“Want to find out more about plant movements?”

 

Scientists call the reaction of the TickleMe Plant to touch, “Thigmonasty.”

*The following information was obtained from Wikipedia (and updated by visitors to our site):

Mimosa pudica is well known for its rapid plant movement. The leaves close up and droop when touched. However, this is not a form of tropism but a nastic movement, a similar phenomenon. The difference is that tropisms are influenced by the direction of their stimulus, while nastic movements are not.

The leaves of Mimosa have the capability to display thigmonasty (touch-induced movement). In the TickleMe Plant or sensitive plant, the leaves respond to being touched, shaken, heated or rapidly cooled. The speed of the response depends on the magnitude of the stimulus. Hitting the leaf hard with the flick of a finger will cause the leaf to close in the blink of an eye whereas a gentle touch or modest heat source applied to leaflets at the tip of a leaf will result in a slower response and the propagation of the stimulus along the leaf can be observed. In Mimosa, the mechanical or heat stimulus induces an electrical signal, similar to the electrical potentials in nerve cells, that can move from cell to cell at a high rate. When the electrical potential reaches specialized “motor cells” in pulvini at the base of each leaflet, the folding is caused by a rapid efflux of potassium followed by rapid water transport out of the motor cells.

Thigmonasty or seismonasty is the nastic response of a plant or fungus to touch or vibration. It differs from thigmotropism in that it is independent of the direction of the stimulus. For example, tendrils from a climbing plant are thigmotropic because they twine around any support they touch. However, the shutting of a venus fly trap is thigmonastic. The time scale of thigmonastic responses tends to be faster than thigmotropism because thigmonasty depends on turgor and bistable mechanisms rather than growth or cell division. Certain dramatic examples such as the sudden drooping of Mimosa pudica are fast enough to observe without time lapse photography.

Mimosa pudica is a plant with compound leaves that has attracted detailed investigation. It appears that contact or injury causes leaflet deformation that in turn triggers an action potential. The action potential travels through the plant until it reaches a pulvinus at the base of the leaflet or petiole.

Thigmotropism is a movement in which an organism moves or grows in response to touch or contact stimuli. The prefix thigmo- comes from the Greek for “touch”. Usually thigmotropism occurs when plants grow around a surface, such as a wall, pot, or trellis. Climbing plants, such as vines, develop tendrils that coil around supporting objects. Touched cells produce auxin and transport it to untouched cells. Some untouched cells will then elongate faster so growth bends around the object. Some seedlings also inhibit triple response, caused by pulses of ethylene which cause the stem to thicken (grow slower and stronger) and curve to start growing horizontally.

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