Heavy-metal-induced reactive oxygen species: phytotoxicity and physicochemical changes in plants

Exploring the role of ATP-binding cassette transporters in tomato (Solanum lycopersicum) under cadmium stress through genome-wide and transcriptomic analysis

ATP-binding cassette (ABC) transporters are integral membrane proteins involved in the active transport of various substrates, including heavy metals, across cellular membrane. In this study, we performed a genome-wide analysis and explored the expression profiles of ABC transporter genes in Solanum lycopersicum to identify their role in cadmium (Cd) stress tolerance. Several techniques were employed to determine the regulatory role of ABC transporters. A total of 154 ABC transporter genes were identified in the genome of S. lycopersicum, located on all 12 chromosomes. Comparative phylogenetic analysis between S. lycopersicum and Arabidopsis thaliana revealed several orthologous gene pairs, which were duly supported by the structural analysis of the genes by studying the exon-intron pattern and motif analysis. Collinearity analysis revealed multiple gene duplication events owing to intra-chromosomal and inter-chromosomal mutations. The cis-regulatory analysis identified several hormone-responsive elements suggesting that ABCs are actively involved in transporting hormones like ABA, SA, MeJA, auxin, and gibberellin. These hormones are known to combat a number of stress conditions, hence validating the role of ABCs in Cd stress. Under Cd stress, expression profiling demonstrated that several SlABCs exhibit significant transcriptional changes, indicating their involvement in Cd transport, sequestration, and detoxification mechanisms. Specific genes, including Groups 3 and 5 members, were upregulated under Cd exposure, suggesting their functional roles in mitigating Cd toxicity. The study revealed differential expressions of various SlABC genes encoding ATP binding cassette transporters, including the upregulation of several genes like Solyc08g067620.2, Solyc08g067610.3, Solyc12g019640.2, Solyc06g036240.2, and Solyc05g053610.2 in response to different concentrations of Cd. This study comprehensively explains the ABC transporter gene family in S. lycopersicum, emphasizing their critical roles in Cd stress tolerance. This study could prove useful in combating Cd stress not only in S. lycopersicum but also in other fleshy fruit plants; however, further advanced studies on specific pathways that lead to differential expression of the ABC genes are required to understand the mechanism behind tolerance to heavy metals fully.

Silicon reduces lead accumulation in Moso bamboo via immobilization and suppression of metal cation transporter genes in roots

Lead (Pb) is a hazardous element that affects the growth and development of plants, while silicon (Si) is a beneficial element for alleviating the stress caused by heavy metals, including Pb. However, the mechanisms by which Si reduces Pb accumulation in Moso bamboo (Phyllostachys edulis (Carr ·) H · de Lehaie) remain unclear. In this study, physiological assessments and transcriptome analyses were conducted to investigate the interaction between Si and Pb. Our findings showed that Si application has no significant effect on alleviating Pb-induced inhibition of root elongation and dry weight in short-term and long-term experiments, respectively. However, it did rescue leaf yellowing and reduce Pb accumulation, particularly in the shoot. Pre-treatment with Si led to a reduction in Pb uptake, translocation and accumulation, coupled with an increase in Pb fixation within the hemicellulose of the root cell wall, resulting in a lower Pb concentration in the cell sap. At the cellular level, Pb was found to be distributed in all cells of roots, and Si pretreatment did not alter Pb distribution. Additionally, Si application downregulated the expression of genes related to ABC and metal cation transporters. These findings indicate that Si reduces Pb accumulation in Moso bamboo by immobilizing Pb in the hemicellulose of root cell walls and downregulating the expression of transporter genes involved in Pb uptake and transport.

Rhizosphere microbial community structure and PICRUSt2 predicted metagenomes function in heavy metal contaminated sites: A case study of the Blesbokspruit wetland

This study investigated the microbial diversity inhabiting the roots (rhizosphere) of macrophytes thriving along the Blesbokspruit wetland, South Africa's least conserved Ramsar site. The wetland suffers from decades of pollution from mining wastewater, agriculture, and sewage. The current study focused on three macrophytes: Phragmites australis (common reed), Typha capensis (bulrush), and Eichhornia crassipes (water hyacinth). The results revealed a greater abundance and diversity of microbes (Bacteria and Fungi) associated with the free-floating E. crassipes compared to P. australis and T. capensis. Furthermore, the correlation between microbial abundance and metals, showed a strong correlation between fungal communities and metals such as nickel (Ni) and arsenic (As), while bacterial communities correlated more with lead (Pb) and chromium (Cr). The functional analysis predicted by PICRUSt2 identified genes related to xenobiotic degradation, suggesting the potential of these microbes to break down pollutants. Moreover, specific bacterial groups - Proteobacteria, Verrucomicrobia, Cyanobacteria, and Bacteroidetes - were linked to this degradation pathway. These findings suggest a promising avenue for microbe-assisted phytoremediation, a technique that utilizes plants and their associated microbes to decontaminate polluted environments.

Oxidative stress and filtration responses in Atlantic ribbed mussels (Geukensia demissa) exposed to radium-226

Bivalves have been extensively utilized as sentinel biomonitoring species, organisms used to predict the extent and severity of environmental contamination. However, significant knowledge gaps remain regarding the operationalization and application of indicator species for radioactive contaminants in the marine environment. Dose-dependent organism responses with validated and practical measurement protocols need to be identified for use within biomonitoring frameworks. Our study explored tissue-specific oxidative stress and filtration responses in Geukensia demissa (Atlantic ribbed mussel) following static renewal exposure to a range of aqueous radium-226 (226Ra) concentrations and exposure durations. We investigated a two-tier antioxidant response system, with radical scavenging activity as the primary response and glutathione S-transferase and lipid peroxidation activities as secondary, downstream responses. A first-stage response of 226Ra exposure was observed, indicated by increased radical scavenging activity in the mantle tissues of mussels exposed to the highest treatment concentration (200 nCi/L = 200 ng/L, 73%) compared with the tissues of control and lower concentration (1, 10, and 100 nCi/L = 1, 10, and 100 ng/L) mussels (18%-44%). However, there was no clear impact for the second-stage responses. A reduction in filtration, quantified via algal removal, was also observed for mussels exposed to the highest 226Ra treatment concentration. This work represents the first investigation on the effects of a marine bivalve exposed to aqueous 226Ra. The responses of bivalves to radiological marine pollution, and the potential for cascading impacts to populations and ecosystems, is still relatively unknown but has important implications for ecological and human well-being.

Heavy metal(loid) bioaccumulation in fish and its implications for human health

Heavy metal(loid)s (HM) pollution in aquatic environments is a serious issue due to the toxicity, persistence, bioaccumulation, and biomagnification of these pollutants. The main sources of HM contamination are industrial activities, mining, agricultural practices, and combustion of fossil fuels. Fish can accumulate HMs through a process called bioaccumulation. As larger predatory fish consume smaller fish, these HMs enter the main food chains and can become increasingly concentrated in their tissues and finally reach humans. Here, we provided a general and concise conclusion from current research findings on the toxicological effects on different body systems. Exposure to HMs can lead to a range of adverse health effects, including neurological damage, developmental disorders, kidney damage, cardiovascular problems, and cancers. Their long-term accumulation can result in chronic toxicity even at low levels of exposure. HMs exert cellular cytotoxicity by disrupting essential cellular processes and structures. They can interfere with enzyme function, disrupt cell membrane integrity, induce oxidative stress, and cause DNA damage, ultimately leading to cell death or dysfunction. Prevention and control of HMs involve implementing measures to reduce their release into the environment through regulations on industrial processes, waste management, and pollution control technologies. Additionally, monitoring and remediation efforts are crucial for identifying contaminated sites and implementing strategies such as soil and water remediation to reduce human exposure and mitigate the impact on ecosystems. To conclude, HM accumulation in fish poses serious risks to public health and the environment, necessitating urgent interdisciplinary efforts to mitigate their harmful effects and promote sustainable practices that reduce HM flow into biological systems.

