Mechanically stimulated motion and fatigue response of Mimosa pudica

Abstract

Mimosa pudica is a common weed found in Singapore and its offshore islands, mainly in grassy fields or under trees and shrubs. Its compound leaves fold inward and droop when touched, shaken, or blown, only to re-open minutes later. This action is termed the seismonastic movement. Furthermore, its leaves fold inward during the night and unfold during the day, this is controlled by a biological clock in the plant known as the circadian clock and the motion is termed as the circadian motion or nyctinastic motion. Over the years, research has been done on the chemical and physical properties which cause such movements in Mimosa pudica and many other plant species with similar physio-motor characteristics. Such motions occur due to the ionic concentrations and osmotic pressure in the motor cells of the pulvini in Mimosa pudica. In this study, it was discovered that there was no relation between plant size and the amount of petiole bending. However, it was observed that there was a slight relation between the response time of the leaf (pinnule) closing and the size of the plant. Furthermore, it was also observed that the plant experiences fatigue due to the repeated and continuous exposure to touch; this is termed as the fatigue response of the plant and it will be the other main focus of this project.