Question

Explain the potassium ion exchange theory for the stomatal transpiration.

Answer 1

Mechanism of stomatal opening for stomatal transpiration on the basis of potassium ion-exchange theory:

1. The stomatal pore opens when guard cells become turgid due to the influx of water inside them.
2. During daytime due to increased photosynthesis, the concentration of CO₂ decreases in the guard cells.
3. The CO₂ gas is responsible for the formation of carbonic acid. As CO₂ is getting reduced, so, the pH of the guard cell will increase.
4. Due to high pH, the starch in the guard cell gets converted into organic acid (Malic acid).
5. This organic acid then breaks into H⁺ and malate ions.
6. With the use of ATP, the H⁺ ions are actively out-fluxed into subsidiary cells in exchange for an influx of K⁺ ions from subsidiary cells.
7. K⁺ enter inside guard cells.
8. This uptake of K⁺ is balanced by the uptake of Cl^- ions.
9. Increased concentration of Malate ions and K⁺ ions inside the guard cells increases the osmotic pressure of the guard cells.
10. As a result of increased osmotic pressure, water from subsidiary cells enter the guard cells.
11. In guard cells, the turgor pressure increases and the stomatal pore opens up.

Diagram showing the Potassium ion-exchange theory: