AhIRT1 and AhNRAMP1 metal transporter expression correlates with Cd uptake in peanuts under iron deficiency.

Fe deficiency may increase Cd accumulation in peanuts. However, the mechanisms are not yet fully understood. In the present study, two contrasting peanut cultivars, Luhua 8 (low seed-Cd cultivar) and Zhenghong 3 (high seed-Cd cultivar) were used to investigate the effect of Fe deficiency on the uptake and accumulation of cadmium (Cd) by hydroponic experiments. Under Fe-sufficient conditions, compared with Luhua 8, Zhenghong 3 had higher specific root length (SRL) and proportion of fine roots with a lower Km for Cd and showed slightly higher expression of AhIRT1 and AhNRAMP1 in the roots. These traits may be responsible for high capacity for Cd accumulation in Zhenghong 3. Under Fe deficiency, the increase of Cd accumulation was much larger in Zhenghong 3 than in Luhua 8. Kinetics studies revealed that the Vmax for Cd influx was 1.56-fold higher in Fe-deficient plants than in Fe-sufficient plants for Zhenghong 3, versus 0.48-fold higher for Luhua 8. Moreover, the increased expression levels of AhIRT1 and AhNRAMP1 induced by Fe deficiency was higher in Zhenghong 3 than in Luhua 8. Yeast complementation assays suggested that the AhIRT1 and AhNRAMP1 may function as transporters involved in Cd uptake. In conclusion, the different Cd accumulation between the two cultivars under Fe deficiency may be correlated with Vmax value for Cd uptake and the expression levels of AhIRT1 and AhNRAMP1 in the roots.

Comparative transcriptome analysis reveals key cadmium transport-related genes in roots of two pak choi (Brassica rapa L. ssp. chinensis) cultivars.

BACKGROUND: Cadmium translocation from roots to shoots is a complex biological process that is controlled by gene regulatory networks. Pak choi exhibits wide cultivar variations in Cd accumulation. However, the molecular mechanism involved in cadmium translocation and accumulation is still unclear. To isolate differentially expressed genes (DEGs) involved in transporter-mediated regulatory mechanisms of Cd translocation in two contrasting pak choi cultivars, Baiyewuyueman (B, high Cd accumulator) and Kuishan'aijiaoheiye (K, low Cd accumulator), eight cDNA libraries from the roots of two cultivars were constructed and sequenced by RNA-sequencing. RESULTS: A total of 244,190 unigenes were obtained. Of them, 6827 DEGs, including BCd10 vs. BCd0 (690), KCd10 vs. KCd0 (2733), KCd0 vs. BCd0 (2919), and KCd10 vs. BCd10 (3455), were identified. Regulatory roles of these DEGs were annotated and clarified through GO and KEEG enrichment analysis. Interestingly, 135 DEGs encoding ion transport (i.e. ZIPs, P1B-type ATPase and MTPs) related proteins were identified. The expression patterns of ten critical genes were validated using RT-qPCR analysis. Furthermore, a putative model of cadmium translocation regulatory network in pak choi was proposed. CONCLUSIONS: High Cd cultivar (Baiyewuyueman) showed higher expression levels in plasma membrane-localized transport genes (i.e., ZIP2, ZIP3, IRT1, HMA2 and HMA4) and tonoplast-localized transport genes (i.e., CAX4, HMA3, MRP7, MTP3 and COPT5) than low Cd cultivar (Kuishan'aijiaoheiye). These genes, therefore, might be involved in root-to-shoot Cd translocation in pak choi.

Cadmium accumulation and growth response to cadmium stress of eighteen plant species.

This study investigated the cadmium (Cd) accumulation and growth response to Cd stress of 18 plant species. After growth for 30 days in the sand containing 0, 2, or 10 mg Cd kg-1, seedlings were evaluated for growth parameters, specific root length, and Cd accumulation. The 18 species differ greatly in Cd accumulation and resistance to Cd stress, depending on Cd concentrations in the sand. Under high Cd condition (10 mg kg-1), the 18 species were classified into two groups: (1) Indian mustard and rapeseed having high Cd tolerance and increased accumulation capacity in shoots could be considered as Cd accumulators, and (2) the remaining 16 non-accumulators constitute a species continuum from the indicators to excluders. Shoot Cd concentration showed exponential decay relationships with biomass production, absolute growth rate, and growth ratio, indicating that biomass production negatively relates to the shoot Cd concentration in non-accumulators via dilution or concentration effect. Species with high biomass generally accumulate low Cd in the shoots and display high Cd-tolerant capacity. Indian mustard and rapeseed are promising species for long-term phytoextraction of Cd-contaminated farmlands for bioenergy production.

Variations in the accumulation and translocation of cadmium among pak choi cultivars as related to root morphology.

A pot experiment was performed to investigate the variations in cadmium (Cd) accumulation among pak choi cultivars and its relationships to root morphology. The biomass, Cd accumulation and root morphology of 20 pak choi cultivars were determined in low and high Cd treatments. Significant variations in Cd accumulation and root morphological parameters were observed between pak choi cultivars. Cd concentrations in shoots differed between cultivars by a factor of 2.3 (13.3-30.8 µg g(-1)) and 2.6 (35.5-94.0 µg g(-1)) for low and high Cd treatments, respectively. The total Cd in plants positively correlated to the root length, root surface area, root volume, and root length/shoot biomass ratio in both Cd treatments. The shoot Cd concentration was also positively correlated with the root length, root surface area, and root length/shoot biomass ratio. Moreover, the proportion of fine roots (diameter less than 0.2 mm) was positively correlated with the total Cd in plants in low Cd treatment, and positively correlated with percentage of Cd in shoots in high Cd treatment. These results suggested that root morphology might be partially responsible for variation of Cd accumulation among pak choi cultivars. High Cd cultivars exhibit longer root length, greater root surface area, higher root volume, and a higher proportion of fine roots than low Cd cultivars.

Effects of drought on cadmium accumulation in peanuts grown in a contaminated calcareous soil.

This study aimed to investigate the effects of drought stress on cadmium (Cd) accumulation in peanut (Arachis hypogaea L.) grown in contaminated calcareous soils. Five peanut cultivars were grown in a calcareous soil spiked with 4 mg Cd kg(-1) soil (dry weight) under well-watered, mild drought, and severe drought conditions. The biomass production, gas exchange, spectral reflectance, and Cd accumulation in plant tissues were determined. The five cultivars significantly differed from each other in biomass production, gas exchange, spectral reflectance, and Cd accumulation. The effect of drought on Cd accumulation in peanuts varies with plant tissues, cultivars, and developmental stages. Drought decreased root Cd concentrations in seedlings of the two high Cd-accumulating cultivars (Haihua 1 and Zhenghong 3), which is associated with increasing leaf active Fe content. However, for the mature plants, drought stress caused an increase in Cd accumulation in roots, pod walls, and seeds depending on peanut cultivars. Negative correlations were found between seed Cd concentration and biomasses in both preflowering seedlings and mature plants. The seed Cd concentration in mature plants was also observed to be positively correlated with the shoot Cd concentration in preflowering seedlings. The increased Cd concentration in seeds of drought-stressed peanut plants grown in Cd-contaminated calcareous soils might be attributed to the drought-induced decrease of biomass production.