Nastic movements are non-directional
responses to
stimuli (e.g.
temperature,
humidity, light
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
), and are usually associated with
plants. The movement can be due to changes in
turgor. Decrease in turgor pressure causes shrinkage while increase in turgor pressure brings about swelling. 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's position. The tropic movement is growth movement but nastic movement may or may not be growth movement. 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), movement of euglena, chlamydomonas towards the source of light. They are named with the suffix "-nasty" and have prefixes that depend on the stimuli:
* Epinasty: downward-bending from growth at the top, for example, the bending down of a heavy flower.
*
Hyponasty
* 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
* Seismonasty: response to shock
* Geonasty/gravinasty: response to gravity
*
Thigmonasty/seismonasty/haptonasty: response to contact
The suffix may come from Greek νάσσω = "I press", ναστός = "pressed", ἐπιναστια = "the condition of being pressed upon".
See also
For other types of movement, see:
*
Taxis
*
Tropism
*
Kinesis
References
External links
'Daisy - 'Day's Eye or Eye of the Day'.
Physiology
Articles containing video clips
{{Botany-stub
de:Pflanzenbewegung#Nastien und Tropismen