Distribution and chemical forms of copper in the root cells of castor seedlings and their tolerance to copper phytotoxicity in hydroponic culture

Microbe-citric acid assisted phytoremediation of chromium by castor bean (Ricinus communis L.)

Chromium is one of the highly toxic heavy metals to plant growth and development especially hexavalent chromium (Cr+6) due to its readily available nature and mobility into the environment. The chelating agents and hyperaccumulator plant can contribute to remediating the heavy metals from the contaminated medium. This study was conducted to analyze the role of citric acid and chromium resistant bacteria in castor bean to remediate Cr+6 from the polluted soil. The soil was spiked with different levels of citric acid (0, 2.5, 5 mM) and chromium (0, 10, 20 mg kg-1). The ripened plants were harvested and analyzed for growth parameters, chlorophyll contents, gas exchange parameters, oxidative stress markers, antioxidant enzymes activities and chromium accumulation in different parts of plants. The high concentration of chromium 20 mg kg-1 drastically reduced the plant growth, decreased photosynthetic rate and increased oxidative stress. The application of CA improved the plant growth even at the highest concentration of chromium which was further boosted by the combined application of CA and chromium resistant bacteria. However, the performance of staphylococcus aureus was found significantly better than Bacillus subtilis due to its better ability to tolerate chromium toxicity even at high concentrations. The findings proved that castor bean has excellent potential to tolerate high chromium concentrations and can be effectively used to remediate metals contaminated soil. Further, CA and metal resistant bacteria can significantly enhance the phytoremediation potential of castor bean and other hyperaccumulator plants. The bacteria assisted phytoremediation coupled with the chelating agent can be a practical approach to remediate the metals contaminating soils.

Selection for low-cadmium cultivars and cadmium subcellular distribution comparison between two selected cultivars of eggplant (Solanum melongena L.)

Excessive accumulation of cadmium (Cd) in vegetables poses a serious threat to human health; therefore, it is urgent to screen and cultivate vegetable cultivars with low Cd accumulation in the edible parts. Eggplant has a high tendency for Cd accumulation, but research on its low Cd accumulation cultivars is still rare. In this study, to screen low-Cd cultivars, 30 eggplant cultivars were screened using soils containing 0.22 mg/kg, 2.9 mg/kg (low-Cd), and 4.7 mg/kg of Cd (high-Cd). MYCQ and ZGQ were confirmed as low-Cd cultivars, BXGZ and WCCQ were confirmed as high-Cd cultivars, and a 2.52-3.88-fold difference in Cd concentration was observed in their fruits. The subcellular distribution revealed that the root cell wall and vacuole Cd concentrations of a typical low-Cd cultivar (MYCQ) were significantly higher than those of a typical high-Cd cultivar (BXGZ); however, the Cd concentrations in the cell wall and vacuole in fruits, leaves, and stems were significantly lower in MYCQ than in BXGZ. These results indicated that the low-Cd cultivars of eggplant could lessen Cd toxicity through the elevated Cd retention and sequestration levels of root cell walls and vacuoles, thus reducing Cd transport from roots to aboveground tissues, leading to low Cd accumulation. The findings of this study can provide a physiological and biochemical foundation for the screening and breeding of low-Cd cultivars of fruit vegetables and demonstrates that the application of low-Cd cultivars is necessary for food safety in humans.

Malus rootstocks affect copper accumulation and tolerance in trees by regulating copper mobility, physiological responses, and gene expression patterns

