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A pot experiment was conducted to investigate the interactive effects of cadmium (Cd) and selenium (Se) on their accumulation in three rice cultivars, which remains unclear. The results showed that Se reduced Cd-induced growth inhibition, and increased and decreased Se and Cd concentrations in brown rice, respectively. Cadmium concentrations in all tissues of the hybrid were similar to those in its male parent yet significantly lower than those in its female parent. Selenium reduced Cd accumulation in rice when Cd concentration exceeded 2.0 mg kg; however Se accumulation depended on the levels of Cd exposure. Finally, Cd had minimal effect on Se translocation within the three cultivars. We concluded that Cd concentration in brown rice is a heritable trait, making crossbreeding a feasible method for cultivating high-yield, low-Cd rice cultivars. Selenium effectively decreased the toxicity and accumulation of Cd, and Cd affected Se uptake but not translocation.

Cultivars of hot pepper (Capsicum annuum L.) differ widely in their fruit cadmium (Cd) concentrations. Previously, we suggested that low-Cd cultivars are better able to prevent the translocation of Cd from roots to aboveground parts, but the corresponding mechanisms are still unknown. In this study, we aimed to improve understanding of the root morphological characteristics of the mechanisms involved in two low-Cd and a high-Cd cultivar. Seedlings were grown in nutrient solutions containing 0 (control), 2, and 10 μM Cd for 20 days, and Cd contents for the three cultivars were compared with changes in root morphology. The total root length (RL), root surface area (SA), number of root tips (RT), and specific root length (SRL) of all cultivars were decreased significantly by the 10 μM Cd treatment with the exception of the SA in JFZ, which showed no obvious change. For each cultivar, the 10 μM Cd treatment decreased significantly RL and SA specifically in roots with diameters (RD) of RD ≤ 0.2 mm or 0.2 mm < RD ≤ 0.4 mm, and increased significantly RL and SA specifically in roots with diameters of 0.6 mm < RD ≤ 0.8 mm. Hot pepper cultivars differ greatly in Cd accumulation and root morphology. In the 10 μM Cd treatment, root volume (RV), SA, and RT of all cultivars were negatively correlated with Cd concentration and amount in roots. However, RL, SA, RV, and RT of all cultivars were positively correlated with Cd concentration and amount in shoots, and translocation rate of Cd. The two low-Cd cultivars of hot pepper had less root tips, shorter root length, and smaller root surface area than the high-Cd cultivar in 10 μM Cd treatment, which may play a vital role in reducing root-to-shoot Cd translocation.

Cultivars of hot pepper (Capsicum annuum L.) have different abilities to accumulate Cd in their fruits. Previously, we suggested that low-Cd cultivars take up more Cd, but can better prevent the Cd translocation from roots to aerial parts. However, the mechanisms involved in those processes are still unclear. In this study, we explored the roles of rhizosphere soil Cd fractions and root secretions of low molecular weight organic acids in the uptake, translocation, and accumulation of Cd in a low-Cd and high-Cd cultivar. The results showed that there was no significant difference in exchangeable Cd between rhizosphere soils of the two cultivars, which might be related to their similar root's Cd uptake ability. The total content of low molecular weight organic acids released from roots of the low-Cd cultivar was almost equal to that released from roots of the high-Cd cultivar at the same Cd level; however, the composition of low molecular weight organic acids were determined by cultivars and Cd exposure levels. In the higher Cd (10 μM) treatment, the roots of the low-Cd cultivar excreted significantly less tartaric acid and more oxalic and acetic acids than those of the high-Cd cultivar. Additionally, there was no difference in the concentration of citric or succinic acid between the two cultivars. These results indicate that some kinds of low molecular weight organic acids efflux from hot pepper roots played an important role in the difference of Cd accumulation between low- and high-Cd cultivars.

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