Nastic movements

"Nastic" redirects here. For other uses, seeNastic (disambiguation).

Photonastic movement ofOxalis triangularisin response to light. At lowered light levels the leaves fold down; timelapse recorded at ~750x actual speed and covering a 1.5 hr period of time.

Inbiology,nastic movementsare non-directional responses tostimuli(e.g.temperature,humidity,lightirradiance) that occur more rapidly thantropismsand are usually associated withplants.The movement can be due to changes inturgor(internal pressure withinplant cells). Decrease in turgor pressure causes shrinkage, while increase in turgor pressure brings about swelling. Nastic movements differ fromtropic movementsin 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 orfrequencyof these responses increases as intensity of the stimulus increases. An example of such a response is the opening and closing offlowers(photonastic response), movement ofeuglena,chlamydomonastowards 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:upward bending of leaves from growth in thepetiole(leaf stalk)
• 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

External links

• 'Daisy - 'Day's Eye or Eye of the Day'.