Luftporen

Luftporen, also known as stomata, are microscopic pores located on the epidermis of leaves and some stems that regulate gas exchange between the internal leaf tissues and the atmosphere. Each pore is typically surrounded by a pair of specialized guard cells that control its opening and closing.

The structure and operation of Luftporen involve the guard cells, which change shape to modulate the pore aperture. Opening is driven by turgor pressure increase in the guard cells, largely through the active transport of ions such as potassium and accompanying osmotic water uptake. Light, especially blue light, activates proton pumps and promotes ion uptake, causing the pore to open. CO2 concentration inside the leaf, humidity, and water availability influence this process as well. In many species, Luftporen close at night or during water stress to reduce water loss.

The primary functions of Luftporen are gas exchange and water regulation. They allow carbon dioxide to enter the leaf for photosynthesis and permit oxygen to exit as a byproduct. At the same time, water vapor is lost through transpiration, which also helps to cool the leaf. The degree of openness, or stomatal conductance, reflects a balance between carbon gain and water conservation.

Distribution and variation are notable. Luftporen are found on the aerial parts of most land plants, with density and distribution varying by species, leaf surface, and environmental adaptation. They are typically more abundant on the underside of leaves to minimize water loss, but some plants have stomata on both surfaces or adapted structures such as sunken stomata or stomatal crypts in arid environments.

Development and evolution: Luftporen arose early in land plant evolution and are formed through differentiation of epidermal cells into guard cells. Their development and patterning are regulated by genetic and hormonal signals that coordinate stomatal density and distribution.