Explain the mechanism of opening and closing of stomata.

Opening of Stomata :
* Levitt (1974) proposed K⁺ pump theory.
* It explains the mechanism of opening and closing of photoactive stomata.
* According to this theory, K⁺ ions accumulated in guard cells in the presence of light.
* This coupled with efflux of protons leads to increase in pH of the guard cells.
* Accumulation of K⁺ ions into the guard cells is associated with passive influx of Cl^– ions.
* It results decreasing the water potential of the guard cells.
* Water enters into the guard cells, making them turgid.
* As a result stomata open.
Closing of Stomata :
* At night, in the absence of light, the K⁺ and Cl^– ions move out of the guard cells.
* Influx of protons occurs.
* Decrease in the pH of guard cells.
* Due to which the water potential of guard cells increases.
* Water starts moving out of them leading to
closure of stomata.