Cadmium Uptake Research Articles

A Dark Septate Endophyte Improves Cadmium Tolerance of Maize by Modifying Root Morphology and Promoting Cadmium Binding to the Cell Wall and Phosphate.

Dark septate endophytes (DSEs) can improve the performance of host plants grown in heavy metal-polluted soils, but the mechanism is still unclear. A sand culture experiment was performed to investigate the effects of a DSE strain (Exophiala pisciphila) on maize growth, root morphology, and cadmium (Cd) uptake under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg-1). The results indicated that the DSE significantly improved the Cd tolerance of maize, causing increases in biomass, plant height, and root morphology (length, tips, branch, and crossing number); enhancing the Cd retention in roots with a decrease in the transfer coefficient of Cd in maize plants; and increasing the Cd proportion in the cell wall by 16.0-25.6%. In addition, DSE significantly changed the chemical forms of Cd in maize roots, resulting in decreases in the proportions of pectates and protein-integrated Cd by 15.6-32.4%, but an increase in the proportion of insoluble phosphate Cd by 33.3-83.3%. The correlation analysis revealed a significantly positive relationship between the root morphology and the proportions of insoluble phosphate Cd and Cd in the cell wall. Therefore, the DSE improved the Cd tolerance of plants both by modifying root morphology, and by promoting Cd binding to the cell walls and forming an insoluble phosphate Cd of lower activity. These results of this study provide comprehensive evidence for the mechanisms by which DSE colonization enhances Cd tolerance in maize in root morphology with Cd subcellular distribution and chemical forms.

Nano silicon dioxide reduces cadmium uptake, regulates nutritional homeostasis and antioxidative enzyme system in barley seedlings (Hordeum vulgare L.) under cadmium stress

Cadmium (Cd) toxicity is one of the most severe environmental threats inhibiting crop growth and productivity. Strategies to mitigate the adverse effects of Cd stress on plants are under scrutiny. Nano silicon dioxide (nSiO2) is an emerging material and could protect plants against abiotic stress. Can nSiO2 alleviate Cd toxicity in barley, and the possible mechanisms are poorly understood. A hydroponic experiment was conducted to study the mitigation effects of nSiO2 on Cd toxicity in barley seedlings. The results showed that the application of nSiO2 (5, 10, 20, and 40mg/L) increased barley plant growth and chlorophyll and protein content, improving photosynthesis, compared with Cd-treated alone. Specifically, 5-40mg/L nSiO2 addition increased net photosynthetic rate (Pn) by 17.1, 38.0, 30.3, and - 9.7%, respectively, relative to the Cd treatment alone. Furthermore, exogenous nSiO2 reduced Cd concentration and balanced mineral nutrient uptake. The application of 5-40mg/L nSiO2 decreased Cd concentration in barley leaves by 17.5, 25.4, 16.7, and 5.8%, respectively, relative to the Cd treatment alone. Moreover, exogenous nSiO2 lowered malondialdehyde (MDA) content by 13.6-35.0% in roots, and by 13.5-27.2% in leaves, respectively, compared with Cd-treated alone. Besides, nSiO2 altered antioxidant enzyme activities and alleviated detrimental effects on Cd-treated plants, attaining maximal values at 10mg/L nSiO2. These findings revealed that exogenous nSiO2 application may be a viable option for addressing Cd toxicity of barley plants.

Microbial extracellular polymeric substances alleviate cadmium toxicity in rice (Oryza sativa L.) by regulating cadmium uptake, subcellular distribution and triggering the expression of stress-related genes

Cadmium (Cd) accumulation in crops causes potential risks to human health. Microbial extracellular polymeric substances (EPS) are a complex mixture of biopolymers that can bind various heavy metals. The present work examined the alleviating effects of EPS on Cd toxicity in rice and its detoxification mechanism. The 100 μM Cd stress hampered the overall plant growth and development, damaged the ultrastructures of both leaf and root cells, and caused severe lipid peroxidation in rice plants. However, applying EPS at a concentration of 100 mg/L during Cd stress resulted in increased biomass, reduced Cd accumulation and transport, and minimized the oxidative damage. EPS application also enhanced Cd retention in the shoot cell walls and root vacuoles, and actively altered the expression of genes involved in cell wall formation, antioxidant defense systems, transcription factors, and hormone metabolism. These findings provide new insights into EPS-mediated mitigation of Cd stress in plants and help us to develop strategies to improve crop yield in Cd-contaminated soils in the future.