An Innovative Approach: Alleviating Cadmium Toxicity in Grapevine Seedlings Using Smoke Solution Derived from the Burning of Vineyard Pruning Waste

Although plant-derived smoke solutions (SSs) have exhibited growth-promoting properties in various plant species, their potential role in mitigating heavy metal stress, specifically in grapevines, has remained unexplored and unreported. This knowledge gap prompted the present study to evaluate the efficacy of foliar application of SSs derived from vineyard pruning waste at concentrations of 0%, 0.5%, 1%, and 2% in mitigating Cadmium (Cd) phytotoxicity in grape saplings. In our study, cadmium stress was induced by applying 10 mg/kg CdCl2 to the root area of the saplings, in conjunction with fertilizers. Our findings showed that exposure to Cd toxicity impeded the growth of grapevine saplings, adversely affecting shoot and root length, as well as fresh weight. Furthermore, it resulted in a reduction in chlorophyll content, stomatal conductance, and leaf water content while significantly increasing membrane damage and lipid peroxidation. Notably, the application of 0.5% SS enhanced grapevine sapling growth and alleviated Cd stress-induced damage by more effectively regulating physiological and biochemical responses compared to the control and other concentrations. Based on our results, under Cd stress conditions, the application of 0.5% SS effectively increased chlorophyll content, relative water content (RWC), stomatal conductance (1.79 mmol.m-2.sn-1), and total phenolic content (1.89 mg.g-1), whereas it significantly reduced malondialdehyde (MDA) levels and membrane damage (1.35 nmol.g-1). Additionally, it significantly elevated the activities of antioxidant enzymes, including superoxide dismutase (SOD) (2.16 U.mg-1), catalase (CAT) (1.55 U.mg-1), and ascorbate peroxidase (APX) (3.03 U.mg-1). The study demonstrated that plant-derived SS mitigates Cd stress in grapevines by enhancing antioxidative defence mechanisms.

Trophic transfer of heavy metals across a food chain in a wastewater-irrigated agroecosystem

Wastewater irrigation is often practiced in arid regions, which can increase the chance of heavy metals contaminating the agricultural system. This contamination poses risks to both the environment and human health. This research looked into how cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) move through a food chain involving soil, plants, and arthropods. The study was conducted in El-Gabal El-Asfar, Egypt, comparing treated and untreated wastewater irrigation areas. Six soil-irrigated sites and one reference site were sampled for soil, alfalfa (Medicago sativa), two grasshopper species (Aiolopus thalassinus and Calephorus compressicornis), and a wolf spider (Hogna ferox). The samples were analyzed for their heavy metal content. Metal concentrations in all components of the wastewater irrigated system were significantly higher compared to the reference site. The wolf spider and the soil contained the highest levels of Cd, Pb, and Cu, while the greatest concentrations of Zn were found in the spider and grasshoppers. Despite limited transfer from soil to plant, trace elements biomagnified within the terrestrial food chain, specifically from grasshoppers to wolf spiders. The correlation analysis of metal levels between soils, plants, and arthropods in the present study reflects its transfer across the trophic levels. It suggests that dietary intake is the main source of metal accumulation in arthropods. The present study, therefore, quite clearly indicated the possibility of heavy metal biomagnification in terrestrial food chains of wastewater-irrigated agroecosystems. Continuous monitoring and management of such systems are advocated to avoid environmental and public health risks.

Plants' molecular behavior to heavy metals: from criticality to toxicity

The contamination of soil and water with high levels of heavy metals (HMs) has emerged as a significant obstacle to agricultural productivity and overall crop quality. Certain HMs, although serving as essential micronutrients, are required in smaller quantities for plant growth. However, when present in higher concentrations, they become very toxic. Several studies have shown that to balance out the harmful effects of HMs, complex systems are needed at the molecular, physiological, biochemical, cellular, tissue, and whole plant levels. This could lead to more crops being grown. Our review focused on HMs' resources, occurrences, and agricultural implications. This review will also look at how plants react to HMs and how they affect seed performance as well as the benefits that HMs provide for plants. Furthermore, the review examines HMs' transport genes in plants and their molecular, biochemical, and metabolic responses to HMs. We have also examined the obstacles and potential for HMs in plants and their management strategies.

Potential of the plant growth-promoting rhizobacterium Rhodococcus qingshengii LMR356 in mitigating lead stress impact on Sulla spinosissima L

Mining-related lead (Pb) pollution of the soil poses serious hazards to ecosystems and living organisms, including humans. Improved heavy metal phytoremediation efficacy, achieved by using phytostabilizing plants assisted by plant-growth-promoting (PGP) microorganisms, has been presented as an effective strategy for remediating polluted soils. The objective of this research was to examine the response and potential of the plant-growth-promoting bacterium LMR356, a Rhodococcus qingshengii strain isolated from an abandoned mining soil, under lead stress conditions. Compared to non-contaminated culture media, the presence of lead induced a significant decrease in auxin production (from 21.17 to 2.65 μg mL-1) and phosphate solubilization (from 33.60 to 8.22 mg L-1), whereas other PGP traits increased drastically, such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (from 38.17 to 71.37 nmol mg-1 h-1 α-ketobutyrate), siderophore production (from 69 to 83%), exopolysaccharide production (from 1952.28 to 3637.72 mg mL-1), biofilm formation, and motility. We, therefore, investigated the behavior of Sulla spinosissima L. in the presence or absence of this strain under a variety of experimental conditions. Under hydroponic conditions, Sulla plants showed endurance to varying lead concentrations (500-1000 μM). Inoculation of plants with Rhodococcus qingshengii strain LMR356 enhanced plant tolerance, as demonstrated by the increase in plant biomass (ranging from 14.41 to 79.12%) compared to non-inoculated Pb-stressed and non-stressed control plants. Antioxidant enzyme activities (increasing by -42.71 to 126.8%) and chlorophyll (383.33%) and carotenoid (613.04%) content were also augmented. In addition to its impact on plant lead tolerance, strain LMR356 showed a growth-promoting effect on Sulla plants when cultivated in sterilized non-contaminated sand. Parameters such as plant biomass (16.57%), chlorophyll (24.14%), and carotenoid (30%) contents, as well as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT) activities, were all elevated compared to non-inoculated plants. Furthermore, when the same plant species was cultivated in highly polluted soil, inoculation increased plant biomass and improved its physiological properties. These findings demonstrate that LMR356 is a phytobeneficial bacterial strain capable of enhancing Sulla growth under normal conditions and improving its heavy metal tolerance in multi-polluted soils. Thus, it can be considered a promising biofertilizer candidate for growing Sulla spinosissima L. or other selected plants intended for application in restoration and stabilization initiatives aimed at reviving and safeguarding environmentally compromised and polluted soils after mining activities.

SEM-EDS-based rapid measurement and size-fractionated speciation of airborne particulate matter and associated metals utilizing plant leaves

This study was conducted to assess particulate matter pollution and the accumulation of airborne toxic metals by studying the foliar deposition pattern in an urban environment. To this end, two commonly growing plants (Senna siamea (Lam.) H.S.Irwin & Barneby and Alstonia scholaris (L.) R.Br.) from the busiest traffic squares of the city (Nehru Chowk) in Bilaspur, India, were selected for detailed study. For this purpose, plant leaf samples of both plant species were collected from pollution-affected areas and a reference site (unpolluted) in the city and examined by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) to estimate the accumulation of PM-bound toxic metals at the leaf surfaces. The results of this study showed that the leaves of both plants accumulate PM in different size ranges. Although both plant leaves showed accumulation of PM from respirable suspended particulate matter (RSPM) to ultra-fine particles (UFPs: < 0.1: less than 100 nm) range along with toxic metals, S. siamea retained a higher level of PM than A. scholaris due to better micro-morphological properties on both leaf surfaces. The size of some PM was found to be smaller than the stoma openings. The EDS study proved the presence of harmful airborne toxic metals (Pb, Cd, Cu, Zr, Al, Co, etc.) in these PMs of ambient air. This indicates that toxic metals can enter the leaves through stomatal openings. The results of this study recommended that both plants can be used as a tool to minimise PM pollution.

Photosynthesis and stress response of coal fly ash on stem elongation in wheat

Coal is one of the primary energy sources in China and is widely used for electricity generation. Crops growing in overlapped areas of farmland and coal resources (OAFCR) suffer from coal fly ash stress, especially during stem elongation, which is a key stage that impacts wheat yield and is sensitive to environmental stress. As a primary food crop of China, wheat is essential for food security. However, the characteristics of wheat under the combined stress of fly ash and various heavy metals have not been sufficiently investigated. In this study, we explored the response of stem elongation in wheat to different levels of coal fly ash stress and determined the content of heavy metals (HMs) in wheat leaves. We found that with an increase in fly ash content, the Cu content in the shoots increased, while that in the roots decreased. Coal fly ash exposure reduced the proportions of Pb and Zn in the cytoderm, and the proportion of Cu in the soluble constituents decreased from 58.3% to 45.7%. Total chlorophyll, chlorophyll a, and chlorophyll b levels decreased significantly, whereas peroxidase (POD) and catalase (CAT) activities generally increased with increasing fly ash dose. Meanwhile, chloroplasts, mitochondria, and their internal structures were damaged, and the cell structures of leaves, such as the internal membrane structure, were damaged.

