Nyctinasty is the circadian rhythmic nastic movement of higher plants in response to the onset of darkness. Examples are the closing of the petals of a flower at dusk and the sleep movements of the leaves of many legumes.
Nyctinastic movements are associated with diurnal light and temperature changes and controlled by the circadian clock and the light receptor phytochrome. Several leaf-opening and leaf-closing factors have been characterized biochemically. 
Anatomically, the movements are mediated by pulvini. In the SLEEPLESS mutation of Lotus japonicus, the pulvini are changed into petiole-like structures, rendering the plant incapable of closing its leaflets at night.
- Ueda M, Nakamura Y (2007). "Chemical basis of plant leaf movement". Plant Cell Physiol. 48 (7): 900–907. doi:10.1093/pcp/pcm060. PMID 17566057.
- Kawaguchi M (2003). "SLEEPLESS, a gene conferring nyctinastic movement in legume". J. Plant Res. 116 (2): 151–154. doi:10.1007/s10265-003-0079-5. PMID 12736786.
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