Tissue age as an endogenous factor controlling in vitro bud formation on explants from the inflorescence of Nicotiana tabacum L.

Croes, A. F., Creemers-Molenaar, T., van den Ende, G., Kemp, A. and Barendse, G. W. M. 1985. Tissue age as an endogenous factor controlling in vitro bud formation on expiants from the inflorescence of Nicotiana tabacum L.—J. exp. Bot. 36: 1771-1779. The in vitro formation of generative buds was studied on expiants from flower and fruit stalks and from internodes of the floral ramifications of tobacco. A floral gradient was found to exist along the axis of the branch. The gradient concerns the number of flower buds formed in vitro and is present in both types of tissues. The number of flower buds is greater on tissues from the apical than from the basal portion of the branch. The capacity to generate these buds is largely determined by tissue age at the moment of the excision. Consequently, the gradient moves along the axis during the outgrowth of the inflorescence. The alternative possibility that some apex-derived stimulus predetermines the morphogenetic capacity of the tissue prior to excision is excluded by the observation that the gradient remains virtually unaltered if the apex is removed one week before the onset of culturing. Auxin affects the floral gradient. Increasing the auxin concentration in internode tissue culture causes a steeper gradient of flower bud generation by almost completely abolishing bud formation on older tissues. Key words—Auxin, flower buds, gradient, tissue culture, tobacco. Correspondence to: Department of Botany, University, NL-6525 ED Nijmegen, Netherlands.