Physiological and antioxidative responses of medicinal plants exposed to heavy metals stress

Emerging role of osmoprotectant glycine betaine to mitigate heavy metals toxicity in plants: a systematic review

Heavy metals (HMs) toxicity has become one of the major global issues and poses a serious threat to the environment in recent years. HM pollution in agricultural soil is caused by metal mining, smelting, volcanic activity, industrial discharges, and excessive use of phosphate fertilizers. HMs above a threshold level adversely affect the cellular metabolism of plants by producing reactive oxygen species (ROS), which attack cellular proteins. There are different mechanisms (physiological and morphological) adopted by plants to survive in the era of abiotic stress. Various osmoprotectants or compatible solutes, including amino acids, sugar, and betaines, enable the plants to counteract the HM stress. Glycine betaine (GB) is an effective osmolyte against HM stress among compatible solutes. GB has been shown to improve plant growth, photosynthesis, uptake of nutrients, and minimize oxidative stress in plants under HM stress. Additionally, GB increases the activity of antioxidant enzymes such as CAT (catalase), SOD (superoxide dismutase), and POD (peroxidase), which are effective in scavenging unwarranted ROS. Since not all species of plants can naturally produce or accumulate GB in response to stress, various approaches have been explored for introducing them. Plant hormones like salicylic acid, ABA (abscisic acid), and JA (jasmonic acid) co-ordinately stimulate the accumulation of GB inside the cell under HM stress. Apart from the exogenous application, the introduction of GB pathway genes in GB deficient species via genetic engineering also seems to be efficient in mediating HM stress. This review complied the beneficial effects of GB in mitigating HM stress and its role as a plant growth regulator. Additionally, the review explores the potential for engineering GB biosynthesis in plants as a strategy to bolster their resilience to HMs.

Response of antioxidant activity, active constituent and rhizosphere microorganisms of Salvia miltiorrhiza to combined application of microbial inoculant, microalgae and biochar under Cu stress

Salvia miltiorrhiza, a widely used medicinal herb renowned for its properties in promoting blood circulation, removing blood stasis and alleviating pain, is currently facing quality degradation due to excessive heavy metal levels, posing a threat to medication safety. In order to investigate the effects of microbial inoculant, microalgae and biochar on the growth of Salvia miltiorrhiza under copper (Cu) stress, as well as its Cu absorption, antioxidant activity, active component contents and rhizosphere microbial community, a pot experiment was conducted. Salvia miltiorrhiza plants were cultivated in the soil containing 400 mg/kg of Cu for six months and treated with microbial inoculant, microalgae and biochar, either individually or in combination. Almost all soil amendment treatments led to an increase in root biomass. Notably, co-application of microbial inoculant and microalgae had the optimal effect with a 63.07 % increase compared to the group treated solely with Cu. Moreover, when microbial inoculant was applied alone or in combination with microalgae, the Cu content in plant roots was reduced by 19.29 % and 25.37 %, respectively, whereas other treatments failed to show a decreasing trend. Intriguingly, Cu stress increased the active component contents in plant roots, and they could also be enhanced beyond non-stress levels when microbial inoculant and microalgae were applied together or in combination with biochar. Analyses of plant antioxidant activity, soil properties and rhizosphere microorganisms indicated that these amendments may alleviate Cu stress by enhancing peroxidase activity, facilitating plant nutrient absorption, and enriching beneficial microorganisms capable of promoting plant growth and mitigating heavy metal-induced damage. This study suggests that the combined application of microbial inoculant and microalgae can reduce Cu levels in Salvia miltiorrhiza while enhancing its quality under Cu stress.

Interaction between Haematococcus pluvialis microalgae and lead nitrate: lead adsorption from water

Our study aims to investigate the response of the unicellular alga, Haematococcus pluvialis, to the toxicity of lead and propose a low-cost, highly efficient biological adsorbent for the purification of wastewater and lead-contaminated water. The first part examines the effects of lead toxicity on certain physiological indicators of this alga. In the second part, the potential of this alga in lead removal and its adsorption capacity was assessed. The alga was cultivated in a BG11 medium and treated with lead nitrate concentrations of 10, 50, and 200 mg/L during its exponential growth. The results showed that with an increase in lead concentration up to 200 mg/L, the growth rate, chlorophyll a, chlorophyll b, carotenoid and total protein content decreased, while malondialdehyde (MDA) content increased. The astaxanthin content slightly increased at the 10 mg/L but decreased at the 200 mg/L treatment. Maximum lead adsorption was observed at 98.69% under optimal conditions, including a pH of 6, an adsorbent dose of 1 g/L, a lead concentration of 25 mg/L, a temperature of 25 °C, and an exposure time of 120 min. The results of this study demonstrate that Haematococcus pluvialis has the potential for effective lead removal from aquatic environments.

Role of the molecular structure of humified organic matter in rice plant response to environmental lead pollution

Humified organic matter has been shown to decrease Pb toxicity in plants. However, there are still gaps in our understanding of the mechanism by which this phenomenon occurs. In this study, we aimed to assess the ability of humic substances (HSs), humic acids (HAs), and fulvic acids (FAs) to enhance defense mechanisms in rice plants under lead (Pb)-stressed conditions. HS fractions were isolated from vermicompost using the chemical fractionation methodology established by the International Humic Substances Society. These fractions were characterized by solid-state NMR and FTIR. Chemometric analysis was used to compare humic structures and correlate them with bioactivity. Three treatments were tested to evaluate the protective effect of humic fractions on rice plants. The first experiment involved the application of humic fractions along with Pb. The second comprised pretreatment with humic fractions followed by subsequent exposure to Pb stress. The third experiment involved Pb stress and subsequent treatment with humic fractions. The root morphology and components of the antioxidative defense system were evaluated and quantified. The results showed that HS + Pb, HA + Pb, and FA + Pb treatment preserved root growth and reduced the levels of O2- and malondialdehyde (MDA) in the roots by up to 5% and 2%, respectively. Pretreatment of the plants with humic fractions promoted the maintenance of root growth and reduced the contents of O2-, H2O2, and MDA by up to 48%, 22%, and 20%, respectively. Combined application of humic fractions and Pb reduced the Pb content in plant tissues by up to 60%, while pretreatment reduced it by up to 80%. The protective capacity of humic fractions is related to the presence of peptides, lignin, and carbohydrate fragments in their molecular structures. These results suggest that products could be developed that can mitigate the adverse effects of heavy metals on agricultural crops.

Toxicity, physiological response, and biosorption mechanism of Dunaliella salina to copper, lead, and cadmium

Background

Heavy metal pollution has become a global problem, which urgently needed to be solved owing to its severe threat to water ecosystems and human health. Thus, the exploration and development of a simple, cost-effective and environmental-friendly technique to remove metal elements from contaminated water is of great importance. Algae are a kind of photosynthetic autotroph and exhibit excellent bioadsorption capacities, making them suitable for wastewater treatment.

Methods

The effects of heavy metals (copper, lead and cadmium) on the growth, biomolecules accumulation, metabolic responses and antioxidant response of Dunaliella salina were investigated. Moreover, the Box-Behnken design (BBD) in response surface methodology (RSM) was used to optimize the biosorption capacity, and FT-IR was performed to explore the biosorption mechanism of D. salina on multiple heavy metals.

Results

The growth of D. salina cells was significantly inhibited and the contents of intracellular photosynthetic pigments, polysaccharides and proteins were obviously reduced under different concentrations of Cu2+, Pb2+ and Cd2+, and the EC50 values were 18.14 mg/L, 160.37 mg/L and 3.32 mg/L at 72 h, respectively. Besides, the activities of antioxidant enzyme SOD and CAT in D. salina first increased, and then descended with increasing concentration of three metal ions, while MDA contents elevated continuously. Moreover, D. salina exhibited an excellent removal efficacy on three heavy metals. BBD assay revealed that the maximal removal rates for Cu2+, Pb2+, and Cd2+ were 88.9%, 87.2% and 72.9%, respectively under optimal adsorption conditions of pH 5-6, temperature 20-30°C, and adsorption time 6 h. Both surface biosorption and intracellular bioaccumulation mechanisms are involved in metal ions removal of D. salina. FT-IR spectrum exhibited the main functional groups including carboxyl (-COOH), hydroxyl (-OH), amino (-NH2), phosphate (-P=O) and sulfate (-S=O) are closely associated with the biosorption or removal of heavy metalsions.

Discussion

Attributing to the brilliant biosorption capacity, Dunaliella salina may be developed to be an excellent adsorbent for heavy metals.

Impact of Heavy Metal Pollution in the Environment on the Metabolic Profile of Medicinal Plants and Their Therapeutic Potential

The paper provides a comprehensive examination of heavy metal stress on medicinal plants, focusing on its impact on antioxidant capacity and biosynthetic pathways critical to their therapeutic potential. It explores the complex relationship between heavy metals and the physiological and biochemical responses of medicinal plants, highlighting how metal stress disrupts biosynthetic pathways, altering concentrations of secondary metabolites. This disruption may compromise the overall quality and efficacy of medicinal plants, requiring a holistic understanding of its cumulative impacts. Furthermore, the study discusses the potential of targeted genetic editing to enhance plant resilience against heavy metal stress by manipulating genes associated with antioxidant defenses. This approach represents a promising frontier in safeguarding medicinal plants in metal-contaminated environments. Additionally, the research investigates the role of phytohormone signaling in plant adaptive mechanisms to heavy metal stress, revealing its influence on biochemical and physiological responses, thereby adding complexity to plant adaptation. The study underscores the importance of innovative technologies and global cooperation in protecting medicinal plants' therapeutic potential and highlights the need for mitigation strategies to address heavy metal contamination effectively.

Unlocking hormesis and toxic effects induced by cadmium in Polygonatum cyrtonema Hua based on morphology, physiology and metabolomics

Traditional Chinese medicine materials (TCMMs) are widely planted and used, while cadmium (Cd) is a widespread pollutant that poses a potential risk to plant growth and human health. However, studies on the influences of Cd on TCMMs have been limited. Our study aims to reveal the antioxidation-related detoxification mechanism of Polygonatum cyrtonema Hua under Cd stress based on physiology and metabolomics. The results showed that Cd0.5 (total Cd: 0.91 mg/kg; effective Cd: 0.45 mg/kg) induced hormesis on the biomass of roots, tubers and aboveground parts with increases of 22.88%, 27.12% and 17.02%, respectively, and significantly increased the flavonoids content by 57.45%. Additionally, the metabolism of caffeine, glutamine, arginine and purine was upregulated to induce hormesis in Cd0.5, which enhanced the synthesis of resistant substances such as spermidine, choline, IAA and saponins. Under Cd2 stress, choline and IAA decreased, and fatty acid metabolites (such as peanut acid and linoleic acid) and 8-hydroxyguanosine increased in response to oxidative damage, resulting in a significant biomass decrease. Our findings further reveal the metabolic process of detoxification by antioxidants and excessive Cd damage in TCMMs, deepen the understanding of detoxification mechanisms related to antioxidation, and enrich the relevant theories of hormesis induced by Cd.

Safe utilization evaluation of two typical traditional Chinese medicinal materials in Cd-contaminated soil based on the analysis of Cd transfer and AHP model

Due to the increasing scarcity of wild resources, most traditional Chinese medicinal materials (TCMMs) in the market are produced via artificial cultivation. The widespread pollution of cadmium (Cd) in soil limits the safe cultivation and use of TCMMs. This study investigated Cd accumulation, distribution, and the medicinal component content under simulated field conditions to clarify the differences in the Cd absorption, transfer and detoxification mechanisms of Polygonatum cyrtonema Hua and Bletilla striata, and provide the preliminary safe utilization conditions of TCMMs based on the analytic hierarchy process (AHP). The results showed that the Cd content of P. cyrtonema Hua was lower than the safety threshold under a high soil Cd concentration of 0.91 mg/kg (Cd-L), while B. striata was safe only at a low Cd concentration of 0.25 mg/kg (CK). Cd at 0.91 mg/kg induced hormesis affecting the net increase in biomass and medicinal component content for both TCMMs, while P. cyrtonema Hua showed better potential for safe utilization. Additionally, P. cyrtonema Hua had stronger resistance to Cd stress, exhibiting superior characteristics for synergistic absorption of Cd with mineral elements, transfer to nonmedical part and safer fixation forms in subcellular components. In contrast, B. striata showed insufficient Cd tolerance, and Cd was easily accumulated in organelles to inhibit plant growth. Our findings may attract more attention to the safe cultivation of TCMMs and provide insight into guidance for the safe utilization of slightly Cd-contaminated soil.

Alleviation of cadmium toxicity in pea (Pisum sativum L.) through Zn-Lys supplementation and its effects on growth and antioxidant defense

Cadmium significantly impacts plant growth and productivity by disrupting physiological, biochemical, and oxidative defenses, leading to severe damage. The application of Zn-Lys improves plant growth while reducing the stress caused by heavy metals on plants. By focusing on cadmium stress and potential of Zn-Lys on pea, we conducted a pot-based study, organized under completely randomized block design CRD-factorial at the Botanical Garden of Government College University, Faisalabad. Both pea cultivars were grown in several concentrations of cadmium @ 0, 50 and 100 μM, and Zn-Lys were exogenously applied @ 0 mg/L and 10 mg/L with three replicates for each treatment. Cd-toxicity potentially reduces plant growth, chlorophyll contents, osmoprotectants, and anthocyanin content; however, an increase in MDA, H2O2 initiation, enzymatic antioxidant activities as well as phenolic, flavonoid, proline was observed. Remarkably, exogenously applied Zn-Lys significantly enhanced the plant growth, biomass, photosynthetic attributes, osmoprotectants, and anthocyanin contents, while further increase in enzymatic antioxidant activities, total phenolic, flavonoid, and proline contents were noticed. However, application of Zn-Lys instigated a remarkable decrease in levels of MDA and H2O2. It can be suggested with recommendation to check the potential of Zn-Lys on plants under cadmium-based toxic soil.

Graphene oxide-based aerogel stimulates growth, mercury accumulation, photosynthesis-related gene expression, antioxidant efficiency and redox status in wheat under mercury exposure

Mercury (Hg) pollution is a global concern in cropland systems. Hg contamination causes a disruption in the growth, energy metabolism, redox balance, and photosynthetic activity of plants. In the removal of Hg toxicity, a recent critical strategy is the use of aerogels with biodegradability and biocompatibility. However, it is unknown how graphene oxide-based aerogels stimulate the defense systems in wheat plants exposed to Hg toxicity. Therefore, in this study, the photosynthetic, genetic, and biochemical effects of reduced graphene oxide aerogel treatments (gA; 50-100-250 mg L-1) were examined in wheat (Triticum aestivum) under Hg stress (50 μM HgCl2). The relative growth rate (RGR) significantly decreased (84%) in response to Hg stress. However, the reduced RGR and water relations (RWC) of wheat were improved by gA treatments. The impaired gas exchange levels (stomatal conductance, carbon assimilation rate, intercellular CO2 concentrations, and transpiration rate) caused by stress were reversed under Hg plus gAs. Additionally, stress hampered chlorophyll fluorescence (Fv/Fo, Fv/Fm), and under Hg toxicity the expression of psaA genes was reduced (>0.4-fold), but psaB gene was significantly up-regulated (>3-fold) which are the genes involved in PSI. By increasing expression patterns of both genes relating to PSI, gAs reversed the adverse consequences on Fv/Fo and Fv/Fm in the presence of excessive Hg concentration. The activities of glutathione S-transferase (GST), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) decreased under Hg toxicity. On the other hand, the activities of superoxide dismutase (SOD), APX, GST, and glutathione peroxidase (GPX) increased following gA treatments against stress, leading to the successful elimination of toxic levels of H2O2 and lipid peroxidation (TBARS content) by decreasing the levels by about 30%, and 40%, respectively. By modulating enzyme/non-enzyme activity/contents including the AsA-GSH cycle, gAs contributed to the protection of the cellular redox state. Most important of all, gA applications were able to reduce Hg intake by approximately 66%. Therefore, these results showed that gAs were effective in highly inhibiting Hg uptake and could significantly increase wheat tolerance to toxicity by eliminating Hg-induced oxidative damage and inhibiting metabolic processes involved in photosynthesis. The findings obtained from the study provide a new perspective on the alleviation roles of reduced graphene oxide aerogels as an effective adsorbent for decreasing damages of mercury toxicity in wheat plants.

The apple lipoxygenase MdLOX3 positively regulates zinc tolerance

Various abiotic stresses, especially heavy metals near factories around the world, limit plant growth and productivity worldwide. Zinc is a light gray transition metal, and excessive zinc will inactivate enzymes in the soil, weaken the biological function of microorganisms, and enter the food chain through enrichment, thus affecting human health. Lipoxygenase (LOX) can catalyze the production of fatty acid derivatives from phenolic triglycerides in plants and is an important pathway of fatty acid oxidation in plants, which usually begins under unfavorable conditions, especially under biotic and abiotic stresses. Lipoxygenase can be divided into 9-LOX and 13-LOX. MdLOX3 is a homolog of AtLOX3 and has been identified in apples (housefly apples). MdLOX3 has a typical conserved lipoxygenase domain, and promoter analysis shows that it contains multiple stress response elements. In addition, different abiotic stresses and hormonal treatments induced the MdLOX3 response. In order to explore the inherent anti-heavy metal mechanism of MdLOX3, this study verified the properties of MdLOX3 based on genetic analysis and overexpression experiments, including plant taproots length, plant fresh weight, chlorophyll, anthocyanins, MDA, relative electrical conductivity, hydrogen peroxide and superoxide anion, NBT\DAB staining, etc. In the experiment, overexpression of MdLOX3 in apple callus and Arabidopsis effectively enhanced the tolerance to zinc stress by improving the ability to clear ROS. Meanwhile, tomato materials with overexpression of ectopia grew better under excessive zinc ion stress. These results indicated that MdLOX3 had a good tolerance to heavy metal zinc. Homologous mutants are more sensitive to zinc, which proves that MdLOX3 plays an important positive role in zinc stressed apples, which broadens the range of action of LOX3 in different plants.

