Definitions

photonastic

Nastic movements

Nastic movements are non-directional responses to stimuli (e.g. temperature, humidity, light irradiance). The movement can be due to changes in turgor or changes in growth. Nastic movements differ from tropic movements in that the direction of tropic responses depends on the direction of the stimulus, whereas the direction of nastic movements is independent of the stimulus. The rate or frequency of these responses increases as intensity of the stimulus increases. An example of such a response is the opening and closing of flowers (photonastic response). Nastic responses are usually associated with plants. They are named with the suffix "-nasty" and have prefixes that depend on the stimuli:

  • Photonasty: response to light
  • Nyctinasty: movements at night or in the dark
  • Chemonasty: response to chemicals or nutrients
  • Hydronasty: response to water
  • Thermonasty: response to temperature
  • Geonasty/gravinasty: response to gravity
  • Thigmonasty/seismonasty/haptonasty: response to touch

Also see taxis, kinesis and tropism for other types of movement.

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