Alleviating effects of zinc and 24-epibrassionlide on cadmium accumulation in rice plants under nitrogen application

Heavy metals such as cadmium (Cd) in farmland soil not only affect crop production, but also endanger human health through the food chain. Rice is the main food crop with the strongest ability to absorb Cd, remediation techniques to reduce soil uptake and grain accumulation of Cd are urgently required, for which the application of foliar spraying seems to be a convenient and auspicious method. This study clarified the effects of nitrogen (N), zinc (Zn), 24-epibrassionlide (EBL) and their combined application on the growth performance and physiological characteristics of Cd and Zn in rice plants under Cd stress. Experimental results showed that N and its combination with Zn, EBL treatments promoted rice growth and yield, especially raised the yield level by 81.12% under N + EBL treatment. Additionally, three EBL treatments (EBL, N + EBL, Zn + EBL) significantly reduced the TF values of Cd in TF stems-grains, TF leaves-grains and TF glumes-grains by 42.70%, 43.67% and 50.33%, while the EF soil-roots under Zn and N + Zn treatments was the lowest, which decreased by 55.39% and 57.71%, respectively. Further, the application of N, Zn, EBL and their combined treatments significantly increased glutathione (GSH) and phytochelatins (PCs) content as well as enhanced Cd distribute into cell walls of rice shoots and roots by 15.18% and 13.20%, respectively. In addition, N, Zn, EBL and their combined application increased Zn concentration, free amino acid and glutelin content, and decreased the Cd accumulation in albumin, glutelin and globulin, thus lowered Cd concentration in grains by 27.55%, 58.29% and 51.56%, respectively. These results comprehensive suggest that the possibility of N management combined with Zn or EBL application for maintaining high yield and alleviating Cd stress by regulating the absorption and remobilization process under mild stress.