Some of the theories have been put forward which reveals the fact that the potassium ions are also involved in the conversion of starch and sugar and the stomatal movements. During the day time the guard cells take up the K+ ions from the surrounding cells, the Cl- and the organic counter ions together will decrease the water potential within the guard cell. This decrease in the water potential causes the water to enter there by guard cells become turgid and the stomata opens. There is no accumulation of the K+ ions in the darkness. Instead the K+ ions are transported into the subsidiary cells from the guard cells. So that this will increase the water potential in the guard cell; the guard cells become flaccid and thus the stomata remains closed.
