Hyperaccumulator Solanum Nigrum Research Articles

Zinc Enhances Cadmium Accumulation in Shoots of Hyperaccumulator Solanum nigrum by Improving ATP-Dependent Transport and Alleviating Toxicity.

Solanum nigrum is a cadmium (Cd) and zinc (Zn) accumulator with potential for phytoextraction of soil contaminated with heavy metals. However, how Zn affects Cd accumulation in S. nigrum remains unclear. In this study, S. nigrum seedlings were treated with 100 μmol·L-1 Zn (Zn100), 100 μmol·L-1 Cd (Cd100), and the Zn and Cd combination (Zn100+Cd100) for 10 days under hydroponic culture. Compared with Cd100, the Cd content in stems, leaves, and xylem saps was 1.8, 1.6, and 1.3 times more than that in Zn100+Cd100, respectively. In addition, the production of reactive oxygen species in leaves was significantly upregulated in Cd100 compared with the control, and it was downregulated in Zn100. Comparative analyses of transcriptomes and proteomes were conducted with S. nigrum leaves. Differentially expressed genes (DEGs) were involved in Cd uptake, transport, and sequestration, and the upregulation of some transporter genes of Zn transporters (ZIPs), a natural resistance associated macrophage protein (Nramp1), a metal-nicotianamine transporter (YSL2), ATP-binding cassette transporters (ABCs), oligopeptide transporters (OPTs), and metallothionein (MTs) and glutathione S-transferase (GSTs) genes was higher in Zn100+Cd100 than in Cd100. In addition, differentially expressed proteins (DEPs) involved in electron transport chain, ATP, and chlorophyll biosynthesis, such as malate dehydrogenases (MDHs), ATPases, and chlorophyll a/b binding proteins, were mostly upregulated in Zn100. The results indicate that Zn supplement increases Cd accumulation and tolerance in S. nigrum by upregulating ATP-dependent Cd transport and sequestration pathways.

Exogenous γ‐aminobutyric acid (GABA) improves the cadmium phytoremediation capacity of Solanum nigrum var. humile under cadmium stress

Abstractγ‐aminobutyric acid (GABA) has shown promise in enhancing crop tolerance to heavy metal stress. To improve the cadmium (Cd) phytoremediation capacity of hyperaccumulator Solanum nigrum var. humile, the effects of exogenous GABA on the growth and Cd accumulation of S. nigrum var. humile were studied. When exposed to Cd stress (0.1 mg/L) through irrigation, S. nigrum var. humile exhibited inhibited growth, characterized by decreased biomass and contents of photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid). However, the application of exogenous GABA at 1 and 2 g/L increased various organs biomass and photosynthetic pigment content of S. nigrum var. humile to certain degree under Cd stress. Compared with the Cd treatment, the concentrations of 1 and 2 g/L GABA increased the shoot biomass by 8.24% and 16.62%, respectively. GABA also increased the Cd contents, bioconcentration factors, and Cd extractions in various organs of S. nigrum var. humile. Compared with the Cd treatment, the concentrations of 1 and 2 g/L GABA increased the shoot Cd extraction by 17.66% and 24.47%, respectively. Moreover, correlation and gray relational analyses showed that the shoot biomass, chlorophyll b content, and total chlorophyll content were the top three parameters closely related to shoot Cd extraction. These findings suggest that GABA can alleviate Cd‐induced stress in S. nigrum var. humile, thus enhancing its phytoremediation capacity for Cd‐contaminated soils.

Hyperaccumulator Solanum nigrum L. Intercropping Reduced Rice Cadmium Uptake under a High-Bed and Low-Ditch Planting System

