Characteristics of Cd accumulation and distribution in two sweet potato cultivars.

In this study, we compared the chemical forms and subcellular distribution of Cd in high-Cd (X16) and low-Cd (N88) sweet potato cultivars through hydroponic experiments and examined the Cd distribution in their roots by histochemical staining. The results showed that inorganic and pectate/protein-integrated Cd predominated in the leaves, and Cd concentrations were significantly higher in X16 than in N88. However, in the roots, Cd was mostly integrated with pectate and protein, and Cd concentration was higher in N88 than in X16. It was mainly stored through vacuolar sequestration and cell wall binding. In the leaves and stems, Cd concentrations in all subcellular fractions were higher in X16 than in N88; the opposite was observed in the roots. In X16, Cd was mostly accumulated in the root stele, and its Cd translocation factor was higher than that of N88. Overall, the subcellular fractions of X16 roots retained less Cd than N88 roots, and more Cd entered the root stele of X16 and subsequently moved to the shoots. The higher amounts of inorganic, water-soluble, and pectate/protein-integrated Cd with high mobility in the shoots of X16 than in N88 might facilitate Cd remobilization to other tissues, but this needs to be further studied.

Effects of Interaction between Cadmium (Cd) and Selenium (Se) on Grain Yield and Cd and Se Accumulation in a Hybrid Rice (Oryza sativa) System.

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-1; 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.

Variation in Cd accumulation among radish cultivars and identification of low-Cd cultivars.

Heavy metals have serious health consequences and ecosystem impacts. A pot experiment was conducted to investigate the variation of cadmium (Cd) uptake and accumulation among 40 cultivars of radish (Raphanus sativus L.) at three Cd levels, including 0.31 (T1), 0.83 (T2), and 1.13 (T3) mg kg-1. Most of the tested cultivars had higher taproot biomass in the T3 treatment when compared to those in the T1 treatment, indicating a Cd stress-induced growth in radish. Taproot Cd concentrations in 95 and 5% of the tested cultivars were lower than 0.1 mg kg-1 (fresh weight, FW) in the T1 and T2 treatments, respectively; however, there was no cultivar suitable for safe consumption in the T3 treatment. Radish production showed potential risk of Cd pollution as high as some leafy vegetables when grown in the soils where Cd concentration exceeded 0.8 mg kg-1. When compared with Chinese heat-resisting or imported cultivars, Chinese common cultivars had significantly higher taproot Cd concentrations. Three low-Cd cultivars and five high-Cd cultivars were identified. Taproot Cd concentrations showed significant correlations between any two of the three treatments (p < 0.01), suggesting that Cd accumulation in taproot of radish was genotype-dependent.

Identification of low-Cd cultivars of sweet potato (Ipomoea batatas (L.) Lam.) after growing on Cd-contaminated soil: uptake and partitioning to the edible roots.

Cadmium (Cd) contamination in agricultural products presents a threat to humans when consumed. Sweet potato is the world's seventh most important food crop. The aims of this study were to screen for low-Cd sweet potato cultivars and clarify the mechanisms of low-Cd accumulation in edible roots. A pot experiment was conducted to investigate the variation of Cd uptake and translocation among 30 sweet potato cultivars grown in contaminated soils with three different Cd concentrations. Cadmium concentrations in edible roots were significantly different among cultivars and were significantly affected by Cd treatment, and the interaction between cultivar and Cd treatment. High-Cd cultivars have higher ratios of edible root/shoot Cd concentration and edible root/feeder root Cd concentration than low-Cd cultivars; however, the ratio of shoot/feeder root Cd concentration seems unrelated to the ability of Cd accumulation in edible roots. Four sweet potato cultivars, Nan88 (No. 10), Xiang20 (No. 12), Ji78-066 (No. 15), and Ji73-427 (No. 16), were identified as low-Cd cultivars. Cadmium translocation from feeder roots to edible roots via the xylem, and from shoots to edible roots via the phloem, controls Cd accumulation in edible roots of sweet potato cultivars.

