Injured Plants Warn Neighbors of Danger

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©. Jeff Chase/University of Delaware

Another study adds to the growing body of research on how plants can communicate with each other.

In a perfect world – or perfectly, wonderfully weird world, at least – plants and all the animals would speak the same language. Can you imagine? Though it would certainly make being on top of the food chain emotionally challenging, it sure would be enlightening.

As it stands, most humans don’t give much credence to the communication talents of other kingdoms – but just because they don’t speak a language we understand, it doesn’t mean plants are not getting messages to one another.

The latest in a string of studies looking at how plants and trees communicate comes to similar conclusions as its predecessors. This time around, a young high school science student and his botanist mentor spent two years studying plants. They discovered that when a leaf of Arabidopsis thaliana, also known as mustard weed, was injured, the hurt plant sent out an emergency alert to neighboring plants, which began shoring up their defenses.

"A wounded plant will warn its neighbors of danger," says Harsh Bais, the botanist from the University of Delaware, who is an associate professor of plant and soil sciences in UD's College of Agriculture and Natural Resources. "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."

Connor Sweeney, now a senior at Charter School of Wilmington, is the first author of the research, which was published in the scientific journal Frontiers in Plant Science.

The discovery came about after Sweeney had placed two of the many plants they were working with a few centimeters apart on the same petri plate – and then made two small nicks on one’s leaf to mimic an insect's attack.

What happened next, as Sweeney says, was "an unexpected surprise," notes the University of Delaware: The next day, the roots on the uninjured neighbor plant had grown noticeably longer and more robust – with more lateral roots poking out from the primary root.

"It was crazy – I didn't believe it at first," Bais says.

The team repeated the experiment numerous times in different arrays to rule out communication between the root systems, a method that has been observed before.

"The reason why the uninjured plant is putting out more roots is to forage and acquire more nutrients to strengthen its defenses," Bais says. "So we began looking for compounds that trigger root growth."

They found that the injured plant was releasing volatile organic compounds (VOCs) as its warning alarm. As described in the study: "The emission of VOCs induces a response in the neighboring plant communities and can improve plant fitness by alerting nearby plants of an impending threat and prompting them to alter their physiology for defensive purposes."

"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.

Admittedly there are many questions that remain unanswered, but it's nonetheless an exciting time for rethinking what we think we know about plants and how they're talking. While they may not be whispering, "psst, buddy, caterpillar approaching," they're still clearly getting their messages across.

Read the whole study here.