Mimosa pudica: The Defensive Revelations Behind “Shyness”

The “shyness” of Mimosa pudica is really an astounding floral behavior in the botanical world. You, I and everyone might have enjoyed playing, touching and shaking its leaves to make them fold inward and droop right before one’s eye, and might have associated that this amazing plant is “sleeping” and/or just “shy” as it feels being tickled. As curiosity have driven me off, I’ve gathered information and found out the how’s and why’s of this plant’s shyness.

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Mimosa pudica, called by numerous names such as sensitive plant, sleepy plant, humble plant, touch-me-not, TickleMe plant, shame plant or shy plant, is often grown for its great characteristic: the compound leaves fold inward and droop when touched or shaken, and re-open a few minutes later. The species are native to South America and Central America, but is now a pantropical weed. It can also be found in Asia in countries such as Thailand, Indonesia, Malaysia, Philippines, and Jamaica. It grows mostly in undisturbed shady areas, under trees or shrubs.

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The leaves-closing mechanism is caused by various stimuli, such as touching, warming, blowing, or shaking. These movements have been termed seismonastic movements, the reaction to physical shock. The movement occurs when specific regions of cells lose turgor pressure, which is the force that is applied onto the cell wall by water within the cell (mostly in the central vacuole) which, in turn, this turgor pressure exerts inwardly a mechanical wall pressure against the protoplast. The two equal and opposing pressures give strength to the cell and columns of water-

filled cells keep the plant erect.

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When the plant is disturbed and tickled, an electrical signal goes through the plant cells. These electrical signals stimulated specific regions on the stems to release chemicals including potassium ions which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse hence, causes the leaflets and stalks to wilt; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. The stimulus can also be transmitted to neighboring leaves. This reaction to touch or being tickled is called thigmonasty or thigmotropism.

The changes in leaf orientation termed "sleep" also happens at night. The leaves will also fold and bend in movements known as nyctitropism or nyctinastic movements (the changing of the position of the leaves of plants at night). It then reopens as the sun rises.

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The plant’s nyctitropism may be a way to reduce water loss by transpiration as the leaves fold down upon each other.  During cold weather, the leaves will close as well, could this be a way to maintain its body temperature?

Many scientists think that the plant mainly uses its ability to shrink as
a defense mechanism against different predators. Grazing animals tend to be frightened of the moving plant’s leaves just enough to stop them from eating the leaves. The sudden movement also dislodges harmful insects. It`s one of the nature’s wonderful floral defense mechanisms ever created by God, isn’t it?

References:

https://answers.yahoo.com/question/index?qid=20070828022305AAJRso2 Retrieved: 05/11/16

https://en.wikipedia.org/wiki/Mimosa_pudica Retrieved: 05/11/16

http://biology.stackexchange.com/questions/1114/why-did-the-sensitive-plant-mimosa-pudica-evolve-its-leaf-closing-mechanism Retrieved: 05/11/16