Thigmonasty
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In
biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...
, thigmonasty or seismonasty is the
nastic In biology, nastic movements are non-directional responses to stimuli (e.g. temperature, humidity, light irradiance) that occur more rapidly than tropisms and are usually associated with plants. The movement can be due to changes in turgor ( ...
(non-directional) response of a
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
or
fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
to touch or vibration. Conspicuous examples of thigmonasty include many species in the
leguminous Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
Mimosoideae The Mimosoideae are a traditional subfamily of trees, herbs, lianas, and shrubs in the pea family (Fabaceae) that mostly grow in tropical and subtropical climates. They are typically characterized by having radially symmetric flowers, with petal ...
, active
carnivorous plant Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods, and occasionally small mammals and birds. They have adapted to grow in waterlo ...
s such as '' Dionaea'' and a wide range of pollination mechanisms.


Distinctive aspects

Thigmonasty differs from
thigmotropism In plant biology, thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twining plants and tendrils, however plant biologists have also found thigmotro ...
in that nastic motion is independent of the direction of the stimulus. For example, tendrils from a climbing plant are thigmotropic because they twine around any support they touch, responding in whichever direction the stimulus came from. However, the shutting of a
venus fly trap The Venus flytrap (''Dionaea muscipula'') is a carnivorous plant native to the temperate and subtropical wetlands of North Carolina and South Carolina, on the East Coast of the United States. Although various modern hybrids have been created i ...
is thigmonastic; no matter what the direction of the stimulus, the trap simply shuts (and later possibly opens). The time scales of thigmonastic responses tend to be shorter than those of thigmotropic movements because many examples of thigmonasty depend on pre-accumulated
turgor Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilib ...
or on bistable mechanisms rather than growth or cell division. Certain dramatic examples of
rapid plant movement Rapid plant movement encompasses movement in plant structures occurring over a very short period, usually under one second. For example, the Venus flytrap closes its trap in about 100 milliseconds. The traps of Utricularia are much faster, closi ...
such as the sudden drooping of ''
Mimosa pudica ''Mimosa pudica'' (also called sensitive plant, sleepy grass, sleepy plant, action plant, humble plant, touch-me-not, touch-and-die, or shameplant) is a creeping annual or perennial flowering plant of the pea/legume family Fabaceae. It is often ...
'' or the trapping action of ''Dionaea'' or ''
Utricularia ''Utricularia'', commonly and collectively called the bladderworts, is a genus of carnivorous plants consisting of approximately 233 species (precise counts differ based on classification opinions; a 2001 publication lists 215 species).Salmon, B ...
'' are fast enough to observe without time lapse photography; some take less than a second. Speed is no clear distinction however; for example the re-erection of ''
Mimosa ''Mimosa'' is a genus of about 600 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. Species are native to the Americas, from North Dakota to northern Argentina, and to eastern Africa (Tanzania, Mozambique, and ...
'' leaves is nastic, but typically takes some 15 to 30 minutes, rather than a second or so. Similarly, re-opening of the ''Dionaea'' trap, though also nastic, typically takes days to complete. Botanical physiologists have discovered signalling
molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s called turgorins, that help mediate the loss of turgor. In species with the fastest response time, vacuoles are believed to provide temporary, high speed storage for calcium ions.


Examples of plants exhibiting thigmonasty


In the Asteraceae

Thigmonasty other than leaf closure occurs in various species of
thistle Thistle is the common name of a group of flowering plants characterized by leaves with sharp spikes on the margins, mostly in the family Asteraceae. Prickles can also occur all over the planton the stem and on the flat parts of the leaves. T ...
s. When an insect lands on a flower, the anthers shrink and rebound, loading the insect with pollen. The effect results from turgor changes in specialized, highly elastic cell walls of the anthers. Similar pollination strategy occurs in ''
Rudbeckia hirta ''Rudbeckia hirta'', commonly called black-eyed Susan, is a North American flowering plant in the family Asteraceae. It grows to tall with daisy-like yellow flower heads. There are numerous cultivars. It is toxic when ingested by cats, but was us ...
''.


In the Droseraceae

The
Venus flytrap The Venus flytrap (''Dionaea muscipula'') is a carnivorous plant native to the temperate and subtropical wetlands of North Carolina and South Carolina, on the East Coast of the United States. Although various modern hybrids have been created ...
(''Dionaea muscipula'') presents a spectacular example of thigmonasty; when an insect lands on a trap formed by two curved lobes of a single leaf, the trap rapidly switches from an open to a closed configuration. Investigators have observed an
action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...
and changes in leaf
turgor Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilib ...
that accompany the
reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
; they trigger the rapid elongation of individual cells. The common term for the elongation is
acid growth Acid growth refers to the ability of plant cells and plant cell walls to elongate or expand quickly at low (acidic) pH. The cell wall needs to be modified in order to maintain the turgor pressure. This modification is controlled by plant hormones ...
although the process does not involve
cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...
. The sundews (genus ''Drosera'') are all capable of moving their glandular tentacles toward the center of a leaf in response to a prey item landing on it. The speed of the movement varies by species.


