Plants can detect when touch starts and stops, study says

PULLMAN, Wash. (KOMO) — A Washington State University-led study revealed plants can sense when something touches them and when it is let go.

The study investigated how individual plant cells responded to touch. A set of 84 experiments included a combination of thale cress and tobacco plants specially bred to include calcium sensors.

Researchers used a very fine glass rod to find out. By sending slow waves of calcium signals to other plant cells and when the pressure was released, the plant sent more rapid waves. These experiments showed that plant cells can send different signals when touch is started and stopped.

Michael Knoblauch, WSU biological sciences professor and senior author of the study in theJournal Nature Plants, and his colleagues saw many complex responses depending on the force and duration of the touch, however, the difference between touch and removal was clear.

When researchers applied 30 seconds of touch to a plant cell, they saw slow waves of calcium ions, called cytosolic calcium. These slow waves travel from the cell through other plant cells which last around three to five minutes. However, removal of touch from a plant cell showed an instant set of faster waves that disappeared within a minute.

To measure the pressure theory, researchers inserted a tiny glass capillary pressure probe into a plant cell. Capillary pressure is the pressure between two non-homogeneous liquids in a thin tube which results from the interaction of forces between the fluid and solid walls of the tube.

Researchers found that increasing and decreasing pressure inside the cell resulted in similar calcium waves initiated by the start and stop of a touch. Meaning that the mechanism in plants appears to be the increase of decrease of internal cell pressure which any cell on the surface can do.

The study was able to differentiate the calcium waves between touch and letting go, however, how the plant’s genes respond to these signals remains a mystery.