MAGIC BEHIND TOUCH-ME-NOT PLANT

The scientific name of the touch-me-not plant is Mimosa pudica, which belongs to the family of Fabaceae and originates in tropical Central and South America.

It shows sensitivity to touch. This phenomenon is scientifically known as seismonastic movement. It is a result of a quick drop in turgor pressure in the cells at the base of the leaflets. "Flaccid" cells cannot support the weight of the leaflet and they start to close.

What is the molecular mechanism behind it?

When a plant detects a stimulus, it sends a signal to the top cell of the pulvinus (plant motor organ) via an action potential. Active transport keeps potassium and chloride, inside the cell at higher concentrations than outside the cell.

However, when the action potential reaches a top cell, potassium and chloride specific ion channels are opened in response to the change in electric charge. This allows ions to move out of the cells through ion channels and triggering water to leave the cells through osmosis.

Much of this water comes out from the cell vacuole. This phenomenon makes vacuole smaller and causing the cell to shrink.

How this process transmitted to neighbouring leaves?

The ions released by the top cells are pumped into the bottom cells by active transport and consequently bottom cells will have high concentrations. The water moves in, again due to osmosis, and is stored in the vacuole, causing the bottom cells to swell.

If a stimulus is strong, pulvini at the bases of the leaves and the petiole (the stalk that joints leaf and the stem) also react. However, in these pulvini, the behaviour of the top and bottom cells is reversed, which means that activation drives the petiole downwards rather than upwards.

So, the combined effect is that leaflets fold up, but the whole leaf is pushed closer to the ground, giving the appearance of lifeless.

Credits: Sabitha

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