Maize roots and shoots show distinct profiles of oxidative stress and antioxidant defense under heavy metal toxicity

Toxicity assessment of heavy metals translocation in maize grown in the Ganges delta floodplain soils around the Payra power plant in Bangladesh

As a cereal crop, maize ranked third place after wheat and rice in terms of land area coverage for its cultivation, and in Bangladesh, it ranked second place after rice in its production. As the substitution of wheat products, maize has been used widely in baking for human consumption and animal fodder. However, maize grown in this soil around the coal-burning power plant may cause heavy metals uptake that poses a risk to humans. The study was conducted at the maize fields in the Ganges delta floodplain soils of Bangladesh to know the concentration of eight heavy metals (Ni, Cr, Cd, Mn, As, Cu, Zn, and Pb) in soil and maize samples using an inductively coupled plasma mass spectrometer (ICP-MS) and to estimate the risk of heavy metals in maize grains. Mean concentrations of heavy metals (mg/kg) in soil were in decreasing order of Zn (10.12) > Cu (10.02) > Mn (5.48) > Ni (4.95) > Cr (3.72) > As (0.51) > Pb (0.27) > Cd (0.23). The plant tissues showed the descending order of heavy metal concentration as roots > grains > stems > leaves. BCF values for As, Cd, Pb, and Mn in roots were higher than 1.0, indicating considerable accumulation of these elements in maize via roots. Total hazard quotient (ƩTHQ) of heavy metals through maize grain consumption was 3.7E+00 and 3.9E+00 for adults and children, respectively, indicating non-cancer risk to the consumers. Anthropogenic influences contributed to the heavy metals enrichment in the Ganges delta floodplain soils around the thermal plant, and potential risks (non-carcinogenic and carcinogenic) were observed due to the consumption of maize grain cultivated in the study area.

The underlying mechanisms by which boron mitigates copper toxicity in Citrus sinensis leaves revealed by integrated analysis of transcriptome, metabolome and physiology

Both copper (Cu) excess and boron (B) deficiency are often observed in some citrus orchard soils. The molecular mechanisms by which B alleviates excessive Cu in citrus are poorly understood. Seedlings of sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) were treated with 0.5 (Cu0.5) or 350 (Cu350 or Cu excess) μM CuCl2 and 2.5 (B2.5) or 25 (B25) μM HBO3 for 24 wk. Thereafter, this study examined the effects of Cu and B treatments on gene expression levels revealed by RNA-Seq, metabolite profiles revealed by a widely targeted metabolome, and related physiological parameters in leaves. Cu350 upregulated 564 genes and 170 metabolites, and downregulated 598 genes and 58 metabolites in leaves of 2.5 μM B-treated seedlings (LB2.5), but it only upregulated 281 genes and 100 metabolites, and downregulated 136 genes and 40 metabolites in leaves of 25 μM B-treated seedlings (LB25). Cu350 decreased the concentrations of sucrose and total soluble sugars and increased the concentrations of starch, glucose, fructose and total nonstructural carbohydrates in LB2.5, but it only increased the glucose concentration in LB25. Further analysis demonstrated that B addition reduced the oxidative damage and alterations in primary and secondary metabolisms caused by Cu350, and alleviated the impairment of Cu350 to photosynthesis and cell wall metabolism, thus improving leaf growth. LB2.5 exhibited some adaptive responses to Cu350 to meet the increasing need for the dissipation of excessive excitation energy (EEE) and the detoxification of reactive oxygen species (reactive aldehydes) and Cu. Cu350 increased photorespiration, xanthophyll cycle-dependent thermal dissipation, nonstructural carbohydrate accumulation, and secondary metabolite biosynthesis and abundances; and upregulated tryptophan metabolism and related metabolite abundances, some antioxidant-related gene expression, and some antioxidant abundances. Additionally, this study identified some metabolic pathways, metabolites and genes that might lead to Cu tolerance in leaves.

The trade-off regulation of arbuscular mycorrhiza on alfalfa growth dose-dependent on gradient Mo exposure

Molybdenum (Mo) is an essential nutrient for leguminous plants, but the effects of Mo exposure on plant growth, especially in relation to soil microorganisms, are not fully understood. This study employed alfalfa (Medicago sativa L.) to evaluate the physiochemical responses to gradient soil Mo variations and explore the potential regulatory role of rhizosphere microorganism - arbuscular mycorrhizal fungi (AMF) in modulating Mo's impact on plant physiology, with a focus on metabolic pathways. The results showed that Mo exerted hormetic effect (facilitation at low doses; inhibition at high doses) on alfalfa growth, promoting biomass (below 90.94 mg/kg, with a 63.98 % maximum increase), root length (below 657.11 mg/kg, with a 39.29 % maximum increase), and plant height (below 304.03 mg/kg, with an 18.4 % maximum increase). Excess Mo (1000 mg/kg) resulted in a reduction in photosynthesis and biomass growth due to increased oxidative stress (p < 0.05). Within the stimulatory zones, AMF enhanced Mo accumulation in alfalfa, augmenting its phytological effects. Exceed the stimulatory zones, AMF enhanced alfalfa Fe uptake and reduced the generation of reactive oxygen species (ROS) induced by excess Mo by shifting the redox homeostasis-controlled enzyme from peroxidase (POD) to superoxide dismutase (SOD), thereby improving alfalfa's tolerance to Mo. Metabolomic analysis further revealed that AMF promoted the biosynthesis of indole acetic acid (IAA) and various amino acids in Mo-stressed alfalfa (p < 0.05), which accelerated alfalfa growth and mitigated Mo-induced phytotoxicity. These insights provide a foundation for developing sustainable management strategies for Mo-exposed soils using AMF inoculants, such as minimizing Mo fertilizer application in Mo-deficient soils and facilitating the reclamation of Mo-contaminated soils.

Overexpression of histone demethylase gene SlJMJ18 and SlJMJ23 from tomato confers cadmium tolerance by regulating metal transport and hormone content in Arabidopsis

A lower concentration of cadmium (Cd), a hazardous and non-essential element for plant growth, will have deleterious effects on plants and endanger human health. Histone demethylase (JHDM) is important for plants' ability to withstand abiotic stress, according to an increasing number of studies. The degree of expression of the SlJMJ18 and SlJMJ23 genes in different tomato tissues was confirmed by this study. These two genes were responsive to the heavy metals Cd, Hg, Pb, and Cu stress, according to fluorescence quantification and GUS staining. Interestingly, the overexpression transgenic Arabidopsis plants of two genes have different responses to Cd stress. While SlJMJ18-OE lines consistently display Cd resistance but an early-flowering phenotype, SlJMJ23-OE plants have sensitivity during the post-germination stage and then greater tolerance to Cd stress. It was discovered that these two genes may affect cadmium tolerance of plants by regulating the expression of hormone synthesis related genes and hormone contents (BRs and ABA). Moreover, SlJMJ23 may resist cadmium stress by increasing the total phenol content in plants. The functional significance of JMJs is better understood in this study, which also offers a theoretical foundation for the use of molecular technology to develop plants resistant to Cd and an experimental basis for the efficient use of land resources.

Evaluation of heavy metal accumulation and tolerance in oxalic acid-treated Phragmites australis wetlands for textile effluent remediation

Water contamination with metals poses significant environmental challenges. The occurrence of heavy metals (HMs) prompts modifications in plant structures, emphasizing the necessity of employing focused safeguarding measures. Cadmium (Cd), lead (Pb), and chromium (Cr) emerge as particularly menacing toxins due to their high accumulation potential. Increasing the availability of organic acids is crucial for optimizing toxic metal removal via phytoremediation. This constructed wetland system (CWs) was used to determine how oxalic acid (OA) treatments of textile wastewater (WW) effluents affected morpho-physiological characteristics, antioxidant enzyme activity, oxidative stress, and HM concentrations in Phragmites australis. Multiple treatments, comprising the application of OA at a concentration of 10 mM and WW at different dilutions (25%, 50%, 75%, and 100%), were employed, with three replications of each treatment. WW stress decreased chlorophyll and carotenoid content, and concurrently enhanced HMs adsorption and antioxidant enzyme activities. Furthermore, the application of WW was found to elevate oxidative stress levels, whereas the presence of OA concurrently mitigated this oxidative stress. Similarly, WW negatively affected soil-plant analysis development (SPAD) and the total soluble proteins (SP) in both roots and shoots. Conversely, these parameters showed improvement with OA treatments. P. australis showed the potential to enhance HM accumulation under 100% WW stress. Specifically, there is an increase in root SP ranging from 9% to 39%, an increase in shoot SP from 6% to 91%, and an elevation in SPAD values from 4% to 64% compared to their respective treatments lacking OA inclusion. The OA addition resulted in decreased EL contents in the root and shoot by 10%-19% and 13%-15%, MDA by 9%-14% and 9%-20%, and H2O2 by 14%-21% and 9%-17%, in comparison to the respective treatments without OA. Interestingly, the findings further revealed that the augmentation of OA also contributed to an increased accumulation of Cr, Cd, and Pb. Specifically, at 100% WW with OA (10 mM), the concentrations of Cr, Pb, and Cd in leaves rose by 164%, 447%, and 350%, in stems by 213%, 247%, and 219%, and in roots by 155%, 238%, and 195%, respectively. The chelating agent oxalic acid effectively alleviated plant toxicity induced by toxins. Overall, our findings demonstrate the remarkable tolerance of P. australis to elevated concentrations of WW stress, positioning it as an eco-friendly candidate for industrial effluent remediation. This plant exhibits efficacy in restoring contaminants present in textile effluents, and notably, oxalic acid emerges as a promising agent for the phytoextraction of HMs.

