Wounded Plants Warn Neighbors Of Potential Danger

You might not think of plants as particularly chatty but in reality, they communicate surprisingly well with each other, especially when faced with danger. According to a recent study in the journal Frontiers in Plant Science injured plants send out emergency signals to alert neighbors to start building up their defenses.

The chain of events that led to this surprising discovery began about two years ago, after University of Delaware botanist Harsh Bais agreed to mentor 16-year-old Connor Sweeney on a research project. The ecstatic high school student got to work right away, spending all his free time, including weekends and summer breaks, in Bais's lab at the Delaware Biotechnology Institute.

His project entailed culturing Arabidopsis thaliana, also known as mustard weed, for use in experiments. The young researcher would place the seeds in Petri dishes and test tubes filled with agar to promote growth. The seeds would germinate about six days later and transform into delicate three-inch saplings with bright green leaves.

One day, Sweeney sliced a mustard weed leaf in two spots mimicking an insect bite to see how it would begin the repair process. The following day, the young researcher was surprised to find that while the injured plant remained unchanged, the roots of the neighboring young mustard weed sapling had grown considerably longer and even had lateral offshoots.

“It was crazy — I didn’t believe it at first. I would have expected the injured plant to put more resources into growing roots. But we didn’t see that.” said Bais, who conducted a similar study in 2012, where he found that soil bacteria living near the roots of a plant helped boost its immunity by signaling the leaf pores, or stomata, to close in the presence of pathogens. To ensure that it was not the same system at work, Sweeney partitioned the plants to prevent any communication between their root bacteria and repeated the experiment multiple times. The results were the same!

To see what was triggering the root growth, the scientists conducted further tests and discovered that the injured plants were releasing volatile organic compounds (VOCs) to warn its neighbors of the impending danger. Believing the healthy plant was growing its roots to absorb more nutrients to strengthen its defenses, Bais and Sweeney began looking for compounds that help trigger the increase in size. Sure enough, each time an injured plant sent out a warning, the neighboring mustard weeds began expressing more auxin, a key plant growth hormone.

The researchers are not sure what the volatile organic compounds comprise, or the length of time they persist in the atmosphere. "We don't know yet," says Bais, "but if you go through a field of grass after it's been mowed or a crop field after harvesting, you'll smell these compounds." Though Sweeney is heading off to MIT to pursue a double major in economics and biological engineering this fall, Bais plans to continue the research and get to the bottom of this fascinating style of communication that does not require a single spoken word!

This is not the first study that’s analyzed plants ‘talking’ to one another. In previous studies conducted on willow trees, poplars, and sugar maples, scientists observed that when warned about a possible insect attack, nearby uninjured plants begin spewing out bug-repelling chemicals to ward off the attack. Who would have thought that plants were so smart and resourceful?

Resources: Treehugger.com, journal.frontiersin.org,eurakaalert.com