CBSE Class 10 Answered

Seismonastic movement is the temporary movement of a plant in reaction to touch, warmth, or lack of water. Thigmotropism is the directional response of plant to touch and is permanent. 

Seismonasty is a type of nastic movement whereas thigmotropism is a type of tropic movement.

Thigmotropism contributes to growth whereas seismonastic movements do not usually contribute to growth, but is a quick and temporary response to a stimulus.

The winding movement of tendrils of climbing plants around a strong support is an example of thigmotropism. The folding up of the leaves of the 'touch me not plant' on being touched is an example of seismonastic movement.

Seismonastic movement occurs when specific regions of cells lose turgor pressure. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals 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; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole.