Morpho-physiological traits, gaseous exchange attributes, and phytoremediation potential of jute (Corchorus capsularis L.) grown in different concentrations of copper-contaminated soil

Elucidating the role of rice straw biochar in modulating Helianthus annuus L. antioxidants, secondary metabolites and soil post-harvest characteristics in different types of microplastics

The emergence of microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant threats to soil ecosystems. Given the widespread contamination of ecosystems by various types of MPs, including polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE), it is crucial to understand their effects on agricultural productivity. The present study was conducted to investigate the effects of different types of MPs (PS, PVC, and PE) on various aspects of sunflower (Helianthus annuus L.) growth with the addition of rice straw biochar (RSB). This study aimed to examine plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators, and the response of various antioxidants (enzymatic and non-enzymatic) and their specific gene expression, proline metabolism, the AsA-GSH cycle, cellular fractionation in the plants and post-harvest soil properties. The research outcomes indicated that elevated levels of different types of MPs in the soil notably reduced plant growth and biomass, photosynthetic pigments, and gas exchange attributes. Different types of MPs also induced oxidative stress, which caused an increase in various enzymatic and non-enzymatic antioxidant compounds, gene expression and sugar content; notably, a significant increase in proline metabolism, AsA-GSH cycle, and pigmentation of cellular components was also observed. Favorably, the addition of RSB significantly increased plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and relevant gene expression while decreasing oxidative stress. In addition, RSB amendment decreased proline metabolism and AsA-GSH cycle in H. annuus plants, thereby enhancing cellular fractionation and improving post-harvest soil properties. These results open new avenues for sustainable agriculture practices and show great potential for resolving the urgent issues caused by microplastic contamination in agricultural soils.

Phytobial remediation advances and application of omics and artificial intelligence: a review

Industrialization and urbanization increased the use of chemicals in agriculture, vehicular emissions, etc., and spoiled all environmental sectors. It causes various problems among living beings at multiple levels and concentrations. Phytoremediation and microbial association are emerging as a potential method for removing heavy metals and other contaminants from soil. The treatment uses plant physiology and metabolism to remove or clean up various soil contaminants efficiently. In recent years, omics and artificial intelligence have been seen as powerful techniques for phytobial remediation. Recently, AI and modeling are used to analyze large data generated by omics technologies. Machine learning algorithms can be used to develop predictive models that can help guide the selection of the most appropriate plant and plant growth-promoting rhizobacteria combination that is most effective at remediation. In this review, emphasis is given to the phytoremediation techniques being explored worldwide in soil contamination.

Red light mitigates Cd toxicity in Egeria densa by restricting Cd accumulation and modulating antioxidant defense system

Controlling light qualities have been acknowledged as an effective method to enhance the efficiency of phytoremediation, as light has a significant impact on plant growth. This study examined the effects of light qualities on cadmium (Cd) tolerance in aquatic plant Egeria densa using a combination of biochemical and transcriptomic approaches. The study revealed that E. densa exhibits higher resistance to Cd toxicity under red light (R) compared to blue light (B), as evidenced by a significant decrease in photosynthetic inhibition and damage to organelle ultrastructure. After Cd exposure, there was a significantly reduced Cd accumulation and enhanced levels of both glutathione reductase (GR) activity and glutathione (GSH), along with an increase in jasmonic acid (JA) in R-grown E. densa compared to B. Transcriptional analysis revealed that R caused an up-regulation of Cd transporter genes such as ABCG (G-type ATP-binding cassette transporter), ABCC (C-type ATP-binding cassette transporter), and CAX2 (Cation/H+ exchanger 2), while down-regulated the expression of HIPP26 (Heavy metal-associated isoprenylated plant protein 26), resulting in reduced Cd uptake and enhanced Cd exportation and sequestration into vacuoles. Moreover, the expression of genes involved in phytochromes and JA synthesis was up-regulated in Cd treated E. densa under R. In summary, the results suggest that R could limit Cd accumulation and improve antioxidant defense to mitigate Cd toxicity in E. densa, which might be attributed to the enhanced JA and phytochromes. This study provides a foundation for using light control methods with aquatic macrophytes to remediate heavy metal contamination in aquatic systems.

Exploring Bacillus mycoides PM35 efficacy in enhancing rice (Oryza sativa L.) response to different types of microplastics through gene regulation and cellular fractionation

Soil contamination with microplastics (MPs) is a persistent threat to crop production worldwide. With a wide range of MP types, including polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE), contaminating our environment, it is important to understand their impact on agricultural productivity. The present study was conducted to investigate the effects of different types of MPs (PS, PVC and PE) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and non-enzymatic), gene expression, proline metabolism, the AsA-GSH cycle and cellular fractionation and nutritional status, in different parts of rice (Oryza sativa L.) seedlings, which were also exposed to plant growth promoting rhizobacteria (PGPR), i.e. Bacillus mycoides PM35, i.e. 20 μL. The research outcomes indicated that the different types of MPs in the soil notably reduced plant growth and biomass, photosynthetic pigments and gas exchange attributes. However, MP stress also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolyte leakage (EL) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the fractionations of cellular components was observed. Although the application of B. mycoides PM35 showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased oxidative stress. In addition, the application of B. mycoides PM35 enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in O. sativa plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of MP contamination in agricultural soils.

Nanoparticles synergy: Enhancing wheat (Triticum aestivum L.) cadmium tolerance with iron oxide and selenium

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO - NPs) and selenium nanoparticles (Se - NPs) have been studied in many literatures. However, the combined application of FeO and Se - NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine various growth and biochemical parameters in wheat (Triticum aestivum L.) under the toxic concentration of cadmium (Cd) i.e., 50 mg kg-1 which were primed with combined application of two levels of FeO and Se - NPs i.e., 15 and 30 mg L-1 respectively. The results showed that the Cd toxicity in the soil showed a significantly (P < 0.05) declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in T. aestivum. However, Cd toxicity significantly (P < 0.05) increased oxidative stress biomarkers, enzymatic and non-enzymatic antioxidants including their gene expression in T. aestivum. Although, the application of FeO and Se - NPs showed a significant (P < 0.05) increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, and Cd uptake. In addition, individual or combined application of FeO and Se - NPs enhanced the cellular fractionation and decreases the proline metabolism and AsA - GSH cycle in T. aestivum. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Unlocking the phytoremediation potential of organic acids: A study on alleviating lead toxicity in canola (Brassica napus L.)

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. Organic chelating agents such as maleic acid (MA) and tartaric acid (TA) are more efficient, environmentally friendly, and biodegradable compared to inorganic chelating agents and they enhance the solubility, absorption, and stability of metals. To investigate this, we conducted a hydroponic experiment to assess the impact of MA (0.25 mM) and TA (1 mM) on enhancing the phytoremediation of Pb under its toxic concentration of 100 μM, using the oil seed crop canola (Brassica napus L.). Results from the present study showed that the Pb toxicity significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes and nutritional contents from the roots and shoots of the plants. In contrast, toxic concentration of Pb significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, increased enzymatic and non-enzymatic antixoidants and their specific gene expression and also increased organic acid exudation patter in the roots of B. napus. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double membranous organelles while Fourier-transform infrared (FTIR) spectroscopy showed an nveiled distinct peak variations in Pb-treated plants, when compared to control. Additionally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double-membrane organelles, while Fourier-transform infrared (FTIR) spectroscopy unveiled distinct peak variations in Pb-treated plants compared to the control. The negative impact of Pb toxicity can overcome the application of MA and TA, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in B. napus. With the application of MA and TA, the values of the bioaccumulation factor (BAF) and translocation factor (TF) exceeded 1, indicating that the use of MA and TA enhances the phytoremediation potential of B. napus under Pb stress conditions. This finding could be beneficial for field environment studies, especially when explored through in-depth genetic and molecular analysis.

Physiological, transcriptome and gene functional analysis provide novel sights into cadmium accumulation and tolerance mechanisms in kenaf

Kenaf is considered to have great potential for remediation of heavy metals in ecosystems. However, studies on molecular mechanisms of root Cd accumulation and tolerance are still inadequate. In this study, two differently tolerant kenaf cultivars were selected as materials and the physiological and transcriptomic effects were evaluated under Cd stress. This study showed that 200 µmol/L CdCl2 treatment triggered the reactive oxygen species (ROS) explosion and membrane lipid peroxidation. Compared with the Cd-sensitive cultivar 'Z', the Cd-tolerant cultivar 'F' was able to resist oxidative stress in cells by producing higher antioxidant enzyme activities and increasing the contents of ascorbic acid (AsA) and glutathione (GSH). The root cell wall of 'F' exhibited higher polysaccharide contents under Cd treatment, providing more Cd-binding sites. There were 3,439 differentially expressed genes (DEGs) that were co-regulated by Cd treatment in two cultivars. Phenylpropanoid biosynthesis and plant hormone signal transduction pathways were significantly enriched by functional annotation analysis. DEGs associated with pectin, cellulose, and hemi-cellulose metabolism were involved in Cd chelation of root cell wall; V-ATPases, ABCC3 and Narmp3 could participated in vacuolar compartmentalization of Cd; PDR1 was responsible for Cd efflux; the organic acid transporters contributed to the absorption of Cd in soil. These genes might have played key roles in kenaf Cd tolerance and Cd accumulation. Moreover, HcZIP2 was identified to be involved in Cd uptake and transport in kenaf. Our findings provide a deeper understanding of the molecular pathways underlying Cd accumulation and detoxification mechanisms in kenaf.

