This research was supported by funding from the National Science Foundation.
Posted Date – Sun, 04 Jun 23 03:33 PM
Washington: According to a study done at Washington State University, a plant can sense when it’s touched and when it lets go without nerves.
In one set of experiments, individual plant cells responded to the touch of very thin glass rods by sending slow-wave calcium signals to other plant cells, and when the pressure was released, they sent faster waves. While scientists already knew that plants could respond to touch, this study showed that plant cells signal differently when touch starts and ends.
“Amazingly, plant cells are very sensitive — they can tell when something is touching them. They feel stress, and when the stress is released, they feel a drop in stress,” said Washington State University Biosciences. Michael Nobrauch, professor and senior author of the 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 very good level.” Knoblauch and his colleagues conducted a study of 12 plant species using Arabidopsis and tobacco plants. For 84 experiments, the plants were specially bred to include calcium sensors, a relatively new technology. After placing fragments of these plants under a microscope, they gently touched individual plant cells with a microcantilever, which is basically a tiny glass rod the size of a hair. They saw a number of complex responses depending on the strength and duration of the 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) pass from that cell through neighboring plant cells for about three to five minutes. Removing the touch revealed an almost instantaneous set of faster waves that dissipated within a minute.
The authors suggest that these waves are likely due to changes in pressure within the cell. Unlike animal cells, which have permeable membranes, plant cells also have strong cell walls that are not easily broken, so just a light touch can temporarily increase the pressure inside a plant cell.
The researchers tested the stress theory mechanistically by inserting tiny glass capillary pressure probes into plant cells. Increasing and decreasing the pressure inside the cells causes similar calcium waves to be triggered by the onset and cessation of touch.
“Humans and animals perceive touch through sensory cells. The mechanism in plants seems to be through an increase or decrease in internal cellular pressure,” Knoblauch said. “And it doesn’t matter which cell it is. We humans may need nerve cells, but in plants, any cell on the surface can do it.” Previous research has shown that when a pest like a caterpillar bites a plant When the leaves are damaged, it initiates the plant’s defense responses, such as releasing chemicals that make the leaves less palatable or even toxic to pests. An earlier study also showed that brushing the plants triggers calcium waves that activate different genes.
The current study was able to distinguish calcium waves between touching and letting go, but exactly how the plants’ genes respond to these signals remains to be seen. With new technologies like the calcium sensor used in this study, scientists can begin to unravel this mystery, Knoblauch said.
“In future studies, we’ll have to trigger signals in different ways than before to know what signals, if touched or let go, trigger downstream events,” he said.
This research was supported by funding from the National Science Foundation. The international team included researchers from the Technical University of Denmark; Germany’s Ludwig Maximilian Universitaet Muenchen and Westfaelische Wilhelms-Universitaet Muenster; and the University of Wisconsin-Madison and WSU.
