A MONOCLONAL-ANTIBODY RECOGNIZES A 65 KDA HIGHER-PLANT MEMBRANE POLYPEPTIDE WHICH UNDERGOES CATION-DEPENDENT ASSOCIATION WITH CALLOSE SYNTHASE IN-VITRO AND COLOCALIZES WITH SITES OF HIGH CALLOSE DEPOSITION IN-VIVO

A monoclonal antibody (MAb) capable of immobilizing detergent-solubilized UDP-glucose: (1 --> 3)-beta-glucan (callose) synthase activity from higher plants has been selected and characterized. On Western blots this MAb recognizes a polypeptide of about 65 kDa found in membranes isolated from a variety of plant sources. The polypeptide recognized by this MAb does not appear to bind the substrate UDP-glucose, and evidence is presented which indicates that this polypeptide associates with the enzyme complex in a cation-dependent manner under conditions where the callose synthase assumes a larger size. Indirect immunofluorescence localization with this MAb was positive with sieve plates of cucumber (Cucumis sativus) seedlings, and with plasmodesmata of onion (Allium cepa) epidermal cells, both being sites of localized, stress-induced callose deposition.