Question

Which of the following theory of stomatal opening and closing is given by Levitt?

• A. Theory of starch - glucose transformation
• B. Theory of active $K^{+}$ transport
• C. Theory of starch - sugar interconversion
• D. None of the above

Answer 1

The correct option is B Theory of active $K^{+}$ transport

There are three main theories about the mechanism of stomatal movement.

1. 'Guard Cell Photosynthesis' (proposed by Schwendener, 1881).
2. 'Starch Hydrolysis' and Starch sugar interconversion theory (proposed by Sayre, 1923 and 1926 and other contributions were made by Lloyd and Steward)
3. Malate or potassium ion pump hypothesis (proposed by Levitt, 1974).

According to the potassium ion pump theory, rise in pH of guard cells (due to photosynthesis and consequent decrease of carbon dioxide) causes 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. This results in absorption of water from adjacent cells, guard cells become turgid and stomata open.