We investigated the roles of rootstocks in Cu accumulation and tolerance in Malus plants by grafting 'Hanfu' (HF) scions onto M. baccata (Mb) and M. prunifolia (Mp) rootstocks, which have different Cu tolerances. The grafts were exposed to basal or excess Cu for 20 d. Excess Cu-treated HF/Mb had less biomass, and pronounced root architecture deformation and leaf ultrastructure damage than excess Cu-challenged HF/Mp. Root Cu concentrations and bio-concentration factor (BCF) were higher in HF/Mp than HF/Mb, whereas HF/Mb had higher stem and leaf Cu concentrations than HF/Mp. Excess Cu lowered root and aerial tissue BCF and translocation factor (T_f) in all plants; however, T_f was markedly higher in HF/Mb than in HF/Mp. The subcellular distribution of Cu in the roots and leaves indicated that excess Cu treatments increased Cu fixation in the root cell walls, which decreased Cu mobility. Compared to HF/Mb, HF/Mp sequestered more Cu in its root cell walls and less Cu in leaf plastids, nuclei, and mitochondria. Moreover, HF/Mp roots and leaves had higher concentrations of water-insoluble Cu compounds than HF/Mb, which reduced Cu mobility and toxicity. Fourier transform infrared spectroscopy analysis showed that the carboxyl, hydroxyl and acylamino groups of the cellulose, hemicellulose, pectin and proteins were the main Cu binding sites in the root cell walls. Excess Cu-induced superoxide anion and malondialdehyde were 28.6% and 5.1% lower, but soluble phenolics, ascorbate and glutathione were 10.5%, 41.9% and 17.7% higher in HF/Mp than HF/Mb leaves. Compared with HF/Mb, certain genes involved in Cu transport were downregulated, while other genes involved in detoxification were upregulated in HF/Mp roots and leaves. Our results show that Mp inhibited Cu translocation and mitigated Cu toxicity in Malus scions by regulating Cu mobility, antioxidant defense mechanisms, and transcription of key genes involved in Cu translocation and detoxification.

Evaluation of two wild castor (Ricinus communis L.) accessions for cadmium tolerance in relation to antioxidant systems and lipid peroxidation

The present study was conducted to assess the effect of toxicity of cadmium (Cd) on growth, tolerance index (TI), antioxidant activities, and malondialdehyde (MDA) content in two contrasting wild castor accessions (16-024 and S2-4) via hydroponic experiment (0 and 100 mg/L Cd). The results showed that Cd significantly reduced the growth rate, seedling height, root length, and shoot length of the castor accessions compared to the control, with the Cd effect being more severe in S2-4 than in 16-024. In addition, biomass response including the root and shoot fresh weight and root dry weight decreased in both accessions compared to the control. Compared to the control group, the shoot dry weight of accession S2-4 declined by 21.7%, whereas there was no change in 16-024, suggesting a level of tolerance in 16-024. Analysis of TI on all the growth parameters and biomass content revealed that accession 16-024 was highly tolerant to Cd stress than S2-4. The results further revealed that the expression of the antioxidant enzymes, viz., superoxide dismutase (SOD), catalase (CAT), non-enzymatic antioxidant, glutathione, and MDA content, was influenced by genotype. S2-4 exhibited a higher antioxidant activity (SOD, CAT) and lipid peroxidation activity than 16-024, indicative of oxidative damage from Cd stress.

The positive effects of inoculation using arbuscular mycorrhizal fungi and/or dark septate endophytes on the purification efficiency of CuO-nanoparticles-polluted wastewater in constructed wetland

The extent to which, and mechanisms by which, arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) purify wetlands polluted by metallic nanoparticles (metallic NPs) are not well understood. In this study, micro-vertical flow constructed wetlands (MVFCWs) with the Phragmites australis (reeds)-AMF/DSE symbiont were used to treat CuO nanoparticles (CuO-NPs)-polluted wastewater. The results showed that (1) the removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and CuO-NPs in three inoculated groups significantly exceeded those in the control check (CK) groups by 28.94-98.72%, 16.63-47.66%, and 0.53-19.12%, respectively; (2) inoculation with AMF and/or DSE significantly promoted the growth, nutrient content, and photosynthesis of reeds, increased the osmoregulation substance content and antioxidant enzyme activities, and decreased the malondialdehyde and reactive oxygen species contents of reeds under CuO-NPs stress; (3) higher Cu accumulation and smaller transport coefficients were found in the inoculated groups than in the CK group; (4) inoculation with AMF and/or DSE changed the subcellular structure distribution and chemical form of Cu in reeds. We therefore conclude that inoculation with AMF and/or DSE in MVFCWs improves the purification of CuO-NPs-polluted wastewater, and the MVFCW-reeds-AMF/DSE associations exhibit great potential for application in remediation of metallic-NPs-polluted wastewater.

