Metal ions interaction in Nicotiana plant tissue cultures: biochemical and molecular approaches

The metal resistance in plants is determined by specific physiological mechanisms which allow the plants to carry out their normal functional roles even in the presence of toxic metals at high concentration. The molecular basis of metal tolerance is not well understood and different physiological mechanisms have been suggested. This study examines the changes occurring in the gene expression induced by different metal ion stresses on the in vitro test system of Nicotiana glauca. Pith tissues, treated and no-treated, at different culture times after the explant, with different concentrations of Cd, Cu and Hg ions, have been analysed by biochemical and molecular techniques in order to individuate genes activated by ion treatments and possibly involved in metal stress tolerance. Biochemical results have shown variations in the synthetic activity of total protein extracts from control and treated tissues. Metal ion treatments specifically modulate protein synthesis. At molecular level, differential cDNA libraries from treated and control tissues evidenced specific genes activation. Metallothioneins (MTs) are cysteine-rich low molecular weight proteins that are able to bind metal ions. Their role in metal homeostasis/detoxification is well known, while in plants it is still a matter of discussion. Conserved regions of five MT-like genes (NgMT) were amplified, cloned and sequenced. The NgMTs expression was studies in control and in in vitro treated cultured pith tissues. The results showed that NgMT genes are expressed both in control and treated tissues: but interestingly, a NgMT clone is present only in the 100 mM Cu treated tissue.