This theory explains how the hydrogen ion concentration changes in the eytoplasm and the chloroplast of the guard cells and exchange with K’ ions from the neighbouring cells. Basically, it is similar to K” transport theory.
1. During night C02 is not utilised so its accumulation in the substomatal cavities make it acidic.
In this condition the hormone ABA (abscise acid) inhibits the uptake of KT ions from the neighbouring cells by changing the permeability of the membrane.
The organic acids are used up by the metabolic process thereby decreasing the ion concentration in the guard cells.
4. So II” ions from neighbouring cells enter into the guard cells in exchange of K’ ions.
5. ion concentration decreases in the guard cells and so also the osmotic concentration.
6. Water goes out by exosmosis, guard cells become flaccid and stoma closes.
7. Organic acids particularly, malice acid arc formed during opening.