What occupies the space between the cell wall and the shrunken protoplast in the plasmolysed cell ?

Explanation

When the cell (or tissue) is placed in an isotonic solution, there is no net flow of water towards the inside or outside.
If external solution balances the osmotic pressure of the cytoplasm it is said to be isotonic.
When water flows into the cell and out of the cell and are in equilibrium, the cells are said to be flaccid.
Plasmolysis : The process of plasmolysis is usually reversible.
When the cells are placed in a hypotonic solution, water diffuses into the cell causing the cytoplasm to build up a pressure against the wall, that is called turgor pressure.
The pressure exerted by the protoplasts due to entry of water against the rigid walls is called pressure potential `Psi_p`. (`Psi_P` s positive value)
Because of the rigidity of the cell wall, the cell does not rupture.
This turgor pressure is ultimately responsible for enlargement and extension growth of cells.