Abstract
Cadmium (Cd) is a harmful heavy metal. We isolated a gene homologous to Arabidopsis NRAMP1 from a low Cd accumulating plant, Solanum torvum (StNRAMP1). Expression of StNRAMP1 gene was induced by iron deficiency and repressed by Cd treatment. Yeast cells expressing StNRAMP1 were sensitive to Cd and the GFP-fused protein predominantly localized in plasma membrane in onion epidermal cells. These results suggest that StNRAMP1 is an influx iron and Cd transporter. Furthermore, we developed transgenic tobacco plants expressing StNRAMP1 under the control of 35S promoter. Transformants showed intercostal chlorosis even in standard culture condition and the symptoms were more severe in older leaves. Cd content in the newest leaves of transformants was decreased to 20% compared to those of non-transformants when plants were grown hydroponically with 0.1 μM Cd for 5 days. Cd content of second newest leaves with intercostal chlorosis was also decreased while the iron content was 2-times higher than those of non-transformants. These results suggest that overexpression of StNRAMP1 changes the distribution of iron resulting in inhibition of Cd translocation or accumulation in tobacco plant.
