Translocation Of Cu Research Articles

Rice transcription factor OsWRKY37 positively regulates flowering time and grain fertility under copper deficiency.

Efficient uptake, translocation, and distribution of Cu to rice (Oryza sativa) spikelets is crucial for flowering and yield production. However, the regulatory factors involved in this process remain unidentified. In this study, we isolated a WRKY transcription factor gene induced by Cu deficiency, OsWRKY37, and characterized its regulatory role in Cu uptake and transport in rice. OsWRKY37 was highly expressed in rice roots, nodes, leaf vascular bundles, and anthers. Overexpression of OsWRKY37 promoted the uptake and root-to-shoot translocation of Cu in rice under -Cu condition but not under +Cu condition. While mutation of OsWRKY37 significantly decreased Cu concentrations in the stamen, the root-to-shoot translocation and distribution ratio in brown rice affected pollen development, delayed flowering time, decreased fertility, and reduced grain yield under -Cu condition. yeast one-hybrid, transient co-expression and EMSAs, together with in situ RT-PCR and RT-qPCR analysis, showed that OsWRKY37 could directly bind to the upstream promoter region of OsCOPT6 (copper transporter) and OsYSL16 (yellow stripe-like protein) and positively activate their expression levels. Analyses of oscopt6 mutants further validated its important role in Cu uptake in rice. Our study demonstrated that OsWRKY37 acts as a positive regulator involved in the uptake, root-to-shoot translocation, and distribution of Cu through activating the expression of OsCOPT6 and OsYSL16, which is important for pollen development, flowering, fertility, and grain yield in rice under Cu deficient conditions. Our results provide a genetic strategy for improving rice yield under Cu deficient condition.

Nitrogen metabolism and P-Cu interaction in Cajanus cajan (L.) Millsp contributes to the removal of excess copper in viticulture soil

ABSTRACT Copper, a micronutrient in low concentrations, in excess causes negative changes in the growth and development of plants. This study advances understanding in the dynamics of potentially toxic elements in areas with different uses, making it possible to evaluate the potential of C. cajan to remedy/reduce excess Cu in the soil. It was observed that in C. cajan grown in agricultural soil with high P availability, the translocation of Cu to shoot was 5−7 times greater than in grassland and grassland contaminated with Cu, where the preferred allocation for Cu was the root. The efficiency of the photosynthetic and symbiotic system was not affected; but an increase in the concentration of amino acids was observed. Because of considerable accumulation of Cu in the root and shoot, C. cajan was tolerant to a dose of approximately 100 mg kg−1 of Cu in viticulture soil and may be indicated as a phyto-extractor agent for this metal in agricultural soils.

Enhancing Phytoextraction Potential of Brassica napus for Contaminated Dredged Sediment Using Nitrogen Fertilizers and Organic Acids.

Dredged sediment contaminated with heavy metals can be remediated through phytoremediation. The main challenge in phytoremediation is the limited availability of heavy metals for plant uptake, particularly in multi-contaminated soil or sediment. This study aimed to assess the effect of the nitrogen fertilizers (ammonium nitrate (AN), ammonium sulfate (AS), and urea (UR)), organic acids (oxalic (OA) and malic (MA) acids), and their combined addition to sediment on enhancing the bioavailability and phytoremediation efficiency of heavy metals. The sediment dredged from Begej Canal (Serbia) had high levels of Cr, Cd, Cu, and Pb and was used in pot experiments to cultivate energy crop rapeseed (Brassica napus), which is known for its tolerance to heavy metals. The highest accumulation and translocation of Cu, Cd, and Pb were observed in the treatment with AN at a dose of 150 mg N/kg (AN150), in which shoot biomass was also the highest. The application of OA and MA increased heavy metal uptake but resulted in the lowest biomass production. A combination of MA with N fertilizers showed high uptake and accumulation of Cr and Cu.