Plant Cadmium Toxicity and Biomarkers Are Differentially Modulated by Degradable and Nondegradable Microplastics in Soil

The impact of microplastics (MPs) as emerging pollutants on plant heavy metal toxicity has been extensively reported in vegetable-soil systems over recent years. However, little attention has been given to cultivar variations between degradable and non-degradable MPs. This study investigated the effects of degradable polylactic acid (PLA) and nondegradable polypropylene (PP) MPs on plant growth and biomarker (malonaldehyde (MDA) and antioxidant enzymes) performance in Cd-contaminated arable soil. The results show that both types of MPs significantly impacted plant biomass and biomarker contents across all three Cd levels. The degree of impact was significantly sensitive to both the type and dose of MPs, as they reduced the soil pH and cation exchange capacity (CEC) while increasing soil dissolved organic carbon (DOC), microbial biomass carbon, and nitrogen. PP exhibited greater root growth inhibition and phytotoxicity at higher doses of 1% and 5% compared to PLA. Specifically, the highest MDA contents were 1.44 and 2.20 mmol mg-1 protein for shoots and roots, respectively, in the 5% PLA treatment under a 10.1 mg kg-1 Cd level, which were 1.22 and 1.18 times higher than those in corresponding treatments of 5% PP. Overall, PLA had less significant effects on plant phytotoxicity, Cd availability, and soil properties compared to PP. Regression pathway analysis indicated that MPs increased shoot Cd uptake by altering both soil physical-chemical and microbial characteristics. Among the soil variables, pH, CEC, and Cd bioavailability were found to play vital roles. Yet, no single variable acts alone in the mechanism for plant Cd uptake. PLAs are suggested to replace conventional non-biodegradable plastics to control environmental MP pollution, particularly in agricultural systems with higher Cd contamination. However, the long-term effects of the by-products generated during the biodegradation process require further investigation.

Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste

BACKGROUND

This study aimed to investigate the alterations in biochemical and physiological responses of oat plants exposed to antimony (Sb) contamination in soil. Specifically, we evaluated the effectiveness of an arbuscular mycorrhizal fungus (AMF) and olive mill waste (OMW) in mitigating the effects of Sb contamination. The soil was treated with a commercial strain of AMF (Rhizophagus irregularis) and OMW (4% w/w) under two different levels of Sb (0 and 1500 mg kg-1 soil).

RESULTS

The combined treatment (OMW + AMF) enhanced the photosynthetic rate (+ 40%) and chlorophyll a (+ 91%) and chlorophyll b (+ 50%) content under Sb condition, which in turn induced more biomass production (+ 67-78%) compared to the contaminated control plants. More photosynthesis in OMW + AMF-treated plants gives a route for phenylalanine amino acid synthesis (+ 69%), which is used as a precursor for the biosynthesis of secondary metabolites, including flavonoids (+ 110%), polyphenols (+ 26%), and anthocyanins (+ 63%) compared to control plants. More activation of phenylalanine ammonia-lyase (+ 38%) and chalcone synthase (+ 26%) enzymes in OMW + AMF-treated plants under Sb stress indicated the activation of phenylpropanoid pathways in antioxidant metabolites biosynthesis. There was also improved shifting of antioxidant enzyme activities in the ASC/GSH and catalytic pathways in plants in response to OMW + AMF and Sb contamination, remarkably reducing oxidative damage markers.

CONCLUSIONS

While individual applications of OMW and AMF also demonstrated some degree of plant tolerance induction, the combined presence of AMF with OMW supplementation significantly enhanced plant biomass production and adaptability to oxidative stress induced by soil Sb contamination.

Impacts of mining on vegetation phenology and sensitivity assessment of spectral vegetation indices to mining activities in arid/semi-arid areas

Measuring the impact of mining activities on vegetation phenology and assessing the sensitivity of vegetation indices (VIs) to it are crucial for understanding land degradation in mining areas and enhancing the carbon sink capacity following the ecological restoration of mines. To this end, we have developed a novel technical framework to quantify the impact of mining activities on vegetation, and applied it to the Bainaimiao copper mining area in Inner Mongolia. Phenological indices are extracted based on the VI time series data of Sentinel-2, and changes in phenological differences in various directions are used to quantify the impact of mining activities on vegetation. Finally, indicators such as mean difference, standard deviation, index value distribution interval, and concentration of index value distribution were selected to assess the sensitivity of the Enhanced Vegetation Index (EVI), Green Chlorophyll Index (GCI), Global Environmental Monitoring Index (GEMI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Vegetation Index (NDVI), Renormalized Difference Vegetation Index (RDVI), Red-Edge Chlorophyll Index (RECI), and Soil-Adjusted Vegetation Index (SAVI) to mining activities. The results of the study show that the impact of mining activities on surrounding vegetation extends to an area three times larger than the actual mining activity area. When compared with the reference and unaffected areas, the affected area experienced a delay of approximately 10 days in seasonal vegetation development. Environmental pollution caused by the tailings pond was identified as the primary factor influencing this delay. Significant variations in the sensitivity of each VI to assess mining activities in arid/semi-arid areas were observed. Notably, GCI, GNDVI and RDVI displayed relatively high sensitivity to discrepancies in the spectral attributes of vegetation within the affected area, while SAVI reflected the overall spectral stability of the vegetation in the affected area. The research findings have the potential to provide valuable technical guidance for holistic environmental management in mining areas and hold great significance in preventing further land degradation and supporting ecological restoration in mining areas.

The Influence of Copper and Zinc on Photosynthesis and Phenolic Levels in Basil (Ocimum basilicum L.), Borage (Borago officinalis L.), Common Nettle (Urtica dioica L.) and Peppermint (Mentha piperita L.)

This work is aimed at relationships which govern zinc and copper uptake by four popular medicinal herbs: basil (Ocimum basilicum L.), borage (Borago officinalis L.), common nettle (Urtica dioica L.) and peppermint (Mentha piperita L.). They are often grown in soils with significant copper or zinc levels. Herbs were cultivated by a pot method in controlled conditions. Manganese, iron, copper and zinc concentrations were determined by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry. The efficiency of photosynthesis was estimated by measuring the chlorophyll content, water use efficiency, net photosynthesis, intercellular CO2, stomatal conductance, and transpiration rate. Phenolic compounds were determined by the Folin-Ciocalteu method. Analysis of variance showed that herbs grown in soil treated with copper exhibited a lower iron content in roots, while manganese behaved in the opposite way. The only exception was borage, where a decrease in the manganese content in roots was observed. Both copper and zinc supplementations increased the total content of phenolics, while the highest increases were observed for common nettle and basil. Peppermint and borage responded less to supplementation. In the majority of samples, zinc and copper did not significantly affect the photosynthesis. Herbal extracts from common nettle and basil had unique antioxidant properties and may be good free radical scavengers.

Cadmium negatively affects the growth and physiological status and the alleviation effects by exogenous selenium in silage maize (Zea mays L.)

Increasing soil cadmium (Cd) contamination is a serious threat to human food health and safety. In order to reduce Cd uptake and Cd toxicity in silage maize, hydroponic tests were conducted to investigate the effect of exogenous Cd on the toxicity of silage maize in this study. In the study, a combination of Cd (5, 20, 50, 80, and 10 μM) treatments was applied in a hydroponic system. With increasing Cd concentration, Cd significantly inhibited the total root length (RL), root surface area (SA), root volume (RV), root tip number (RT), and branching number (RF) of maize seedlings, which were reduced by 28.1 to 71.3%, 20.2 to 64.9%, 11.2 to 56.5%, 43.7 to 63.4%, and 38.2 to 72.6%, respectively. The excessive Cd accumulation inhibited biomass accumulation and reduced silage maize growth, photosynthesis, and chlorophyll content and activated the antioxidant systems, including increasing lipid peroxidation and stimulating catalase (CAT) and peroxidase (POD), but reduced the activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in the root. Besides, selenium (Se) significantly decreased the Cd concentration of the shoot and root by 27.1% and 35.1% under Cd50, respectively. Our results reveal that exogenously applied Cd reduced silage maize growth and impaired photosynthesis. Whereas silage maize can tolerate Cd by increasing the concentration of ascorbate and glutathione and activating the antioxidant defense system, the application of exogenous selenium significantly reduced the content of Cd in silage maize.

Toxic effects of atmospheric deposition in mining areas on wheat seedlings

Storage and transportation of coal, as well as operation of coal-fired power plants, produce amounts of metallic exhaust that may lead to different atmospheric environment in the overlapped areas of farmland and coal resource (OAFCR) environment. To investigate the effects of different atmospheric environment in the OAFCR region (north of Xuzhou) on wheat seedlings (AK-58), a box experiment was conducted and compared to an area far from the OAFCR (south of Xuzhou). The study revealed that (1) compared to the southern suburb of Xuzhou, the fresh and dry weight, activities of photosynthetic enzymes and POD of wheat seedlings in the OAFCR reduced obviously. (2) Significantly higher levels of Cr, Cd, Pb, Zn, and Cu were found in the shoots and roots of wheat seedlings in the OAFCR, with lower transfer factor for heavy metals (except Cd and As) in comparison to those in the southern suburb. And the bioconcentration factors of heavy metals (except As) in wheat seedlings in the OAFCR were significantly higher. (3) Nearly 90% of heavy metals (Pb, Cu, Cd, Zn, and Cr) absorbed by wheat were stored in cell walls and soluble fractions, with significantly higher contents of Cu and Cr in wheat seedlings' cell walls and higher contents of Pb, Zn, and Cd in soluble components found in the OAFCR. Our results showed that atmospheric deposition in the mining area has a certain toxic effect on wheat seedlings, and this study provides a theoretical basis for OAFCR crop toxicity management.

