Body receptors respond to touch. They respond whenever their shape is altered or distorted and trigger extremely sensitive fast firing neutrons.
Vertebrates have two kinds of tactile receptors, those that register pressure and those that respond to touch.
But Mimosa pudica is more sensitive than others. The opening and closing of the plants' leaflets and the entire leaf are controlled by a fluid filled sac-like structures found at the base of the compound leaf and each leaflet.
The swollen base of the leaf stalk is called `pulvinus'. When the plant is touched, electrical signals are flashed by the cells. The cells in the `pulvinus' respond to this signal by flushing out potassium and water. With the massive loss of water, the pulvinus bends over and the leaflets fold.
The responses of the plant were first observed by Indian scientist Jagadish Chandra Bose to prove that plants also feel pain.
Published in The Hindu on Dec 6, 2001.