Role of organic and inorganic amendments on physiological attributes of germinating pea seedlings under arsenic stress

There are scarce data regarding the effects of soil amendments on biophysicochemical responses of plants at the early stages of growth/germination. This study critically compares the effects of ethylene-diamine-tetra-acetic-acid (EDTA) and calcium (Ca) on biophysicochemical responses of germinating pea seedlings under varied arsenic levels (As, 25, 125, 250 µM). Arsenic alone enhanced hydrogen peroxide (H2O2) level in pea roots (176%) and shoot (89%), which significantly reduced seed germination percentage, pigment contents, and growth parameters. Presence of EDTA and Ca in growth culture minimized the toxic effects of As on pea seedlings, EDTA being more pertinent than Ca. Both the amendments decreased H2O2 levels in pea tissues (16% in shoot and 13% in roots by EDTA, and 7% by Ca in shoot), and maintained seed germination, pigment contents, and growth parameters of peas close to those of the control treatment. The effects of all As-treatments were more pronounced in the pea roots than in the shoot. The presence of organic and inorganic amendments can play a useful role in alleviating As toxicity at the early stages of pea growth. The scarcity of data demands comparing plant biophysicochemical responses at different stages of plant growth (germinating vs mature) in future studies.

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

Embryo growth alteration and oxidative stress responses in germinating Cucurbita pepo seeds exposed to cadmium and copper toxicity

This study investigated the influence of cadmium (Cd) and copper (Cu) heavy metals on germination, metabolism, and growth of zucchini seedlings (Cucurbita pepo L.). Zucchini seeds were subjected to two concentrations (100 and 200 μM) of CdCl2 and CuCl2. Germination parameters, biochemical and phytochemical attributes of embryonic axes were assessed. Results revealed that germination rate remained unaffected by heavy metals (Cd, Cu). However, seed vigor index (SVI) notably decreased under Cd and Cu exposure. Embryonic axis length and dry weight exhibited significant reductions, with variations depending on the type of metal used. Malondialdehyde and H2O2 content, as well as catalase activity, did not show a significant increase at the tested Cd and Cu concentrations. Superoxide dismutase activity decreased in embryonic axis tissues. Glutathione S-transferase activity significantly rose with 200 μM CdCl2, while glutathione content declined with increasing Cd and Cu concentrations. Total phenol content and antioxidant activity increased at 200 μM CuCl2. In conclusion, Cd and Cu heavy metals impede zucchini seed germination efficiency and trigger metabolic shifts in embryonic tissue cells. Response to metal stress is metal-specific and concentration-dependent. These findings contribute to understanding the intricate interactions between heavy metals and plant physiology, aiding strategies for mitigating their detrimental effects on plants.

Influence of bioaugmented fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora Sw. DC in heavy metal-polluted landfill soil

The research aimed to determine the influence of endophytic fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora in heavy metal-polluted landfill soil. A consortium of 13 fungal isolates as well as Prosopis juliflora Sw. DC was used to decontaminate heavy metal-polluted landfill soil. Enhanced plant growth (biomass and root and shoot lengths) and production of carotenoids, chlorophyll and amino acids L-phenylalanine and L-leucine that are known to enhance growth were found in the treated P. juliflora. Better accumulations of heavy metals were observed in fungi-treated P. juliflora over the untreated one. An upregulated activity of peroxidase, catalase and ascorbate peroxidase was recorded in fungi-treated P. juliflora. Additionally, other metabolites, such as glutathione, 3,5,7,2',5'-pentahydroxyflavone, 5,2'-dihydroxyflavone and 5,7,2',3'-tetrahydroxyflavone, and small peptides, which include Lys Gln Ile, Ser Arg Ala, Asp Arg Gly, Arg Ser Ser, His His Arg, Arg Thr Glu, Thr Arg Asp and Ser Pro Arg, were also detected. These provide defence supports to P. juliflora against toxic metals. Inoculating the plant with the fungi improved its growth, metal accumulation as well as tolerance against heavy metal toxicity. Such a combination can be used as an effective strategy for the bioremediation of metal-polluted soil.

Effects of Cd treatment on morphology, chlorophyll content and antioxidant enzyme activity of Elymus nutans Griseb., a native plant in Qinghai-Tibet Plateau

Cd pollution is a global environmental problem. However, the response mechanism of the alpine plant Pelagia under Cd stress remains unclear. Therefore, in this study, a native plant(Elymus nutans Griseb.) of the Qinghai-Tibet Plateau was used as the material to quantify plant height, leaf number, length of leaf, crown width, root number, biomass, Dry weight malondialdehyde (MDA), free proline, superoxide dismutase (SOD), ascorbate enzyme (APX), catalase (CAT) and chlorophyll contents under different Cd concentrations. The results showed that the growth of Elymus nutans Griseb. was a phenomenon of "low concentration promotes growth, high concentration inhibited growth" under Cd treatment. It meant that 10 mg·L^-1 Cd promoted the growth of leaf number, plant height, crown width and tiller number, while 40 mg·L^-1 Cd inhibited the growth of root number and biomass of Elymus nutans Griseb. compare with the control. The MDA content, free proline content, SOD activity, APX activity and CAT activity of Elymus nutans Griseb. was increased with the increase of Cd treatment concentration to resist the oxidative damage caused by Cd to the body. At the same time, the accumulation of chlorophyll A, chlorophyll B and chlorophyll AB was decreased with the increase of Cd stress concentration. In addition, the carotenoid content did not change much between the control group and the treatment group, indicating that Cd treatment had little effect on it. The results could provide a reference for the mechanism of heavy metal resistance and the selection and improvement of Cd -resistant varieties of Elymus nutans Griseb.

Risk assessment of trace element accumulation in soil and Brassica oleracea after wastewater irrigation

The risk assessment of trace elements has received substantial attention for the achievement of UN Sustainable Developmental Goals (UN-SDGs). The present study aimed to evaluate health and ecological risks associated with trace element accumulation in Brassica oleracea under wastewater irrigations from three different areas. This study, for the first time, compared the pros and cons of mixed water crop irrigation (wastewater with fresh/groundwater). A pot experiment was conducted to evaluate the buildup of eight trace elements (As, Cu, Cd, Mn, Fe, Pb, Ni and Zn) in soil and B. oleracea plants irrigated with wastewater alone and mixed with fresh/groundwater. Specific ecological [degree of contamination (Cd), potential ecological risk index (PERI), pollution load index (PLI), geo-accumulation index (Igeo)], phytoaccumulation [bioconcentration factor (BCF) and transfer factor (TF)] and health risk models [chronic daily intake (CDI), hazard quotient (HQ), cancer risk (CR)] were applied to assess the overall contamination of trace elements in the soil-plant-human system. Moreover, these indices were compared with the literature data. The concentration of Cd, Fe and Mn exceeded the threshold limits of 10, 500 and 200 mg kg-1, respectively, for agricultural soil. Overall, all the irrigation waters caused significant pollution load in soil indicating high ecological risk (Cd > 24, PERI > 380, Igeo > 5, PLI > 2). Not all the mixing treatments caused a reduction in trace element buildup in soil. The mixing of wastewater-1 with either groundwater or freshwater increased trace element levels in the soil as well as risk indices compared to wastewater alone. The BCF and TF values were > 1, respectively, for 66% and 7% treatments. Trace element concentration in plants and associated health risk were minimized in mixed wastewater treatments. There were 22% and 32% reduction in HQ and CR when wastewater was mixed with freshwater and 29% and 8% when mixed with groundwater. Despite total reduction, a great variation in % change in risk indices was observed with respect to the area of wastewater collection. Therefore, mixed water irrigation may be a good management strategy, but its recommendation depends on soil properties and composition of waters used for mixing. Moreover, it is recommended that the freshwater and wastewater of the particular area may be continuously monitored to avoid potential associated health hazards.

A critical analysis of wastewater use in agriculture and associated health risks in Pakistan

Freshwater shortage and its contamination with various types of pollutants are becoming the most alarming issues worldwide due to impacts on socioeconomic values. Considering an increasing freshwater scarcity, it is imperative for the growers, particularly in semiarid and arid areas, to use wastewater for crop production. Wastewaters generally contain numerous essential inorganic and organic nutrients which are considered necessary for plant metabolism. Besides, this practice provokes various hygienic, ecological and health concerns due to the occurrence of toxic substances such as heavy metals. Pakistan nowadays faces a severe freshwater scarcity. Consequently, untreated wastewater is used routinely in the agriculture sector. In this review, we have highlighted the negative and positive affectivity of wastewater on the chemical characteristics of the soil. This review critically delineates toxic metal accumulation in soil and their possible soil-plant-human transfer. We have also estimated and deliberated possible health hazards linked with the utilization of untreated city waste effluents for the cultivation of food/vegetable crops. Moreover, we carried out a multivariate analysis of data (144 studies of wastewater crop irrigation in Pakistan) to trace out common trends in published data. We have also compared the limit values of toxic metals in irrigation water, soil and plants. Furthermore, some viable solutions and future viewpoints are anticipated taking into account the on-ground situation in Pakistan-such as planning and sanitary matters, remedial/management technologies, awareness among local habitants (especially farmers) and the role of the government, NGOs and pertinent stakeholders. The data are supported by 13 tables and 7 figures.