Plant biomarkers as early detection tools in stress management in food crops: a review

MAIN CONCLUSION

Plant Biomarkers are objective indicators of a plant's cellular state in response to abiotic and biotic stress factors. They can be explored in crop breeding and engineering to produce stress-tolerant crop species. Global food production safely and sustainably remains a top priority to feed the ever-growing human population, expected to reach 10 billion by 2050. However, abiotic and biotic stress factors negatively impact food production systems, causing between 70 and 100% reduction in crop yield. Understanding the plant stress responses is critical for developing novel crops that can adapt better to various adverse environmental conditions. Using plant biomarkers as measurable indicators of a plant's cellular response to external stimuli could serve as early warning signals to detect stresses before severe damage occurs. Plant biomarkers have received considerable attention in the last decade as pre-stress indicators for various economically important food crops. This review discusses some biomarkers associated with abiotic and biotic stress conditions and highlights their importance in developing stress-resilient crops. In addition, we highlighted some factors influencing the expression of biomarkers in crop plants under stress. The information presented in this review would educate plant researchers, breeders, and agronomists on the significance of plant biomarkers in stress biology research, which is essential for improving plant growth and yield toward sustainable food production.

Integrated Assessment of Pb(II) and Cu(II) Metal Ion Phytotoxicity on Medicago sativa L., Triticum aestivum L., and Zea mays L. Plants: Insights into Germination Inhibition, Seedling Development, and Ecosystem Health

Environmental pollution with heavy metals has become a problem of major interest due to the harmful effects of metal ions that constantly evolve and generate serious threats to both the environment and human health through the food chain. Recognizing the imperative need for toxicological assessments, this study revolves around elucidating the effects of Pb(II) and Cu(II) ions on three plant species; namely, Medicago sativa L., Triticum aestivum L., and Zea mays L. These particular species were selected due to their suitability for controlled laboratory cultivation, their potential resistance to heavy metal exposure, and their potential contributions to phytoremediation strategies. The comprehensive phytotoxicity assessments conducted covered a spectrum of critical parameters, encompassing germination inhibition, seedling development, and broader considerations regarding ecosystem health. The key metrics under scrutiny included the germination rate, the relative growth of root and stem lengths, the growth inhibition index, and the tolerance index. These accurately designed experiments involved subjecting the seeds of these plants to an array of concentrations of PbCl2 and CuCl2 solutions, enabling an exhaustive evaluation of the phytotoxic potential of these metal ions and their intricate repercussions on these plant species. Overall, this study provides valuable insights into the diverse and dynamic responses of different plant species to Pb(II) and Cu(II) metal ions, shedding light on their adaptability and resilience in metal-contaminated environments. These findings have important implications for understanding plant-metal interactions and devising phytoremediation strategies in contaminated ecosystems.

Salinity alleviates arsenic stress-induced oxidative damage via antioxidative defense and metabolic adjustment in the root of the halophyte Salvadora persica

MAIN CONCLUSION

Arsenic tolerance in the halophyte Salvadora persica is achieved by enhancing antioxidative defense and modulations of various groups of metabolites like amino acids, organic acids, sugars, sugar alcohols, and phytohormones. Salvadora persica is a facultative halophyte that thrives under high saline and arid regions of the world. In present study, we examine root metabolic responses of S. persica exposed to individual effects of high salinity (750 mM NaCl), arsenic (600 µM As), and combined treatment of salinity and arsenic (250 mM NaCl + 600 µM As) to decipher its As and salinity resistance mechanism. Our results demonstrated that NaCl supplementation reduced the levels of reactive oxygen species (ROS) under As stress. The increased activities of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR) maintained appropriate levels of ROS [superoxide (O2•-) and hydrogen peroxide (H2O2)] under salinity and/or As stress. The metabolites like sugars, amino acids, polyphenols, and organic acids exhibited higher accumulations when salt was supplied with As. Furthermore, comparatively higher accumulations of glycine, glutamate, and cystine under combined stress of salt and As may indicate its role in glutathione and phytochelatins (PCs) synthesis in root. The levels of phytohormones such as salicylate, jasmonate, abscisic acid, and auxins were significantly increased under high As with and without salinity stress. The amino acid metabolism, glutathione metabolism, carbohydrate metabolism, tricarboxylic acid cycle (TCA cycle), phenylpropanoid biosynthesis, and phenylalanine metabolism are the most significantly altered metabolic pathways in response to NaCl and/or As stress. Our study decoded the important metabolites and metabolic pathways involved in As and/or salinity tolerance in root of the halophyte S. persica providing clues for development of salinity and As resistance crops.

Heavy metal stress in plants: Ways to alleviate with exogenous substances

Accumulation and enrichment of excessive heavy metals due to industrialization and modernization not only devastate our ecosystem, but also pose a threat to the global vegetation, especially crops. To improve plant resilience against heavy metal stress (HMS), numerous exogenous substances (ESs) have been tried as the alleviating agents. After a careful and thorough review of over 150 recently published literature, 93 reported ESs and their corresponding effects on alleviating HMS, we propose that 7 underlying mechanisms of ESs be categorized in plants for: 1) improving the capacity of the antioxidant system, 2) inducing the synthesis of osmoregulatory substances, 3) enhancing the photochemical system, 4) detouring the accumulation and migration of heavy metals, 5) regulating the secretion of endogenous hormones, 6) modulating gene expressions, and 7) participating in microbe-involved regulations. Recent research advances strongly indicate that ESs have proven to be effective in mitigating a potential negative impact of HMS on crops and other plants, but not enough to ultimately solve the devastating problem associated with excessive heavy metals. Therefore, much more research should be focused and carried out to eliminate HMS for the sustainable agriculture and clean environmental through minimizing towards prohibiting heavy metals from entering our ecosystem, phytodetoxicating polluted landscapes, retrieving heavy metals from detoxicating plants or crop, breeding for more tolerant cultivars for both high yield and tolerance against HMS, and seeking synergetic effect of multiply ESs on HMS alleviation in our feature researches.

Effects of attapulgite on the growth status of submerged macrophytes Vallisneria spiralis and sediment microenvironment

The effects of raw attapulgite clay and thermally modified attapulgite clay on the growth status of submerged plant Vallisneria Spiralis (V. spiralis) and the microenvironment of sediment were first explored. The results demonstrated that the attapulgite could effectively promote the development of V. spiralis and improve plant stress resistance by enhancing the activity of antioxidant enzymes. The 10% addition of attapulgite clay increased the biomass of V. spiralis by 27%∼174%, and the promoted rate of raw attapulgite clay was 2∼5 times of modified attapulgite clay. The attapulgite increased redox potential in sediment (P < 0.05) and provided proper niches for organism propagation, further promoting the degradation of organic matter and nutrient metabolism in sediment. The value of Shannon, Chao, and Ace was 9.98, 4865.15, 5029.08 in the 10% modified attapulgite group, and 10.12, 4856.85, 4947.78 in the 20% raw attapulgite group, respectively, indicating that the attapulgite could increase the microbial diversity and abundance in sediment. Additionally, the nutrient elements, such as Ca, Na, S, Mg, K, Zn, and Mo, that dissolved from attapulgite may also promote the V. spiralis growth. This study provided an environment-friendly approach to facilitating submerged macrophyte restoration in the eutrophic lake ecosystem.

Elevated CO2 reduced antimony toxicity in wheat plants by improving photosynthesis, soil microbial content, minerals, and redox status

Introduction

Antimony (Sb), a common rare heavy metal, is naturally present in soils at low concentrations. However, it is increasingly used in industrial applications, which in turn, leads to an increased release into the environment, exerting a detrimental impact on plant growth. Thus, it is important to study Sb effects on plants under the current and future CO2 (eCO2).

Methods

To this end, high Sb concentrations (1500 mg/kg soil) effects under ambient (420 ppm) and eCO2 (710 ppm) on wheat growth, physiology (photosynthesis reactions) and biochemistry (minerals contents, redox state), were studied and soil microbial were evaluated.

Results and discussion

Our results showed that Sb uptake significantly decreased wheat growth by 42%. This reduction could be explained by the inhibition in photosynthesis rate, Rubisco activity, and photosynthetic pigments (Cha and Chb), by 35%, 44%, and 51%, respectively. Sb significantly reduced total bacterial and fungal count and increased phenolic and organic acids levels in the soil to decrease Sb uptake. Moreover, it induced oxidative markers, as indicated by the increased levels of H2O2 and MDA (1.96 and 2.8-fold compared to the control condition, respectively). To reduce this damage, antioxidant capacity (TAC), CAT, POX, and SOD enzymes activity were increased by 1.61, 2.2, 2.87, and 1.86-fold, respectively. In contrast, eCO2 mitigated growth inhibition in Sb-treated wheat. eCO2 and Sb coapplication mitigated the Sb harmful effect on growth by reducing Sb uptake and improving photosynthesis and Rubisco enzyme activity by 0.58, 1.57, and 1.4-fold compared to the corresponding Sb treatments, respectively. To reduce Sb uptake and improve mineral availability for plants, a high accumulation of phenolics level and organic acids in the soil was observed. eCO2 reduces Sb-induced oxidative damage by improving redox status. In conclusion, our study has provided valuable insights into the physiological and biochemical bases underlie the Sb-stress mitigating of eCO2 conditions. Furthermore, this is important step to define strategies to prevent its adverse effects of Sb on plants in the future.

