Like animals, plants are eukaryotes — multicellular organisms — that split from a common ancestor called Luca billions of years ago. To survive, we all sense threats, relay messages about them within our bodies or tissues and respond to these challenges. Our actions vary, adapted for the lifestyles we maintain in different environments, but much of our basic cellular machinery is the same. Biology kept it that way: If it ain’t broke, don’t fix it.

One mechanism our cells share is fluctuating levels of calcium ions, which carry an electrical charge. In humans, this charge assists in controlling when your neurons fire messages. Changes in calcium ions make your heart beat or your muscles contract so you can get up and leave when something threatens you.

Plants, obviously, can’t run away. But researchers knew that genes that make receptors kind of like those for glutamate initiate electrical signals that travel through plants after being wounded. They turn on genes elsewhere in the plant, allowing them to respond.

With the help of glutamate, calcium ions can flow, carrying their signal through channels that open like floodgates when glutamate fits into these special receptor spaces, like keys in locks. These channels aren’t quite the same as those in the mammalian nervous system, but they look very similar and probably worked similarly. They led Dr. Gilroy and his team to look into calcium ion flow.

To make the action visible, the researchers engineered Arabidopsis plants, botany’s lab rat, to make a protein originally from jellyfish that glows green under a microscope. This sensor, in this case, shines brighter when calcium levels increase.

They also made plants that lack the glutamate-like receptor. In these, the fluorescent signal was weak: