New Discoveries Made in How Plants Warn Each Other of Danger

Tiny bites from a caterpillar don't seem small to the plant on which it feasts. Those tiny bites helped clue in researchers that plants might have their own unique way of yelling out in 'pain' and sharing that response with other plants.

The research comes from a team at the University of Wisconsin-Madison. Professor of Botany Simon Gilroy and postdoc researcher Masatsugu Toyota collaborated on the find. The pair has since collected over a dozen videos displaying the reaction of plants in response to stress. 

Plants using calcium for communication

In the videos, a plant encounters a very hungry caterpillar. Just seconds after taking a bite, fluorescent light moves over the entire leaf and alerts the surrounding plants. The fluorescent light tracks calcium throughout the plant's tissue. More than tracking calcium, it also tracks glutamate -- a neurotransmitter found in animals -- and how glutamate activates the calcium after a plant gets hurt. 

These videos are the best proof to date of the hidden communication between plants. Gilroy and Toyota collaborated with an international team of researchers, including botanists from the Japan Science and Technology Agency, Michigan State University and the University of Missouri.

“We know there’s this systemic signaling system, and if you wound in one place the rest of the plant triggers its defense responses,” said Gilroy. “But we didn’t know what was behind this system.”

“We do know that if you wound a leaf, you get an electrical charge, and you get a propagation that moves across the plant,” Gilroy added.

However, what triggered the electric charge and how that charge moved through a plant were unknown before these videos. The researchers guessed calcium had something to do with the charge. 

Calcium is found nearly everywhere and it often serves as a living organism's signaling device regarding change in environment. Calcium also carries a charge and can produce an electrical signal. 

To best test their theory, the team didn't just need new videos; they needed new types of plants. Toyota developed plants that produced a protein that emits light in the presence of calcium. This allowed the researchers to track both the presence of calcium and its concentration. 

After issuing the cut or bite or bend on the plant, the signals moved quickly throughout the plants at roughly one millimeter per second. 

What this means for botany

Gilroy and Toyota's research reaffirms and furthers previous studies conducted by Swiss scientist Ted Farmer. Farmer showed the connection between defense-related electrical signals and the glutamate. He also showed how mutant plants missing those glutamate receptors lost their electrical response to threats. 

This caused Gilroy and Toyota to look at the calcium flow during a plant being wounded.

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“Lo and behold, the mutants that knock out the electrical signaling completely knock out the calcium signaling as well,” said Gilroy.

The new study connects with similar research in recent years that continue to prove that plants are far from inert. And Gilroy said he has plenty of videos for anyone looking to question their research.

“Without the imaging and seeing it all play out in front of you, it never really got driven home — man, this stuff is fast!” he says.