Localization and Speciation of Chromium in Coptis chinensis Franch. using Synchrotron Radiation X-ray Technology and Laser Ablation ICP-MS

Cr(VI) behaves differently than Cr(III) in the uptake, translocation and detoxification in rice roots

Excessive accumulation of chromium (Cr) causes severe damage to both physiological and biochemical processes and consequently growth repression in plants. Hexavalent chromium [Cr(VI)]-elicited alterations in plants have been widely elucidated at either physiological or molecular level, whereas little is known about trivalent chromium [Cr(III)]. Here, we found that both Cr(III) and Cr(VI) significantly inhibited root growth in rice plants. However, rice plants under Cr(VI) showed significantly less inhibition in root growth than those under Cr(III) at low levels, which might be attributed to the different hormetic effects of Cr(III) and Cr(VI) on rice plants. It was unexpected that Cr(III) could be actively taken up by rice roots similarly to Cr(VI); whereas they exhibited different kinetic uptake patterns. Furthermore, root-to-shoot Cr translocation under Cr(VI) was much lower than that under Cr(III). These results indicate that the uptake, translocation, and toxicity of Cr(III) differed greatly from those of Cr(VI). Transcriptome profiling of rice roots revealed that a series of gene families involved in detoxification, including ATP-binding cassette (ABC) transporters, multidrug and toxic compound extrusion proteins (MATEs), and Tau class glutathione S-transferases (GSTUs), were significantly associated with Cr accumulation and detoxification in rice roots. In addition, much more members of these gene families were upregulated by Cr(VI) compared to Cr(III), suggesting their vital roles in Cr uptake, translocation, and detoxification, especially under Cr(VI) stress. Further comparison of gstu9 and gstu10/50 mutants with their wild type confirmed that GSTUs play complex roles in the intracellular Cr transport and redox homeostasis during Cr(III) or Cr(VI) stress. Taken together, our findings provides new insights into the differential behaviors of Cr(III) and Cr(VI) in rice roots, as well as new candidate genes such as OsABCs and OsGSTUs, to further elucidate the mechanisms of the uptake, translocation, and detoxification of Cr(III) and Cr(VI).

Mass spectrometry imaging reveals flavor distribution in edible mushrooms

The spatial distribution of molecules and compounds responsible for the flavor profile of edible button mushrooms (Agaricus bisporous) has never been determined. The food industry is interested in knowing the localization of these compounds. Such knowledge would enable extraction of flavor compounds from a particular regions of the mushroom, which is safer for consumption compared to alternatives such as synthetic flavoring agents. The present study utilizes matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI), to determine the spatial distribution of flavor compounds in a mushroom. As MALDI-MSI requires very thin sections, a sample preparation protocol was optimized and sectioning fresh frozen mushrooms at 35 µm thickness was considered the best method to evaluate the distribution of flavor compounds. Further, the effect of heat on the spatial distribution of flavor compounds was investigated by heating whole mushrooms to 140 ℃ prior to sectioning. Heating reduced the water content of the mushroom and thus enabled the generation of even-thinner 17 µm thick sections. MALDI-MSI measurements performed on underivatized and on-tissue derivatized fresh frozen and heat-treated mushroom sections elucidated the spatial distribution of several flavor-related compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05883-0.

Research progress of the detection and analysis methods of heavy metals in plants

Heavy metal (HM)-induced stress can lead to the enrichment of HMs in plants thereby threatening people's lives and health via the food chain. For this reason, there is an urgent need for some reliable and practical techniques to detect and analyze the absorption, distribution, accumulation, chemical form, and transport of HMs in plants for reducing or regulating HM content. Not only does it help to explore the mechanism of plant HM response, but it also holds significant importance for cultivating plants with low levels of HMs. Even though this field has garnered significant attention recently, only minority researchers have systematically summarized the different methods of analysis. This paper outlines the detection and analysis techniques applied in recent years for determining HM concentration in plants, such as inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), X-ray absorption spectroscopy (XAS), X-ray fluorescence spectrometry (XRF), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), non-invasive micro-test technology (NMT) and omics and molecular biology approaches. They can detect the chemical forms, spatial distribution, uptake and transport of HMs in plants. For this paper, the principles behind these techniques are clarified, their advantages and disadvantages are highlighted, their applications are explored, and guidance for selecting the appropriate methods to study HMs in plants is provided for later research. It is also expected to promote the innovation and development of HM-detection technologies and offer ideas for future research concerning HM accumulation in plants.

