DNA synthesis in wounded or TMV-infected leaves from sensitive and hypersensitive tobacco plants

After wounding or viral infection, tobacco leaves synthesized DNA, as evidenced by [3H]thymidine incorporation. This synthesis was maximal 22 h after infection or 46 h after wounding. It took place before necrotic lesions appeared in hypersensitive leaves. Effects of wounding or infection was transmitted to non-damaged halves of leaves in which they also induced DNA synthesis of similar kinetics but of less magnitude. This synthesis was mostly nuclear but non-mitotic. The extent of synthesis varied with the viral inoculum concentration and with the age of the leaves and correlated with the subsequent necrotic reaction.