noun, plural: nastic movements
The non-directional movement (of plants) in response to a stimulus (e.g. humidity, temperature, light irradiance, nutrients, gravity, etc.)
Nastic movements pertain to the plant movements in response to a stimulus. Nastic movements are different from tropic movements (tropisms). Tropisms are directional movements or growth response of a plant to the stimulus. In nastic movements, the response of the plant is non-directional. An example of tropism is thigmotropism, which is a growth response to the touch stimulus. Since it is directional, it has two types: positive (i.e. towards the stimulus) and negative (i.e. away from the stimulus). An example of thigmotropism is the coiling of tendrils or twiners upon contact to objects for support. In nastic movement, the movement response of the plant to contact is called thigmonasty. An example of thigmonastic movement is the shutting of a venus fly trap.
Another form of nastic movement is the nyctinasty. Nyctinasty is the nastic movement of plant parts such as leaves and petals in response to darkness. Some plants are able to assume a position at night that is different from their position during daytime. It is a biological rhythm since this behavior recurs in each circadian day. The sleeping position of these plants are said to be associated with pulvinar movement, circadian clock, and light signal transduction through phytochrome.
Other forms of nastic movements are epinasty, hyponasty, photonasty, chemonasty, hydronasty, thermonasty, and genoasty.