Table of Contents
Turgor Pressure Definition
Turgor pressure is the pressure that water exerts on the cell wall in a biological environment. As an illustration of turgor pressure, consider a balloon being inflated with water. As more water is drawn in, the balloon expands. The turgor pressure exerted against the wall is analogous to the pressure produced by the water against the balloon’s walls.
What is Turgor Pressure?
The turgor pressure definition in biology refers to the pressure that a fluid (such as water) exerts against the cell wall. Hydrostatic pressure is another name for it. The density of the liquid, the acceleration of gravity, and the depth of the fluid column may all be used to calculate the pressure in a liquid at rest.
Osmotic pressure refers to the pressure exerted by a fluid containing water as a result of inflow over a semi-permeable barrier. Water diffuses to where there are more solutes due to variations in solute concentrations across solutions. The ability of water to flow from one location to another is referred to as “water potential.” The cell becomes turgid when water is introduced. Turgidity is a state in which a cell is turgid or enlarged.
The importance of turgor pressure to the plant’s essential activities cannot be overstated. It stiffens and rigidifies the plant cell. The plant cell becomes floppy without it. Plants may wilt as a result of prolonged flaccidity. Stomate formation is also influenced by turgor pressure. The guard cells’ sturdiness provides a space for gas exchange. Photosynthesis might be aided by the entry of carbon dioxide. Apical development, nastic movement, and seed dissemination are the other roles.
Turgor Pressure Etymology
Turgor is derived from the Latin word turgre, which means “to swell.” The word pressure originates from the Latin words pressūra, pressus, and premere, which imply “to press.” Hydrostatic pressure, pressure potential, and wall pressure are all terms used to describe turgor pressure.
Turgor Pressure and Osmosis
Water mobility is regulated by the cell in nature. Water may diffuse through a biological membrane since it is a tiny molecule. Osmosis is the passive movement of molecules of water from a low-solute-concentration area to a high-solute-concentration area across a membrane. Osmosis is the net flow of water molecules through a membrane from one area of higher water potential to another area with lower water potential, according to another definition. Turgidity is caused by a net positive flow of water into the cell. Excessive osmosis in animal cells might result in the cell bursting. The cells of plants do not rupture. Turgor is required for structural integrity and stiffness in plant cells.
Turgor Pressure in Plants
In contrast to the wilted plant on the left, which contains turgid cells, the plant on the right has lost its turgor. Turgidity aids the plant’s upright position. When a cell’s turgor pressure is lost, the cell becomes floppy, causing the plant to wilt.
On a cellular level, the plant has characteristics that allow it to control internal turgor pressure. They have cell walls that protect their cells from lysis (bursting) when there is a lot of water in the environment. Their cell’s vacuole is bigger than any of the subcellular components. Osmoregulation causes water inflow in the vacuole.
Turgor Pressure and Cell Wall
The plant cell wall is responsible for the turgidity and stiffness of the plant. The plant cell’s cell wall prevents it from bursting owing to the entry of water. The cell is able to endure the osmotic pressure imposed by the water molecules rather than exploding. As a result, the cell remains turgid. A single layer of cell wall exists in some plant cells. Primary and secondary cell walls are seen in other plant cells. The second cell layer contains a lot of lignin, which serves to keep the cell watertight.
Turgor pressure occurs when a plant’s cells become turgid due to the pressure exerted by water molecules on the cell wall. In contrast to a mammal cell, its cell membrane prevents it from bursting despite considerable water inflow. Plant cells have both a cell membrane and a cell membrane, but animal cells only have one. The cell wall protects the cell membrane by acting as a barrier. It aids in the resistance to osmotic pressure, which is caused by the osmotic flow of water caused by differences in solute concentrations between extracellular and intracellular fluid.
The cell wall of a plant is a strong, inflexible structure made primarily of cellulose. A single or double layer of cellulosic material might be used. The main cell wall (also known as the primary cell wall) secretes a secondary cell wall underneath and on top of the cell membrane as the plant cell grows. The high lignin concentration of the “secondary cell wall” contributes to cell waterproofing.
Osmoregulation by Vacuoles
Osmoregulation is the process of adjusting water potential in order to maintain an optimum osmotic pressure inside the cell. It is the mechanism by which a cell maintains a proper concentration of solutes and water in proportion to the surrounding fluid. Water potential, as previously stated, is the ‘’tendency” of water to migrate from one location to another. Plants may regulate their water potential through osmoregulation, and the vacuole is a crucial cytoplasmic component in this biological process.
