Differential Expression of a GlycosylInositol Phospholipid Antigen on the PeribacteroidMembrane during Pea Nodule Development. Silvia Perotto . John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK. Neil Donovan(1,2), Bjorn K. Drobak(1) and Nicholas J. Brewin(1). (1)John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK, and (2) Department of Biological Sciences, University of the West of England, Coldharbour Lane, Bristol BS 16 1QY, UK. MPMI 8:560-568. Accepted 6 March 1995. Copyright 1995 The American Phytopathological Society.

Monoclonal antibody JIM18 recognizes a glycosylaled form of an inositol-containing phospholipid. In pea (Pisurn salivum), this epitope is associated with the plasma membrane of both infected and uninfected cells in root nodules induced by Rhizobium leguminosarum bv. viciae. On the plant-derived peribacteroid membrane that surrounds endosymbiotic bacteria in infected host cells, expression of the JIM18 epitope was found to be developmentally regulated. In situ immunolocalization studies revealed that the JIM18 epitope was present on the peribacteroid membrane surrounding actively dividing bacteria (juvenile bacteroids), but reactivity with the JIM18 antibody probe was abruptly lost from this membrane as differentiation of the symbiotic compartment progressed. This loss of reactivity was concomitant with accumulation of starch granules in infected host cells. This stage in host cell differentiation occurs earlier than the accumulation of nodule-specific proteins, such as leghemoglobin and nitroge-nase. The biochemical nature of the JIM18 antigen in pea and carrot was investigated by thin-layer chromatography and by analysis of the effects of various chemical modifications. In carrot cells, the incorporation of radiolabeled precursors was investigated.