Phytoremediation of Heavy Metals: An Indispensable Contrivance in Green Remediation Technology

Biotechnological approaches for enhancement of heavy metal phytoremediation capacity of plants

Heavy metals are extremely hazardous for human health due to their toxic effects. They are non-biodegradable in nature, thus remain in the environment and enter and accumulate in the human body through biomagnification; hence, there is a serious need of their remediation. Phytoremediation has emerged as a green, sustainable, and effective solution for heavy metal removal and many plant species could be employed for this purpose. Plants are able to sequester substantial quantity of heavy metals, in some cases thousands of ppm, due to their robust physiology enabling high metal tolerance and anatomy supporting metal ion accumulation. Identification and modification of potential target genes involved in heavy metal accumulation have led to improved phytoremediation capacity of plants at the molecular level. The introduction of foreign genes through genetic engineering approaches has further enhanced phytoremediation capacity manifolds. This review gives an insight towards improving the phytoremediation efficiency through a better understanding of molecular mechanisms involved, expression of different proteins, genetic engineering approaches for transgenic production, and genetic modifications. It also comprehends novel omics tools such as genomics, metabolomics, proteomics, transcriptomics, and genome editing technologies for improvement of phytoremediation ability of plants.

The effects of monoculture and intercropping on photosynthesis performance correlated with growth of garlic and perennial ryegrass response to different heavy metals

BACKGROUND

The potential of phytoremediation using garlic monoculture (MC) and intercropping (IC) system with perennial ryegrass to enhance the uptake of cadmium (Cd), chromium (Cr), and lead (Pb) were investigated.

RESULTS

Positive correlations were found between MC and IC systems, with varying biomass. Production of perennial ryegrass was affected differently depending on the type of toxic metal present in the soil. Root growth inhibition was more affected than shoot growth inhibition. The total biomass of shoot and root in IC was higher than MC, increasing approximately 3.7 and 2.9 fold compared to MC, attributed to advantages in root IC crop systems. Photosystem II efficiency showed less sensitivity to metal toxicity compared to the control, with a decrease between 10.07-12.03%. Among gas exchange parameters, only Cr significantly affected physiological responses by reducing transpiration by 69.24%, likely due to leaf chlorosis and necrosis.

CONCLUSION

This study exhibited the potential of garlic MC and IC with perennial ryegrass in phytoremediation. Although the different metals affect plant growth differently, IC showed advantages over MC in term biomass production.

Lead Tolerance and Remediation Potential of Four Indocalamus Species in Lead-Contaminated Soil

Indocalamus plants are low-growing shrubby bamboos with growth advantages, such as high biomass and strong resistance, and they are rich in germplasm resources in southern China. This study conducted soil lead (Pb) stress experiments on Indocalamus latifolius (Keng) McClure (LA), Indocalamus hunanensis B.M. Yang (HU), Indocalamus chishuiensis Y.L. Yang and Hsueh (CH) and Indocalamus lacunosus Wen (LC). Five Pb treatments (0, 500, 1000, 1500 mg·kg-1 Pb, and 1000 mg·kg-1 Pb + 1000 mg·kg-1 ethylenediamine tetraacetic acid (EDTA)) were established. EDTA was applied to explore the tolerance mechanism of different Indocalamus species after absorbing large amounts of heavy metals. The results were as follows: (1) under Pb treatment, the total relative biomass of LA, HU and LC was <100%, whereas the total relative biomass of CH was >100%; (2) after applying EDTA, the bioconcentration coefficient, translocation factor, and free proline content of the four Indocalamus species increased; and (3) the Pb mobility and distribution rates of the underground parts of the four Indocalamus species were consistently greater than those of the aboveground parts. The Pb mobility and distribution rates in the stems increased after applying EDTA, while those in the leaves decreased, as the plants tended to transfer Pb to their stems, which have lower physiological activity than their leaves.