B2 O3 nanoparticles alleviate salt stress in maize leaf growth zones by enhancing photosynthesis and maintaining mineral and redox status

Salt stress induces significant loss in crop yield worldwide. Although the growth-stimulating effects of micronutrient nanoparticles (NPs) application under salinity have been studied, the molecular and biochemical mechanisms underlying these effects are poorly understood. The large size of maize leaf growth zones provides an ideal model system to sample and investigate the molecular and physiological bases of growth at subzonal resolution. Using kinematic analysis, our study indicated that salinity at 150 mM inhibited maize leaf growth by decreasing cell division and expansion in the meristem and elongation zones. Consistently, salinity downregulated cell cycle gene expression (wee1, mcm4, and cyclin-B2-4). B2 O3 NP (BNP) mitigated the stress-induced growth inhibition by reducing the decrease in cell division and expansion. BNP also enhanced the photosynthesis-related parameters. Simultaneously, chlorophyll, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase were stimulated in the mature zone. Concomitant with growth stimulation by BNP, mineral homeostasis, particularly for B and Ca, was monitored. BNP reduced oxidative stress (e.g., lessened H2 O2 generation along the leaf zones and reduced lipid peroxidation in the mature zone) induced by salinity. This resulted from better maintenance of the redox status, that is, increased the glutathione-ascorbate cycle in the meristem and elongation zones, and flavonoids and tocopherol levels in the mature zone. Our study has important implications for assessing the salinity stress impact mitigated by BNP on maize growth, providing a basis to improve the resilience of crop species under salinity stress conditions.

Phenolic Compounds of the Medicinal Plants in an Anthropogenically Transformed Environment

In this article, the impact of an anthropogenically transformed environment on the content of pharmaceutically valuable biologically active compounds in medicinal plants is analyzed. The studied biologically active substances included phenolic compounds (flavonoids, anthocyanins, tannins, and phenolic acids). The number of transmissible forms of heavy metals (HMs), including cadmium, lead, and mercury, were discharged from factories that are present in the soil. Plants uptake these toxic metals from the soil. HM causes changes in the activity of the several enzymes such as phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI) and other enzymes. These enzymes play an important role in biosynthesis of phenolic compounds in medicinal plants. It has been demonstrated that plant materials possess high antioxidant potential due to their high phenolic content. As a result, the present review discusses a thorough investigation of anthropogenically transformed environment effects on the quantity of pharmaceutically valuable phenolic compounds in medicinal plants.

Responses to Airborne Ozone and Soilborne Metal Pollution in Afforestation Plants with Different Life Forms

With the current increases in environmental stress, understanding species-specific responses to multiple stress agents is needed. This science is especially important for managing ecosystems that are already confronted with considerable pollution. In this study, responses to ozone (O3, ambient daily course values + 20 ppb) and mixed metal contamination in soils (MC, cadmium/copper/lead/zinc = 25/1100/2500/1600 mg kg-1), separately and in combination, were evaluated for three plant species (Picea abies, Acer pseudoplatanus, Tanacetum vulgare) with different life forms and ecological strategies. The two treatments elicited similar stress reactions, as shown by leaf functional traits, gas exchange, tannin, and nutrient markers, irrespective of the plant species and life form, whereas the reactions to the treatments differed in magnitude. Visible and microscopic injuries at the organ or cell level appeared along the penetration route of ozone and metal contamination. At the whole plant level, the MC treatment caused more severe injuries than the O3 treatment and few interactions were observed between the two stress factors. Picea trees, with a slow-return strategy, showed the highest stress tolerance in apparent relation to an enhancement of conservative traits and an exclusion of stress agents. The ruderal and more acquisitive Tanacetum forbs translocated large amounts of contaminants above ground, which may be of concern in a phytostabilisation context. The deciduous Acer trees-also with an acquisitive strategy-were most sensitive to both stress factors. Hence, species with slow-return strategies may be of particular interest for managing metal-polluted sites in the current context of multiple stressors and for safely confining soil contaminants below ground.

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.

An integrated transcriptome, metabolomic, and physiological investigation uncovered the underlying tolerance mechanisms of Monochoria korsakowii in response to acute/chronic cadmium exposure

Identifying the physiological response and tolerance mechanism of wetland plants to heavy metal exposure can provide theoretical guidance for an early warning for acute metal pollution and metal-contaminated water phytoremediation. A hydroponic experiment was employed to investigate variations in the antioxidant enzyme activity, chlorophyll content, and photosynthesis in leaves of Monochoria korsakowii under 0.12 mM cadmium ion (Cd2+) acute (4 d) and chronic (21 d) exposure. Transcriptome and metabolome were analyzed to elucidate the underlying defensive strategies. The acute/chronic Cd2+ exposure decreased chlorophyll a and b contents, and disturbed photosynthesis in the leaves. The acute Cd2+ exposure increased catalase activity by 36.42%, while the chronic Cd2+ exposure markedly increased ascorbate peroxidase, superoxide dismutase, and glutathione peroxidase activities in the leaves. A total of 2 685 differentially expressed genes (DEGs) in the leaves were identified with the plants exposed to the acute/chronic Cd2+ contamination. In the acute Cd2+ exposure treatment, DEGs were preferentially enriched in the plant hormone transduction pathway, followed by phenylrpopanoid biosynthesis. However, the chronic Cd2+ exposure induced DEGs enriched in the biosynthesis of secondary metabolites pathway as priority. With acute/chronic Cd2+ exposure, a total of 157 and 227 differentially expressed metabolites were identified in the leaves. Conjoint transcriptome and metabolome analysis indicated the plant hormone signal transduction pathway and biosynthesis of secondary metabolites was preferentially activated by the acute and chronic Cd2+ exposure, respectively. The phenylpropanoid pathway functioned as a chemical defense, and the positive role of deoxyxylulose phosphate pathway in leaves against acute/chronic Cd2+ exposure was impaired.

Effect of natural soil nanocolloids on the fate and toxicity of cadmium to rice (Oryza sativa L.) roots

Toxic heavy metals are common contaminants and will most likely interact with ubiquitous natural nanocolloids (Ncs) in the soil environment. However, the effect of soil Ncs on the fate and health risk of cadmium (Cd) have not been well addressed. Here, the interaction between Ncs and Cd is investigated using two-dimensional correlation spectroscopy (2DCOS) combined with synchronous fluorescence and Fourier transform infrared spectroscopy. Our results reveal that Cd binding to the soil Ncs surface is mainly driven through strong hydrophilic effects and π - π interactions, which contribute to a high adsorption capacity (366-612 mg/g) and strong affinity (K_L = 4.3-9.7 L/mg) of Cd to soil Ncs. Interestingly, soil Ncs and Cd coexposure can significantly mediate the phytotoxicity (e.g., uptake, root growth, and oxidative stress) of Cd to rice (Oryza sativa L.) roots after 7 days of exposure. At the molecular level, metabolomic analysis reveals that the downregulated metabolic pathways (e.g., isoquinoline alkaloid and aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism) may contribute to the above adverse phytotoxicity. This study provides new insight into the effect of natural Ncs on the fate and health risks of toxic heavy metals in soil environments.

Roles of Hormones in Elevated pH-Mediated Mitigation of Copper Toxicity in Citrus sinensis Revealed by Targeted Metabolome

The effects of copper (Cu)-pH interactions on the levels of hormones and related metabolites (HRMs) in Citrus sinensis leaves and roots were investigated. Our findings indicated that increased pH mitigated Cu toxicity-induced alterations of HRMs, and Cu toxicity increased low-pH-induced alterations of HRMs. Increased pH-mediated decreases in ABA, jasmonates, gibberellins, and cytokinins, increases in (±)strigol and 1-aminocyclopropanecarboxylic acid, and efficient maintenance of salicylates and auxins homeostasis in 300 μM Cu-treated roots (RCu300); as well as efficient maintenance of hormone homeostasis in 300 μM Cu-treated leaves (LCu300) might contribute to improved leaf and root growth. The upregulation of auxins (IAA), cytokinins, gibberellins, ABA, and salicylates in pH 3.0 + 300 μM Cu-treated leaves (P3CL) vs. pH 3.0 + 0.5 μM Cu-treated leaves (P3L) and pH 3.0 + 300 μM Cu-treated roots (P3CR) vs. pH 3.0 + 0.5 μM Cu-treated roots (P3R) might be an adaptive response to Cu toxicity, so as to cope with the increased need for reactive oxygen species and Cu detoxification in LCu300 and RCu300. Increased accumulation of stress-related hormones (jasmonates and ABA) in P3CL vs. P3L and P3CR vs. P3R might reduce photosynthesis and accumulation of dry matter, and trigger leaf and root senescence, thereby inhibiting their growth.

Alleviating the toxic effects of Cd and Co on the seed germination and seedling biochemistry of wheat (Triticum aestivum L.) using Azolla pinnata

One of the most significant environmental challenges in the twenty-first century is heavy metal pollution. The potential use of fresh Azolla pinnata to alleviate the toxic effects of Cd and Co on the germination measurements of wheat seeds (Triticum aestivum L.) and the biochemistry of seedlings was studied. Two concentrations (80 and 100 mg L^-1 solutions) of CdNO₃ and CoCl₂ were used before and after treatment with A. pinnata. The highest removal efficiency (RE) by A. pinnata was obtained on the fifth day, with a Cd RE = 55.9 and 49.9% at 80 and 100 mg L^-1, respectively. Cadmium and cobalt solutions reduced the germination percentage, and the measured variables of wheat seeds meanwhile increased the radicle phytotoxicity. In contrast, the presence of A. pinnata in the germination medium increased all the measured variables and decreased radicle phytotoxicity. At 80 and 100 mg L^-1, Cd significantly reduced the fresh and dry biomass, and height of wheat seedlings after 21 days of cultivation compared to Co. Cadmium and high concentrations of cobalt increased the contents of H₂O₂, proline, MDA, phenolic, and flavonoid compounds. The application of treated Cd and Co solutions by A. pinnata showed a decrease in H₂O₂, proline, phenolic, and flavonoid compounds levels accompanied by a reduction in catalase and peroxidase activities compared to the control. This study showed the positive role of A. pinnata in alleviating the metal impacts, particularly Cd, on the seedling growth of wheat and its germination.

