Assessment of lovastatin application as tool in probing cytokinin‐mediated cell cycle regulation

Abstract

Lovastatin, a potent inhibitor of the mevalonate pathway, has been used in plant cell cycle studies to eliminate the cytosolic cytokinin biosynthesis. However, several implications can blur the results, as cytokinins may be alternatively formed from isopentenylpyrophosphate produced by the plastid 1‐deoxy‐xylulose 5‐phosphate pathway and because the endogenous cytokinin levels oscillate considerably in the course of a cell cycle. In the work presented here, short‐ and long‐term effects of lovastatin on suspension‐ cultured Nicotiana tabacum (L.) BY‐2 cells were differentiated. The short‐term experiments revealed a fast action of lovastatin, resulting in a significantly, though not completely, decreased content of endogenous cytokinins that became visible already after 10 min and was most pronounced after 30 min. But the impact of lovastatin on cell cycle progression depended also on the phase of the cell cycle at which it was administered. Lowering of the cytokinin level during the early S phase, when the endogenous cytokinin levels increased, delayed the S/G2 transition, whereas the same treatment in the late S phase, when the cellular cytokinin concentrations had already started to decrease, promoted it. Incubation periods longer than 48 h resulted in about 50% loss of viable of the cells and also in a reduced capability of division of the survivors. These cells later on resumed cell division. A second treatment with lovastatin of that culture again killed about 50% of the cells, but the surviving cells showed faster re‐growth. In conclusion, lovastatin appears as a useful inhibitor of cytokinin biosynthesis in short‐term studies, but its use in long‐term experiments may create complex effects and therefore requires substantial caution.