A pulvinus (pl. ''pulvini'') may refer to a

joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

-like thickening at the base of a plant

leaf A leaf (: leaves) is a principal appendage of the plant stem, 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 leav ...

or leaflet that facilitates growth-independent movement. Pulvinus is also a botanical term for the persistent peg-like bases of the leaves in the coniferous genera ''

Picea A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Northern hemisphere. ''Picea'' is the sole genus ...

'' and ''

Tsuga ''Tsuga'' (, from Japanese (), the name of '' Tsuga sieboldii'') is a genus of conifers in the subfamily Abietoideae of Pinaceae, the pine family. The English-language common name "hemlock" arose from a perceived similarity in the smell of it ...

''. Pulvinar movement is common, for example, in members of the bean family

Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...

(Leguminosae) and the prayer plant family Marantaceae. Pulvini may be present at the base of the leaf stalk or on its other end (

apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...

), where the leaf is attached, or in a compound leaf at the place where the leaflets are joined to its middle stem. They consist of a core of

vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. T ...

within a flexible, bulky cylinder of thin-walled

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

cells. A pulvinus is also sometimes called a geniculum (meaning a knee-like structure in Latin). Pulvinar movement is caused by changes in

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 ...

pressure leading to a contraction or expansion of the parenchyma tissue. The response is initiated when

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

is unloaded from the

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is ...

into the

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 ...

. The increased sugar concentration in the apoplast decreases the

water potential Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and mat ...

and triggers the efflux of

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 ...

ions from the surrounding cells. This is followed by an efflux of water, resulting in a sudden change of turgor pressure in the cells of the pulvinus.

Aquaporins Aquaporins, also called water channels, are channel proteins from a larger protein family, family of major intrinsic proteins that form Ion channel pore, pores in the cell membrane, membrane of cell (biology), biological cells, mainly facilitati ...

on the

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

membrane of pulvini allow for the efflux of water that contributes to the change in turgor pressure. The process is similar to the mechanism of

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

tal closure. Common examples for pulvinar movements include the night closure movement of

legume 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 ...

leaves and the touch response of the sensitive plant ''

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 ...

''. Sleep movements ( nyctinastic movements) are controlled by the

circadian clock A circadian clock, or circadian oscillator, also known as one’s internal alarm clock is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time. Such a clock's ''in vivo'' period is necessarily almost exact ...

and light signal transduction through

phytochrome Phytochromes are a class of photoreceptor proteins found in plants, bacteria and fungi. They respond to light in the red and far-red regions of the visible spectrum and can be classed as either Type I, which are activated by far-red light, or ...

. Touch response ( thigmonastic) movements appear to be regulated through electrical and chemical signal transduction spreading the stimulus throughout the plant.

Pulvinus in ''Mimosa pudica''

In ''

'', the internal biological clock mediates the closing of leaflets at night and opening during day. Rapid (''seismonastic'') movement of leaves is triggered in response to touch and temperature. A pulvinus is located at the base of each leaflet of the plant. Mechanical stimulation via touch is perceived and is translated to electrical stimulation causing the flow of ions out of the pulvinus cells. An upregulation of water channel proteins (''

aquaporin Aquaporins, also called water channels, are channel proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells, mainly facilitating transport of water between cells. The cell membranes of ...

s'') and membrane proteins which move solutes across a cell membrane (H+ -

ATPase ATPases (, Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, ATP hydrolase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or ...

) allows for the rapid flux of water out of these motor cells. Water flux out of the cell's symplast and into its surrounding

results in a decrease in turgor pressure, and the characteristic closing of the leaves of ''Mimosa pudica''. The drop in turgor pressure is reversible but slow. Leaves slowly open to their initial position after 20 minutes of lack of stimulation. It has been demonstrated that seismonastic movement can be inhibited with the use of

anaesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...

s. Using

nuclear magnetic resonance Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a ...

, upward movement of water within the pulvinus joint in response to electrical stimulation was observed in the pulvinus at the base of the petiole (=the leaf stalk). Movement of water to the upper or lower part of the pulvinus causes asymmetric swelling, therefore causing the stalk to either droop or rise.

Pulvinus in ''Mimosa pudica''

References

Further reading