Tolerance capacities of Broussonetia papyrifera to heavy metal(loid)s and its phytoremediation potential of the contaminated soil

Broussonetia papyrifera, is a promising fast-growing woody plant for the phytoremediation of heavy metal(loid) (HM)-contaminated soil. In this study, a greenhouse experiment was conducted to explore the tolerance capacities of B. papyrifera and its phytoremediation potential in the HM-contaminated soil. The results indicated that B. papyrifera could effectively decrease malondialdehyde (MDA) content by enhancing the antioxidant enzyme activities along with the cultivation in the HM-contaminated soil. Significant (p < 0.05) negative relationships were found between MDA content and superoxide dismutase (r = -0.620) and catalase activities (r = -0.702) in B. papyrifera leaves. Fourier Transform Infrared Spectroscopy analysis indicated that the main functional groups in B. papyrifera roots were slightly influenced by HMs, and organic acids, carbohydrates, protein, and amino acids might bind with HMs in plant roots to alleviate the adverse effect of HMs on plants growth. Meanwhile, B. papyrifera had great potential used for the phytoextraction of Cd and Zn in HM-contaminated soil. The maximum total Cd and Zn accumulation amount in B. papyrifera shoots could attach to 2.26 and 66.8 mg·pot^-1, respectively. These observations suggested that B. papyrifera has large biomass and high tolerance to HMs, which can be regarded as a promising plant for the eco-remediation of HM-contaminated sites.Novelty statement In this study, a fast-growing woody plant, Broussonetia papyrifera, was used for heavy metal(loid) (HM)-contaminated soil remediation. We found that B. papyrifera can effectively alleviate the adverse effect of HMs on plant growth by enhancing the antioxidant enzyme activities in leaves and binding HMs with organic acids, carbohydrates, protein, and amino acids in roots. Furthermore, the maximum total Cd and Zn accumulation amount in B. papyrifera shoots could attach to 2.26 and 66.8 mg·pot^-1, which suggested that B. papyrifera might be regarded as a promising woody plant used for the phytoextraction of Cd and Zn in the contaminated soil.

Phytotoxicity and accumulation of Cu in mature and young leaves of submerged macrophyte Hydrilla verticillata (L.f.) Royle

Phytotoxicity and accumulation of Cu in mature and young leaves of submerged macrophyte Hydrilla verticillata (L.f.) Royle were investigated by analyzing the chlorophyll contents, chloroplast ultrastructure and leaf surface structure under different Cu treatments (0, 0.01, 0.05 and 0.1 f mg L^-1). The results showed that 0.05 and 0.1 mg L^-1 Cu treatment decreased the contents of Chl a and Chl b, and caused damage on leaf surface structure and chloroplast ultrastructure compared with control (0 mg L^-1 Cu treatment). Higher concentration of Cu induced Chlorophyll decreases and the damages on the leaf surface structure and chloroplast ultrastructure were more pronounced in mature than in young leaves. It was observed that leaf Cu concentration increased almost linearly with exposure time and majority of the Cu accumulated in the cell walls. Among different cell wall fractions, the majority of Cu accumulated in cell walls was bound to the hemicellulose 1 and cellulose, followed by the pectin, hemicellulose 2. Mature leaves had significantly higher the concentrations of total Cu and bound-Cu in cell walls due to higher uronic acid content in their cell wall fractions (pectin, hemicellulose 1 and cellulose) than young leaves. Distinct cell wall composition might partially contribute to the different Cu toxicity and accumulation between mature and young leaves of submerged macrophyte H. verticillata. Our results show that mature leaves are more efficient in the uptake and accumulation of Cu than young leaves, which might explain why mature leaves sustain more severe damage.

Effects of low molecular weight organic acids on Cu accumulation by castor bean and soil enzyme activities

Chelating agents have been considered as an important phytoremediation strategy to enhance heavy metal extraction from contaminated soil. A pot experiment was conducted to explore the effects of low molecular weight organic acids (LMWOAs) on the phytoremediation efficiency of copper (Cu) by castor bean, and soil enzyme activities. Results indicated that the addition of all the three kinds of LMWOAs (citric, tartaric, oxalic acids) did not decrease the biomass of castor bean, despite the fact they reduced the concentration of chlorophyll-a in leaves compared to the control. The Cu concentrations in the roots and shoots significantly increased by 6-106% and 5-148%, respectively, in the LMWOAs treatments so that the total accumulation of Cu by whole plants in all the LMWOAs treatments increased by 21-189% in comparison with the control. The values of the translocation factor (TF) and bio-concentration factor (BCF) of Cu in castor bean also rose following the addition of LMWOAs, indicating that the LMWOAs enhanced the uptake and transportation of Cu. Moreover, the application of LMWOAs did not significantly change the soil pH but significantly increased the activity of soil enzymes (urease, catalase, and alkaline phosphatase). The addition of exogenous LMWOAs increased the available Cu significantly in the soil, thus promoted the phytoextraction efficiency of Cu by castor bean. These results will provide some new insights into the practical use of LMWOAs for the phytoremediation of heavy-metal-contaminated soil employing castor bean.

