Foliar application of Zn reduces Cd accumulation in grains of late rice by regulating the antioxidant system, enhancing Cd chelation onto cell wall of leaves, and inhibiting Cd translocation in rice

Paddy soil contaminated by cadmium (Cd) has attracted worldwide attention, while foliar spraying of zinc (Zn) could be considered a cost-effective and practical agronomic measure for reducing Cd accumulation in rice grain. However, the effects due to foliar spraying of Zn on different cultivars, as well as the mechanism of subsequent processes taking place are not fully understood up to now. To go a step ahead, a field experiment was conducted with the aim of studying the capability of foliar application of Zn (0.4% ZnSO4) to reduce Cd concentration in grain in five late rice cultivars (here named JLYHZ, FYY272, JY284, CLY7 and LXY130), and the antioxidant activities and subcellular distribution of Cd in the leaves. The results indicate that foliar Zn application significantly decreased grain yield in JY284, CLY7 and JLYHZ, compared to controls. In addition, foliar application of Zn significantly decreased Cd concentration in grain of the five rice cultivars, while increased Zn concentration. The effect of foliar application of Zn on transport coefficients of Cd varied greatly for the different rice cultivars. Foliar application of Zn significantly decreased the malondialdehyde (MDA) concentration in rice leaves, and increased peroxidase (POD) activity. Also, it changed the distribution of Cd in the soluble fraction in leaves (expressed as proportion), which was significantly decreased, and the proportion of Cd in the cell wall increased. The structural equation model (SEM) revealed the positive effects of flag leaf Cd, first node Cd, old leaf Cd, and root Cd concentration on grain Cd concentration. Flag leaf Cd had the highest standardized total effects on grain Cd concentration, followed by old leaf Cd. These results indicated that foliar application of Zn was effective in reducing grain Cd concentration of late rice by enhancing antioxidant activities and Cd chelation onto cell wall of leaves, and reducing Cd concentrations in leaves.