A low content in zeatin type cytokinins is not restrictive for the occurrence of G(1)/S transition in tobacco BY-2 cells

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