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Rock Doc: Plants respond to sounds of insects eating leaves

By E. Kirsten Peters, College of Agricultural, Human & Natural Resource Sciences

peters-e-k-2010-80PULLMAN, Wash. – Plants are not as dumb as they look.

At least to me, plants have never seemed like the brightest bulb in the box. They stand around, looking green, hoping for a sunny day but not able to walk, talk or turn on the TV. However, due to a recent university press release, I’ve got to rethink my attitudes about vegetation.

Two scientists at the University of Missouri, Heidi Appel and Rex Cocroft, studied a plant called Arabidopsis. That’s a common experimental plant used by researchers because it’s fast growing and a great deal is known about it. It is a flowering plant that you can think of as a cousin to mustard and cabbage.

The researchers let caterpillars feed on a group of Arabidopsis plants. Using special devices, they recorded the sounds or vibrations made by the insects chewing on the leaves.

Next Appel and Cocroft and their team took two new sets of plants and separated them. To one set, they played back recordings of the sounds and vibrations the insects made as they fed on the Arabidopsis leaves. To the second set of plants, they played back a silent tape – in other words, this second set of plants was the “control” in their experiment.

Then the team let caterpillars feed on both sets of plants. Results showed that the Arabidopsis that had been exposed to the sounds of the insects feeding on leaves had more mustard oils in their leaves than did the control group. Mustard oils are chemicals many insects don’t like and will avoid.

“What is remarkable is that the plants exposed to different vibrations, including those made by a gentle wind or different insect sounds…did not increase their chemical defenses,” Cocroft said in a press release. “This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration.”

Plants really are not dim bulbs.

“Plants have many ways to detect insect attack,” Cocroft said in the press release. “But (insect) feeding vibrations are likely the fastest way for distant parts of the plant to perceive the attack and begin to increase their defenses.”

Next steps for the researchers include learning more about exactly how vibrations are sensed by the plants and what parts of the complex sounds may be the most important. The results of this type of work are not just academic. A long way down the road, such research may be able to improve crop plants, giving them a natural way to boost their own defenses against insect pests.

“Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture,” Appel said. “This research 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.”

I’ve got a new respect for plants – and the researchers who are learning surprising things about them.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

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