Exogenous application of low and high molecular weight organic acids differentially affected the uptake of cadmium in wheat-rice cropping system in alkaline calcareous soil

Anthropogenic cadmium (Cd) in arable soils is becoming a global concern due to its harmful effects on crop yield and quality. The current study examined the role of exogenously applied low molecular weight organic acids (LMWOAs) including oxalic acid (OxA), tartaric acid (TA) and high molecular weight organic acids (HMWOAs) like citric acid (CA) and humic acid (HA) for the bioavailability of Cd in wheat-rice cropping system. Maximum increase in root dry-weight, shoot dry-weight, and grain/paddy yields was recorded with HA for both crops. The HA significantly decreased AB-DTPA Cd in contaminated soils which remained 41% for wheat and 48% for rice compared with their respective controls. The minimum concentration of Cd in roots, shoots and grain/paddy was observed in HA treatment in both crops. The organic acids significantly increased the growth parameters, photosynthetic activity, and relative leaf moisture contents for both wheat and rice crops compared to that with the contaminated control. Application of OxA and TA increased the bioavailability of Cd in soils and plant tissues while CA and HA decreased the bioavailability of Cd in soils and plants. The highest decrease in Cd uptake, bioaccumulation, translocation factor, immobilization, translocation, harvest, and health risk indices were observed with HA while maximum increase was recorded with OxA for both wheat and rice. The results concluded that use of HMWOAs is effective in soil Cd immobilization being maximum with HA. While LMWOAs can be used for the phytoextraction of Cd in contaminated soils having maximum potential with OxA.

Silicon Calcium Fertilizer Application and Foliar Spraying with Silicon Fertilizer Decreases Cadmium Uptake and Translocation in Rice Grown in Polluted Soil

Rice cultivated in Cd-polluted acidic paddy soil poses important health risks in China. Decreasing Cd accumulation in rice is important for food safety and human health. Early rice cultivar ZY-819 and late rice cultivar XWX-13 with low Cd-accumulation potentials, and early rice cultivar LY-996 and late rice cultivar YZX with high Cd-accumulation potentials, were grown in mildly polluted double-cropping paddy fields (Cd content 0.3–0.6 mg kg−1). The effects of adding biochar (10 t ha−2), lime (1500 kg ha−2), and silicon–calcium fertilizer (SC; 2250 kg ha−2) and foliar spraying with silicon fertilizer solution (Si; 1500 g ha−2) on Cd uptake and transport in rice, were assessed in plot experiments. The soil amendments and foliar spraying decreased the Cd content of brown rice from the high Cd-accumulation potential cultivars. The soil amendments decreased the Cd content of LY-996 and YZX brown rice by 25.24–32.40% and 32.99–44.16%, respectively, and SC decreased the Cd content most. Foliar spraying with Si decreased the Cd content of LY-996 and YZC brown rice by 23.79% and 26.40%, respectively. When soil amendments and foliar spraying were combined, the Cd content of brown rice was decreased most by the SC–Si treatment. Compared with the control, the SC–Si treatment decreased the Cd content of LY-996, ZY-819, YZX, and XWX-13 brown rice by 45.63%, 35.67%, 52.79%, and 32.03%, respectively. Soil amendments can effectively decrease Cd uptake by rice roots and Cd migration from roots to shoots. Compared with the control, the soil amendments increased the soil pH and decreased Cd availability. The strongest effects were for the lime and SC treatments. Foliar spraying with Si can effectively decrease Cd translocation through stems and leaves to brown rice. Applying SC fertilizer and foliar spraying with Si is the best method for decreasing the Cd content of rice grown in mildly Cd-polluted paddy fields.