Alleviation of cadmium-induced photoinhibition and oxidative stress by melatonin in Chlamydomonas reinhardtii

As one of the most threatening challenges to the natural environment and human health, cadmium (Cd) pollution has seriously impacted natural organisms. Green algae, such as Chlamydomonas reinhardtii (C. reinhardtii), can provide a safer, lower cost, and more effective ecological approach to the treatment of heavy metal ions in wastewater due to their sorption properties. However, heavy metal ions affect C. reinhardtii when adsorbed. Melatonin is able to protect the plant body from damage when the plant is under biotic/abiotic stress. Therefore, we investigated the effects of melatonin on the cell morphology, chlorophyll content, chlorophyll fluorescence parameters, enzymatic activity of the antioxidant system, gene expression, and the ascorbic acid (AsA)-glutathione (GSH) cycle of C. reinhardtii under the stress of Cd (13 mg/L). Our results indicated that Cd significantly induced photoinhibition and overaccumulation of reactive oxygen species (ROS). By application with the concentration of 1.0 μM melatonin, the algal solute of C. reinhardtii under the Cd stress gradually regained its green color, the cell morphology became intact, and the photosynthetic electron transport function was retained. However, in the melatonin-silenced strain, there was a significant decrease in all of the above indicators. In addition, the use of exogenous melatonin or the expression of endogenous melatonin genes could enhance the intracellular enzyme activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). It also upregulated the expression of active enzyme genes such as SOD1, CAT1, FSD1, GSH1, GPX5, and GSHR1. These results indicate that the presence of melatonin effectively protects the activity of photosynthetic system II in C. reinhardtii, enhances antioxidant activity, upregulates gene expression in the AsA-GSH cycle, and reduces the level of ROS, thereby alleviating the damage caused by Cd toxicity.

Low-level cadmium exposure induced hormesis in peppermint young plant by constantly activating antioxidant activity based on physiological and transcriptomic analyses

As one of the most toxic environmental pollutants, cadmium (Cd) has lastingly been considered to have negative influences on plant growth and productivity. Recently, increasing studies have shown that low level of Cd exposure could induce hormetic effect which benefits to plants. However, the underlying mechanisms of Cd-triggered hormesis are poorly understood. In this study, we found that Cd stress treatment showed a hormetic effect on peppermint and Cd treatment with 1.6 mg L-1 concertation manifested best stimulative effects. To explore the hormesis mechanisms of Cd treatment, comparative transcriptome analysis of peppermint young plants under low (1.6 mg L-1) and high (6.5 mg L-1) level of Cd exposure at 0 h, 24 h and 72 h were conducted. Twelve of differentially expressed genes (DEGs) were selected for qRT-PCR validation, and the expression results confirmed the credibility of transcriptome data. KEGG analysis of DEGs showed that the phenylpropanoid biosynthesis and photosynthesis were important under both low and high level of Cd treatments. Interestingly, GO and KEGG analysis of 99 DEGs specifically induced by low level of Cd treatment at 72 h indicated that these DEGs were mainly involved in the pathway of phenylpropanoid biosynthesis and their functions were associated with antioxidant activity. The expression pattern of those genes in the phenylpropanoid biosynthesis pathway and encoding antioxidant enzymes during 72 h of Cd exposure showed that low level of Cd treatment induced a continuation in the upward trend but high level of Cd treatment caused an inverted V-shape. The changes of physiological parameters during Cd exposure were highly consistent with gene expression pattern. These results strongly demonstrate that low level of Cd exposure constantly enhanced antioxidant activity of peppermint to avoid oxidative damages caused by Cd ion, while high level of Cd stress just induced a temporary increase in antioxidant activity which was insufficient to cope with lasting Cd toxicity. Overall, the results presented in this study shed a light on the underlying mechanisms of the Cd-mediated hormesis in plant. Moreover, our study provided a safe method for the efficient utilization of mild Cd-contaminated soil as peppermint is an important cash plant.

Chromium toxicity, speciation, and remediation strategies in soil-plant interface: A critical review

In recent decades, environmental pollution with chromium (Cr) has gained significant attention. Although chromium (Cr) can exist in a variety of different oxidation states and is a polyvalent element, only trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] are found frequently in the natural environment. In the current review, we summarize the biogeochemical procedures that regulate Cr(VI) mobilization, accumulation, bioavailability, toxicity in soils, and probable risks to ecosystem are also highlighted. Plants growing in Cr(VI)-contaminated soils show reduced growth and development with lower agricultural production and quality. Furthermore, Cr(VI) exposure causes oxidative stress due to the production of free radicals which modifies plant morpho-physiological and biochemical processes at tissue and cellular levels. However, plants may develop extensive cellular and physiological defensive mechanisms in response to Cr(VI) toxicity to ensure their survival. To cope with Cr(VI) toxicity, plants either avoid absorbing Cr(VI) from the soil or turn on the detoxifying mechanism, which involves producing antioxidants (both enzymatic and non-enzymatic) for scavenging of reactive oxygen species (ROS). Moreover, this review also highlights recent knowledge of remediation approaches i.e., bioremediation/phytoremediation, or remediation by using microbes exogenous use of organic amendments (biochar, manure, and compost), and nano-remediation supplements, which significantly remediate Cr(VI)-contaminated soil/water and lessen possible health and environmental challenges. Future research needs and knowledge gaps are also covered. The review's observations should aid in the development of creative and useful methods for limiting Cr(VI) bioavailability, toxicity and sustainably managing Cr(VI)-polluted soils/water, by clear understanding of mechanistic basis of Cr(VI) toxicity, signaling pathways, and tolerance mechanisms; hence reducing its hazards to the environment.

Chemokine expression in human 3-dimensional cultured epidermis exposed to PM2.5 collected by cyclonic separation

Fine particulate matter (PM2.5) exposure has a risk of inducing several health problems, especially in the respiratory tract. The skin is the largest organ of the human body and is therefore the primary target of PM2.5. In this study, we examined the effects of PM2.5 on the skin using a human 3-dimensional cultured epidermis model. PM2.5 was collected by cyclonic separation in Yokohama, Japan. Global analysis of 34 proteins released from the epidermis revealed that the chemokines, chemokine C-X-C motif ligand 1 (CXCL1) and interleukin 8 (IL-8), were significantly increased in response to PM2.5 exposure. These chemokines stimulated neutrophil chemotaxis in a C-X-C motif chemokine receptor 2-dependent manner. The oxidative stress and signal transducer and activator of transcription 3 pathways may be involved in the increased expression of CXCL1 and IL-8 in the human epidermis model. Interestingly, in the HaCaT human keratinocyte cell line, PM2.5 did not affect chemokine expression but did induce IL-6 expression, suggesting a different effect of PM2.5 between the epidermis model and HaCaT cells. Overall, PM2.5 could induce the epidermis to release chemokines, followed by neutrophil activation, which might cause an unregulated inflammatory reaction in the skin.

Assessing the Cooling and Air Pollution Tolerance among Urban Tree Species in a Tropical Climate

We present the results of classifying plants at species level that can tolerate air pollution, provide cooling, and simultaneously survive and thrive in urban environments. For this purpose, we estimated the air pollution tolerance index (APTI) and anticipated performance index (API) of several species growing in a park located in central Bangkok, Thailand. The cooling effect was quantified by calculating the reduction in soil and air temperatures. Melaleuca quinquenervia (Cav.) S.T. Blake, Albizia saman (Jacq.) Merr., Chukrasia tabularis A. Juss. had the highest API score and were able to substantially reduce the temperature and were in a group of highly recommended species which also included other species like A. saman, C. tabularis, Tabebuia rosea (Bertol.) Bertero ex A. DC., Dalbergia cochinchinensis Pierre etc. Species from both evergreen and deciduous habitat were able to provide ambient cooling but were vulnerable to air pollution and included Elaeocarpus grandifloras Sm. and Bauhinia purpurea L. However, there were other species which had a high air pollution tolerance but failed to provide adequate cooling, such as Hopea odorata Roxb. and Millingtonia hortensis L.f. The results would be of interest to urban greenspace landscapers in such climates while selecting suitable species that can provide multiple ecosystem services ranging from air pollution tolerance to temperature reduction without reducing plant vitality.

