Plants distinguish when contact begins and ends

2023-05-31 13:51:14

A microscopic view of what happens when a single cell of a thale cress plant is touched by a fine glass rod. – WASHINGTON STATE UNIVERSITY/NATURE PLANTS

MADRID, 31 May. (EUROPA PRESS) –

Even without nervous system, Plants can sense when something touches them and when it is released, a study led by Washington State University has 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 that pressure was released, they sent out much faster waves. While scientists knew that plants can respond to touch, this study shows that plant cells send different signals when contact begins and ends.

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

Knoblauch and his colleagues carried out a series of 84 experiments on 12 plants using thale cress and tobacco plants that had been specially bred to include calcium sensors, a relatively new technology. After placing pieces of these plants under a microscope, they lightly touched individual plant cells with a micro-cantilever, essentially a tiny glass rod about the size of a human hair. They saw many complex responses based on the strength and duration of the touch, but the difference between the touch and its 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 through adjacent plant cells, lasting between three and five minutes. The removal of touch it showed an almost instantaneous set of faster waves that dissipated within a minute.

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

The researchers mechanically tested the pressure theory by inserting a tiny glass capillary pressure probe into a plant cell. The increase and decrease in pressure within the cell resulted in similar calcium waves triggered by the start and end of a touch.

“Humans and animals perceive touch through sensory cells. The mechanism in plants appears to be through this increase or decrease in internal cellular pressure,” Knoblauch said. “And it doesn’t matter what cell it is. Humans may need nerve cells, but in plants, any cell on the surface can do this.”

Previous research has shown that when a pest such as a caterpillar bites into a plant leaf, it can initiate the plant’s defensive responses, such as the release of chemicals that make the leaves less palatable or even toxic to the pest. An earlier study also revealed that brushing a plant triggers calcium waves that activate different genes.

The current study was able to differentiate the calcium waves between touching and releasing, but exactly how the plant’s genes respond to those signals remains to be seen. With new technologies such as the calcium sensors used in this study, scientists can begin to unravel that mysteryKnoblauch said.

“In future studies, we need to trigger the signal in a different way than has been done before to find out which signal, touched or released, triggers downstream events,” he said.