In 1943, scientist Imammura first discovered the role of K+ in stomatal opening. In 1959, Japanese scientists Imammura & Fujino using radioactive isotopes proved that the opening and closing of stomata is regulated by the active absorption of K+ ions.
(i) Stomatal opening technique
During the day, guard cells absorb large amounts of K+ and Cl- ions. As a result, the osmotic pressure of the guard cell increases and water enters the guard cell in the process of endosmosis. At this time the turgor pressure (TP) of the guard cell increases and the guard cell bends like a bow. As a result, the pore opens.
(ii) Mechanism of stomatal closure
K+ and Cl- ions are released from the guard cell at night. As a result, the osmotic pressure of the guard cell decreases and water escapes from the guard cell in the process of exudation. At this time the turgor pressure (TP) of the guard cell decreases and the guard cell relaxes. As a result, the stomata are closed.