Trends in phytoremediation of heavy metals-contaminated soils: A Web of science and CiteSpace bibliometric analysis

Heavy metals pollution in soils is an urgent environmental issue worldwide. Phytoremediation is a green and eco-friendly way of remediating heavy metals. However, a systematic overview of this field is limited, and little is known about future development trends. Therefore, we used CiteSpace software to conduct bibliometric and visual analyses of published literature in the field of phytoremediation of heavy metals in soils from the Web of Science core collection and identified research hotspots and development trends in this field. Researchers are paying increased attention to phytoremediation of heavy metals in soils, especially environmental researchers. A total of 121 countries or regions, 3790 institutions, 4091 funded organisations and 15,482 authors have participated in research in this area. China, India, and Pakistan are the largest contributors. There has been extensive cooperation between countries, institutions, and authors worldwide, but there is a lack of cooperation among top authors. 'Calcareous soil', 'Co-contaminated soil' and 'Metal availability' are the most intensively investigated topics. 'EDTA', 'Plant growth-promoting Rhizobacteria', 'Photosynthesis', 'Biochar' and 'Phytoextraction' are research hotspots in this field. In addition, more and more researchers are beginning to pay attention to research on co-contaminated soil, metal availability, chelating agents, and microbial-assisted phytoremediation. In summary, bibliometric, and visual analyses in the field of phytoremediation of heavy metals in soils identifies probable directions for future research and provides a resource through which to better understand this rapidly advancing subject.

Emerging trends in wastewater treatment: Addressing microorganic pollutants and environmental impacts

This review focuses on the challenges and advances associated with the treatment and management of microorganic pollutants, encompassing pesticides, industrial chemicals, and persistent organic pollutants (POPs) in the environment. The translocation of these contaminants across multiple media, particularly through atmospheric transport, emphasizes their pervasive nature and the subsequent ecological risks. The urgency to develop cost-effective remediation strategies for emerging organic contaminants is paramount. As such, wastewater-based epidemiology and the increasing concern over estrogenicity are explored. By incorporating conventional and innovative wastewater treatment techniques, this article highlights the integration of environmental management strategies, analytical methodologies, and the importance of renewable energy in waste treatment. The primary objective is to provide a comprehensive perspective on the current scenario, imminent threats, and future directions in mitigating the effects of these pollutants on the environment. Furthermore, the review underscores the need for international collaboration in developing standardized guidelines and policies for monitoring and controlling these microorganic pollutants. It advocates for increased investment in research and development of advanced materials and technologies that can efficiently remove or neutralize these contaminants, thereby safeguarding environmental health and promoting sustainable practice.

Efficacy of priming wheat (Triticum aestivum) seeds with a benzothiazine derivative to improve drought stress tolerance

We evaluated the effects of different concentrations (0.05 and 0.15mM) of a benzothiazine (BTh) derivative on wheat (Triticum aestivum L.) in normal (100% field water capacity, FWC) and drought (60% FWC) conditions. Various morphological and physiological characteristics, and the uptake of osmo-protectants and nutrients were measured under the two FWC conditions. Results show that the drought conditions significantly reduced plant growth, affected plant composition, reduced the concentrations of photosynthetic pigments and affected gaseous exchange attributes, stomatal behaviour, and uptake fluxes of essential nutrients, while increasing the contents of different osmo-protectants and enzymatic and non-enzymatic antioxidants to decrease the production of reactive oxygen species (ROS) within the cells/tissues. However, seed priming with BTh reduced water stress conditions by increasing plant growth and biomass, photosynthetic pigments, stomatal behaviour, different gaseous exchange attributes, and uptake fluxes of essential nutrients compared with unprimed plants. In addition, the plant has a strong antioxidant defense system, which further increased its activities under BTh derivative treatments, to scavenge ROS production and maintain cell turgor under water stress conditions. In conclusion, drought stress-induced oxidative stress and altered the growth of T. aestivum , whereas seed priming increased plant growth and antioxidant production by improving the plant tolerance to drought. We suggest that seed priming with a BTh derivative as an effective priming technique in T. aestivum for reducing drought stress tends to benefit a grower in terms of better growth to fulfil the market demand for food cereals.

Effect of citric acid on phytoextraction potential of Cucurbita pepo, Lagenaria siceraria, and Raphanus sativus plants exposed to multi-metal stress

Phytoextraction is a novel technique that involves using plants to remove heavy metals from contaminated soils. An outdoor pot experiment was designed to evaluate the phytoextraction potential of three plant species Cucurbita pepo, Lagenaria siceraria, and Raphanus sativus in soil contaminated with multiple metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) under the application of citric acid. The results showed that Raphanus sativus, out of all the studied plants, had the highest root and shoot dry weight and the capacity to accumulate all heavy metals at higher concentrations except for Cu. The application of citric acid into the polluted soil significantly increased plant growth, biomass, and heavy metal uptake. High bioconcentration values indicate that Raphanus sativus is a promising plant for absorbing and accumulating Cd and Ni from the soil. The maximum values of bioconcentration were also observed by the application of citric acid. The values of metal translocation from the root to the shoot were varied by plant species and the citric acid application. Regarding the biomass, metal content, as well as removal metal percentage values, it became apparent that the Raphanus sativus plant was the most effective crop in removing heavy metals from multi-metal contaminated Soil. Generally, these findings emphasize that the application of citric acid could be a useful approach to assist Cd and Ni phytoextraction by Raphanus sativus plants. When these plants are growing as vegetable crops, more attention should be given to evaluating the heavy metal content in them, especially when adding citric acid to their soil through fertigation systems to avoid food chain contamination.

Root development in Leucaena leucocephala (Lam.) de Wit enhances copper accumulation

Potentially toxic elements (PTE) in soil like copper (Cu) have been common in agricultural and mining areas worldwide. The sustainable remediation of these areas has been shown to have high socio-environmental relevance and phytoremediation is one of the green technologies to be considered. The challenge is to identify species that are tolerant to PTE, and to assess their phytoremediation potential. The objective of this study was to evaluate the physiological response of Leucaena leucocephala (Lam.) de Wit and to determine the species tolerance and phytoremediation potential to concentrations of Cu in the soil (100, 200, 300, 400 and 500 mg/dm3). The photosynthetic rate was not affected, while the content of chlorophylls decreased as Cu concentrations increased. There was an increased in stomatal conductance and water use efficiency from the treatment of 300. The root biomass and the length were bigger than the shoots, in the treatments above 300. Cu accumulation was greater in the roots than in the shoot of the plants, thus, the Cu translocation index to the shoot was lower. The ability to absorb and accumulate, mainly, Cu in the roots, allowed the development and growth of plants, since the parameters of photosynthesis and biomass accumulation were not affected by the Cu excess. This accumulation in the roots is characterized as a strategy for the phytostabilization of Cu. Therefore, L. leucocephala is tolerant to the Cu concentrations evaluated and has a potential phytoremediation of Cu in the soil.

New insights in to the ameliorative effects of zinc and iron oxide nanoparticles to arsenic stressed spinach (Spinacia oleracea L.)

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO-NPs) and zinc oxide nanoparticle (ZnO-NPs) have been studied in many literatures. However, the combined application of FeO and ZnO-NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine the plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants in spinach (Spinacia oleracea L.) under the different As concentrations i.e., 0 (no As), 60 and 120 μM] which were primed with combined application of two levels of FeO-NPs (10 and 20 mg L^-1) and ZnO-NPs (20 and 40 mg L^-1). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of S. oleracea. The negative impact of As toxicity can overcome the combined application of ZnO-NPs and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in S. oleracea by decreasing the As contents in the roots and shoots of the plants. Research findings, therefore, suggest that the combined application of ZnO-NPs and FeO-NPs can ameliorate As toxicity in S. oleracea, resulting in improved plant growth and composition under As stress, as depicted by balanced exudation of organic acids.

Application of silicon and sodium hydrosulfide alleviates arsenic toxicity by regulating the physio-biochemical and molecular mechanisms of Zea mays

Soil contamination with toxic heavy metals (such as arsenic (As)) is becoming a serious global problem due to rapid development of social economy, although the use of silicon (Si) and sodium hydrosulfide (NaHS) has been found effective in enhancing plant tolerance against biotic and abiotic stresses including the As toxicity. For this purpose, a pot experiment was conducted using the different levels of As toxicity in the soil, i.e., (0 mM (no As), 50, and 100 µM) which were also supplied with the different exogenous levels of Si, i.e., (0 (no Si), 1.5, and 3 mM) and also with the NaHS, i.e., (0 (no NaHS), 1, and 2 mM) on growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, antioxidant machinery (enzymatic and non-enzymatic antioxidants), and their gene expression, ion uptake, organic acid exudation, and As uptake of maize (Zea mays L.). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in terms of malondialdehyde, hydrogen peroxide, and electrolyte leakage and also increased organic acid exudation patter in the roots of Z. mays, although the activities of enzymatic antioxidants and the response of their gene expressions in the roots and shoots of the plants and non-enzymatic such as phenolic, flavonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50 µM As, but decreased by the increasing the As concentration 100 µM in the soil. The negative impact of As toxicity can overcome the application of Si and NaHS, which ultimately increased plant growth and biomass by capturing the reactive oxygen species and decreased oxidative stress in Z. mays by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the Si was more sever and showed better results when we compared with NaHS under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of Si and NaHS can ameliorate As toxicity in Z. mays, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Bacillus mycoides PM35 in combination with titanium dioxide (TiO2)⎯nanoparticles enhanced morpho-physio-biochemical attributes in Barley (Hordeum vulgare L.) under cadmium stress

Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria and are known to induce plant growth promotion and titanium dioxide (TiO₂)⎯nanoparticles (NPs) used in a range of applications that need increased whiteness, improved corrosion resistance and photocatalytic activity. Keeping in view the stress mitigation potential of TiO₂⎯NPS and B. mycoides PM35, the existing research work was premeditated to inspect the beneficial role of seed priming with using different levels of TiO₂⎯NPs i.e., [(0 no TiO₂⎯NPs), 25 and 50 μg/ml] and soil incubation plant growth promoting rhizobacteria (B. mycoides PM35) i.e., [(0 no B. mycoides PM35), 10 and 20 μL] on biochemical, morphological and physiological characteristics of Barley (Hordeum vulgare L.) plants under different levels of Cd in the soil i.e., [(0 Cd), 50 and 100 mg kg^-1]. Results from the present study showed that the increasing levels of Cd in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of Cd in the soil significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of H. vulgare. Although, the activities of enzymatic antioxidants and the response of their gene expressions in the roots and shoots of the plants and non-enzymatic such as phenolic, flavonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50 mg kg^-1 Cd, but decreased by the increasing the Cd concentration 100 mg kg^-1 in the soil. The negative impact of Cd toxicity can overcome the application of PGPR (B. mycoides PM35) and TiO₂⎯NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in H. vulgare by decreasing the Cd contents in the roots and shoots of the plants. Our results also showed that the TiO₂⎯NPs were more sever and showed better results when we compared with PGPR (B. mycoides PM35) under the same treatment of Cd in the soil. Research findings, therefore, suggest that the combined application of PGPR (B. mycoides PM35) and TiO₂⎯NPs can ameliorate Cd toxicity in H. vulgare, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Interactive effect of 24-epibrassinolide and plant growth promoting rhizobacteria inoculation restores photosynthetic attributes in Brassica juncea L. under chlorpyrifos toxicity

Chlorpyrifos (CP) is a commonly used organophosphorous pesticide that is frequently utilised in the agricultural industry because of its great efficiency and inexpensive cost. The focus of the present study was to assess the impact of CP toxicity on Brassica juncea L. and to unravel the ameliorative potential of phytohormone, 24-epibrassinolide (EBL) mediated plant-microbe (Pseudomonas aeruginosa (B1), Burkholderia gladioli (B2)) interaction in B. juncea L. The maximum significant increment in the total chlorophyll, carotenoids, xanthophyll, anthocyanin and flavonoid content with EBL and B2 treatment in CP stressed B. juncea seedlings on spectrophotometric analysis were observed. Autofluorescence imaging of photosynthetic pigments i.e. chlorophyll, carotenoids, and total phenols with confocal microscopy showed maximum fluorescence with EBL and B2. Furthermore, when compared to CP stressed seedlings, scanning electron microscopy (SEM) study of the abaxial surface of leaves revealed a recovery in stomatal opening. The supplementation of EBL and PGPR (plant growth promoting rhizobacteria) improved the level of psb A (D1 subunit PSII) and psb B (CP 47 subunit of PSII) genes expression. The expression analysis of chalcone synthase (CHS), Phenylalanine ammonialyase (PAL), Phyotene synthase (PSY) with RT-PCR system showed up-regulation in the expression when supplemented with EBL and PGPR. As a result, the current study suggests that EBL and PGPR together, can reduce CP-induced toxicity in B. juncea seedlings and recovering the seedling biomass.

Assessment of health risk, genotoxicity, and thiol compounds in Trigonella foenum-graecum (Fenugreek) under arsenic stress

Arsenic (As) traces have been reported worldwide in vegetables and crops cultivated in As-polluted soils. Being carcinogenic, the presence of As in edibles is of great concern as it ultimately reaches humans and animals through the food chain. Besides, As toxicity adversely affects the growth, physiology, metabolism, and productivity of crops. In the present study, Trigonella foenum-graecum (Fenugreek) was exposed to the As stress (0, 50, 100, and 150 μM sodium arsenate) for a week. Further, evaluation of As accumulation in roots and shoots, magnitude and visualization of oxyradicals, and thiol-based defence offered by Fenugreek was assessed. The root and leaf accumulated 258-453 μg g^-1 dry wt (DW) and 81.4-102.1 μg g^-1 DW of As, respectively. An arsenic-mediated decline in the growth index and increase in oxidative stress was noted. Arsenic stress modulated the content of thiol compounds; especially cysteine content increased from 0.36 to 0.43 µmole g^-1 FW protein was noted. Random Amplified Polymorphic DNA (RAPD)-based analysis showed DNA damage in As-treated plants. Health risk assessment parameters showed that As concentration in the consumable plant shoot was below the critical hazard level (hazard quotient < 1). Moreover, T. foenum-graecum showed varied responses to As-induced oxidative stress with applied concentrations (150 μM being more toxic than lower concentrations). In addition, the RAPD profile and level of thiol compounds were proved significant biomarkers to assess the As toxicity in plants. The conclusion of this study will help users of fenugreek to have a clue and create awareness regarding the consumption.

Could nitrogen compounds be indicators of tolerance to high doses of Cu and Fe in the cultivation of Leucaena leucocephala?

Nitrogen metabolism and the production of primary and secondary metabolites vary according to biotic and abiotic factors such as trace elements (TE) stress, and can, therefore, be considered biomarkers. The present study evaluated the effect of copper (Cu) and iron (Fe) TE, separately, on the metabolism of nitrogen compounds and biomass production, partitioned into shoot and roots of Leucaena leucocephala (Lam.) de Wit., and identified possible defense mechanisms linked to nitrogen metabolism. At 120 days of cultivation, the biomass production of L. leucocephala was higher when exposed to excess Fe than Cu. Nonetheless, the biomass gain (%) of plants exposed to Cu was higher, especially the biomass gains in roots. The tolerance and biomass production of L. leucocephala is related to the regulation of nitrogen metabolism and production of secondary metabolites. The biochemistry of plant metabolism against the excess of Cu and Fe TE manifested similarly, but with some specifics regarding the chemical nature of each metal. There was a reduction in the content of ureides and proteins and an increase in amino acids in the roots in relation to the increase in Cu and Fe concentrations. There was low accumulation of proline in the roots in treatments 400 and 500 mg/dm³ compared to the control for both TE. On the other hand, the total phenolic compounds in the roots increased. Our results indicate that the increased synthesis of amino acids and the accumulation of phenolic compounds is involved in the tolerance of L. leucocephala to Cu and Fe.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Ecotoxicological effects and bioaccumulation in Eichhornia crassipes induced by long-term exposure to triclosan

In this study, the ecotoxicological effects and bioaccumulation of triclosan (TCS) in Eichhornia crassipes (E. crassipes) were investigated with 28 d exposure experiments. The results showed that chlorophyll content was increased after 7 d exposure to 0.05-0.1 mg L^-1 TCS, while it was inhibited significantly by 0.5 mg L^-1 TCS after 21 d exposure. The concentrations of soluble protein in the leaves increased during the initial stage (7 d and 14 d), whereas they decreased during 21 d and 28 d. The concentrations of soluble protein in the roots gradually reduced during the exposure time. The antioxidant enzyme activities in roots decreased continually with the exposure time. However, the antioxidant enzyme (SOD and CAT) activities in leaves decreased after exposure longer than 14 d. Moreover, differentially expressed genes (DEGs) were observed in the root of E. crassipes after a 28 d exposure to 0.5 mg L^-1 TCS, with 11023 DEGs down-regulated and 3947 DEGs up-regulated. 5 SOD down-regulated genes and 3 CAT down-regulated genes were identified from transport and catabolism in cellular processes. After 28 d exposure, the TCS content in roots and leaves stressed by 0.5 mg L^-1 TCS were up to 13.04 μg g^-1 and 1.97 μg g^-1, respectively. SOD in leaves was negatively correlated with TCS content in leaves, CAT in roots was negatively correlated with TCS content in roots. These results provide experimental data to assess the ecological risk of TCS with long exposure in aquatic systems.

Benzylaminopurine and Abscisic Acid Mitigates Cadmium and Copper Toxicity by Boosting Plant Growth, Antioxidant Capacity, Reducing Metal Accumulation and Translocation in Bamboo [Pleioblastus pygmaeus (Miq.)] Plants

An in vitro experiment was conducted to determine the influence of phytohormones on the enhancement of bamboo resistance to heavy metal exposure (Cd and Cu). To this end, one-year-old bamboo plants (Pleioblastus pygmaeus (Miq.) Nakai.) contaminated by 100 µM Cd and 100 µM Cu both individually and in combination were treated with 10 µM, 6-benzylaminopurine and 10 µM abscisic acid. The results revealed that while 100 µM Cd and 100 µM Cu accelerated plant cell death and decreased plant growth and development, 10 µM 6-benzylaminopurine and 10 µM abscisic acid, both individually and in combination, increased plant growth by boosting antioxidant activities, non-antioxidants indices, tyrosine ammonia-lyase activity (TAL), as well as phenylalanine ammonia-lyase activity (PAL). Moreover, this combination enhanced protein thiol, total thiol, non-protein, glycine betaine (GB), the content of proline (Pro), glutathione (GSH), photosynthetic pigments (Chlorophyll and Carotenoids), fluorescence parameters, dry weight in shoot and root, as well as length of the shoot. It was then concluded that 6-benzyl amino purine and abscisic acid, both individually and in combination, enhanced plant tolerance under Cd and Cu through several key mechanisms, including increased antioxidant activity, improved photosynthesis properties, and decreased metals accumulation and metal translocation from root to shoot.

