Immunolocalization of LM2 arabinogalactan protein epitope associated with endomembranes of plant cells

Arabinogalactan proteins (AGPs) are proteoglycans detected in high amounts at plant cell surfaces; however, details of their subcellular localization are largely unknown. Immunolocalization studies with the anti-AGP monoclona l antibody LM2 have indicated that this AGP epitope is associated with secr etory compartments such as endoplasmic reticulum and Golgi apparatus within plant cells actively producing and secreting AGPs. The LM2 epitope contain s a P-linked glucuronic acid residue and occurs in the polysaccharide moiet y of AGPs. We have localized this AGP epitope also to the tonoplast and to cytoplasmic strands. Endomembrane association of AGPs was confirmed with tw o other monoclonal antibodies, JIM13 and MAC207, both reacting with carbohy drate AGP epitopes containing GlcpA-beta(1-->3)-D-GalpA-alpha(1-->2)-L-Rha residues Immunocytochemistry is supported by biochemical analysis which sho ws that LM2 reacts with the microsomal fraction and also with low-molecular -weight material of the detergent phase after Triton X-114 phase separation prepared from maize roots. Our results indicate that some AGP epitopes are closely associated with endomembranes.