Effect of boron supply on the uptake and translocation of cadmium in Capsicum annuum

Large areas of soil in southern China are contaminated with cadmium (Cd) and are deficient in boron (B). Previously, we suggested that B supplementation could reduce Cd accumulation in hot peppers (Capsicum annuum L.); however, the physiological mechanisms underlying this reduction remain unclear. In this study, the uptake and translocation of Cd in hot pepper plants were investigated using hydroponic experiments with different B and Cd treatments. A pot experiment was performed to verify whether B decreased the Cd concentration in hot peppers by minimizing the Cd translocation rate. The results of the dose- and time-dependent experiments showed that B supplementation reduced root Cd uptake and root-to-shoot Cd translocation. Additionally, B supplementation increased the root length, diameter, volume, surface area, and number of root forks and tips, as well as improving the relative absorbance of carboxyl groups under Cd exposure, leading to enhanced Cd fixation in the cell walls of the roots. As a result, the fruit Cd concentration decreased because B inhibited Cd translocation from the roots. Overall, the results demonstrate that B supplementation can reduce Cd accumulation in hot peppers by promoting normal root growth and development and by limiting the uptake and translocation of Cd.

Foliar cadmium uptake, transfer, and redistribution in Chili: A comparison of foliar and root uptake, metabolomic, and contribution

Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdSN), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

Uptake and Distribution of Cadmium and Copper by Solanum lycopersicum L. and Changes in the Metabolite Production

Uptake and Distribution of Cadmium and Copper by Solanum lycopersicum L. and Changes in the Metabolite Production

Evaluation of cadmium uptake and consumption of parsley in Lebanese diet

Evaluation of cadmium uptake and consumption of parsley in Lebanese diet

Single and combined effects of cadmium, microplastics, and their mixture on whole-body serotonin and feeding behaviour following chronic exposure and subsequent recovery in the freshwater leech, Nephelopsis obscura

Microplastics and metals are contaminants detected in many freshwater systems globally. Interactions of microplastics with other contaminants including cadmium poses potential threats to the health of aquatic organisms including Nephelopsis obscura, a predatory leech species that is widespread and serves important ecological and economic roles. The feeding biology of N. obscura has been well-described, including that serotonin regulates feeding behaviour. Further, exposure to cadmium has been found to cause decrease whole-body concentrations of serotonin. The influence that microplastic contamination and co-contamination of cadmium and microplastics has on N. obscura is unknown. The present study had three objectives: (1) to determine if water or sediment contaminated with cadmium, microplastics, or their mixture resulted in greater cadmium uptake by N. obscura, (2) to assess effects of chronic (21-day) exposure of N. obscura to waterborne cadmium, microplastics, and their mixture on bioaccumulation of cadmium, concentrations of serotonin, and feeding behaviour (latency to feeding, time spent feeding, and distance moved), and (3) to reassess the bioaccumulation of cadmium, concentrations of serotonin, and feeding behaviour following transfer to an uncontaminated environment for a one-week recovery period. This study revealed that access to and presence of sediment is protective against cadmium uptake and that cadmium is more readily accumulated from waterborne sources, even in environments where both sediment and surface water are contaminated. After 21-days of exposure to waterborne cadmium, microplastics, and their mixture, accumulation of cadmium, decreased concentrations of serotonin, and impaired feeding behaviours were greatest in leeches from the co-exposures compared to leeches from either single contaminant exposure group. Finally, after one week of depuration and recovery in freshwater following the 21-day exposures, concentrations of serotonin and feeding behaviour were restored in individuals from the microplastic exposure; however, cadmium-exposed individuals continued to show decreased concentrations of serotonin and behavioural deficits. The co-exposure of leeches to cadmium and microplastics resulted in additive effects to serotonin synthesis and feeding behaviour; however, this study demonstrated that leeches were able to recover from microplastic toxicity within a week whereas cadmium toxicity persisted.

Silicon facilitated the physical barrier and adsorption of cadmium of iron plaque by changing the biochemical composition to reduce cadmium absorption of rice roots