Unraveling the potential of hydrogen sulfide as a signaling molecule for plant development and environmental stress responses: A state-of-the-art review

Over the past decade, a plethora of research has illuminated the multifaceted roles of hydrogen sulfide (H2S) in plant physiology. This gaseous molecule, endowed with signaling properties, plays a pivotal role in mitigating metal-induced oxidative stress and strengthening the plant's ability to withstand harsh environmental conditions. It fulfils several functions in regulating plant development while ameliorating the adverse impacts of environmental stressors. The intricate connections among nitric oxide (NO), hydrogen peroxide (H2O2), and hydrogen sulfide in plant signaling, along with their involvement in direct chemical processes, are contributory in facilitating post-translational modifications (PTMs) of proteins that target cysteine residues. Therefore, the present review offers a comprehensive overview of sulfur metabolic pathways regulated by hydrogen sulfide, alongside the advancements in understanding its biological activities in plant growth and development. Specifically, it centres on the physiological roles of H2S in responding to environmental stressors to explore the crucial significance of different exogenously administered hydrogen sulfide donors in mitigating the toxicity associated with heavy metals (HMs). These donors are of utmost importance in facilitating the plant development, stabilization of physiological and biochemical processes, and augmentation of anti-oxidative metabolic pathways. Furthermore, the review delves into the interaction between different growth regulators and endogenous hydrogen sulfide and their contributions to mitigating metal-induced phytotoxicity.

Sesamol as a potent anticancer compound: from chemistry to cellular interactions

Sesamol (SM), a well-known component isolated from sesame seeds (Sesamum indicum), used in traditional medicines in treating numerous ailments. However, numerous molecular investigations revealed the various mechanisms behind its activity, emphasizing its antiproliferative, anti-inflammatory, and apoptosis-inducing properties, preventing cancer cell spread to distant organs. In several cells derived from various malignant tissues, SM-regulated signal transduction pathways and cellular targets have been identified. This review paper comprehensively describes the anticancer properties of SM and SM-viable anticancer drugs. Additionally, the interactions of this natural substance with standard anticancer drugs are examined, and the benefits of using nanotechnology in SM applications are explored. This makes SM a prime example of how ethnopharmacological knowledge can be applied to the development of contemporary drugs.

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.

Reducing Heavy Metal Contamination in Soil and Water Using Phytoremediation

The increase in industrialization has led to an exponential increase in heavy metal (HM) soil contamination, which poses a serious threat to public health and ecosystem stability. This review emphasizes the urgent need to develop innovative technologies for the environmental remediation of intensive anthropogenic pollution. Phytoremediation is a sustainable and cost-effective approach for the detoxification of contaminated soils using various plant species. This review discusses in detail the basic principles of phytoremediation and emphasizes its ecological advantages over other methods for cleaning contaminated areas and its technical viability. Much attention has been given to the selection of hyperaccumulator plants for phytoremediation that can grow on heavy metal-contaminated soils, and the biochemical mechanisms that allow these plants to isolate, detoxify, and accumulate heavy metals are discussed in detail. The novelty of our study lies in reviewing the mechanisms of plant-microorganism interactions that greatly enhance the efficiency of phytoremediation as well as in discussing genetic modifications that could revolutionize the cleanup of contaminated soils. Moreover, this manuscript discusses potential applications of phytoremediation beyond soil detoxification, including its role in bioenergy production and biodiversity restoration in degraded habitats. This review concludes by listing the serious problems that result from anthropogenic environmental pollution that future generations still need to overcome and suggests promising research directions in which the integration of nano- and biotechnology will play an important role in enhancing the effectiveness of phytoremediation. These contributions are critical for environmental scientists, policy makers, and practitioners seeking to utilize phytoremediation to maintain the ecological stability of the environment and its restoration.