Proteomic analysis of T. qataranse exposed to lead (Pb) stress reveal new proteins with potential roles in Pb tolerance and detoxification mechanism

Soil lead (Pb) contamination is one of the environmental problems facing the modern world. Sources of Pb in soil include industrial activities such as mining and smelting processes, agricultural activities such as application of insecticide and municipal sewage sludges, and urban activities such as use of lead in gasoline, paints, and other materials. Phytoremediation is the direct use of living green plants and is an effective, cheap, non-invasive, and environmentally friendly technique used to transfer or stabilize all the toxic metals and environmental pollutants in polluted soil or groundwater. Current work in this area is invested in elucidating mechanisms that underpin toxic-metal tolerance and detoxification mechanisms. The present study aims to gain insight into the mechanisms of Pb tolerance in T. qataranse by comparative proteomics. MALDI-TOF/MS and in silico proteome analysis showed differential protein expression between treated (50 mg kg^⎯1 Pb) and untreated (0 mg kg^⎯1 Pb) T. qataranse. A total of eighty-six (86) differentially expressed proteins, most of which function in ion and protein binding, antioxidant activity, transport, and abiotic response stress, were identified. In addition, essential stress-regulating metabolic pathways, including glutathione metabolism, cellular response to stress, and regulation of HSF1-mediated heat shock response, were also enriched. Also, at 52- and 49-kDa MW band areas, up to six hypothetical proteins with unknown functions were identified. Of these, protein AXX17_AT2G26660 is highly rich in glycine amino acid residues (up to 76%), suggesting that it is a probable glycine-rich protein (GRP) member. Although GRPs are known to be involved in plant defense against abiotic stress, including salinity and drought, there is no report on their role on Pb tolerance and or detoxification in plants. Further enrichment analysis in the current study reveals that the hypothetical proteins do not interact with known proteins and are not part of any enriched pathway. However, additional research is needed to functionally validate the role of the identified proteins in Pb detoxification mechanism.

Short-term responses of Spinach (Spinacia oleracea L.) to the individual and combinatorial effects of Nitrogen, Phosphorus and Potassium and silicon in the soil contaminated by boron

While of lesser prevalence than boron (B) deficient soils, B-rich soils are important to study as they can cause B toxicity in the field and subsequently decrease crop yields in different regions of the world. We have conducted the present study to examine the role of the individual or combined application of silicon (Si) and NPK fertilizer in B-stressed spinach plants (Spinacia oleracea L.). S. oleracea seedlings were subjected to different NPK fertilizers, namely, low NPK (30 kg ha-2) and normal NPK (60 kg ha-2)], which were also supplemented by Si (3 mmol L-1), for varying levels of B in the soil i.e., 0, 250, and 500 mg kg-1. Our results illustrated that the increasing levels of B in the soil caused a substantial decrease in the plant height, number of leaves, number of stems, leaf area, plant fresh weight, plant dry weight, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, magnesium content in the roots, magnesium contents in the shoots, phosphorus content in the roots, phosphorus content in the leaves in the shoots, iron content in the roots, iron content in the shoots, calcium content in the roots, and calcium content in the shoots. However, B toxicity in the soil increased the concentration of malondialdehyde, hydrogen peroxide, and electrolyte leakage which were also manifested by the increasing activities of enzymatic [superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)], and non-enzymatic antioxidants (phenolic, flavonoid, ascorbic acid, and anthocyanin content). B toxicity in the soil further increased the concentration of organic acids in the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid, and fumaric acid. The addition of Si and fertilizer levels in the soil significantly alleviated B toxicity effects on S. oleracea by improving photosynthetic capacity and ultimately plant growth. The increased activity of antioxidant enzymes in Si and NPK-treated plants seems to play a role in capturing stress-induced reactive oxygen species, as was evident from the lower levels of oxidative stress indicators, organic acid exudation, and B concentration in the roots and shoots of Si and NPK-treated plants. Research findings, therefore, suggested that the Si and NPK application can ameliorate B toxicity in S. oleracea seedlings and result in improved plant growth and composition under metal stress as depicted by the balanced exudation of organic acids.

Impact of Plantago ovata Forsk leaf extract on morpho-physio-biochemical attributes, ions uptake and drought resistance of wheat (Triticum aestivum L.) seedlings

The present study was conducted to examine the potential role of Plantago ovata Forsk leaf extract (POLE) which was applied at various concentration levels (control, hydropriming, 10, 20, 30, and 40% POLE) to the wheat (Triticum aestivum L.) seedlings. Drought stressed was applied at 60% osmotic potential (OM) to the T. aestivum seedlings to study various parameters such as growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress and response of various antioxidants and nutritional status of the plants. Various growth parameters such as gaseous exchange attributes, antioxidants and nutritional status of T. aestivum were investigated in this study. It was evident that drought-stressed condition had induced a negative impact on plant growth, photosynthetic pigment, gaseous exchange attributes, stomatal properties, and ion uptake by different organs (roots and shoots) of T. aestivum. The decrease in plant growth resulted from oxidative stress and overcome by the antioxidant (enzymatic and non-enzymatic) compounds, since their concentration increased in response to dehydration. Seed priming with POLE positively increased plant growth and photosynthesis, by decreasing oxidative stress indicators and increasing activities of antioxidant (enzymatic and non-enzymatic) compounds, compared to the plants which were grown without the application of POLE. Our results also depicted that optimum concentration of POLE for T. aestivum seedlings under drought condition was 20%, while further increase in POLE (30 and 40%) induced a non-significant (P < 0.05) effect on growth (shoot and root length) and biomass (fresh and dry weight) of T. aestivum seedling. Here we concluded that the understanding of the role of seed priming with POLE in the increment of growth profile, photosynthetic measurements and nutritional status introduces new possibilities for their effective use in drought-stressed condition and provides a promising strategy for T. aestivum tolerance against drought-stressed condition.

Heavy Metal Accumulation and Phytoremediation Potentiality of Some Selected Mangrove Species from the World's Largest Mangrove Forest

Toxic metal pollution is a global issue, and the use of metal-accumulating plants to clean contaminated ecosystems is one of the most rapidly growing ecologically beneficial and cost-effective technologies. In this study, samples of sediment and three mangrove species (Excoecaria agallocha, Avicennia officinalis, Sonneratia apetala) were collected from the world’s largest mangrove forest (along the Northern Bay of Bengal Coast) with the aim of evaluating metal concentrations, contamination degrees, and phytoremediation potentiality of those plants. Overall, the heavy metals concentration in sediment ranged from Cu: 72.41−95.89 mg/kg; Zn: 51.28−71.20 mg/kg; Fe: 22,760−27,470 mg/kg; Mn: 80.37−116.37 mg/kg; Sr: 167.92−221.44 mg/kg. In mangrove plants, the mean concentrations were in the order of E. agallocha > A. officinalis > S. apetala. The mean (± SD) concentration of each metal in the plant tissue (root) was found following the descending order of Fe (737.37 ± 153.06) > Mn (151.13 ± 34.26) > Sr (20.98 ± 6.97) > Cu (16.12 ± 4.34) > Zn (11.3 ± 2.39) mg/kg, whereas, in the leaf part, the mean concentration (mg/kg) of each metal found in the order of Fe (598.75 ± 410.65) > Mn (297.27 ± 148.11) > Sr (21.40 ± 8.71) > Cu (14.25 ± 2.51) > Zn (12.56 ± 2.13). The contamination factor (CF) values for the studied metals were in the descending order of Cu > Sr > Zn > Fe > Mn. The values of Igeo (Geo-accumulation index) and CF showed that the area was unpolluted to moderately polluted by Zn, Fe, Mn, Cu and Sr. Enrichment factor (EF) values in both sampling stations portrayed moderate to minimum enrichment. Phytoremediation potentiality of the species was assessed by bio-concentration factor (BCF) and translocation factor (TF). BCF values showed less accumulation for most of the heavy metals (<1) except Mn which was highly accumulated in all mangrove plants. The translocation factor (TF) values depicted that most of the heavy metals were strongly accumulated in plant tissues (>1). However, the BCF value depicts that Mn was highly bioconcentrated in E. agallocha, but the translocation on leaves tissue were minimum, which reveals that E. agallocha is phytoextractor for Mn, and accumulated in root tissues. All the examined plants can be used as phytoextractors as they have bioconcentration factors <1 and translocation factors >1. However, A. officinalis is clearly more suitable for metal extraction than S. apetala and E. agallocha in terms of hyper-metabolizing capabilities.

Response of Cajanus cajan to excess copper in the soil: tolerance and biomass production

Soil contamination by excess heavy metals or trace elements is a global concern, as these elements are highly bioaccumulated in living organisms, migrating throughout the food chain, and causing health problems. Sustainable technologies, using plants, have been increasingly studied and used to contain, reduce, or extract these elements from the soil. In this sense, it is essential to identify plant species that tolerate certain elements, present high biomass production and are resistant to adverse soil conditions. For this reason, we evaluated the biomass production and tolerance of Cajanus cajan in response to different concentrations of copper (30, 60, 120, and 240 mg/dm³, in addition to the control treatment) in the soil, as well as the effect of this metal on photosynthetic pigments and gas exchange. C. cajan was sown in soil previously contaminated with copper sulfate and cultivated in a greenhouse for 60 days after emergence. C. cajan is copper tolerant, approximately 88% copper is accumulated in the roots and therefore there is low copper translocation to the shoot, consequently, the chlorophyll content, the net photosynthesis rate, carbon assimilation, dry biomass, the root system development, and nodulation were not affected by copper. C. cajan can be explored in strategies to improve soil conditions and is a promising species in soil phytoremediation studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01203-6.

Hydrogen sulphide and nitric oxide mitigate the negative impacts of waterlogging stress on wheat (Triticum aestivum L.)

