When protoplasts inoculated with tobacco rattle virus (TRV) were sampled after successive intervals at 22 or 25 °C in light, the following sequence of events was detected. Infective TRV-RNA appeared at 7 h and approached its maximum concentration by 12 h. Antigen detected by staining with fluorescent antibody to TRV particles, infective TRV nucleoprotein, and both long and short TRV particles were produced by 9 h, and increased up to about 40 h. Infective RNA synthesized at about 9 h was apparently incorporated into nucleoprotein particles about 4 to 5 h later. Up to 16 h, long virus particles outnumbered short, but their proportion steadily decreased until 40 h, when it stabilized at about 20%. Half the final yield of long particles was produced by 22 h, and half that of short particles by 30 h. Nearly all the long virus particles were associated with mitochondria at all times, but after the first few hours the short ones were predominantly free in the cytoplasm. Inoculating short virus particles up to 8 h before, or 4 h after long particles instead of simultaneously, did not greatly affect the number of antigen-producing infections produced, but somewhat decreased the proportion of infective RNA incorporated into nucleoprotein. These results provide support for the idea that separation in time or place within the cell of the synthesis, translation or assembly into nucleoprotein of the different genome parts may be one of the advantages of multipartite genomes as a modus vivendi for plant viruses.
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