Progress in phytoremediation of chromium from the environment

As chromium (Cr) in ecosystems affects human health through food chain exposure, phytoremediation is an environmentally friendly and efficient way to reduce chromium pollution in the environment. Here, we review the mechanism of absorption, translocation, storage, detoxification, and regulation of Cr in plants. The Cr(VI) form is more soluble, mobile, and toxic than Cr(III), reflecting how various valence states of Cr affect environmental risk characteristics, physicochemical properties, toxicity, and plant uptake. Plant root's response to Cr exposure leads to reactive oxygen species (ROS) generation and apoptosis. Cell wall immobilization, vacuole compartmentation, interaction of defense proteins and organic ligand with Cr, and removal of reactive oxygen species by antioxidants continue plant life. In addition, the combined application of microorganisms, genetic engineering, and the addition of organic acids, nanoparticles, fertilization, soil amendments, and other metals could accelerate the phytoremediation process. This review provides efficient methods to investigate and understand the complex changes of Cr metabolism in plants. Preferably, fast-growing, abundantly available biomass species should be modified to mitigate Cr pollution in the environment as these green and efficient remediation technologies are necessary for the protection of soil and water ecology.

Enhanced edible plant production using nano-manganese and nano-iron fertilizers: Current status, detection methods and risk assessment

BACKGROUND

Nanotechnology offers many benefits in the globally important field of food production and human nutrition, particularly by implementing agricultural nanoproducts. Of these, edible plant fertilizers enriched with nanosized forms of essential metals, Mn and Fe, are growing in importance with the advantages of enhanced action on plant roots.

SCOPE AND APPROACH

This review focuses on the importance of tracking the bioaccumulation and biodistribution of these pertinent nanofertilizers. An emphasis is given to the critical analysis of the state-of-the-art analytical strategies to examine the Mn and Fe nanoparticles in edible plant systems as well as to shedding light on the vast gap in the methodologies dedicated to the speciation, in vitro simulation, and safety testing of these promising nanomaterials. Also provided are guidances for the food chemists and technologists on the lights and shadows of particular analytical approaches as a matter of authors' expertise as analytical chemists.

KEY FINDINGS AND CONCLUSIONS

While the use of nanotechnology in agriculture seems to be growing increasingly, there is still a lack of analytical methodologies capable of investigating novel Mn- and Fe-based nanomaterials as potential fertilizers. Only the advent of reliable analytical tools in the field could bridge the gaps in our knowledge about processes in which those materials participate in the plant systems and their effects on crop production and quality of the produced food.

Individual and combined effects of chromium and ultraviolet-B radiation on defense system, ultrastructural changes, and production of secondary metabolite psoralen in a medicinal plant Psoralea corylifolia L

