SUMMARY

Conditions favouring the infection of isolated tobacco mesophyll protoplasts by potato virus X (PVX) were studied in detail, and a procedure to effect infection in 7o ~ of protoplasts was developed. PVX required higher concentrations of both inoculum virus and poly-L-ornithine than tobacco mosaic virus (TMV) or cucumber mosaic virus (CMV). PVX infection showed aunique response to varying pH of the inoculation medium. The time course of PVX multiplication i protoplasts re-sembled that of TMV. Unlike the infection by TMV and CMV, PVX infection was partially inhibited by actinomycin D. Inclusion bodies characteristic for PVX infection were present in the infected protoplasts, but their involvement in virus production appeared to be unlikely