Metal stress response and tolerance of cultured cells from Silene vulgaris and Lycopersicon peruvianum:: Role of heat stress proteins

The influence of the heavy metal ions Hg++, Cu++, Cd++ and Zn++ and of arsenite on growth, amino acid uptake, protein- and heat shock protein synthesis was investigated in cell cultures of a heavy metal tolerant Silene vulgaris and the sensitive Lycopersicon peruvianum. A distinct tolerance of Silene cell growth in comparison to tomato cells against Cu, Cd and Zn was observed. Synthesis of the small heat stress proteins was induced in both species, however, with quantitative differences depending on species and metal ion. While in tomato cells all metals induce HSP synthesis, in Silene the induction by Cu and Cd was found to be significantly lower in comparison to Hg and arsenite, and Zn did not induce HSP. Therefore, generally a lower tolerance of the cells against a metal is connected with a higher HSP synthesis. From comparison of cell growth and HSP accumulation in the presence of metal ions it was further concluded that HSP synthesis is a part of HM stress response of tolerant and non tolerant cells as under heat shock, but HSPs are not responsible for the heritable metal tolerance of Silene. In contrast to heat shock, metal stress does not inhibit the cell protein synthesis directly. In cultured tomato and Silene cells the inhibition of protein synthesis under metal stress was found to be a consequence of the inhibition of amino acid uptake. Zn has no effect on amino acid uptake of Silene cells. It is concluded that only Zn tolerance of Silene seems to be related with membrane stability.