The present study focuses on the effects of individual and combined stress of chromium (Cr) and ultraviolet-B (UV-B) radiation on Psoralea corylifolia L. The experiment comprised four sets: (i) control, (ii) eUV-B (elevated UV-B i.e., ambient + 7.2 kJ m^-2 day^-1 UV-B), (iii) Cr (chromium; 30 mg kg^-1 soil), and (iv) Cr + eUV-B (chromium and elevated UV-B; Cr 30 mg kg^-1 and ambient + 7.2 kJ m^-2 day^-1 UV-B). The eUV-B and Cr individually and in combination showed the variable responses on ultrastructure, physiology and biomass however, the impact was more prominent under individual Cr treatment followed by Cr + eUV-B and eUV-B. Higher bioconcentration factor and the lowered translocation factor consequently led to a higher reduction in the below ground biomass and the lesser reduction in above ground biomass under Cr + eUV-B treatment as compared to individual Cr treatment. In addition, higher induction in the enzymatic (glutathione reductase, ascorbate peroxidase, superoxide dismutase, and glutathione-S-transferase) and non-enzymatic antioxidants (glutathione reduced) were found to be responsible for efficient scavenging of hydrogen peroxide and superoxide radical leading to lowered MDA content under combined treatment as compared to Cr treatment. Deposition of Cr as electron dense granules in the cytoplasm, vacuoles, and cell wall under Cr and Cr + eUV-B is contemplated as one of the cellular mechanisms of P. corylifolia against the toxicity of Cr. Psoralen increased under all treatments with a maximum increase under Cr + eUV-B treatment. Taken together our results accentuated that P. corylifolia can be grown in an area contaminated with Cr and has a higher influx of UV-B for the attainment of psoralen considering its pharmaceutical perspectives.

Removal of CrO42-, a Nonradioactive Surrogate of 99TcO4-, Using LDH-Mo3S13 Nanosheets

Removal of chromate (CrO₄^2-) and pertechnetate (TcO₄^-) from the Hanford Low Activity Waste (LAW) is beneficial as it impacts the cost, life cycle, operational complexity of the Waste Treatment and Immobilization Plant (WTP), and integrity of vitrified glass for nuclear waste disposal. Here, we report the application of [Mo^IV₃S₁₃]^2- intercalated layer double hydroxides (LDH-Mo₃S₁₃) for the removal of CrO₄^2- as a surrogate for TcO₄^-, from ppm to ppb levels from water and a simulated LAW off-gas condensate of Hanford's WTP. LDH-Mo₃S₁₃ removes CrO₄^2- from the LAW condensate stream, having a pH of 7.5, from ppm (∼9.086 × 10⁴ ppb of Cr⁶⁺) to below 1 ppb levels with distribution constant (K_d) values of up to ∼10⁷ mL/g. Analysis of postadsorbed solids indicates that CrO₄^2- removal mainly proceeds by reduction of Cr⁶⁺ to Cr³⁺. This study sets the first example of a metal sulfide intercalated LDH for the removal of CrO₄^2-, as relevant to TcO₄^-, from the simulated off-gas condensate streams of Hanford's LAW melter which contains highly concentrated competitive anions, namely F^-, Cl^-, CO₃^2-, NO₃^-, BO₃^3-, NO₂^-, SO₄^2-, and B₄O₇^2-. LDH-Mo₃S₁₃'s remarkable removal efficiency makes it a promising sorbent to remediate CrO₄^2-/TcO₄^- from surface water and an off-gas condensate of nuclear waste.

Speciation and Bio-Imaging of Chromium in Taraxacum officinale Using HPLC Post-column ID-ICP-MS, High Resolution MS and Laser Ablation ICP-MS Techniques