Silicon effectively inhibits cadmium (Cd) uptake in rice, iron plaque on root surface was the primary link and first interface of Cd entering into rice root. To elucidate the mechanism of iron plaque under silicon treatment on root Cd uptake, the morphological characteristics of iron plaque, mechanisms of Cd adsorption of iron plaque and effect of iron plaque on Cd uptake by rice roots of Yuzhenxiang (YZX) and Xiangwanxian (XWX) rice varieties were studied by employing energy spectrum analysis technique, non-invasive micro-test technique, and isothermal-kinetic adsorption method. Scanning electron microscopy-X-ray energy dispersive (SEM-EDX) analysis showed that denser crystal structure of iron plaque was observed at Si treatment, silicon promoted the thickening of iron plaque and strengthened the isolation of iron plaque to Cd, which reduced the Cd content of white roots of YZX and XWX varieties by 30.2% and 20.9% respectively. However, the blocking effect of iron plaque on Cd was weakened under silicon treatment with iron plaque removed, Cd content in iron plaque of YZX and XWX cultivars was significantly decreased by 36.3% and 18.4%, Cd concentrations in white root and shoot was significantly increased, and the influxes of Cd2+ at elongation and maturation zone of root were increased in multiples. The results of adsorption test showed that the adsorption process of iron plaque was mainly a monolayer adsorption completed by boundary diffusion. The X-ray photoelectron spectroscopy (XPS) results demonstrated that silicon changed the biochemical composition of iron plaque and increased the density of the carbon-oxygen bound groups on iron plaque, which is the most likely reasons for the higher affinity of Cd adsorption ability of iron plaque observed in the silicon treated iron plaque. This study suggested the silicon-facilitated iron plaque have played critical effects in controlling the Cd accumulation in rice roots by changing the morphology and chemical composition of iron plaque.

Identification of ferritin variants with increased cadmium selectivity by in vivo cloning and mutagenesis in Saccharomyces cerevisiae

Uptake of heavy metals into microorganisms is an attractive bioremediation strategy, but low cost, safe and effective solutions remain lacking. Diverse organisms express ferritin, a multimeric protein that stores thousands of ferric ions and can take up other metals, with the notable exception of Saccharomyces cerevisiae. Nonetheless, this yeast has been shown to express functional ferritin subunits from soybean, increasing iron accumulation but with little impact on cadmium uptake. Compared to soybean, pea and horse ferritins bind more cadmium, pointing to amino acid residues that might be responsible for the different specificities. Chimeric soybean ferritins were constructed and analyzed in yeast. Additionally, random mutagenesis and screening were applied to identify another variant that accumulate more cadmium. Although expression was similar for each variant, cadmium accumulation varied. Importantly, tested in a model for bioremediation, culturing the ferritin-expressing strains in media containing 100 μM CdCl2 led to 80 % removal of the metal.

Individual and mutual effects of elevated carbon dioxide and temperature on salt and cadmium uptake and translocation by rice seedlings.

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO2 and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO2 concentrations (ambient CO2: 360 ppm; medium CO2: 450 ppm; high CO2: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1g Na/L) and cadmium nitrate (Cd(NO3)2·4H2O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO2 alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO2. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO2 stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO2. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.

The use of various magnetic adsorbents for cadmium uptake from dyes-containing wastewater

Simultaneous presence of organic dyes with Cd(II) is possible and may affect Cd(II) removal from wastewater. This study involved various magnetic adsorbents for Cd(II) removal in the presence of various organic dyes (Tartrazine, Allura red, Rhodamine). Magnetic carbon nanotubes (MCNT), magnetic graphene oxide (MGO) and magnetic olive wood (MOW) were involved as adsorbents. The following adsorption issues were considered at various pHs: Effect of magnetic adsorbent type on Cd(II) uptake in presence and absence of Tartrazine; Effect of dye type on Cd(II) uptake by MCNT; Adsorption of organic dyes’ onto MCNT; Effect of other adsorption factors [“magnetite:CNT” mass ratio; “Cd: Rhodamine” molar ratio]. It was found that the presence of dyes caused an enhanced uptake of Cd(II) uptake by MCNT, which was attributed to suraface-dye-Cd ternary complex formation, in which Rhodamine caused the maximum Cd(II) uptake at pH 8. The maximum Cd(II) uptake conditions [using MCNT at pH 8 in (1:3) “Cd:Rhoadamine” molar ratio] gave Cd(II) adsorption capacity of 23 mg g−1. The method was re-useable, applicable on environmental waters and selective with a 20% decrease in its performance in presence of competing ions.

Zinc Supply Affects Cadmium Uptake and Translocation in the Hyperaccumulator Sedum Plumbizincicola as Evidenced by Isotope Fractionation.