Nitric oxide (NO) and hydrogen sulphide (H₂ S) are important gaseous signalling molecules that regulate key physiochemical mechanisms of plants under environmental stresses. A number of attempts have been made to improve waterlogging tolerance in plants, but with limited success. Having said that, NO and H₂ S are vital signalling molecules, but their role in mitigating waterlogging effects on crop plants is not well established. We investigated the efficacy of exogenous NO and H₂ S to alleviate waterlogging effects in two wheat cultivars (Galaxy-2013 and FSD-2008). Waterlogging produced a noticeable reduction in plant growth, yield, chlorophyll, soluble sugars and free amino acids. Besides, waterlogging induced severe oxidative damage seen as higher cellular TBARS and H₂ O₂ content. Antioxidant enzyme activity increased together with a notable rise in Fe²⁺ and Mn²⁺ content. Proline content was higher in waterlogged plants compared with non-waterlogged plants. In contrast, waterlogging caused a substantial decline in endogenous levels of essential nutrients (K⁺ , Ca²⁺ and Mg²⁺ ). Waterlogged conditions led to Fe²⁺ and Mn²⁺ toxicity due to rapid reduction of Fe³⁺ and Mn³⁺ in the soil. Exogenous NO and H₂ S significantly protected plants from waterlogging effects by enhancing the oxidative defence and regulating nutritional status. Besides, the protective effects of exogenous NO were more prominent as compared with effects of H₂ S. Further, we did not study the effect of H₂ S and NO on photosynthetic attributes and expression of stress-related genes. Therefore, future studies should examine the effects of H₂ S and NO on wheat physiology and gene expression under waterlogging.

Zinc Oxide Nanoparticles and Their Biosynthesis: Overview

Zinc (Zn) is plant micronutrient, which is involved in many physiological functions, and an inadequate supply will reduce crop yields. Its deficiency is the widest spread micronutrient deficiency problem; almost all crops and calcareous, sandy soils, as well as peat soils and soils with high phosphorus and silicon content are expected to be deficient. In addition, Zn is essential for growth in animals, human beings, and plants; it is vital to crop nutrition as it is required in various enzymatic reactions, metabolic processes, and oxidation reduction reactions. Finally, there is a lot of attention on the Zn nanoparticles (NPs) due to our understanding of different forms of Zn, as well as its uptake and integration in the plants, which could be the primary step toward the larger use of NPs of Zn in agriculture. Nanotechnology application in agriculture has been increasing over recent years and constitutes a valuable tool in reaching the goal of sustainable food production worldwide. A wide array of nanomaterials has been used to develop strategies of delivery of bioactive compounds aimed at boosting the production and protection of crops. ZnO-NPs, a multifunctional material with distinct properties and their doped counterparts, were widely being studied in different fields of science. However, its application in environmental waste treatment and many other managements, such as remediation, is starting to gain attention due to its low cost and high productivity. Nano-agrochemicals are a combination of nanotechnology with agrochemicals that have resulted in nano-fertilizers, nano-herbicides, nano-fungicides, nano-pesticides, and nano-insecticides being developed. They have anti-bacterial, anti-fungal, anti-inflammatory, antioxidant, and optical capabilities. Green approaches using plants, fungi, bacteria, and algae have been implemented due to the high rate of harmful chemicals and severe situations used in the manufacturing of the NPs. This review summarizes the data on Zn interaction with plants and contributes towards the knowledge of Zn NPs and its impact on plants.

Spatial variations in the biochemical potential of okra [Abelmoschus esculentus L. (Moench)] leaf and fruit under field conditions

Okra (Abelmoschus esculentus L. (Moench) plays a significant role in humans nutrition because its fresh leaves, stems, flowers, pods and seeds, are used for multiple purposes. The present study attempted to determine the spatial variations in biochemical attributes of osmoprotectants and the oxidative defense system of okra plants. Samples of soil and okra plants (leaves and fruits) were collected from three different locations: Faisalabad region-1 (7 JB-I), Faisalabad region-2 (7 JB-II) and Pindi Bhattian. Chlorophyll contents, glycine betaine (GB), ascorbic acid (AsA), total phenolics, hydrogen peroxide (H2O2), proline, and malondialdehyde (MDA) contents were analyzed in the leaves and fruits of okra plants. Soil analyses showed that pH, electrical conductivity (EC), phosphorus (P), potassium (K), iron (Fe), and saturation of soil were higher in Faisalabad region 2, while organic matter, sand, Zn, and Cu were higher in the Pindi Bhattian region. The results from okra leaves showed that Pindi Bhattian had higher chlorophyll a, GB and H2O2 contents, while Faisalabad region 1 had a higher ratio of chlorophyll a/b compared to the other regions. However, Faisalabad regions 2 and 1 had higher leaf phenolic contents, Faisalabad regions 1 and 2 showed higher leaf proline contents, and Faisalabad region 2 possessed higher AsA and MDA contents. Analyses of okra fruits showed that Faisalabad region 2 had higher chlorophyll a and total chlorophyll contents, while Faisalabad region 1 had higher chlorophyll b contents. Faisalabad region 2 and Pindi Bhattian had higher ratios of chlorophyll a/b, and Faisalabad region 1 showed higher phenolic, AsA, H2O2, and MDA contents of okra fruit, whereas the Faisalabad regions exhibited higher proline and GB contents than the Pindi Bhattian region. Overall, okra leaves and fruits showed better responses in the Faisalabad regions, and these results may be used to screen for okra cultivars with better tolerance under different environmental conditions.

Development of phytoremediator screening strategy and exploration of Pennisetum aided chromium phytoremediation mechanisms in soil

Screening of chromium (Cr) phytoremediators (i.e., hyperaccumulator plants and accumulation plants) is essential for the phytoremediation of Cr-contaminated soils but less tackled previously. In this study, we proposed a stepwise strategy for screening Cr phytoremediators and explored tolerance mechanism of the screened species. To achieve effective screening of Cr phytoremediators, seed germination, hydroponic, and pot experiment were performed sequentially, and an improved indicator system was established accordingly. Pennisetum was selected from nine plants, with its high growth rate and Cr remediation efficiency successfully demonstrated in the field. Antioxidant enzymes (i.e., superoxide dismutase (SOD) and catalase (CAT)) and photosynthesis under Cr stress were monitored for tracking the tolerance mechanism. Results showed that the enhanced SOD and CAT contributed to the strong tolerance of Pennisetum to Cr. The SOD and CAT were positively correlated with net photosynthetic rate (Pn), resulting in a phenomenon that Cr had no significant effect on Pn of Pennisetum even at 400 mg kg^-1. The research findings helped obtain powerful Cr phytoremediators, deepen our understanding of the tolerance mechanisms associated with phytoremediation, and eventually facilitate effective Cr removal in soil.

S-Fertilizer (Elemental Sulfur) Improves the Phytoextraction of Cadmium through Solanum nigrum L

Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem due to the rapid development of the social economy. This study was carried out to assess the beneficial role of two different kinds of (S)-fertilizer in the phytoremediation of Cd contaminated soil through Solanum nigrum L. Gypsum (Gyp) and Elemental sulfur (ES) was applied alone and in combination with different ratios (0, 100:0, 0:100, 50:50 mg kg^-1) accompanied by different Cd levels (0, 25, 50 mg kg^-1). After seventy days of sowing, plants were harvested for determination of growth, physiological characteristics, oxidants and antioxidants, along with Cd uptake from different parts of the plant. Cd toxicity significantly inhibited growth, physiology and plant defence systems, and also increased Cd uptake in the roots and shoots of Solanum nigrum L. The application of Gyp 100 mg kg^-1 boosted plant growth and physiology along with oxidants and antioxidants activity as compared to ES 100 mg kg^-1 alone, and combine application of GYP+ES 50 + 50 mg kg^-1. The application of ES 100 mg kg^-1 showed an effective approach to decreasing Cd uptake as compared to Gyp 100 mg kg^-1. Overall results showed that the combined application of GYP+ES 50 + 50 mg kg^-1 significantly enhanced the phytoremediation potential of S. nigrum in Cd contaminated soil. Thus, it is highly recommended to apply the combined application of GYP+ES for phytoremediation of Cd contaminated soil.

Silicon Fertigation Regimes Attenuates Cadmium Toxicity and Phytoremediation Potential in Two Maize (Zea mays L.) Cultivars by Minimizing Its Uptake and Oxidative Stress

Silicon (Si) is an important plant-derived metabolite that is significantly involved in maintaining the stability of a plant’s metabiological, structural and physiological characteristics under the abiotic stressed environment. We conducted the present study using maize (Zea mays L.) cultivars (Sadaf and EV-20) grown in sand artificially contaminated with cadmium (500 µM) in Hoagland’s nutrient solution to investigate its efficiency. Results from the present study evidenced that the toxic concentration of Cd in sand significantly reduced shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight by 88, 94, 89, 86 99 and 99%, respectively, in Sadaf while decreasing by 98, 97, 93, 99, 84 and 91%, respectively, in EV-20. Similarly, Cd toxicity decreased total chlorophyll and carotenoid content in both varieties of Z. mays. Moreover, the activities of various antioxidants (superoxidase dismutase, peroxidase and catalase) increased under the toxic concentration of Cd in sand which was manifested by the presence of membrane permeability, malondialdehyde (MDA), and hydrogen peroxide (H2O2). Results additionally showed that the toxic effect of Cd was more severe in EV-20 compared with Sadaf under the same conditions of environmental stresses. In addition, the increased concentration of Cd in sand induced a significantly increased Cd accumulation in the roots (141 and 169 mg kg−1 in Sadaf and EV-20, respectively), and shoots (101 and 141 mg kg−1 in Sadaf and EV-20, respectively), while; EV-20 accumulated higher amounts of Cd than Sadaf, with the values for both bioaccumulation factor (BAF) and translocation factor (TF) among all treatments being less than 1. The subsequent negative results of Cd injury can be overcome by the foliar application of Si which not only increased plant growth and biomass, but also decreased oxidative damage induced by the higher concentrations of MDA and H2O2 under a Cd-stressed environment. Moreover, external application of Si decreased the concentration of Cd in the roots and shoots of plants, therefore suggesting that the application of Si can ameliorate Cd toxicity in Z. mays cultivars and results in improved plant growth and composition under Cd stress by minimizing oxidative damage to membrane-bound organelles.

