A theory, originally proposed in 1970 by R. Cleland, A. Hager, and co-workers, that describes how auxins stimulate cell expansion in certain plant tissues, notably in coleoptiles of cereals and other grasses, such as oat (Avena). It asserts that the auxins induce acidification of the immediate cell-wall environment, thereby activating enzymes that loosen load-bearing bonds within the cell wall. This permits expansion of the walls by the cell's internal turgor pressure, and thus enlargement of the cell. It is thought that the auxin binds with auxin-binding proteins in the plasma membrane and stimulates proton pumps (also in the cell's plasma membrane) to excrete protons (H+) into the cell wall from the cytoplasm. The consequent lowered cell-wall pH activates the wall enzymes.
Subjects: Biological Sciences — Chemistry.