In an isotonic solution, the concentration of solutes outside the plant cell is the same as the concentration of solutes inside the cell. This means that there is no net movement of water across the cell membrane.

Here's what happens to the plant cell:

* No change in cell volume: The cell neither gains nor loses water, maintaining its normal size and shape.

* Normal turgor pressure: The pressure exerted by the cell contents against the cell wall remains constant.

* Optimal conditions for cell function: The cell is in its most stable and functional state, as the internal environment is balanced with the external environment.

In summary, plant cells in an isotonic solution are in a state of equilibrium, with no significant changes in their size, shape, or internal pressure.