stomata physiology

• Stomata regulate the exchange of carbon dioxide (CO₂) and water vapour (H₂O). • 90% of atmospheric exchange occurs through stomata. • Stomata control evapotranspiration and CO₂ uptake.

• Composed of two guard cells and surrounding subsidiary cells. • Together, they form the stomatal complex. • Stomata shape and distribution vary across species.

It is the ratio of the number of stomata to the total number of epidermal cells.

• Asymmetric division of epidermal cells forms the guard cells. • Specialization leads to functioning guard cells and recruitment of subsidiary cells. • Adaptations occur in morphology, density, and distribution of stomata.

• Guard cells act as hydraulic valves, opening when they increase in volume due to osmotic uptake. • Stomatal closure is triggered by water loss and reduced hydrostatic pressure in guard cells.

• K+ ions enter guard cells, driven by an electrochemical gradient. • Cl- and malate also enter, creating an osmotic force that draws water into the cell, causing expansion and pore opening. • Sucrose is transported from mesophyll cells to guard cells, contributing to osmotic pressure and energy supply.

• Ca2+ ions enter guard cells and cytosolic pH changes. • These triggers cause K+ efflux, reducing osmotic pressure and causing water to leave the guard cells.

• Electrophysiology (e.g., patch clamp) • Pharmacology • Genetics • Imaging techniques

• Internal CO₂ concentration: High CO₂ leads to stomatal closure. • Light: Blue light causes stomatal opening, with phytochrome and cryptochrome involved in mediating the effect. • Water vapour: Water loss triggers stomatal closure. • Abscisic acid (ABA): Mediates stomatal closure during water stress.

• Stomata of C3 and C4 plants open during the day and close at night. • Stomata of CAM plants open primarily at night.