Investigation of plant tumorigenesis is a way to clarify the mechanisms of systemic control of plant cell division and differentiation. Two spacious groups of plant tumors are exist. The first are tumors which are induced by different pathogens. Most known tumorigenic plant pathogens are the representatives of the Agrobacterium genus which use a specific way to genetically colonize and insert a plasmid DNA fragment (T-DNA) into the host genome. The second group includes spontaneous tumors that form on plants with certain genotypes: interspecific hybrids in some genera (most known of them are Nicotiana interspecific hybrids), inbred lines of some cross-pollinating species (eg tumorous lines of radish Raphanus sativus var. radicula Pers.), tumorous mutants and transgenic plants (eg pas and tsd mutants of Arabidopsis thaliana, CHRK1-supressed transgenic Nicotiana tabacum plants). The cause for all types of …