Effect of pokeweed antiviral protein (PAP) on the infection of plant viruses

At a concentration of 0.4-mu-g purified pokeweed antiviral protein (PAP)/ml, the formation of local lesions on tobacco leaves caused by tobacco mosaic virus infection was completely inhibited and at 25 ng PAP/ml, 68% inhibition was still obtained. PAP protected plants from infection by viruses from seven virus groups-five RNA viruses: tobacco mosaic virus, cucumber mosaic virus, alfalfa mosaic virus, potato virus X and potato virus Y; and two DNA viruses: African cassava mosaic virus (ssDNA) and cauliflower mosaic virus (dsDNA). Virus infection was probably blocked by PAP at a very early stage. PAP infiltrated into the intercellular spaces through the lower surfaces of leaves inhibited infection by virus inoculated on the upper leaf surface, and partially prevented PVY transmission by aphids. However, PAP did not show any activity against two bacterial and six fungal pathogens.