Toxic risk evaluation of effluents from a swine biodigester in the plant models Lactuca sativa and Allium cepa

Pig farming is recognized as an activity with great polluting potential. The aim was to investigate possible environmental risks of effluents from the stabilization pond (SP) and the raw effluent (RE) from the biodigestion process of swine residues, in different concentrations in the models Lactuca sativa and Allium cepa. Seeds were germinated in different dilutions, 100% (C1), 50% (C2), 25% (C3), 12.5% (C4), 6.25% (C5), 3.12% (C6), 0.78% (C7), and 0.39% (C8). Distilled water was used as the negative control (CN) and trifluralin (0.84 g/L-1) as the positive control. Germination (GR), root growth (RG), cell cycle, and oxidative stress (OS) were analyzed. To assess OS, the activity of the enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) and the quantification of glutathione (GSH) and lipid peroxidation (LPO) were analyzed. Data were submitted to ANOVA (one way), followed by the Kruskal-Wallis mean test (P ≤ 0.05). Chemical analysis showed high values of Cu, Fe, Mn, and Zn. Dilutions (C1, C2, C3 RE) and (C1 and C2 SP) inhibited GR and RG of L. sativa and A. cepa than other concentrations. The mitotic index showed a reduction in C5 (RE), C6, and C7 (SP) of L. sativa and C3 and C4 (SP) of A. cepa in relation to CN and higher frequencies of chromosomal alterations. Regarding the OS, only the concentrations of SP treatment showed statistical difference in relation to the NC: in L. sativa model, GSH at (C5 and C8) concentrations and LPO (C7); in A. cepa model, SOD (C3 and C4), GST (C4, C5 and C6), GSH (C5 and C8), and CAT (C3 and C7). The alterations in metabolism are possibly related to the metals, such as zinc and copper, observed in high amounts in the raw waste. The results allowed us to conclude that the raw and stabilization pond effluents offer environmental risks, requiring caution and monitoring in the use of these effluents.

Unraveling the influence of TiO2 nanoparticles on growth, physiological and phytochemical characteristics of Mentha piperita L. in cadmium-contaminated soil

Among the metals contaminants, cadmium (Cd) is one of the most toxic elements in cultivated soils, causing loss of yield and productivity in plants. Recently, nanomaterials have been shown to mitigate the negative consequences of environmental stresses in different plants. However, little is known about foliar application of titanium dioxide nanoparticles (TiO2 NPs) to alleviate Cd stress in medicinal plants, and their dual interactions on essential oil production. The objective of this study was to investigate the effects of foliar-applied TiO2 NPs on growth, Cd uptake, chlorophyll fluorescence, photosynthetic pigments, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, total phenols, anthocyanins, flavonoids, antioxidant enzymes (SOD, CAT and POD) activity and essential oil content of Mentha piperita L. (peppermint) under Cd stress. For this purpose, plants were grown in Cd-contaminated (0, 20, 40, and 60 mg L-1) soil, and different concentrations of TiO2 NPs (0, 75, and 150 mg L-1) were foliar sprayed at three times after full establishment until the beginning of flowering. Exposure to TiO2 NPs significantly (P < 0.01) increased shoot dry weight (37.8%) and the number of lateral branches (59.4%) and decreased Cd uptake in plant tissues as compared to the control. Application of TiO2 NPs increased the content of plastid pigments, and the ratio Fv/Fm (13.4%) as compared to the control. Additionally, TiO2 NPs reduced the stress markers, MDA and H2O2 contents and enhanced the activity of the phenylalanine ammonia-lyase (PAL) enzyme (60.5%), total phenols (56.1%), anthocyanins (42.6%), flavonoids (25.5%), and essential oil content (52.3%) in Cd-stressed peppermint compared to the control. The results also demonstrated that foliar spray of TiO2 NPs effectively improved the growth and chlorophyll fluorescence parameters and reduced Cd accumulation in peppermint, which was mainly attributed to the reduction of oxidative burst and enhancement of the enzymatic (SOD, CAT, and POD) antioxidant defense system due to the uptake of NPs. The findings provide insights into the regulatory mechanism of TiO2 NPs on peppermint plants growth, physiology and secondary metabolites production in Cd-contaminated soil.

Emergence of toxic trace elements in plant environment: Insights into potential of silica nanoparticles for mitigation of metal toxicity in plants

Emergence of trace elements at potentially toxic concentrations in the environment has become a global issue in recent times. Owing to the rapid population growth, unregulated industrialisation, intensive farming practices and excessive mining activities, these elements are accumulating in environment at high toxic concentrations. The exposure of plants to metal-contaminated environments severely influences their reproductive and vegetative growth, eventually affecting crop performance and production. Hence, it is crucial to find alternatives to mitigate the stress caused by toxic elements, in plants of agricultural importance. In this context, silicon (Si) has been widely recognized to alleviate metal toxicity and promote plant growth during various stress conditions. Amending soil with silicates has shown to ameliorate the lethal effects of metals and stimulates crop development. However, in comparison to silicon in bulk form, nano-sized silica particles (SiNPs) have been demonstrated to be more efficient in their beneficial roles. SiNPs can be used for various technological applications, viz. Improving soil fertility, agricultural yield, and remediating heavy metal-polluted soil. The research outcomes of studies focussing on role of silica nanoparticles to specifically mitigate the metal toxicity in plants have not been reviewed earlier in depth. The aim of this review is to explore the potential of SiNPs in alleviating metal stress and improving plant growth. The benefits of nano-silica over bulk-Si fertilizers in farming, their performance in diverse plant varieties, and the possible mechanisms to mitigate metal toxicity in plants have been discussed in detail. Further, research gaps are identified and future prospects are envisioned for advanced investigations in this field. The growing interest towards nano-silica related research will facilitate exploration of the true prospective of these nanoparticles for mitigation of metal stress in crops and in other fields of agriculture as well.

Heavy Metal Induced Oxidative Stress Mitigation and ROS Scavenging in Plants

Although trace elements are essential for life, environmental contamination due to metal accumulation and overuse in various sectors, such as healthcare, agriculture, industry, and cosmetics, poses significant health concerns. Exposure of plants to heavy metals leads to the overproduction of reactive oxygen species (ROS) due to their ability to change mitochondrial membrane permeability and restrict the action of ROS clearance enzymes in the cellular antioxidant system. The interaction of ROS with cellular membranes, heavy-metal-induced interactions directly or indirectly with different macromolecules, and signaling pathways leads to the accumulation of environmental pollutants and oxidative stress in exposed organisms. The heavy metal-ROS-cell signaling axis affects various pathological processes such as ATP depletion, excess ROS production, mitochondrial respiratory chain damage, decoupling of oxidative phosphorylation, and mitochondrial death. This review focuses on discussing the toxic effects of different heavy metals on plants, with particular emphasis on oxidative stress, its consequences, and mitigation strategies.

Melatonin and strigolactone mitigate chromium toxicity through modulation of ascorbate-glutathione pathway and gene expression in tomato

Chromium (Cr) is considered one of the most hazardous metal contaminant reducing crop production and putting human health at risk. Phytohormones are known to regulate chromium stress, however, the function of melatonin and strigolactones in Chromium stress tolerance in tomato is rarely investigated. Here we investigated the potential role of melatonin (ML) and strigolactone (SL) on mitigating Chromium toxicity in tomato. With exposure to 300 μM Cr stress a remarkable decline in growth (63.01%), biomass yield (50.25)%, Pigment content (24.32%), photosynthesis, gas exchange and Physico-biochemical attributes of tomato was observed. Cr treatment also resulted in oxidative stress closely associated with higher H2O2 generation (215.66%), Lipid peroxidation (50.29%), electrolyte leakage (440.01%) and accumulation of osmolytes like proline and glycine betine. Moreover, Cr toxicity up-regulated the transcriptional expression profiles of antioxidant, stress related and metal transporter genes and down-regulated the genes related to photosynthesis. The application of ML and SL alleviated the Cr induced phytotoxic effects on photosynthetic pigments, gas exchange parameters and restored growth of tomato plants. ML and SL supplementation induced plant defense system via enhanced regulation of antioxidant enzymes, ascorbate and glutathione pool and transcriptional regulation of several genes. The coordinated regulation of antioxidant and glyoxalase systems expressively suppressed the oxidative stress. Hence, ML and SL application might be considered as an effective approach for minimizing Cr uptake and its detrimental effects in tomato plants grown in contaminated soils. The study may also provide new insights into the role of transcriptional regulation in the protection against heavy metal toxicity.

