Mimosa pudica, known as the Sensitive Plant, is a prickly subshrub plant native to tropical regions in America, but now found distributed throughout the tropics, including India (Ahmad et al. 2012). It is small (generally shorter than half a metre in height) and has pink or lilac-coloured spherical flowers (Rico, 2013).
Its most fascinating feature by far is its ability to react to external stimuli by rapid movement of its leaves. This is known as seismonastic movement and can be provoked by gently touching the leaves, or by heating, shaking blowing, or applying electrical voltage to the plant (Kwan et al. 2013). The leaves fold inward and then droop downward, returning to their normal, unfolded state several minutes later (Chen et al. 2013).
The mechanism of the leaf movement in M. pudica has been the subject of much speculation. One model, which seems to be supported by mathematical data, suggests that motor organs called ‘pulvini’ are present at three key junctions in the plant: between each small leaf (pinnule) and the pinna (midrib of the group of 10-26 pinnule pairs), between each pinna and its ‘stalk’ (petiole), and between each petiole and the stem (Rico, 2013; Kwan et al. 2013). According to the model, stimulation will cause water to flow out of the cells in one side of the pulvinus, resulting in movement (Kwan et al. 2013). Studies have suggested that aquaporins (water channels) located in the tonoplast (vacuole membrane) and cell membrane of M. pudica cells play a role in this process (Uehlein and Kaldenhoff, 2008).
M. pudica has seen extensive use as a traditional medicinal plant for conditions ranging from seizures to urogenital infections (Ahmad et al. 2012). In studies involving rats as model organisms, M. pudica was shown to have wound healing, sciatic nerve regeneration, and diuretic properties, amongst others (Ahmad et al. 2012).
Ahmad, H., Sehgal, S., Mishra, A., & Gupta, R. (2012). Mimosa pudica L. (Laajvanti): An overview. Pharmacognosy Review, 6(12). Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3459453/
Chen, M., Mao, W., & Cui, M. (2013). Adaptive anatomical structure for nastic movement in Mimosa Pudica L. Bangladesh Journal of Botany 42(1). Retrieved from http://www.banglajol.info/index.php/BJB/article/view/15876/11256
Kwan, K.W., Ye, Z.W., Chye, M.L., & Ngan, A.H.W. (2013). A Mathematical Model on Water Redistribution Mechanism of the Seismonastic Movement of Mimosa Pudica. Biophysical Journal, 105(1). Retrieved from http://www.sciencedirect.com/science/article/pii/S0006349513006395
Rico, L. (2013). Mimosa pudica (sensitive plant). Kew Royal Botanical Gardens. Retrieved from http://www.kew.org/plants-fungi/Mimosa-pudica.htm
Uehlein, N. & Kaldenhoff, R. (2008). Aquaporins and plant leaf movements. Annals of Botany 101 (1). Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701841/