Turgor Pressure


Turgor pressure is the hydrostatic pressure in excess of ambient atmospheric pressure which can build up in living, walled cells. Turgor is generated through osmotically driven inflow of water into cells across a selectively permeable membrane; this membrane is typically the plasma membrane. The maintenance of turgor in cells requires energy. Turgor pressures can be as small as 0.1–0.4 MPa yet can also exceed 2–3 MPa. Cells of many organisms can build up turgor pressure. In plants, turgor pressure plays an important role in key processes such as growth, development, mechanical support, signalling, organ movement, flowering and responses to stress. The ability to build up significant turgor pressure in cells has been key to the evolutionary success of terrestrial plants to pursue a sessile life strategy.

Key Concepts

  • Turgor pressure refers to the hydrostatic pressure in cells in excess of ambient (normal) atmospheric pressure.
  • Turgor pressure is best known in plant cells but also occurs in walled cells of other organismal kingdoms.
  • The build‐up and maintenance of turgor pressure requires five key components: water, solutes, a selectively permeable membrane, a wall and metabolic energy.
  • Values of turgor pressures cover a wide range; they can be as small as 0.1–0.4 MPa yet also exceed 2–3 MPa.
  • Turgor pressure in plants plays a key role in processes such as growth, development, mechanical support, signalling, flowering and stress response.
  • Turgor pressure is an ideal means in plant cells through which the energy content of water molecules (water potential) can be adjusted quickly, within seconds.
  • The ability of plants to establish significant cell turgor pressure was key to their evolutionary success to colonise land while pursuing a sessile life strategy.
  • The best‐known example of rapid changes in cell turgor causing microscopic movements is the reversible opening and closing of stomatal pores in leaves.
  • As plant cells are generally very small (picolitre‐range volumes), eating a fruit such as an apple which contains highly pressurised cells does not hurt.

Keywords: cell; energy; hydrostatic pressure; osmosis; plasma membrane; solute; stress; turgor; water potential

Figure 1. Scheme which shows the basic ingredients required to establish turgor pressure in a cell. (a) A hypothetical walled cell containing distilled water is bathed in distilled water. (b) The cell has spent energy to accumulate solutes. Owing to osmosis, the solutes drive net water uptake into the cell, and turgor pressure builds up. (c) When the energy source is removed, solutes start to leak out of the cell across the plasma membrane (PM) and turgor is lost. Note: even though the PM is often said to be ‘semipermeable’ it is rather ‘selectively permeable’ as it permits water to cross faster than solutes, but small‐molecular‐weight solutes can still cross it.
Figure 2. Scheme which quantifies processes involved in turgor generation. (a) A cell, which contains no solutes (osmotic pressure, π, being 0 MPa) and no above‐atmospheric pressure (P = 0), has a water potential (Ψ) of 0 MPa. The same applies to the distilled water in which the cell is bathed. (b) The cell has accumulated 200 mM of solutes (π of 0.5 MPa), which would lower cell Ψ by the same amount, where it not for the fast inflow of water. The net water inflow proceeds until cell Ψ equals solution Ψ. The result is a cell turgor of 0.5 MPa. Note that the solution is considered here much larger in volume than the cell volume, so that the equilibrium between cell Ψ and solution Ψ is very much determined through the latter. (c) The solution π has been increased by 0.2 MPa (80 mM solutes) and the cell loses net water. Turgor decreases to 0.3 MPa.
Figure 3. Pressure–volume relation of plant cells. A cell loses typically only 15–30% of its maximum cell volume when turgor (P) decreases from its maximum value to 0 MPa. As the loss in turgor is initially exponential and accompanied by a significant drop in water potential ‘Ψ’, cells can rapidly adjust to changes in external Ψ while still conserving some of their water and turgor. In the longer term, turgor can be recovered through active solute accumulation, which increases cell osmotic pressure (π).
Figure 4. An outline of approaches used to determine turgor in cells, in particular plant cells. P, turgor; Ψ, water potential; π, osmotic pressure.


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Further Reading

Chaumont F and Tyerman SD (2014) Aquaporins: highly regulated channels controlling plant water relations. Plant Physiology 164: 1600–1618.

Fricke W (2012) Single‐cell sampling and analysis (SICSA). In: Shabala S and Cuin TA (eds) Plant Salt Tolerance, vol. 913, pp. 79–100. Methods in Molecular Biology. Berlin, Heidelberg: Springer‐Verlag.

Knipfer T, Besse M, Verdeil J‐L, et al. (2011) Aquaporin‐facilitated water uptake in barley (Hordeum vulgare L.) roots. Journal of Experimental Botany 62: 4115–4126.

Steudle E (1989) Water flows in plants and its coupling with other processes: an overview. Methods in Enzymology 174: 183–225.

Steudle E (2000) Water uptake by plant roots: an integration of views. Plant and Soil 226: 45–56.

Touati M, Knipfer T, Visnovity T, et al. (2015) Limitation of cell elongation in barley (Hordeum vulgare L.) leaves through mechanical and tissue‐hydraulic properties. Plant and Cell Physiology 56: 1364–1373.

Zeuthen T (2010) Water‐transporting proteins. Journal of Membrane Biology 234: 57–73.

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Fricke, Wieland(Jan 2017) Turgor Pressure. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001687.pub2]