Turgor Pressure

Turgor Pressure is the pressure exerted by the protoplasm against the cell wall.

In a turgid cell, the turgor pressure is equal to the back pressure exerted by the cell wall against the protoplasm. This back pressure exerted by the cell wall onto the protoplasm or the cell contents, is called as wall pressure (WP). These two pressures are equal and opposite in direction.

Turgor pressure is maximum when the cell wall cannot stretch any more. Such a cell is said to be fully turgid. At this point a dynamic equilibrium reaches i.e. the amount of water entering the cell is equal to amount of water leaving the cell.

Turgor pressure develops in the plant cells only because of the presence of cell wall which is able to resist the pressure generated by the protoplasm due to entry of water. It is a real pressure not a potential one and can occur to a great extent. In case of animal cells, where the cell wall is lacking, the plasma membrane bursts if the turgor pressure increases.

Turgor pressure plays a very important role in plants:

  • Turgor pressure helps in maintaining the shape and form of the plant.
  • The stems of herbaceous plants and the ones with non-woody tissues like maize, sugarcane and banana are held straight by fully turgid cells packed tightly together.
  • Turgor pressure holds the leaves in a flat and horizontal position by keeping the mesophyll cells turgid.
  • Turgor pressure helps in cell enlargement and consequently in stretching of the stems.
  • Opening and closing of stomata is governed by turgidity and flaccidity of the guard cells.
  • Certain plants like bean and Touch Me Not plant- Mimosa pudica show quick response of leaves due to change in light intensity or by touch stimulus followed by changes in the turgidity of cells present at the bases of leaves and leaflets.