Reversal of the neoplastic state in plants.

Crown-gall transformation involves the gradual and progressive activation of several biosynthetic capacities of the normal cell. These changes in cellular heredity, although extremely stable, are nonetheless potentially reversible and leave the cell totipotent. There is growing evidence that tumor-inducing principle is a self-replicating entity similar to a plasmid. Thus, it could be argued that tumor progression involves changes in the number or state of these entities in the cell. Studies of CDF habituation bear directly on this problem. Conversion of a cell division factor (CDF)-requiring normal cell to the CDF-autotrophic state is a key event in transformation. The fact that CDF habituation is progressive, occurs in the absence of agents of bacterial origin, and has an epigenetic basis indicates that it is not necessary to invoke either somatic mutation or the addition of foreign genes to account for tumor stability and progression in crown-gall. This conclusion provides further support for the hypothesis that, in the words of Braun,(78) "... the cancer problem is basically a problem of anomolous differentiation... Neoplastic growth, like developmental processes, stems from epigenetic modifications against a constant cellular genome."