According to the theory the change in turgor pressure that open and close the stomata results from the reversible absorption and loss of potassium ions (K+ ). Light induced stomata opening is accompanied by transport of K+ from subsidiary cell to the guard cells. It is an energy-requiring process.
During day, starch produced change into malic acid which dissociates in malate anions and H+ in guard cell H+ is exchanged with K+ in subsidiary cells. It is active process. K+ ions and malate ions results in increase osmotic pressure and water moves into guard cells from surrounding cells. Increase in turgor, results in opening stomata.
During night, the reversal of K+ – K– pump, low osmotic pressure of guard cell, inducing closure of stomata through exosmosis.
