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Feelin’ No Pain?

An amazing short story, entitled “The Sound Machine”, by the British writer Roald Dahl was first published in the September 17, 1949 issue of the New Yorker. In this story, “A man named Klausner invents a machine that can hear sound the human ear cannot hear. It reproduces the sounds on a lower pitch so that human beings can hear it. With this machine he hears roses scream as his neighbor cuts them. The next morning he hears a tree scream when he cuts into it with an axe.” (from The New Yorker)

Note: If you can’t access a copy of the story, you can view a video dramatization of it on YouTube.

Here’s a brief excerpt from “The Sound Machine”:
He put the earphones on his head and switched on the machine. He listened for a moment to the faint familiar humming sound; then he picked up the axe, took a stance with his legs wide apart and swung the axe as hard as he could at the base of the tree trunk. The blade cut deep into the wood and stuck there, and at the instant of impact he heard a most extraordinary noise in the earphones. It was a new noise, unlike any he had heard before-a harsh, noteless, enormous noise, a growling, low-pitched, screaming sound, not quick and short like the noise of the roses, but drawn out like a sob, lasting for fully a minute, loudest at the moment when the axe struck, fading gradually fainter and fainter until it was gone.

That plants could experience pain (let alone scream) in response to wounding is a silly notion, right? Since plants don’t have a nervous system or a brain, like animals, how could a plant feel pain?

Mr. Klausner posits: “You might say,” he went on, “that a rosebush has no nervous system to feel with, no throat to cry with. You’d be right. It hasn’t. Not like ours, anyway. But how do you know, Mrs. Saunders, – and here he leaned far over the fence and spoke in a fierce whisper – “how do you know that a rosebush doesn’t feel as much pain when someone cuts its stem in two as you would feel if someone cut your wrist off with a garden shears? How do you know that? It’s alive isn’t it?

But how would a plant scientist likely respond to Mr. Klausner?

No Pain, No Gain?

A likely response from most plant physiologists can be found in the popular book “What a Plant Knows” by Dr. Daniel Chamovitz: “While plants feel touch, they don’t feel pain.

This statement is from Chapter Three of this book, entitled “What a Plant Feels”. In this chapter, Dr. Chamovitz compares and contrasts the perceptions of, and responses to, varying degrees of mechanical stimulation in plants versus people.

He introduces the notion that plants can sense physical disturbances with: “It’s probably a bit surprising, and maybe even a bit disconcerting, to discover that plants know when they’re being touched. Not only do they know when they’re being touched, but plants can differentiate between hot and cold, and know when their branches are swaying in the wind. Plants feel direct contact: some plants, like vines, immediately start rapid growth upon contact with an object like a fence they can wrap themselves around, and the Venus flytrap purposely snaps its jaws shut when an insect lands on its leaves. And plants seemingly don’t like to be touched too much, as simply touching or shaking a plant can lead to growth arrest.

OK, but I’d say that plants do not “know” or “feel” anything, with respect to the common usage of these words. For example, would you say that an iPhone or iPad “feels” the touch of fingertips on the touch-screen? I think not. But I get that anthropomorphizing plants sells more books, and I’ve already had my rant on this subject, so I’ll drop it for now.

Anyway, it’s generally accepted that plant cells can indeed detect or sense mechanical disturbances (in nature, mostly caused by wind). This is amply supported by cellular and molecular evidence. (For example, please see Ref. 1 below)

And we also know that, when physically wounded with cellular damage – by cutting or by herbivory, for instance – parts of the plant far removed from the wound site may begin to produce defensive chemicals. (Please see Ref. 2 below, for example.)

In other words, most experimental evidence supports the idea that plants respond systematically to physical wounding (cellular damage), sometimes within minutes, and that such “wound responses” are different than how plants respond to mechanical stimulation (without cellular damage) such as wind or touch.

Interestingly, this is somewhat analogous to the difference between “touch” and “pain” receptors in our nervous system.

Given that there appears to be systemic wound signals in plants that may travel from the wound site throughout the whole plant within minutes, the question remains: Do plants experience something akin to what we call physical “pain”?

I’d say that the evidence supports the idea that plants do indeed experience “pain” when physically wounded, which, in turn, triggers wound responses.

This very much depends, however, on how one defines “pain”.

To Be Continued….

References

1. Monshausen, G. B. and E. S. Haswell (2013) “A force of nature: molecular mechanisms of mechanoperception in plants.” Journal of Experimental Botany, Vol. 64, pp. 4663-4680. doi: 10.1093/jxb/ert204 (Full Text)

2. León, J, E. Rojo and J. J. Sánchez‐Serrano (2000) “Wound signalling in plants.” Journal of Experimental Botany, Vol. 52, pp. 1-9. doi: 10.1093/jexbot/52.354.1 (Full Text)

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