A new analytical procedure for the speciation of chromium (Cr) in plants by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was developed using a strong anion-exchange Mono Q column for the separation of the Cr species. To optimize the analytical procedure, Cr complexes were first synthesized from Cr-nitrate with the addition of an excess of ligand (90°C). Cr-oxalate, Cr-malate, Cr-citrate, Cr-aconitate and Cr-quinate complexes and Cr-nitrate (pH 6.5) were chromatographically separated from Cr(VI) by applying linear gradient elution from 100% water to 100% NH4Cl at a flow rate of 1.5 ml min−1 in 10 min. The column recoveries ranged from 100 to 104%. The exception was Cr-aconitate (column recovery 33%), where a quantitative synthesis was not possible. Good repeatability of the measurements (relative standard deviations better than ± 3%) and low limits of detection (below 0.37 ng ml−1 Cr) were achieved for the individual Cr species. The developed analytical procedure was applied to Cr speciation for dandelions (Taraxacum officinale) grown in soil with a high Cr content and a study of the uptake and metabolism of Cr species in dandelions grown in soil with a low Cr content treated with solutions of Cr(VI) or Cr-nitrate (5000 ng ml−1 Cr, pH 6.5) for 48 h. The separated Cr species were quantified by post-column isotope dilution ICP-MS, while the identification was based on retention times and was also supported by mass spectra obtained with high resolution mass spectrometry (HR-MS). The data indicate that for dandelions grown in Cr-rich soil and that treated with Cr-nitrate (pH 6.5), the Cr was mainly accumulated in the roots, while in plants treated with Cr(VI) (pH 6.5), the Cr was evenly distributed between the roots and the leaves. The Cr species found in dandelion roots and leaves were Cr-aconitate, Cr-malate, and Cr-quinate. The results revealed that Cr(VI) was completely reduced and metabolized to Cr(III) complexes. LA-ICP-MS data showed that the Cr in a leaf of dandelion grown in Cr-rich soil was localized mainly at the apex of the leaf.

Applied Analytical Methods for Detecting Heavy Metals in Medicinal Plants

For thousands of years, medicinal plants (MPs) have been one of the main sources of drugs worldwide. However, recently, heavy metal pollution has seriously affected the quality and safety of MPs. Consuming MPs polluted by heavy metals such as Pb, Hg, and Cu significantly threaten the health of consumers. To manage this situation, the levels of heavy metals in MPs must be controlled. In recent years, this field has attracted significant attention, but few researchers have systematically summarized various analytical methods. Therefore, it is necessary to investigate methods that can accurately and effectively detect the amount of heavy metals in MPs. Herein, some important analytical methods used to detect heavy metals in MPs and their applications have been introduced and summarized in detail. These include atomic absorption spectrometry, atomic fluorescence spectrometry, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, neutron activation analysis, and anodic stripping voltammetry. The characteristics of these methods were subsequently compared and analyzed. In addition, high-performance liquid chromatography, ultraviolet spectrophotometry, and disposable electrochemical sensors have also been used for heavy metal detection in MPs. To elucidate the systematic and comprehensive information, these methods have also been briefly introduced in this review.

Analytical Methodologies for Agrometallomics: A Critical Review

Agrometallomics, as an independent interdiscipline, is first defined and described in this review. Metallic elements widely exist in agricultural plants, animals and edible fungi, seed, fertilizer, pesticide, feedstuff, as well as the agricultural environment and ecology, and even functional and pathogenic microorganisms. So, the agrometallome plays a vital role in molecular and organismic mechanisms like environmetallomics, metabolomics, proteomics, lipidomics, glycomics, immunomics, genomics, etc. To further reveal the inner and mutual mechanism of the agrometallome, comprehensive and systematic methodologies for the analysis of beneficial and toxic metals are indispensable to investigate elemental existence, concentration, distribution, speciation, and forms in agricultural lives and media. Based on agrometallomics, this review summarizes and discusses the advanced technical progress and future perspectives of metallic analytical approaches, which are categorized into ultrasensitive and high-throughput analysis, elemental speciation and state analysis, and spatial- and microanalysis. Furthermore, the progress of agrometallomic innovativeness greatly depends on the innovative development of modern metallic analysis approaches including, but not limited to, high sensitivity, elemental coverage, and anti-interference; high-resolution isotopic analysis; solid sampling and nondestructive analysis; metal chemical species and metal forms, associated molecular clusters, and macromolecular complexes analysis; and metal-related particles or metal within the microsize and even single cell or subcellular analysis.

Recent progress in the development of MOF-based optical sensors for Fe3

Fe(iii) is a common pollutant released into our ecosystem from various industrial and anthropogenic activities which when in excess interferes with human health. A plethora of sensors based on various designs and working principles are being continuously synthesized and improvised for its facile detection. In the present review, we have provided a brief overview of the developments made in the field of metal organic framework (MOF) based optical sensors for Fe3+. MOFs have exponentially emerged in the field of research due to their high porosity, modular construction and easy tunability. These inorganic-organic hybrid porous materials are being essentially promoted as optical sensors because of their unique photophysical properties and potential sensing applications.