Anthropogenic activities have raised cadmium (Cd) concentrations in agricultural soil, emerging as a primary catalyst for the decline in crop yield. Intercropping of two or several plants is one technique among many Cd phytoremediation techniques that has gained enormous attention recently. However, the impact of cultivation modes on Cd movement in rice plants when intercropped with heavy metal (HM) hyperaccumulator plants remains unclear. Thus, this study was designed to explore the effects of cultivation modes and the intercropping of rice with Solanum nigrum L. on rice growth and Cd uptake in Cd-contaminated soil. The experimental design encompassed five treatments: dry cultivation of monocultured rice, monocultured Solanum nigrum L., and intercropped rice–Solanum nigrum L.; flood cultivation of monocultured rice; and intercropped rice–Solanum nigrum L. in a high-bed and low-ditch planting system. The results revealed a significant increase in rice growth when intercropped with Solanum nigrum L., with a notable increase of 18.32 g∙plant−1 observed in rice biomass in dry cultivation under the intercropping system. In contrast, a more modest increase of 3.67 g∙plant−1 was observed in the high-bed and low-ditch intercropped rice–Solanum nigrum L. mode. The soil total Cd was higher in dry cultivation of monocultured rice and Solanum nigrum L. compared to intercropped rice/Solanum nigrum L.-cultivated soil, with lower values recorded for intercropped rice/Solanum nigrum L. under the high-bed and low-ditch planting system. In contrast, no significant effect was noted on soil exchangeable Cd content based on the planting pattern and cultivation mode. Intercropping with Solanum nigrum L. demonstrated a significant reduction of Cd content in various rice tissues, particularly in roots at the maturity stage, while Cd content was reduced across all rice tissues under the high-bed and low-ditch planting system. The Cd content in the stem, leaves, and bran of monocropped rice was higher compared to intercropped rice. This study suggests that the rice–Solanum nigrum L. intercropping system effectively reduces rice Cd uptake, particularly under the high-bed and low-ditch planting system.

Regulation of cadmium uptake in the hyperaccumulator Solanum nigrum is mediated by glutathione

Solanum nigrum is a common hyperaccumulator of the heavy metal cadmium (Cd). Our study aims to investigate the impact of glutathione regulation, specifically glutathione overproduction or reduction, on the growth of S. nigrum and its soil remediation potential. To achieve this, plants were subjected to treatments using a glutathione inhibitor (buthionine sulfoximine) and a glutathione promoter (L-2-oxothiazolidine-4-carboxylic acid [OTC]). We assessed plant height, root length and biomass to evaluate the influence of Cd and glutathione regulation on plant growth. Furthermore, we analyzed chlorophyll content. Cd and malondialdehyde (MDA) contents were measured to determine the effect of glutathione regulation on Cd accumulation and lipid peroxidation. Our findings revealed that glutathione overproduction significantly increased the biomass of S. nigrum, resulting in an approximately 12% increase. Additionally, it led to a ca. 10% rise in chlorophylls content. The application of exogenous OTC enhanced reduced glutathione (GSH) content, accompanied by enhanced Cd accumulation. GSH can be converted to oxidized glutathione, which aids in combatting and mitigating Cd toxicity. The MDA content in plants also increased. The overproduction of glutathione holds promise for enhancing heavy metal accumulation and tolerance in hyperaccumulator plants. It provides a theoretical basis for improving hyperaccumulator plants genetically.

NaCl-mediated strategies for the trade-off between Cd bioconcentration and translocation in Solanum nigrum L

Salt interference significantly affects the behavior of heavy metals in the environment. This study compared and analyzed the response process, migration, and transformation of cadmium (Cd) in the hyperaccumulator Solanum nigrum (S. nigrum) under different NaCl levels to reveal the interference mechanisms of salt in plant remediation of Cd-contaminated soil. The results showed that Cd and salt stress significantly inhibited the growth of plants. The stress effect had more potent growth inhibition at the root than aboveground, thus inducing changes in the spatial configuration of the plants (decreased root-to-aboveground biomass ratio). Salt could activate Cd in plants, enhancing the inhibitory effect on plant growth. Salt increased Cd bioavailability due to the rhizosphere acidification effect, increasing plants’ Cd accumulation. The Cd bioconcentration factor in plant roots peaked during the high Cd-high salt treatment (117.10), but the Cd accumulation of plants peaked during the high Cd-low salt treatment (233.04 μg plant−1). Salt additions and increased Cd concentrations enhanced root compartmentalization, inhibiting Cd transport to the aboveground. Changes in Fourier-transform infrared spectroscopy (FTIR) measurements confirmed that the functional groups in plants provided binding sites for Cd. These findings can help guide the phytoremediation of Cd contamination under saline soil conditions.

