Loebenstein, G., The Volcani Institute of Agricultural Research, Bet Dagan, Israel
Rabina, S., The Volcani Institute of Agricultural Research, Bet Dagan, Israel
Van Praagh, T., The Volcani Institute of Agricultural Research, Bet Dagan, Israel

Development of localized acquired resistance to tobacco mosaic virus (TMV) in Nicotiana tabacum L. var. Samsun NN and Phaseolus vulgaris L. var. Pinto was partially or completely inhibited in the presence of actinomycin D. In tobacco plants challenged 5 days after the inducing inoculation, acquired resistance was almost completely abolished when actinomycin D had been injected intercellularly 3 days before the challenge. When tobacco plants were challenged 6 days after the inducing inoculation, acquired resistance was partially inhibited by actinomycin D which had been injected 3 days before the challenge. However, no inhibition resulted when actinomycin D was injected close in time to the challenges, inoculated 5 or 6 days after the inducing inoculation. In Pinto bean plants acquired resistance was also significantly reduced in the presence of actinomycin D. These results suggest that development of localized acquired resistance depends on the transcription mechanism of the cell from DNA to RNA, thereby producing a resistance-inducing substance. Sensitivity of acquired resistance to actinomycin D negates the hypothesis that acquired resistance is caused by drainage of metabolites. © 1968.