Monoclonal antibodies against phloem P‐protein from plant tissue cultures. II. Taxonomic distribution of cross‐reactivity

P-protein, a filamentous protein found in the sieve elements of most angiosperms, is believed to function in the sealing of phloem wound sites. We report here on the use of a highly sensitive immunomicroscopy assay to study the ability of P-protein specific monoclonal antibodies RS21, RS22, and RS23, made against the P-protein from Streptanthus tortuosus (Brassicaceae), to recognize the native P-protein in a number of different plant genera. RS2 1, RS22, and RS23 all recognized the P-protein in other genera within the Brassicaceae including Arabidopsis and in the closely related family, Capparaceae. RS21 and RS22 also were able to bind to the P-protein in plants more distantly related to S. tortuosus. The labeling of P-protein was also observed in the monocots Iris and Narcissus probed with RS2 1. No label was seen with members of the Poaceae that are reported to lack P-protein. None of the monoclonal antibodies was able to bind to the P-protein in members of the Cucurbitaceae.