Callose is a plant polysaccharide. Its production is due to the glucan synthase-like gene (GLS) in various places within a plant. It is produced to act as a temporary cell wall in response to stimuli such as stress or damage.[1] Callose is composed of glucose residues linked together through β-1,3-linkages, and is termed a β-glucan. It is thought to be manufactured at the cell wall by callose synthases and is degraded by β-1,3-glucanases. Callose is very important for the permeability of plasmodesmata (Pd) in plants; the plant's permeability is regulated by plasmodesmata callose (PDC). PDC is made by callose synthases and broken down by β-1,3-glucanases (BGs). The amount of callose that is built up at the plasmodesmatal neck, which is brought about by the interference of callose synthases (CalSs) and β-1,3-glucanases, determines the conductivity of the plasmodesmata.[2]
Callose is laid down at plasmodesmata, at the cell plate during cytokinesis, and during pollen development. Endothecium contains a substance callose, which makes it thicker. Callose is produced in response to wounding, infection by pathogens,[3] aluminium, and abscisic acid. When there is wounding in the plant tissue, it is fixed by the deposition of callose at the plasmodesmata and cell wall; this process happens within minutes after damage. Even though callose is not a constitutional component of the plant's cell wall, it is related to the plant's defense mechanism.[4] Deposits often appear on the sieve plates at the end of the growing season.[5] Callose also forms immediately around the developing meiocytes and tetrads of sexually reproducing angiosperms but is not found in related apomictic taxa.[6] Callose deposition at the cell wall has been suggested as an early marker for direct somatic embryogenesis from cortical and epidermal cells of Cichorium hybrids.[7] Temporary callose walls are also thought to be a barrier between a cell and its environment, while the cell is undergoing a genetic programming that allows it to differentiate.[8] This is because, callose walls can be found around nucellar embryos during Nucellar embryony.[9]