Growth inhibition and IRT1 induction of Arabidopsis thaliana in response to bismuth

Bismuth (Bi) is used in cosmetics and in semiconductor. And more, Bismuth is used in water pipes as substitute of lead. However, the Bi concentration in soil has not been investigated and no environmental quality standard is available in Japan. Here we investigated the effect of Bi on growth of Arabidopsis thaliana and identified the responsible genes with microarray analysis. The seeds, which were soaked with various concentrations of Bi including agar medium, were not able to germinate by more than 7 µM Bi. The root elongation and shoot growth were significantly inhibited by more than 2 µM Bi. Then, the mRNA was extracted from 2 µM Bi treated seedlings and the gene expression levels were analyzed by microarray. In response to Bi, 13 metal homeostasis genes were expressed 2-fold higher than that of control. The relative transcription level of AtIRT1, the primary Fe2+ uptake transporter in the root, was about 5-fold higher compared to the control. This data is indicating that Bi induces AtIRT1 expression in roots. Moreover, ferritin protein coding genes were one half lesser than that of the control. Bi exposure increased Fe accumulation in roots. These results suggest that Bi might disturb iron homeostasis in seedlings.