(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.
Other plant parts where callose can be found are in phloem sieve plates, pollen tubes, cotton fibers, at the base of a lemma or palea in grasses, and other specialized cells.
Word origin: From Latin callōsus, callous.