Work Step by Step
Light causes the phosphorylation of ATP synthase in the plasma membranes of guard cells, which results in positively charged hydrogen ions being pumped out of the guard cells. This causes the opening of gated transport proteins because of the difference in voltage across the membrane. Positively charged potassium ions can now enter the guard cells. Water follows the potassium ions into the cells, causing the guard cells to swell up and open the stomata.