The physiological effect of organophosphate flame retardants (OPFRs) on wheat (Triticum aestivum L.) seed germination and seedling growth under the presence of copper

This study investigated the physiological and biochemical impacts of organophosphate flame retardants (OPFRs) on wheat (Triticum aestivum L.) germination and growth performance in the presence and absence of copper. The study evaluated seed germination, growth, OPFRs concentrations, chlorophyll fluorescence index (F_v/F_m and F_v/F₀), and antioxidant enzyme activity. It also calculated the root accumulation of OPFRs and their root-stem translocation. At the germination stage, at a concentration of 20 μg·L^-1 OPFR exposure, wheat germination vigor, root, and shoot lengths were significantly decreased compared to the control. However, the addition of a high concentration of copper (60 mg·L^-1) decreased by 80%, 82%, and 87% in the seed germination vitality index and root and shoot elongation, respectively, compared to 20 μg·L^-1 of OPFR treatment. At the seedling stage, a concentration of 50 μg·L^-1 of OPFRs significantly decreased by 42% and 5.4% in wheat growth weight and the photochemical efficiency of photosystem II (Fv/Fm) compared to the control. However, the addition of a low concentration of copper (15 mg·L^-1) slightly enhanced the growth weight compared to the other two co-exposure treatments, but the results were not significant (p > 0.05). After 7 days of exposure, the activity of superoxide dismutase (SOD) and malondialdehyde (MDA) (indicates lipid peroxidation) content in wheat roots significantly increased compared to the control and was higher than in leaves. MDA contents in wheat roots and shoots were decreased by 18% and 6.5% when OPFRs were combined with low Cu treatment compared with single OPFRs treatment, but SOD activity was slightly improved. These results suggest that the co-exposure of copper and OPFRs enhances reactive oxygen species (ROS) production and oxidative stress tolerance. Seven OPFRs were detected in wheat roots and stems, with root concentration factors (RCFs) and translocation factors (TFs) ranging from 67 to 337 and 0.05 to 0.33, respectively, for the seven OPFRs in a single OPFR treatment. The addition of copper significantly increased OPFR accumulation in the root and aerial parts. In general, the addition of a low concentration of copper promoted wheat seedling elongation and biomass and did not significantly inhibit the germination process. OPFRs could mitigate the toxicity of low-concentration copper on wheat but had a weak detoxification effect on high-concentration copper. These results indicated that the combined toxicity of OPFRs and Cu had antagonistic effects on the early development and growth of wheat.

Isolation and characterization of a plant growth‑promoting rhizobacterium strain MD36 that promotes barley seedlings and growth under heavy metals stress

Plant growth, promoting, bacteria, (PGPB) can improve plant germination and growth in heavy metal-contaminated land and enhance heavy metal removal efficiency. In this study, we isolated PGPR bacterial strains which can withstand heavy metal pollution and tested their ability to improve barley germination under heavy metal stress. Out of 16 multi-resistant heavy metal isolates, strain MD36 was identified by 16S rRNA sequencing and shared close relation to different species of the genus Glutamicibacter. The new isolated strain showed other important PGPR activities, mainly IAA production and salt tolerance. The effect of adding the strain MD36 to barley grains under heavy metal stress enhanced their germination up to 100%, while the percentage of germination ranged between 0 and 20% for non-inoculated grains. In addition, in these conditions, MD36 can significantly enhance barley growth by reducing the heavy metal effect. This study strongly recommends the use of MD36 as seed coatings trials in the field to enhance growth and yield in soils contaminated with heavy metals, as well as in bioremediation of HM-contaminated salt-containing soils and water.

Aphanothece sp. as promising biostimulant to alleviate heavy metals stress in Solanum lycopersicum L. by enhancing physiological, biochemical, and metabolic responses

Heavy metals (H.M) are a major environmental concern around the world. They have harmful impact on plant productivity and pose a serious risk to humans and animals health. In the present study, we investigated the effect of Aphanothece crude extract (ACE) on physiological, biochemical, and metabolic responses of tomato plant exposed to 2 mM Pb and Cd. The results showed a significant reduction of tomato plant weights and perturbation in nutrients absorption under 2 mM Pb and Cd conditions. Moreover, ACE treatment showed a significant enhancement of plant biomass compared to plants under Pb and Cd. On the other hand, ACE application favoured H.M accumulation in root and inhibited their translocation to shoot. In addition, ACE treatment significantly enhanced several stress responses in plant under Pb and Cd stress such as scavenging enzymes and molecules: POD, CAT, SOD, proline, and polyphenols etc. Furthermore, ACE treatment showed remodulation of metabolic pathways related to plant tolerance such as wax construction mechanism, particularly SFA, UFA, VLFA, alkanes, alkenes, and sterols biosynthesis to enhance tolerance and resistance to H.M stress. In the present study, we emphasized that ACE alleviates H.M stress by minimizing metal translocation to above-part of plant and enhancing plant growth, nutrients absorption, and biochemical responses.

Effects of biochar on the physiology and heavy metal enrichment of Vetiveria zizanioides in contaminated soil in mining areas

The effects of biochar addition on the physiological and biochemical characteristics of Vetiveria zizanioides, and the enrichment of heavy metals, were studied herein. The aim was to provide a theoretical reference for biochar to regulate the growth of V. zizanioides in the heavy metal-contaminated soil of mining areas and the enrichment capacity of Cu, Cd, and Pb. The results showed that the addition of biochar significantly increased the contents of various pigments in the middle and late growth stages of V. zizanioides, reduced the contents of malondialdehyde (MDA) and proline (Pro) in each growth period, weakened the peroxidase (POD) activity during the entire growth period; superoxide dismutase (SOD) activity decreased in the initial stages and substantially increased in the middle and late stages. The addition of biochar reduced the enrichment of Cu in the roots and leaves of V. zizanioides, while the enrichment of Cd and Pb increased. In conclusion, it was found that biochar could reduce the toxicity of heavy metals in contaminated soil in the mining area, affect the growth of V. zizanioides and its accumulation of Cd and Pb, and is, therefore, beneficial to the restoration of contaminated soil and the overall ecological restoration of the mining area.

Nerium oleander could be used for sustainable management of traffic-borne elemental-enriched roadside soils

Metal pollutants released from motor vehicles are deposited in roadside environments. Metals are non-biodegradable and biomagnify in the food chain causing significant health hazards at all levels of the ecosystem. Hence, management of contaminated roadside verges is critically important and should be kept in mind while planning specific management strategies of such areas. Native vegetation could help to decontaminate heavy metal polluted soils in the best sustainable way. Therefore, this study was designed to assess the potential of Nerium oleander to accumulate heavy metals commonly released by automobiles such as Pb, Cd, Ni, and Zn along with various C and N compounds from five different locations along a busy road in Punjab, Pakistan, during summer and winter seasons. N. oleander showed the ability to absorb C, N, and heavy metals Pb and Cd; the maximum concentration of Pb and Cd was 8.991 mg kg-1 and 0.599 mg kg-1, respectively. These pollutants negatively affected photosynthetic pigments, gas exchange attributes, soluble proteins, and free amino acids. But antioxidant activity of N. oleander was found to be increased in both seasons. The metal accumulation in the plant was higher in the summer though. We highly recommend that by growing N. oleander at roadside verges for decontamination of vehicular pollutants could lead to sustainable management of these corridors.

Water deficit aggravated the inhibition of photosynthetic performance of maize under mercury stress but is alleviated by brassinosteroids

Mercury (Hg) significantly inhibits maize (Zea mays L.) production, which could be aggravated by water deficit (WD) due to climate change. However, there is no report on the maize in response to combined their stresses. This work was conducted for assessing the response and adaptive mechanism of maize to combined Hg and WD stress using two maize cultivars, Xianyu (XY) 335 and Yudan (YD) 132. The analysis was based on plant growth, physiological function, and transcriptomic data. Compared with the single Hg stress, Hg accumulation in whole plant and translocation factor (TF) under Hg+WD were increased by 64.51 % (1.44 mg kg^-1) and 260.00 %, respectively, for XY 335; and 50.32 % (0.62 mg kg^-1) and 220.02 %, respectively, for YD 132. Combined Hg and WD stress further increased the reactive oxygen species accumulation, aggravated the damage of the thylakoid membrane, and decreased chlorophyll content compared with single stress. For example, Chl a and Chl b contents of XY 335 were significantly decreased by 48.67 % and 28.08 %, respectively at 48 h after Hg+WD treatment compared with Hg stress. Furthermore, transcriptome analysis revealed that most of down-regulated genes were enriched in photosynthetic-antenna proteins, photosynthesis, chlorophyll and porphyrin metabolism pathways (PsbS1, PSBQ1 and FDX1 etc.) under combined stress, reducing light energy capture and electron transport. However, most genes related to the brassinosteroids (BRs) signaling pathway were up-regulated under Hg+WD stress. Correspondingly, exogenous BRs significantly enhanced the maize tolerance to stress by decreasing Hg accumulation and TF, and raising activities of antioxidant enzyme, the content of chlorophyll and photosynthetic performance. The PI, Fv/Fm and Fv/Fo of Hg+WD+BR treatment were increased by 29.88 %, 32.06 %, and 14.56 %, respectively, for XY 335 compared to Hg+WD. Overall, combined Hg and WD stress decreased photosynthetic efficiency by adversely affecting light absorption and electron transport, especially in stress-sensitive variety, but BRs could alleviate the inhibition of photosynthesis, providing a novel strategy for enhancing crop Hg and WD tolerance and food safety.

