The effect of cadmium on cell cycle control in suspension culture cells of soybean

Heavy metals inhibit plant growth. This proces may be directly or indirectly connected with mechanisms regulating cell division. We analyzed the effect of Cd2+ on cell cycle progression in partially synchronized soybean (Glycine max) cell suspension culture and followed the expression of cell cycle genes (cyclin B 1 and cyclin-dependent kinase A-CDK-A). We have checked the hypothesis that Cd2+-induced impairment of cell division is connected with DNA damage. The [H-3]-thymidine incorporation in cell Cultures synchronized either with hydroxyurea (HU) or phosphate starvation have shown, that Cd2+ strongly affects the S phase of soybean cell cycle, by causing the earlier entry of cells into S phase and by decreasing the rate of DNA synthesis. RT-PCR analysis indicated that Cd2+ decreases the level of cyclin B 1 mRNA and has no effect on CDK-A mRNA. The result of comet assay indicated the damaging effect of Cd2+ on DNA of soybean cells. We suggest that Cd2+ affects plant cell cycle at two major checkpoints, the G1/S - by damaging of DNA, and G2/M - by decreasing the level of cyclin B 1 mRNA.