A low content in zeatin type cytokinins is not restrictive for the occurrence of G1/S transition in tobacco BY-2 cells

Theories on the importance of cytokinins in G(1)/S transition control are manifold and contradictory. By establishing a double A phi-PZ block, maximal synchronization of a BY-2 suspension culture was obtained to investigate the effect of cytokinin depletion on G(1)/S transition, Lovastatin,vas used as a specific inhibitor of cytokinin biosynthesis, Flow cytometry showed that the G(1)/S transition occurred regardless of the cytokinin drop. This observation indicates an extremely low dose requiry for that stage of the cell cycle. It is very likely that precisely the downregulation of zeatin type cytokinins matters for the G(1)/S transition to occur, since cytokinin addition at early G(1) blocked the cycle at G(1)/S. (C) 1999 Federation of European Biochemical Societies.