Functions and strategies for enhancing zinc availability in plants for sustainable agriculture

Zinc (Zn), which is regarded as a crucial micronutrient for plants, and is considered to be a vital micronutrient for plants. Zn has a significant role in the biochemistry and metabolism of plants owing to its significance and toxicity for biological systems at specific Zn concentrations, i.e., insufficient or harmful above the optimal range. It contributes to several cellular and physiological activities of plants and promotes plant growth, development, and yield. Zn is an important structural, enzymatic, and regulatory component of many proteins and enzymes. Consequently, it is essential to understand the interplay and chemistry of Zn in soil, its absorption, transport, and the response of plants to Zn deficiency, as well as to develop sustainable strategies for Zn deficiency in plants. Zn deficiency appears to be a widespread and prevalent issue in crops across the world, resulting in severe production losses that compromise nutritional quality. Considering this, enhancing Zn usage efficiency is the most effective strategy, which entails improving the architecture of the root system, absorption of Zn complexes by organic acids, and Zn uptake and translocation mechanisms in plants. Here, we provide an overview of various biotechnological techniques to improve Zn utilization efficiency and ensure the quality of crop. In light of the current status, an effort has been made to further dissect the absorption, transport, assimilation, function, deficiency, and toxicity symptoms caused by Zn in plants. As a result, we have described the potential information on diverse solutions, such as root structure alteration, the use of biostimulators, and nanomaterials, that may be used efficiently for Zn uptake, thereby assuring sustainable agriculture.

Impact of foliar application of syringic acid on tomato (Solanum lycopersicum L.) under heavy metal stress-insights into nutrient uptake, redox homeostasis, oxidative stress, and antioxidant defense

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. However, accumulation of Pb in plant parts is very toxic for plant growth and decreases crop yield and productivity. In the present study, we have investigated the different concentrations of Pb in the soil i.e., [0 (no Pb), 50, and 100 mg kg^-1] to study plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators and the response of various antioxidants (enzymatic and non-enzymatic), nutritional status of the plant, organic acid exudation pattern and also Pb accumulation in the roots and shoots of the plants of two varieties of tomato (Solanum lycopersicum L.) i.e., Roma and Cchuas, grown under different levels of synergic acid [no spray (NS), water spray (WS), 0.3-0.5°μM]. Results from the present study showed that the increasing levels of Pb in the soil decreased non-significantly (P < 0.05) shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), and phosphorus (P) contents in the roots and shoots of the plants. However, Pb toxicity also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and electrolyte leakage (EL) which also induced increased the compounds of various enzymatic and non-enzymatic antioxidants and also organic acids exudation pattern in the roots such as fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents and increased the concentration of Pb in different parts of the plants. Results also show that the Cchuas showed better growth and development compared to Roma, under the same levels of Pb in the soil. The alleviation of Pb toxicity was induced by the application of synergic acid, and results showed that the application of synergic acid increased plant growth and biomass and also increased the gas exchange characteristics and antioxidant capacity in the roots and shoots of the plants. Research findings, therefore, suggested that synergic acid application can ameliorate Pb toxicity in S. lycopersicum varieties and result in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

Interactive effects of gibberellic acid and NPK on morpho-physio-biochemical traits and organic acid exudation pattern in coriander (Coriandrum sativum L.) grown in soil artificially spiked with boron

It was aimed to examine the role of gibberellic acid (GA₃) and NPK fertilizer in alleviating boron (B) toxicity in coriander (Coriandrum sativum L.) plants. Two weeks old C. sativum seedlings were subjected to different NPK fertilizers [low NPK (30 kg ha^-1) and normal NPK (60 kg ha^-1)], which were also supplied by GA₃ (50 mg L^-1), under varying levels of B i.e., 0, 200 and 400 mg kg^-1 in the soil. Results revealed that B toxicity led to a substantial decreased in the plant growth and biomass, photosynthetic pigments, gas exchange characteristics, sugars and essential nutrients in the roots and shoots of C. sativum seedlings. However, B toxicity boosted the production of reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of oxidative stress in C. sativum seedlings and was also manifested by hydrogen peroxide (H₂O₂) contents and electrolyte leakage (EL) to the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), non-enzymatic antioxidants like phenolic, flavonoid, ascorbic acid and anthocyanin contents and organic acids from the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid and fumaric acid contents were increased with the increasing levels of B in the soil. The application if NPK and GA₃ mitigated B toxicity by stimulated plant growth and biomass, photosynthetic efficiency, nutritional status and antioxidant machinery of the plant by decreasing MDA contents, H₂O₂ initiation and EL (%) in the roots and leaves of C. sativum seedlings. In addition, the application of NPK and GA₃ further decreased the organic acids exudation contents in the roots C. sativum seedlings. Research findings, therefore, suggested that NPK and GA₃ application can ameliorate B toxicity in C. sativum seedlings and resulted in improved plant growth and composition under B stress as depicted by balanced contents of organic acids.

Jute Responses and Tolerance to Abiotic Stress: Mechanisms and Approaches

Jute (Corchorus spp.) belongs to the Malvaceae family, and there are two species of jute, C. capsularis and C. olitorious. It is the second-largest natural bast fiber in the world according to production, which has diverse uses not only as a fiber but also as multiple industrial materials. Because of climate change, plants experience various stressors such as salt, drought, heat, cold, metal/metalloid toxicity, and flooding. Although jute is particularly adapted to grow in hot and humid climates, it is grown under a wide variety of climatic conditions and is relatively tolerant to some environmental adversities. However, abiotic stress often restricts its growth, yield, and quality significantly. Abiotic stress negatively affects the metabolic activities, growth, physiology, and fiber yield of jute. One of the major consequences of abiotic stress on the jute plant is the generation of reactive oxygen species, which lead to oxidative stress that damages its cellular organelles and biomolecules. However, jute’s responses to abiotic stress mainly depend on the plant’s age and type and duration of stress. Therefore, understanding the abiotic stress responses and the tolerance mechanism would help plant biologists and agronomists in developing climate-smart jute varieties and suitable cultivation packages for adverse environmental conditions. In this review, we summarized the best possible recent literature on the plant abiotic stress factors and their influence on jute plants. We described the possible approaches for stress tolerance mechanisms based on the available literature.

Foliar application of ascorbic acid enhances salinity stress tolerance in barley (Hordeum vulgare L.) through modulation of morpho-physio-biochemical attributes, ions uptake, osmo-protectants and stress response genes expression

Barley (Hordeum vulgare L.) is a major cereal grain and is known as a halophyte (a halophyte is a salt-tolerant plant that grows in soil or waters of high salinity). We therefore conducted a pot experiment to explore plant growth and biomass, photosynthetic pigments, gas exchange attributes, stomatal properties, oxidative stress and antioxidant response and their associated gene expression and absorption of ions in H. Vulgare. The soil used for this analysis was artificially spiked at different salinity concentrations (0, 50, 100 and 150 mM) and different levels of ascorbic acid (AsA) were supplied to plants (0, 30 and 60 mM) shortly after germination of the seed. The results of the present study showed that plant growth and biomass, photosynthetic pigments, gas exchange parameters, stomatal properties and ion uptake were significantly (p < 0.05) reduced by salinity stress, whereas oxidative stress was induced in plants by generating the concentration of reactive oxygen species (ROS) in plant cells/tissues compared to plants grown in the control treatment. Initially, the activity of antioxidant enzymes and relative gene expression increased to a saline level of 100 mM, and then decreased significantly (P < 0.05) by increasing the saline level (150 mM) in the soil compared to plants grown at 0 mM of salinity. We also elucidated that negative impact of salt stress in H. vulgare plants can overcome by the exogenous application of AsA, which not only increased morpho-physiological traits but decreased oxidative stress in the plants by increasing activities of enzymatic antioxidants. We have also explained the negative effect of salt stress on H. vulgare can decrease by exogenous application of AsA, which not only improved morpho-physiological characteristics, ions accumulation in the roots and shoots of the plants, but decreased oxidative stress in plants by increasing antioxidant compounds (enzymatic and non-enzymatic). Taken together, recognizing AsA's role in nutrient uptake introduces new possibilities for agricultural use of this compound and provides a valuable basis for improving plant tolerance and adaptability to potential salinity stress adjustment.

Negative impact of long-term exposure of salinity and drought stress on native Tetraena mandavillei L

Tetraena mandavillei L. is a perennial shrub native to the Middle Eastern countries of Asia, which is extensively regarded as a drought-tolerant plant. However, the plant reduces growth and biomass when grown in high concentrations of sodium chloride in the soil. We conducted a pot experiment to influence the negative impact of different levels of salinity (0, 10, and 20 dSm^-1 ) and drought stress (100, 80, 60, and 40% water field capacity), to study different growth-related parameters, physiological alterations and ion uptake by T. mandavillei. Both salinity and drought stress caused a negative impact by affecting several attributes of T. mandavillei, but the plants showed some resistance against drought stress conditions in terms of growth and biomass. In addition to that, we noticed that a combinatorial and individual impact of drought and salinity stress decreased photosynthetic pigments and gas exchange parameters in T. mandavillei. Results also depicted that the combination of the abiotic stress conditions drought and salinity induced reactive oxygen species (ROS), indicating that the plants undergo oxidative damaged. However, due to the active plant defense system, the plant enhanced its performance under abiotic stress conditions, but due to the severe drought condition (40% water field capacity), a significant (P < 0.05) decrease in the activities of antioxidant compounds was caused. Furthermore, osmolytes also increased under both salinity and drought stress conditions in this study. Our results also showed that increased salinity and drought stress in the soil caused a significant increase in sodium (Na⁺ ) and chloride (Cl^- ) ions in roots and shoots of T. mandavillei. In contrast to that, the contents of Calcium (Ca²⁺ ) and potassium (K⁺ ) were decreased in all organs of the plants with increasing levels of salinity and drought stress. Taken together, T. mandavillei can be classified as a facultative halophyte with the ability to tolerate drought stress and using salt accumulation mechanisms to tolerate salinity stress.

