Copper and mercury induced oxidative stresses and antioxidant responses of Spirodela polyrhiza (L.) Schleid

Duckweed is recognized as a phytoremediation aquatic plant due to the production of large biomass and a high level of tolerance in stressed conditions. A laboratory experiment was conducted to investigate antioxidant response and mechanism of copper and mercury tolerance of S. polyrhiza (L.) Schleid. To understand the changes in chlorophyll content, MDA, proline, and activities of ROS-scavenging enzymes (SOD, CAT, GPOD) during the accumulation of Cu⁺² and Hg⁺², S. polyrhiza were exposed to various concentrations of Cu⁺² (0.0–40 μM) and Hg⁺² (0.0–0.4 μM). antioxidant activity initially indicated enhancing trend with application of 10 μM Cu⁺²; 0.2 μM Hg⁺² (SOD), of 20 μM Cu⁺²; 0.2 μM Hg⁺² (CAT) and of 10 μM Cu⁺²;0.2 μM Hg⁺² (GPOD) and then decreased consistently up to 40 μM Cu⁺² and 0.4 μM Hg⁺². In the experiment chlorophyll and frond multiplication initially showed increasing tendency and decreased gradually with the application of increased metal concentration. Application of heavy metal has constantly enhanced proline and MDA content while the maximum increase was observed with the application of 40 μM Cu; 0.4 μM Hg for proline and MDA respectively. The upregulation of antioxidant enzymes and proline reveals that S. polyrhiza has strong biochemical strategies to deal with the heavy metal toxicity induced by the accumulation of Cu⁺² and Hg⁺².     

Ratiometric optical detection of pyrophosphate based on aggregation-caused dual-signal response of gold nanoclusters

Sensing of pyrophosphate ion (PPi) has received much attention due to the strong demand for clinical diagnostics. Here, based on gold nanoclusters (Au NCs), a ratiometric optical detection method for PPi is developed by simultaneously detecting the dual signals of fluorescence (FL) and second-order scattering (SOS). The PPi is detected by inhibiting the formation of aggregates of Fe³⁺ with Au NCs. Binding of Fe³⁺ to Au NCs causes aggregation of Au NCs, which leads to fluorescence quenching and scattering increasing. The presence of PPi can competitively bind Fe³⁺ to re-disperse the Au NCs and finally recover the fluorescence and reduce the scattering signal. The designed PPi sensor shows a high sensitivity with a linear range 5–50 μM and a detection limit of 1.2 μM. In addition, the assay has excellent selectivity for PPi, which makes its application in real biological samples extremely valuable.     

Selective fluorescence quenching of papain–Au nanoclusters by self‐polymerization of dopamine

In this paper, we synthesized a papain‐stabilized fluorescent Au nanocluster (NC) probe and studied its interaction with dopamine. As fluorescence of papain–Au NCs is quenched in the presence of dopamine under alkaline conditions, we were able to establish a simple, selective analytical method for dopamine determination. By studying the fluorescence lifetime and dynamic light scattering of the NCs before and after interaction with dopamine, we found that this fluorescence quenching mechanism was possibly due to dopamine self‐polymerization that produced polydopamine that cross‐linked papain–Au NCs. Based on this new phenomenon, we proposed a highly selective analytical method for dopamine detection. Other small organic molecules, such as amino acids, ascorbic acid and uric acid did not interfere with dopamine detection. Dopamine in the range 20–100 μM can be linearly detected by the fluorescence quenching ratio of gold nanoclusters. Dopamine detection could be visually realized by watching color changes of papain–Au NCs under UV light or daylight, as both fluorescence and absorption of the papain–Au NCs changed during dopamine polymerization.     

Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Zeolitic imidazolate framework‐8 (ZIF‐8) loading rhodamine‐B (ZIF‐8@rhodamine‐B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu²⁺). Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF‐8@rhodamine‐B nanocomposites. The results showed the rhodamine‐B was successfully assembled on ZIF‐8 based on the π‐π interaction and the hydrogen bond between the nitrogen atom of ZIF‐8 and –COOH of rhodamine‐B. The as‐obtained ZIF‐8@rhodamine‐B nanocomposites were octahedron with size about 150–200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF‐8 at 335 nm and rhodamine‐B at 575 nm. The Cu²⁺ could quench fluorescence of ZIF‐8 rather than rhodamine‐B. The ZIF‐8 not only acted as the template to assemble rhodamine‐B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine‐B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu²⁺. The resulted ZIF‐8@rhodamine‐B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu²⁺ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF‐8 and other fluorescent molecules.     