Heavy metal distribution, fractionation, and biotoxicity in sediments around villages in Baiyangdian Lake in North China

The effects of human activities on heavy metal distributions and fractionation in sediments from villages around Baiyangdian Lake (BYDL), North China, were assessed. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in sediments from five villages were determined, and the potential ecological risk index, risk assessment code, and Chironomus sp. larvae toxicity assay were used to assess the bioavailabilities and toxicities of the metals. The contribution of Cd to the potential ecological risk was 45.13-89.53%, the highest among the heavy metals investigated. The contributions of Cd, Pb, and Zn in the non-residual fractions to the total concentrations were 66.23-90.57%, 18.31-96.28%, and 8.89-76.84%, respectively, which indicated that these metals had important anthropogenic sources and were very bioavailable. The mean risk assessment codes decreased in the order of Cd (49.82%) > Zn (20.95%) > Cu (9.35%) > Pb (6.88%) > Ni (4.85%) > Cr (0.30%), and the toxicity of Cd and Zn to biota around BYDL is of concern. The mean survival rate of Chironomus sp. larvae in sediments from Dizhuang village was 44.02%, which indicated that there was a high degree of heavy metal toxicity, particularly in waterways around the village. Carboxylesterase and superoxide dismutase analysis results indicated that heavy metals could markedly increase or decrease enzyme activities in Chironomus sp. larvae. Overall, the results indicated that heavy metal pollution in villages around BYDL should be taken into consideration for its ecological management.

Interaction between zinc and selenium bio-fortification and toxic metals (loid) accumulation in food crops

Biofortification is the supply of micronutrients required for humans and livestock by various methods in the field, which include both farming and breeding methods and are referred to as short-term and long-term solutions, respectively. The presence of essential and non-essential elements in the atmosphere, soil, and water in large quantities can cause serious problems for living organisms. Knowledge about plant interactions with toxic metals such as cadmium (Cd), mercury (Hg), nickel (Ni), and lead (Pb), is not only important for a healthy environment, but also for reducing the risks of metals entering the food chain. Biofortification of zinc (Zn) and selenium (Se) is very significant in reducing the effects of toxic metals, especially on major food chain products such as wheat and rice. The findings show that Zn- biofortification by transgenic technique has reduced the accumulation of Cd in shoots and grains of rice, and also increased Se levels lead to the formation of insoluble complexes with Hg and Cd. We have highlighted the role of Se and Zn in the reaction to toxic metals and the importance of modifying their levels in improving dietary micronutrients. In addition, cultivar selection is an essential step that should be considered not only to maintain but also to improve the efficiency of Zn and Se use, which should be considered more climate, soil type, organic matter content, and inherent soil fertility. Also, in this review, the role of medicinal plants in the accumulation of heavy metals has been mentioned, and these plants can be considered in line with programs to improve biological enrichment, on the other hand, metallothioneins genes can be used in the program biofortification as grantors of resistance to heavy metals.

Supplementation of nitric oxide and spermidine alleviates the nickel stress-induced damage to growth, chlorophyll metabolism, and photosynthesis by upregulating ascorbate-glutathione and glyoxalase cycle functioning in tomato

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO46H2O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg-prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

The regulatory role of abscisic acid on cadmium uptake, accumulation and translocation in plants

To date, Cd contamination of cropland and crops is receiving more and more attention around the world. As a plant hormone, abscisic acid (ABA) plays an important role in Cd stress response, but its effect on plant Cd uptake and translocation varies among plant species. In some species, such as Arabidopsis thaliana, Oryza sativa, Brassica chinensis, Populus euphratica, Lactuca sativa, and Solanum lycopersicum, ABA inhibits Cd uptake and translocation, while in other species, such as Solanum photeinocarpum and Boehmeria nivea, ABA severs the opposite effect. Interestingly, differences in the methods and concentrations of ABA addition also triggered the opposite result of Cd uptake and translocation in Sedum alfredii. The regulatory mechanism of ABA involved in Cd uptake and accumulation in plants is still not well-established. Therefore, we summarized the latest studies on the ABA synthesis pathway and comparatively analyzed the physiological and molecular mechanisms related to ABA uptake, translocation, and detoxification of Cd in plants at different ABA concentrations or among different species. We believe that the control of Cd uptake and accumulation in plant tissues can be achieved by the appropriate ABA application methods and concentrations in plants.

A hydrogen sulfide application can alleviate the toxic effects of cadmium on ginger (Zingiber officinale Roscoe)

Cadmium (Cd) is a poisonous element for human health. This study was conducted to explore whether H2S can alleviate the toxic effects of Cd on ginger. Specifically, ginger plants were grown in soil and treated with 7.5 mg·l-1 CdCl2, after which water (T1), 0.8 mM NaHS (T2), or 0.8 mM NaHS and 0.15 mM HT (T3) were added to the soil. The application of NaHS increased the activities of antioxidant enzymes (APX, GR, MDHAR, and DHAR) during the early treatment stage. It also inhibited the decrease in Pn, Gs, and Ls under Cd stress conditions while also limiting the increase in Ci. An analysis of the expression of Cd uptake-related genes indicated that NaHS upregulated the expression of ZoNramp1, which encodes a metal transporter, in roots as well as ZoPCS1, which encodes a phytochelatin synthase. In contrast, NaHS downregulated ZoHMA2 expression in the rhizomes and roots under Cd stress conditions.

Effects of urease-producing bacteria and eggshell on physiological characteristics and Cd accumulation of pakchoi (Brassica chinensis L.) plants

Soil cadmium (Cd) contamination resulting from anthropogenic activity poses severe threats to food safety and human health. In this study, a pot experiment was performed to evaluate the possibility of using urease-producing bacterium UR21 and eggshell (ES) waste for improving the physiological characteristics and reducing Cd accumulation of pakchoi (Brassica chinensis L.) plants. UR21 has siderophore and IAA production ability. The application of UR21 and ES individually or in combination could improve the root and shoot length, and fresh and dry weight of pakchoi plants under Cd stress. In Cd + ES + UR21-treated plants, the dry weight of shoot and root were increased by 61.54% and 72.73%, respectively. The chlorophyll a, chlorophyll b, and carotenoid content were increased by 52.19%, 42.95%, and 95.56% in Cd + ES + UR21-treated plants. Meanwhile, the H₂O₂ and MDA content were decreased while the SOD and POD activity were increased, and an increase of soluble protein level in pakchoi plants was observed under Cd + ES + UR21 treatment. Importantly, eggshell and UR21 alone or in combination induced a decline of Cd content in pakchoi plants, especially that Cd + ES + UR21 treatment decreased Cd content in shoot and root by 26.96% and 42.91%, respectively. Meanwhile, the soil urease and sucrase activities were enhanced. Generally, the combined application of ureolytic bacteria UR21 and eggshell exhibited better effects than applied them individually in terms of alleviating Cd toxicity in pakchoi plants. Our findings may give a unique perspective for an eco-friendly and sustainable strategy to remediate heavy metal-polluted soils.

Endofungal Rhizobium species enhance arsenic tolerance in colonized host plant under arsenic stress

Arsenic (As) is a toxic metalloid that is present in natural surroundings in many forms with severe consequences to sustainable agriculture and human health. Plant growth-promoting Rhizobia have been found involved in the induction of plant tolerance under various biotic and abiotic stresses. An endofungal Rhizobium species associated with arbuscular mycorrhizal fungi (AMF) Serendipita indica deploy beneficial role in the promotion of plant growth and tolerance against various biotic and abiotic stresses. In the current study, we have determined the role of endofungal Rhizobium species in protection of host plant growth under As stress. We observed that endofungal Rhizobium species strain Si001 tolerate AsV up to 25 mM and its inoculation enhances tomato seed germination and seedling growth. A hyper-colonization of Rhizobium species Si001 in tomato roots was observed under As stress and results in modulation of GSH and proline content with reduced ROS. Rhizobium species Si001 colonization in host plant recovered pigment contents (chlorophyll-a and chlorophyll-b up to 189.5% and 192%, respectively), photosynthesis (157%), and water use efficiency (166%) compared to As-treated plants. Interestingly, bacterial colonization results in 40% increased As accumulation in the root, while a reduction in As translocation from root to shoot up to 89% was observed as compared to As treated plants. In conclusion, endofungal Rhizobium species Si001 association with the host plant may improve plant health and tolerance against As stress with reduced As accumulation in the crop produce.

