A new study investigates a curious phenomena: The same anesthetics that render humans and other animals unconscious also, apparently, work on plants. And as The New York Times' Joanna Klein reports, the analysis could provide clues to how anesthetics work in humans—and further smudges the increasingly hazy line between plants and animals.
Anesthetics are strange compounds. As Jennifer Frazer at Scientific American reports, researchers have long known that they can stun not only plants but bacteria and even chloroplasts. But nearly two hundred years after the first use of a crude form of anesthesia, scientists still don't entirely understand how these drugs work. And our leafy friends might be just the organisms to help us figure this out.
There are two leading theories about what's going on with the knock-out gas. One suggests that the anesthetic compound binds to receptors—think of a molecular lock and key—which activates a cascade of chemical activity that leads to loss of consciousness. A second theory suggests anesthesia affects the lipid layers of cell membranes, which act as the gatekeeper for compounds that attempt to move in and out of cells. If anesthetics affect these membranes, the compounds could prevent the movement of certain biochemicals, causing an organism to lose consciousness.
To dig into how this works, an international team of researchers tested diethyl ether and lidocane on several plants that were previously known sensitive to anesthetics, Mimosa (or "sensitive") plants, and Venus flytraps. They also tested several new candidates for sedation: pea tendrils, which are known to twirl while searching for something to wrap around, and sundew traps. They either enclosed the plants in chambers with ether vapor or washed their roots with the topical lidocaine—the same drug used to numb your scrapes. As Beth Mole at Ars Technica reports, all of the plants seem to have some response to anesthetics: Venus flytraps didn't snap closed when prodded, the sensitive plants didn't respond to stimuli with their usual leaf curl, the carnivorous sundew plants failed to react to prey, and the pea tendrils became unresponsive. The researchers describe their results in December in a study published in The Annals of Botany.
More importantly, by measuring the electrical pulses of the Venus flytrap cells, the researchers found that these signals drop to zero under the influence of the drug. This is similar to humans, reports Mole, in which anesthesia knocks the bioelectrical system offline. "That two groups separated by such a profound evolutionary gulf share the same drive train hints at a deeper biological truth surrounding how Venus flytraps count and other signs of plant intelligence," writes Frazer.
The researchers also examined the roots of anesthetized Arabidopsis, a flowering plant related to mustard that is used in many experiments. By studying the cell membranes while the plant was anesthetized, they found that the sedated cells weren't functioning normally and couldn't effectively move “cargo” in and out. As Frazer reports, the new study lends support to the membrane hypothesis of anesthesia. But the debate is far from resolved; researchers are still not sure exactly how the anesthesia affects the cell membranes.
So what does the study say about plant consciousness? In recent years, researchers have found signs that plants are more than simple chlorophyll factories. As Simon Worrall at National Geographic reported in 2016, plants can develop “memories” of stressful events, trees communicate insect attacks via pheromones and even “trade” nutrients to one another through a network of fungi.
“Plants are not just robotic, stimulus-response devices,” co-author Frantisek Baluska of the University of Bonn in Germany tells Klein. “They’re living organisms which have their own problems, maybe something like with humans feeling pain or joy. In order to navigate this complex life, they must have some compass.”
Whether those actions are akin to human consciousness, however, is debatable. As Michael Pollen tells Science Friday, what plants can do blurs easy definitions. “The issue is, is it right to call it learning? Is that the right word? Is it right to call it intelligence? Is it right, even, to call what they are conscious,” he says. “Some of these plant neurobiologists believe that plants are conscious — not self-conscious, but conscious in the sense they know where they are in space ... and react appropriately to their position in space.”
Whatever the case, it’s good to know the next time your Venus flytrap gets a little rowdy you can calm it down with a spritz of ether.