Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims: Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant. Methods: A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars. Results: Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O₂ kg^-1 root d.w. h^-1), Fe plaque formation (Fe: 6,117-48,167 mg kg^-1; Mn: 127-1,089 mg kg^-1), heavy metals in shoot (Cd: 0.13-0.35 mg kg^-1; Pb: 4.8-8.1 mg kg^-1) and root tissues (Cd: 1.1-3.5 mg kg^-1; Pb: 45-199 mg kg^-1), and in Fe plaque (Cd: 0.54-2.6 mg kg^-1; Pb: 102-708 mg kg^-1). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues. Conclusions: ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues.