Even without nerves, plants can sense when something touches them and when it lets go, a study has found. In a set 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 much more rapid waves (Nature Plants).
While scientists have known that plants can respond to touch, this study shows that plant cells send different signals when touch is initiated and ended. Within 30 seconds of the applied touch to a cell, the researchers saw slow waves of calcium ions, called cytosolic calcium, travelling from that cell through the adjacent plant cells, lasting about three to five minutes, according to a release. Removal of the touch showed an almost instant set of more rapid waves that dissipated within a minute. These waves are likely due to the change in pressure inside the cell. Unlike animal cells with permeable membranes, plant cells also have strong cellular walls that cannot be easily breached, so just a light touch will temporarily increase pressure in a plant cell.