Heavy metals and arsenic stress in food crops: Elucidating antioxidative defense mechanisms in hyperaccumulators for food security, agricultural sustainability, and human health

The spread of heavy metal(loid)s at soil-food crop interfaces has become a threat to sustainable agricultural productivity, food security, and human health. The eco-toxic effects of heavy metals on food crops can be manifested through reactive oxygen species that have the potential to disturb seed germination, normal growth, photosynthesis, cellular metabolism, and homeostasis. This review provides a critical overview of stress tolerance mechanisms in food crops/hyperaccumulator plants against heavy metals and arsenic (HM-As). The HM-As antioxidative stress tolerance in food crops is associated with changes in metabolomics (physico-biochemical/lipidomics) and genomics (molecular level). Furthermore, HM-As stress tolerance can occur through plant-microbe, phytohormone, antioxidant, and signal molecule interactions. Information regarding the avoidance, tolerance, and stress resilience of HM-As should help pave the way to minimize food chain contamination, eco-toxicity, and health risks. Advanced biotechnological approaches (e.g., genome modification with CRISPR-Cas9 gene editing) in concert with traditional sustainable biological methods are useful options to develop 'pollution safe designer cultivars' with increased climate change resilience and public health risks mitigation. Further, the usage of HM-As tolerant hyperaccumulator biomass in biorefineries (e.g., environmental remediation, value added chemicals, and bioenergy) is advocated to realize the synergy between biotechnological research and socio-economic policy frameworks, which are inextricably linked with environmental sustainability. The biotechnological innovations, if directed toward 'cleaner climate smart phytotechnologies' and 'HM-As stress resilient food crops', should help open the new path to achieve sustainable development goals (SDGs) and a circular bioeconomy.

Out of site, out of mind: Changes in feather moss phyllosphere microbiota in mine offsite boreal landscapes

Plant-microbe interactions play a crucial role in maintaining biodiversity and ecological services in boreal forest biomes. Mining for minerals, and especially the emission of heavy metal-enriched dust from mine sites, is a potential threat to biodiversity in offsite landscapes. Understanding the impacts of mining on surrounding phyllosphere microbiota is especially lacking. To investigate this, we characterized bacterial and fungal communities in the phyllosphere of feather moss Pleurozium schreberi (Brid). Mitt in boreal landscapes near six gold mine sites at different stages of the mine lifecycle. We found that (1) both mining stage and ecosystem type are drivers of the phyllosphere microbial community structure in mine offsite landscapes; (2) Bacterial alpha diversity is more sensitive than fungal alpha diversity to mining stage, while beta diversity of both groups is impacted; (3) mixed and deciduous forests have a higher alpha diversity and a distinct microbial community structure when compared to coniferous and open canopy ecosystems; (4) the strongest effects are detectable within 0.2 km from operating mines. These results confirmed the presence of offsite effects of mine sites on the phyllosphere microbiota in boreal forests, as well as identified mining stage and ecosystem type as drivers of these effects. Furthermore, the footprint was quantified at 0.2 km, providing a reference distance within which mining companies and policy makers should pay more attention during ecological assessment and for the development of mitigation strategies. Further studies are needed to assess how these offsite effects of mines affect the functioning of boreal ecosystems.

Integrated transcriptome and metabolome analysis reveals the mechanism of tolerance to manganese and cadmium toxicity in the Mn/Cd hyperaccumulator Celosia argentea Linn

Understanding the molecular mechanism of tolerance to heavy metals in hyperaccumulators is important for improving the efficiency of phytoremediation and is interesting for evolutionary studies on plant adaption to abiotic stress. Celosia argentea Linn. was recently discovered to hyperaccumulate both manganese (Mn) and cadmium (Cd). However, the molecular mechanisms underlying Mn and Cd detoxification in C. argentea are poorly understood. Laboratory studies were conducted using C. argentea seedlings exposed to 360 μM Mn and 8.9 μM Cd hydroponic solutions. Plant leaves were analyzed using transcriptional and metabolomic techniques. A total of 3960 differentially expressed genes (DEGs) in plants were identified under Cd stress, among which 17 were associated with metal transport, and 10 belonged to the ATP transporter families. Exposures to Mn or Cd led to the differential expression of three metal transport genes (HMA3, ABCC15, and ATPase 4). In addition, 33 and 77 differentially expressed metabolites (DEMs) were identified under Mn and Cd stresses, respectively. Metabolic pathway analysis showed that the ABC transporter pathway was the most affected in Mn/Cd exposed seedlings. Conjoint transcriptome and metabolome analysis showed that the glutathione (GSH) metabolic pathway was over-represented in the KEGG pathway of both DEGs and DEMs. Our results confirm that the ABC transporter and GSH metabolic pathways play important roles in Mn and Cd detoxification. These findings provide new insight into the molecular mechanisms of tolerance to Mn and Cd toxicity in plants.

Melatonin alleviates arsenic (As) toxicity in rice plants via modulating antioxidant defense system and secondary metabolites and reducing oxidative stress

The Arsenic (As) load on the environment has increased immensely due to large-scale industrial and agricultural uses of As in several synthetic products, such as fertilizers, herbicides, and pesticides. Melatonin is a plant hormone that has a key role in abiotic stress inhibition, but the mechanism of resilience to As stress remains unexplored in rice plants. In this study, we determined how As affects rice plant and how melatonin facilitate As stress tolerance in rice. Here we investigated that, exogenous melatonin reduced As stress by inducing anthocyanin biosynthesis. Melatonin induced the expression of anthocyanin biosynthesis genes such as PAL, CHS, CHI, F₃H, DFR, and ANS, which resulted in 1659% and 389% increases in cyanidin and delphinidin, respectively. Similarly, melatonin application significantly induced SA and ABA accumulation in response to As stress in rice plant. Application of melatonin also significantly reduced expression of PT-2 and PT-8 (transporter genes) and reduced uptake of As and its translocation to other compartments. Melatonin and As analysis revealed that melatonin application significantly reduced As contents in the melatonin-supplemented plants, suggesting that As uptake is largely dependent on either the melatonin basal level or anthocyanin in rice plants. In this study, we investigated new symptoms on leaves, which can severely damage leaves and impair photosynthesis. However, anthocyanin as a chelating agent, detoxifies As in vacuole and reduces oxidative stress induced by As.

Jack Bean Development in Multimetal Contaminated Soil Amended with Coffee Waste-Derived Biochars

Coffee waste-derived biochar was found to immobilize heavy metals in contaminated soil, although there are few studies involving these materials. Given the large amount of waste generated in the coffee industry, this presents a relevant opportunity to contribute to the circular economy and environmental sustainability. Therefore, the objective of this study was to evaluate the effects of the application of biochars derived from coffee grounds and coffee parchment in the remediation of a Cd, Zn and Pb contaminated soil and at the development of jack beans (Canavalia ensiformis) in this area’s revegetation. The biochars were pyrolyzed at 700 °C, and the treatments were: contaminated soil (CT); contaminated soil + calcium carbonate (CaCO3); contaminated soil + 5% (weight (w)/weitght (w)) coffee ground biochar and contaminated soil + 5% (w/w) coffee parchment biochar. These treatments were incubated for 90 days, followed by the cultivation of jack beans for 60 days. Soil samples, soil solution and plants were analyzed for nutrients and heavy metals. The addition of coffee grounds and coffee parchment biochars significantly reduced the contents of heavy metals in the soil compared to the Control (32.13 and 42.95%, respectively, for Zn; 26.28 and 33.06%, respectively, for Cd and 28.63 and 29.67%, respectively, for Pb), all of which had a superior performance than the CaCO3 treatment. Thus, following the observed reduction in the soil soluble fraction of metals, its uptake by the plants was also reduced, especially limiting Cd and Pb accumulation in plant dry matter. In addition, coffee parchment biochar promoted a greater accumulation of nutrients in the shoots, i.e., for K and P (1450 and 21.5 mg pot−1, respectively, dry matter basis) compared to the control (54.4 and 9.3 mg pot−1, respectively). Therefore, coffee parchment biochar use in association with jack beans may represent a viable tool for the remediation of metal contamination concomitantly with revegetation of the contaminated area.

Heavy metal and metalloid toxicity in horticultural plants: Tolerance mechanism and remediation strategies

Heavy metal/metalloids (HMs) are among the primary soil pollutants that limit crop production worldwide. Plants grown in HM contaminated soils exhibit reduced growth and development, resulting in a decrease in crop production. The exposure to HMs induces plant oxidative stress due to the formation of free radicals, which alter plant morphophysiological and biochemical mechanisms at cellular and tissue levels. When exposed to HM toxicity, plants evolve sophisticated physiological and cellular defense strategies, such as sequestration and transportation of metals, to ensure their survival. Plants also have developed efficient strategies by activating signaling pathways, which induce the expression of HM transporters. Plants either avoid the uptake of HMs from the soil or activate the detoxifying mechanism to tolerate HM stress, which involves the production of antioxidants (enzymatic and non-enzymatic) for the scavenging of reactive oxygen species. The metal-binding proteins including phytochelatins and metallothioneins also participate in metal detoxification. Furthermore, phytohormones and their signaling pathways also help to regulate cellular activities to counteract HM stress. The excessive levels of HMs in the soil can contribute to plant morpho-physiological, biochemical, and molecular alterations, which have a detrimental effect on the quality and productivity of crops. To maintain the commercial value of fruits and vegetables, various measures should be considered to remove HMs from the metal-polluted soils. Bioremediation is a promising approach that involves the use of tolerant microorganisms and plants to manage HMs pollution. The understanding of HM toxicity, signaling pathways, and tolerance mechanisms will facilitate the development of new crop varieties that help in improving phytoremediation.

