Question

Changes in turgidity of guard cells are controlled by

• A. Potassium
• B. Chloride
• C. Malic acid
• D. All of the above

Answer 1

Answer: (D)

All of the above

Turgidity of guard cells are controlled by potassium, chloride and malic acid. When the rate of photosynthesis is high, the concentration of carbon dioxide decreases in the guard cells. This results in increase in the pH. At high pH, starch in the guard cells is converted into organic acid like malic acid. Hydrogen ions are generated which are actively transported out of the cell using ATP. At the same time, potassium ions are transported into the cell. This process is called as H${}^{+}$−K${}^{+}$−pump. The uptake of potassium ion is balanced by uptake of chloride ions. High concentration of potassium, chloride and malate ions in the guard cells increases the osmotic pressure of guard cells. As a result, water enters in the cells by the process of endosmosis. Turgor pressure of guard cells increases and stomata open.

Thus, the correct answer is option D.