There are many ways through which plants regulate water in them-
Leaf Fall- leaves and roots of terrestrial plants regulate the water balance in protoplast. During drought, they shed their leaves so that water loss may not occur via transpiration.
Increased number of Root Hairs- The function of root hairs is both to increase surface area and water absorption. During unfavourable conditions root hairs adapt plant by absorbing more water from the soil. Distribution of root system in soil affects water balance in plants. In aquatic plants, water balance is maintained by increased leaf area and reduced root surfaces.
Mineral Pumping- Some plants absorb minerals in their root cells. This results in a high concentration of solutes in the cell cytoplasm. Consequently, soil water moves into a cell through osmosis. Thus, they meet out water demand.
Position and Number of Stomata- Stomata are the openings of leaf surface that regulate gaseous exchange. In xerophytic plants stomata are sunken in leaves. PLants having sunken stomata significantly reduce transpiration. They are less or high in number on lower sides. Closing and opening of stomata regulate water loss during transpiration.
Cutinised and Waxy thickening of Epidermis- Plants protect water loss through leaves by depositing a thin film of cutin, suberin or waxy materials on the epidermis. Therefore, less water loss occurs from cutinised leaves than uncutinised leaves.