Sedate a Plant, and It Seems to Lose Consciousness. Is It Conscious?

Plants don’t get enough credit.

They move. You know this. Your houseplant salutes the sun each morning. At night, it returns to center.

You probably don’t think much of it. This is simply what plants do: Get light. Photosynthesize. Make food. Live.

But what about all the signs of plant intelligence that have been observed?

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Under poor soil conditions, the pea seems to be able to assess risk. The sensitive plant can make memories and learn to stop recoiling if you mess with it enough. The Venus fly trap appears to count when insects trigger its trap. And plants can communicate with one another and with caterpillars.

Now, a study published recently in Annals of Botany has shown that plants can be frozen in place with a range of anesthetics, including the types that are used when you undergo surgery.

Insights gleaned from the study may help doctors better understand the variety of anesthetics used in surgeries. But the research also highlights that plants are complex organisms, perhaps less different from animals than is often assumed.

“Plants are not just robotic, stimulus-response devices,” said Frantisek Baluska, a plant cell biologist at the University of Bonn in Germany and co-author of the study. “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.”

Plants sometimes use that compass to deal with stress, competition or development. They take in information from their environment and produce their own anesthetics like menthol, ethanol and cocaine, similar to how humans release chemicals that dull pain during trauma. These may act within the plant itself or float off in the air to affect neighboring plants.

Our anesthetics work on plants too, the study confirmed, although what exactly they’re working on is unclear.

The researchers trapped pea plants in glass chambers with ether, soaked roots of the sensitive plant and seedlings of garden cress in lidocaine and even measured the electrical activity of a Venus fly trap’s cells. An hour or so later the plants became unresponsive. The seedlings stayed dormant. And the Venus fly trap didn’t react to a stimulus similar to a bug crawling across its maw. Its cells stopped firing.

When the dope wore off, the plants returned to life, as if something had hit pause — almost like they were regaining consciousness, something we typically don’t think they possess. It’s all so animal-like.

“How organisms are perceiving the environment or responding or adapting are based on some very similar principles,” Dr. Baluska said.

Researchers already knew that anesthetics with different chemical structures or elements all seem to halt pain, consciousness or activity in plants and animals — even bacteria. But how they render us unconscious or how so many different kinds physically act on the human nervous system still elude usafter more than a century of use. Some bind to receptors to turn off activity. But this can’t explain them all.

Under anesthetics, cell membranes fill up with fluids. Apply pressure to the cells, lose the fluid and the anesthetic wears off — in plants and animals. This suggests that something simple, like what is physically happening to a cell’s membrane, may be the common denominator explaining anesthetics’ effects across the plant and animal kingdoms, Dr. Baluska said.

In some plant root cells under anesthesia, Dr. Baluska and his colleagues found that membranes were having trouble doing what they normally do, recycling bits of cellular material by transporting it in and out of cells.

Dr. Baluska can’t say what was altering membrane function in the plants, but membranes are important for transferring messages via electricity from one cell to another, messages that would lead to action or movement.

The electrical activity that moves across neurons is thought by some scientists to contribute to human consciousness. If electrical activity is being disrupted by anesthetic in plants, too, causing them to “lose consciousness,” does that mean, in some way, that they are conscious?

“No one can answer this because you cannot ask them,” said Dr. Baluska.

Even so, perhaps we’re more alike, us and plants, than we think.