GENOTYPE VARIATION IN Cd ACCUMULATION AND, CHEMICAL FORMS AND HISTOCHEMICAL DISTRIBUTION OF Cd IN LOW- AND HIGH-Cd CULTIVARS OF CHINESE LEAF MUSTARD

In the present study, the first pot experiment was conducted to screen for Cd pollution-safe cultivars (Cd-PSCs) from 27 cultivars of Chinese leaf mustard (Brassica juncea L. Czern. et cross. var. juncea) under three Cd treatments (0.31, 0.71 and 1.71 mg kg super(-1)). The results indicated that eight cultivars could be considered as typical Cd-PSCs and only one cultivar was typical non-Cd-PSC (high Cd accumulative cultivar). Shoot Cd concentrations showed significant correlations between any two treatments (p < 0.05), which suggested that Cd accumulation in shoot of Chinese leaf mustard was genotype-dependent. In the second pot experiment, the accumulation of Cd in the nine typical cultivars was investigated under three levels of co-exposures to Cd (0.55 mg kg super(-1)) and Pb (48.84, 78.06 and 116.79 mg kg super(-1)). The results showed that shoot Cd concentrations were increased according to the levels of Pb in soil, which may indicate that the presence of Pb in soil facilitated the Cd accumulation in shoot of Chinese leaf mustard. Two cultivars (low-Cd cultivar (cv. YXZ) and high-Cd cultivar (cv. JTN)) were employed to determine the chemical speciation and trace the path of Cd. Results showed that the greatest amount of Cd was found in the extraction of 1M NaCl and 2% HAC, and the least in residues in all test tissues. Histochemical detection of cadmium (with dithizone) in tissues showed that it was up-taked by the root hairs and then transported through vascular bundles to the leaves. The Cd in root hairs of JTN was much more than those of YXZ, which may be due to the higher ability to uptake cadmium in root hairs of JTN.