Stomata

Stomatal transpiration is the process in which plants release water through stomata. It accounts for 90% of the moisture that the leaves lose, also known as foliar transpiration. The microscopic apertures seen on the leaf epidermis are known as stomata. Stomata can be seen beneath a microscope. Some plants have stomata on their stems and other sections.

Stomatal Structure

Each stoma has two guard cells surrounding it. Chloroplasts are found in the guards, which are kidney-shaped. In each stoma, there is a breathing chamber.

Plants acquire the necessary carbon dioxide during photosynthesis and release the oxygen created into the atmosphere. This gas exchange takes place through openings in the epidermis of plant leaves. A stoma is a single orifice derived from the Greek word for “mouth”. Stomata respond to a range of environmental stimuli by opening and closing.

Two specialised guard cells border each stoma, opening when these cells suck in water. The amount of water in the guard cell is controlled by ion transport.

The guard cells that surround the stomata have thickened radial cell walls. These cell walls are entirely thickened on the side facing the stoma (ventral side). Alternating bands of thick and thin cell walls run along the outside (dorsal side). What causes the stomata to open when exposed to light? A proton pump exports protons (H⁺) when phototropin detects blue light. The pump is powered by adenosine triphosphate (ATP), produced by photosynthesis. The cytosol is often more negative than the extracellular solution, and this distinction is important.

Role of Abscisic Acid in Stomatal Movement Regulation

The diurnal stomatal motions are linked to the ABA mode of action. This association is thought to be based on both the molecular links between ABA and circadian-clock pathways and ABA production and light response. Although multiple studies have linked the diurnal cycle to ABA signalling, further research is needed to understand this connection.

The stomata are opened when the guard cell turgor pressure rises. If leaves kept in the dark are illuminated, the guard cells perceive the light stimulus as an opening signal, triggering a series of responses.

Proton-Ketose Pump Hypothesis

Levit, in 1974, combined the points in Scarth’s and Steward’s hypothesis and gave a modified version of the mechanism of stomatal movement, which was called the proton-potassium pump hypothesis. According to this theory, the change in the turgor pressure of the guard cells that open and close the stomata causes the absorption and loss of potassium ions by guard cells.

Theory of Glycolate Metabolism

Zelitch (1963) proposed that the production of glycolic acid in the guard cells is an important factor in stomatal opening. Glycolate is produced under a low concentration of CO₂. He suggested that glycolate gives rise to carbohydrates, raising the osmotic pressure and that it could participate in the production of ATP, which might provide the energy required for the opening of stomata.

Facts about Stomata

• Submerged plant species, fungi, and algae do not have stomata.
• In monocotyledonous plants, stomata are evenly distributed and are found on both the lower and upper surfaces of the leaves.
• In dicotyledonous plants, stomata are not evenly distributed as they are mostly found on the lower surface compared to the upper surface.

Conclusion

Plants acquire the necessary carbon dioxide during photosynthesis and release the oxygen created into the atmosphere. This gas exchange takes place through openings in the epidermal of plant leaves. A stoma is a single orifice (hole) derived from the Greek word for “mouth.” Stomata respond to a range of environmental stimuli by opening and closing. Some of the water in the soil is consumed by the roots, while the rest evaporates into the atmosphere. Water is evaporated into the atmosphere by plant parts – stems, tiny pores on leaves and flowers. It is the process by which water from plant leaves and other parts evaporates into the atmosphere.