Plant growth promoting endophyte promotes cadmium accumulation in Solanum nigrum L. by regulating plant homeostasis

The homeostasis regulating mechanism of endophyte enhancing cadmium (Cd) extraction by hyperaccumulator is poorly understood. Here, an endophyte strain E3 that belonged to Pseudomonas was screened from Cd hyperaccumulator Solanum nigrum L., which significantly improved the Cd phytoextraction efficiency of S. nigrum by 40.26%. The content and translocation factor of nutrient elements indicated that endophyte might regulate Cd accumulation by affecting the uptake and transport of magnesium and iron in S. nigrum. Gene transcriptional expression profile further revealed that SnMGT, SnIRT1, and SnIRT2, etc., were the key genes involved in the regulation of S. nigrum elements uptake by endophyte. However, changes in elemental homeostasis did not negatively affect plant growth. Endophyte inoculation promoted plant growth by fortifying photosynthesis as well as recruiting specific bacteria in S. nigrum endosphere, e.g., Pseudonocardiaceae, Halomonas. Notably, PICRUSt2 analysis and biochemical characterization jointly suggested that endophyte regulated starch degradation in S. nigrum leaves to maintain photosynthetic balance. Our results demonstrated that microecological characteristics of hyperaccumulator could be reshaped by endophyte, also the homeostasis regulation in endophyte enhanced hyperaccumulator Cd phytoextraction was significant.

Super-resolution reconstruction, recognition, and evaluation of laser confocal images of hyperaccumulator Solanum nigrum endocytosis vesicles based on deep learning: Comparative study of SRGAN and SRResNet.

It is difficult for laser scanning confocal microscopy to obtain high- or ultra-high-resolution laser confocal images directly, which affects the deep mining and use of the embedded information in laser confocal images and forms a technical bottleneck in the in-depth exploration of the microscopic physiological and biochemical processes of plants. The super-resolution reconstruction model (SRGAN), which is based on a generative adversarial network and super-resolution reconstruction model (SRResNet), which is based on a residual network, was used to obtain single and secondary super-resolution reconstruction images of laser confocal images of the root cells of the hyperaccumulator Solanum nigrum. Using the peak signal-to-noise ratio (PSNR), structural similarity (SSIM) and mean opinion score (MOS), the models were evaluated by the image effects after reconstruction and were applied to the recognition of endocytic vesicles in Solanum nigrum root cells. The results showed that the single reconstruction and the secondary reconstruction of SRGAN and SRResNet improved the resolution of laser confocal images. PSNR, SSIM, and MOS were clearly improved, with a maximum PSNR of 47.690. The maximum increment of PSNR and SSIM of the secondary reconstruction images reached 21.7% and 2.8%, respectively, and the objective evaluation of the image quality was good. However, overall MOS was less than that of the single reconstruction, the perceptual quality was weakened, and the time cost was more than 130 times greater. The reconstruction effect of SRResNet was better than that of SRGAN. When SRGAN and SRResNet were used for the recognition of endocytic vesicles in Solanum nigrum root cells, the clarity of the reconstructed images was obviously improved, the boundary of the endocytic vesicles was clearer, and the number of identified endocytic vesicles increased from 6 to 9 and 10, respectively, and the mean fluorescence intensity was enhanced by 14.4% and 7.8%, respectively. Relevant research and achievements are of great significance for promoting the application of deep learning methods and image super-resolution reconstruction technology in laser confocal image studies.

Foliar application of lanthanum promotes growth and phytoremediation potential Solanum nigrum L

The hormetic effect of rare earth elements (REEs) has been found in a variety of crops and has been promoting crop growth for decades. Spraying leaves with REEs can enhance the endocytosis of plant roots. The non-selectivity of endocytosis is conducive to the direct absorption of environmental pollutants. The hyperaccumulator Solanum nigrum L. (S. nigrum), as a plant with high biomass and heavy metal tolerance, is a good candidate for phytoremediation. La(III), as a typical light REE, also has an obvious hormetic effect on S. nigrum. At 10 μM La(III), the biomass of S. nigrum reached the maximum, which was 89% greater than the control, and La(III) concentration was much lower than the previously reported optimum of 56 μM for general plants. In the present study, enhanced endocytosis after foliar spraying of La(III) was firstly observed in the root cell of hyperaccumulation plants, and La(III) increased the biomass of S. nigrum by improving the photosynthetic system, and promoting nutrient uptake and root development. The antioxidant defense system improved by La(III) contributed to the tolerance of S. nigrum to heavy metals. Applying a reasonable range of La(III) is beneficial to improving S. nigrum growth and tolerance of heavy metals. Compared with spraying deionized water, the translocation factor and bioaccumulation factor value of S. nigrum to cadmium increased by 15% and 21% respectively when spraying 10 μM La(III). Our findings provide a reference for improving hyperaccumulator plant growth and biomass, which improves phytoremediation efficiency.

