Infected seedlings (typically 40 g) were harvested and crude haustoria prepared by sucrose density gradient centrifugation as described in Section 2.2. The haustoria resulting from this were washed in PBS and resuspended finally in 1 mL PBS. These were then separated into 250 L aliquots and precipitated using magnetic beads as follows.A50L suspension of magnetic beads charged with protein A was prepared separately for each 250 L haustoria aliquot: following the instruction of the manufacturer (Dynabeads, Life Technologies, Burlington, ON), the beads were decorated with donkey anti mouse-IgM--chain (Jackson Immuno Research) and the anti-haustoriamonoclonal IgM in tissue culture solution, and washed in PBS before use. Each 250 L haustoria aliquot was then mixed with 50 L decorated bead suspension and allowed to cross-react for 30 min at room temperature with end-over-end mixing. The beads were then captured with a rare-earth magnet and washed three times with PBS. Haustoria were released from the beads using 0.1Mglycine, pH 2.5. The quality of each preparation was assessed by microscopy by staining a 1 L sampling with calcofluorwhite and viewing it under a fluorescence microscope as described previously [18]. Haustoria were lyophilized and stored at –80°C until required.