Variations of dissolved organic matter and Cu fractions in rhizosphere soil induced by the root activities of castor bean

The root soil interaction affects metal bioavailability in the rhizosphere, thus impacting the uptake and accumulation of metals by plants. In this study, a greenhouse experiment using a root-bag technique for castor bean plants was conducted to determine the i) rhizosphere effect on the fractions of Cu, and ii) the characteristics of dissolved organic matter (DOM) in the rhizosphere soil. Results showed that the Cu concentration in the leaves, stems, and roots was 15.41, 6.71, and 47.85 mg kg-1, respectively, in the control and reached up to 96.5, 254.9, and 3204 mg kg-1 in Cu400 treatment, respectively. After cultivating castor bean plants, the concentration of acid exchangeable Cu in rhizosphere soil was higher than that in the bulk soil for the same Cu addition, whereas the concentrations of reducible Cu, oxidizable Cu, and residual Cu in the rhizosphere soil were all lower than those in the bulk soil, respectively. In comparison to the bulk soil, the pH decreased while the total nitrogen and total carbon concentrations both increased in the rhizosphere soil. Moreover, the concentrations of total low molecular weight organic acids (LMWOAs) and total amino acids in the rhizosphere soil of the Cu treatments increased by between 15.18% to 47.17% and 36.35%-200%, respectively with respect to the control. The less complex DOM with a high LMWOAs concentration in the rhizosphere soil shifted the soil Cu from a relative stable fraction to available fractions.

Phytoremediation of soil heavy metals (Cd and Zn) by castor seedlings: Tolerance, accumulation and subcellular distribution

Cd and Zn pollution was observed to often occur simultaneously in soils. However, previous studies focused on single heavy metal instead of Cd and Zn combined pollution. Castor (Ricinus communis) is considered to have great potential for contaminated soil remediation. The resistance of castor seedlings to heavy metals and the mechanism behind it remain unknown. In this study, the tolerance and accumulation ability of castor seedlings to Cd and Zn were investigated, and the accumulation mechanism involving the subcellular distribution in different tissues was further explored. The results on biomass and chlorophyll revealed that castor seedlings have good tolerance to the pollution with 0-5 mg/kg Cd and 380 mg/kg Zn, while not to the heavy pollution with 25 mg/kg Cd and 380 mg/kg Zn. The maximum accumulation concentrations of Cd and Zn, 175.3 mg Cd/kg and 386.8 mg/kg Zn, appeared in castor seedling root instead of stem and leaf, indicating that root played a significant part in accumulating Zn and Cd. The relative low dosage of Cd (0-5 mg/kg) promoted the accumulation of Zn in the subcellular component, while high dosage (25 mg/kg) inhibited the accumulation of Zn. In subcellular accumulation and distribution of castor seedlings, Cd (27.1%-69.4%) and Zn (39.6%-66.6%) in the cell wall was the highest. With the increase of Cd addition, the accumulation of Cd increased in cell wall while decreased in organelle and soluble fraction. Hydroxyl, amino, amides and carboxyl functional groups on cell wall might provided the main binding sites for Cd and Zn.

Contributions of root cell wall polysaccharides to Cu sequestration in castor (Ricinus communis L.) exposed to different Cu stresses

Cell wall polysaccharides play a vital role in binding with toxic metals such as copper (Cu) ions. However, it is still unclear whether the major binding site of Cu in the cell wall varies with different degrees of Cu stresses. Moreover, the contribution of each cell wall polysaccharide fraction to Cu sequestration with different degrees of Cu stresses also remains to be verified. The distribution of Cu in cell wall polysaccharide fractions of castor (Ricinus communis L.) root was investigated with various Cu concentrations in the hydroponic experiment. The results showed that the hemicellulose1 (HC1) fraction fixed 44.9%-67.8% of the total cell wall Cu under Cu stress. In addition, the pectin fraction and hemicelluloses2 (HC2) fraction also contributed to the Cu binding in root cell wall, accounting for 11.0%-25.9% and 14.1%-26.6% of the total cell wall Cu under Cu treatments, respectively. When the Cu levels were ≤25 μmol/L, pectin and HC2 contributed equally to Cu storage in root cell wall. However, when the Cu level was higher than 25 μmol/L, the ability of the pectin to bind Cu was easy to reach saturation. Much more Cu ions were bound on HC1 and HC2 fractions, and the HC2 played a much more important role in Cu binding than pectin. Combining fourier transform infrared (FT-IR) and two-dimensional correlation analysis (2D-COS) techniques, the hemicellulose components were showed not only to accumulate most of Cu in cell wall, but also respond fastest to Cu stress.

