Question

Describe mechanism of opening and closing of stomata with reference to Proton transport theory.

Answer 1

Proton transport theory:

1. According to theory of proton transport (Levitt-1974), stomatal movement occurs due to the transport of protons H⁺ and K⁺ ions.
2. During daytime, starch is converted into malic acid. Malic acid dissociates to form Malate and protons. Protons are transported to subsidiary cells and K⁺ ions are imported from them. 
3. Potassium malate is formed that increases osmolarity and causes endosmosis. Uptake of K⁺ ions is always accompanied with CI⁻ ions.
4. At night, uptake of K⁺ and CI⁻ ions is prevented by abscissic acid, changing the permeability of guard cells. Due to this guard cells become hypotonic and thereby become flaccid.