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-solubili zed UDP-glucose: (1 --> 3)-beta-glucan (callose) synthase activity fro m higher plants has been selected and characterized. On Western blots this MAb recognizes a polypeptide of about 65 kDa found in membranes i solated from a variety of plant sources. The polypeptide recognized by this MAb does not appear to bind the substrate UDP-glucose, and evide nce is presented which indicates that this polypeptide associates with the enzyme complex in a cation-dependent manner under conditions wher e the callose synthase assumes a larger size. Indirect immunofluoresce nce localization with this MAb was positive with sieve plates of cucum ber (Cucumis sativus) seedlings, and with plasmodesmata of onion (Alli um cepa) epidermal cells, both being sites of localized, stress-induce d callose deposition.