nothing to the second set. Caterpillars were then introduced to both sets of plants. The researchers found that the plants that had been made aware that the caterpillars were coming produced an increased level of mustard oils in an attempt to repel the invaders.

“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. This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration,” said Cocroft.

In the future, the researchers hope to look more closely at how the vibrations are sensed by the plants. They also hope to gain further insights into what specific parts of the sound are important to plants and the process involved in the biological defense mechanism.

The study, “Plants respond to leaf vibrations caused by insect herbivore chewing,” was published in the journal Oecologia.