Despite numerous studies, the role of hormones in the induction of shoot apical meristem leading to reproductive development, especially regarding thermoperiodic plants, is still not fully understood. The key problem is separating the effects of the low temperature required for vernalization from those responsible for low temperature stress. An earlier experiment demonstrated the correlation between an increase of cytokinin level in the apical parts of winter rapeseed and the transition time into their reproductive phase during vernalization, i.e., low temperature treatment. From data obtained from the presented experiments, this study aims to contribute to the understanding the role of cytokinins in the induction of flowering based on the grafting of vegetative apical parts of winter rapeseed (scion) on the reproductive (stock) winter and spring genotypes. On the basis of analyses carried out using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry in combination with microscopic observation of changes at the apical meristem, it was indicated that the increase in the amount of trans-zeatin and trans- and cis-zeatin-O-glucoside derivatives appeared in the early stages of apex floral differentiation. During further development, the content of all investigated cytokinins passed through the maximum level followed by their decrease. The final level in reproductive apices was found to be higher than that in vegetative ones.

Department of Biochemistry Biophysics and Biotechnology Pedagogical University Podchorązych 2 30 084 Krakow Poland

Institute of Botany Jagiellonian University Gronostajowa 9 30 387 Kraków Poland

Institute of Experimental Botany The Czech Academy of Sciences Rozvojová 263 CZ 165 02 Prague 6 ⁻ Lysolaje Czech Republic

Institute of Plant Physiology Polish Academy of Sciences Niezapominajek 21 30 239 Krakow Poland

Laboratory of Growth Regulators The Czech Academy of Sciences Institute of Experimental Botany Palacký University Šlechtitelů 27 CZ 783 71 Olomouc Czech Republic

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