Effect of different vegetation on copper accumulation of copper-mine abandoned land in tongling, China

Mining activity and abandoned mine land are one of the major sources of heavy metal pollution. Thus, ecological rehabilitation of abandoned mine lands is crucial to control heavy metal pollution. This research aims to explore the influencing factors and effects of different vegetation on copper (Cu) accumulation and soil amelioration. In this study, the abandoned land of Tongguanshan Cu mine in Tongling city, Anhui province, China, was chosen as the test area, and nine sampling points were established. Samples of soil and plants were collected from each plot, and the impacts of Cu pollution on soil enzymes and other features were analyzed, as well as the correlation between Cu accumulation of different plants and soil properties. The results showed that Cu content of soil in the Tongguanshan area varied greatly with the depth of the soil profile. Moreover, Cu in the soil can inhibit soil enzyme activities; and the correlation coefficients of total soil Cu with urease and catalase were -0.83 and -0.73, respectively. Clearly, the accumulation of Cu in plants was positively correlated with Cu content in soil. It was found that Pueraria lobata had the best remediation effect on soil Cu pollution in a short period of time. Hence the preliminary tests clearly indicate that phytoremediation in abandoned mine lands can not only reduce heavy metal pollution, but also enhance soil nutrition and enzyme activity, helping to ameliorate degraded land and promote regional socioeconomic sustainable development.

Anatomical adaptations and ionic homeostasis in aquatic halophyte Cyperus laevigatus L. Under high salinities

Salinity is extremely hazardous to agriculture worldwide and its expanding constantly. Soil of almost 100 countries facing salinity problem including Pakistan. Cyperus laevigatus also act as salinity indicator species is a naturally adapted halophyte dispersed in subtropical regions of world. Six populations of C. laevigatus were collected from different saline habitats to evaluate adaptations regarding anatomical and physiological characteristics. C. laevigatus is perfectly adapted to harsh environmental conditions like dry barren soils, saline lakes, hyper-saline wetlands and salt marshes. Ecological success of this species is due to plasticity in physiological and anatomical characteristics to adapt variable environmental conditions. C. laevigatus is a halophyte, exhibited increased biomass production in moderately saline habitat. Higher uptake of K+ occurs to compensate the uptake of Na+ ion contents, a striking feature of salt-tolerant and halophytic species. Accumulation of osmoprotectants like proline, free amino acids, soluble sugar and protein contribute significantly to osmotic adjustment. Stem thickness enhanced as salinity level of habitat increased to store water in parenchymatous tissues under physiological drought. Intensive sclerification in root cortex provide mechanical strength to plant as well as prevent the radial leakage of water. Well-developed aerenchyma, increased vascular bundle area, broader vessels, small and dense stomata are critical to cope with environmental hazards. Population of Jahlar lake showing maximum biomass production indicate that this species grows better in moderate salinities. Therefore, this species will prove very useful for revegetation of salt affected rangeland and prairies by direct growth of such halophytic ecotypes.

Copper: uptake, toxicity and tolerance in plants and management of Cu-contaminated soil

Copper (Cu) is an essential mineral nutrient for the proper growth and development of plants; it is involved in myriad morphological, physiological, and biochemical processes. Copper acts as a cofactor in various enzymes and performs essential roles in photosynthesis, respiration and the electron transport chain, and is a structural component of defense genes. Excess Cu, however, imparts negative effects on plant growth and productivity. Many studies have summarized the adverse effects of excess Cu on germination, growth, photosynthesis, and antioxidant response in agricultural crops. Its inhibitory influence on mineral nutrition, chlorophyll biosynthesis, and antioxidant enzyme activity has been verified. The current review focuses on the availability and uptake of Cu by plants. The toxic effects of excess Cu on seed germination, plant growth and development, photosynthesis, and antioxidant response in plants are discussed. Plant tolerance mechanisms against Cu stress, and management of Cu-contaminated soils are presented.

Regression models to stratify the copper toxicity responses and tolerance mechanisms of Glycine max (L.) Merr. plants

MAIN CONCLUSION

Root antioxidant defense, restricted root-to-shoot Cu translocation, altered nutrient partition, and leaf gas exchange adjustments occurred as tolerance mechanisms of soybean plants to increasing soil Cu levels. The intensive application of copper (Cu) fungicides has been related to the accumulation of this metal in agricultural soils. This study aimed to evaluate the effects of increasing soil Cu levels on soybean (Glycine max) plants. Soybean was cultivated under greenhouse conditions in soils containing different Cu concentrations (11.2, 52.3, 79.4, 133.5, 164.0, 205.1, or 243.8 mg kg-1), and biochemical and morphophysiological plant responses were analyzed through linear and nonlinear regression models. Although Cu concentrations around 50 mg kg-1 promoted some positive effects on the initial development of soybean plants (e.g., increased root length and dry weight), these Cu concentrations also induced root oxidative stress and activated defense mechanisms (such as the induction of antioxidant response, N and S accumulation in the roots). At higher concentrations, Cu led to growth inhibition (mainly of the root), nutritional imbalance, and damage to the photosynthetic apparatus of soybean plants, resulting in decreased CO2 assimilation and stomatal conductance. In contrast, low translocation of Cu to the leaves, conservative water use, and increased carboxylation efficiency contributed to the partial mitigation of Cu-induced stress. These responses allowed soybean plants treated with Cu levels in the soil as high as 90 mg kg-1 to maintain growth parameters higher than or similar to those of plants in the non-contaminated soil. These data provide a warning for the potentially deleterious consequences of the increasing use of Cu-based fungicides. However, it is necessary to verify how the responses to Cu contamination are affected by different types of soil and soybean cultivars.

Synergistic effect of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the establishment of vegetation cover and amelioration of mine tailings

Mine tailings pose a huge hazard for environmental and human health, and the establishment of vegetation cover is crucial to reduce pollutant dispersion for the surroundings. However, their hostile physicochemical conditions hamper plant growth, compromising phytoremediation strategies. This study aims to investigate the role of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the improvement of mine tailings properties and Lolium perenne L. (ryegrass) growth. Plants were grown in mine tailings mixed with an agricultural soil (1:1), 10% compost, and supplied with two different inorganic amendments - rock phosphate (6%) or lime (3%), and inoculated with the rhizobacterial strains Advenellakashmirensis BKM20 (B1) and Mesorhizobium tamadayense BKM04 (B2). The application of organo-mineral amendments ameliorated tailings characteristics, which fostered plant growth and further enhanced soil fertility and microbial activity. These findings were consistent with the increase of total organic carbon levels, with the higher numbers of heterotrophic and phosphate solubilizing bacteria, and higher dehydrogenase and urease activities, found in these substrates after plant establishment. Plant growth was further boosted by PGPR inoculation, most noticeable by co-inoculation of both strains. Moreover, inoculated plants showed increased activities for several antioxidant enzymes (catalase, peroxidase, polyphenoloxidase, and glutathione reductase) which indicate a reinforced antioxidant system. The application of agricultural soil, compost and lime associated with the inoculation of a mixture of PGPR proved to enhance the establishment of vegetation cover, thus promoting the stabilization of Kettara mine tailings. Nonetheless, further studies are needed in order to confirm its effectiveness under field conditions.

Copper bioavailability, uptake, toxicity and tolerance in plants: A comprehensive review

Copper (Cu) is an essential element for humans and plants when present in lesser amount, while in excessive amounts it exerts detrimental effects. There subsists a narrow difference amid the indispensable, positive and detrimental concentration of Cu in living system, which substantially alters with Cu speciation, and form of living organisms. Consequently, it is vital to monitor its bioavailability, speciation, exposure levels and routes in the living organisms. The ingestion of Cu-laced food crops is the key source of this heavy metal toxicity in humans. Hence, it is necessary to appraise the biogeochemical behaviour of Cu in soil-plant system with esteem to their quantity and speciation. On the basis of existing research, this appraisal traces a probable connexion midst: Cu levels, sources, chemistry, speciation and bioavailability in the soil. Besides, the functions of protein transporters in soil-plant Cu transport, and the detrimental effect of Cu on morphological, physiological and nutrient uptake in plants has also been discussed in the current manuscript. Mechanisms related to detoxification strategies like antioxidative response and generation of glutathione and phytochelatins to combat Cu-induced toxicity in plants is discussed as well. We also delimits the Cu accretion in food crops and allied health perils from soils encompassing less or high Cu quantity. Finally, an overview of various techniques involved in the reclamation and restoration of Cu-contaminated soils has been provided.

Application of abscisic acid and 6-benzylaminopurine modulated morpho-physiological and antioxidative defense responses of tomato (Solanum lycopersicum L.) by minimizing cobalt uptake

A hydroponic study was conducted to determine the effects of single and/or combined application of different doses (0, 5 and 10 μM L^-1) of abscisic acid (ABA) and 6-benzylaminopurine (BAP) on cobalt (Co) accumulation, morpho-physiological and antioxidative defense attributes of tomato (Solanum lycopersicum L.) exposed to severe Co stress (400 μM L^-1). The single Co treatment (T1), prominently decreased tomato growth, relative water contents, photosynthetic pigments (chlorophyll a and chlorophyll b), whereas enhanced oxidative stress and Co accumulation in shoot and root tissues. Nonetheless, the supplementation of ABA and 6-BAP via nutrient media significantly (P < 0.05) enhanced plant biomass, root morphology and chlorophyll contents of tomato, compared to only Co treatment (T1). Moreover, the oxidative stress indicators such as malondialdehyde, proline and H₂O₂ contents were ameliorated through activation of enzymatic antioxidant activities i.e. ascorbate peroxidase, superoxide dismutase, catalase, and peroxidase, in growth modulator treatments in comparison to T1. The Co uptake, translocation (TF) and bioaccumulation factor (BAF) by shoot and root tissues of tomato were significantly reduced under all the treatments than that of T1. The supply of 6-BAP alone or in combination with ABA at 10 μM L^-1 application (T7) rate was found the most effective to reduce Co accumulation in the roots and shoots by 48.4% and 70.2% respectively than T1 treatment. It can be concluded that two plant growth modulators could improve the stress tolerance by inhibition of Co uptake in tomato plants.