Proteomic analysis reveals differential responsive mechanisms in Solanum nigrum exposed to low and high dose of cadmium

Cadmium (Cd) contamination is becoming a widespread environmental problem. However, the differential responsive mechanisms of Cd hyperaccumulator Solanum nigrum to low or high dose of Cd are not well documented. In this study, phenotypic and physiological analysis firstly suggested that the seedlings of S. nigrum showed slight leaf chlorosis symptoms under 25 μM Cd and severe inhibition on growth and photosynthesis under 100 μM Cd. Further proteomic analysis identified 105 differentially expressed proteins (DEPs) in the Cd-treated leaves. Under low dose of Cd stress, 47 DEPs are mainly involved in primary metabolic processes, while under high dose of Cd stress, 92 DEPs are mainly involved in photosynthesis, energy metabolism, production of phytochelatin and reactive oxygen species (ROS). Protein-protein interaction (PPI) network analysis of DEPs support above differential responses in the leaves of S. nigrum to low and high dose of Cd treatments. This work provides the differential responsive mechanisms in S. nigrum to low and high dose of Cd, and the theoretical foundation for the application of hyperaccumulating plants in the phytoremediation of Cd-contaminated soils.

Insight into the subcellular mechanism of maximizing Cd accumulation in hyperaccumulator Solanum nigrum L. under the action of biodegradable chelating agent

Under the promotion of biodegradable chelating agents, hyperaccumulators can accumulate large amounts of heavy metals. However, in practical application, excessive accumulation of heavy metals will lead to the reduction of biomass, resulting in the reduction of heavy metal accumulation efficiency. Therefore, here we seek to investigate the dynamic process of vacuolar compartmentalization regulated by biological chelators, to provide guidance for improving the accumulation efficiency of heavy metals and alleviating the reduction of biomass. In this study, subcellular isolation was used to study the changes of enzyme activities, total cadmium (Cd), Cd2+, glutathione and reactive oxygen species (ROS) contents in protoplasts and vacuoles of leaf cells of Solanum nigrum L. The results indicate that vacuolar compartmentalization is a dynamic regulation process of continuous glutathione consumption. Under the promotion of biodegradable chelating agent N, N-bis glutamic acid (GLDA), more glutathione was induced and preferentially entered the vacuole to chelate and store Cd. Moreover, for large amounts of Cd accumulation, the insufficient supply of glutathione (GSH) preferentially maintains vacuolar homeostasis and causes redox damage outside the vacuole. These results showed that insufficient glutathione production led to the reduction of biomass. Therefore, in the practical application of GLDA, the consumption inside and outside the vacuole can be met by controlling the production of glutathione, so as to increase the efficiency of heavy metal accumulation.

Attenuating Effect of an Extract of Cd-Hyperaccumulator Solanum nigrum on the Growth and Physio-chemical Changes of Datura innoxia Under Cd Stress

PurposeThe use of plant extracts obtained from plants that are highly tolerant to heavy metal toxicity has been beneficial in improving the growth of plants grown under metal toxicity conditions. A lab experiment was performed to elucidate the alleviating role of foliar applied cadmium (Cd)-hyperaccumulator Solanum nigrum (S. nigrum) extract on Datura innoxia (D. innoxia) plants grown under Cd stress (0, 50, and 100 mg Cd kg-1 soil).MethodsGrowth parameters, photosynthetic pigment content, osmo-metabolic compounds, reduced glutathione and phytochelatins content, oxidative damage, and lignin content and its related enzyme (cell wall-bound peroxidase, POX) were determined.ResultsApart from the foliar application response of S. nigrum leaf extract (SNE) in either Cd exposed or non-Cd exposed plants, growth parameters of D. innoxia plant grown under both Cd concentrations (50 and 100 mg Cd kg-1 soil) in terms of root and shoot fresh, dry weight, length, and leaf area were noticeably diminished by 29 and 51%, 29 and 54%, 35 and 70%, 40 and 53%, 30 and 69%, 40 and 60%, and 11 and 23%, respectively, compared with untreated control plants. Foliar delivered SNE secured the photosynthetic pigment, free amino acids, soluble proteins, and soluble sugar content. Additionally, it lessened the adverse effects of Cd stress on D. innoxia plants by curtailing the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) by 28 and 27%, and 21 and 23%, respectively, compared with the plants subjected to 50 and 100 mg Cd kg-1 only. The findings herein indicated that the plant water extract and their interactions in the investigated Cd rates significantly augmented phenolics, alkaloids, reduced glutathione and phytochelatins content. Cell wall stiffening in D. innoxia indicated that lignin content and POX were significantly higher in plants exposed to 100 mg Cd kg-1 soil displaying increase values of 275 and 300%, respectively, against non-Cd treated control. The magnitude of increment imposed by Cd stress was lessened by using SNE that reflects on adequate cell growth advocated by limited lignification, in terms of lignin content, and downregulated POX activity. Owing to SNE application, root and leaves Cd contents were efficiently reduced reflecting apparent plant liveliness compared with the SNE non-treated Cd-stressed plants.ConclusionsThe outcomes of this study designate that foliar application of the Cd-hyperaccumulator S. nigrum leaf extract can be counted as an unconventional and innovative approach in the alleviation of Cd stress and can be employed as integrated practice when Cd-contaminated regions were exploited for sustainable agriculture of the multipurpose plants.