Chromium Stress in Plants: Toxicity, Tolerance and Phytoremediation

Extensive industrial activities resulted in an increase in chromium (Cr) contamination in the environment. The toxicity of Cr severely affects plant growth and development. Cr is also recognized as a human carcinogen that enters the human body via inhalation or by consuming Cr-contaminated food products. Taking consideration of Cr enrichment in the environment and its toxic effects, US Environmental Protection Agency and Agency for Toxic Substances and Disease Registry listed Cr as a priority pollutant. In nature, Cr exists in various valence states, including Cr(III) and Cr(VI). Cr(VI) is the most toxic and persistent form in soil. Plants uptake Cr through various transporters such as phosphate and sulfate transporters. Cr exerts its effect by generating reactive oxygen species (ROS) and hampering various metabolic and physiological pathways. Studies on genetic and transcriptional regulation of plants have shown the various detoxification genes get up-regulated and confer tolerance in plants under Cr stress. In recent years, the ability of the plant to withstand Cr toxicity by accumulating Cr inside the plant has been recognized as one of the promising bioremediation methods for the Cr contaminated region. This review summarized the Cr occurrence and toxicity in plants, role of detoxification genes in Cr stress response, and various plants utilized for phytoremediation in Cr-contaminated regions.

Synthesis and characterization of MOFs constructed from 5-(benzimidazole-1-yl)isophthalic acid and highly selective fluorescence detection of Fe(iii) and Cr(vi) in water

In this work, four novel metal–organic frameworks [Cd(bipa)]_n (1), {[Zn₂(bipa)₂]·2C₂H₅OH}_n (2), {[Co(bipa)]·C₂H₅OH}_n (3), {[Ni(bipa)₂]·2DMA}_n (4), (H₂bipa = 5-(benzimidazole-1-yl)isophthalic acid) were successfully synthesized under solvothermal conditions. Complexes 1–4 were characterized by powder X-ray diffraction, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Interestingly, the coordination patterns and 3D network structures of complexes 1–3 are very similar, while complex 4 is relatively unique. Complexes 1–2 exhibit potential fluorescent properties. Complex 1 can selectively and sensitively detect trace Fe(iii) and Cr(vi) in water by fluorescence quenching detection, and the quenching mechanism is further discussed.

In this work, four novel MOFs [Cd(bipa)]_n (1), {[Zn₂(bipa)₂]·2C₂H₅OH}_n (2), {[Co(bipa)]·C₂H₅OH}_n (3), {[Ni(bipa)₂]·2DMA}_n (4), (H₂bipa = 5-(benzimidazole-1-yl)isophthalic acid) were successfully synthesized under solvothermal conditions.

Trophic transfer and biotransformation of selenium in the mosquito (Aedes albopictus) and interactive effects with hexavalent chromium

As an essential micronutrient for animals with a narrow range between essentiality and toxicity, selenium (Se) usually coexists with chromium (Cr) in contaminated aquatic environments. This study investigated effects of three diets (Microcystis aeruginosa, Chlorella vulgaris and biofilms) exposed to Se or/and Cr on Aedes albopictus as a vector for the aquatic-terrestrial transfer of Se and Cr. Se(IV)-exposed mosquitoes concentrated Se up to 66-fold faster than Se(VI)-exposed ones, corresponding to the greater Se enrichment in Se(IV)-treated diets. Analysis using synchrotron-based X-ray absorption spectroscopy (XAS) showed that Se(0) (61.9-74.6%) dominated Se(VI)-exposed mosquitoes except for the C. vulgaris-fed larvae (organo-Se, 94.0%), while organo-Se accounted for 93.3-100.0% in Se(IV)-exposed mosquitoes. Cr accumulation in larvae (56.40-87.24 μg Cr/g DW) or adults (19.41-50.77 μg Cr/g DW) was not significantly different among all Cr(VI) treatments, despite varying diet Cr levels. With Cr(0) being dominant (57.7-94.0%), Cr(VI)-exposed mosquitoes posed little threat to predators. Although mosquitoes exposed to Se or Cr had shorter wings, adults supplied with C. vulgaris or biofilms co-exposed to Se(VI) and Cr(VI) had wings significantly (1.1-1.2 fold) longer than Se(VI) only exposed ones. Overall, our study reveals the role of Ae. albopictus in transferring waterborne Se and Cr from the contaminated aquatic ecosystem to the terrestrial ecosystem with the resulting eco-risks to wildlife in both ecosystems.