Influence of nitrogen forms and application rates on the phytoextraction of copper by castor bean (Ricinus communis L.)

Fertilization is an important agricultural strategy for enhancing the efficiency of phytoremediation in copper (Cu)-contaminated soils. In this study, the effects of nitrogen (N) forms, including ammonium (NH4+-N) and nitrate (NO3--N), on the growth, translocation, and accumulation of Cu in the tissues of Ricinus communis L. were investigated in pot and hydroponic experiments. The results demonstrated that higher biomass and N contents in plants were obtained when N was supplied as NO3--N rather than NH4+-N. Application of N increased the Cu content in the roots of R. communis, with a higher content after NH4+-N (53.10-64.20 mg kg-1) than NO3--N (37.62-53.75 mg kg-1) treatment. On the contrary, the levels of Cu translocation factors were much higher in NO3--fed plants (0.34-0.45) than in NH4+-fed plants (0.28-0.38). The suggested amount of N for fertilizer application is 225 kg hm-2, which resulted in the highest Cu content in R. communis and optimal plant growth. As the main Cu-binding site, root cell walls accumulated less Cu in plants treated with NH4+-N compared with NO3--N. Additionally, NH4+-N induced a higher malondialdehyde content and more severe root damage compared with NO3--N. In the leaf, a larger number of black granules, which could be protein and starch grains involved in the detoxification of Cu in R. communis, were present after NH4+-N than NO3--N treatment. These results illustrate that N forms are especially important for Cu translocation and accumulation and that immobilization and transformation of Cu in roots were improved more by NH4+-N than NO3--N. In conclusion, N fertilizers containing the appropriate forms applied at suitable rates may enhance the biomass and Cu accumulation of R. communis and thereby the remediation efficiency of Cu-contaminated soils.

Differential responses of growth, photosynthesis, oxidative stress, metals accumulation and NRAMP genes in contrasting Ricinus communis genotypes under arsenic stress

Effect of arsenate [As(V)] on biomass, photosynthetic rate, stomatal conductance, transpiration, oxidative stress, accumulation of As, Fe, Zn, Cu and Mn and expression of NRAMP genes was investigated in As(V) tolerant and sensitive genotypes of bioenergy crop Ricinus communis. As(V) treatments (100 and 200 μM) led to significant reduction in root and leaf biomass, photosynthetic rate, stomatal conductance and transpiration in GCH 2 and GCH 4 genotypes but no significant change or increase was observed in WM and DCH 177 genotypes. No significant difference was observed in hydrogen peroxide content and lipid peroxidation in As(V)-treated tolerant genotypes compared to control, whereas these parameters enhanced significantly in As(V)-treated sensitive genotypes. GCH 2 accumulated around two times As in leaves and showed significant reduction in concentration of Zn and Mn in the leaves and roots due to 200 μM As(V) treatment compared to WM. NRAMP genes are critical for uptake and distribution of essential divalent metal cations, photosynthesis and controlled production of reactive oxygen species in plants. RcNRAMP2, RcNRAMP3 and RcNRAMP5 genes showed differential expression in response to 200 μM As(V) in GCH 2 and WM suggesting that NRAMP genes are associated with differential responses of WM and GCH 2 genotypes to As(V) stress.

