Cytokinins in shoot apices of Brassica napus plants during vernalization

Tarkowská D., Filek M., Biesaga-Kościelniak J., Marcińska I., Macháčková I., Krekule J., Strnad M.

Keywords: cytokinins; vernalization; winter rape; flowering
Abstract: The putative role of cytokinins in processes leading to reproductive development of plants was investigated by analysing the shoot apical parts of a winter cultivar of oilseed rape (Brassica napus L. var. oleifera, cv. Górczański). The endogenous cytokinin levels were measured by liquid chromatography–tandem mass spectrometry (LC-MS) in the shoot apices of vegetative plants (grown at 20/17 °C with a 16/8 h day/night regime) and vernalized plants (56 days at 5/2 °C with a 16/8 h photoperiod) at different times during floral transition. During vernalization, the content of all isoprenoid cytokinins increased significantly, coinciding well with the onset of the early stages of reproductive development. Cytokinin levels reached their maxima when most of the plants became irreversibly reproductive (after 42 days of cold treatment). Cis-zeatin riboside (unequivocally identified by quadrupole–time-of-flight MS) accounted for ca. 87–89% of the total isoprenoid cytokinin content in control and vernalized plants, while N6-isopentenyladenosine (~6% in control and ~8% in vernalized plants) and cis-zeatin (~2% in control and ~1% in vernalized plants) were the next most abundant cytokinins. In the post-vernalization period, endogenous cytokinin levels decreased, but remained significantly higher in the reproductive plants than in the vegetative controls. These results suggest that cytokinins, especially those of the cis-zeatin type, are involved in vernalization-induced reproductive development of B. napus.
DOI: IEB authors: Jan Krekule, Miroslav Strnad, Danuše Tarkowská