When plants are wounded, they send out warning signals that spread to other leaves, raising the alarm and activating defense mechanisms for the undamaged areas. Now, researchers have captured this burst of activity in a set of mesmerizing videos that are helping to explain the tricky topic of plant “intelligence.”
“Plants look like they are just so intelligent—they do the right thing at the right time, they sense a huge amount of environmental information, and they process it,” says Simon Gilroy, who runs the botany lab that at the University of Wisconsin-Madison. “But they don’t have the brain, the information processing unit that we think should be necessary to make those really elegant calculations.”
To see how plants communicate internally, researchers from Gilroy’s lab genetically modified plants with a green fluorescent protein that originally comes from jellyfish. This glowing protein can be linked to specific substances, so that the team can see how various chemicals inside plants react to stimuli.
After an attack, like a caterpillar taking a bite out of a leaf, plants release an amino acid called glutamate. This in turn activates calcium levels throughout the rest of plant, which triggers defense mechanisms to help ward off further damage. Some plants release volatile compounds to repel attacking insects or even attract other insects that prey on the plant aggressors. Cotton plants, when damaged by moth larvae, attract wasps that feed on the moths.
For this study, Gilroy’s team combined the fluorescent protein with another protein that binds to calcium, and the result is a mutant plant that glows when calcium levels spike. (See pictures of plants that glow.)
When they looked at the injured plants under a microscope, they could see in real-time as the signal spread across the plant in a matter of minutes. Similar research on plant communication had pointed to glutamate and calcium as being integral to this process, but Gilroy and his lab are the first to show the activity in such vivid detail.
Both glutamate and calcium play similar roles in all kingdoms of life, including humans.
“Your heart is beating because there are flashes of calcium being released inside the cells that are triggering muscle contractions,” Gilroy says. “So you can find that theme of calcium signaling runs throughout biology
However, science is only beginning to understand how plants use these shared biological tools to communicate, Gilroy says, so studies like this may help with long-term applications for speaking plant language.
“If we know enough about how plants preemptively trigger their natural defenses, we might be able to do that on call,” he says. “In which case, we could go, OK, there’s an indication of an outbreak of some pest, I’m gonna switch these plants on to already be defended against that pest before it becomes a problem.”