This study reports the effects of thidiazuron (TDZ) on the endogenous levels of
indoleacetic acid (IAA), zeatin, zeatin riboside ([9R]Z), isopentenyladenine and
isopentenyladenosine ([9R]iP) as well as structural changes in the apical meristem of
Dendrobium Second Love shoots during flower induction and initial development in
vitro. The results revealed that the presence of 1.8 mM TDZ had a profound effect on
the endogenous cytokinins (CKs) and IAA levels of the explants, when compared to
those grown on a TDZ-free medium. A significant increase in CKs (especially [9R]iP and
[9R]Z) and IAA in the first samples (taken at day 5) grown on TDZ-enriched medium
was associated with flower induction, while a second increase in the level of these
hormones after 25 d of culture was related to flower development. The histological
changes detected in the shoot apical meristem of explants grown in the presence of
1.8 mM TDZ during 30 d of culture are also described. Based on these findings, it is
suggested that both auxin and CKs seem to be involved with the floral transition of