Metallothioneins enhance chromium detoxification through scavenging ROS and stimulating metal chelation in Oryza sativa.

Metallothioneins (MTs) is a metal ion binding protein to detoxify heavy metal stress in plant cells. This study examines involvement of MTs in metal chelation and ROS scavenging in rice seedling under Cr induction either Cr(VI) or Cr(III) at three different effective concentrations using Agilent 44K rice microarray and real-time PCR technology. Results showed that the concentration of Cr was higher in roots than in shoots in both Cr treatments. Accumulation of both H₂O₂ and O₂^- in rice tissues was evident, but the fluctuation of H₂O₂ was more remarkable than O₂^-. Both Cr exposures resulted in enhancement of MTs in plant tissues. Results from PCR analysis confirmed that ten specific OsMT genes responsible for regulating ROS removal were expressed differentially in plant tissues as well as in Cr variants, suggesting that their different regulation and responsiveness strategies. Expression patterns of metal chelation-related OsMT genes, after Cr exposure were also inconsistent in rice tissues. Longer exposure periods caused more transcriptional changes in both Cr treatments. We also noticed that OsMT1b might carry more weight during Cr chelation in roots rather than in shoots, while OsMT2c had more important role in eliminating H₂O₂ accumulation in shoots than roots. These results suggest that different speciation of Cr in rice tissues resulted in inconsistent transcriptional changes of OsMT genes, which functioned in different regulation and responsiveness pathways responsible for metal ions chelating and ROS scavenging during Cr detoxification.