Alleviation of cadmium toxicity in Zea mays L. through up-regulation of growth, antioxidant defense system and organic osmolytes under calcium supplementation

Calcium (Ca) is a macronutrient and works as a modulator to mitigate oxidative stress induced by heavy metals. In this study, we investigated the role of Ca to ameliorate the Cd toxicity in Zea mays L. by modulating the growth, physio-biochemical traits, and cellular antioxidant defense system. Maize genotype Sahiwal-2002 was grown under a controlled glasshouse environment with a day/night temperature of 24 ± 4°C/14 ± 2°C in a complete randomized design with three replications and two Cd levels as (0 and 150 μM) and six regimes of Ca (0, 0.5, 1, 2.5, 5, and 10 mM). Maize seedlings exposed to Cd at 150 μM concentration showed a notable decrease in growth, biomass, anthocyanins, chlorophylls, and antioxidant enzymes activities. A higher level of Cd (150 μM) also caused an upsurge in oxidative damage observed as higher electrolyte leakage (increased membrane permeability), H2O2 production, and MDA accumulation. Supplementation of Ca notably improved growth traits, photosynthetic pigments, cellular antioxidants (APX, POD, and ascorbic acid), anthocyanins, and levels of osmolytes. The significant improvement in the osmolytes (proteins and amino acids), and enzymatic antioxidative defense system enhanced the membrane stability and mitigated the damaging effects of Cd. The present results concluded that exogenously applied Ca potentially improve growth by regulating antioxidants and enabling maize plants to withstand the Cd toxicity.

Effects of Tetracycline and Copper on Water Spinach Growth and Soil Bacterial Community

The effects of tetracycline (TC) and copper (Cu) on the growth of water spinach and the bacterial community structure in soil were examined in this study. The results revealed that a single Cu treatment decreased water spinach development more severely than TC, and that the toxic effects of TC and Cu on water spinach were synergistic at low doses and antagonistic at high concentrations. The single Cu treatment had the largest influence on the activities of three antioxidant enzymes (Superoxide Dismutase (SOD), Peroxidase (POD), Catalase (CAT)) and the content of Malondialdehyde (MDA) in water spinach leaves, followed by the TC and Cu composed treatment, with the single TC treatment having the least effect. The results of 16Sr RNA sequence analysis showed that the richness and diversity of soil bacterial communities were reduced by either a single TC or Cu treatment. Cu had a greater effect on the composition of the microbial community at genus level than TC. In conclusion, Cu had a greater influence on the growth of water spinach and soil microbial community composition than TC. TC and Cu exhibited synergistic effects at low concentrations and antagonistic effects at high concentrations on relevant indicators when Cu concentration was fixed.

Combined toxicity of microplastic and lead on submerged macrophytes

Microplastic pollution has become ubiquitous due to industrialization and wide use of plastic products. The continuous discharge of microplastics into aquatic ecosystems, combined with different toxic chemicals can create serious environmental pollution. Lead is an extremely toxic metal which can strongly adsorb to microplastics, however, little is known about their combined toxicity on submerged macrophytes. To test our hypothesis that microplastic can aggravate lead toxicity on submerged macrophytes, we designed a five-day hydroponic experiment to explore the toxic effects of microplastic and lead alone, and in combination, on Potamogeton crispus and Vallisneria denseserrulata. Photosynthetic pigment, chlorophyll fluorescence (Fv/Fm and ETRmax), soluble sugar, protein and malondialdehyde (MDA) declined with increasing lead concentration alone and in the combined treatment. In both submerged macrophytes, the level of superoxide dismutase (SOD) and lead bioaccumulation increased with increasing lead concentration. However, microplastic aggravated lead toxicity on chlorophyll a and SOD activity in P. crispus only under the highest lead concentration. In conclusion, lead alone and combined exposure caused a series of toxic effects on physio-biochemical traits of submerged macrophytes that appeared to be synergistic and species-specific. Our comprehensive results have important implications for appropriate management of microplastics and lead alone, or in combination, for submerged macrophytes.

The Activity and Gene Expression of Enzymes in Mycelia of Pleurotus Eryngii under Cadmium Stress

Cadmium (Cd) is a highly toxic pollutant and a nonessential element for plant growth. Here, we investigated the levels of malondialdehyde (MDA), H2O2, sugars, and the activity and gene expression of antioxidant enzymes and sugar metabolism-related enzymes in the mycelia of Pleurotus eryngii grown in the presence of 0, 0.5, 1, 1.5, 2.0, and 4.0 mg·L−1 Cd. Raising Cd concentration resulted in increases, followed by decreases in the levels of malondialdehyde (MDA) and H2O2 in the mycelia. The maximum concentrations of MDA and H2O2 reached 318.61 and 7411.40 μmol·L−1, respectively, at a Cd concentration of 1 mg·L−1. Antioxidative enzymes (superoxide dismutase (SOD), catalase, glutathione peroxidase (GPX), and ascorbate peroxidase (APX)) activities peaked at 1 mg·L−1 Cd. Furthermore, Pleurotus eryngii produced trehalose, glucose, fructose, and maltose in the fermentation broth in response to Cd stress. The levels of trehalose, arabinose, and fructose in the fermentation broth decreased continuously. The levels of glucose increased continuously, whereas those of maltose first increased and then decreased. Gene expression level of chitin synthase, glucose-1-phosphate uridyl transferase peaked significantly at 2 mg·L−1 of Cd, while that of trehalase 2 is 0.5 mg·L−1, and those for fructose-diphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, reached the maximum at 4 mg·L−1.

Identification and evolutionary analysis of the metal-tolerance protein family in eight Cucurbitaceae species

Metal-tolerance proteins (MTPs) are divalent cation transporters and play fundamental roles in plant metal tolerance and ion homeostasis. Despite that, a systematic investigation of MTPs in Cucurbitacea is still lacking. In this study, 142 MTPs were identified from 11 released genomes of 8 Cucurbitaceae species. They were phylogenetically separated into three clusters (Zn-cation diffusion facilitator proteins [CDFs], Fe/Zn-CDFs, and Mn-CDFs) and further subdivided into seven groups (G1, G5, G6, G7, G8, G9, and G12). Characterization analysis revealed that most MTPs were plasma membrane-located hydrophobic proteins. Motif and exon/intron analysis showed that members in the same group contained similar conserved motifs and gene structures. Moreover, 98 pairs of segmental-like duplication events were found. The nonsynonymous/synonymous substitution ratios between each pair were less than 1, implying that Cucurbitaceae MTPs were under purification selection. Expression profiling suggested that several MTP genes, such as CsCLMTP1, CmeMTP3, LsMTP3, and Cl97103MTP3, were constitutively expressed in corresponding Cucurbitaceae species, and their expression levels were not significantly altered by NaCl, drought, or pathogen infection. The expression patterns of cucumber MTP genes under Zn²⁺ , Cu²⁺ , Mn²⁺ , and Cd²⁺ stress were studied by quantitative real-time polymerase chain reaction and the results showed that these MTPs were induced by at least one metal ion, suggesting their involvement in metal tolerance or transportation. The identification and comprehensive investigation of MTP family members will provide a basis for the analysis of ion transport functions and ion tolerance mechanisms of Cucurbitaceae MTPs.

The Potential of Cistus salviifolius L. to Phytostabilize Gossan Mine Wastes Amended with Ash and Organic Residues

The São Domingos mine is within the Iberian Pyrite Belt, a mining district with large concentrations of polymetallic massive sulfide deposits. Mine waste heaps are considered extreme environments, since they contain high total concentrations of potentially hazardous elements (PHE), which contribute to inhibiting the development of most plants. Autochthonous plant species, such as Cistus salviifolius L., are able to grow naturally in this degraded environment, and may contribute to minimizing the negative chemical impacts and improving the landscape quality. However, the environmental rehabilitation processes associated with the development of these plants (phytostabilization) are very slow, so the use of materials/wastes to improve some physicochemical properties of the matrix is necessary in order to speed up the process. This work studied the effectiveness of the phytostabilization with C. salviifolius of gossan mine wastes from the mine of São Domingos amended with organic and inorganic wastes in order to construct Technosols. The mine wastes have an acid pH (≈3.5), high total concentrations of PHE and low concentrations of organic C and available nutrients. The best vegetative development occurred without visible signs of toxicity in the Technosols containing a mixture of agriculture residues. These treatments allowed the improvement of the soil-plant system providing a better plant cover and improved several chemical properties of mine wastes, helping to speed up the environmental rehabilitation.

