In 1974 scientist Lavitt published the modern theory of stomatal opening and closing. Later Raschke, (1975), Noggle, Fritz (1976) and other scientists supported this theory. This is universally accepted doctrine.
Stomatal opening technique
(i) Blue (430-460nm) light enters the guard cell during the day. Under the influence of blue light, the white matter of the guard cells is converted into phosphoenol pyruvic acid.
(ii) phosphoenol pyruvic carboxylase enzyme reacts phosphoenol pyruvic acid and CO2 to produce oxaloacetic acid.
Oxaloacetic acid is converted to malic acid under the action of (Rorr) malic dehydrogenase enzyme.
(iii) Malic acid dissociates to form hydrogen ion (H+) and malate ion [R(COO-)2].
(iv) H+ moves from the guard cell into the accessory cell and K+ from the accessory cell into the guard cell.
(v) K+ reacts with malate ions in the guard cell to form potassium malate.
(vi) Potassium malate increases the osmotic pressure of the guard cell and water enters the guard cell in the process of endosmosis. This causes swelling of the guard cells and opening of the stomata.
stomatal closure technique
(i) K+ and malate ions are produced by breakdown of potassium malate in guard cells at night.
(ii) K+ moves from the guard cell into the accessory cell and H+ from the accessory cell into the guard cell.
(iii) reacts with hydrogen ion (H+) and malate ion [R(COO – )2] in the guard cell to form malic acid.
(iv) As K+ escapes from the guard cell, the osmotic pressure of the guard cell decreases and water escapes by the process of exudation.
(v) Guard cells lose water and become silent and stomata close.