This study employs stable isotope analysis to investigate the mechanisms of cadmium (Cd) and zinc (Zn) interaction in the metal hyperaccumulating plant species Sedum plumbizincicola. To this end, the Cd and Zn isotope compositions of root, stem, leaf, and xylem sap samples were determined during metal uptake and translocation at different Cd and Zn concentrations. The enrichment of light isotopes of both elements in plants during uptake was less pronounced at low metal supply levels, likely reflecting the switch from a low-affinity to a high-affinity transport system at lower levels of external metal supply. The lower δ114/110Cd values of xylem sap when treated with a metabolic inhibitor decreasing the active Cd uptake further supports the preference of heavier Cd isotopes during high-affinity transport. The Δ66Znplant-initialsolution or Δ66Znplant-finalsolution values were similar at different Cd concentrations, indicating negligible interaction of Cd in the Zn uptake process. However, decreasing Zn supply levels significantly increased the enrichment of light Cd isotopes in plants (Δ114/110Cd = -0.08‰) in low-Cd treatments but reduced the enrichment of light Cd isotopes in plants (Δ114/110Cd = 0.08‰) under high Cd conditions. A systematic enrichment of heavy Cd and light Zn isotopes was found in root-to-shoot translocation of the metals. The Cd concentrations of the growth solutions thereby had no significant impact on Zn isotope fractionation during root-to-shoot translocation. However, the Δ114/110Cdtranslocation values hint at possible competition between Cd and Zn for transporters during root-to-shoot transfer and this may impact the transport pathway of Cd. The stable isotope data demonstrate that the interactions between the two metals influenced the uptake and transport mechanisms of Cd in S. plumbizincicola but had little effect on those of Zn.

Co-application of organic amendments and Cd-tolerant rhizobacteria for suppression of cadmium uptake and regulation of antioxidants in tomato

Cadmium (Cd) contamination is a major environmental concern with well-reported adverse impacts on environment and living entities. It limits the productivity of agricultural crops due to its excessive entry to plant tissues, and subsequent toxic effects on their growth and physiology. Application of metal tolerant rhizobacteria in combination with organic amendments has shown beneficial impacts in sustaining plant growth, on account of amendments mediated decreased metal mobility via different functional groups, as well as provision of carbon to microorganisms. We evaluated the effect of organic amendments (compost and biochar) and Cd-tolerant rhizobacteria on growth, physiology, and Cd uptake in tomato (Solanum lycopersicum). Plants were grown under Cd contamination (2 mg kg−1), and were supplemented with 0.5% w/w of compost and biochar along with rhizobacterial inoculation in pot culture. We observed a significant reduction in shoot length, fresh and dry biomass (37, 49 and 31%) and root attributes such as root length, fresh and dry weights (35, 38 and 43%). However, Cd tolerant PGPR strain ‘J-62’ along with compost and biochar (0.5% w/w) mitigated the Cd induced adverse impacts on different plant attributes and improved these attributes such as root and shoot lengths (112 and 72%), fresh (130 and 146%) and dry weights (119 and 162%) of tomato roots and shoots as compared to relative control treatment. Furthermore, we observed significant increments in different antioxidant activities such as SOD (54%), CAT (49%) and APX (50%) under Cd contamination. Combined application of ‘J-62’ strain and organic amendments also decreased Cd translocation towards different above-ground plant parts as was pragmatic in terms of bioconcentration and translocation factors of Cd, which indicated phyto-stabilization ability of our inoculated strain for Cd. Hence, Cd tolerant PGPR in combination with organic amendments can immobilize Cd in soil and thereby, can alleviate Cd induced adverse impacts on tomato growth.

The mechanism of silicon on alleviating cadmium toxicity in plants: A review.

Cadmium is one of the most toxic heavy metal elements that seriously threaten food safety and agricultural production worldwide. Because of its high solubility, cadmium can easily enter plants, inhibiting plant growth and reducing crop yield. Therefore, finding a way to alleviate the inhibitory effects of cadmium on plant growth is critical. Silicon, the second most abundant element in the Earth's crust, has been widely reported to promote plant growth and alleviate cadmium toxicity. This review summarizes the recent progress made to elucidate how silicon mitigates cadmium toxicity in plants. We describe the role of silicon in reducing cadmium uptake and transport, improving plant mineral nutrient supply, regulating antioxidant systems and optimizing plant architecture. We also summarize in detail the regulation of plant water balance by silicon, and the role of this phenomenon in enhancing plant resistance to cadmium toxicity. An in-depth analysis of literature has been conducted to identify the current problems related to cadmium toxicity and to propose future research directions.

Synergistic Effects of Water Management and Silicon Foliar Spraying on the Uptake and Transport Efficiency of Cadmium in Rice (Oryza sativa L.)

