Cadmium Uptake and Translocation in Wheat Differing in Grain Cadmium Accumulation

To better understand the physiological mechanisms underlying the variation of Cadmium (Cd) accumulation in wheat, Cd absorption, translocation, and distribution in five low grain-Cd-accumulating wheat (LCA) and five high grain-Cd-accumulating wheat (HCA) were studied at four growth stages under three soil Cd concentrations. Grain Cd concentration of HCA was 2.92 times, 1.61 times, and 1.40 times more than that of LCA under the soil with 0.3 mg/kg,1.5 mg/kg, and 7.5 mg/kg Cd concentrations, respectively. LCA was more tolerant of Cd pollution than HCA. Consequently, dry matter in LCA roots, stems + leaves, glumes, grains, and the entire plant was significantly higher than that of HCA at all growth stages under all three soil Cd concentrations, and the most pronounced difference was observed during the maturity stage. The critical period governing the disparity in Cd uptake between LCA and HCA primarily occurred before jointing and the maturity stage. LCA absorbed more Cd than HCA under the three Cd soil concentrations before the jointing stage, during which Cd uptake of LCA was 1.92 times, 1.86 times, and 1.46 times that of HCA under 0.3, 1.5 and 7.5 Cd soil concentrations. But LCA absorbed less Cd than HCA at the maturity stage, during which Cd uptake of LCA was 50%, 50%, and 49% of HCA under 0.3,1.5 and 7.5 mg/kg soil Cd concentrations, respectively. Cd uptake or accumulation per plant in LCA was significantly lower than that of HCA throughout the entire growth period, but the difference between them becomes increasingly smaller as the concentration of Cd contamination increases. Early absorption and accumulation of Cd played a limited role in grain Cd accumulation, and Cd transport played a critical role in determining grain Cd content at maturity. In addition, tolerance to Cd was higher, and grain Cd concentration was lower.