OsMYB84, a transcriptional regulator of OsCOPT2 and OsHMA5, modulates copper uptake and transport and yield production in rice

Transcription factors regulating crop uptake and translocation of the micronutrient Cu have not been identified. We isolated a novel R2R3-MYB transcription factor, OsMYB84, and showed that it was a positive regulator involved in uptake and transport of Cu via activation of OsCOPT2 and OsHMA expression. OsMYB84 was highly expressed in roots and anthers and induced by Cu. Overexpression of OsMYB84 promoted uptake and root-to-shoot translocation of Cu in rice, facilitated Cu distribution into grain and increased grain yield. In contrast, mutation of OsMYB84 reduced Cu concentration in xylem sap. OsMYB84 bound to the promoter region of OsCOPT2 and OsHMA5 and upregulated their expression. OsCOPT2 mutants showed reduced uptake of Cu and OsHMA5 overexpression lines showed increased root-to-shoot translocation of Cu.

Copper and zinc accumulation, distribution, and tolerance in Pistia stratiotes L.; revealing the role of root caps

Pollution by potentially toxic trace metals, such as copper or zinc, is global. Both Cu and Zn are essential microelements, which in higher concentrations become toxic. The aquatic plant Pistia stratiotes(L. has great potential for phytoremediation. Also, it has an unusually large and easily detachable root cap, which makes it a suitable model for studying the potential role of the root cap in metal uptake. Plant response to environmentally relevant concentrations of Cu (0.1, 0.3, and 1 μM) and Zn (0.3, 1, and 3 μM) was investigated with the aim of studying their interaction and distribution at the root tissue level as well as revealing their tolerance mechanisms. Changes in the root anatomy and plant ionome were determined using light and fluorescence microscopy, ICP-MS, and μXRF imaging. Alterations in photosynthetic activity caused by Cu or Zn excesses were monitored by direct imaging of fast chlorophyll fluorescence kinetics (OJIP). Fe and Mn were preferentially localized in the root cap, while Ca, Cu, Ni, and Zn were mainly in the root tip regardless of the Cu/Zn treatment. Translocation of Cu and Zn to the leaves increased with higher doses, however the translocation factor was the lowest in the highest treatments. Measurements of photosynthetic parameters showed a higher susceptibility of electron transport flux from QA to QB under increasing Cu than Zn supply. This, along with our findings regarding the root anatomy and the differences in Ca accumulation and distribution, led to the conclusion that P. stratiotes is more effective for Zn remediation than Cu.

Combined pollution effects of Cu and benzotriazole in rice (Oryza sativa L.) verified by split-root experiment.

Although the combined effect of organic ligands and heavy metals in the environment on plants have been frequently reported, their complexed interaction in plants and the physiological effects remain to be revealed. Metal complexing agent benzotriazole (BTR) has extensive environmental pollution. In this study, root-splitting experiments were designed to identify the in vivo and in vitro effects of BTR on the accumulation and translocation of Cu in rice (Oryza sativa L.), and the concentrations and translocation factor (TF) of Cu and BTR in different parts of rice were measured. In the in vitro interaction treatments, low BTR concentrations enhanced Cu uptake and lateral transport in rice, while higher levels of BTR's exposure (i.e., ≥ 100 μM) resulted in opposite effects. Differently, significant increase in the lateral transport of Cu and vertical translocation of BTR in rice presented in the in vivo interaction treatments. TF of Cu from root A to root B (TFRA-RB) increased from 0.05 to 0.272 with the BTR concentration increasing from 0 to 100 μM, and higher TF of BTR from root to shoot (TFR-S), ranging from 1.00 to 1.75, compared with single BTR exposure treatments was observed. The phytotoxicity of BTR expressed by the catalase activity was significantly alleviated by the in vivo accumulated Cu in rice.

