Digging into a healthful salad can make you feel pretty good about yourself, but what if I told you those leafy greens might not be too thrilled about the the whole arrangement? Unfortunately for vegetarians and vegans, plants know when they are being eaten and may even try to fight back. This doesn't mean every time a grapefruit squirts juice in your eye it's a defense mechanism, but according to a 2014 study from the University of Missouri plants have amazing abilities to sense a threat and respond in kind. While no evidence suggests that plants have brains, neurons or synapses, they do have certain "analogous structures" that aid in the processing information, explains Michael Pollan in his 2014 New Yorker article, "The Intelligent Plant." The way that plants are able to sense and process environmental information and then produce an "appropriate" response is being studied in the relatively new field of plant neurobiology, and the findings published in the journal Oecologia further bolster the idea that we have been seriously underestimating plant intelligence.
In the study, researchers at the University of Missouri used audio and chemical analysis to test how plants respond to ecological threats. Hungry caterpillars were placed on thale cress, known scientifically as Arabidopsis — a small flowering plant and member of the Brassicaceae family, which is similar to mustard greens, cabbage, and everyone's favorite superfood, kale.
Thale cress is often used as a "model organism" in plant biology as it was the first to have its genome to be sequenced in 2000. As the caterpillar began to munch, the movement of the leaf was measured with a laser and a piece of reflective material. In response to the feeding, the plant leaves produce a mustard oil that is mildly toxic as a defense.
Later, a recording of the caterpillar's feeding vibrations were played for one set of plants, while another set were not exposed to any aural stimuli. When the caterpillars fed on the plants, those that had been exposed to the vibrations previously were found to produce more mustard oils than the other test group.
The study also found that the thale cress could seemingly differentiate between different types of common vibrations, such as caterpillars eating and wind. “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,” Rex Cocroft, a professor of biology at MU, said in a press release. “This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration.”
Scientists are hoping further information on how plants respond to these threatening vibrations will encourage new ways to help protect our crops from certain "insect pests" and more resilient plant breeding. “Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture,” lead author Heidi Appel said in a press release. “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.” So whether it's a caterpillar munching on a piece of kale, or a human going in for another bite, there is no doubt that plants are not into it.
Food for thought, eh?