Replication of tobacco mosaic virus or its nucleic acid in cell-free preparations from plants has recently been claimed. Some of the evidence supporting such claims has been based on increases in infectivity measured by inoculating assay plants with these preparations or phenol extracts from them (1–5). During attempts to repeat this work it was observed that such increases in infectivity also occurred in conditions precluding the replication of the virus or its nucleic acid.

Cell-free preparations were made from leaves of , type White Burley, var. Judy's Pride, 5 to 6 days after they were inoculated with tobacco mosaic virus. The leaf tissue was ground with pestle and mortar adding per gram of leaf 1 ml. of buffer containing 0·04 -sucrose, 0·05 2-amino-2-hydroxymethylpropane-1,3-diol (tris) adjusted to pH 7·5 with HCl, and 0·005 -MgCl. The mush was strained through two layers of cheesecloth, and the filtrate centrifuged for 1½ hr at 106,000, or for 3½ hr at 42,000 (all operations at 0 to 4°).


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