Plants don't have ears or a central nervous system, but new research out of the University of Missouri has demonstrated that they might still have the ability to "hear," reports the Washington Post. More specifically, plants have been shown to exhibit an immune response to the mere sound of a hungry insect.

For the study, researchers played the sound of a caterpillar chewing to a group of plants, which caused subtle vibrations on the plants' leaves. The plants were able to recognize these vibration patterns as danger, and responded by mounting the appropriate immune response. In other words, it appears that plants can "hear" themselves being chewed on.

Although this isn't hearing in the same sense that animals can hear, it would appear that plants can sense their environment in far more sophisticated ways than previously believed. Plants, too, have an ability to respond to sound; it's a plant's version of hearing.

Researchers hypothesize that plants achieve this remarkable ability thanks to proteins that respond to pressure found within their cell membranes. Vibrations cause pressure changes within the cell, which can alter the behavior of the proteins; however, additional study will be required to confirm or deny this theory.

Once researchers identify the exact mechanisms at play in this process, it could lead to advances in crop protection. Farmers could potentially learn to use sound to elicit a plant's natural chemical defenses against insect threats, rather than resorting to pesticides.

“We can imagine applications of this where plants could be treated with sound or genetically engineered to respond to certain sounds that would be useful for agriculture,” said study author Heidi Appel.

The study adds to the growing list of ways that plants have been shown to sense their environments. They are not the boring, inanimate organisms that many people assume they are. For instance, some plants are able to communicate with each other and signal impending danger to their neighbors by releasing chemicals into the air. Plants can respond to light (think about sunflowers) and temperature. Some can even respond to touch, such as the Venus flytrap, which snaps shut when prey stimulates its trigger hairs.

So, if plants can "hear" themselves being eaten, does this mean they might also respond to other types of sound, such as music? For instance, some gardeners claim that plants grow better when music is playing.

So far such claims have been unsubstantiated by science, and it's a difficult thing to study. Controlling for the range of sounds in Beethoven's Symphony No. 9, for instance, is not an easy task. Furthermore, while it's easy to understand why learning to respond to the sounds of a chomping insect might be evolutionarily advantageous for plants, it's not immediately clear why they should develop an ear for classical music.

But who knows, maybe there's something universal about certain kinds of music. Those prone to play tunes to their tomato plants will just have to wait for further study to know for sure. 

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