DIFFERENTIAL EXPRESSION OF A GLYCOSYL INOSITOL PHOSPHOLIPID ANTIGEN ON THE PERIBACTEROID MEMBRANE DURING PEA NODULE DEVELOPMENT

Monoclonal antibody JIM18 recognizes a glycosylated form of an inosito l-containing phospholipid. In pea (Pisum sativum), this epitope is ass ociated with the plasma membrane of both infected and uninfected cells in root nodules induced by Rhizobium leguminosarum by, viciae. On the plant-derived peribacteroid membrane that surrounds endosymbiotic bac teria in infected host cells, expression of the JIM18 epitope was foun d to be developmentally regulated. In situ immunolocalization studies revealed that the JIM18 epitope was present on the peribacteroid membr ane surrounding actively dividing bacteria (juvenile bacteroids), but reactivity with the JIM18 antibody probe was abruptly lost from this m embrane as differentiation of the symbiotic compartment progressed. Th is loss of reactivity was concomitant with accumulation of starch gran ules in infected host cells. This stage in host cell differentiation o ccurs earlier than the accumulation of nodule-specific proteins, such as leghemoglobin and nitrogenase, The biochemical nature of the JIM18 antigen in pea and carrot was investigated by thin-layer chromatograph y and by analysis of the effects of various chemical modifications, In carrot cells, the incorporation of radiolabeled precursors was invest igated.