When humans are attacked, sensory cells transmit signals through our nervous system, spitting out the neurotransmitter–glutamate. Glutamate stimulates our brain’s amygdala and hypothalamus. This triggers the stress hormone–adrenaline–that jolts us into fight or flight mode. Plants don’t have neurotransmitters. They don’t have nervous systems. The don’t have brains. But now, for the first time, scientists are able to observe how a plant responds to an attack with vivid real-time imagery that illuminates the remarkable differences and similarities between plants and humans. Same substance, same results, different anatomy. In the video below, a plant gets chomped on by a caterpillar. At the site of the wound, the plant spills out glutamate–the same chemical as our glutamate neurotransmitter, but not a neurotransmitter. This triggers a calcium wave throughout the plant body, stimulating a plant stress hormone that prepares it for the vegetal version of fight or flight.
To observe what’s happening, scientists sampled a gene from jellyfish that makes them glow green. Then they genetically modified plants to produce a protein that fluoresces around calcium. The results are a blazing calcium wave that undulates through the plant vascular system when it gets bit.
“[For] the first time, it’s been shown that glutamate leakage at a wound site triggers a system-wide wound response, and the first time we’ve been able to visualize this process happening ,” says Simon Gilroy, professor of botany at the Gilroy Lab at the University of Wisconsin-Madison, and senior author on the paper out today in the journal Science.
An incidental breakthrough
The discovery came about via “the classic opportunistic randomness of science,” says Gilroy. The lab wasn’t investigating plant wounds. It was looking at how plants take in and assimilate information. One day, postdoctoral researcher and first author on the paper, Masatsugu Toyota, approached the team: “‘You have to see this. This is amazing,” he said.’ It just played out in front of us,” says Gilroy.
‘Fight or Flight’ in plants is more like ‘Repulse and Rebuild’
Fight or flight is not an appropriate response for 80% of life on earth that is slow moving and tethered to the ground. Plants have to do some sophisticated information processing.
“If you’re an animal, dealing with the world at some level is relatively straightforward because you don’t really have to know what’s going on,” says Gilroy. “All you have to know is if something bad is happening and you go, ‘Oh, oh, this doesn’t feel good. I don’t really know what’s going on, but I’m going to leave.’ Movement gives you a tremendous ‘out’ that doesn’t require you to be enormously sophisticated… But for a plant, it doesn’t have that luxury. Plants actually have to know a lot more.”
A plant’s perspective
“In response to wounding, there’s a lot of things that you want to trigger if you’re a plant.” Gilroy explains, ‘‘’Somebody’s chewing on my leaf. I want all the rest of my leaves now to taste awful so that I can survive. But I’ve also got to deal with the fact that I’ve now lost a bit of leaf or lost a branch.’’’ A plant’s rapid information system is “all about freaking out, and then there’s a whole set of developmental things that you’re going to trigger. Long-term things which are really just designed to replace and regenerate and deal with the fact that bad things have happened and maybe you’ve lost part of yourself. For an animal that could be devastating. But for plant, the way they deal with it is they just rebuild themselves.”
The plant’s architecture has the same ‘theme’ as our own nervous system
The fluorescent wave surging through the plant vein evokes imagery of a nerve impulse. “You want to make it nerve conduction, because that’s what it looks like,” says Gilroy. “But there are no nerves so you have to take a step backwards.” Gilroy adds, “ They look like a bit of the nervous system has been sort of conserved inside a plant–but not quite. It kind of looks like it, but clearly that isn’t what it is.” Scientists already knew plants and animals (including us) have to do the same bodily thing at a very fundamental level to process information about how our bodies interact with the environment. “The amazing bit of it is that we can now visualize the same kinds of processes going on in plants.” The plant architecture, it’s anatomy, is remarkably different from ours given all other similarities. “The kinds of cells transmitting the signal are clearly not nerve cells, but the goal is the same. Something bad is happening in one part of the organism and it’s trying to rapidly tell another part of the organism to do something about it and it’s just kind of mind-blowing.”
Gilroy says this work is still in its infancy but he’s excited about what’s to come; from investigating whether they’ve found the hardwiring system of information exchange, to being able to tell plants they’re about to be attacked so they can preemptively defend themselves. “Classic science. You think you found one thing and there’s a thousand questions that come from it.”