Phytochemicals mitigation of Brassica napus by IAA grown under Cd and Pb toxicity and its impact on growth responses of Anagallis arvensis

Beginning of industrialization accelerates the heavy metal pollution in the biosphere. Plant being the immovable entity utilizes different mechanisms to flee from unfavourable conditions. To alleviate toxic impact of metals like cadmium (Cd) and lead (Pb), phytohormones such as indole acetic acid (IAA) has been applied exogenously. This manuscript aims to evaluate the significant change occurring in biochemical parameters of Indian mustard (Brassica napus) grown under individual and combined treatments of IAA with Cd and Pb. Herbicidal potential of treated Brassica extracts were evaluated on growth and development of Anagallis arvensis. Quantum yield parameters were more sensitive to Cd than Pb stress resulted in reduced photosynthetic pigments. However, exogenously applied IAA together with Cd and Pb considerably improved the level of photosynthetic attributes along with reduced accumulation of Cd and Pb in Brassica plant. Cd and Pb enhanced the activities of reactive oxygen species (ROS) and antioxidant machinery. However, addition of IAA with Cd and Pb mitigated the effect of heavy metals on antioxidant system. Moreover, activity of the phenylalanine ammonia lyase enzyme and the defensive metabolites (phenolic, flavonoid and anthocyanin compounds) were boosted under individual treatments of Cd and Pb responsible for increasing herbicidal potential of Brassica plant. Our results exhibited essentiality of IAA in mitigating Cd and Pb stress in Brassica through up-regulated mechanisms of the antioxidant system for balancing ROS related injuries. Increased metabolites enhancing herbicidal potential of Brassica napus against Anagallis weed were also observed.

Cadmium-induced hormesis effect in medicinal herbs improves the efficiency of safe utilization for low cadmium-contaminated farmland soil

Compared to other soil remediation technologies, Cd-contaminated farmland soil with low cadmium accumulation (LCA) plant-based safe utilization is more catered to developing countries with food in high demand. Hormesis, which describes the fortification of plant growth performance by a low level of environmental stress, can be innovatively used to achieve increases in crop yield and plant functional components, thus amplifying the safe utilization efficiency of low Cd-contaminated soil by LCA plants. In the present study, the growth and physiological responses of Polygonatum sibiricum, a traditional Chinese medicinal herb, were investigated under laboratory conditions of gradient Cd dosage concentrations and times. As a result, the growth performance of P. sibiricum reached the peak of an inverse U-shaped curve of hormesis under e⁰ mg kg^-1 and 9 months of Cd stress, with elevations in tuber biomass (medicinal part), plant height and polysaccharide content (medicinal components) of 143%, 25% and 90%, respectively. Meanwhile, trace Cd accumulation (0.41 mg kg^-1) in the tuber guaranteed medicinal edible safety. In addition, Cd-induced hormesis in P. sibiricum was verified to be overcompensated by antioxidation systems. In conclusion, such 'win-win' results, including low Cd accumulation and enhancement of plant pharmaceutical value, provided medicinal herbs with a possibility for safe soil utilization.

Activation of antioxidative and detoxificative systems in Brassica juncea L. plants against the toxicity of heavy metals

Plant metal hyperaccumulators, to which Brassica juncea belongs, must have very efficient defence mechanisms that enable growth and development in an environment polluted with various heavy metals. B. juncea (Indiana mustard) v. Małopolska was exposed to the activity of trace elements such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in combinations: CuPb, CuCd, CuZn, PbCd, PbZn, and ZnCd in a concentration of 25 μM each for 96 h during control cultivation. We observed a clear tendency for metal uptake and accumulation in above-ground parts which is characteristic of hyperaccumulators. The combinations of CuCd, CuZn, and PbCd inhibited the development of the seedlings the most. The used metal combinations increased the levels of reactive oxygen species (ROS) such as: hydrogen peroxide (H₂O₂), superoxide anion (O₂^.-) and oxidized proteins in B. juncea organs, generating oxidative stress conditions in the cells. We determined the level of transcription of the respective defence proteins of the detoxification and antioxidant systems. We have shown that in the first 24 h of stress condiction, activation of glutamylcysteine-γ synthetase (yECS) and glutathione reductase (GR1) enzymes related to the detoxification of heavy metals is important for B. juncea plants. In addition, the data provide important information on how plants respond to the presence of heavy metals in the first days of stress conditions.

Physiological responses and health risks of edible amaranth under simultaneous stresses of lead from soils and atmosphere

Lead (Pb) is widely distributed in the environment that can impose potential risks to vegetables and humans. In this work, we conducted a pot experiment in Southern China to examine the physiological response and risk of edible amaranth (Amaranthus tricolor L.) under the simultaneous stresses of lead from soil and atmosphere. The results indicate that the lead content of amaranth substantially exceeded China's national standard when Pb concentration from soils and atmosphere was high, and comparing to teenagers and adults, children exposed a higher health risk after consuming the contaminated amaranth. Under the co-stress, the lead in roots of amaranth mainly came from the soil, but the Pb from atmospheric deposition can significantly affect the lead concentration in leaves. While lead from atmospheric deposition is found to promote the growth of amaranth, the stress of lead from the soils shows an inhibitory effect, as indicated by the increase in H₂O₂ content, the damage in cell membranes, and the limitation in chlorophyll synthesis. The antioxidant system in stems and leaves of amaranth can effectively alleviate the Pb toxicity. However, the stress of high lead concentration from soils can substantially suppress the antioxidant enzyme activity of roots. While it is found that heavy metals in soils can significantly affect the vegetables grown in a multi-source pollution environment, we also call for the attention on the potential health risk imposed by the lead from atmospheric deposition. This study provides an important reference for the prevention and control of crop contamination in multi-source pollution environments.

Ecophysiological, anatomical, and apigenin changes due to uptake and accumulation of cadmium in Matricaria chamomilla L. flowers in hydroponics

Cadmium (Cd) is one of the most important heavy metals in the environment which has several effects on the morphology, physiology, and anatomy of plants. It is a mobile heavy metal that can be transferred easily into plants, thus entering into the human food chain. Chamomile (Matricaria chamomilla L.) as an important medicinal plant can uptake and accumulate Cd in its root and aerial organs. In this research, the effects of different concentrations of Cd (90, 180, and 360 μM) were investigated on the growth parameters, anatomical features, and enzymatic antioxidant activities in flowers of chamomile after 7 days of exposure. The content of apigenin, a flavone compound mostly synthesizing in chamomile flowers, was also analyzed after 72 h from Cd treatment. The results showed that all concentrations of Cd reduced the length and biomass of roots and shoots, the diameter of flowers, as well as the number of pollen grains in tubular florets, while increased trichome density on the florets. Cd-treated plants showed an increase in antioxidant enzymes, superoxide dismutase (SOD), and peroxidase (POX) activities. After 7 days of treatment to Cd major concentration, flowers accumulated Cd and enhanced the apigenin production with the increase of Cd contamination in hydroponic solution. This increase of apigenin is most likely due to its antioxidant and sequestering property as a resistance response to Cd excess.

Antioxidant system response, mineral element uptake and safe utilization of Polygonatum sibiricum in cadmium-contaminated soil

Chinese herbal medicine is widely cultivated in Southwest China, where the soil cadmium (Cd) contamination of farmland is more serious than that in China as a whole. In this study, Polygonatum sibiricum was exposed to Cd at concentrations of e⁻¹, e⁰, e², and e⁴ mg/kg for 30, 60, and 90 days, and the physiological stress responses, Cd and mineral element uptake, antioxidant enzyme activities, and content changes of pharmaceutical ingredients (polysaccharides) were analyzed to decipher the feasibility of safe utilization in Cd-contaminated soil. The results show that the activity of antioxidant enzymes (SOD and CAT) in the aboveground part was always higher than that in the underground part. The underground part of Polygonatum sibiricum mobilizes nonenzymatic systems to facilitate the synthesis of polysaccharides (PCP1, PCP2) with antioxidant properties to cope with Cd stress. Mineral elements (P, K, Ca, Mg, Fe, Cu, and Zn) significantly (p < 0.05) changed after 90 d of cultivation. In particular, the changes in the iron and zinc content were significantly correlated (p < 0.05) with the activities of SOD and POD. Soil Cd at e⁰ mg/kg can guarantee the safe production and utilization of Polygonatum sibiricum, and the stimulation of Cd promotes polysaccharide synthesis and biomass growth.

Health assessment of medicinal herbs, celery and parsley related to cadmium soil pollution-potentially toxic elements (PTEs) accumulation, tolerance capacity and antioxidative response

Celery and parsley are recognized as medicinal herbs and nutraceutical vegetables due to their valuable pharmacological properties and numerous health benefits. However, in recent years, soil loadings with various PTEs have become a serious concern across the world, leading to plants pollution, which can consequently diminish their quality and safety for human consumption. Therefore, we attempted to quantify quality and safety of celery and parsley grown in Cd polluted soil. We examined the presence of PTEs: As, Cu, Fe, Mn, Ni, Cu and Cd in soil and selected herbs, as well as their physiological responses to different Cd exposures (control-without Cd addition, 3 and 6 µg/g Cd of dry soil). Following elevation of Cd in plants, both species showed increasing trend of As, Pb and Cu in plants, which overcome safe limits, with exception for Cu. Further, celery showed strong phytoextraction ability (99.9 µg/g Cd of dry weight) with high potential to tolerate Cd due to the efficient antioxidative machinery. Besides that herbs pollution was evident on the basis of target hazard quotients (HQ), hazard index (HI) and cancerogenic risk (CR), revealing that chronic consumption of contaminated herbs can consequently endanger human health. HI was greater than 1, while CR exceeded safe limits in treated plants, with exception for As. In the point of view of toxicology and food safety, growing of medicinal plants should be strictly regulated and distinguished based on the purpose of growing, and further herbs usage.

