Distribution of cucumber mosaic virus in systemically infected tobacco leaves

Abstract

Distinct green and yellow areas developed in Xanthi-nc and White Burley tobacco leaves following inoculation with cucumber mosaic virus (CMV) Price No. 6. Green areas in the first cluster of leaves with such symptoms contained less than 5% of the infectivity extracted from the yellow areas, though symptom patterns on Xanthi-nc and White Burley plants inoculated with extracts from green areas were similar to those obtained with extracts from yellow areas. Green areas did not contain infectious RNA. They were resistant to reinfection with three strains of CMV but not to infection with tobacco mosaic virus. No viral antigen could be detected in extracts from green areas with either CMV or CMV coat antiserum, and only 2–7% of “green” protoplasts fluoresced when treated with CMV or CMV coat antiserum and counterstained with fluorescent antibody. When plants were kept at 30°, green areas were invaded by CMV and extractable infectivity reached that in yellow areas. However, in plants kept at 30° without supplemental mineral feeding, CMV-6 was present apparently as free RNA, and could be recovered only by phenol extraction. Incubation of “green” protoplasts at 18 and 25° did not increase infectivity, indicating a continuous resistant state. Infectivity of “yellow” protoplasts during incubation decreased with time especially at 25°, whereas incubation at 4° for 24 hr consistently increased extractable infectivity. Apparently, resistance of green areas does not seem to be due to capture of the superinfecting genome by coat protein of the protecting genome or to the presence of a strain different from that in yellow areas.