Question

Which of the following conditions help in opening of stomata?

• A. Darkness, pH 5, high $C{O}_2$ concentration
• B. pH 7, low $C{O}_2$ concentration and light
• C. pH 5, low $C{O}_2$ concentration and light
• D. High $C{O}_2$ concentration, low $K^{+}$ ion concentration in guard cells

Answer 1

The correct option is B pH 7, low $C{O}_2$ concentration and light

Malate or potassium ion pump hypothesis was first proposed by Levitt, 1974. According to this theory, there is a decrease of carbon dioxide in guard cells. During light exposure there is hydrolysis of starch to form phospho enol pyruvate (PEP). PEP combines with carbon dioxide to form organic acids, like oxalic acid. The organic acids get ionised and the proton passes out of guard cells and potassium ion is actively absorbed and accumulated.

Potassium ions combine with malate and passes into small vacuoles. Chloride ions are also absorbed from outside to maintain electroneutrality. As a result of accumulation of ions there is a reduction in water potential of guard cells. The reduction in water potential causes absorption of water from adjacent cells, guard cells become turgid and stomata open.