engleski

Cytokinins in the Christmas rose (Helleborus niger L.)

In fertilized flowers of the Christmas rose (Helleborus niger L.), the sepals (initially white) develop functional chloroplasts and persist until the seeds are ripe. In unfertilized flowers, the greening process may be initiated by treatment with exogenous cytokinins. The biologically active endogenous cytokinins and their reversible conjugates in fruit-bearing flowers were analyzed by a combination of chromatographic methods and mass spectrometry. Trans- and cis-zeatin, dihydrozeatin, N^6-(2-isopentenyl)adenine, and the corresponding O-glucosides, riboside O-glucosides, and ribotides were detected, in addition to minor amounts of aromatic cytokinins (e. g. N^6-benzyladenine). In the fruit, the overall level of active cytokinins increased enormously, during early seedling growth, and remained high until ~2 weeks before ripening (most advanced stage checked so far), possibly because embryo development is not complete and continues after the seeds are shed. In the sepals, only the concentrations of cis-zeatin riboside and ribotide were about the same, or higher than, in the fruit from the same flowers and increased consistently during the greening process, while the levels of the other cytokinins examined remained low and showed no obvious systematic changes.

Christmas rose; Helleborus niger L.; flower and fruit development; cytokinin analysis

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