Effects of phosphorus supplied in soil on subcellular distribution and chemical forms of cadmium in two Chinese flowering cabbage (Brassica parachinensis L.) cultivars differing in cadmium accumulation

Differences in the subcellular distribution and chemical speciation of Cd between two Chinese flowering cabbage (Brassica parachinensis L.) cultivars, Lubao70 (LB70, low-Cd cultivar) and ChixinNO.4 (CX4, high-Cd cultivar) were investigated under various soil Cd and P treatments. Subcellular fractionation of Cd-containing tissues showed that a higher proportion of Cd was bound to the cell wall fraction of LB70 than that of CX4, indicating that Cd compartment functioned better in LB70. Compared to CX4, LB70 had lower proportions of Cd in inorganic form and water-soluble form, but higher proportions of Cd in proteins/pectates integrated form, implying that the low Cd accumulation in LB70 is associated with the low in vivo mobility of Cd. In both cultivars, shoot and root Cd concentration and translocation of Cd from the roots to the shoots obviously decreased with increasing soil P level. It was found that phosphorus (P) played important roles in Cd uptake and translocation via the processes involved in bonding Cd to the cell wall fraction and forming Cd-phosphate complexes. It is suggested that use of low-Cd cultivars in conjunction with P supply is a much useful way to reduce the pollution risk of Cd in the food chain.