Terbium (III) coordination polymer–copper (II) compound as fluorescent probe for time‐resolved fluorescence ‘turn‐on’ detection of hydrogen sulfide

With recognition of the biological importance of hydrogen sulfide (H₂S), we present a simple and effective fluorescent probe for H₂S using a Tb³⁺ coordination polymer–Cu²⁺ compound (DPA/Tb/G–Cu²⁺). Dipicolinic acid (DPA) and guanosine (G) can coordinate with Tb³⁺ to form a macromolecular coordination polymer (DPA/Tb/G). DPA/Tb/G specifically binds to Cu²⁺ in the presence of coexisting cations, and obvious fluorescence quenching is observed. The quenched fluorescence can be exclusively recovered upon the addition of sulfide, which is measured in the mode of time‐resolved fluorescence. The fluorescence intensities of the DPA/Tb/G–Cu²⁺ compound enhance linearly with increasing sulfide concentrations from 1 to 30 μM. The detection limit for sulfide in aqueous solution is estimated to be 0.3 μM (at 3σ). The DPA/Tb/G–Cu²⁺ compound was successfully applied to sense H₂S in human serum samples and exhibited a satisfactory result. It displays some desirable properties, such as fast detection procedure, high selectivity and excellent sensitivity. This method is very promising to be utilized for practical detection of H₂S in biological and environmental samples.     

Silver nanoclusters stabilized with denatured fish sperm DNA and the application on trace mercury ions detection

In this study, fluorescent silver nanoclusters (Ag NCs) were synthesized using denatured fish sperm DNA as the template. In contrast to other methods, this method did not use artificial DNA as the template. After their reaction with denatured fish sperm DNA, Ag⁺ ions were reduced by NaBH₄ to form Ag NCs. The Ag NCs showed a strong fluorescence emission at 650 nm when excited at 585 nm. The fluorescence intensity increased fourfold at pH 3.78, controlled with Britton–Robinson buffer solution. The fluorescence of the Ag NCs was quenched in the presence of trace mercury ions (Hg²⁺) in a weakly acidic medium and nitrogen atmosphere. The extent of the fluorescence quenching of Ag NCs strongly depends on the Hg²⁺ ion concentration over a linear range from 2.0 nmol L^?1 to 3.0 μmol L^?1. The detection limit (3σ/k) for Hg²⁺ was 0.7 nmol L^?1. Thus, a sensitive and rapid method was developed for the detection of Hg²⁺ ions.     

Functional characterization of Legionella pneumophila Cu+ transport ATPase. The activation by Cu+ and ATP

Cu⁺-ATPases are integral membrane proteins belonging to the IB subfamily of the P-type ATPases that couple Cu⁺ transport to the hydrolysis of ATP. As some structural and functional particularities arise for Cu⁺-ATPases, several authors suggest that some of the reaction steps of the Albers-Post model postulated for other P-ATPases may be different. In this work we describe a functional characterization of Legionella pneumophila Cu⁺-ATPase (LpCopA), the first P_IB-ATPase whose structure was determined by X-ray crystallography. Cu⁺-ATPase activity of the enzyme presents a maximum at ～37 °C and pH 6.6–6.8. Phospholipids enhance LpCopA Cu⁺-ATPase activity in a non-essential mode where optimal activity is achieved at an asolectin molar fraction of 0.15 and an amphiphile-protein ratio of ~30,000. As described for other P-ATPases, Mg²⁺ acts as an essential activator. Furthermore, Cu⁺-ATPase activity dependence on [Cu⁺] and [ATP] can both be described by a sum of two hyperbolic functions. Based on that, and the [Cu⁺] and [ATP] dependencies of the best fitting parameters of the hyperbolae pointed above, we propose a minimal reaction scheme for the catalytic mechanism that shares the basic reaction steps of the Albers-Post model for P-type ATPases. The reaction scheme postulated contemplates two different binding affinities for a single ATP (apparent affinities of 0.66 and 550 μM at [Cu⁺] → ∞) and binding of at least 2 Cu⁺ with different affinities as well (apparent affinities of 1.4 and 102.5 μM at [ATP] → ∞).     

BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

Copper nanocluster‐based fluorescence enhanced determination of d‐penicillamine

Taking advantage of the compelling properties of d ‐penicillamine (d ‐PA) combined with copper, a method for the sensitive and selective determination of d ‐PA was established using copper nanocluster (Cu NC)‐based fluorescence enhancement. d ‐PA molecules containing a thiol compound showed a strong tendency to combine with the surface of Cu NCs, causing the re‐dispersion of nanoclusters and therefore fluorescence intensity was enhanced. Fluorescence enhancement efficiency of Cu NCs induced by d ‐PA was linear, with the d ‐PA concentration varying from 0.6–30 μg ml^?1 (R² = 0.9952) and with a detection limit of 0.54 μg ml^?1. d ‐PA content in human urine samples was detected with recoveries of 104.8–112.99%. Fluorescence‐enhanced determination of d ‐PA using Cu NCs was established for the first time and this rapid, easy and sensitive method should attract much attention for this application.     

