Anesthesia Works on Plants Too, and We Don’t Know Why

Plants and animals are separated by 1.5 billion years of evolution, but still have many similarities. Cell structures are broadly the same, though plants add chloroplasts and cell walls to the mix. Animals evolved muscles and discrete internal organs for processing nutrients from the environment, while plant cells are more homogenous. A plant cell from one part of the organism is more similar to one from another part than two randomly selected animal cells. Other than these details and new tissue types, cells haven’t changed much in the last 1.5 billion years. That’s what, in theory, makes plants good candidates for this research. Though they may be similar in cell structure, plants are still they’re missing the major element that anesthesia shuts down in animals, neurons.

Drawing of Purkinje cells (A) and granule cells (B) from pigeon cerebellum by Santiago Ramón y Cajal, 1899; Instituto Cajal, Madrid, Spain. Santiago Ramon y Cajal was a groundbreaking pioneer in neuron imaging and his pictures and drawings of them are some of the best ever created.

Neurons are the essential element of the nervous system and found only in animals, not plants. They transfer information about sensation and motion from peripheral parts of the body to the brain and back. By sending electro-chemical signals in the form of atomic ions, neurons can communicate great distances through the body. In someone as tall as Shaquille O’Neal, those signals travel over 8 feet, from the top of his brain to the tips of his toes. Most of this information is passed as sodium ions — atom-sized charged particles that pass through channels to zap from one neuron to the other. Lidocaine, a local anesthetic commonly used by dentists, blocks these sodium channels, stopping neurons from sending information to each other. That’s why they make your mouth numb, the neurons there can’t send pain sensations to your brain. They’re stopped.

Plants don’t have neurons, but lidocaine still deadens their movements and sensations. Just watch this video from the researchers testing Venus flytraps before and after their roots are soaked in lidocaine.

Here’s the Venus flytrap before lidocaine was applied.And here it is after.

There are no neurons for the lidocaine to affect, and no nervous system for it to deaden. So what’s going on? We can only speculate. Plant sensation and behavior seem to be decentralized. There’s no brain controlling what they do and no clear organization of their “thought processes”. Animals, with brains and nervous systems, are quite the opposite. They have clear organization. In plants, it’s more fuzzy. But even though they’re not organized, they do pass information from cell to cell just like we do, via ion channels. That’s probably where lidocaine does its work in plants, blocking these channels and cutting off communication. That’s why the hair cells in the Venus flytrap can’t tell the motor cells to contract, there’s no signal being passed between them.

So, that’s lidocaine. Though it affects completely different cell types, it follows a similar mechanism in both plants and animals. But what about ether? That’s the real mystery.

Ether and lidocaine are remarkably different chemicals, with vastly different structures, but they both work as anesthetics in plants and animals. In animals, we have some guesses about how ether works. Some results have pointed to it messing with cell membranes and somehow stopping them from communicating without completely breaking them. These membranes are layers of fat molecules that wrap every cell in our bodies, protecting them from the outside environment. It seems like ether perturbs the membranes and stops cells from communicating. Probably. But we’re not sure. Plant membranes are incredibly different though, and ether still works. It shouldn’t, but it does.

A summary of the difference between plant and animal cells.

Plant cells have cell walls to provide stiff structure and membranes to control what can enter and exit them. These cell membranes are similar to animal membranes, but have vastly different molecules in them. They’re like adobe compared to a bricks. They both work as walls for a house, but are completely different structures. Still, ether messes with them somehow. We think. We’re not sure.

That’s the conclusion scientists keep returning to with ether. We’ve known it works as an anesthetic for almost 175 years, but we just don’t know how. Now we know that it works with plants, but that only adds more to the mystery. It shows that ether is even more powerful than we knew, we just don’t know exactly what that power is. And we’ve known this for a long time. The French physiologist, Claude Bernard, discovered that ether can still plants almost 150 years ago. Today, we’re a bit closer to the answer to why, but not much. Plants might get us there.

Because of the incredible differences between plant and animal physiology, plants provide a new window into anesthetic research. Since plants and animals are quite different, this research lets us zoom in on the similar elements of the two. Anesthetics probably affect the cells of plants and animals in the same way, so plants can provide a window into their mechanism in our cells. If you’re trying to diagnose a problem, you pare it down to the fewest possible variables and eliminate as many factors as possible. It’s tough to do that with whole organisms, so comparing plants and animals could provide us with that perspective. By looking at these radically different organisms, we can zoom in on the few things that are the same in both, hoping that it’s the source of anesthesia’s effect.

So far, we’ve learned that anesthetics do stop these plants, but that’s about all. There have been a few scientists hacking away at the problem, but they haven’t made it very far yet. Fortunately, this work may go faster than anesthetic research in animals. There are fewer ethical issues surrounding plant research, so more studies can be done. Plants are easier to maintain and control than animals too, so this work could be done more rapidly and consistently than if it were tried with rats or pigs.

While research on anesthesia’s effect in plants hasn’t brought us any closer to understanding why it works on them, it could help us figure out how it works on us. We know how to give anesthesia safely, how to wake up anesthetized people, and how to dose it just right so no one feels pain in surgery. We know a lot about anesthesia, but plants may be the answer to figuring out the details. Right now, anesthesia science is like physics before Einstein. We understood that gravity existed, knew how to measure and use it, and had mathematical formulas that relied on it that worked perfectly, but we still didn’t understand what it was. Einstein realized that it’s the curvature of space-time and changed physics forever by explaining just why gravity does what it does. Anesthesia’s Einstein may be a botanist who’s currently poking a Venus flytrap over and over, seeking to know just why it’s not doing what it’s not doing.

References

Perouansky, M. (2012). The quest for a unified model of anesthetic action: A century in Claude Bernard’s shadow. Anesthesiology, 117(3), 465–474. https://doi.org/10.1097/ALN.0b013e318264492e

Yokawa, K., Kagenishi, T., Pavlovič, A., Gall, S., Weiland, M., Mancuso, S., & Baluška, F. (2018). Anaesthetics stop diverse plant organ movements, affect endocytic vesicle recycling and ROS homeostasis, and block action potentials in Venus flytraps. Annals of Botany, 122(5), 747–756. https://doi.org/10.1093/aob/mcx155

Yokawa, Ken, Kagenishi, T., & Baluška, F. (2019). Anesthetics, Anesthesia, and Plants. Trends in Plant Science, 24(1), 12–14. https://doi.org/10.1016/j.tplants.2018.10.006