Histological study of organogenesisin vitrofrom callus cultures of twoNicotianaspecies

摘要

The histological events leading to shoot formation inNicotiana glaucaand in the nontumorousNicotiana glaucatimes;Nicotiana langsdorffiihybrid have been studied. Organized development begins from a single vacuolated parenchyma cell which divides and precociously differentiates tracheidal cells, forming a growth center with nodular structures with xylem in the center and phloem outside. The vascular tissue is precociously separated from the surrounding callus by a layer of cells which are shown to be endodermal by position and by histochemical reactions. Further growth leads to the formation of a mound of meristematic tissue which later forms shoot apical meristems. The sequences of events are discussed in relation to other known systems of regeneration in calluses.The system described could be suitable for evaluating the effects of various physical and chemical agents on the different steps of differentiation.