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

A new Schiff base receptor 1 was synthesized and its photophysical properties were investigated by absorption, emission and excitation techniques. Furthermore, its chromogenic and fluorogenic sensing abilities towards various metal ions were examined. Receptor 1 selectively detects Cu²⁺ ion through fluorescence quenching and detection was not inhibited in the presence of other metal ions. From fluorescence titration, the limit of detection of receptor 1 as a fluorescent ‘turn‐off’ sensor for the analysis of Cu²⁺ was estimated to be 0.35 μM.     

A highly selective and sensitive turn‐on fluorescent probe for the detection of Al3+ and its bioimaging

A novel fluorescent sensor, 1‐((2‐hydroxynaphthalen‐1‐yl)methylene)urea (ocn) has been designed and applied as a highly selective and sensitive fluorescent probe for recognition of Al³⁺ in Tris–HCl (pH = 7.20) solution. The probe ocn exhibits an excellent selectivity to Al³⁺ over other examined metal ions, anions and amino acids with a prominent fluorescence ‘turn‐on’ at 438 nm. ocn binds to Al³⁺ with a 2:1 binding stoichiometry and the detection limit was 0.3 μM. Furthermore, its capability of biological application was evaluated and the results showed that the sensor could be used to detect Al³⁺ in living cells.     

Application of hybrid SiO2‐coated CdTe nanocrystals for sensitive sensing of Cu2+ and Ag+ ions

A new ion sensor based on hybrid SiO₂‐coated CdTe nanocrystals (NCs) was prepared and applied for sensitive sensing of Cu²⁺ and Ag⁺ for the selective quenching of photoluminescence (PL) of NCs in the presence of ions. As shown by ion detection experiments conducted in pure water rather than buffer solution, PL responses of NCs were linearly proportional to concentrations of Cu²⁺ and Ag⁺ ions < 3 and 7 uM, respectively. Much lower detection limits of 42.37 nM for Cu²⁺ and 39.40 nM for Ag⁺ were also observed. In addition, the NC quenching mechanism was discussed in terms of the characterization of static and transient optical spectra. The transfer and trapping of photoinduced charges in NCs by surface energy levels of CuS and Ag₂S clusters as well as surface defects generated by the exchange of Cu²⁺ and Ag⁺ ions with Cd²⁺ ion in NCs, resulted in PL quenching and other optical spectra changes, including steady‐state absorption and transient PL spectra. It is our hope that these results will be helpful in the future preparation of new ion sensors. Copyright © 2012 John Wiley & Sons, Ltd.     

Dual emission fluorescent silver nanoclusters for sensitive detection of the biological coenzyme NAD+/NADH

Fluorescent silver nanoclusters (Ag NCs) displaying dual-excitation and dual-emission properties have been developed for the specific detection of NAD⁺ (nicotinamide adenine dinucleotide, oxidized form). With the increase of NAD⁺ concentrations, the longer wavelength emission (with the peak at 550 nm) was gradually quenched due to the strong interactions between the NAD⁺ and Ag NCs, whereas the shorter wavelength emission (peaking at 395 nm) was linearly enhanced. More important, the dual-emission intensity ratio (I₃₉₅/I₅₅₀), fitting by a single-exponential decay function, can efficiently detect various NAD⁺ levels from 100 to 4000 μM, as well as label NAD⁺/NADH (reduced form of NAD) ratios in the range of 1–50.     

A carbonothioate‐based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate‐based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16 μM and fluorescence intensity showed a good linear relationship (y = 22106× + 53108, R² = 0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.     