Common weeds as heavy metal bioindicators: a new approach in biomonitoring

Environmental pollution by heavy metals affects both urban and non-urban areas of Europe and the world. The use of bioindicator plants for the detection of these pollutants is a common practice. An important property of potential bioindicators is their easy availability and wide distribution range, which means that they can be practically used over a wide area. Therefore, common and widely distributed weeds: Trifolium pratense L., Rumex acetosa L., Amaranthus retroflexus L., Plantago lanceolata L., ornamental species Alcea rosea L., and Lolium multiflorum L. var. Ponto were selected as a potential bioindicators of heavy metals (Cd, Pb, Cu, Zn). Plants were exposed in the same soil conditions in three sample sites in the Poznań city. It was found that all species had heavy metal accumulation potential, especially A. rosea, P. lanceolata and L. multiflorum for Zn (BCF = 6.62; 5.17; 4.70) and A. rosea, P. lanceolata for Cd (BCF = 8.51; 6.94). Translocation of Cu and Zn was the most effective in T. pratense (TFCu = 2.55; TFZn = 2.67) and in A. retroflexus (TFCu = 1.50; TFZn = 2.23). Cd translocation was the most efficient in T. pratense (TFCd = 1.97), but PB was the most effective translocated in A. retroflexus (TFPb = 3.09).. Based on physiological response to stress, it was detected an increasing level of hydrogen peroxide (H2O2) in roots and leaves of all samples, with the highest in all organs of A. rosea. Enzymatic activity levels of CAT, APOX, and also the marker of polyunsaturated fatty acid peroxidation MDA, were higher after 6 weeks of exposure in comparison to control samples and varied in time of exposure and between species and exposure. After the experiment, in almost all samples we detected a reduction of chlorophyll content and relative water content, but in efficiency of photosynthesis parameters: net photosynthesis rate, intercellular CO2 concentration and stomatal conductance, we noted increased values, which proved the relatively good condition of the plants. The examined weeds are good bioindicators of heavy metal contamination, and their combined use makes it possible to comprehensively detection of environmental threats.

How Much Phosphorus Uptake Is Required for Achieving Maximum Maize Grain Yield? Part 2: Impact of Phosphorus Uptake on Grain Quality and Partitioning of Nutrients

Previous studies have shown that excess phosphorus (P) uptake by maize can lead to a decreased grain yield. Part one of this study demonstrated that maize experienced luxury consumption of P in three phases of P uptake. The objective of this work was to further explore how P uptake indirectly impacts the uptake of other nutrients and their translocation within the plant to explain the yield penalty associated with luxury P consumption. Three maize hybrids were grown under optimal conditions using sand-culture hydroponics for precise control of the root environment. Plants were grown to maturity with six different P concentrations followed by biomass and nutrient partitioning analysis of various maize parts. All non-P nutrients achieved maximum grain content at P uptake levels that coincided with the maximum grain yield, while the partitioning of K, Mg, Mn, B, N, S, and Fe into other non-grain tissue continued with further P uptake. With luxury P consumption beyond the point corresponding with maximum grain yield, the N, S, Fe, Cu, and Zn grain content significantly decreased along with the grain yield. With luxury P consumption, Cu, Zn, and Fe accumulated in the roots. Grain production with luxury P uptake may have been limited by P-inhibited translocation of Cu, Zn, and Fe from roots to grain. This decrease in translocation did not prevent further non-grain tissue growth since those nutrients were not as limiting as they were for grain. Data suggest that these micronutrients limited protein production, which was evident from the decrease in grain N and S content and concentration that coincided with the decrease in grain yield concomitant with luxury P uptake.

Assisted Phytostabilization of Mine-Tailings with Prosopis laevigata (Fabaceae) and Biochar.

Phytoremediation is a cost-effective technique to remediate heavy metal (HM) polluted sites. However, the toxic effects of HM can limit plant establishment and development, reducing phytoremediation effectiveness. Therefore, the addition of organic amendments to mine wastes, such as biochar, improves the establishment of plants and reduces the bioavailability of toxic HM and its subsequent absorption by plants. Prosopis laevigata can establish naturally in mine tailings and accumulate different HM; however, these individuals show morphological and genetic damage. In this study, the effect of biochar on HM bioaccumulation in roots and aerial tissues, HM translocation, morphological characters and plant growth were evaluated, after three and six months of exposure. Plants grown on mine tailings with biochar presented significantly higher values for most of the evaluated characters, in respect to plants that grew on mine tailing substrate. Biochar addition reduced the bioaccumulation and translocation of Cu, Pb, and Cd, while it favored the translocation of essential metals such as Fe and Mn. The addition of biochar from agro-industrial residues to mine tailings improves the establishment of plants with potential to phytoextract and phytostabilize metals from polluted soils. Using biochar and heavy metal accumulating plants constitutes an assisted phytostabilization strategy with great potential for HM polluted sites such as Cd and Pb.

Molecular mechanism of Cu metal and drought stress resistance triggered by Porostereum spadiceum AGH786 in Solanum lycopersicum L.

