What controls the opening and closing of pores?

The opening and closing of stomata is controlled by guard cells.

Stomatal is one of many small openings in epithelial cells of leaves, stems and other plant organs, and it is a unique structure of plant epidermis. Stomata usually exist in the aboveground parts of plants, especially on the epidermis of leaves, and can also be seen on young stems and petals, but most submerged plants do not. In a narrow sense, convex lens pores formed between guard cells are often called pores.

Guard cells are different from epidermal cells in that they contain chloroplasts in their structures, but they are small in size, few in number and underdeveloped in lamellar structure, but they can synthesize carbohydrates through photosynthesis. Sometimes it is accompanied by 2 ~ 4 secondary guard cells adjacent to the guard cells. Including these cells is stomata (or stomatal apparatus) in a broad sense. There is a wide intercellular space (air chamber) just below the stomata.

Stomatal movement:

The chloroplasts of guard cells photosynthesize under light, and the pH value in cells increases due to CO2. Starch phosphorylase hydrolyzes starch into glucose phosphate, which reduces the water potential in cells. CO2 produced by respiration in the dark reduces the pH value of guard cells, and starch phosphorylase synthesizes glucose into starch, so the concentration of cell fluid decreases, the water potential increases, the guard cells lose water and the stomata close. The osmotic system of guard cells is also regulated by potassium.

The light reaction of photosynthesis (cyclic and acyclic photophosphorylation) produces ATP, which absorbs K by active transport against the difference of ion concentration, reduces the water potential of guard cells, and absorbs water to open stomata. Note: if the light intensity is lower than the light compensation point, the stomata will close; Red light and blue-violet light have the best effect on the light quality that causes stomatal opening; Sedum plants open stomata at night, absorb and store CO2 (malic acid is stored in vacuoles), and close stomata during the day, and malic acid is decomposed into pyruvate to release CO2 for photosynthesis.