Stein, A., Virus Laboratory, Volcani Institute of Agricultural Research, Bet Dagan, Israel
Loebenstein, G., Virus Laboratory, Volcani Institute of Agricultural Research, Bet Dagan, Israel

PREVIOUSLY it was reported from our laboratory that when yeast RNA was injected intercellularly into leaves of Nicotiana tabacum L. Samsun NN, induced resistance developed from the third day on1. Interference was highest when plants were inoculated with tobacco mosaic virus (TMV) 5-6 days after RNA was injected at a concentration of 5 mg/ml., and remained high even after 20 days. In the resistant tissue, TMV lesion numbers decreased by 80-90 per cent, compared with those developing in water-injected control tissues. The development of resistance was inhibited if actinomycin D was applied shortly after the induction with yeast RNA. These results were confirmed with yeast RNA and with RNA isolated from plants different from the test species (foreign RNA), whereas the resistance response was not elicited by RNA isolated from plants of the test species2. A similarity between yeast RNA induced resistance in plants and interference in animal virology mediated through interferon was suggested1,2. © 1970 Nature Publishing Group.