Zeatin is indispensable for the G2-M transition in tobacco BY-2 cells

The importance of N-6-isoprenoid cytokinins in the G(2)-M transition of Nicotiana tabacum BY-2 cells was investigated. Both cytokinin biosynthesis and entry in mitosis were partially blocked by application at early or late G(2) of lovastatin (10 mu M), an inhibitor of mevalonic acid synthesis. LC-MS/MS quantification of endogenous cytokinins proved that lovastatin affects cytokinin biosynthesis by inhibiting HMG-CoA reductase. Out of eight different aminopurines and a synthetic auxin tested for their ability to override lovastatin inhibition of mitosis, only zeatin was active. Our data point to a keg role for a well-defined cytokinin (here, zeatin) in the G(2)-M transition of tobacco BY-2 cells. (C) 1998 Federation of European Biochemical Societies.