Revitalizing contaminated lands: A state-of-the-art review on the remediation of mine-tailings using phytoremediation and genomic approaches

The mining industry has historically served as a critical reservoir of essential raw materials driving global economic progress. Nevertheless, the consequential by-product known as mine tailings has consistently produced a substantial footprint of environmental contamination. With annual discharges of mine tailings surpassing 10 billion tons globally, the need for effective remediation strategies is more pressing than ever as traditional physical and chemical remediation techniques are hindered by their high costs and limited efficacy. Phytoremediation utilizing plants for remediation of polluted soil has developed as a promising and eco-friendly approach to addressing mine tailings contamination. Furthermore, sequencing of genomic DNA and transcribed RNA extracted from mine tailings presents a pivotal opportunity to provide critical supporting insights for activities directed towards the reconstruction of ecosystem functions on contaminated lands. This review explores the growing prominence of phytoremediation and metagenomics as an ecologically sustainable techniques for rehabilitating mine-tailings. The present study envisages that plant species such as Solidago chilensis, Festuca arundinacea, Lolium perenne, Polygonum capitatum, Pennisetum purpureum, Maireana brevifolia, Prosopis tamarugo etc. could be utilized for the remediation of mine-tailings. Furthermore, a critical evaluation of the organic and inorganic ammendments that optimize conditions for the remediation of mine tailings is also provided. The focus of this review extends to the exploration of environmental genomics to characterize microbial communities in mining sites. By delving into the multifaceted dimensions of phytoremediation and genomics for mine tailings, this study contributes to the ongoing efforts to revitalize contaminated lands for a sustainable and environmentally friendly future.

Pb uptake, accumulation, and translocation in plants: Plant physiological, biochemical, and molecular response: A review

Lead (Pb) is a highly toxic contaminant that is ubiquitously present in the ecosystem and poses severe environmental issues, including hazards to soil-plant systems. This review focuses on the uptake, accumulation, and translocation of Pb metallic ions and their toxicological effects on plant morpho-physiological and biochemical attributes. We highlight that the uptake of Pb metal is controlled by cation exchange capacity, pH, size of soil particles, root nature, and other physio-chemical limitations. Pb toxicity obstructs seed germination, root/shoot length, plant growth, and final crop-yield. Pb disrupts the nutrient uptake through roots, alters plasma membrane permeability, and disturbs chloroplast ultrastructure that triggers changes in respiration as well as transpiration activities, creates the reactive oxygen species (ROS), and activates some enzymatic and non-enzymatic antioxidants. Pb also impairs photosynthesis, disrupts water balance and mineral nutrients, changes hormonal status, and alters membrane structure and permeability. This review provides consolidated information concentrating on the current studies associated with Pb-induced oxidative stress and toxic conditions in various plants, highlighting the roles of different antioxidants in plants mitigating Pb-stress. Additionally, we discussed detoxification and tolerance responses in plants by regulating different gene expressions, protein, and glutathione metabolisms to resist Pb-induced phytotoxicity. Overall, various approaches to tackle Pb toxicity have been addressed; the phytoremediation techniques and biochar amendments are economical and eco-friendly remedies for improving Pb-contaminated soils.

Revolutionizing soil heavy metal remediation: Cutting-edge innovations in plant disposal technology

Soil contamination with heavy metals has emerged as a global environmental threat, compromising agricultural productivity, ecosystem integrity, and human health. Conventional remediation techniques often fall short due to high costs, operational complexities, and environmental drawbacks. Plant-based disposal technologies, including biochar, phytometallurgy, and phrolysis, have emerged as promising solutions in this regard. Grounded in a novel experimental framework, biochar is studied for its dual role as soil amendment and metal adsorbent, while phytometallurgy is explored for its potential in resource recovery and economic benefits derived from harvested metal-rich plant biomass. Pyrolysis, in turn, is assessed for transforming contaminated biomass into value-added products, thereby minimizing waste. These plant disposal technologies create a circular model of remediation and resource utilization that holds the potential for application in large-scale soil recovery projects, development of environmentally friendly agro-industries, and advancement in sustainable waste management practices. This review mainly discussed cutting-edge plant disposal technologies-biochar application, phytometallurgy, and pyrolysis-as revolutionary approaches to soil heavy metal remediation. The efficacy, cost-effectiveness, and environmental impact of these innovative technologies are especially evaluated in comparison with traditional methods. The success of these applications could signal a paradigm shift in how we approach both environmental remediation and resource recovery, with profound implications for sustainable development and circular economy strategies.

