CYTOKININS IN ROSA-HYBRIDA IN RELATION TO BUD BREAK

To assess the role of endogenous cytokinins in growth and development of Rosa hybrida, their concentrations in bleeding sap and in roots, st em, leaves, axillary shoots and bottom breaks in three stages of devel opment were quantified. Cytokinins were purified by means of immunoaff inity chromatography and HPLC, and identified by retention time, UV sp ectrum and GC-MS. The major translocation form in the xylem was zeatin riboside (ZR). In all mature tissues, cytokinins of the zeatin-type w ere predominant, amounting to 80-90% of the total cytokinin concentrat ion. The stems contained high concentrations of cytokinins, probably c aused by lateral movement of ZR from the xylem to adjacent stem tissue and the ability of the stem to metabolize cytokinins. In young leaves the contribution of isopentenyl adenine (iP)-type cytokinins to the t otal cytokinin pool was about 50%, indicating that these leaves might be capable of de novo synthesis of cytokinins. In older leaves, the co ncentration of an unidentified cytokinin-like compound increased to mo re than 50% of total cytokinins. This compound, which was also found i n the roots, might be a storage form of cytokinins. In young axillary shoots, about 50% of the cytokinins are iP-compounds, suggesting eithe r import of iP-type cytokinins via the phloem or de novo synthesis of cytokinins. In buds forming bottom breaks, ZR and zeatin riboside mono phosphate (ZRMP) are the main cytokinins, indicating that these buds r eceive their cytokinins from the roots.