A new study shows how plants emit internal warning signals and activate their defense mechanism in response to an attack by herbivores.
When an insect eats on a leaf, it triggers many physiological reactions within a plant. Plants use calcium as a threat signal that quickly spreads to other leaves. This calcium flux indirectly also forms the defense mechanism of the plant.
Researchers at the University of Wisconsin-Madison have now explained this whole process by adding green, fluorescent protein. More than a dozen videos have shown how glutamate – an abundant neurotransmitter in animals – activates the calcium wave when the plant is attacked by an insect. In a video, a hungry caterpillar could be taken out of a leaf a bit. Within seconds, the plant glows when calcium flows from the damaged area into other leaves.
The flood of fluorescent light shows that calcium is involved in processing information and sending rapid alerts so plants can respond quickly in the situation. These videos allow researchers to track the calcium flux in the plants and get the best view of their communication systems that would otherwise remain hidden.
"We know that this systemic signaling system exists, and if you get wounded at one point, the rest of the plant will trigger its defense responses, but we did not know what was behind that system," said Simon Gilroy, a professor of botany at the University of California University of Wisconsin-Madison.
"We know that when you twist a leaf, you get an electrical charge and you get a spread that moves across the plant," adds Gilroy. What triggered this electrical charge and how it moved through the plant was unknown. "
The researchers found that the warning signal moved quickly, about one millimeter per second. It's fast enough to deliver wound signals in plant cells within minutes. It only takes a few minutes to activate the defense mechanism so that the plants can prepare themselves for future attacks by caterpillars or other insects. Understanding how plants react and defend themselves against insects is crucial to the way these attacks can be stopped.