Do sulfur addition and rhizoplane iron plaque affect chromium uptake by rice (Oryza sativa L.) seedlings in solution culture?

Heavy metal uptake is confined by other elements, namely iron (Fe) and sulfur (S). There are yet no reports on the contribution of S supply to the attenuation of chromium (Cr) uptake when different species of Cr are employed. The bioaccumulation of Cr in two cultivars of rice seedlings subjected to 1.0 mg L^-1 Cr (III and VI) stress under S deprived or non-deprived conditions were examined in a hydroponic experiment. Sulfur nutrition promoted the root and shoot growth of rice cultivars under Cr stress. For both + S/ - S seedlings, the concentration of both Cr species followed the sequence ACA (ascorbic citrate acetic) extract > root > shoot, with less Cr accumulated in shoots of + S seedlings to that of - S seedlings. The concentrations of Cr and Fe in ACA extracts were found to be significantly correlated. Compared to + S treatment, Cr and Fe contents in iron plaque without S treatment were markedly reduced, especially for Cr (VI). Cr content in roots and shoots was indicated to be at par between cultivars; however, it significantly differed for S and Cr treatments. The Cr translocation between different parts of plaque-harboring seedlings was more pronounced in Cr (VI) treatment relative to Cr (III) treatment. Increased immobilization of Cr in iron plaque of + S seedlings and its subsequent reduction in aerial tissues may likely shed some light on the barrier function of iron plaques in the uptake of both Cr species by rice seedlings.

Assessment of chromium species dynamics in root solutions using isotope tracers

BACKGROUND

Chromium (Cr) exists in the environment in two chemical forms; CrIII is an essential micronutrient for glucose and lipid metabolism, whereas CrVI is toxic and a recognised carcinogen through inhalation. Numerous studies have attempted to evaluate their transfer mechanisms from soil and solution media into plants, usually with respect to the hyperaccumulation, detoxification and tolerance of the plant to CrVI.

METHODS

Isotopically enriched species of Cr, added as 50CrIII and 53CrVI, were used to investigate transfer from solution into the root systems of Spinacia oleracea. In addition the effect of sulphate (SO42-), as a competitor for CrVI uptake, was investigated. Separation of 50CrIII and 53CrVI was undertaken using HPLC-ICP-QQQ following isolation of root solutions using freeze/thaw centrifugation.

RESULTS

Irrespective of supplied CrVI concentration (250, 500 or 1000 μg L-1), the dominant species in both apoplastic (routed through cell wall and intercellular space as a passive mechanism) and symplastic (routed through cytoplasm as an active mechanism) root solutions was CrIII. There was evidence for CrVI reduction in the rhizosphere prior to uptake as an additional detoxification mechanism. Sulphate promoted uptake of CrVI through the active pathway, although increases in SO42- concentration did not yield a proportional increase in Cr symplastic solution concentration; CrIII was also the dominant species in these root solutions.

CONCLUSION

The results indicate that Spinacia oleracea plants can effectively reduce CrVI to CrIII and that the uptake pathways for both CrIII and CrVI are more complex than previously reported. Further work is required to understand the physiological processes that result in the reduction of CrVI prior to, and during, uptake. The efficacy of sulphate to augment existing agricultural management strategies, such as liming and organic reincorporation, also requires further investigation to establish suitable application rates and applicability to other environmental contaminants.