Arsenic-induced oxidative stress in Brassica oleracea: Multivariate and literature data analyses of physiological parameters, applied levels and plant organ type

Plant redox homeostasis governs the uptake, toxicity and tolerance mechanism of toxic trace elements and thereby elucidates the remediation potential of a plant. Moreover, plant toxicity/tolerance mechanisms control the trace element compartmentation in edible and non-edible plant organs as well as the associated health hazards. Therefore, it is imperative to unravel the cellular mechanism involved in trace element toxicity and tolerance. The present study investigated the toxicity and tolerance/detoxification mechanisms of four levels of arsenic (As(III): 0, 5, 25 and 125 µM) in Brassica oleracea under hydroponic cultivation. Increasing As levels significantly decreased the pigment contents (up to 68%) of B. oleracea. Plants under As stress showed an increase in H₂O₂ contents (up to 32%) in roots while a decrease (up to 72%) in leaves because As is mostly retained in plant roots, while less is translocated toward the shoot, as evident from the literature. Arsenic treatments caused lipid peroxidation both in the root and leaf cells. Against As-induced oxidative stress, B. oleracea plants mediated an increase in the activities of peroxidase and catalase. Contradictory, the ascorbate peroxidase and superoxide dismutase activities slightly decreased in the As-stressed plants. In conclusion and as evident from the literature data analysis, As exposure (especially high level, 125 µM) caused pigment toxicity and oxidative burst in B. oleracea. The ability of B. oleracea to tolerate As-induced toxicity greatly varied with applied treatment levels (As-125 being more toxic than lower levels), plant organ type (more toxicity in leaves than roots) and physiological response parameter (pigment contents more sensitive than other response variables). Moreover, the multivariate statistical analysis appeared to be a useful method to estimate plant response under stress and trace significant trends in the data set.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.

Microbial Interventions in Bioremediation of Heavy Metal Contaminants in Agroecosystem

Soil naturally comprises heavy metals but due to the rapid industrialization and anthropogenic events such as uncontrolled use of agrochemicals their concentration is heightened up to a large extent across the world. Heavy metals are non-biodegradable and persistent in nature thereby disrupting the environment and causing huge health threats to humans. Exploiting microorganisms for the removal of heavy metal is a promising approach to combat these adverse consequences. The microbial remediation is very crucial to prevent the leaching of heavy metal or mobilization into the ecosystem, as well as to make heavy metal extraction simpler. In this scenario, technological breakthroughs in microbes-based heavy metals have pushed bioremediation as a promising alternative to standard approaches. So, to counteract the deleterious effects of these toxic metals, some microorganisms have evolved different mechanisms of detoxification. This review aims to scrutinize the routes that are responsible for the heavy metal(loid)s contamination of agricultural land, provides a vital assessment of microorganism bioremediation capability. We have summarized various processes of heavy metal bioremediation, such as biosorption, bioleaching, biomineralization, biotransformation, and intracellular accumulation, as well as the use of genetically modified microbes and immobilized microbial cells for heavy metal removal.

Phytochemical analysis reveals an antioxidant defense response in Lonicera japonica to cadmium-induced oxidative stress

Cadmium (Cd), though potentially beneficial at lower levels to some plant species, at higher levels is a toxic metal that is detrimental to plant growth and development. Cd is also a carcinogen to humans and other contaminated plant consumers, affecting the kidneys and reducing bone strength. In this study we investigated responses of growth, chlorophyll content, reactive oxygen species levels, and antioxidant responses to Cd in honeysuckle leaves (Lonicera japonica Thunb.), a potential Cd hyperaccumulator. Results indicated that plant height, dry weight, leaf area, and chlorophyll content increased when honeysuckle was exposed to 10 mg kg^-1 or 30 mg kg^-1 Cd (low concentration). However, in response to 150 mg kg^-1 or 200 mg kg^-1 Cd (high concentration) these growth parameters and chlorophyll content significantly decreased relative to untreated control plant groups. Higher levels of superoxide radical (O₂^·-) and hydrogen peroxide (H₂O₂) were observed in high concentration Cd groups. The activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase were enhanced with exposure to increasing levels of Cd. Additionally, the Ascorbate-Glutathione (AsA-GSH) cycle was activated for the removal of H₂O₂ in honeysuckle in response to elevated Cd. The Pearson correlation analysis, a redundancy analysis, and a permutation test indicated that proline and APX were dominant antioxidants for removing O₂^·- and H₂O₂. The antioxidants GSH and non-protein thiols (NPTs) also increased as the concentration of Cd increased.

Effect of silicon application with mycorrhizal inoculation on Brassica juncea cultivated under water stress

Brassica juncea L. is a significant member of the Brassicaceae family, also known as Indian mustard. Water is a limiting factor in the successful production of this crop. Here, we tested the effect of water shortage in B. juncea plants supplemented with or without the application of silicon and arbuscular mycorrhizal fungi in total 8 different treatments compared under open filed conditions using a randomised complete block design (RCBD). The treatments under control conditions were control (C, T1); C+Silicon (Si, T2); C+My (Mycorrhiza; T3); and C+Si+My (T4). In contrast, treatments under stress conditions were S (Stress; T5); S+Si (T6); S+My (T7) and S+Si+My (T8), respectively. In total, we evaluated 16 traits, including plant response to stress by evaluating peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity. The fresh weight (g) increased only 7.47 percent with mycorrhiza (C+My) and 22.39 percent with silicon (C+Si) but increased 291.08 percent with both mycorrhiza and silicon (C+Si+My). Using mycorrhiza (S+My) or silicon (S+Si) alone produced a significant increase of 53.16 percent and 55.84 percent in fresh weight, respectively, while using both mycorrhiza and silicon (S+Si+My) together produced a dramatic increase of 380.71 percent under stress conditions. Superoxidase dismutase concentration (Ug⁻¹ FW) was found to be increased by 29.48 percent, 6.71 percent, and 22.63 percent after applying C+My, C+Si and C+Si+My, but treatment under stress revealed some contrasting trends, with an increase of 11.21 percent and 19.77 percent for S+My, S+Si+My, but a decrease of 13.15 percent for S+Si. Finally, in the presence of stress, carotenoid content (mg/g FW) increased by 58.06 percent, 54.83 percent, 183.87 percent with C+My, and 23.81 percent with S+My and S+Si+My, but decreased by 22.22 percent with S+Si. Silicon application proved to be more effective than AMF treatment with Rhizophagus irregularis, and the best results were obtained with the combination of Si and AMF. This work will help to suggest the measures to overcome the water stress in B. juncea.

Reactive Oxygen Species Partly Mediate DNA Methylation in Responses to Different Heavy Metals in Pokeweed

DNA methylation is a rapid response strategy promoting plant survival under heavy metal (HM) stress. However, the roles of DNA methylation underlying plant adaptation to HM stress remain largely unknown. Here, we used pokeweed, a hyperaccumulator of manganese (Mn) and cadmium (Cd), to explore responses of plant to HM stress at phenotypic, transcriptional and DNA methylation levels. Mn- and Cd-specific response patterns were detected in pokeweed. The growth of pokeweed was both inhibited with exposure to excess Mn/Cd, but pokeweed distinguished Mn and Cd with different subcellular distributions, ROS scavenging systems, transcriptional patterns including genes involved in DNA methylation, and differentially methylated loci (DML). The number of DML between Mn/Cd treated and untreated samples increased with increased Mn/Cd concentrations. Meanwhile, pretreatment with NADPH oxidase inhibitors prior to HM exposure markedly reduced HM-induced reactive oxygen species (ROS), which caused reductions in expressions of DNA methylase and demethylase in pretreated samples. The increased levels of HM-induced demethylation were suppressed with alleviated ROS stress, and a series of HM-related methylated loci were also ROS-related. Taken together, our study demonstrates that different HMs affect different DNA methylation sites in a dose-dependent manner and changes in DNA methylation under Mn/Cd stress are partly mediated by HM-induced ROS.

