Localization of Pectic Galactan in Tomato Cell Walls Using a Monoclonal Antibody Specific to (1[->]4)-β-D-Galactan

To develop antibody probes for the neutral side chains of pectins, antisera were generated to a pectic galactan isolated from tomato (Lycopersicon esculentum) pericarp cell walls and to a (1[->]4)-[beta]-galactotetraose-bovine serum albumin neoglycoprotein. The use of these two antisera in immunochemical assays and immunolocalization studies indicated that they had very similar specificities. A monoclonal antibody (LM5) was isolated and characterized subsequent to immunization with the neoglycoprotein. Hapten inhibition studies revealed that the antibody specifically recognized more than three contiguous units of (1[->]4)-[beta]-galactosyl residues. The antigalactan antibody was used to immunolocalize the galactan side chains of pectin in tomato fruit pericarp and tomato petiole cell walls. Although the LM5 epitope occurs in most cell walls of the tomato fruit, it was absent from both the locular gel and the epidermal and subepidermal cells. Furthermore, in contrast to other anti-pectin antibodies, LM5 did not label the cell wall thickenings of tomato petiole collenchyma.