Carbon nanoparticles improve the effect of compost and arbuscular mycorrhizal fungi in drought-stressed corn cultivation

Drought is an important threat worldwide, therefore, it is vital to create workable solutions to mitigate the negative effects of drought stress. To this end, we investigated the interactive effect of compost (Comp), arbuscular mycorrhizal fungi (AMF) and carbon nanoparticles (CNPs) on maize plant crops under drought stress. The combined treatments were more effective at increasing soil fertility and promoting the growth of maize plants under both control and drought stress conditions by 20.1% and 39.4%, respectively. The interactions between treatments, especially the effects of Comp-AMF-CNPs mixture, reduce the activity of photorespiration induced H₂O₂ production that consequently reduces drought-related oxidative damages (lipid peroxidation and protein oxidation). Plants treated with Comp-AMF or Comp-AMF-CNPs showed an increase in their antioxidant defense system. Comp-AMF-CNPs increased enzyme activities by 50.3%, 30.1%, and 71% for ascorbate peroxidase (APX), dehydro-ASC reductase (DHAR), and monodehydro-ASC reductase (MDHAR), respectively. Comp-AMF-CNPs also induced the highest increase in anthocyanins (69.5%) compared to the control treatment. This increase was explained by increased anthocyanin percussor, by 37% and 13% under control and drought, respectively. While the increases in biosynthetic key enzymes, phenylalanine aminolayse (PAL) and chalcone synthase (CHS) were 77% and 5% under control and 69% and 89% under drought, respectively. This work advanced our understanding on how Comp-AMF-CNPs improve growth, physiology, and biochemistry of maize plants under drought stress conditions. Overall, this study suggests the effectiveness of Comp-AMF-CNPs as a promising approach to enhance the growth of maize plants in dry areas.

Phyto-interactive impact of green synthesized iron oxide nanoparticles and Rhizobium pusense on morpho-physiological and yield components of greengram

The iron oxide nanoparticles (IONPs) prepared by green synthesis method using Syzigium cumini leaf extract was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD confirmed the crystalline structure of green synthesized NPs measuring around 33 nm while SEM revealed its nearly spherical shape. Rhizobium species recovered from greengram nodules, identified by 16s rRNA gene sequencing as Rhizobium pusense produced 30% more exopolysaccharides (EPS) in basal medium treated with 1000 μg IONPs/ml. Compositional variation in EPS was observed by Fourier-transform infrared spectroscopy (FTIR). There was no reduction in rhizobial viability and no damage to bacterial membrane was observed under SEM and confocal laser scanning microscopy (CLSM), respectively. Effects of IONPs and R. pusense, used alone and in combination on the growth and development of greengram plants varied considerably. Plants grown with IONPs and R. pusence, used alone and in combination, showed a significant increase in seed germination rate, length and dry biomass of plant organs and seed components compared to controls. The IONPs in the presence of rhizobial strain further increased seed germination, plant growth, seed protein and pigments. Greater protein content (442 mg/g) was observed in seeds at 250 mg/kg of IONPs compared to control. Plants raised with mixture of IONPs plus R. pusense had maximum chlorophyll content (39.2 mg/g FW) while proline content decreased by 53% relative to controls. This study confirms that the green synthesis of IONPs from S. cumini leaf possess useful plant growth promoting effects and could be developed as a nano-biofertilizer for optimizing legume production.

Growth, physiological, and temperature characteristics in chinese cabbage pakchoi as affected by Cd- stressed conditions and identifying its main controlling factors using PLS model

BACKGROUND

Although hormesis induced by heavy metals is a well-known phenomenon, the involved biological mechanisms are not fully understood. Cadmium (Cd) is a prevalent heavy metal in the environment. Exposure of Cd, via intake or consumption of Cd-contaminated air or food, poses a huge threat to human health. Chinese cabbage pakchoi (Brassica chinensis L.) is widely planted and consumed as a popular vegetable in China. Therefore, studying the response of Chinese cabbage pakchoi to Cd- stressed conditions is critical to assess whether cabbage can accumulate Cd and serve as an important Cd exposure pathway to human beings. In this study, we investigated the influence of Cd stress on growth, photosynthetic physiology, antioxidant enzyme activities, nutritional quality, anatomical structure, and canopy temperature in Chinese cabbage pakchoi. A partial least squares (PLS) model was used to quantify the relationship between physical and chemical indicators with Cd accumulation in cabbage, and identify the main controlling factors.

RESULTS

Results showed that Cd stress significantly inhibited cabbage's growth and development. When Cd stress was increased, the phenotypic indicators were significantly reduced. Meanwhile, Cd stress significantly enhanced the oxidative stress response of cabbage, such as the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and the content of malondialdehyde (MDA) in leaves. Such a change tended to increase fenestrated tissues' thickness but decrease the thickness of leaf and spongy tissues. Moreover, Cd stress significantly increased soluble sugar, protein, and vitamin C contents in leaves as well as the temperature in the plant canopy. The PLS model analysis showed that the studied phenotypic and physicochemical indicators had good relationships with Cd accumulation in roots, shoots, and the whole plant of cabbage, with high coefficient of determination (R²) values of 0.891, 0.811, and 0.845, and low relative percent deviation (RPD) values of 3.052, 2.317, and 2.557, respectively. Furthermore, through analyzing each parameter's variable importance for projection (VIP) value, the SOD activity was identified as a key factor for indicating Cd accumulation in cabbage. Meanwhile, the effects of CAT on Cd accumulation in cabbage and the canopy mean temperature were also high.

CONCLUSION

Cd stress has significant inhibitory effects and can cause damage cabbage's growth and development, and the SOD activity may serve as a key factor to indicate Cd uptake and accumulation in cabbage.

Phenolic root exudates enhance Avicennia marina tolerance to cadmium under the mediation of functional bacteria in mangrove sediments

This study was carried out to demonstrate the mechanism of phenolic root exudates affecting microbial-mediated cadmium (Cd) speciation transformation thus enhancing the Avicennia marina tolerance to Cd. A rhizo-box experiment was conducted including eight treatments with four Cd levels (0, 1, 2, and 4 mg Cd kg^-1) and two phenol levels (0, 15 mg kg^-1). The results showed that the addition of phenols increased the pH, reduced the number of iron-reducing bacteria (IRB) and sulfur-oxidizing bacteria (SOB) in the rhizosphere sediments, meanwhile promoted the transformation of Cd to low activity speciation. Furthermore, the sulfate accumulation and synthesis of flavonoid phenols in plants were also enhanced. The results indicated that phenolic root exudates inhibit functional bacteria-mediated Fe and S cycles and promote the immobilization of Cd in the sediments. In conclusion, the mitigation of Cd phytotoxicity induced by phenolic root exudates enhanced the Cd tolerance of A. marina.

Citric acid assisted phytoextraction of nickle from soil helps to tolerate oxidative stress and expression profile of NRAMP genes in sunflower at different growth stages

Introduction

Soil polluted with Nickel (Ni) adversely affects sunflower growth resulting in reduced yield. Counterbalancing Ni toxicity requires complex molecular, biochemical, and physiological mechanisms at the cellular, tissue, and whole plant levels, which might improve crop productivity. One of the primary adaptations to tolerate Ni toxicity is the enhanced production of antioxidant enzymes and the elevated expression of Ni responsive genes.

Methods

In this study, biochemical parameters, production of ROS, antioxidants regulation, and expression of NRAMP metal transporter genes were studied under Ni stress in sunflower. There were four soil Ni treatments (0, 50, 100, and 200 mg kg-1 soil), while citric acid (CA, 5 mM kg-1 soil) was applied on the 28th and 58th days of plant growth. The samples for all analyses were obtained on the 30th and 60th day of plant growth, respectively.

Results and discussion

The results indicated that the concentrations of Ni in roots and shoots were increased with increasing concentrations of Ni at both time intervals. Proline contents, ascorbic acid, protein, and total phenolics were reduced under Ni-stress, but with the application of CA, improvement was witnessed in their contents. The levels of malondialdehyde and hydrogen peroxide were enhanced with the increasing concentration of Ni, and after applying CA, they were reduced. The contents of antioxidants, i.e., catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase, were increased at 50 ppm Ni concentration and decreased at higher concentrations of Ni. The application of CA significantly improved antioxidants at all concentrations of Ni. The enhanced expression of NRAMP1 (4, 51 and 81 folds) and NRAMP3 (1.05, 4 and 6 folds) was found at 50, 100 and 200ppm Ni-stress, respectively in 30 days old plants and the same pattern of expression was recorded in 60 days old plants. CA further enhanced the expression at both developmental stages.

Conclusion

In conclusion, CA enhances Ni phytoextraction efficiency as well as protect plant against oxidative stress caused by Ni in sunflower.