Layered Double Hydroxide Catalysts Preparation, Characterization and Applications for Process Development: An Environmentally Green Approach

The adage of new generation of fine chemicals process is the best process applied in the absence of conventional methods. However, many methods use different reaction parameters, such as basic and acidic catalysts, for example oxidation, reduction, bromination, water splitting, cyanohydrin, ethoxylation, syngas, aldol condensation, Michael addition, asymmetric ring opening of epoxides, epoxidation, Wittig and Heck reaction, asymmetric ester epoxidation of fatty acids, combustion of methane, NOx reduction, biodiesel synthesis, propylene oxide polymerization. Layered Double Hydroxides (LDHs) have received considerable attention due their potential applications in flame retardant and has excellent medicinal property for reducing acidity. These catalysts are characterized using analytical techniques, such as: X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Raman spectroscopy, Thermogravimetric-Differential Thermal Analyzer (TG-DTA), Scanning electron microscope (SEM), Transmission electron microscopes (TEM), Brunauer-Emmett-Teller (BET) surface area, N2 Adsorption-desorption, Temperature programmed reduction (TPR), X-ray photoelectrons spectroscopy (XPS), which gives its overall picture of its structure, porosity, morphology, thermal stability, reusability, and activity of catalysts. LDHs catalysts have proven to be economic and environmentally friendly. The above discussed applications make these catalysts unique from Green Chemistry point of view since they are reusable, and eco-friendly catalysts. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Root Reinforcement Improved Performance, Productivity, and Grain Bioactive Quality of Field-Droughted Quinoa (Chenopodium quinoa)

Modern agriculture is facing multiple and complex challenges and has to produce more food and fiber to feed a growing population. Increasingly volatile weather and more extreme events such as droughts can reduce crop productivity. This implies the need for significant increases in production and the adoption of more efficient and sustainable production methods and adaptation to climate change. A new technological and environment-friendly management technique to improve the tolerance of quinoa grown to maturity is proposed using native microbial biostimulants (arbuscular mycorrhizal fungi; AMF) alone, in the consortium, or in combination with compost (Comp) as an organic matter source under two water treatments (normal irrigation and drought stress (DS)). Compared with controls, growth, grain yield, and all physiological traits under DS were significantly decreased while hydrogen peroxide, malondialdehyde, and antioxidative enzymatic functions were significantly increased. Under DS, biofertilizer application reverted physiological activities to normal levels and potentially strengthened quinoa's adaptability to water shortage as compared to untreated plants. The dual combination yielded a 97% improvement in grain dry weight. Moreover, the effectiveness of microbial and compost biostimulants as a biological tool improves grain quality and limits soil degradation under DS. Elemental concentrations, particularly macronutrients, antioxidant potential (1,1-diphenyl-2-picrylhydrazyl radical scavenging activity), and bioactive compounds (phenol and flavonoid content), were accumulated at higher levels in biofertilizer-treated quinoa grain than in untreated controls. The effects of AMF + Comp on post-harvest soil fertility traits were the most positive, with significant increases in total phosphorus (47%) and organic matter (200%) content under drought conditions. Taken together, our data demonstrate that drought stress strongly influences the physiological traits, yield, and quality of quinoa. Microbial and compost biostimulation could be an effective alternative to ensure greater recovery capability, thereby maintaining relatively high levels of grain production. Our study shows that aboveground stress responses in quinoa can be modulated by signals from the microbial/compost-treated root. Further, quinoa grains are generally of higher nutritive quality when amended and inoculated with AMF as compared to non-inoculated and compost-free plants.

Genome-Wide Analysis of the ATP-Binding Cassette (ABC) Transporter Family in Zea mays L. and Its Response to Heavy Metal Stresses

The ATP-binding cassette (ABC) transporter family is one of the largest eukaryotic protein families. Its members play roles in numerous metabolic processes in plants by releasing energy for substrate transport across membranes through hydrolysis of ATP. Maize belongs to the monocotyledonous plant family, Gramineae, and is one of the most important food crops in the world. We constructed a phylogenetic tree with individual ABC genes from maize, rice, sorghum, Arabidopsis, and poplar. This revealed eight families, each containing ABC genes from both monocotyledonous and dicotyledonous plants, indicating that the amplification events of ABC gene families predate the divergence of plant monocotyledons. To further understand the functions of ABC genes in maize growth and development, we analyzed the expression patterns of maize ABC family genes in eight tissues and organs based on the transcriptome database on the Genevestigator website. We identified 133 ABC genes expressed in most of the eight tissues and organs examined, especially during root and leaf development. Furthermore, transcriptome analysis of ZmABC genes showed that exposure to metallic lead induced differential expression of many maize ABC genes, mainly including ZmABC 012, 013, 015, 031, 040, 043, 065, 078, 080, 085, 088, 102, 107, 111, 130 and 131 genes, etc. These results indicated that ZmABC genes play an important role in the response to heavy metal stress. The comprehensive analysis of this study provides a foundation for further studies into the roles of ABC genes in maize.

miR160: An Indispensable Regulator in Plant

MicroRNAs (miRNA), recognized as crucial regulators of gene expression at the posttranscriptional level, have been found to be involved in the biological processes of plants. Some miRNAs are up- or down-regulated during plant development, stress response, and secondary metabolism. Over the past few years, it has been proved that miR160 is directly related to the developments of different tissues and organs in multifarious species, as well as plant-environment interactions. This review highlights the recent progress on the contributions of the miR160-ARF module to important traits of plants and the role of miR160-centered gene regulatory network in coordinating growth with endogenous and environmental factors. The manipulation of miR160-guided gene regulation may provide a new method to engineer plants with improved adaptability and yield.

Role of phytomelatonin responsive to metal stresses: An omics perspective and future scenario

A pervasive melatonin (N-acetyl-5-methoxytryptamine) reveals a crucial role in stress tolerance and plant development. Melatonin (MT) is a unique molecule with multiple phenotypic expressions and numerous actions within the plants. It has been extensively studied in crop plants under different abiotic stresses such as drought, salinity, heat, cold, and heavy metals. Mainly, MT role is appraised as an antioxidant molecule that deals with oxidative stress by scavenging reactive oxygen species (ROS) and modulating stress related genes. It improves the contents of different antioxidant enzyme activities and thus, regulates the redox hemostasis in crop plants. In this comprehensive review, regulatory effects of melatonin in plants as melatonin biosynthesis, signaling pathway, modulation of stress related genes and physiological role of melatonin under different heavy metal stress have been reviewed in detail. Further, this review has discussed how MT regulates different genes/enzymes to mediate defense responses and overviewed the context of transcriptomics and phenomics followed by the metabolomics pathways in crop plants.

Autotoxin Rg1 Induces Degradation of Root Cell Walls and Aggravates Root Rot by Modifying the Rhizospheric Microbiome

Management of crop root rot disease is one of the key factors in ensuring sustainable development in agricultural production. The accumulation of autotoxins and pathogens in soil has been reported as a primary driver of root rot diseases; however, less is known about the correlation of plants, their associated pathogens and microbiome mediated by autotoxins as well as the contributions autotoxins make to the occurrence of root rot disease. Here, we integrated metabolomic, transcriptomic, and rhizosphere microbiome analyses to identify the root cell wall degradants cellobiose and d-galacturonic acid as being induced by the autotoxic ginsenoside Rg₁ of Panax notoginseng, and we found that exogenous cellobiose and d-galacturonic acid in addition to Rg₁ could aggravate root rot disease by modifying the rhizosphere microbiome. Microorganisms that correlated positively with root rot disease were enriched and those that correlated negatively were suppressed by exogenous cellobiose, d-galacturonic acid, and Rg₁. In particular, they promoted the growth and infection of the soilborne pathogen Ilyonectria destructans by upregulating pathogenicity-related genes. Cellobiose showed the highest ability to modify the microbiome and enhance pathogenicity, followed by Rg₁ and then d-galacturonic acid. Collectively, autotoxins damaged root systems to release a series of cell wall degradants, some of which modified the rhizosphere microbiome so that the host plant became more susceptible to root rot disease.

IMPORTANCE The accumulation of autotoxins and pathogens in soil has been reported as a primary driver of root rot disease and one of the key factors limiting sustainable development in agricultural production. However, less is known about the correlation of plants, their associated pathogens, and the microbiome mediated by autotoxins, as well as the contributions autotoxins make to the occurrence of root rot disease. In our study, we found that autotoxins can damage root systems, thus releasing a series of cell wall degradants, and both autotoxins and the cell wall degradants they induce could aggravate root rot disease by reassembling the rhizosphere microbiome, resulting in the enrichment of pathogens and microorganisms positively related to the disease but the suppression of beneficial microorganisms. Deciphering this mechanism among plants, their associated pathogens, and the microbiome mediated by autotoxins will advance our fundamental knowledge of and ability to degrade autotoxins or employ microbiome to alleviate root rot disease in agricultural systems.