Copper toxicity and sulfur metabolism in Chinese cabbage are affected by UV radiation

Biomass production, dry matter content, specific leaf area and pigment content of Chinese cabbage were all quite similar, when plants were grown in the absence or presence of UV-A + B (2.2 mW cm⁻²). Elevated Cu²⁺ concentrations (2–10 μM) in the root environment and UV radiation had negative synergistic effects for Chinese cabbage and resulted in a more rapid and stronger decrease in plant biomass production and pigment content. The quantum yield of photosystem II photochemistry (F_v/F_m) was only decreased at ≥5 μM Cu²⁺ in the presence of UV radiation, when leaf tissue started to become necrotic. The enhanced Cu toxicity in the presence of UV was largely due to a UV-induced enhanced accumulation of Cu in both roots and shoots. An enhanced Cu content strongly affected the uptake and assimilation of sulfur in plants. The total sulfur content of the root increased at ≥2 μM Cu²⁺ in presence of UV and at 10 μM Cu²⁺ in absence of UV and that of the shoot increased at ≥2 μM Cu²⁺ in presence of UV and at ≥5 μM Cu²⁺ in absence of UV. In the shoot it could be attributed mainly to an increase in sulfate content. Moreover, there was a strong increase in the water-soluble non-protein thiol content upon Cu²⁺ exposure in the root and, to a lesser extent in the shoot, both in the presence and absence of UV. The regulation of the uptake of sulfate responded to the occurrence of Cu toxicity directly, since it was more rapidly affected in the presence than in the absence of UV radiation. For instance, the expression and activity of the high affinity sulfate transporter, Sultr1;2, were enhanced at ≥2 μM in the presence of UV, and at ≥5 μM Cu²⁺ in the absence of UV. In the shoot, the expression of the vacuolar sulfate transporter, Sultr4;1, was upregulated at ≥5 μM Cu²⁺ in the presence and absence of UV whilst the expression of a second vacuolar sulfate transporter, Sultr4;2, was upregulated at 10 μM Cu²⁺ in the presence of UV. It is suggested that high Cu tissue levels may interfere/react with the signal compounds involved in the regulation of expression and activity of sulfate transporters. The expression of adenosine 5′-phosphosulfate reductase in the root was hardly affected and was slightly down-regulated at 2 μM in the presence of UV and at 10 μM in the absence of UV. The expression and activity of sulfate transporters were enhanced upon exposure at elevated Cu²⁺ concentrations; this may not be simply due to a greater sulfur demand at higher Cu levels, but more likely is the consequence of Cu toxicity, since it occurred more rapidly in the presence compared to the absence of UV.     

Effects of copper on expression of methane monooxygenases,trichloroethylene degradation,and community structure in methanotrophic consortia

Copper plays a key role in regulating the expression of enzymes that promote biodegradation of contaminants in methanotrophic consortia (MC). Here, we utilized MC isolated from landfill cover to investigate cometabolic degradation of trichloroethylene (TCE) at nine different copper (Cu²⁺) concentrations. The results demonstrated that an increase in Cu²⁺ concentration from 0 to 15 μM altered the specific first‐order rate constant k_1,TCE, the expression levels of methane monooxygenase (pmoA and mmoX) genes, and the specific activity of soluble methane monooxygenase (sMMO). High efficiency TCE degradation (95%) and the expression levels of methane monooxygenase (MMO) were detected at a Cu²⁺ concentration of 0.03 μM. Notably, sMMO‐specific activity ranged from 74.41 nmol/(mg_cell h) in 15 μM Cu²⁺ to 654.99 nmol/(mg_cell h) in 0.03 μM Cu²⁺, which contrasts with cultures of pure methanotrophs in which sMMO activity is depressed at high Cu²⁺ concentrations, indicating a special regulatory role for Cu²⁺ in MC. The results of MiSeq pyrosequencing indicated that higher Cu²⁺ concentrations stimulated the growth of methanotrophic microorganisms in MC. These findings have important implications for the elucidation of copper‐mediated regulatory mechanisms in MC.     

Response to copper excess in Arabidopsis thaliana: Impact on the root system architecture,hormone distribution,lignin accumulation and mineral profile

Growth, in particular reorganization of the root system architecture, mineral homeostasis and root hormone distribution were studied in Arabidopsis thaliana upon copper excess. Five-week-old Arabidopsis plants growing in hydroponics were exposed to different Cu²⁺ concentrations (up to 5 μM). Root biomass was more severely inhibited than shoot biomass and Cu was mainly retained in roots. Cu²⁺ excess also induced important changes in the ionome. In roots, Mg, Ca, Fe and Zn concentrations increased, whereas K and S decreased. Shoot K, Ca, P, and Mn concentrations decreased upon Cu²⁺ exposure. Further, experiments with seedlings vertically grown on agar were carried out to investigate the root architecture changes. Increasing Cu²⁺ concentrations (up to 50 μM) reduced the primary root growth and increased the density of short lateral roots. Experiment of split-root system emphasized a local toxicity of Cu²⁺ on the root system. Observations of GUS reporter lines suggested changes in auxin and cytokinin accumulations and in mitotic activity within the primary and secondary root tips treated with Cu²⁺. At toxic Cu²⁺ concentrations (50 μM), these responses were accompanied by higher root apical meristem death. Contrary to previous reports, growth on high Cu²⁺ did not induce an ethylene production. Finally lignin deposition was detected in Cu²⁺-treated roots, probably impacting on the translocation of nutrients. The effects on mineral profile, hormonal status, mitotic activity, cell viability and lignin deposition changes on the Cu²⁺-induced reorganization of the root system architecture are discussed.     

