Genetic tumors in Nicotiana and other plants

Genetic tumors that occur in intraspecific and interspecific hybrids of cer tain plant genera, in particular Nicotiana, are reviewed. Tumors occur an c ertain interspecific hybrids, as well as on parasexual hybrids in Nicotiana , substantiating the genetic control of tumor formation, The morphology, hi stology, fine structure, cytology and genetic control of tumors are discuss ed. The effect of environmental factors, including radiation, are considere d in relation to tumor expression, and the induction of mutations from tumo r to nontumor state. The rob of phytohormones, cytokinins, and auxins are d iscussed with respect to habituation and growth autonomy. The relevance of cellular T-DNA sequences of bacterial (Agrobacterium) origin in certain Nic otiana species to tumor formation, and the molecular biology of genetic tum ors in Nicotiana, are examined. The origin of tumors and the regulation of genetic components involved in genetic tumors are considered in the framewo rk of current genetic models of the initiation and development of genetic t umors.