Plant Water Relations

Since most of the water (90%) is lost through stomata, plants regulate the degree of stomatal opening to reduce the water loss.

Each stomata consists of a minute pore called stoma surrounded by two guard cells. The stoma acts as a turgor operated valve which closes and opens according to the turgidity of guard cells. The guard cells are the only epidermal cells that contain chloroplasts. The guard cells have unevenly thickened walls. The cell wall around stoma is tough and flexible and the one away from stoma is thinner. The shape of guard cells differs in dicots and monocots though the mechanism remains the same.