Turgor Pressure

Abstract 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.