Copper accumulation, subcellular partitioning and physiological and molecular responses in relation to different copper tolerance in apple rootstocks

To unravel the physiological and molecular regulation mechanisms underlying the variation in copper (Cu)accumulation, translocation and tolerance among five apple rootstocks, seedlings were exposed to either basal or excess Cu. Excess Cu suppressed plant biomass and root architecture, which was less pronounced in Malus prunifolia Borkh., indicating its relatively higher Cu tolerance. Among the five apple rootstocks, M. prunifolia exhibited the highest Cu concentration and bio-concentration factor in roots but the lowest translocation factor, indicating its greater ability to immobilize Cu and restrict translocation to the aerial parts. Higher Cu concentration in cell wall fraction but lower Cu proportion in membrane-containing and organelle-rich fractions were found in M. prunifolia. Compared with the other four apple rootstocks under excess Cu conditions, M. prunifolia had a lower increment of hydrogen peroxide in roots and leaves and malondialdehyde in roots, but higher concentrations of carbohydrates and enhanced antioxidants. Transcript levels of genes involved in Cu uptake, transport and detoxification revealed species-specific differences that are probably related to alterations in Cu tolerance. M. prunifolia had relatively higher gene transcript levels including copper transporters 2 (COPT2), COPT6 and zinc/iron-regulated transporter-related protein 2 (ZIP2), which probably took part in Cu uptake, and C-type ATP-binding cassette transporter 2 (ABCC2), copper chaperone for Cu/Zn superoxide dismutase (CCS), Cu/Zn superoxide dismutase 1 (CSD1) and metallothionein 2 (MT2) probably implicated in Cu detoxification, and relatively lower mRNA levels of yellow stripe-like transporter 3 (YSL3) and heavy metal ATPase 5 (HMA5) involved in transport of Cu to aerial parts. These results suggest that M. prunifolia is more tolerant to excess Cu than the other four apple rootstocks under the current experimental conditions, which is probably attributed to more Cu retention in roots, subcellular partitioning, well-coordinated antioxidant defense mechanisms and transcriptional expression of genes involved in Cu uptake, translocation and detoxification.

Effect of spent mushroom substrate on strengthening the phytoremediation potential of Ricinus communis to Cd- and Zn-polluted soil

Phytoremediation is a kind of efficient strategy for remediating soils polluted with heavy metals. The aim of this study was to investigate the influence of spent mushroom substrate (SMS) on the phytoremediation potential of Ricinus communis in Cd- and Zn-polluted soil. We treated the soil with SMS before growing plants and analyzed the contents, distribution of heavy metals, and response of plants after growth. SMS increased the contents of Cd (5%-13%) and Zn (16%-20%) in the cell wall. This finding suggested that high amounts of Cd and Zn were absorbed and bonded to the cell wall through metabolism adaption and formed stable compounds, which reduced the damage of the heavy metal to cells. SMS also decreased the levels of superoxide dismutase, peroxidase, and catalase by 9.5%-27.7%, 8.8%-30.0% and 8.5%-28.1%, respectively. Treatment of SMS alleviated the toxicity of heavy metal in plants and increased the extracted amounts of Zn and Cd by 101%-227% and 51%-189%, respectively. Hence, SMS treatment could reduce the toxicity of heavy metals to plants and strengthen the phytoremediation potential.

Stress response of NAD+-dependent formate dehydrogenase in Gossypium hirsutum L. grown under copper toxicity

Cotton (Gossypium hirsutum L.), which is not directly involved in the food chain, appears to be a suitable candidate to remove heavy metals from the food chain and to be a commercial plant which could be planted in contaminated soils. The key point of this approach is selection of the right genotype, which has heavy metal resistance or hyperaccumulation properties. Therefore, in the present study, two G. hirsutum genotypes, Erşan-92 and N-84S, were grown under copper stress and investigated to obtain further insights about the heavy metal tolerance mechanisms of plants by focusing on the expression of NAD⁺-dependent formate dehydrogenase (FDH). In accordance with the results, which were obtained from RT-PCR analysis and activity measurements, in the Erşan-92 root tissue, FDH activity increased significantly with increasing metal concentrations and a 6.35-fold higher FDH activity was observed in the presence of 100-μM Cu. As opposed to Erşan-92, the maximum FDH activity in the roots of N-84S, which were untreated with copper as the control plants, was measured as 0.0141-U mg^-1 g^-1 FW, and the activity decreased significantly with the increasing metal concentrations. The metallothionein (GhMT3a) transcript level of the plants grown in a medium containing different Cu concentrations showed nearly the same pattern as that of the FDH gene transcription. It was observed that while the tolerance of N-84S in the lower Cu concentration reduces remarkably, Erşan-92 continues to struggle up to 100-μM Cu. The results of the SOD analysis also confirm this activity of Erşan-92 against the Cu stress.

