Plants ‘warn’ one another when in danger, study finds

NEWARK, Del. — You can’t hear it when you’re mowing the lawn or trimming the bushes, but there’s a lot of chatter going on among the plants. That’s because vegetation sends out an “emergency alert” to its neighbors, a new study finds, when under attack, causing nearby plants to batten down the hatches if a threat is near.

The interesting finding was actually unearthed by a high school student, 18-year-old Connor Sweeney of Wilmington, who co-authored the research with University of Delaware botanist Harsh Bais. The teen had reached out to Bais for mentoring on his research project two years ago, after Bais and other UD researchers found in 2012 that root systems can send signals to others when in danger of invasive pathogens. But similar signals hadn’t yet been uncovered when it came to the leaves of plants.

Garlic mustard weed plants
When the mustard weed is “injured,” it sends an emergency alert to neighboring plants to beef up their defenses.

For their study, Sweeney and Bais used two mustard weed plants, placing them just a few centimeters away from one another, before slicing the leaves of one of the plants in two spots in the same manner an insect might. The next day, the researchers noticed the roots of the untouched plant had grown considerably, with lateral roots even protruding from the primary one.

“It was crazy — I didn’t believe it at first,” says Bais, an associate professor of plant and soil sciences in UD’s College of Agriculture and Natural Resources, in a university news release. “I would have expected the injured plant to put more resources into growing roots. But we didn’t see that.

Sweeney completed the experiment again numerous times, ensuring the results weren’t related to the root system signals that Bais discovered years earlier. They weren’t, and the pair determined that the roots grew as a means to “forage and acquire more nutrients to strengthen its defenses.”

The researchers noted that a key growth hormone, auxin, was increasingly present in an unharmed plant when a nicked one was nearby. They also found that the unharmed plant strengthened itself by attracting more microbes in soil — the so-called “nutrients” — to its roots when in the presence of the injured plant.

“So the injured plant is sending signals through the air. It’s not releasing these chemicals to help itself, but to alert its plant neighbors,” Bais says. “It doesn’t shout or text, but it gets the message across. The communication signals are in the form of airborne chemicals released mainly from the leaves.”

The exact makeup and method of the chemical compounds being released is not yet known, but Bais is already investigating that question as a follow-up to the study. He says the compounds can be detected by the human nose after grass has been mowed — perhaps part of that common scent we associate with a freshly cut lawn.

Sweeney won’t be in the UD lab for the next segment of the study with Bais — instead he’ll be beginning his freshman year at MIT, where he’s double-majoring in economics and biological engineering. Still, he’s thrilled to be able to say he had research published in the journal Frontiers in Plant Science as a high schooler.

“Working with Dr. Bais has been great,” Sweeney says. “Most kids don’t get to work in a lab. I’ve actually completed the whole project and written a paper. It’s very exciting.”


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