Malate theory (stomatal opening)

• 1


  Chloroplasts in the guard cells produce ATP during photosynthesis
• 2


  ATP is used to actively transport the K+ ions into the guard cells
• 3


  Starch is converted into malate ions
• 4


  K+ and malate ions decrease the water potential to below that of surrounding (epidermal) cells, therefore water moves in by osmosis
• 5

  Due to the unequal distribution of cellulose cell walls of the guard cells, as the cell becomes turgid, the stomata opens. The reverse happens in the dark.