Mitigation of Negative Effects of Chromium (VI) Toxicity in Faba Bean (Vicia faba) Plants through the Supplementation of Kinetin (KN) and Gibberellic Acid (GA3)

The present study was carried out to explore the possible role of kinetin and gibberellic acid (GA3) on faba bean under chromium (Cr) stress. Cr treatment negatively affected growth and biomass production, reduced photosynthetic pigments, and inhibited photosynthesis, gas exchange parameters, antioxidant enzymes, and the glyoxylase cycle. Moreover, Cr stress enhanced the production of malondialdehyde (MDA, 216.11%) and hydrogen peroxide (H₂O₂, 230.16%), electrolyte leakage (EL, 293.30%), and the accumulation of proline and glycine betaine. Exogenous application of kinetin and GA3 increased growth and biomass, improved pigment contents and photosynthesis, as well as up-regulated the antioxidant system by improving the antioxidant enzyme activities and the content of nonenzymatic components, and the glyoxylase cycle. Additionally, kinetin and GA3 application displayed a considerable enhancement in proline (602.61%) and glycine betaine (423.72), which help the plants to maintain water balance under stress. Furthermore, a decline in Cr uptake was also observed due to kinetin and GA3 application. Exogenous application of kinetin and GA3 ameliorated the toxic effects of Cr in faba bean plants, up-shooting the tolerance mechanisms, including osmolyte metabolism and the antioxidant system.

Optical imaging spectroscopy coupled with machine learning for detecting heavy metal of plants: A review

Heavy metal elements, which inhibit plant development by destroying cell structure and wilting leaves, are easily absorbed by plants and eventually threaten human health via the food chain. Recently, with the increasing precision and refinement of optical instruments, optical imaging spectroscopy has gradually been applied to the detection and reaction of heavy metals in plants due to its in-situ, real-time, and simple operation compared with traditional chemical analysis methods. Moreover, the emergence of machine learning helps improve detection accuracy, making optical imaging spectroscopy comparable to conventional chemical analysis methods in some situations. This review (a): summarizes the progress of advanced optical imaging spectroscopy techniques coupled with artificial neural network algorithms for plant heavy metal detection over ten years from 2012-2022; (b) briefly describes and compares the principles and characteristics of spectroscopy and traditional chemical techniques applied to plants heavy metal detection, and the advantages of artificial neural network techniques including machine learning and deep learning techniques in combination with spectroscopy; (c) proposes the solutions such as coupling with other analytical and detection methods, portability, to address the challenges of unsatisfactory sensitivity of optical imaging spectroscopy and expensive instruments.

The Alleviation of Metal Stress Nuisance for Plants—A Review of Promising Solutions in the Face of Environmental Challenges

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

Proteomic Changes in Paspalum fasciculatum Leaves Exposed to Cd Stress

(1) Background: Cadmium is a toxic heavy metal that is widely distributed in water, soil, and air. It is present in agrochemicals, wastewater, battery waste, and volcanic eruptions. Thus, it can be absorbed by plants and enter the trophic chain. P. fasciculatum is a plant with phytoremediation capacity that can tolerate Cd stress, but changes in its proteome related to this tolerance have not yet been identified. (2) Methods: We conducted a quantitative analysis of the proteins present in P. fasciculatum leaves cultivated under greenhouse conditions in mining soils doped with 0 mg kg−1 (control), 30 mg kg−1, or 50 mg kg−1. This was carried out using the label-free shotgun proteomics technique. In this way, we determined the changes in the proteomes of the leaves of these plants, which allowed us to propose some tolerance mechanisms involved in the response to Cd stress. (3) Results: In total, 329 variable proteins were identified between treatments, which were classified into those associated with carbohydrate and energy metabolism; photosynthesis; structure, transport, and metabolism of proteins; antioxidant stress and defense; RNA and DNA processing; and signal transduction. (4) Conclusions: Based on changes in the differences in the leaf protein profiles between treatments, we hypothesize that some proteins associated with signal transduction (Ras-related protein RABA1e), HSPs (heat shock cognate 70 kDa protein 2), growth (actin-7), and cellular development (actin-1) are part of the tolerance response to Cd stress.

Alleviation of Cadmium and Nickel Toxicity and Phyto-Stimulation of Tomato Plant L. by Endophytic Micrococcus luteus and Enterobacter cloacae

Cadmium (Cd) and nickel (Ni) are two of the most toxic metals, wreaking havoc on human health and agricultural output. Furthermore, high levels of Cd and Ni in the soil environment, particularly in the root zone, may slow plant development, resulting in lower plant biomass. On the other hand, endophytic bacteria offer great promise for reducing Cd and Ni. Moreover, they boost plants’ resistance to heavy metal stress. Different bacterium strains were isolated from tomato roots. These isolates were identified as Micrococcus luteus and Enterobacter cloacae using 16SrDNA and were utilized to investigate their involvement in mitigating the detrimental effects of heavy metal stress. The two bacterial strains can solubilize phosphorus and create phytohormones as well as siderophores. Therefore, the objective of this study was to see how endophytic bacteria (Micrococcus luteus and Enterobactercloacae) affected the mitigation of stress from Cd and Ni in tomato plants grown in 50 μM Cd or Ni-contaminated soil. According to the findings, Cd and Ni considerably lowered growth, biomass, chlorophyll (Chl) content, and photosynthetic properties. Furthermore, the content of proline, phenol, malondialdehyde (MDA), H₂O₂, OH, O₂, the antioxidant defense system, and heavy metal (HM) contents were significantly raised under HM-stress conditions. However, endophytic bacteria greatly improved the resistance of tomato plants to HM stress by boosting enzymatic antioxidant defenses (i.e., catalase, peroxidase, superoxide dismutase, glutathione reductase, ascorbate peroxidase, lipoxygenase activity, and nitrate reductase), antioxidant, non-enzymatic defenses, and osmolyte substances such as proline, mineral content, and specific regulatory defense genes. Moreover, the plants treated had a higher value for bioconcentration factor (BCF) and translocation factor (TF) due to more extensive loss of Cd and Ni content from the soil. To summarize, the promotion of endophytic bacterium-induced HM resistance in tomato plants is essentially dependent on the influence of endophytic bacteria on antioxidant capacity and osmoregulation.

Coal gangue modified bioretention system for runoff pollutants removal and the biological characteristics

In this study, coal gangue (CG) was applied as media in bioretention system to remove runoff pollutant. CG modified bioretention systems show good removal efficiency towards runoff pollutant due to the high adsorption capacity of CG. The removal of total phosphorus (TP), total nitrogen (TN), ammonia (NH₄⁺-N) and chemical oxygen demand (COD) by CG modified bioretention systems was influenced by diverse rainfall conditions including rainfall concentration, recurrence period and drying period, and their removal rate ranged 94-99%, 30-70%, 83-97% and 33-86%, respectively. The effluent concentration of Zn, Pb and Cu was as low as 3.14-10.99 μg/L, 0.66-2.56 μg/L and 0.60-3.15 μg/L, respectively. In addition, CG could promote the plant heavy metal uptake and thus decrease their accumulation in soil to a certain extent. Meanwhile, Malondialdehyde (MDA) content and peroxidases (POD) activities of plants in CG modified bioretention were lower than that in tradition bioretention, indicating that CG could help plants recovery and lessened the oxidative stress for the negative impact of high heavy metals accumulation. CG-based media alleviated the inhibitory effect of rainwater runoff pollutant accumulation (especially heavy metals) on microbial diversity and the enhancement of the dominant bacteria (such as Proteobacteria and Bacteroidota) could conduce the nutrients removal in the bioretention systems. In overall, this study demonstrated that the CG modified bioretention systems show an excellent removal performance combine with biological effects.

Selection of Newly Identified Growth-Promoting Archaea Haloferax Species With a Potential Action on Cobalt Resistance in Maize Plants

Soil contamination with cobalt (Co) negatively impacts plant growth and production. To combat Co toxicity, plant growth-promoting microorganisms for improving plant growth are effectively applied. To this end, unclassified haloarchaeal species strain NRS_31 (OL912833), belonging to Haloferax genus, was isolated, identified for the first time, and applied to mitigate the Co phytotoxic effects on maize plants. This study found that high Co levels in soil lead to Co accumulation in maize leaves. Co accumulation in the leaves inhibited maize growth and photosynthetic efficiency, inducing oxidative damage in the tissue. Interestingly, pre-inoculation with haloarchaeal species significantly reduced Co uptake and mitigated the Co toxicity. Induced photosynthesis improved sugar metabolism, allocating more carbon to defend against Co stress. Concomitantly, the biosynthetic key enzymes involved in sucrose (sucrose-P-synthase and invertases) and proline (pyrroline-5- carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR)) biosynthesis significantly increased to maintain plant osmotic potential. In addition to their osmoregulation potential, soluble sugars and proline can contribute to maintaining ROS hemostasis. Maize leaves managed their oxidative homeostasis by increasing the production of antioxidant metabolites (such as phenolics and tocopherols) and increasing the activity of ROS-scavenging enzymes (such as POX, CAT, SOD, and enzymes involved in the AsA/GSH cycle). Inside the plant tissue, to overcome heavy Co toxicity, maize plants increased the synthesis of heavy metal-binding ligands (metallothionein, phytochelatins) and the metal detoxifying enzymes (glutathione S transferase). Overall, the improved ROS homeostasis, osmoregulation, and Co detoxification systems were the basis underlying Co oxidative stress, mitigating haloarchaeal treatment's impact.

