Wilting point refers to the state when the only water left in a soil is unavailable to plants, so that they will wilt permanently unless water is added. Pressure potential is pressure exerted by the atmosphere on the plant. Solute potential refers to the higher concentration of solutes within the root contributing to the increase of diffusion of water from the surrounding soil into the plant. The leaf structures that help regulate this are the stomata, cuticle, and substomatal spaces. Plants must be exposed to a constant source of water because so much is lost that it must be replenished for metabolic activities to continue.
Root hairs are turgid as a result of their greater solute potential.
Energy is expended to accumulate minerals in a plant root because their concentration is much greater in the root than in soil so ions must be pumped in at a cost of ATP and against a concentration gradient. Mineral passage is nonselective, except passage through the endodermis. This results because of the presence of waxy Casperian strips which cause minerals to pass selectively through endodermis plasma membrane. Almost no transpiration occurs under these circumstances. Active transport does continue and causes higher concentrations of ions, which pulls even more water in by osmosis, so that water moves upward in the xylem.