![Fig139Movement of Plants](https://upload.wikimedia.org/wikipedia/commons/2/2b/Fig139Movement_of_Plants.png)
Nyctinasty is the
circadian rhythm
A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...
ic
nastic
Nastic movements are non-directional responses to stimuli (e.g. temperature, humidity, light irradiance), and are usually associated with plants. The movement can be due to changes in turgor. Decrease in turgor pressure causes shrinkage while ...
movement of higher plants in response to the onset of darkness, or a plant "sleeping". Nyctinastic movements are associated with diurnal light and temperature changes and controlled by the
circadian clock
A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase (waves), phase and is synchronized with solar time.
Such a clock's ''in vivo'' period is necessarily almost exactly 24 hours (the earth's curre ...
. It has been argued that for plants that display foliar nyctinasty, it is a crucial mechanism for survival; however, most plants do not exhibit any nyctinastic movements.
Nyctinasty is found in a range of plant species and across
xeric
Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature. Deserts and xeric (ancient Greek xērós, “dry") shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area. Ecoregions in this h ...
,
mesic, and aquatic environments, suggesting that this singular behavior may serve a variety of evolutionary benefits. Examples are the closing of the
petal
Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...
s of a flower at dusk and the sleep movements of the leaves of many
legume
A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...
s.
Physiology
Plants use
phytochrome
Phytochromes are a class of photoreceptor in plants, bacteria and fungi used to detect light. They are sensitive to light in the red and far-red region of the visible spectrum and can be classed as either Type I, which are activated by far-re ...
to detect red and far red light. Depending on which kind of light is absorbed, the protein can switch between a Pr state that absorbs red light and a Pfr state that absorbs far red light. Red light converts Pr to Pfr and far red light converts Pfr to Pr. Many plants use phytochrome to establish circadian cycles which influence the opening and closing of leaves associated with nyctastic movements. Anatomically, the movements are mediated by
pulvini
A pulvinus (pl. ''pulvini'') is a joint-like thickening at the base of a plant leaf or leaflet that facilitates growth-independent movement. Pulvini are common, for example, in members of the bean family Fabaceae (Leguminosae) and the prayer plant ...
. Pulvinus cells are located at the base or apex of the petiole and the flux of water from the dorsal to ventral motor cells regulates leaf closure. This flux is in response to movement of potassium ions between pulvinus and surrounding tissue. Movement of potassium ions is connected to the concentration of Pfr or Pr. In ''
Albizia julibrissin
''Albizia julibrissin'', the Persian silk tree, pink silk tree, or mimosa tree, is a species of tree in the family Fabaceae, native to southwestern Asia and eastern Asia.
The genus is named after the Italian nobleman Filippo degli Albizzi, w ...
'', longer darker periods, leading to low Pfr, result in a faster leaf opening. 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.
Non-pulvinar mediated movement is also possible and happens through differential cell division and growth on either side of the petiole, resulting in a bending motion within the leaves to the desired position.
Leaf movement is also controlled by bioactive substances known as leaf opening or leaf closing factors. Several leaf-opening and leaf-closing factors have been characterized biochemically.
These factors differ among plants. Leaf closure and opening is mediated by the relative concentrations of leaf opening and closing factors in a plant. Either the leaf opening or closing factor is a glycoside, which is inactivated by hydrolysis of the glycosidic bond via beta glucosidase. In ''
Lespedeza cuneata'' the leaf opening factor, potassium lespedezate, is hydrolyzed to
4 hydroxy phenyl pyruvic acid. In ''
Phyllanthus urinaria
''Phyllanthus urinaria'', commonly called chamber bitter, gripeweed, shatterstone, stonebreaker (but can refer to other Phyllanthus species as well) or leafflower, is a species of suffruticose ( woody and perennial at the base with the above bein ...
'', leaf closing factor Phyllanthurinolactone is hydrolyzed to its aglycon during the day. Beta glucosidase activity is regulated via circadian rhythms.
