A variation potential (VP) (also called slow wave potential) is a hydraulically propagating electrical signal occurring exclusively in

plant cell Plant cells are the cells present in green plants, photosynthetic eukaryotes of the kingdom Plantae. Their distinctive features include primary cell walls containing cellulose, hemicelluloses and pectin, the presence of plastids with the capabi ...

s. It is one of three propagating signals in plants, the other two being

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

(AP) and

wound potential A wound is a rapid onset of injury that involves lacerated or punctured skin (an ''open'' wound), or a contusion (a ''closed'' wound) from blunt force trauma or compression. In pathology, a ''wound'' is an acute injury that damages the epider ...

(WP) (also unique to plants).Stahlberg R, Robert E, Cleland RE, van Volkenburgh E (2006) Slow wave potentials—a propagating electrical signal unique to higher plants. Variation potentials are responsible for the induction of many physiological processes and are a mechanism for plant systematic responses to local wounding. They induce changes in gene expression; the production of

abscisic acid Abscisic acid (ABA) is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to environmental ...

jasmonic acid Jasmonic acid (JA) is an organic compound found in several plants including jasmine. The molecule is a member of the jasmonate class of plant hormones. It is biosynthesized from linolenic acid by the octadecanoid pathway. It was first isolated ...

, and

ethylene Ethylene ( IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

; temporary decreases in

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

; and increases in respiration. Variation potentials have been widely shown in

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s. A variation potential, like an action potential, is a temporary change in the membrane potential of the plant cell by depolarization and consequent repolarization. However, it is distinguished by its slower, delayed repolarization phase, variability in shape and amplitude, and the decrease in its velocity with increasing distance from the initial point. Variation potentials can only be produced if the pressure in the xylem is disturbed and followed by an increase in xylem pressure. Additionally, it uses vascular bundles to complete systemic potential throughout the plant. Variation potentials are distinct from action potentials in their cause of stimulation. Depolarization arises from an increase in plant cell

turgor pressure 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 equilibri ...

from a hydraulic pressure wave that moves through the

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived fr ...

after events like rain, embolism, bending, local wounds, organ excision, and local burning. Unlike action potentials, variation potentials are not all or nothing. Depolarization of a variation potential is determined by the difference in pressure between the atmosphere and the plant's intact interior. However, it has been shown that variation potentials can be suppressed by high humidity and continued darkness. The ionic mechanism is assumed to involve a brief shutdown of the P-type H+ -ATPase in the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. Variation potential propagation is accomplished hydraulically by moving with a rapid pressure increase that establishes an axial pressure gradient in the xylem. This gradient transforms with distance into increasing lag phases for the pressure-induced depolarization in the epidermal cells. This allows for communication between the leaf and stem that can move in both directions along the axis of the plant.

References

{{reflist Plant physiology