A plant vacuole is a large cytoplasmic membrane-bound vesicle. Water, inorganic compounds, and organic molecules are all found in the vacuole. It regulates the osmotic flow of water to maintain turgor pressure. It has the ability to absorb and store ions, carbohydrates, and other solutes. As a result, the intracellular fluid becomes hypertonic in comparison to the external fluid (which, in this case, is hypotonic relative to the cell). Water pulls in because there are more solutes inside the cell than in the extracellular fluid. Osmotic pressure, also known as turgor pressure, is the outcome of a positive net inflow of water.
Plant cells have a cell wall that protects them from large water influxes that animal cells are vulnerable to, but it cannot protect them from drought or water scarcity. Water molecules will tend to migrate out of the cell if there isn’t enough water in the extracellular fluid, resulting in a neutral or negative net water movement and a low turgor pressure. In an isotonic solution, a plant cell’s turgor pressure might drop, causing it to become flaccid. If this was done for a long time, the plant would finally get sick and withered. The situation may be improved if there was enough water available.
Turgor Pressure and Stomata
Guard cells utilise turgor pressure to produce a stoma, or opening. An open stoma (above) develops when K+ ions reach the guard cells, permitting water to flow into the cells, as shown in this schematic figure. The guard cells’ turgor pressure rises as a result of this. When K+ ions exit the cell, a closed stoma occurs. Water is ejected as a result of this. As a result, the turgor pressure in the guard cells drops.
Stomates are the small holes that enable gas exchange in plants. They are usually located on the lowest epidermal layer of the leaf’s surface. They can also be seen on the stems of certain plants. Stomates are openings that occur when two guard cells are opened. When the two guard cells are turgid, they produce an opening.
The osmotic pressure sucks water in, causing the guard cells to expand in bulk, or swell. Because the inner wall of the pore is more stiff than the wall on the opposite side of the cell, the swelling forces the guard cells to bend apart. Stomates rely on the opening formed by the turgid guard cells to operate properly. It provides a pathway for carbon dioxide to enter through these holes. One of the reactants in photosynthesis is carbon dioxide. Plants, in turn, waste oxygen as one of the byproducts of photosynthesis through the stomates.
Negative Turgor Pressure
While most cells have a positive turgor pressure, the xylem of a transpiring plant has a negative turgor pressure. The xylem is a vascular tissue that transports water and nutrients from the roots to the shoots and leaves, so this is not surprising. Evaporation is how the plant loses water as it transpires. The stomates allow the water vapour to escape. The xylem experiences high surface tension and negative turgor pressure because to water loss through transpiration. This allows water to flow from the roots to the plant’s apical portions.
Function of Turgor Pressure in Plants
i. Rigidity: Turgor pressure is essential for plants, particularly those that dwell on land. This pressure gives them the turgidity and stiffness they require to stand upright against gravity while positioning themselves towards the source of light.
ii. Stomates Formation: Turgor pressure is important for transpiration, water transport, and photosynthesis because it is used by guard cells to generate stomates.
iii. Nastic Movements: Some plants utilise a process similar to that used by stomates to get into a sleeping posture at night. These plants are erect throughout the day to collect light for photosynthesis. Their leaves and petals close and droop at night, indicating that they are sleeping. The pulvinar cells near the base of a plant leaf (or leaflet) or at the apex of the petiole appear to be involved in this movement (called nyctinasty, a type of nastic movement). Plant drooping is also evident in Mimosa pudica, where the leaves lose turgor pressure while the pulvinar cells increase it in reaction to contact.
iv. Apical Growth: Turgor pressure is also linked to plant growth. The pressure causes the cell wall to expand. As a result, this pressure is responsible for root tip apical development.
v. Seed Dispersal: Turgor pressure is employed to disperse seeds in Ecballium elaterium (squirting cucumber). The fruit detaches from the stem due to a build-up of pressure inside the fruit. Once a result, as the fruit falls to the ground, the seeds and water inside are expelled. As a result, the pressure inside the fruit ranges between 0.003 to 1.0 MPs.
Turgor Pressure Citations
- Interplay between turgor pressure and plasmodesmata during plant development. J Exp Bot . 2020 Jan 23;71(3):768-777.
- Turgor Pressure and Possible Constriction Mechanisms in Bacterial Division. Front Microbiol . 2018 Jan 31;9:111.
- Regulation of microbial growth by turgor pressure. Curr Opin Microbiol . 2018 Apr;42:62-70.