Transcriptomics, proteomics, and metabolomics interventions prompt crop improvement against metal(loid) toxicity

The escalating challenges posed by metal(loid) toxicity in agricultural ecosystems, exacerbated by rapid climate change and anthropogenic pressures, demand urgent attention. Soil contamination is a critical issue because it significantly impacts crop productivity. The widespread threat of metal(loid) toxicity can jeopardize global food security due to contaminated food supplies and pose environmental risks, contributing to soil and water pollution and thus impacting the whole ecosystem. In this context, plants have evolved complex mechanisms to combat metal(loid) stress. Amid the array of innovative approaches, omics, notably transcriptomics, proteomics, and metabolomics, have emerged as transformative tools, shedding light on the genes, proteins, and key metabolites involved in metal(loid) stress responses and tolerance mechanisms. These identified candidates hold promise for developing high-yielding crops with desirable agronomic traits. Computational biology tools like bioinformatics, biological databases, and analytical pipelines support these omics approaches by harnessing diverse information and facilitating the mapping of genotype-to-phenotype relationships under stress conditions. This review explores: (1) the multifaceted strategies that plants use to adapt to metal(loid) toxicity in their environment; (2) the latest findings in metal(loid)-mediated transcriptomics, proteomics, and metabolomics studies across various plant species; (3) the integration of omics data with artificial intelligence and high-throughput phenotyping; (4) the latest bioinformatics databases, tools and pipelines for single and/or multi-omics data integration; (5) the latest insights into stress adaptations and tolerance mechanisms for future outlooks; and (6) the capacity of omics advances for creating sustainable and resilient crop plants that can thrive in metal(loid)-contaminated environments.

Tryptophan Seed Treatment Improves Morphological, Biochemical, and Photosynthetic Attributes of the Sunflower under Cadmium Stress

Tryptophan, as a signal molecule, mediates many biotic and environmental stress-induced physiological responses in plants. Therefore, an experiment was conducted to evaluate the effect of tryptophan seed treatment in response to cadmium stress (0, 0.15, and 0.25 mM) in sunflower plants. Different growth and biochemical parameters were determined to compare the efficiency of the treatment agent. The results showed that cadmium stress reduced the growth attributes, including root and shoot length, dry and fresh weight, rate of seed germination, and the number of leaves. Cadmium stress also significantly reduced the contents of chlorophyll a, b, and total chlorophyll, carotenoid contents, phenolics, flavonoids, anthocyanin, and ascorbic acid. Whereas cadmium stress (0.15 and 0.25 mM) enhanced the concentrations of malondialdehyde (45.24% and 53.06%), hydrogen peroxide (-11.07% and 5.86%), and soluble sugars (28.05% and 50.34%) compared to the control. Tryptophan treatment decreased the effect of Cd stress by minimizing lipid peroxidation. Seed treatment with tryptophan under cadmium stress improved the root (19.40%) and shoot length (38.14%), root (41.90%) and shoot fresh weight (13.58%), seed germination ability (13.79%), average leaf area (24.07%), chlorophyll b (51.35%), total chlorophyll (20.04%), carotenoids (43.37%), total phenolic (1.47%), flavonoids (19.02%), anthocyanin (26.57%), ascorbic acid (4%), and total soluble proteins (12.32%) compared with control conditions. Overall, the tryptophan seed treatment showed positive effects on sunflower plants' growth and stress tolerance, highlighting its potential as a sustainable approach to improve crop performance.

