-50- 



incubated with TRITC-con jugated pre-immune serum or 

 heterologous antisera. 

 Protein A-Gold Labelling 



Colloidal gold particles, 15 nm diameter, were 

 selectively labelled on CyMV, ORSV, CMV virions and BYMV 

 cylindrical inclusions in thin sections, which were 

 treated with homologous antisera and protein A-gold 

 complex, respectively (Figs. 47, 48, 49, 51, 53 and 55). 

 Very few gold particles were found on cell components not 

 containing virions or viral inclusions or on intercellular 

 spaces of infected tissue. Likewise, gold particles were 

 not found to be specifically reacted in tissue sections 

 treated with normal serum rather than homologous 

 antiserum, nor were they detected in sections exposed to 

 heterologous antisera (Figs. 50, 54 and 56). By this 

 method, virus-like or non-related virus particles are 

 easily distinguished, which is not possible by using 

 conventional thin sectioning techniques. In some orchid 

 cells, for example, some thread-like particles are easily 

 mistaken for CyMV virions, but these can be differentiated 

 because they do not show any specific gold labelling (Fig. 

 52) . 



Dilution of antisera affected the non-specific 

 labelling of gold particles. A high concentration of 

 antisera used for incubation resulted in more nonspecific 

 gold labellings (Fig. 47). For this reason, antisera 

 dilutions of 1/500 to 1/2000 were used in this study. 



