Transient accumulation of cis- and trans-zeatin type cytokinins and its relation to cytokinin oxidase activity during cell cycle of synchronized tobacco BY-2 cells

Changes in levels of endogenous cytokinins and activity of cytokinin oxidase (EC 1.4.3.6) were followed during the cell cycle progression in large-scale (ca. 30 g FW) synchronized culture of the tobacco cell line BY-2. Synchronization was induced either by 4 mM hydroxyurea or 15 muM aphidicolin alone (a single block of the cell cycle at G(1)/S) or in combination with 1 muM oryzalin (double blocking at G(1)/S and G(1)/M). Up to 46% synchrony was obtained. Two distinct cytokinin peaks were detected at 0-2 h and 8.5-9 h after the release from the first block coinciding with the beginning of the S phase and with the onset of mitosis, respectively. Interestingly, as identified by MS/MS, very sharp and transient premitotic peak of cytokinins contained, in addition to traps-zeatin, also considerable amounts of cis-zeatin and zeatin-O-glucoside. Cytokinin oxidase activity exhibited conspicuous maximum parallel to the first peak of cytokinin accumulation and deep minimum corresponding to the culmination of mitotic index. Possible roles of zeatin cis-trans isomerisation, glucosylation and degradation by cytokinin oxidase in regulation of cytokinin levels during the cell cycle progression are discussed. (C) 2002 Editions scientifiques et medicates Elsevier SAS. All rights reserved.