In the Fabaceae

''Mimosa pudica'' is a plant with
compound leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, fl ...
that droop abruptly when stimulated. This is a classic example of thigmonastic action and has attracted detailed investigation. Contact or injury that causes leaflets to deform will trigger an action potential. The action potential travels through the plant, initiating drooping of the leaflets as it passes. However, it does not pass the
pulvinus A pulvinus (pl. ''pulvini'') may refer to a joint-like thickening at the base of a plant leaf or leaflet that facilitates growth-independent movement. Pulvinus is also a botanical term for the persistent peg-like bases of the leaves in the conif ...
at the base of a
petiole Petiole may refer to: *Petiole (botany), the stalk of a leaf, attaching the blade to the stem *Petiole (insect anatomy) In entomology, petiole is the technical term for the narrow waist of some hymenopteran insects, especially ants, bees, and ...
, and so a local disturbance will not cause all the leaves on the plant to collapse. The pulvinus is a motor structure consisting of a rod of
sclerenchyma The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. This tissue system is present between the dermal tissue and forms the main bulk of th ...
surrounded by
collenchyma The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. This tissue system is present between the dermal tissue and forms the main bulk of th ...
. Such pulvini occur widely in the
Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...
. In its extended position, the
cell Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...
s of the entire collar of collenchyma are distended with water. On receiving the action potential signal, the cells in the lower half of the pulvinus respond by expelling
potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
and
chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
and taking up of
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
ions. This results in an
osmotic gradient Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...
that draws water out of the affected cells, so that they temporarily shrink. This pulls the entire structure downward like a folding fan. Many other Fabaceae react to touch with the same rapid leaf closure motion. The
pea Pea (''pisum'' in Latin) is a pulse or fodder crop, but the word often refers to the seed or sometimes the pod of this flowering plant species. Peas are eaten as a vegetable. Carl Linnaeus gave the species the scientific name ''Pisum sativum' ...
vine thigmonastically closes its leaves around a support. Catclaw Brier, a prairie mimosa, native to North America, shuts its leaves on contact. The plant is attractive to
herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...
s, and this behavior presumably provides protection against grazing.


In the Loasaceae

Members of the subfamily Loasoideae exhibit rapid
stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...
movement when pollinators are present. In order to obtain nectar, specialized floral components known as nectar scales must be manipulated by the pollinator. This action causes the stamens to move between 90 and 120 degrees toward the center of the flower within 1-2 minutes. When there is a lack of pollinators the stamen movement is slower and dependent upon ambient light and temperature. The plants are capable of extending their staminate and carpellate phases to ensure
self-pollination Self-pollination is a form of pollination in which pollen arrives at the stigma of a flower (in flowering plants) or at the ovule (in gymnosperms) of the same plant. The term cross-pollination is used for the opposite case, where pollen from ...
.


In the Oxalidaceae

Sensitive leaves also occur in plants of the
wood sorrel ''Oxalis'' ( (British English) or (American English)) is a large genus of flowering plants in the wood-sorrel family, Oxalidaceae, comprising over 550 species. The genus occurs throughout most of the world, except for the polar areas; species ...
family. Examples include many species of ''
Oxalis ''Oxalis'' ( (British English) or (American English)) is a large genus of flowering plants in the wood-sorrel family, Oxalidaceae, comprising over 550 species. The genus occurs throughout most of the world, except for the polar areas; species ...
'', ''
Biophytum sensitivum ''Biophytum sensitivum'', also known as little tree plant, or Mukkutti (in Malayalam) is a species of plant in the genus ''Biophytum'' of the family Oxalidaceae. It is commonly found in Kerala, wet lands of Nepal, tropical India and in other Sout ...
'', and
Averrhoa carambola ''Averrhoa carambola'' is a species of tree in the family Oxalidaceae native to tropical Southeast Asia; it has a number of common names, including carambola, star fruit and five-corner. It is a small tree or shrub that grows tall, with rose to ...
(the plant which produces
starfruit Carambola, also known as star fruit, is the fruit of ''Averrhoa carambola'', a species of tree native to tropical Southeast Asia. The edible fruit has distinctive ridges running down its sides (usually 5–6). When cut in cross-section, it res ...
).


Other forms

Some
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
exhibit trap closure similar to the venus fly trap. Mycologists have discovered action potentials in fungi but it is not currently clear whether they have any significance to thigmonastic behavior.


See also

*
Apoplast The ''apoplast '' is the extracellular space outside of plant cell membranes, especially the fluid-filled cell walls of adjacent cells where water and dissolved material can flow and diffuse freely. Fluid and material flows occurring in any extr ...
*
Rapid plant movement Rapid plant movement encompasses movement in plant structures occurring over a very short period, usually under one second. For example, the Venus flytrap closes its trap in about 100 milliseconds. The traps of Utricularia are much faster, closi ...


References


External links


Two videos showing severe thigmonasty in mimosa plantsPulvinus-actuated leaf movementsThigmonastic Movement
* {{Tropism Plant physiology Plant intelligence