Quantitative studies of bud initiation in cultured tobacco tissues.

After transferring leaf, pith, and stemcortex tissues ofNicotiana tabacum L. cv. "Havana 425" from a complete medium containing auxin and cytokinin to an inductive medium with auxin deleted, there is lag phase of approx. 14d followed by a linear phase in which the rate of bud initiation is constant. The incidence of buds formed is very low, approx. one bud per 10(3) or 10(4) cells. Statistical analysis of the distribution of buds among explants and subcloning experiments provide evidence that the paucity of buds results from neither negative interactions among bud forming centers nor a paucity of cells with the potential for organogenesis. Our results are consistent with the hypothesis that the frequency of bud initiation is determined by the availability of competent cells, by position effects, or by a combination of both mechanisms.