(botany) A plant polysaccharide composed of glucose residues linked together through β-1, 3-linkages secreted by an enzyme complex (callose synthase), resulting in the hardening or thickening of plant cell walls.
Callose separates developing pollen grains, preventing their underlying walls from fusing. It also functions in the formation of the cell plate, plasmodesmata, tracheids, and root hairs. It is also produced in plant cells in response to wounding, heavy metal treatment (e.g. aluminum) and pathogen infection.