To study the synergistic effects of water management and silicon (Si) foliar spraying on the uptake and transport of cadmium (Cd) in rice, we designed four treatments: conventional intermittent flooding + no Si foliar spraying (CK), continuous flooding throughout the growth stage + no Si foliar spraying (W), conventional intermittent flooding + Si foliar spraying (Si) and continuous flooding throughout the growth stage + Si foliar spraying (WSi). The results show that WSi treatment reduced the uptake and translocation of Cd by rice and significantly reduced the brown rice Cd content, with no effect on rice yield. Compared with CK, the Si treatment increased the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of rice by 6.5-9.4%, 10.0-16.6% and 2.1-16.8%, respectively. The W treatment decreased these parameters by 20.5-27.9%, 8.6-26.8% and 13.3-23.3%, respectively, and the WSi treatment decreased them by 13.1-21.2%, 3.7-22.3% and 2.2-13.7%, respectively. The superoxide dismutase (SOD) and peroxidase (POD) activity decreased by 6.7-20.6% and 6.5-9.5%, respectively, following the W treatment. Following the Si treatment, SOD and POD activity increased by 10.2-41.1% and 9.3-25.1%, respectively, and following the WSi treatment, they increased by 6.5-18.1% and 2.6-22.4%, respectively. Si foliar spraying ameliorated the detrimental effects of continuous flooding throughout the growth stage on photosynthesis and antioxidant enzyme activity. We conclude that synergistic continuous flooding throughout the growth stage, combined with Si foliar spraying, can significantly block Cd uptake and translocation and is therefore an effective means of reducing the accumulation of Cd in brown rice.

Nitrate_dependent suberization regulates cadmium uptake and accumulation in maize

In this study, effect of nitrate-dependent suberization in maize root on cadmium (Cd) uptake and accumulation was investigated. Suberization in maize roots was significantly lower in plants grown with a high nitrate supply compared with low nitrate. This decrease was seen in the total amount of suberin, in which the aliphatic suberin amount was significantly decreased, whereas no difference in aromatic suberin content between different N-treatments. RNA-sequencing showed that suberin biosynthesis genes were upregulated in low nitrate treatment, which correlated well with the increased suberin content. Bioimaging and xylem sap analysis showed that reduced exodermal and endodermal suberization in roots of plants grown under high nitrate promoted radial Cd transport along the crown root. The enhanced suberization in crown roots of plants grown in low nitrate restricted the radial transport of Cd from epidermis to cortex via decreased accessibility to Cd related transporters at the plasmalemma. Also, under low nitrate supply, the Cd transport gene ZmNramp5 was upregulated in the crown root, which may enhance Cd uptake by root tip where exodermis and endodermis were not fully suberized. These results suggest that high nitrate supply enhances Cd uptake and radial transport in maize roots by reducing exodermal and endodermal suberization.

Suppression of highly efficient cadmium translocation by exogenous gibberellin provides insights into the molecular regulation mechanism of hyperaccumulation in Sedum plumbizincicola

Sedum plumbizincicola is a hyperaccumulating species with highly efficient uptake, translocation and distribution system for cadmium (Cd), a non-essential and toxic heavy metal. To understand the molecular regulation mechanisms of Cd transport and accumulation in this hyperaccumulator is still a challenge. In this study, we observed that exogenous gibberellin A3 (GA3) significantly reduced Cd loading efficiency from root to shoot and uploading efficiency from stem to leaves in S. plumbizincicola under Cd treatments, which provided us a remarkable opportunity to study the signaling mechanisms for regulation of highly efficient Cd transport and translocation in S. plumbizincicola. Here, we constructed a de novo full-length transcriptome database with the integration of full-length and next-generation transcriptome sequences for Cd-treated S. plumbizincicola with or without exogenous GA3 application. From this database, we identified 1461 differentially expressed genes (DEGs), which were related to solute transport, cell wall metabolism and signal transduction, and most of them were down-regulated by the exogenous application of gibberellin. In particularly, a substantial number of the downregulated genes belong to calmodulin-like (CML) proteins, calcium-dependent protein kinase, calcium-permeable channel, mitochondrial calcium uniporter (MCU) and Na+/Ca2+ exchanger-like proteins (NCL/EF-CAX). These results indicated that calcium homeostasis and signal transduction may play an important role in the regulation of highly efficient translocation of cadmium in hyperaccumulator S. pumbizincicola.