engleski

Cytokinins in the perianth, carpels and developing fruit of Helleborus niger L.

Reproductive development in the Christmas rose (Helleborus niger L.) differs from that in commonly investigated model plants in two important aspects. 1. The perianth develops a photosynthetic system, after fertilization, and persists until seed ripening. 2. The ripe seed contains an immature embryo which continues to mature off the mother plant. Here we investigate the possible roles of cytokinins in these processes, analyzing extracts of the perianth and the carpels/maturing fruit, prepared during anthesis and four stages of post floral development. trans-Zeatin, dihydrozeatin, N^6-(isopentenyl)adenine and their ribosides were identified by tandem mass spectrometry. Single ion monitoring demonstrated the presence of the corresponding riboside-5'-monophosphates, O-glucosides, and 9-glucosides and afforded quantitative data on the whole set of endogenous cytokinins. Fruit cytokinins were mostly localized in the seeds. Their overall concentration increased dramatically during early seed development and remained high for six to eight weeks, until shortly before seed ripening (last time point covered in this work). Overall cytokinin levels in the perianth did not change markedly, in the period covered, but the level of N^6-(isopentenyl)adenine-type cytokinins appeared to increase slightly and transiently during the greening phase. The perianths of unpollinated or depistillated flowers, which survived, but did not pass through the complete greening process, contained significantly less cytokinins than observed in fruit-bearing flowers. This suggests that perianth greening requires defined cytokinin levels and supports the role of the developing fruit in their maintenance.

Christmas rose; cytokinin identification and quantification; fruit and seed development; Helleborus niger L.; perianth greening

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