LEVELS OF ENDOGENOUS CYTOKININS, INDOLE-3-ACETIC-ACID AND ABSCISIC-ACID DURING THE CELL-CYCLE OF SYNCHRONIZED TOBACCO BY-2 CELLS

Correlation between cell cycle progression and endogenous levels of pl ant hormones was studied in synchronized tobacco BY-2 cell suspension cultures. Sixteen different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) were extracted using solid-phase anion exchange c hromatography in combination with immunoaffinity purification, and qua ntified by mass spectrometry. No significant correlation could be iden tified for IAA and ABA, In contrast, there were sharp peaks in the lev els of specific cytokinins (zeatin- and dihydrozeatin-type) at the end of the S phase and during mitosis. The levels of other cytokinins ana lyzed, including zeatins N- and O-glucosides, remained low, suggesting that the increased amounts of their corresponding non-glucosylated fo rm resulted from de novo synthesis. These findings suggest that zeatin - and dihydrozeatin-type cytokinins might play a specific regulatory r ole in the progression of the plant cell cycle. One hypothesis to expl ain cytokinin action is based on a specific interaction with kinases t hat regulate cell cycle progression, as has been recently shown for th e cytokinin analogue olomoucine.