The effects of various concentrations of cadmium onNicotiana tabacum L.cv. Xanthi suspension cells were examined. Surprisingly, certain concentrations of Cd (100–150 μM) stimulated growth of cell cultures considerably, whereas all other concentrations were inhibitory. Synthesis of DNA was severly affected in a dose-dependent manner by Cd concentrations of 250 μM and higher. In contrast, RNA and protein synthesis were similarly stimulated by 100 μM Cd, thus indicating that enhancement of RNA synthesis was the primary cause for the observed stimulation of cell culture growth. The transient expression of a chimeric chloramphenicol-acetyltransferase gene was similarly affected by Cd. When the effects of other heavy metals (Cu, Zn, Pb, Co, Mn, Al) on these cellular processes were investigated, only Zn showed a comparable stimulation of RNA and protein synthesis, although a tenfold higher concentration of Zn compared with Cd was required. As Zn and Cd are chemically very similar, these results are discussed in view of the well-known role of Zn in the regulation of transcrip
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