Colonization of Pea Roots by the Mycorrhizal Fungus Glomus versiforme and by Rhizobium Bacteria: Immunological Comparison Using Monoclonal Antibodies as Probes for Plant Cell Surface Components. Silvia Perotto. Department of Plant Biology, University of Torino, V. le Mattioli 25, 10125 Torino, Italy. Nicholas J. Brewin(2), and Paola Bonfante(1). (1) Department of Plant Biology, University of Torino, V.le Mattioli 25, 10125 Torino, Italy; (2) John Innes Institute, Colney Lane, Norwich NR4 7UH, United Kingdom. MPMI 7:91-98. Accepted 7 September 1993. Copyright 1994 The American Phytopathological Society.

Monoclonal antibodies raised to plant cell surface components expressed during colonization of pea (Pisum sativum) nodules by Rhizobium were used to investigate common features of pea roots colonized by the arbuscular mycorrhizal fungus Glomus versiforme. An extracellular plant glycoprotein recognized by MAC 265 and abundant in the infection threads in pea nodules was completely absent around the mycorrhizal fungus at all stages of host tissue invasion. Antigenic components of the plant glycocalyx recognized by MAC 268 and other antibodies were similarly found on the perisymbiotic membranes that surround the differentiated bacteroids and the fungal arbuscules during the endosymbiotic stage of the interaction. However, the abundance of soluble antigenic components recognized by monoclonal antibody MAC 266 was found to be greatly increased on the interface created around the mycorrhizal fungus during the formation of the arbus-cule. Soluble antigens recognized by MAC 266 monoclonal antibody also accumulate in the peribacteroid compartment of pea nodule cells, but some of the antigenic components recognized in mycorrhizal pea roots by MAC 266 may be specific to the mycorrhizal association.