OLOMOUCINE, AN INHIBITOR OF THE CDC2 CDK2 KINASES ACTIVITY, BLOCKS PLANT-CELLS AT THE G1 TO S AND G2 TO M CELL-CYCLE TRANSITIONS/

The cdc2/cdk2 protein kinases play key roles in the cell cycle at two control points: the GI/S transition and the entry into mitosis. Olomou cine, a specific inhibitor of these kinases, was tested in two plant c ell systems: Petunia mesophyll protoplasts induced to divide and Arabi dopsis thaliana cell suspension cultures. The cell cycle status was an alysed from DNA histograms or through continuous labelling of cells wi th 5-bromodeoxyuridine (BrdUrd) followed by double staining with bis-b enzimide (Hoechst 33258) and propidium iodide (PI). Such analyses reso lve cells from several generations according to the extent of their DN A replication. Olomoucine was shown to reversibly arrest differentiate d Petunia cells induced to divide at G1 phase and cycling Arabidopsis cells in late G1 and G2. A comparison of the effects of aphidicolin, o ryzalin and olomoucine suggests that in the Arabidopsis cell suspensio n culture, a cdc2/cdk2-like kinase is activated at a restriction point in late G1.