Study on the migration behaviour of heavy metals at the improved mine soil-plant rhizosphere interface

With the increasing shortage of land resources and the aggravation of soil pollution in mining areas, the remediation of soil in abandoned mining areas has gradually attracted people's attention. The remediation of heavy metal contaminated soil in mining areas is the key to reduce the harm of heavy metals to the environment and human health. In this study, municipal sludge and phytoremediation technology were combined to investigate the migration and transformation of heavy metals at the soil-plant interface in improved mining areas through indoor pot experiments. The results showed that heavy metals in non-rhizosphere soil entered the rhizosphere environment with the growth of plants, leading to the increase of heavy metal content in rhizosphere soil. The cumulative amounts of Cu, Zn, Pb and Cd were 1299.32, 832.10, 347.89 and 71.34 mg/kg, respectively. The content of oxidized Cu and Zn decreased with increasing planting days, while the oxidized Pb and Cd showed an increasing trend. Under acidic conditions, H+ is easy to compete with heavy metal ions for exchangeable positions in the clay mineral layer, so that the reducible heavy metals are easy to be converted into exchangeable states. In this paper, the effects of various factors on the distribution of heavy metals were discussed by adjusting soil pH, adding humic acid and root exudates, so as to analyse the migration and transformation mechanism of heavy metals at the soil-plant interface, and provide a reliable theoretical basis for soil remediation in mining areas.

Regulation of cadmium-induced biofilm formation by artificial polysaccharide-binding proteins for enhanced phytoremediation

Phytoremediation is an economic way to attenuate soil heavy metal pollution, but is frequently limited by its low pollutant-removing efficiency. Recently, we revealed the close relation between polysaccharide-based biofilm formation and cadmium removal. In this study, for improving the phytoremediation efficiency, an artificial polysaccharide-binding protein was designed by synthetic biology techniques to regulate biofilm formation. The artificial protein Syn contained two polysaccharide-binding domains from the Ruminococcus flavefaciens CttA and the Clostridium cellulolyticum CipC, preferentially binding polysaccharides exposed on both cadmium-treated bacteria and plant roots. Under cadmium stress, Syn remarkably promoted bacterial polysaccharide production from 99 mg/L to 237 mg/L, leading to 1.23-fold higher biofilm biomass. During treatment of the remediation plants with exogenous cadmium-capturing bacteria, Syn improved root biofilm formation, with the root surface polysaccharide contents increasing by 79%, and the Log10 CFU/g root increasing from 7.01 to 7.80. Meanwhile, Syn remodeled the rhizosphere microbiome, especially increasing the abundance of the bacterial groups involved in biofilm formation and stress tolerance, e.g., Pseudomonas, Enterobacter, etc. Consequently, Syn promoted plant cadmium adsorption, with the cadmium-removing efficiency increasing from 17.2% to 33.8%. This study sheds light on synthetic biology-based regulation of biofilm formation for enhanced phytoremediation.

Physiological and Germination Responses of Muskmelon (Cucumis melo L.) Seeds to Varying Osmotic Potentials and Cardinal Temperatures via a Hydrothermal Time Model

