Abstract:
Cuttings excised from diferent nodal positions in stock plants can difer in subsequent adventitious root formation. We investigated the involvement of the auxin–cytokinin balance in position-afected rooting of Rosa hybrida. Leafy
single-node stem cuttings of two rose cultivars were excised from top versus bottom positions. Concentrations of IAA and
cytokinins were monitored in the bud region and the stem base during 8 days after planting using chromatography–MS/MS
technology. The efects of nodal position and external supply of indole-butyric acid on rooting were analyzed. Most cytokinins
increased particularly in the bud region and peaked at day two before the bud break was recorded. IAA increased in both
tissues between day one and day eight. Top versus bottom cuttings revealed higher levels of isopentenyladenosine (IPR) in
both tissues as well as higher concentrations of IAA and a higher ratio of IAA to cytokinins particularly in the stem base.
The dynamic of hormones and correlation analysis indicated that the higher IPR contributed to the enhanced IAA in the bud
region which served as auxin source for the auxin homeostasis in the stem base, where IAA determined the auxin–cytokinin
balance. Bottom versus top cuttings produced lower numbers and lengths of roots, whereas this defcit was counterbalanced
by auxin application. Further considering other studies of rose, it is concluded that cytokinin-, sucrose- and zinc-dependent
auxin biosynthesis in the outgrowing buds is an important factor that contributes to the enhanced IAA levels and auxin/
cytokinin ratios in the stem base of apical cuttings, promoting root induction.