The Mechanism of Metal Homeostasis in Plants: A New View on the Synergistic Regulation Pathway of Membrane Proteins, Lipids and Metal Ions

Heavy metal stress (HMS) is one of the most destructive abiotic stresses which seriously affects the growth and development of plants. Recent studies have shown significant progress in understanding the molecular mechanisms underlying plant tolerance to HMS. In general, three core signals are involved in plants' responses to HMS; these are mitogen-activated protein kinase (MAPK), calcium, and hormonal (abscisic acid) signals. In addition to these signal components, other regulatory factors, such as microRNAs and membrane proteins, also play an important role in regulating HMS responses in plants. Membrane proteins interact with the highly complex and heterogeneous lipids in the plant cell environment. The function of membrane proteins is affected by the interactions between lipids and lipid-membrane proteins. Our review findings also indicate the possibility of membrane protein-lipid-metal ion interactions in regulating metal homeostasis in plant cells. In this review, we investigated the role of membrane proteins with specific substrate recognition in regulating cell metal homeostasis. The understanding of the possible interaction networks and upstream and downstream pathways is developed. In addition, possible interactions between membrane proteins, metal ions, and lipids are discussed to provide new ideas for studying metal homeostasis in plant cells.

Harnessing Endophytic Fungi for Enhancing Growth, Tolerance and Quality of Rose-Scented Geranium (Pelargonium graveolens (L'Hér) Thunb.) Plants under Cadmium Stress: A Biochemical Study

Heavy metal contamination in soil is increasing rapidly due to increasing anthropogenic activities. Despite the importance of rose-scented geranium as a medicinal plant, little attention was paid to enhancing its productivity in heavy metal-polluted soil. In this regard, endophytes improve plant resistance to heavy metal toxicity and enhance its tissue quality. Here, the impact of the three endophytic fungi Talaromyces versatilis (E6651), Emericella nidulans (E6658), and Aspergillus niger (E6657) on geranium growth, tolerance, and tissue quality under cadmium (Cd) stress was investigated. In contrast to E. nidulans, T. versatilis and A. niger enhanced geranium growth and the stimulatory effect was more pronounced under Cd-stress. The three endophytes significantly alleviated Cd accumulation and increased mineral content in geranium leaves. In addition, endophytic fungi successfully alleviated Cd-induced membrane damage and reinforced the antioxidant defenses in geranium leaves. Inoculation with endophytes stimulated all the antioxidant enzymes under Cd-stress, and the response was more obvious in the case of T. versatilis and A. niger. To reduce the toxicity of tissue-Cd levels, T. versatilis and A. niger upregulated the detoxification mechanisms; glutathione-S-transferase, phytochelatin, and metallothionein levels. Moreover, endophytic fungi improved the medicinal value and quality of geranium by increasing total antioxidant capacity (TAC), phenolic compound biosynthesis (phenylalanine ammonia-lyase), and vitamin content as well as the quantity and quality of essential oil, particularly under Cd-stress conditions. The variation in the mechanisms modulated by the different endophytic fungi was supported by Principal Component Analysis (PCA). Overall, this study provided fundamental insights into endophytes' impact as a feasible strategy to mitigate the phytotoxicity hazards of Cd-stress in geranium and enhance its quality, based on the growth and biochemical investigations.

Differences in Cadmium Accumulation, Detoxification and Antioxidant Defenses between Contrasting Maize Cultivars Implicate a Role of Superoxide Dismutase in Cd Tolerance

Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, 12 Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and we determined their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd-tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. A principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd-tolerance, we studied the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT). Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology, antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd-tolerance.

Wheat Leaf Antioxidative Status—Variety-Specific Mechanisms of Zinc Tolerance during Biofortification

In this study, we evaluated the leaf antioxidative responses of three wheat varieties (Srpanjka, Divana, and Simonida) treated with two different forms of zinc (Zn), Zn-sulfate and Zn-EDTA, in concentrations commonly used in agronomic biofortification. Zn concentration was significantly higher in the flag leaves of all three wheat varieties treated with Zn-EDTA compared to control and leaves treated with Zn-sulfate. Both forms of Zn increased malondialdehyde level and total phenolics content in varieties Srpanjka and Divana. Total glutathione content was not affected after the Zn treatment. Zn-sulfate increased the activities of glutathione reductase (GR) and guaiacol peroxidase (GPOD) in both Srpanjka and Divana, while glutathione S-transferase (GST) was only induced in var. Srpanjka. Chelate form of Zn increased the activities of GST and GPOD in both Simonida and Divana. Catalase activity was shown to be less sensitive to Zn treatment and was only induced in var. Srpanjka treated with Zn-EDTA where GPOD activity was not induced. Concentrations of Zn used for agronomic biofortification can induce oxidative stress in wheat leaves. The antioxidative status of wheat leaves could be a good indicator of Zn tolerance, whereas wheat genotype and chemical form of Zn are the most critical factors influencing Zn toxicity.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 1, Plant Defence Mechanisms

Miscanthus × giganteus demonstrated good phytostabilization potentials in toxic element (TE) contaminated soils. However, information about its tolerance to elevated concentrations is still scarce. Therefore, an ex-situ pot experiment was launched using three cultivars (termed B, U, and A) grown in soils with a gradient Cd, Pb and Zn concentrations. Control plants were also cultivated in non-contaminated soil. Results show that the number of tillers per plant, stem diameter as well as leaf photosynthetic pigments (chlorophyll a, b and carotenoids) were negatively impacted by soil contamination. On the other hand, phenolic compounds, flavonoids, tannins, and anthocyanins levels along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase increased in the plants grown on contaminated soils. Altogether, these data demonstrate that miscanthus is impacted by concentrations of toxic elements yet is able to tolerate high levels of soil contamination. These results may contribute to clarifying the miscanthus tolerance strategy against high contamination levels and its efficiency in phytoremediation.

The Effect of Plasma Activated Water on Maize (Zea mays L.) under Arsenic Stress

Plasma activated water (PAW) is a source of various chemical species useful for plant growth, development, and stress response. In the present study, PAW was generated by a transient spark discharge (TS) operated in ambient air and used on maize corns and seedlings in the 3 day paper rolls cultivation followed by 10 day hydroponics cultivation. For 3 day cultivation, two pre-treatments were established, “priming PAW” and “rolls PAW”, with corns imbibed for 6 h in the PAW and then watered daily by fresh water and PAW, respectively. The roots and the shoot were then analyzed for guaiacol peroxidase (G-POX, POX) activity, root tissues for their lignification, and root cell walls for in situ POX activity. To evaluate the potential of PAW in the alleviation abiotic stress, ten randomly selected seedlings were hydroponically cultivated for the following 10 days in 0.5 Hoagland nutrient solutions with and without 150 μM As. The seedlings were then analyzed for POX and catalase (CAT) activities after As treatment, their leaves for photosynthetic pigments concentration, and leaves and roots for As concentration. The PAW improved the growth of the 3 day-old seedlings in terms of the root and the shoot length, while roots revealed accelerated endodermal development. After the following 10 day cultivation, roots from PAW pre-treatment were shorter and thinner but more branched than the control roots. The PAW also enhanced the POX activity immediately after the imbibition and in the 3 day old roots. After 10 day hydroponic cultivation, antioxidant response depended on the PAW pre-treatment. CAT activity was higher in As treatments compared to the corresponding PAW treatments, while POX activity was not obvious, and its elevated activity was found only in the priming PAW treatment. The PAW pre-treatment protected chlorophylls in the following treatments combined with As, while carotenoids increased in treatments despite PAW pre-treatment. Finally, the accumulation of As in the roots was not affected by PAW pre-treatment but increased in the leaves.

Liquiritoside Alleviated Pb Induced Stress in Brassica rapa subsp. Parachinensis: Modulations in Glucosinolate Content and Some Physiochemical Attributes

Current research was conducted to explore the effects of liquiritoside on the growth and physiochemical features of Chinese flowering cabbage (Brassica rapa subsp. parachinensis) under lead (Pb) stress. Lead stressed B. rapa plants exhibited decreased growth parameters, chlorophyll, and carotenoid contents. Moreover, Pb toxicity escalated the synthesis of malondialdehyde (MDA), hydrogen peroxide (H2O2), flavonoids, phenolics, and proline in treated plants. Nevertheless, foliar application of liquiritoside mitigated Pb toxicity by decreasing oxidative stress by reducing cysteine, H2O2, and MDA contents in applied plants. Liquiritoside significantly increased plant height, shoot fresh weight and dry weight, number of leaves, and marketable value of Chinese flowering cabbage plants exposed to Pb toxicity. This biotic elicitor also enhanced the proline, glutathione, total phenolics, and flavonoid contents in Chinese flowering cabbage plants exposed to Pb stress compared with the control. Additionally, total glucosinolate content, phytochelatins (PCs), and non-protein thiols were effectively increased in plants grown under Pb regimes compared with the control plants. Overall, foliar application of liquiritoside can markedly alleviate Pb stress by restricting Pb translocation in Chinese flowering cabbage.