Climatic changes have a direct negative impact on the growth, development, and productivity of crops. The water potential (ψ) and temperature (T) are important limiting factors that influence the rate of seed germination and growth indices. To examine how the germination of seed responds to changes in water potential and temperature, the hydrotime model and hydrothermal model (HTT) have been employed. The HTT calculates the concept of germination time across temperatures, between Tb-To, with alteration, and between Tb-Tc, in supra-optimal ranges. The seeds of Cucumis melo L. were germinated in the laboratory for a hydro-thermal time experiment. Seeds were sown in Petri dishes containing a double-layered filter paper at different osmotic potentials (0, -0.2, -0.4, -0.6, and -0.8 MPa) by providing PEG 6000 (drought stress enhancer) at different temperatures (15, 20, 25, 30, and 35 °C). The controlled replicate was treated with 10 mL of distilled water and the rest with 10 mL of PEG solution. Results indicated that the seed vigor index (SVI-II) was highest at 15 °C with 0 MPa and lowest at 30 °C with -0.2 MPa. However, the highest activity was shown at 15 °C by catalase (CAT) and guaiacol peroxidase (GPX) at (-0.6 MPa), while the lowest values of CAT and GPX were recorded for control at 35 °C with -0.8 MPa at 35 °C, respectively. Germination energy was positively correlated with germination index (GI), germination percentage (G%), germination rate index, seed vigor index-I (SVI-I), mean moisture content (MMC), and root shoot ratio (RSR) and had a negative correlation with mean germination rate, percent moisture content of shoot and root, CAT, superoxide dismutase, peroxidase ascorbate peroxidase, and GPX. In conclusion, thermal and hydrotime models correctly predicted muskmelon germination time in response to varying water potential and temperature. The agronomic attributes were found to be maximum at 30 °C and minimum at 15 °C.

Effects of Poultry Manure on the Growth, Physiology, Yield, and Yield-Related Traits of Maize Varieties

Industries play a significant role in the improvement of lifestyle and in the development of a country. However, the byproducts from these industries are a source of environmental pollution. The proper use of the byproducts of these industries can help to cope with environmental pollution. Some byproducts have high nutritional content and are good for crop plants. The purpose of this research was to investigate the effect of different rates of poultry manure on the soil chemical properties, growth, and yield of maize. A pot experiment was conducted in the botanical garden of the Department of Botany, University of Sargodha, Pakistan to investigate the effect of various treatments of poultry manure (0, 25, 50, 75, and 100 g/pot) on the morphological, physiological, and yield attributes of two maize varieties, Pearl and MMRI. Treatment T₁ was a mixture of soil and 75 g/pot poultry manure, T₂ was a mixture of soil and 50 g/pot poultry manure, T₃ was a mixture of soil and 25 g/pot poultry manure, and T₄ was 100 g/pot poultry manure. Soil without any industrial byproduct (100% soil only) was used as the control (T₀). The results revealed that the use of poultry manure enhanced the physical properties of the soil. Available P and soil organic matter were improved in soil amended with poultry manure. It is evident from the results that the vegetative growth of both maize varieties was significantly enhanced by growing in soil amended with poultry manure as compared to their respective control. Similar responses were also recorded for the physiological attributes of leaf area, photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency of both varieties. Yield and yield-contributing traits of both maize varieties were significantly improved by growing plants in soil amended with 50 and 75 g/pot of poultry manure. It is also inferred that the use of 50 g/pot poultry manure in soil amendment is an eco-friendly and economically effective option for maize growers of arid and semiarid regions to enhance the kernel yield and profit per annum. Poultry manure could be useful to ameliorate the adverse effects of salinity stress on all parameters, particularly the grain yield. Furthermore, this would be a useful and economical method for the safe disposal of byproducts.

Ameliorative Effects of Exogenous Potassium Nitrate on Antioxidant Defense System and Mineral Nutrient Uptake in Radish (Raphanus sativus L.) under Salinity Stress

