What is opening and closing of stomata?

What is opening and closing of stomata?

Aug 09, 2022, 16:45 IST

Mechanism of stomatal opening and closing.

• The stomata is the turgor operated valve in the epidermis. The opening and closing of the stomata are controlled by the size and shape of the guard cells which have differential wall thickening and turegidity.
• Stomatal movements are closely associated with metabolic changes and solute levels of guard cells. It is explained by k ⁺ pump hypothesis.
• The mechanism can be divided into 2 stages (i) Opening of stomata (ii) Closing of stomata.

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Opening of stomata

It takes place step wise

1. The plants are exposed to light
2. Accumulation of K ⁺ in guard cell from the surrounding epidermal cells.
3. Formation of ATP (required for accumulation of K ⁺ )
4. Active pumping of H ⁺ out of the guard cells into surrounding epidermal cells due to ATPase present within the membrane.
5. The Cl ^- moves into guard cell in response to the electrical difference created by the K ⁺ uptake into the guard cells. Malic acid serves both as a proton donor for the export of H ⁺ and as a source of balancing malate ions for the influx of potassium ions.
6. Due to presence of K ⁺ , Cl ^- and malate in the guard cell, water potential become negative.
7. Movement of water from surrounding cell to guard cell.
8. Turgidity of G.C. increases.
9. Stomata open.

Closing of Stomata

1. During the dark proton pump is switched off
2. The accumulated K ⁺ and C ^- move passively out of the guard cells into the surrounding guard cells along electrochemical gradients.
3. The G.C. dispose off accumulated malate, partly by consumption in the TCA cycle and partly by release to other adjacent epidermal cells.
4. Movement of water out of G.C. into the adjacent cells.
5. Loss of turgidity by G.C.
6. Turgor pressure of the G.C. decreases due to exosomosis of water.
7. The inner walls return to their original position resulting in the closure of the pore.

What is opening and closing of stomata? pdf