How does opening and closing of stomata take place?

Explanation

Mechanism of opening and closing of stomata : Levitt (1974) proposed `K^+` pump theory to explain the opening and closing of stomata. According to this, `K^+` ions are accumulated into guard cells from the subsidiary cells in the presence of light. This coupled efflux of protons leads to increase in pH of the guard cells. `K^+` ion accumulation is associated with influx of `CZ^(-)` ions to decrease the water potential of guard cells. Water enters into guard cells making them turgid. The outer walls of the guard cells are thin, expand out- wardly with the help of microfibrils.in the cell walls of guard cells resulting in opening of stomata.
At night, the `K^+` and `Cl^(-)` ions move out of the guard cells due to which the water potential of guard cells increases and water stands moving out of guard cells leading to the closure of stomata.
Under water stress conditions ABA (Abscisic acid), a natural antitranspirant drives the `K^+` ions out of guard cell making them close.