DIFFERENTIAL LOCALIZATION OF CARBOHYDRATE EPITOPES IN PLANT-CELL WALLS IN THE PRESENCE AND ABSENCE OF ARBUSCULAR MYCORRHIZAL FUNGI

Two monoclonal antibodies (McAbs) generated against rhamnogalacturonan I and characterized as specific for a terminal alpha-(1-->2)-linked f ucosyl-containing epitope (CCRC-M1) and for an arabinosylated beta-(1, 6)-galactan epitope (CCRC-M7) were used in immunogold experiments to d etermine the distribution of the epitopes in four plants. Allium porru m, Zea mays, Trifolium repens, and Nicotiana tabacum plants were chose n as representatives of monocots and dicots with different wall struct ures. Analyses were performed on root tissues in the presence and abse nce of arbuscular mycorrhizal fungi. A differential localization of th e two cell wall epitopes was found between tissues and between species : for example, in leek, CCRC-M1 labeled epidermal and hypodermal cells , whereas CCRC-M7 labeled cortical cells only. Clover walls were label ed by both McAbs, whereas maize and tobacco were only labeled by CCRC- M7. In the presence of the arbuscular mycorrhizal fungi, labeling was additionally found in an apoplastic compartment typical of the symbios is (the interface) occurring around the intracellular hyphae. Epitopes binding both McAbs were found in the interfacial material, and their distribution mirrored the pattern found in the host cell wall. These f indings demonstrate that the composition of the interface zone in a fu ngus-plant symbiosis reflects the composition of the wall of the host cell.