Rapid industrialization and global warming have threatened the plants with multiple abiotic stresses, such as heavy metals and drought stress. For crop cultivation, the conventional approach of cleaning the soils by excavation is very costly and not feasible for large scale. Establishing toxin-free and drought-resistant crops is a major challenge in the environment under natural and anthropogenic pressure. In the past decades, copper contamination of agricultural land has become an emerging concern. For dry land reclamation, several new strategies, including bioremediation (phytoremediation and microbial remediation), have been used. Owing to the potential of Cu hyperaccumulators, the current project aims to enhance the drought tolerance and the phytoremediation potential of Solanum lycopersicum L. with the inoculation of copper and 12% polyethylene glycol (PEG)-induced drought stress-tolerant endophytic fungus Porostereum spadiceum AGH786 under the combined stress of copper heavy metal and PEG-induced drought stress. When S. lycopersicum L. was watered with individual stress of copper (Cu) concentration (400 ppm) in the form of copper sulfate (CuSO4.5H2O), 12% PEG-induced drought stress and the combined stress of both negatively affected the growth attributes, hormonal, metabolic, and antioxidant potential, compared with control. However, the multistress-resistant AGH786 endophytic fungus ameliorated the multistress tolerance response in S. lycopersicum L. by positively affecting the growth attributes, hormonal, metabolic, and antioxidant potential, and by restricting the root-to-shoot translocation of Cu and inducing its sequestration in the root tissues of affected plants. AGH786-associated plants exhibited a reduction in the severity of copper (Cu) and drought stress, with higher levels of SlCOPT (Cu transporters) and SlMT (metallothionine) gene expressions in root and shoot tissues, indicating that AGH786 contributed to resistance to copper metal toxicity and drought stress in the host S. lycopersicum L.

Synergistic Interaction between Copper and Nitrogen-Uptake, Translocation, and Distribution in Rice Plant.

Interactions among nutrients have been widely recognized in plants and play important roles in crop growth and yield formation. However, the interplay of Cu and N in rice plants is not yet clear. In this study, rice plants were grown with different combinations of Cu and N supply. The effects of Cu-N interaction on the growth, yield production, Cu and N transport, and gene expression levels were analyzed. The results showed that the effect of N supply on rice growth and yield formation was more pronounced than that of Cu supply. The Cu supply significantly improved the uptake of N (by 9.52–30.64%), while the N supply significantly promoted the root-to-shoot translocation of Cu (by 27.28–38.45%) and distributed more Cu (1.85–19.16%) into the shoots and leaves. The results of qRT-PCR showed that +Cu significantly up-regulated the expression levels of both NO3− and NH4+ transporter genes OsNRTs and OsAMTs, including OsNRT1.1B, OsNRT2.1, OsNRT2.3a, OsNRT2.4, OsAMT1.2, OsAMT1.3, and OsAMT3.1. Meanwhile, +N significantly up-regulated the expression levels of Cu transporter genes OsHMA5 and OsYSL16. In addition, the supply of Cu up-regulated the expression levels of OsGS1;2, OsGS2, and OsNADH-GOGAT to 12.61-, 6.48-, and 6.05-fold, respectively. In conclusion, our study demonstrates a synergistic effect between Cu and N in rice plants. It is expected that our results would be helpful to optimize the application of N and Cu fertilizers in agriculture.

Exogenous Pseudomonas aeruginosa application improved the phytoremediation efficiency of Lolium multiflorum Lam on Cu–Cd co-contaminated soil

Pot experiments were conducted to explore the effect of Pseudomonas aeruginosa on the phytoremediation efficiency of ryegrass on jointly Cu- and Cd-contaminated soil. P. aeruginosa application promoted the growth of ryegrass, increased the concentration of Cu and Cd in ryegrass, and enhanced the translocation of Cu and Cd from roots to shoots. The biomass of ryegrass in the T7 treatment increased by 43.1% compared to the T1 treatment. Additionally, P. aeruginosa application improved the bioavailability of Cu and Cd. The concentration of Cu and Cd in ryegrass under the T7 treatment was 48.7% and 32.8% higher than that under the T1 treatment, and the removal efficiencies of Cu and Cd from soil under the T7 treatment reached 89.5% and 89.3%, respectively. The subcellular distribution of Cu and Cd in ryegrass indicated that Cu and Cd were mainly distributed in the cell wall and cell-soluble fraction, and a large amount of Cd entered the shoot cell membrane and organelle-containing fraction under 500 mg⋅kg−1 P. aeruginosa culture application. Thus, application of 500 mg⋅kg−1P. aeruginosa culture to soil can enhance Cu uptake by ryegrass, and the maximum capacity of ryegrass to absorb Cd from the soil was reached with 50 mg⋅kg−1P. aeruginosa culture application. In light of the above results, P. aeruginosa culture application facilitated the phytoremediation of Cu–Cd co-contaminated soil by ryegrass.