Cadmium promotes the absorption of ammonium in hyperaccumulator Solanum nigrum L. mediated by ammonium transporters and aquaporins

Cadmium (Cd) is a toxic heavy metal affecting the normal growth of plants. Nitrate (NO3−) and ammonium (NH4+) are the primary forms of inorganic nitrogen (N) absorbed by plants. However, the mechanism of N absorption and regulation under Cd stress remains unclear. This study found that: (1) Cd treatment affected the biomass, root length, and Cd2+ flux in Solanum nigrum seedling roots. Specifically, 50 μM Cd significantly inhibited NO3− influx while increased NH4+ influx compared with 0 and 5 μM Cd treatments measured by non-invasive micro-test technology. (2) qRT-PCR analysis showed that 50 μM Cd inhibited the expressions of nitrate transporter genes, SnNRT2;4 and SnNRT2;4-like, increased the expressions of ammonium transporter genes, SnAMT1;2 and SnAMT1;3, in the roots. (3) Under NH4+ supply, 50 μM Cd significantly induced the expressions of the aquaporin genes, SnPIP1;5, SnPIP2;7, and SnTIP2;1. Our results showed that 50 μM Cd stress promoted NH4+ absorption by up-regulating the gene expressions of NH4+ transporter and aquaporins, suggesting that high Cd stress can affect the preference of N nutrition in S. nigrum.

Cosmopolitan cadmium hyperaccumulator Solanum nigrum: Exploring cadmium uptake, transport and physiological mechanisms of accumulation in different ecotypes as a way of enhancing its hyperaccumulative capacity

The non-essential element cadmium (Cd) is one of the most problematic priority soil pollutants due to multitude of pollution sources, mobility in the environment and high toxicity to all living organisms. This strongly limits also the number and occurrence of species – Cd hyperaccumulators to be used for soil phytoremediation. However, efficient Cd hyperaccumulator Solanum nigrum L. appeared to commonly occur worldwide as a representative of Solanum nigrum complex of a great taxonomic diversity. This led to the idea that the search among different ecotypes of Solanum nigrum L. may result in the identifying the most efficient Cd hyperaccumulator without applying to soil any additional measures such as chemical ligands. In this first pioneering comparative study, three randomly selected ecotypes of S. nigrum L. ssp. nigrum from Shenyang (SY) and Hanzhong (HZ) in China, and Kyoto (KY) in Japan were used in pot experiments at soil treatments from 0 to 50 mg Cd kg−1. The Cd accumulation capacity appeared to represent KY > HZ > SY range, KY ecotype accumulating up to 73%, and HZ ecotype up to 67% bigger total Cd load than SY ecotype. At Cd content in soil up to 10 mg kg−1, no significant effect on the all ecotype biomass, photosynthetic activities, contents of first line defense antioxidant enzymes (CAT, SOD, GPX), and scavenging antioxidants ASA, GSH, was observed. At Cd in soil>10 mg kg−1all these parameters showed decreasing, and cell damage indicator MDA increasing trend, however total accumulated Cd load further increased up to 30 mg kg Cd in soil in all ecotypes in the same KY > HZ > SY sequence. The study proved the great potential of enhancing Cd accumulation capacity of S. nigrum species by selecting the most efficient ecotypes among commonly occurring representatives of S. nigrum complex worldwide. Moreover, these first comparative experiments convinced that the cosmopolitan character and great variety of species/subspecies belonging to Solanum nigrum complex all over the world opens the new area for successful soil phytoremediation with the use of the most appropriate eco/genotypes of S. nigtum as a tool for the best Cd-contaminated soil management practice.