Comparative transcriptomic analysis reveals key genes and pathways in two different cadmium tolerance kenaf (Hibiscus cannabinus L.) cultivars

Soil cadmium (Cd) contamination has become a massive environmental problem. Kenaf is an industrial fiber crop with high tolerance to heavy metals and could be potentially used for soil phytoremediation. However, the molecular mechanism of Cd in kenaf tolerance remains largely unknown. In the present study, using two contrasting Cd sensitive kenaf (GH and YJ), the key factors accounting for differential Cd tolerance were investigated. GH has a stronger Cd transport and accumulation ability than YJ. In addition, physiological index investigation on malondialdehyde (MDA) contents and antioxidant enzyme (SOD, POD, and CAT) activities showed GH has a stronger detoxification capacity than YJ. Furthermore, the cell ultrastructure of GH is more stable than that of YJ under Cd stress. Transcriptome analysis revealed 2221 (689 up and 1532 down) and 3321 (2451 up and 870 down) genes were differentially expressed in GH and YJ, respectively. More DEGs (differentially expressed genes) were characterized as up-regulated in GH, indicating GH is inclined to activate gene expression to cope with cadmium stress. GO and KEGG analyses indicate that DEGs were assigned and enriched in different pathways. Plenty of critical Cd-induced DEGs such as SOD2, PODs, MT1, DTXs, NRT1, ABCs, CES, AP2/ERF, MYBs, NACs, and WRKYs were identified. The DEGs involved pathways, including antioxidant, heavy metal transport or detoxification, substance transport, plant hormone and calcium signals, ultrastructural component, and a wide range of transcription factors were suggested to play crucial roles in kenaf Cd tolerance, and accounting for the difference in Cd stress sensitivities.

Glycinebetaine-Induced Alteration in Gaseous Exchange Capacity and Osmoprotective Phenomena in Safflower (Carthamus tinctorius L.) under Water Deficit Conditions

Several inorganic and organic compounds including glycine betaine (GB) are presently being used as an exogenous application to enhance tolerance in plants to different environmental stresses. The current study assessed to what extent exogenously applied GB could improve the gaseous exchange capacity and primary and secondary metabolites in two accessions (16178 and 16180) of safflower (Carthamus tinctorius L.) plants under drought stress. Three-week-old plants of both safflower accessions were subjected to well-watered (control) or water-deficit conditions (60% field capacity (FC)). Three levels of GB (control, 50 mM and 100 mM) were sprayed to the foliage of the control and stressed plants after one month of drought application. After two weeks of foliar application of GB, gas exchange characteristics and other biochemical parameters were determined. The results showed that water deficiency markedly suppressed plant biomass, chlorophyll contents, photosynthesis rate (A), water use efficiency (A/E), stomatal conductance (gs) and relative water contents (RWC) of both accessions of safflower, while it enhanced the levels of osmolytes (GB and proline), hydrogen peroxide (H2O2) and total phenolics. Foliar application of GB was effective in enhancing the plant biomass, chlorophyll contents, gs, sub-stomatal CO2 concentration (Ci), Ci/Ca ratio, osmolytes, H2O2, ascorbic acid (AsA), total phenolics and RWC in safflower plants under water shortage. Thus, exogenous application of GB could be used as an effective strategy to improve plant growth, photosynthetic attributes and secondary metabolites in safflower plants under water deficit conditions.

Interactive role of zinc and iron lysine on Spinacia oleracea L. growth, photosynthesis and antioxidant capacity irrigated with tannery wastewater

ABSTRACT

Untreated wastewater contains toxic amounts of heavy metals such as chromium (Cr), which poses a serious threat to the growth and physiology of plants when used in irrigation. Though, Cr is among the most widespread toxic trace elements found in agricultural soils due to various anthropogenic activities. To explore the interactive effects of micronutrients with amino acid chelators [iron-lysine (Fe-lys) and zinc-lysine (Zn-lys)], pot experiments were conducted in a controlled environment, using spinach (Spinacia oleracea L.) plant irrigated with tannery wastewater. S. oleracea was treated without Fe and Zn-lys (0 mg/L Zn-lys and 0 mg/L Fe-lys) and also treated with various combinations of (interactive application) Fe and Zn-lys (10 mg/L Zn-lys and 5 mg/L Fe-lys), when cultivated at different levels [0 (control) 33, 66 and 100%) of tannery wastewater in the soil having a toxic level of Cr in it. According to the results, we have found that, high concentration of Cr in the soil significantly (P < 0.05) reduced plant height, fresh biomass of roots and leaves, dry biomass of roots and leaves, root length, number of leaves, leaf area, total chlorophyll contents, carotenoid contents, transpiration rate (E), stomatal conductance (gs), net photosynthesis (PN), and water use efficiency (WUE) and the contents of Zn and Fe in the plant organs without foliar application of Zn and Fe-lys. Moreover, phytotoxicity of Cr increased malondialdehyde (MDA) contents in the plant organs (roots and leaves), which induced oxidative damage in S. oleracea manifested by the contents of hydrogen peroxide (H₂O₂) and membrane leakage. The negative effects of Cr toxicity could be overturned by Zn and Fe-lys application, which significantly (P < 0.05) increase plant growth, biomass, chlorophyll content, and gaseous exchange attributes by reducing oxidative stress (H₂O₂, MDA, EL) and increasing the activities of various antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) catalase (CAT) and ascorbate peroxidase (APX). Furthermore, the supplementation of Zn and Fe-lys increased the contents of essential nutrients (Fe and Zn) and decreased the content of Cr in all plant parts compared to the plants cultivated in tannery wastewater without application of Fe-lys. Taken together, foliar supplementation of Zn and Fe-lys alleviates Cr toxicity in S. oleracea by increased morpho-physiological attributes of the plants, decreased Cr contents and increased micronutrients uptake by the soil, and can be an effective in heavy metal toxicity remedial approach for other crops.

Elucidating silicon-mediated distinct morpho-physio-biochemical attributes and organic acid exudation patterns of cadmium stressed Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem due to rapid development of social economy. Silicon (Si), being an important fertilizer element, has been found effective in enhancing plant tolerance against biotic and abiotic stresses. The present study investigated the extent to which different levels of Si modulated the Cd tolerance of Ajwain (Trachyspermum ammi L.) seedlings when maintained in artificially Cd spiked regimes. A pot experiment was conducted under controlled conditions for four weeks, by using sand, mixed with different levels of Cd i.e., 0, 1.5 and 3 mM together with the application of Si at 0, 1.5 and 3 mM levels to monitor different growth, gaseous exchange, oxidative stress, antioxidative responses, minerals accumulation, organic acid exudation patterns of T. ammi seedlings. Our results depicted that Cd addition to growth medium significantly decreased plant growth and biomass, gaseous exchange attributes and minerals uptake by T. ammi seedlings as compared to the plants grown without addition of Cd. However, Cd toxicity boosted the production of reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of oxidative stress in T. ammi seedlings and was also manifested by hydrogen peroxide (H₂O₂) contents and electrolyte leakage to the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) initially increased up to a Cd level of 1.5 mM but were significantly diminished at the highest Cd level of 3 mM. Results revealed that the anthocyanin and soluble proteins contents were decreased in seedlings grown under elevating Cd levels but increased the Cd accumulation of T. ammi roots and shoots. The negative impacts of Cd injury were reduced by the application of Si which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, minerals uptake together with diminished exudation of organic acids as well as oxidative stress indicators in roots and shoots of T. ammi by decreasing Cd retention in different plant parts. Research findings, therefore, suggested that Si application can ameliorate Cd toxicity in T. ammi seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

Foliar application of gibberellic acid endorsed phytoextraction of copper and alleviates oxidative stress in jute (Corchorus capsularis L.) plant grown in highly copper-contaminated soil of China

Copper (Cu) is an abundant essential micronutrient element in various rocks and minerals and is required for a variety of metabolic processes in both prokaryotes and eukaryotes. However, excess Cu can disturb normal development by adversely affecting biochemical reactions and physiological processes in plants. The present study was conducted to explore the potential of gibberellic acid (GA₃) on fibrous jute (Corchorus capsularis L.) seedlings grown on Cu mining soil obtained from Hubei Province China. Exogenous application of GA₃ (10, 50, and 100 mg/L) on 60-day-old seedlings of C. capsularis which was able to grow in highly Cu-contaminated soil (2221 mg/kg) to study different morphological, physiological, and Cu uptake and accumulation in different parts of C. capsularis seedlings. According to the results, increasing concentration of GA₃ (more likely 100 mg/L) alleviates Cu toxicity in C. capsularis seedlings by increasing plant growth, biomass, photosynthetic pigments, and gaseous exchange attributes. The results also showed that exogenous application of GA₃ reduced oxidative stress in C. capsularis seedlings by the generation of extra reactive oxygen species (ROS). The reduction in oxidative stress in C. capsularis seedlings is because that plant has strong enzymatic antioxidants [superoxidase dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT)], which ultimately increased their activities to overcome oxidative damage in the cells/tissues. In addition to the plant growth, biomass, and photosynthesis, foliar application of GA₃ also helps to increase metal (Cu) concentration in different parts of the plants when compared to 0 mg/L of application of GA₃. From these findings, we can conclude that foliar application of GA₃ plays a promising role in reducing ROS generation in the plant cells/tissues and increased phytoextraction of Cu in different plant parts. However, more investigation is needed on field experiments to find a combination of GA₃ with a very higher concentration of Cu using fibrous C. capsularis.