Induction of flower bud formation in vitro by dihydrozeatin

Flower stalk explants of tobacco cultured on a medium with an auxin and cytokinin regenerate flower buds within 14 days. The optimal medium concentrations of dihydrozeatin (DHZ) and benzyladenine (BA) were both 1 μM. The presence of DHZ in the culture medium was only essential during an initiation period of 7 days, whereas BA was needed only during the first 4 days. The difference in length of the initiation period is neither explained by the unequal uptake rates of the cytokinins nor by differences in their conjugation. At the medium concentration optimal for bud formation, the internal concentration of DHZ was two to three times the internal concentration of BA, which could be attributed to faster uptake of DHZ. It is concluded from the combined data that DHZ is less active in inducing flower bud formation than BA and that the exogenous cytokinins play only a role during the initiation phase of bud regeneration.