Structure of grafted crown-gall teratoma shoots of tobacco: Regulation of transformed cells.

Crown-gall teratomas are tumors of higher plants with an intrinsic capacity for organogenesis. The growth pattern of tobacco (Nicotiana tabacum L.) teratoma shoots, which is highly aberrant in primary tumors, becomes normal when the shoots are grafted to healthy stock plants. However, certain abnormalities commonly persist; tumors form at the graft junctions, leaves are small, apical dominance is incomplete, the stem and proximal region of the leaf midribs swell excessively, and localized eruptions of neoplastic growth occur on the swollen tissue. Swelling of the shoots is primarily the result of cell hypertrophy in the cortex. Neoplastic divisions do not occur as a general rule; they are restricted, with the exception of tumor formation at the graft junctions, to localized eruptions of teratoid growth on the nodes and leaf midribs where cell hypertrophy is most evident. The histology of the apical meristem and histogenesis of primary tissues is normal, even in grossly distorted shoots. Similarly, there is no evidence of unregulated division in the vascular cambium. It is concluded that cell expansion and division are tightly regulated in meristematic regions of teratoma shoots whereas post-meristematic tissue is prone to excessive hypertrophy and eventual initiation of neoplastic cell division.