Cadmium removal potential of hyperaccumulator Solanum nigrum L. under two planting modes in three years continuous phytoremediation

Solanum nigrum L. is a Cd hyperaccumulator, but the potential for continuous remediation, or different planting methods have not been fully characterized. The potential for continuous phytoremediation of Cd-contaminated farmland soil (2.08 mg kg−1 Cd) by 2 planting methods (flowering harvest twice a year and maturity harvest once a year) was studied in a 3-year pot experiment. The total Cd accumulation (ug plant−1) of the 3-year flowering stage treatments was 26.3% higher than that of the maturity stage treatments, which was mainly due to that flowering harvest twice a year caused 65.5% increase of shoot biomass. Similarly, the Cd decreased concentration in soil and Cd removal rate in the flowering stage treatments were 29.2% and 27.9% higher than that in the maturity stage treatments, respectively. After 3 years of phytoremediation, the extractable Cd concentration in soil was reduced by 36.4% in the flowering stage treatments and by 27.6% in the maturity stage treatments, which also led to the same decreasing trend of Cd accumulation of S. nigrum. In conclusion, the study results have demonstrated that the planting mode of two harvests a year at the flowering stage seems to be a viable option to apply for continuous phytoremediation of Cd-contaminated farmland soil.

Continuous Phytoremediation Potential Comparison of Cd Contaminated Soil by Hyperaccumulator Solanum Nigrum L. Under Two Planting Modes

Continuous Phytoremediation Potential Comparison of Cd Contaminated Soil by Hyperaccumulator Solanum Nigrum L. Under Two Planting Modes

Ammonium has stronger Cd detoxification ability than nitrate by reducing Cd influx and increasing Cd fixation in Solanum nigrum L.

Cadmium (Cd) is a harmful heavy metal that affects the growth and development of plants. Nitrogen (N) is an essential nutrient for plants, and appropriate N management can improve Cd tolerance. The aim of our study was to explore the effects of different forms of N on the molecular and physiological responses of the hyperaccumulator Solanum nigrum to Cd toxicity. Measurement of biomass, photosynthetic parameters, and Cd2+ fluxes using non-invasive micro-test technique, Cd fluorescent dying, biochemical methods and quantitative real-time PCR analysis were performed in our study. Our results showed that ammonium (NH4+) has stronger Cd detoxification ability than nitrate (NO3-), which are likely attributed to the following three reasons: (1) NH4+ decreased the influx and accumulation of Cd2+ by regulating the transcription of Cd transport-related genes; (2) the ameliorative effects of NH4+ were accompanied by the increased retention of Cd in the cell walls of roots; and (3) NH4+ up-regulated SnExp expression.

Comparative study on different organic acids for promoting Solanum nigrum L. hyperaccumulation of Cd and Pb from the contaminated soil

Organic acids-assisted phytoremediation is a promising strategy to remove metal pollutants from the soil. However, few reports have focused on the mechanisms of organic acids promoting the uptake of heavy metals by hyperaccumulators. In this study, 5 types of organic acids, namely polybasic carboxylic acids, acidic amino acids, acidic plant growth regulators, phosphoric and gluconic acids, were comprehensively investigated the effects on the solubility of Cd and Pb in the soil along with their uptake by Cd hyperaccumulator Solanum nigrum L. The results indicated that the addition of Hydroxyethylidene-1,1-diphosphonic acid (HEDP) and d-Gluconic acid (D-GA) effectively extracted the most of acid-extractable and some of reducible and oxidizable fractions of Cd and Pb in the soil, with the extraction rates of 64.8% and 34.4% for total Cd and 53.6% and 30.0% for total Pb, respectively. HEDP and D-GA significantly increased the accumulations of Cd (57.1% and 35.0%) and Pb (43.4% and 31.9%) by S. nigrum without the inhibition of its biomass, making the great removal efficiencies of Cd (1.35% and 1.16%) and Pb (0.039% and 0.036%) from the soil. The enhanced phytoremediation efficiency of S. nigrum was due to the increase of the extractable Cd and Pb in the rhizosphere but little changes of soil pH and enzyme activities (catalase and urease). Among all of organic acids, HEDP may be an alternative to EDTA because of its characteristics of environmental friendliness and high efficiency.