Uranium (U) source, speciation, uptake, toxicity and bioremediation strategies in soil-plant system: A review

Uranium(U), a highly toxic radionuclide, is becoming a great threat to soil health development, as returning nuclear waste containing U into the soil systems is increased. Numerous studies have focused on: i) tracing the source in U contaminated soils; ii) exploring U geochemistry; and iii) assessing U phyto-uptake and its toxicity to plants. Yet, there are few literature reviews that systematically summarized the U in soil-plant system in past decade. Thus, we present its source, geochemical behavior, uptake, toxicity, detoxification, and bioremediation strategies based on available data, especially published from 2018 to 2021. In this review, we examine processes that can lead to the soil U contamination, indicating that mining activities are currently the main sources. We discuss the relationship between U bioavailability in the soil-plant system and soil conditions including redox potential, soil pH, organic matter, and microorganisms. We then review the soil-plant transfer of U, finding that U mainly accumulates in roots with a quite limited translocation. However, plants such as willow, water lily, and sesban are reported to translocate high U levels from roots to aerial parts. Indeed, U does not possess any identified biological role, but provokes numerous deleterious effects such as reducing seed germination, inhibiting plant growth, depressing photosynthesis, interfering with nutrient uptake, as well as oxidative damage and genotoxicity. Yet, plants tolerate U toxicity via various defense strategies including antioxidant enzymes, compartmentalization, and phytochelatin. Moreover, we review two biological remediation strategies for U-contaminated soil: (i) phytoremediation and (ii) microbial remediation. They are quite low-cost and eco-friendly compared with traditional physical or chemical remediation technologies. Finally, we conclude some promising research challenges regarding U biogeochemical behavior in soil-plant systems. This review, thus, further indicates that the combined application of U low accumulators and microbial inoculants may be an effective strategy for the bioremediation of U-contaminated soils.

Ornamental Plant Efficiency for Heavy Metals Phytoextraction from Contaminated Soils Amended with Organic Materials

Accumulation of heavy metals (HMs) by ornamental plants (OPs) from contaminated agriculture soils is a unique technique that can efficiently reduce the metal load in the food chain. Amaranthus tricolor L. has attractive characteristics acquiring a higher growth rate and large biomass when grown at heavy metal contaminated soils. Site-specific detailed information is not available on the use of A. tricolor plant in metal phytoremediation from the polluted sites. The study aimed to enhance the uptake of HMs (Pb, Zn, and Cu) via amending poultry litter extract (PLE), vinasse sugarcane (VSC), and humic acid (HA) as natural mobilized organic materials compared to ethylene diamine tetraacetic acid (EDTA), as a common mobilized chemical agent by A. tricolor plant. The studied soils collected from Helwan, El-Gabal El-Asfar (Cairo Governorate), Arab El-Madabeg (Assiut Governorate), Egypt, and study have been conducted under pot condition. Our results revealed all organic materials in all studied soils, except EDTA in EL-Gabal El-Asfar soil, significantly increased the dry weight of the A. tricolor plant compared to the control treatment. The uptake of Pb and Zn significantly (p > 0.05) increased due to applying all organic materials to the studied soils. HA application caused the highest uptake as shown in Pb concentration by more than 5 times in Helwan soil and EDTA by 65% in El-Gabal El-Asfar soil while VSC increased it by 110% in El-Madabeg soil. Also, an increase in Zn concentration due to EDTA application was 58, 42, and 56% for Helwan, El-Gabal El-Asfar, and El-Madabeg soil, respectively. In all studied soils, the application of organic materials increased the remediation factor (RF) than the control. El-Madabeg soil treated with vinasse sugarcane gave the highest RF values; 6.40, 3.26, and 4.02% for Pb, Zn, and Cu, respectively, than the control. Thus, we identified A. tricolor as a successful ornamental candidate that, along with organic mobilization amendments, most efficiently develop soil health, reduce metal toxicity, and recommend remediation of heavy metal-contaminated soils. Additionally, long-term application of organic mobilization amendments and continued growth of A. tricolor under field conditions could be recommended for future directions to confirm the results.

Methods for metal chelation in plant homeostasis: Review

Metal uptake, transport and storage in plants depend on specialized ligands with closely related functions. Individual studies differing by species, nutrient availability, tissue type, etc. are not comprehensive enough to understand plant metal homeostasis in its entirety. A thorough review is required that distinguishes the role of ligands directly involved in chelation from the myriad of plant responses to general stress. Distinguishing between the functions of metal chelating compounds is the primary focus of this review; reactive oxygen species mediation and other aspects of metal homeostasis are also discussed. High molecular weight ligands (polysaccharides, phytochelatin, metallothionein), low molecular weight ligands (nicotianamine, histidine, secondary metabolites) and select studies which demonstrate the complex nature of plant metal homeostasis are explored.

Soil cadmium and lead affecting biochemical properties of Matricaria chamomilla L. at different growth stages in the greenhouse and field

Heavy metals bioremediation by medicinal plants is an important research issue, which has yet to be investigated. Matricaria chamomilla accumulation of soil cadmium (Cd, 0, 10 and 40 mg/kg) and lead (Pb, 0, 60 and 180 mg/kg) affecting plant biochemical properties L. at different growth stages in the greenhouse and field was investigated. The 10-kg experimental pots (located in the greenhouse and field with 80% of field capacity moisture) were filled with the treated soils, and were planted with M. chamomilla L. seeds (three replicates). Plants were sampled to determine their biochemical properties including Cd and Pb contents, pigments, proline (Pro), leaf relative water (LRW), lipid peroxidation (LX), and superoxide dismutase (SOD, EC 1.15. 1.1), and catalase (CAT, EC 1.11.1.6) activities. Soil final concentration of Cd and Pb was also determined. Heavy metal stress significantly decreased plant pigment contents; however, it significantly increased plant PRO, LRW, LX and SOD, and not CAT. Heavy metal, growth stage, growth location, and their interactions significantly affected plant heavy metal concentrations. Interestingly, although significantly higher concentration of Cd was observed in plant aerial part under greenhouse conditions, plant roots had significantly higher concentrations of Cd under field conditions, and it was reverse for Pb. Increased concentration of Cd and Pb significantly enhanced plant Pro content and the highest one was resulted by Pb3 (913.46 mg/g fresh weight) significantly higher than other treatments including Cd3 (595.34 mg/g fresh weight). M. chamomilla is a suitable species for the bioremediation of soils polluted with Cd and Pb.

Effects of cadmium stress on physiological indexes and fruiting body nutritions of Agaricus brasiliensis

In this study, 0, 0.5, 1, 1.5, 2, 4, 6 and 8 mg·kg^-1 of cadmium were added to the cultivation materials. In order to study the effects of different concentrations of Cd stress on J1 and J77, the contents of antioxidant enzymes, proline and malondialdehyde, Cd content, agronomic traits and yield of fruiting bodies of Agaricus brasiliensis were determined, and the nutritional components such as polysaccharide, triterpene, protein, total sugar and total amino acid were determined. The results showed that the physiological indexes of strain J1 and J77 changed regularly under different concentrations of Cd stress. J1 was a high absorption and low tolerance variety, while J77 was a low absorption and high tolerance variety. Low concentration of Cd promoted the growth of strain J1, and higher concentration of Cd promoted the growth of strain J77. The contents of protein and total amino acids in the two strains changed greatly, followed by polysaccharides, which indicated that Cd stress had the greatest impact on the three nutrients, and other nutrients were not sensitive to Cd stress.

Toxic Metals (As, Cd, Ni, Pb) Impact in the Most Common Medicinal Plant (Mentha piperita)

This study aimed to evaluate the behavior of Mentha piperita under Cd, Pb, Ni, and As soil contamination and their transfer from soil in plants as well as translocation in the roots/stems/leaves system compared with a control without metal addition. The mint seedlings were exposed for a three-month period using two metal mixtures in the same concentrations such as AsCd and AsCdNiPb (23.7 mg/kg As, 5 mg/kg Cd, 136 mg/kg Ni, and 95 mg/kg Pb). The results of metal concentration in plants showed that Cd, Ni, and Pb were accumulated in different parts of the plant, except for As. In plants organs, the order of metal accumulation was roots > stems > leaves. No significant impact on the growth, development, and chlorophyll content compared to the control was observed in the first month of exposure. After three months of exposure, phytotoxic effects occurred. Generally, the transfer coefficients and translocation factors values were less than 1, indicating that Mentha piperita immobilized the metals in root. The laboratory experiments highlighted that for a short period of time, Mentha piperita has the capacity to stabilize the metals at the root level and was a metal-tolerant plant when using a garden rich-substrate.