Auxin regulates growth, photosynthetic efficiency and mitigates copper induced toxicity via modulation of nutrient status, sugar metabolism and antioxidant potential in Brassica juncea

The involvement of auxin (IAA) in growth and development of plants is well known, but its role in the mitigation of metal stress, especially copper (Cu), is not fully understood; therefore, it is time to explore its involvement in minimizing the stress. A pot experiment was conducted to assess the protective function of IAA, applied to the foliage, on photosynthetic machinery, carbohydrate metabolism, and growth of Brassica juncea, grown with Cu (30 or 60 mg kg−1 of soil). Among the different concentrations (10−10, 10−8, or 10−6 M), 10−8 M of IAA alone enhanced the photosynthetic characteristics, sugar accumulation and vegetative growth with minimal cellular oxidative stress level. Moreover, the same concentration of auxin was most effective in decreasing the stress levels generated by Cu and maintained it nearly to that of the control in terms of photosynthetic attributes, gas exchange parameters, PSII activity, electron transport rate, and growth attributes. Auxin also maintained the membrane stability and ultrastructure of chloroplast, stomatal morphology with a reduction in malondialdehyde (MDA), electrolyte leakage (EL) and cell death in test plants even under Cu stress. IAA also improved the translocation of Cu from root to the aerial parts, thus enhanced the Cu-reclamation in metal contaminated soils. Our findings suggest that the application of 10−8 M of IAA maintains the overall growth of plants and may be used as an effective agent to improve growth, photosynthesis and phyto-remediation potential of B. juncea in Cu contaminated soil.

Soil and foliar exposure of soybean (Glycine max) to Cu: Nanoparticle coating-dependent plant responses

In this study, we investigated the effects of citric acid (CA) coated copper oxide nanoparticles (CuO NPs) and their application method (foliar or soil exposure) on the growth and physiology of soybean (Glycine max). After nanomaterials exposure via foliar or soil application, Cu concentration was elevated in the roots, leaves, stem, pod, and seeds; distribution varied by plant organ and surface coating. Foliar application of CuO NPs at 300 mg/L and CuO-CA NPs at 75 mg/L increased soybean yield by 169.5% and 170.1%, respectively. In contrast, foliar and soil exposure to ionic Cu with all treatments (75 and 300 mg/L) had no impact on yield. Additionally, CuO-CA NPs at 300 mg/L significantly decreased Cu concentration in seeds by 46.7%, compared to control, and by 44.7%, compared to equivalent concentration of CuO NPs. Based on the total Cu concentration, CuO NPs appeared to be more accessible for plant uptake, compared to CuO-CA NPs, inducing a decrease in protein content by 56.3% and inhibiting plant height by 27.9% at 300 mg/kg under soil exposure. The translocation of Cu from leaf to root and from the root to leaf through the xylem was imaged by two-photon microscopy. The findings indicate that citric acid coating reduced CuO NPs toxicity in soybean, demonstrating that surface modification may change the toxic properties of NPs. This research provides direct evidence for the positive effects of CuO-CA NPs on soybean, including accumulation and in planta transfer of the particles, and provides important information when assessing the risk and the benefits of NP use in food safety and security.

Phytoremediation Capability and Copper Uptake of Maize (Zea mays L.) in Copper Contaminated Soils