Influence of phosphorous fertilization on copper phytoextraction and antioxidant defenses in castor bean (Ricinus communis L.)

Application of fertilizers to supply appropriate nutrients has become an essential agricultural strategy for enhancing the efficiency of phytoremediation in heavy metal contaminated soils. The present study was conducted to investigate the beneficial effects of three types of phosphate fertilizers (i.e., oxalic acid-activated phosphate rock (APR), Ca(H2PO4)2, and NaH2PO4) in the range of 0-600 mg P kg-1 soil, on castor bean growth, antioxidants [antioxidative enzymes and glutathione (GSH)], and Cu uptake. Results showed that with the addition of phosphorus fertilizers, the dry weight of castor bean and the Cu concentration in roots increased significantly, resulting in increased Cu extraction. The phosphorus concentration in both shoots and roots was increased as compared with the control, and the Ca(H2PO4)2 treatment had the greatest effect. Application of APR, NaH2PO4, and Ca(H2PO4)2 reduced the malondialdehyde (MDA) content, and the activity of the two antioxidant enzymes superoxide dismustase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) in the leaves of castor bean. GSH concentration in leaves increased with the increasing levels of phosphorus applied to soil as well as the accumulation of phosphorus in shoots, compared to the control. These results demonstrated that the addition of phosphorus fertilizers can enhance the resistance of castor bean to Cu and increase the Cu extraction efficiency of the plant from contaminated soils.

Effects of sulfur on toxicity and bioavailability of Cu for castor (Ricinus communis L.) in Cu-contaminated soil

The biogeochemical cycling of sulfur (S) in soil has an important impact on the bioavailability of heavy metals and affects the utilization of soil polluted by heavy metals. In addition, S-containing compounds are involved in heavy metal detoxification. This study investigated the effects of S on the toxicity and bioavailability of copper (Cu) in castor (Ricinus communis L.) grown in Cu-contaminated mine tailings. The results showed that the application of S reduced the accumulation of Cu in castor and promoted its growth. With the addition of S, the malondialdehyde (MDA) content of castor leaves decreased significantly compared with control plants, indicating the alleviation of oxidative stress. Superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) content decreased significantly with the alleviation of oxidative stress. The sequential extraction of Cu fractions showed that the application of S significantly reduced the reducible Cu fraction, and increased the oxidizable Cu fraction. It also increased the residual Cu fraction in the soil. The transformation of chemical speciation reduced the bioavailability of Cu in soil, which then reduced the accumulation of Cu in castor. Our results demonstrated that S application was effective at promoting castor growth by reducing the bioavailability and uptake of Cu in Cu-contaminated mine tailings.

Ricinus communis L. (Castor bean), a potential multi-purpose environmental crop for improved and integrated phytoremediation

Phytoremediation is a plant based environmental cleanup technology to contain (rendering less toxic), sequester and degrade contaminated susbtrates. As can be seen from data metrics, it is gaining cosiderable importance globally. Phytoremediation approach is being applied for cleanup of inorganic (potentially toxic metals), organic (persistent, emergent, poly-acromatic hydrocarbons and crude oil etc.) and co-contaminated (mixture of inorganic and organic) and/or polluted sites globally. Recently new approaches of utilizing abundantly available natural organic amendments have yielded significant results. Ricinus communis L. (Castor bean) is an important multipurpose crop viz., Agricultural, Energy, Environmental and Industrial crop. The current status of knowledge is abundant but scattered which need to be exploited for sustainable development. This review collates and evaluates all the scattered information and provides a critical view on the possible options for exploiting its potential as follows: 1. Origin and distribution, 2. Lead toxicity bioassays, 3. Progress in arbuscular mycorrhizal fungi-assisted phytoremediation, 4. Promising bioenergy crop that can be linked to pytoremediation, 5. A renewable source for many bioproducts with rich chemical diversity, 6. It is a good biomonitor and bioindicator of atmospheric pollution in urban areas, 7. Enhanced chelate aided remediation, 8. Its rhizospheric processes accelerate natural attenuation, 9. It is suitable for remediation of crude oil contaminated soil, 10. It is an ideal candidate for aided phytostabilization, 11. Castor bean is a wizard for phytoremediation and 12. Its use in combined phytoextraction and ecocatalysis. Further, the knowledge gaps and scope for future research on sustainable co-generation of value chain and value addition biobased products for sustainable circular economy and environmental security are described in this paper.