The combined exposure exacerbates the toxic effect of cadmium and uranium on rice seedlings

Studies on the phytotoxicity of cadmium (Cd) and uranium (U) in rice mainly focus on single exposure. However, water, soil, and other environmental media are always co-contaminated by Cd and U. The effects of Cd (5 mg/L) and U (10 mg/L) single and combined exposure for 7 days on rice seedlings were explored by hydroponic experiment. The synergism of U and Cd intensified the inhibitory effect of combined exposure on the rice seedling's growth, accompanied by a remarkable reduction in chlorophyll content, alterations in antioxidant capacity, imbalances in mineral element metabolism, lipid peroxidation-induced destruction observed in rice seedlings, and significantly regulated expression of OsNramp5, OsHMA3, and OsHMA2, the adverse effects on the roots were more severe compared to those on the shoots. Combined exposure of U and Cd altered the distribution of U and Cd in the rice plant and subcellular. The accumulation of U and Cd in the rice seedlings' roots observably exceeded the shoot. Cd is mainly isolated in the vacuole and cell wall; U is primarily trapped in the cell wall. Cd promoted U accumulation in rice seedlings, while U inhibited Cd accumulation in rice seedlings. These findings can not only expand the understanding of the phytotoxicity of heavy metal combined exposure but also have important theoretical and practical significance for evaluating and remedying heavy metals contaminated -paddy soil and ensure for safe production of rice.