Variation potential explained

A variation potential (VP) (also called slow wave potential) is a hydraulically propagating electrical signal occurring exclusively in plant cells. It is one of three propagating signals in plants, the other two being action potential (AP) and wound potential (WP) (also unique to plants).^[1] 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;^[2] the production of abscisic acid, jasmonic acid, and ethylene;^{[3] [4] [5]} temporary decreases in photosynthesis;^[6] and increases in respiration.^[7] Variation potentials have been widely shown in vascular plants.^[8]

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.^[9] Variation potentials can only be produced if the pressure in the xylem is disturbed and followed by an increase in xylem pressure.^[10] Additionally, it uses vascular bundles to complete systemic potential throughout the plant.^[1]

Variation potentials are distinct from action potentials in their cause of stimulation. Depolarization arises from an increase in plant cell turgor pressure from a hydraulic pressure wave that moves through the xylem 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.

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.

Notes and References

1. Stahlberg R, Robert E, Cleland RE, van Volkenburgh E (2006) Slow wave potentials—a propagating electrical signal unique to higher plants.
2. Stankovic´ B, Davies E (1996) Both action potentials and variation potentials induce proteinase inhibitor gene expression in tomato. FEBS Lett 390:275–279.
3. Dziubinska H, Filek M, Koscielniak J, Trebacz K (2003) Variation and action potentials evoked by thermal stimuli accompany enhancement of ethylene emission in distant non-stimulated leaves of Vicia faba minor seedlings. J Plant Physiol 160:1203–1210.
4. Fisahn J, Herde O, Willmitzer L, Pen˜a-Corte´s H (2004) Analysis of the transient increase in cytosolic Ca2? during the action potential of higher plants with high temporal resolution: requirement of Ca2? transients for induction of jasmonic acid biosynthesis and PINII gene expression. Plant Cell Physiol 45:456–459.
5. Hlava´cˇkova´ V, Krchnˇa´k P, Nausˇ J, Nova´k O, Sˇpundova´ M, Strnad M (2006) Electrical and chemical signals involved in short-term systemic photosynthetic responses of tobacco plants to local burning. Planta 225:235–244
6. Koziolek C, Grams TEE, Schreiber U, Matyssek R, Fromm J (2003) Transient knockout of photosynthesis mediated by electrical signals. New Phytol 161:715–722.
7. Filek M, Koscielniak J (1997) The effect of wounding the roots by high temperature on the respiration rate of the shoot and propagation of electric signal in horse bean seedlings (Vicia faba L. minor). Plant Sci 123:39–46.
8. "Result Filters." National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 10 June 2016.
9. Davies E (2006) Electrical signals in plants: facts and hypotheses. In: Volkov AG (ed) Plant electrophysiology. Theory and methods, Springer-Verlag, Berlin, pp 407–422.
10. Stahlberg. R.. Cosgrove. D. J.. 1995. Comparison of electric and growth responses to excision in cucumber and pea seedlings. II. Long-distance effects are caused by the release of xylem pressure. Plant, Cell & Environment. en. 18. 1. 33–41. 10.1111/j.1365-3040.1995.tb00541.x. 11541062. 1365-3040.