Rhizobium leguminosarum bv viciae gains entry to pea root tissues through tip-growing infection threads (Brewin 1998). Growth of bacteria in close association with a deformed root hair cell wall results in the initiation of an infection thread as a tubular ingrowth of the plant cell wall. Rhizobia are propagated from cell to cell because transcellular threads are reinitiated in adjacent cells in the root cortex and subsequently in the invasion zone of the developing nodule (Rae et al. 1992). The lumen of the infection thread is topologically equivalent to an intercellular space and the luminal matrix apparently shares many components with the extracellular matrix. Here, we describe the isolation and characterization of a plant matrix glycoprotein, MGP. This 110 kDa component was originally identified in the lumen of the infection thread using monoclonal antibody, MAC265, which recognizes a carbohydrate epitope.
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