Fluorescence studies have shown that the binding sites of leaf opening and closing factors are located on the surface of the motor cell. Shrinking and expansion of the motor cell in response to this chemical signal allows for leaf opening and closure. The binding of leaf opening and closing factors is specific to related plants. The leaf movement factor of ''
Chamaecrista mimosoides'' (formerly ''Cassia mimosoides'') was found to not bind to the motor cell of ''
Albizia julibrissin
''Albizia julibrissin'', the Persian silk tree, pink silk tree, or mimosa tree, is a species of tree in the family Fabaceae, native to southwestern Asia and eastern Asia.
The genus is named after the Italian nobleman Filippo degli Albizzi, w ...
''. The leaf movement factor of ''Albizia julibrissin'' similarly didn't bind to the motor cell of ''Chamaecrista mimosoides'', but did bind to ''
Albizia saman
''Samanea saman'', also sometimes known as the rain tree, is a species of flowering tree in the pea family, Fabaceae, now in the Mimosoid clade and is native to Central and South America. Its range extends from Mexico south to Peru and Brazil ...
'' and ''
Albizia lebbeck
''Albizia lebbeck'' is a species of ''Albizia'', native to Indomalaya, New Guinea and Northern AustraliaUSDA (1994) and widely cultivated and naturalised in other tropical and subtropical regions. English names for it include Sirisa, Siris, lebbe ...
''.
Function
The functions of nyctinastic movement have yet to be conclusively identified, although several have been proposed. Minorsky hypothesized that nyctinastic behaviors are
adaptive
Adaptation, in biology, is the process or trait by which organisms or population better match their environment
Adaptation may also refer to:
Arts
* Adaptation (arts), a transfer of a work of art from one medium to another
** Film adaptation, a ...
due to the plant being able to reduce its surface area during night time, which can lead to better temperature retention and also reduces night-time herbivory. Minorsky specifically suggests a ''Tritrophic Hypothesis'' in which he considers the predators of herbivores in addition to the plants and herbivores themselves. By moving leaves up or down, herbivores become more visible to nocturnal predators in both a spatial and olfactory sense, increasing herbivore predation and subsequently decreasing damage to a plant's leaves.
Studies using mutant plants with a loss of function gene that results in petiole growth instead of pulvini found that these plants have less biomass and smaller leaf area than the wild type. This indicates nyctinastic movement may be beneficial toward plant growth.
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
believed that nyctinasty exists to reduce the risk of plants freezing.
Nyctinasty may occur to protect the
pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, keeping pollen dry and intact during the nighttime when most
pollinating
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...
insects are inactive.
Conversely, some flowers that are pollinated by
moth
Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s or
bat
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...
s exhibit nyctinastic flower opening at night.
[Why do poppy flowers open in the morning and close at night?](_blank)
BBC Science, Luis Villazon
History
The earliest recorded observation of this behavior in plants dates back to 324 BC when
Androsthenes of Thasos Androsthenes ( grc, Ἀνδροσθένης; literally meaning: "Man's Strength") of Thasos, son of Callistratus, was one of the admirals of Alexander the Great. He sailed as a trierarch with Nearchus, and was also sent by Alexander down the Euphra ...
, a companion to
Alexander the Great
Alexander III of Macedon ( grc, wikt:Ἀλέξανδρος, Ἀλέξανδρος, Alexandros; 20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great, was a king of the Ancient Greece, ancient Greek kingdom of Maced ...
, noted the opening and closing of
tamarind
Tamarind (''Tamarindus indica'') is a Legume, leguminous tree bearing edible fruit that is probably indigenous to tropical Africa. The genus ''Tamarindus'' is monotypic taxon, monotypic, meaning that it contains only this species. It belongs ...
tree leaves from day to night.
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
(1729) proposed that this was the plants sleeping, but this idea has been widely contested.
References
External links
*
{{Tropism
Plant physiology