Small structures with big impact: Multi-walled carbon nanotubes enhanced remediation efficiency in hyperaccumulator Solanum nigrum L. under cadmium and arsenic stress

With the fast development of nanotechnology, nanomaterials are being increasingly applied for the remediation of contaminated soils. However, few researches have been reported on the complex interactions of carbon nanotubes with heavy metal (loid)s in phytoremediation. Here, we conduct a pot experiment to investigate the effects of multi-walled carbon nanotubes (MWCNTs) on the plant growth and behavior of heavy metal (loid)s in hyperaccumulator-soil system. Cd hyperaccumulator Solanum nigrum L. (S. nigrum) were cultivated in Cadmium (Cd) and Arsenic (As) contaminated soils amended with MWCNTs at 100, 500, and 1000 mg kg−1 for 60 days, respectively. The application of MWCNTs increased the shoot length and plant dry biomass by 5.56%∼25.13% and 5.23%∼27.97%. Whereas, root and leaf growth were inhibited in 1000 mg kg−1 MWCNTs treatments. Meanwhile, MWCNTs at 500 mg kg−1 significantly enhanced the accumulation of heavy metal (loid)s in S. nigrum（18.29% for Cd and 32.47% for As）and alleviated co-contamination induced toxicity, by motivating plant growth, stimulating antioxidant enzymatic activities, and increasing micronutrient content (p < 0.05). The bio-concentration factor of As was decreased (15.31–28.08%) under MWCNTs application, which plays an important role in the alleviation of phytotoxicity. Besides, bioavailable Cd and As were reduced in rhizosphere soils, and the most significant reduction (16.29% for Cd and 8.19% for As) were shown in 500 mg kg−1 MWCNTs treatment. These findings demonstrate that suitable concentration of MWCNTs can enhance remediation efficiency. Our study gives a strong evidence to promote the phytoremediation for co-contaminated soils by using nanomaterials.

Strong accumulation capacity of hyperaccumulator Solanum nigrum L. for low or insoluble Cd compounds in soil and its implication for phytoremediation

This experiment is to explore whether one hyperaccumulator shows the strongly accumulative capacities for low or insoluble Cd compounds in soil. Soil potting experiment was conducted to analyze the accumulation capacity of Solanum nigrum L. for 10 different Cd compounds under two levels. The results clearly indicated: The Cd concentrations of shoots and roots were very high for different Cd compounds in soils even with low or insoluble Cd compounds compared with easily soluble Cd in the treatments of soil contaminated with Cd at different concentrations. Furthermore, the EFs and TFs were all larger than 1 either. Based on the results, although the bioavailabilities of some Cd compounds in soil were lower, S. nigrum’s ability to accumulate them was still very strong. Phytoremediation may be widely used to treat with soil contaminated by different cadmium compounds. In addition, the total Cd content is also very important in evaluating the risk of Cd contamination in soil. Thus, phytoextraction is promising.

Optimal voltage and treatment time of electric field with assistant Solanum nigrum L. cadmium hyperaccumulation in soil

We have attempted to obtain optimal conditions of direct current electrical field with switching polarity to increase Cd accumulation of the hyperaccumulator Solanum nigrum L. from soil. The effects of different voltages and treatment times on S. nigrum accumulating Cd were determined. The results showed that Cd concentration in S. nigrum under all electrical field conditions were significantly higher (p < 0.05) than that of the CK. The Cd concentration in shoot and root of treatment T3 (3 V cm−1) were higher than the equal results of treatment T2 (2 V cm−1) and T1 (1 V cm−1) under the same condition of 6 h d−1 treatment time. In different treatments concerning time of T1 (6 h d−1), T4 (10 h d−1) and T5 (14 h d−1) under same voltage of 1 V cm−1, the S. nigrum Cd concentration were with similar trend to the different voltage treatments (T5 with the highest Cd concentration). These results might be caused by positive change trends of pH, EC and extractable Cd concentration in soil. However, the S. nigrum biomasses of T3 were the lowest and the highest biomass happened in treatment of T4. Finally, the highest Cd accumulation in S. nigrm (μg pot−1) was the T4 with the condition of 1 V cm−1 and 10 h d−1, which was also the optimal voltage and treatment time of the electric field. The optimal conditions were important references in the practice of combined use of electrokinetic remediation and phytoremediation.