Copper is a frequently used heavy metal worldwide and known to be an essential micronutrient for most living organisms including plants. However, excessive levels of copper in soil may adversely affect plant growth and survival. The continuing introduction of copper to soil, e.g., through excessive utilization of agrochemicals has raised serious environmental concerns throughout the world. A variety of plants have the capability to eliminate pollutants from soil through different mechanisms; however, limited information is reported on phytoremediation potential of maize (Zea mays L.) and its uptake and the accumulation potential in copper-containing soils. The effects of additions of 0, 50, 100, 200 and 300 mg kg−1 of copper to soil on growth parameters of Z. mays, copper uptake from soil and accumulation in roots and shoots, and phytoremediation potential of Z. mays were investigated in this research. Copper content in soil and plant samples were determined using atomic absorption spectrophotometry. The addition of 50 mg kg−1 Cu stimulated Z. mays growth parameters, while higher content of Cu exhibited inhibitory effects of plant growth. Results indicated that roots accumulated significantly higher levels of Cu than shoots in all treatments, suggesting dominancy of phytostabilization mechanism in remediation of Cu-polluted soil by Z. mays. However, translocation of Cu from the roots to the aerial parts enhanced to some extent with copper level in soil. The greatest Cu accumulation capacity of 5210 µg per pot was gained in Z. mays cultivated in soil treated with 200 mg kg−1 copper. Results demonstrated that Z. mays can promisingly remediate low to moderately copper-contaminated soils.

Metal Accumulation and Biomass Production in Young Afforestations Established on Soil Contaminated by Heavy Metals.

The restoration of forest ecosystems on metal-contaminated sites can be achieved whilst producing valuable plant biomass. Here, we investigated the metal accumulation and biomass production of young afforestations on contaminated plots by simulating brownfield site conditions. On 16 3-m2 plots, the 15 cm topsoil was experimentally contaminated with Zn/Cu/Pb/Cd = 2854/588/103/9.2 mg kg−1 using smelter filter dust, while 16 uncontaminated plots (Zn/Cu/Pb/Cd = 97/28/37/< 1) were used as controls. Both the calcareous (pH 7.4) and acidic (pH 4.2) subsoils remained uncontaminated. The afforestations consisted of groups of conifers, deciduous trees, and understorey plants. During the four years of cultivation, 2254/86/0.35/10 mg m−2 Zn/Cu/Pb/Cd were extracted from the contaminated soils and transferred to the aboveground parts of the plants (1279/72/0.06/5.5 mg m−2 in the controls). These extractions represented 3/2/3% of the soluble soil Zn/Cu/Cd fractions. The conifers showed 4–8 times lower root-to-shoot translocation of Cu and Zn than the deciduous trees. The contamination did not affect the biomass of the understorey plants and reduced that of the trees by 23% at most. Hence, we conclude that the afforestation of brown field sites with local tree species is an interesting option for their reclamation from an ecological as well as economic perspective.

Detrimental effects of copper and EDTA co-application on grapevine root growth and nutrient balance

Continuous application of Cu-based fungicides and molluscicides may lead to Cu accumulation in vineyard soils. Grapevine (Vitis vinifera L.) inoculation with arbuscular mycorrhizal fungi (AMF) can be a suitable strategy to increase plant tolerance to the excessive levels of this element in the soil. However, the simultaneous use of EDTA-based fertilizers or phytosanitary products in those vineyards can affect metal mobility in the soil, with potential negative consequences for plants. Therefore, this study aimed to elucidate the effect of AMF inoculation on grapevine performance in Cu contaminated soils, in the presence or absence of EDTA chelates.Two-year-old plants growing in pots filled with an Arenosol, previously inoculated or not with two different AMF, were subjected to three soil treatments: control, Cu addition; Cu and FeNaEDTA addition. Four months later, at the end of the growing season, plant vegetative growth parameters, root colonization as well as soil, root and leaf nutrient contents were analyzed.In the soil where Cu was applied, Rhizoglomus irregulare- and Funneliformis mosseae-inoculated plants showed significantly higher root biomass than the non-inoculated ones, and R. irregulare-inoculated plants were the ones with the highest root P and Fe concentrations. However, when Cu and FeNaEDTA were applied together to the soil, AMF inoculation was no longer an asset for grapevines, and overall, root biomass decreased, translocation of Cu to leaves was stimulated, and a significant decrease in leaf Mn concentrations was detected, below the levels found in control soils. For this reason, in soils with high Cu-concentrations, although mycorrhizal inoculation can be a suitable strategy to improve plant growth and nutrition, the use of EDTA-based products should be avoided, as it can lead to an amplification of the toxic effects commonly caused by the excess of Cu in plants.

Elucidating the effects of TiO2 nanoparticles on the toxicity and accumulation of Cu in soybean plants (Glycine max L.)

