In 1926, scientist Sayre presented a theory. According to him, the stomata open and close to allow the interconversion of sugars and carbohydrates and to vary the pH of the cell.
(i) Stomatal opening technique
CO2 is used in the photosynthetic process in the guard cells during the day. This decreases the CO2 concentration in the guard cells and increases the pH. Because of this, under the influence of phosphorylase enzyme, the white blood cells of the guard cells are converted into 1-phosphate. As a result, the density of the guard cell increases and water enters the guard cell by the process of endoabsorption. The guard cell takes in water and bends like a bow and the stomata open.
(ii) Mechanism of stomatal closure
CO2 is produced during respiration in the guard cells at night. CO2 reacts with water to form carbonic acid. As a result the pH of the guard cell decreases. Due to this, under the effect of phosphorylase enzyme, glucose 1-phosphate is converted into white sugar. It reduces the density of guard cells. In the process of exudation, water escapes from the guard cells. The guard cell loses water and relaxes and the stomata close.
Bleach → Glucose 1-phosphate
Glucose 1-phosphate → white matter