Scientists have long known that a large number of plants respond to the sound. There have been studies showing that two genes in rice turn on in response to music and clear tones. Another study has shown that corn roots lean toward vibrations of a specific frequency. But why would plants develop the ability to hear? Scientists at the University of Missouri seem to have found the answer. The biggest reason could be to defend themselves from predators.
Plants produce an unappealing chemical to defend themselves
A team of scientists led by Heidi Appel and Rex Cocroft of the University of Missouri found that plants respond defensively after hearing the sound of caterpillars eating their leaves. Plants produce more of mustard oil that is unappealing to caterpillars, which are forced to crawl away. For this study, they placed caterpillars on a small flowering plant Arabidopsis, which is related to cabbage.
They recorded the vibrations caused by caterpillars chewing. Then Cocroft and Appel took two sets of plants. To one set, they played back recordings of the caterpillar feeding vibrations. They kept the second set in silence. Later, when caterpillars fed on both sets of plants, the set that had been previously exposed to eating vibrations produced a lot more mustard oil than the set that was kept in silence.
Plants distinguish between caterpillar vibrations and others
Caterpillars reacted to the mustard oil by crawling away. Researchers said it indicates that the vibrations could enhance plant defenses in agriculture. Appel and Cocroft discovered that plants don’t increase their chemical defenses when exposed to other kinds of vibrations such as a gentle wind. What’s more, they don’t respond even to different insect sounds that resemble caterpillar feeding vibrations in acoustic features.
That means plants are capable of distinguishing caterpillar feeding vibrations from other types of vibrations. The next step for researchers is to find out how plants sense vibrations and what features of the vibrational signal are important. The study was published in the journal Oecologia.