Copper (Cu) pollution is common in the soil. Due to the widespread application of TiO2 NPs, there is a high propensity for the co-occurrence of TiO2 nanoparticles (NPs) and Cu in agricultural soils. It is therefore imperative to evaluate the joint effects of TiO2 NPs and Cu on crops. In this study, the mutual effects of TiO2 NPs and Cu on their toxicity and accumulation in soybean seedlings and on their fates in a hydroponic system were determined. When Cu was at levels of 1 and 2 mg/L, the co-occurring TiO2 NPs at a non-toxic concentration (10 mg/L) significantly enhanced the toxicity and accumulation of Cu and Ti in soybeans, and inhibited the translocation of Cu from soybean roots to shoots. However, when the Cu concentration for co-exposure was ≥ 5 mg/L, such mutual effects disappeared. The amount of Cu ions adsorbed onto TiO2 NPs after 48 h of co-exposure gradually increased from 31 to 118 mg/g when the Cu concentration was increased from 1 to 20 mg/L. The aggregation and sedimentation of TiO2 NPs were significantly increased after 48 h of co-exposure with the Cu at a concentration higher than 5 mg/L, as compared to the single TiO2 NPs exposure. The increasing aggregation and sedimentation might reduce the bioavailability of TiO2 NPs associated with the adsorbed Cu to soybeans, and consequently alleviate or even neutralize the enhanced toxicity and accumulation of Cu in soybeans exerted by the co-existing TiO2 NPs. Our results thus suggest that consideration of the impact of TiO2 NPs on the phytotoxicity of heavy metals, and specifically Cu, needs to be interpreted with care, and highlight the importance of integrating the interaction and fates of TiO2 NPs and metals into their risk assessment.

Five-weeks pot trial evaluation of phytoremediation potential of Helichrysum splendidum Less. for copper- and lead-contaminated soils

This paper describes an investigation into the accumulation and distribution of Cu and Pb in Helichrysum splendidum, to assess the potential use of the plant in the phytoremediation of Cu- and Pb-contaminated soils. Plants of the same age were exposed to soils artificially contaminated with 10, 50, 100, 500 and 1000 mg/L Cu(II) and Pb(II). Although plant growth was not affected by the presence of Cu, high concentrations of Pb (> 500 mg/L) stunted the plants. Chlorophyll production was slightly reduced when plants were exposed to high concentrations of Cu (> 500 mg/L), whereas all the plants growing in Pb-contaminated soils indicated low levels of chlorophyll. Significant amounts of Cu and Pb were accumulated in the roots, with corresponding bioconcentration factors of > 1. Translocation of Cu to the shoots was restricted for plants growing in > 500 mg/L Cu-treated soils, whereas Pb was translocated to the shoots for all treatments, with translocation factors > 1. The Cu and Pb tolerance mechanism was ascribed to chelation and free radical scavenging, through the production of phenolic compounds. Helichrysum splendidum is able to adapt to and ameliorate soils contaminated with low to high levels of Cu(II) and Pb(II) and has potential for application in phytoextraction and phytostabilization of contaminated soils.

Alleviation of heavy metal stress by arbuscular mycorrhizal symbiosis in Glycine max (L.) grown in copper, lead and zinc contaminated soils

There are few reports on the use of arbuscular mycorrhizal fungi (AMF) to promote growth and stress tolerance of soybean (Glycine max L.) in agricultural soils contaminated with heavy metals. The present study evaluated the role of AMF in promoting tolerance and growth, as well as uptake of heavy metals in shoots of soybean plants. Soybean plants were inoculated with AMF (Funneliformis mosseae) in a pot experiment polluted with different concentrations of heavy metals [copper (Cu), lead (Pb) and zinc (Zn)] as well as their combination. The tested AMF inoculum promoted the soybean growth and seed yield. Increased colonization of the soybean roots improved the soybean growth through increased phosphorus uptake and accumulation in the plant tissues by 68.8%. The results showed that soybean grown in the contaminated soils inoculated with AMF were more tolerant in alleviating the metals toxicity by retaining the heavy metals in the roots, thereby reducing translocation of Cu, Pb and Zn by 21.8, 57.6 and 67.3% respectively in the aerial part of the plant and improving the overall plant productivity by 59.1%. The findings provide evidence of the potential of AMF in phytoremediation of agricultural soils contaminated with toxic metals.