Diffusion Pressure Deficit (DPD) or Suction Pressure (SP) in Plants

Diffusion Pressure Deficit (DPD) or Suction Pressure (SP)

Pure solvent (hypotonic) has higher diffusion pressure. Addition of solute in pure solvent lowers its diffusion pressure. The difference between the diffusion pressure of the solution and its solvent at a particular temperature and atmospheric pressure is called as Diffusion Pressure Deficit (DPD) termed by Meyer (1938). DPD is increased by the addition of solute into a solvent system. Increased DPD favours endosmosis or it sucks the water from hypotonic solution; hence Renner (1935) called it as Suction pressure.

It is equal to the difference of osmotic pressure and turgor pressure of a cell. The following three situations are seen in plants:

•         DPD in normal cell: DPD = OP – TP.

•         DPD in fully turgid cell: Osmotic pressure is always equal to turgor pressure in a fully turgid cell.

•         OP = TP or OP-TP =0. Hence DPD of fully turgid cell is zero.

•         DPD in flaccid cell: If the cell is in flaccid condition there is no turgor pressure or TP=0. Hence DPD = OP.