Abstract

The concentration of ribosomes and of total protein decreased in tobacco plants grown at 36°C, and the high temperature had a differential action on the rates of synthesis and breakdown of individual proteins. However, the overall rate of protein synthesis in tobacco at 36° was higher than in unheated plants. It is suggested that one reason for success in the heat therapy of virus-infected plants is that viral RNA competes poorly with host messenger RNA for the limited numbers of ribosomes on which to sythesize their respective proteins. This concept was supported by the finding that demonstrable synthesis of tomato aspermy virus (TAV) occurred in tobacco at 36° in the presence of actinomycin D, an inhibitor of host protein synthesis, but not in its absence. Also, cytokinin applications to heated plants appeared to stimulate their rate of protein synthesis, and the rate of TAV inactivation was higher in plants treated in this way. This concept may also be used to account for the successes in obtaining virus-free material from infected plants by meristem culture.