We could not detect GLRa V-2 in sap extracted from petioles of virus-infected grapevine cv. Muscat d' Alexandrie using Western Blot (Fig. 4, lane c). The virus was detected only in preparations concentrated by ultracentrifugation (Fig. 4, lane d). An additional ten-fold concentration of these preparations by freeze-drying markedly improved the detection of the virus (Fig. 4, lane e). Although multiple bands were observed in SDS-PAGE with preparations concentrated by freeze-drying, only the virus capsid protein band was clearly detected in Western Blots in reaction with antiserum to GLRaV-2. An additional, faint 56.2 kD band was also observed. This band was probably fraction I protein of the grapevine, which is serologically related to the fraction I protein of N. benthamiana (Van Regenmortel; 1982), but occurred in a much lower concentration.
To