Ornamental plants for the phytoremediation of heavy metals: Present knowledge and future perspectives

Environmental matrices are polluted with the plethora of contaminants, and among these, the concerns related to heavy metals (HMs) are also included. Due to the low cost in a long-term application and environmental friendliness, the use of biological remediation has gained significant attention in recent decades. The use of ornamental plants (OPs) in the field of phytoremediation is scarcely reported, and the impacts of HMs on OPs have also not been investigated in great depth. The OPs mediated HMs remediation can simultaneously remove contaminants and bring improvement in aesthetics of the site. The biomass of OPs produced after such activities can be used and sold as pot plants, cut flowers, essential oils, perfumes, air fresheners production, metal phytomining, and feedstock in silk production. The OPs also present a lower risk of HMs bioaccumulation compared to crop plants. This review focuses on the current knowledge of HMs toxicity to OPs, their applicability advantages, methods to improve the tolerance of OPs with incremented HMs uptake, challenges in the field, and future application perspectives. The case studies realted to practical application of OPs, from China, Iran, India, Oman, Pakistan, and Turkey, were also discussed. This work fetches the inter-disciplinary features and understanding for the sustainable treatment of HMs in a new novel way, to which no previous review has focused.

Study on detoxification and removal mechanisms of hexavalent chromium by microorganisms

Extensive industrial activities have led to an increase of the content of chromium in the environment, which causes serious pollution to the surrounding water, soil and atmosphere. The enrichment of chromium in the environment through the food chain ultimately affects human health. Therefore, the remediation of chromium pollution is crucial to development of human society. A lot of scholars have paid attention to bioremediation technology owing to its environmentally friendly and low-cost. Previous reviews mostly involved pure culture of microorganisms and rarely discussed the optimization of bioreduction conditions. To make up for these shortcomings, we not only introduced in detail the conditions that affect microbial reduction but also innovatively introduced consortium which may be the cornerstone for future treatment of complex field environments. The aim of this study is to summary chromium toxicity, factors affecting microbial remediation, and methods for enhancing bioremediation. However, the actual application of bioremediation technology is still facing a major challenge. This study also put forward the current research problems and proposed future research directions, providing theoretical guidance and scientific basis for the application of bioremediation technology.

Additional calcium and sulfur manages hexavalent chromium toxicity in Solanum lycopersicum L. and Solanum melongena L. seedlings by involving nitric oxide

In recent years, nutrient management has gained much attention for mitigating metal stress. But, role of nutrients like calcium (Ca) and sulfur (S) in mitigating Cr(VI) toxicity along with their mechanism of action are still limited. Therefore, the present study was performed to explore role of Ca and S in ameliorating Cr(VI) toxicity in 21 days old seedlings of Solanum lycopersicum L. and Solanum melongena L. Chromium (VI) reduced tolerance index and altered root traits due to greater Cr accumulation in the cell wall and cellular organelles due to down-regulation in thiols and phytochelatins that lead to alterations in photosynthesis. However, Ca or S stimulated vacuolar sequestration of Cr(VI) and reduced its uptake at the cell wall. This was coincided with up-regulation in glutathione-S-transferase activity, and amounts of thiols and phytochelatins. Cr(VI) caused oxidative stress together with up-regulation in superoxide dismutase and catalase, and proline metabolism while Ca and S reversed these effects. Chromium (VI) inhibited nitrate reductase activity while Ca and S reversed this response. NG-nitro-l-arginine methyl ester augmented Cr(VI) toxicity but sodium nitroprusside (SNP) mitigated Cr(VI) toxicity. Overall results show that Ca and S both are able in ameliorating Cr(VI) toxicity and require nitric oxide for this task.

Long-term exposure of high concentration heavy metals induced toxicity, fatality, and gut microbial dysbiosis in common carp, Cyprinus carpio

Heavy metals (HMs) in an aquatic environment mainly affects fish, and thus, fish are convenient pollution bio-indicators. In this study, the toxic effects of HM mixture (chromium (Cr), cadmium (Cd), copper (Cu)) in 0 mg/L to 3.2 mg/L concentration range was investigated in Cyprinus carpio (28 days). HM accumulation, histopathology, oxidative stress, and gut microbial changes were evaluated. HMs accumulated in the order of Cr > Cu > Cd, primarily in the kidneys and finally scales. Reactive oxygen species generation increased in all exposure groups up to day 14, with maximum generation at 3.2 mg/L mixture, which later decreased on day 28 in all. Malondialdehydeand and superoxide dismutase levels increased from day 7 to 28 with increased HM concentrations, while total protein showed an inverse trend. Gill histopathology showed major changes such as uplifted and disintegrated primary lamella, and secondary lamella shortening. The kidneys were characterized by glomerular necrosis, Bowman's capsule expansion, and tubular space dilatation. Proteobacteria and Firmicutes abundance increased up to 59.4% and 99.16% in 0.8 mg/L and 3.2 mg/L treatment groups, respectively. This study provided a better understanding on the physiology and gut microbiota alteration in C. carpio under multiple HM stress.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

Nanotechnology is a tool that in the last decade has demonstrated multiple applications in several sectors, including agroindustry. There has been an advance in the development of nanoparticulated systems to be used as fertilizers, pesticides, herbicides, sensors, and quality stimulants, among other applications. The nanoencapsulation process not only protects the active ingredient but also can affect the diffusion, interaction, and activity. It is important to evaluate the negative aspects of the use of nanoparticles (NPs) in agriculture. Given the high impact of the nanoparticulated systems in the agro-industrial field, this review aims to address the effects of various nanomaterials on the morphology, metabolomics, and genetic modification of several crops.

Biosolid compost with wood shavings and yard trimmings alleviates stress and improves grain quality in soybean grown in lead polluted soils

Heavy metals induce stress in plants, thereby affecting growth, crop quality, and food security. Most studies addressing the mitigation of these effects by soil amendment have focused on metals in soils and plant uptake, with there still being a great deal of uncertainty about how amendment application in polluted soils can modify plant stress response and, consequently, yield and food safety. Thus, the aim of this study was to evaluate the effect of biosolid compost amendment on stress response, growth, and lead accumulation in Glycine max, when applied to lead polluted agricultural soils. Soybean was grown in lead polluted soils with 0%, 5%, or 10% (w/w) biosolid compost amendment under controlled conditions in a greenhouse, and the stress response indicators chlorophylls, proteins, sugars, malondialdehyde, glutathione S-transferase activity, carotenes, and the ferric reducing antioxidant power were investigated. In addition, the biomass and lead accumulation in different organs were determined and evaluated with respect to the plant stress. Our results revealed that the addition of 10% biosolid compost improved the grain biomass and appeared to reduce the amount of defective grains, which was related to higher Pb concentrations. Furthermore, 10% compost treatment reduced the stress in plants, leading to a better performance of the photosynthetic system, and with the antioxidant response being positively correlated to Pb accumulation. Lead uptake in plants was decreased by between 35 and 57% after this treatment in comparison with unamended soils. These results indicate that biosolid compost amendment may be an effective way to alleviate Pb uptake and metal stress in soybeans.

Glycine Betaine Accumulation, Significance and Interests for Heavy Metal Tolerance in Plants

Unexpected biomagnifications and bioaccumulation of heavy metals (HMs) in the surrounding environment has become a predicament for all living organisms together with plants. Excessive release of HMs from industrial discharge and other anthropogenic activities has threatened sustainable agricultural practices and limited the overall profitable yield of different plants species. Heavy metals at toxic levels interact with cellular molecules, leading towards the unnecessary generation of reactive oxygen species (ROS), restricting productivity and growth of the plants. The application of various osmoprotectants is a renowned approach to mitigate the harmful effects of HMs on plants. In this review, the effective role of glycine betaine (GB) in alleviation of HM stress is summarized. Glycine betaine is very important osmoregulator, and its level varies considerably among different plants. Application of GB on plants under HMs stress successfully improves growth, photosynthesis, antioxidant enzymes activities, nutrients uptake, and minimizes excessive heavy metal uptake and oxidative stress. Moreover, GB activates the adjustment of glutathione reductase (GR), ascorbic acid (AsA) and glutathione (GSH) contents in plants under HM stress. Excessive accumulation of GB through the utilization of a genetic engineering approach can successfully enhance tolerance against stress, which is considered an important feature that needs to be investigated in depth.

Effects of silver(I) toxicity on microstructure, biochemical activities, and genic material of Lemna minor L. with special reference to application of bioindicator

In this research, several biochemical variations in plant of Lemna minor L. were investigated to reflect Ag⁺ toxicity. Lemna minor L. changed colorless AgNO₃ to colloidal brown at doses equal to and greater than 1 mg L^-1. Optical and fluorescence microscopy revealed the presence of bright spots in roots of tested plant related to Ag/Ag₂O-NPs. Photosynthetic pigment contents of Lemna minor L. declined upon exposure to Ag⁺ with an evidently higher decrease in chlorophyll a than in chlorophyll b. Similarly, Ag⁺ treatment caused an evident reduction in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). The reduction in antioxidase activity was significantly higher in POD than in SOD and CAT. Ag⁺ treatment resulted in a significant increment in the level of malondialdehyde (MDA) content as the judging criteria of cellular injury which showed sign of dose-related. The alterations occurred in RAPD profiles of treated samples following Ag⁺ toxicity containing loss of normal bands, appearance of new bands, and variation in band intensities compared with the normal plants. In addition, morphological character and biomass of Lemna minor L. subjected to increasing Ag⁺ concentrations were evaluated to reveal Ag⁺ toxicity. Our study demonstrated that Lemna minor L. have a high sensitivity to indicate fluctuation of water quality. It would be beneficial that modulating the genotype of Lemna minor L. to bear high proportion of contaminates.