Effect of sublethal heat injury on tumour induction and RNA synthesis in Agrobacterium tumefaciens

When cells of Agrobacterium tumefaciens are subjected to sublethal heat injury at 45 degrees C for 20 min, less than 5% of the viable population retain their ability to initiate tumour formation on Kalanchöe daigremontiana. If the cells are then incubated in phosphate buffer at 27 degrees C for 2 h, tumour initiation returns to control levels. Inhibitors of DNA and protein synthesis had little effect on the recovery of tumour initiation after heat injury. Rifamycin, a specific inhibitor of RNA synthesis, dramatically reduced recovery of tumour formation. During the heating process large amounts of RNA leaked from the cells which correlated with a degradation of rRNA. The addition of Mg to the heating buffer reduced the loss of RNA into the medium and the degradation of rRNA and tumour initiation was retained at control levels. It is concluded that while current evidence indicates that DNA is probably the transforming agent, RNA synthesis is an important component of the induction process.