Caryological behavior during the first phases of dedifferentiation and habituation inNicotiana bigelovii

Summary Hypocotylar tissues ofNicotiana bigelovii var.quadrivalvis seedlings were induced to dedifferentiate and to habituate after a short treatment with 2,4-D or kinetin.Investigation by cytophotometry and chromosome counts on the nuclear cytology of callus induction and development in minimal medium showed, in addition to diploid cells, an high incidence of aneuploid nuclei. Amitotic phenomena have frequently observed during the culture period. The sequence of nuclear events were not influenced by the hormonal composition of the medium.The origin of these aneuploid cells from nuclear fragmentation processes is hypothesized.The results are discussed in comparison with the cytological status of other habituated and tumorous tissues in plant and animal systems.