FeCl3 and Fe2(SO4)3 differentially reduce Cd uptake and accumulation in Polish wheat (Triticum polonicum L.) seedlings by exporting Cd from roots and limiting Cd binding in the root cell walls

Wheat grown in cadmium (Cd)-contaminated soils easily accumulates more Cd in edible parts than the Chinese safety limit (0.1 mg/kg). FeCl3 and Fe2(SO4)3 have been used to extract Cd from Cd-contaminated soils. Thus, we hypothesized that FeCl3 and Fe2(SO4)3, used as iron (Fe) fertilizers, can reduce Cd uptake and accumulation in wheat. Here, a hydroponic experiment was performed with three FeCl3 and Fe2(SO4)3 concentrations under 80 μM CdCl2 stress on dwarf Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB) seedlings. Compared with Fe deficiency, FeCl3 and Fe2(SO4)3 additions competitively reduced Cd concentrations. The reductions were not associated with changes in dry weight and root morphological parameters. FeCl3 and Fe2(SO4)3 additions reduced Cd concentrations in the following order from smallest to largest reduction: 25 μM Fe2(SO4)3 < 200 μM FeCl3 < 50 μM FeCl3 < 100 μM Fe2(SO4)3. Investigation of subcellular distributions showed that the four Fe fertilizers differentially reduced Cd binding in the root cell walls and enhanced root sucrose and trehalose. Cd chemical form analysis revealed that Fe fertilizer addition also differentially reduced root FE, FW, and FNaCl. Transcriptomic analysis revealed that addition of FeCl3 and Fe2(SO4)3 differentially up-regulated several genes that hydrolyze cell wall polysaccharides and metal transporter genes for Cd uptake (IRT1 and CAX19) and export (ZIP1, ABCG11, ABCG14, ABCG28, ABCG37, ABCG44, and ABCG48) reducing Cd uptake and accumulation. Our results demonstrated that FeCl3 and Fe2(SO4)3 can reduce Cd accumulation in wheat, and 50 μM FeCl3 is the most effective treatment.