Roles of rhizosphere and root-derived organic acids in Cd accumulation by two hot pepper cultivars.

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.

Root morphological responses of three hot pepper cultivars to Cd exposure and their correlations with Cd accumulation.

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.

Translocation analysis and safety assessment in two water spinach cultivars with distinctive shoot Cd and Pb concentrations.

A pot experiment was conducted to investigate the translocation of cadmium (Cd) and lead (Pb) and assess the safety of edible parts in two cultivars of water spinach (Ipomoea aquatica Forsk.) contrasting in shoot Cd and Pb concentrations. A low-Cd-Pb cultivar (QLQ) and a high-Cd-Pb cultivar (T308) were grown in five soils with different concentrations of Cd and Pb. The results showed that QLQ had lower Cd and Pb concentrations in stems and leaves and higher root Cd concentration than T308 did. Root Pb concentration of T308 dramatically increased with increasing soil Pb concentration and was higher than that of QLQ in the highest Pb treatment. The root-to-stem Cd translocation ability in T308 was 2.3-3.0-fold higher than that in QLQ. Nevertheless, there was no significant difference in root-to-stem Pb translocation between QLQ and T308. The bioconcentration factors (BCFs) for Cd and Pb in the two cultivars remained stable in different Cd or Pb treatments, which were attributable to the homeostatic control mechanisms of Cd and Pb in water spinach.

Characterization of cadmium uptake, translocation, and distribution in young seedlings of two hot pepper cultivars that differ in fruit cadmium concentration.

The reasons why some cultivars of hot pepper (Capsicum annuum L.) accumulate low levels of Cd are poorly understood. We aimed to compare the characteristics of Cd uptake and translocation in low-Cd and high-Cd hot pepper cultivars by determining the subcellular locations and chemical forms of Cd, and its distribution among different plant organs. We conducted a hydroponic experiment to investigate the subcellular distribution and chemical forms of Cd in roots, stems, and leaves of a low-Cd (Yeshengchaotianjiao, YCT) and a high-Cd cultivar (Jinfuzaohuangjiao, JFZ). The results showed that the concentrations of Cd in almost all subcellular fractions of roots, and in all chemical forms in roots, were higher in YCT than in JFZ. Compared with YCT, JFZ had higher Cd concentrations in almost all subcellular fractions of stems and leaves, and higher Cd concentrations in almost all chemical forms in stems and leaves. Additionally, YCT had significantly higher total Cd accumulation but a lower Cd translocation rate compared with JFZ. In general, the results presented in this study revealed that root-to-shoot Cd translocation via the xylem is the key physiological processes determining the Cd accumulation level in stems and leaves of hot pepper plants. Immobilization of Cd by the cell walls of different organs is important in Cd detoxification and limiting the symplastic movement of Cd.

Responses of different water spinach cultivars and their hybrid to Cd, Pb and Cd-Pb exposures.

A pot experiment was conducted to investigate the stability of Cd and/or Pb accumulation in shoot of Cd and Pb pollution-safe cultivars (PSCs), the hereditary pattern of shoot Cd accumulation, and the transfer potentials of Cd and Pb in water spinach (Ipomoea aquatica Forsk.). A typical Cd-PSC, a typical non-Cd-PSC (Cd accumulative cultivar), a hybrid from the former two cultivars, and two typical Cd+Pb-PSCs were grown in seven soils with different concentrations of Cd and Pb. The results showed that concentrations of Cd and Pb in shoot of the PSCs were always lower than the non-PSC and the highest Cd and Pb transfer factors were also always observed in the non-PSC, indicating the stability of the PSCs in Cd and Pb accumulation. Shoot Cd concentration seemed to be controlled by high Cd dominant gene(s) and thus crossbreeding might not minimize Cd accumulation in water spinach. Interaction between Cd and Pb in soils affected the accumulations of the metals in shoot of water spinach. Under middle Cd and Pb treatments, the presence of higher Pb promoted the accumulation of Cd. However, under high Pb treatment, accumulations of Cd and Pb were both restricted.