Acquisition of competence for floral development in Nicotiana buds.

Grafting experiments were used to investigate the relative roles of strength of flowering signal(s) and competence of buds to respond to flowering signal(s) in the development of photoperiodic and day-neutral species of Nicotiana. At the time of commitment to floral development, a flowering signal (inhibitory or promotive) could reach a critical level or terminal buds could gain competence to perceive and-or respond to an existing signal. The latter hypothesis appears to be true for day-neutral N. tabacum L. cv. Wisconsin 38, while signal strength appears to be a more critical factor for long-day N. silvestris L. Nicotiana tabacum and N. silvestris differ in terms of signal intensity at anthesis of the terminal flower. Stocks of N. silvestris promote more rapid flowering in seedling scions of both genotypes. Terminal buds of seedlings of both genotypes have the same competence to respond to the signal affecting floral development. The competence of the terminal bud of both species to respond to this signal(s) changes as a function of age.