Genetic tumors in Nicotiana and other plants

Genetic tumors that occur in intraspecific and interspecific hybrids of certain plant genera, in particular Nicotiana, are reviewed. Tumors occur an certain interspecific hybrids, as well as on parasexual hybrids in Nicotiana, substantiating the genetic control of tumor formation, The morphology, histology, fine structure, cytology and genetic control of tumors are discussed. The effect of environmental factors, including radiation, are considered in relation to tumor expression, and the induction of mutations from tumor to nontumor state. The rob of phytohormones, cytokinins, and auxins are discussed with respect to habituation and growth autonomy. The relevance of cellular T-DNA sequences of bacterial (Agrobacterium) origin in certain Nicotiana species to tumor formation, and the molecular biology of genetic tumors in Nicotiana, are examined. The origin of tumors and the regulation of genetic components involved in genetic tumors are considered in the framework of current genetic models of the initiation and development of genetic tumors.