A review on bioremediation approach for heavy metal detoxification and accumulation in plants

Nowadays, the accumulation of toxic heavy metals in soil and water streams is considered a serious environmental problem that causes various harmful effects on plants and animals. Phytoremediation is an effective, green, and economical bioremediation approach by which the harmful heavy metals in the contaminated ecosystem can be detoxified and accumulated in the plant. Hyperaccumulators exude molecules called transporters that carry and translocate the heavy metals present in the soil to different plant parts. The hyperaccumulator plant genes can confine higher concentrations of toxic heavy metals in their tissues. The efficiency of phytoremediation relies on various parameters such as soil properties (pH and soil type), organic matters in soil, heavy metal type, nature of rhizosphere, characteristics of rhizosphere microflora, etc. The present review comprehensively discusses the toxicity effect of heavy metals on the environment and different phytoremediation mechanisms for the transport and accumulation of heavy metals from polluted soil. This review gave comprehensive insights into plants tolerance for the higher heavy metal concentration their responses for heavy metal accumulation and the different mechanisms involved for heavy metal tolerance. The current status and the characteristic features that need to be improved in the phytoremediation process are also reviewed in detail.

Heavy Metal–Resistant Plant Growth–Promoting Citrobacter werkmanii Strain WWN1 and Enterobacter cloacae Strain JWM6 Enhance Wheat (Triticum aestivum L.) Growth by Modulating Physiological Attributes and Some Key Antioxidants Under Multi-Metal Stress

Due to wastewater irrigation, heavy metal (HM) exposure of agricultural soils is a major limiting factor for crop productivity. Plant growth–promoting bacteria (PGPB) may lower the risk of HM toxicity and increase crop yield. In this context, we evaluated two HM-resistant PGPB strains, i.e., Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 isolated from wastewater-irrigated agricultural soils, for their efficacy to mitigate HM (Cd, Ni, and Pb) stress in a pot experiment. Increasing concentrations (0, 50, 100, and 200 ppm) of each HM were used to challenge wheat plants. Heavy metal stress negatively affected wheat growth, biomass, and physiology. The plants under elevated HM concentration accumulated significantly higher amounts of heavy metals (HMs) in shoots and roots, resulting in increased oxidative stress, which was evident from increased malondialdehyde (MDA) content in roots and shoots. Moreover, alterations in antioxidants like superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT) were observed in plants under HM stress. The severity of damage was more pronounced with rising HM concentration. However, inoculating wheat with Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 (107 CFU ml–1) improved plant shoot length (11–42%), root length (19–125%), fresh weight (41–143%), dry weight (65–179%), and chlorophyll a (14%-24%) and chlorophyll b content (2–24%) under HM stress. Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 either alone or in co-inoculation enhanced the antioxidant enzyme activity, which may lower oxidative stress in plants. However, seeds treated with the bacterial consortium showed an overall better outcome in altering oxidative stress and decreasing HM accumulation in wheat shoot and root tissues. Fourier transform infrared spectroscopy indicated the changes induced by HMs in functional groups on the biomass surface that display effective removal of HMs from aqueous medium using PGPB. Thus, the studied bacterial strains may have adequate fertilization and remediation potential for wheat cultivated in wastewater-irrigated soils. However, molecular investigation of mechanisms adopted by these bacteria to alleviate HM stress in wheat is required to be conducted.

Responses of photosynthesis, antioxidant enzymes, and related gene expression to nicosulfuron stress in sweet maize (Zea mays L.)

Weed control in maize (Zea mays L.) crops is usually undertaken using the postemergence herbicide nicosulfuron. The toxicity of nicosulfuron on maize, especially sweet maize, has been widely reported. In order to examine the effect of nicosulfuron on seedling photosynthetic characteristics, chlorophyll fluorescence, reactive oxygen species production, antioxidant enzyme activities, and gene expressions on sweet maize, nicosulfuron-tolerant "HK310" and nicosulfuron-sensitive "HK320" were studied. All experiment samples were subjected to a water or 80 mg kg^-1 of nicosulfuron treatment when sweet maize seedlings grow to the stage of four leaves. After treatment with nicosulfuron, results for HK301 were significantly higher than those for HK320 for net photosynthetic rate, transpiration rate, stomatal conductance, leaf maximum photochemical efficiency of PSII, photochemical quenching of chlorophyll fluorescence, and the electron transport rate. These results were contrary to nonphotochemical quenching and intercellular CO₂ concentration. As exposure time increased, associated effects also increased. Both O₂^·- and H₂O₂ detoxification is modulated by antioxidant enzymes. Compared to HK301, SOD, POD, and CAT activities of HK320 were significantly reduced as exposure time increase. Compared to HK320, the gene expression for the majority of SOD genes, except for SOD2, increased due to inducement by nicosulfuron, and it significantly upregulated the gene expression of CAT in HK301. Results from this study indicate that plants can improve photosynthesis, scavenging capabilities of ROS, and protective mechanisms to alleviate phytotoxic effect of nicosulfuron. Future research is needed to further elucidate the important role antioxidant systems and gene regulation play in herbicide detoxification in sweet maize.

Application of zinc oxide nanoparticles to promote remediation of nickel by Sorghum bicolor: metal ecotoxic potency and plant response

Nickel (Ni) is one of the most toxic metals in human health. Its bioaccumulation in gluten-free crops limits the progressing demand of safe foods for allergic people to gluten. Nanoparticles have shown promising results in enhancing the crop yield and reducing the risk of heavy metal uptake. However, their nanotoxicity has been raised environmental concerns. This study investigated the environmental behavior of Ni (II) with the co-presence of Zinc Oxide Nanoparticles (ZnO-NPs) in sorghum bicolor. The plants were exposed to different treatments of Ni, ZnO-NPs, or their coexistence. The uptake experiments were carried out within nine treatments consisting of 1 or 5 ppm Ni alone or in coexistence with 50 or 100 ppm ZnO-NPs. The physiological impacts on plants as potential fingerprints for nanotoxicity were recorded and assessed in a phenotypic spectrum. The total Ni or Zn contents were quantified using atomic absorption. NPs significantly altered the bioavailability of Ni. The results revealed that at 5 ppm Ni contamination, 50 and 100 ZnO-NPs significantly reduced the Ni uptake by ∼43% and 47%, respectively. Further, the results showed at 50 ppm NPs, the phytotoxicity effects of both Ni and NPs may reduce, leading to higher plant dry biomass yield.Novelty statement Characterization of zinc oxide nanotoxicity threshold by developing a phenotypic spectrum. Also, the study revealed the phytoremediation potential of ZnO nanoparticle in mitigating the nickel uptake in a gluten-free crop (sorghum bicolor).

Unraveling Cadmium Toxicity in Trifolium repens L. Seedling: Insight into Regulatory Mechanisms Using Comparative Transcriptomics Combined with Physiological Analyses

Trifolium repens (T. repens) can accumulate significant amounts of heavy metal ions, and has strong adaptability to wide environmental conditions, and relatively large biomass, which is considered a potential plant for phytoremediation. However, the molecular mechanisms of T. repens involved in Cd tolerance have not yet been studied in detail. This study was conducted to examine the integrative responses of T. repens exposed to a high-level CdCl₂ by investigating the physiological and transcriptomic analyses. The results suggested that T. repens seedlings had a high degree of tolerance to Cd treatment. The roots accumulated higher Cd concentration than leaves and were mainly distributed in the cell wall. The content of MDA, soluble protein, the relative electrolyte leakage, and three antioxidant enzymes (POD, SOD, and APX) was increased with the Cd treatment time increasing, but the CAT enzymes contents were decreased in roots. Furthermore, the transcriptome analysis demonstrated that the differentially expressed genes (DEGs) mainly enriched in the glutathione (GSH) metabolism pathway and the phenylpropanoid biosynthesis in the roots. Overexpressed genes in the lignin biosynthesis in the roots might improve Cd accumulation in cell walls. Moreover, the DEGs were also enriched in photosynthesis in the leaves, transferase activity, oxidoreductase activity, and ABA signal transduction, which might also play roles in reducing Cd toxicity in the plants. All the above, clearly suggest that T. repens employ several different mechanisms to protect itself against Cd stress, while the cell wall biosynthesis and GSH metabolism could be considered the most important specific mechanisms for Cd retention in the roots of T. repens.

Changes in phenolic compounds production as a defensive mechanism against hydrogen sulfide pollution in Scrophularia striata

Increasing pollutants such as hydrogen sulfide (H₂S) from industrial activities is an ecological challenge for plants, which seriously affects their health and productivity. Scrophularia striata is a plant endemic to Iran growing in the province of Ilam, wherein a gas refinery releases toxic agents such as H₂S whose detrimental effects on the function and tolerability of medicinal plants in this region have yet to be elucidated. Thus, we initiated a hydroponic study into hormetic effect of sodium hydrogen sulfide (NaHS) concentrations (0, 3 and 7 mM) as H₂S-donor at different time points on oxidative status and phenolic compounds, focusing more on phenylethanoid glycosides (PhGs) in S. striata. Our results indicated that hydrogen peroxide (H₂O₂) increased significantly at 3 mM NaHS after 48 h, while its peak at 7 mM occurred after 24 h. Nitric oxide (NO) level peaked at 3 mM and 7 mM after 24 h. Treatment with NaHS also resulted in a dose-dependent induction of phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) enzyme activities, phenolic acids production (cinnamic acid, coumaric acid, ferulic acid, caffeic acid and salicylic acid) and acteoside accumulation, ultimately leading to an increase in antioxidant capacity. Modulation of soluble sugars contents including glucose, mannose and rhamnose/xylose, occurred after the treatment with NaHS, likely increasing plant tolerance due to their biological activity and structural effects. Overall, our results suggest that dose-dependent accumulation of phenolics, notably acteoside, leads to an augmentation in antioxidant system to deal with H₂S stress in S. striata.

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.