Acid growth

Acid growth refers to the ability of plant cells to quickly stretch. While typically the word "growth" refers to increase in cell number, acid growth could have more accurately been called acid-induced stretching, acid expansion, wall loosening, or some other similar term. During acid growth plant cells are no longer inhibited from expanding, because their microfibrils have been weakened. A typical sequence leading up to this would involve the introduction of a plant hormone (auxin, for example) that causes protons (H+) to be pumped into the cell. As they increase in number the cell becomes more acidic (pH is a measure of the concentration of H+). Through enzymatic activity this causes the microfibrils to lose their network-like connections. Unrestrained by the cell wall fibers, the cell can swell.