Studies on the interaction of chick brain microsomal (Na+ + K+)-ATPase with copper

Chick brain microsomal ATPase was strongly inhibited by Cu²⁺. (Na⁺ + K⁺)-ATPase was more susceptible to low levels of Cu²⁺ than Mg²⁺-ATPase. The inhibition of (Na⁺ + K⁺)-ATPase could be partially protected from Cu²⁺ in the presence of ATP in the preincubation period. When Cu²⁺ (6 μM) was preincubated with the enzyme in the absence of ATP, only sulfhydryl-containing amino acids (d-penicillamine and l-cysteine) could reverse the inhibition. At lower concentrations of Cu²⁺ (< 1.4 μM), in the absence of ATP during preincubation, the inhibition could be completely reversed by the addition of 5 mM l-phenylalanine and l-histidine as well as d-penicillamine and l-cysteine.Kinetic analysis of action of Cu²⁺ (1.0 μM) on (Na⁺ + K⁺)-ATPase revealed that the inhibition was uncompetitive with respect to ATP. At a low concentration of K⁺ (5 mM), V with Na⁺ was markedly decreased in the presence of Cu²⁺ and K_m was about twice that of the control. However, at high K⁺ concentration (20 mM), the K_m for Na⁺ was not affected. At both low (25 mM) and high (100 mM) Na⁺, Cu²⁺ displayed non-competitive inhibition of the enzyme with respect to K⁺.On the basis of these data, we suggest that Cu²⁺ at higher concentrations (> 6 μM) inactivates the enzyme irreversibly, but that at lower concentrations (< 1.4 μM), Cu²⁺ interacts reversibly with the enzyme.     

A rhodamine‐triazole fluorescent chemodosimeter for Cu2+ detection and its application in bioimaging

A rhodamine‐based fluorescent chemodosimeter rhodamine hydrazide‐triazole (RHT) tethered with a triazole moiety was developed for Cu²⁺ detection. In aqueous medium, the RHT probe exhibited high selectivity and sensitivity toward Cu²⁺ among other metal ions. The addition of Cu²⁺ triggered a fluorescence emission of RHT by 384‐fold (Φ = 0.33) based on a ring‐opening process and a subsequent hydrolysis reaction. Moreover, RHT also showed a selective colorimetric response toward Cu²⁺ from colorless solution to pink, readily observed with the naked eye. The limit of detection of RHT for Cu²⁺ was calculated to be 1 nM (0.06 ppb). RHT was successfully demonstrated to detect Cu²⁺ in Chang liver cells by confocal fluorescence microscopy.     

Effect of mercury and gold on growth,nutrient uptake,and anatomical changes in Chilopsis linearis

Plants of Chilopsis linearis were grown with 0, 50, 100, and 200 μM Hg [as Hg(CH₃COO)₂] and 0 and 50 μM Au (as KAuCl₄) in hydroponics. The results showed that seedling grown with 50 μM Au + 50 μM Hg and 50 μM Au + 100 μM Hg had roots 25 and 55% shorter than control roots, respectively. The element uptake determination using ICP/OES demonstrated that Hg at 50 and 100 μM (with and without Au) significantly increased (p < 0.05) the S concentration in leaves. On the other hand, the concentration of Fe significantly increased in roots of plants treated with Au–Hg. In addition, the stems of plants treated with Hg at 100 μM, with and without Au, had 239 and 876 mg Hg/kg dry biomass (d wt), respectively. Also, at 50 μM Hg, with and without Au, stems accumulated 375 and 475 mg Hg/kg d wt. The Hg concentration in leaves (287 mg Hg/kg d wt) was higher (p < 0.05) for the treatment containing 50 μM Au + 100 μM Hg. Without Au, the Hg concentration in leaves decreased to 75 mg Hg/kg d wt. Toxicity symptoms induced by Hg in cortex cells and the vascular system were lower in plants exposed to 50 μM Au + 50 μM Hg compared to plants exposed to 50 μM Hg only. Further, the SEM micrographs revealed deposition of Au–Hg particles inside the root. Although the concentrations of Hg used in this study showed different degree of toxicity, the plants displayed good agronomic value.