Double Prevention of Cadmium Uptake by Iron and Zinc in Rice Seedling—A Hypotonic Study

Purpose Rice can accumulate high levels of cadmium (Cd) from contaminated soils, leading to negative health effects when consumed. In the present study, we aim to test the hypothesis that pretreating rice seeds with essential metals, such as iron (Fe) and zinc (Zn), will reduce Cd absorption and transport during growth. Methods Six metal ions, namely Fe, Zn, manganese (Mn), copper (Cu), calcium (Ca), and magnesium (Mg), were evaluated under a pretreatment condition at 10 times the regular dose. Based on their comprehensive effect on reducing Cd absorption and their potential as nutrient elements, Fe and Zn were selected for further studies. Rice seeds were placed in micronutrient growth media containing various concentrations of Fe, Zn, or a mixture of both for 30 days. Afterward, parts of the seedlings were collected for Fe and Zn analyses, while the remaining seedlings were transferred into media containing Cd for 5 days, during which Cd accumulation and membrane protein changes in the rice seedlings were monitored. Results Regarding Cd inhibition, Fe was more effective in the shoots ( r = -0.879, P < 0.01), resulting in an approximate reduction of 46.8%, while Zn was more effective in the roots ( r = -0.786, P < 0.01), leading to a decrease of 26.9%. Simultaneously, putative glycine hydroxy methyltransferase, ferritin, and water stress inducible protein were detected in leaf membrane proteins of rice seedlings pretreated with Fe. Conclusions Our study suggests that pretreating rice seeds with a certain concentration of a Fe and Zn mixture may provide double protection by Zn-mediated Cd absorption and by Fe-mediated Cd transport in the rice seedlings from Cd under the hydroponic conditions.