Potassium ion exchange hypothesis of opening and closing of stomata was closed by

The potassium ion exchange hypothesis of the opening and closing of stomata was given by Levitt. According to this theory, the opening and closing of stomata depend on the production of potassium ion gradient.
When the concentration of potassium ions increases in the guard cell, it allows the guard cell to absorb water from the surrounding cells. This turgidity of the guard cell cause opening of the stomata. However, a decrease in the concentration of potassium ions, makes guard cell flaccid and ultimately closed.