Abscisic acid and stomatal closure

• During water stress, hormone abscisic acid (ABA) is produced by plants to stimulate closing of their stomata

  • certain environmental conditions can cause water stress, such as very high temps or reduced water supplies
  • Guard cells have ABA receptors on their cell surface membranes
  • Aba bonds to these receptors inhibiting the proton pumps and therefore stopping the active transport of hydrogen ions out of guard cells
  • ABA also causes calcium ions to move into cytoplasm of the guard cells through the cell surface membranes
  • acts as secondary messengers
• Calcium causes channel protiens to open that allow negatively charged ion to leave guard cells

  • stimulates the opening of further channel proteins that allow potassium ions to leave the guard cells
  • The calcium ions also stimulate the closing of channel proteins that allow potassium ions to enter guard cells
• loss of ions increases the water potential of guard cells

  • water leaves guard cells by osmosis
  • Guard cells become flaccid causing stomata to close
• Diagram of ABA action