Glutathione and hydrogen sulfide are required for sulfur-mediated mitigation of Cr(VI) toxicity in tomato, pea and brinjal seedlings

In plants, investigation on heavy metal toxicity and its mitigation by nutrient elements have gained much attention. However, mechanism(s) associated with nutrients-mediated mitigation of metal toxicity remain elusive. In this study, we have investigated the role and interrelation of glutathione (GSH) and hydrogen sulfide (H2 S) in the regulation of hexavalent chromium [Cr(VI)] toxicity in tomato (Solanum lycopersicum), pea (Pisum sativum) and brinjal (Solanum melongena) seedlings, supplemented with additional sulfur (S). The results show that Cr(VI) significantly reduced growth, total chlorophyll and photosynthetic quantum yield of tomato, pea and brinjal seedlings which was accompanied by enhanced intracellular accumulation of Cr(VI) in roots. Moreover, Cr(VI) enhanced the generation of reactive oxygen species in the studied vegetables, while antioxidant defense system exhibited differential responses. However, additional supply of S alleviated Cr(VI) toxicity. Interestingly, addition of l-buthionine sulfoximine (BSO, a glutathione biosynthesis inhibitor) further increased Cr(VI) toxicity even in the presence of additional S but GSH addition reverses the effect of BSO. Under similar condition, endogenous H2 S, l-cysteine desulfhydrase (DES) activity and cysteine content did not significantly differ when compared to controls. Hydroxylamine (HA, an inhibitor of DES) also increased Cr(VI) toxicity even in the presence of additional S but sodium hydrosulfide (NaHS, an H2 S donor) reverses the effect of HA. Moreover, Cr(VI) toxicity amelioration by NaHS was reversed by the addition of hypotaurine (HT, an H2 S scavenger). Taken together, the results show that GSH which might be derived from supplied S is involved in the mitigation of Cr(VI) toxicity in which H2 S signaling preceded GSH biosynthesis.

Synergistic effects of chromium and copper on photosynthetic inhibition, subcellular distribution, and related gene expression in Brassica napus cultivars

Nowadays, modern plant physiology focuses on complex behavior of metal co-contaminants in agrosystems. Keeping this in view, the current study was conducted to investigate the response of two Brassica napus cultivars (Zheda 622 and ZS 758) under co-contamination of copper (Cu²⁺) and chromium (Cr⁶⁺) to observe their effects on plant growth, photosynthetic parameters, and subcellular distribution of these metals in leaves and roots. The results showed that exposure to Cu and Cr causes decline in plant growth, including biomass and plant height. Significant decrease in pigment concentration and the photosynthetic activity [photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (E), maximal quantum yield of photosystem II (Fv/Fm)] in leaves was also observed. Results of subcellular distribution of metals showed that Cu and Cr were predominantly distributed in cell wall and soluble fraction of roots and leaves. Moreover, Cu and Cr in cellular fractions showed a synergistic accumulation pattern under combined metal stress treatment. Both cultivars showed increased levels of reactive oxygen species (ROS), i.e., hydrogen peroxide (H₂O₂) and superoxide radical (O₂^•-), and significant modulation in the activities of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX)] under Cu/Cr alone or their combined treatments. Similarly, expression levels of defense-related genes, such as BnCat, BnApx, BnPrx, and BnSod, were also generally up-regulated compared with control. Electron micrographs (TEM) of the mesophyll and root tip cells indicated prominent alterations both in cellular and organelle levels. Additionally, Cr was found to be more toxic than Cu but less than their combined effect, as revealed by enhanced production of oxidative stress and a reduction in biomass production and photosynthetic activity. The present results also suggest that cultivar ZS 758 is more resistant to Cu/Cr than Zheda 622, due to better adapted metabolism and maintenance of structural integrity under metal stress.