XVI International Botanical Congess

Major changes in indole-3-acetic acid (IAA) and cytokinin (CK) levels occur at different phenological phases of Tillandsia recurvata shoots. This epiphytic rootless bromeliad was chosen as being suitable material for hormonal analysis, since the CK synthesis is restricted to the shoots, thus avoiding problems associated with the interpretation of results due to translocation and interconversion forms between roots and leaves encountered in plants which posses both of these organs. Young plants of T. recurvata have weak apical dominance, as early in development, side shoots appeared, and branch growth was correlated with a strong increase in the zeatin level. The flowering phase was characterized by a significant increase in free base cytokinins, zeatin and isopenteniladenine, in comparison to the levels found in adult vegetative shoots. In contrast, both free base CKs declined in the fruiting phenological phase while the IAA level increased dramatically. It was concluded that in the phases characterized by intense organ formation, such as in the juvenile and flowering stages, there was an enhancement of CK content, mainly due to zeatin, leading to a lower IAA/CK ratio.