Fe fortification limits rice Cd accumulation by promoting root cell wall chelation and reducing the mobility of Cd in xylem

Fe biofortification and Cd mitigation in rice is essential for human health, thus the effects of fertilization with Fe on Cd uptake and distribution in rice need to be comprehensively studied. In this study, we investigated the roles of root iron (Fe)/manganese (Mn) plaques, root cell wall, organic acid, and expressions of Cd-transport related genes in restricting Cd uptake and translocation. The rice plants were exposed to 1 mu M CdCl2 with or without the addition of three doses of Fe at 5, 50, and 500 mu M EDTA-Na2Fe. The results showed that increasing supply of Fe remarkably reduced Cd accumulation in the shoots, mainly because of inhibited translocation of Cd from roots to shoots. As compared to 5 mu M Fe treatment, 500 mu M Fe significantly increased the ionic soluble pectin (ISP) content and decreased citric acid (CA) in the roots, thereby providing more Cd-binding sites in the cell wall of roots and reducing the mobility of Cd in xylem. Plant Fe status-mediated CA act as the main chelator for Cd mobilization, rather than through decreasing the pH. However, the plants supplied with low Fe or excess Fe facilitated the uptake of Cd in rice roots, as low Fe up-regulated the expression of Cd-transport related genes and excess Fe enhanced Cd enrichment on the root by iron plaque. Importantly, soil fertilization with Fe strongly reduced Cd accumulation in rice grain. Thus, optimizing the soil environmental Fe could effectively reduce Cd accumulation in the shoots by immobilizing Cd in the mots.

Automated summary

This study investigated the effects of fertilization with iron on cadmium (Cd) uptake and distribution in rice. It was found that increasing the supply of iron significantly reduced Cd accumulation in the shoots by inhibiting Cd translocation from roots to shoots. Increasing the ionic soluble pectin (ISP) content and decreasing citric acid (CA) in the roots provided more Cd-binding sites in the cell wall, reducing the mobility of Cd in xylem. However, low iron or excess iron facilitated Cd uptake in rice roots. Soil fertilization with iron strongly reduced Cd accumulation in rice grain by immobilizing Cd in the roots.