Infection of cowpea mesophyll protoplasts with cowpea mosaic virus.

Mesophyll protoplasts were isolated from the primary leaves of cowpeas by a one-step procedure using a mixture of Macerozyme and Cellulase. The protoplasts were inoculated with cowpea mosaic virus and virus multiplication was shown to occur by measuring the virus infectivity at various times after inoculation. Eighty to ninety-six percent of the protoplasts were infected as shown by fluorescent antibody staining. More than 10⁸ progeny virus particles were produced per infected protoplast. A cytopathic structure similar to the structure found in CPMV infected leaf cells occurred in infected protoplasts. Poly-l-ornithine was not essential for CPMV infection of the cowpea mesophyll protoplasts, but it had a stimulating effect. This is the first protoplast system after the tobacco mesophyll protoplast system suitable for virus infection studies. As cowpeas belong to a plant family other than tobacco, the new protoplasts allow comparative infection studies with plant viruses.