Plants distinguish when contact begins and ends

Plants distinguish when contact begins and ends

Even without a nervous system, plants can sense when something is touching them and when to let go, a study led by Washington State University found.

In a series of experiments, individual plant cells responded to the touch of a very fine glass rod by sending slow waves of calcium signals to other plant cells, and when the pressure was released, they sent much faster waves. While scientists have known that plants can respond to touch, this study shows that plant cells send out different signals when touch begins and ends.

“It’s pretty amazing how finely sensitive plant cells are that they can tell when something touches them. They feel pressure, and when they release, they feel a drop in pressure,” said Michael Knoblauch, a WSU professor of biological sciences. author of a study in the journal Nature Plants. “It’s amazing that plants can do this in a very different way than animals, without nerve cells and at a really subtle level.”

Knoblauch and his colleagues conducted a series of 84 experiments on 12 plants using thale cress and tobacco plants that had been specially bred to contain calcium sensors, a relatively new technology. After placing pieces of these plants under a microscope, they lightly touched individual plant cells with a microcantilever, essentially a small glass rod about the size of a human hair. They saw many complex responses based on the strength and duration of touch, but the difference between touch and removal was clear.

Within 30 seconds of touching a cell, the researchers saw slow waves of calcium ions, called cytosolic calcium, travel from that cell to neighboring plant cells, lasting three to five minutes. Removing the touch showed an almost immediate set of faster waves that dissipated within a minute.

The authors believe that these waves are probably caused by a change in pressure inside the cell. Unlike animal cells with permeable membranes, plant cells also have solid cell walls that cannot be easily broken, so just a light touch will temporarily increase the pressure inside the plant cell.


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