Mimosa pudica is well known for its
rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "sleep" or
nyctinasticmovement. The foliage closes during darkness and reopens in light.
[11] This was first studied by the French scientist
Jean-Jacques d'Ortous de Mairan.
The leaflets also close when stimulated in other ways, such as touching, warming, blowing, or shaking. These types of movements have been termed
seismonasticmovements. The stimulus is transmitted as an
action potential from a stimulated leaflet, to the leaflet's swollen base (
pulvinus), and from there to the pulvini of the other leaflets, which run along the length of the leaf's
rachis. The action potential then passes into the
petiole, and finally to the large pulvinus at the end of the petiole, where the leaf attaches to the stem. The action potential causes potassium ions to flow out from the vacuoles of cells in the various pulvini. This causes water to flow out from those cells by
osmosis through
aquaporin channels, making them lose
turgor, which is the force that is applied onto the cell wall by water within the cell. Differences in turgidity in different regions of the leaf and stem results in the closing of the leaflets and the collapse of the leaf
petiole.
[12]
This movement of folding inwards is energetically costly for the plant and also interferes with the process of photosynthesis.
[13] This characteristic is quite common within the
Mimosoideae subfamily of the legume family,
Fabaceae. The stimulus can also be transmitted to neighboring leaves. It is not known exactly why
Mimosa pudicaevolved this trait, but many scientists think that the plant uses its ability to shrink as a defense from herbivores. Animals may be afraid of a fast moving plant and would rather eat a less active one. Another possible explanation is that the sudden movement dislodges harmful insects.[
citation needed]