Effect of actinomycin D and UV irradiation on the replication of cucumber mosaic virus in protoplasts isolated from resistant and susceptible cucumber cultivars

Combined treatment of cucumber protoplasts with actinomycin D and UV irradiation inhibited host RNA synthesis by more than 95%. Cucumber mosaic virus (CMV) replication was however, not affected in either susceptible, Ashley, or resistant, China (Kyoto), cucumber protoplasts, whether the treatment was administered before or immediately after inoculation, or whether the coculum was virus RNA or nucleoprotein. These inhibitors also failed to affect the expression of resistance in China (Kyoto) protoplasts suggesting the absence of an “active defence mechanism” operating at the single cell level.

The lower level of infectious RNA in China (Kyoto) protoplasts was reflected by decreased synthesis of total virus specific RNA rather than a reduction in any one of the CMV RNAs. The amount of the replicating satellite RNA 5 (CARNA 5) associated with this strain was similar, in proportion to genomic RNAs, in protoplasts from each cultivar and therefore could not account for the suppression of disease in China (Kyoto).