Soil salinization has become a major issue around the world in recent years, as it is one of the consequences of climate change as sea levels rise. It is crucial to lessen the severe consequences of soil salinization on plants. A pot experiment was conducted to regulate the physiological and biochemical mechanisms in order to evaluate the ameliorative effects of potassium nitrate (KNO₃) on Raphanus sativus L. genotypes under salt stress. The results from the present study illustrated that the salinity stress induced a significant decrease in shoot length, root length, shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, number of leaves per plant, leaf area chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid, net photosynthesis, stomatal conductance, and transpiration rate by 43, 67, 41, 21, 34, 28, 74, 91, 50, 41, 24, 34, 14, 26, and 67%, respectively, in a 40 day radish while decreased by 34, 61, 49, 19, 31, 27, 70, 81, 41, 16, 31, 11, 21, and 62%, respectively, in Mino radish. Furthermore, MDA, H₂O₂ initiation, and EL (%) of two varieties (40 day radish and Mino radish) of R. sativus increased significantly (P < 0.05) by 86, 26, and 72%, respectively, in the roots and also increased by 76, 106, and 38% in the leaves in a 40 day radish, compared to the untreated plants. The results also elucidated that the contents of phenolic, flavonoids, ascorbic acid, and anthocyanin in the two varieties (40 day radish and Mino radish) of R. sativus increased with the exogenous application of KNO₃ by 41, 43, 24, and 37%, respectively, in the 40 day radish grown under the controlled treatments. Results indicated that implementing KNO₃ exogenously in the soil increased the activities of antioxidants like SOD, CAT, POD, and APX by 64, 24, 36, and 84% in the roots and also increased by 21, 12, 23, and 60% in the leaves of 40 day radish while also increased by 42, 13, 18, and 60% in the roots and also increased by 13, 14, 16, and 41% in the leaves in Mino radish, respectively, in comparison to those plants grown without KNO₃. We found that KNO₃ substantially improved plant growth by lowering the levels of oxidative stress biomarkers, thereby further stimulating the antioxidant potential system, which led to an improved nutritional profile of both R. sativus L. genotypes under normal and stressed conditions. The current study would offer a deep theoretical foundation for clarifying the physiological and biochemical mechanisms by which the KNO₃ improves salt tolerance in R. sativus L. genotypes.

Seed Priming Modulates Physiological and Agronomic Attributes of Maize (Zea mays L.) under Induced Polyethylene Glycol Osmotic Stress

Drought and osmotic stresses are major threats to agricultural crops as they affect plants during their life cycle. The seeds are more susceptible to these stresses during germination and establishment of seedlings. To cope with these abiotic stresses, various seed priming techniques have broadly been used. The present study aimed to assess seed priming techniques under osmotic stress. Osmo-priming with chitosan (1 and 2%), hydro-priming with distilled water, and thermo-priming at 4 °C were used on the physiology and agronomy of Zea mays L. under polyethylene glycol (PEG-4000)-induced osmotic stress (-0.2 and -0.4 MPa). The vegetative response, osmolyte content, and antioxidant enzymes of two varieties (Pearl and Sargodha 2002 White) were studied under induced osmotic stress. The results showed that seed germination and seedling growth were inhibited under osmotic stress and germination percentage, and the seed vigor index was enhanced in both varieties of Z. mays L. with chitosan osmo-priming. Osmo-priming with chitosan and hydro-priming with distilled water modulated the level of photosynthetic pigments and proline, which were reduced under induced osmotic stress; moreover, the activities of antioxidant enzymes were improved significantly. In conclusion, osmotic stress adversely affects the growth and physiological attributes; on the contrary, seed priming ameliorated the stress tolerance resistance of Z. mays L. cultivars to PEG-induced osmotic stress by activating the natural antioxidation enzymatic system and accumulating osmolytes.

Phytoremediation of Pollutants: Applicability and Future Perspective

Environmental pollution is a global issue since it is spreading worldwide, affecting entire ecosystems [...].

Bacterial Communities Associated with the Roots of Typha spp. and Its Relationship in Phytoremediation Processes

Heavy metal pollution is a severe concern worldwide, owing to its harmful effects on ecosystems. Phytoremediation has been applied to remove heavy metals from water, soils, and sediments by using plants and associated microorganisms to restore contaminated sites. The Typha genus is one of the most important genera used in phytoremediation strategies because of its rapid growth rate, high biomass production, and the accumulation of heavy metals in its roots. Plant growth-promoting rhizobacteria have attracted much attention because they exert biochemical activities that improve plant growth, tolerance, and the accumulation of heavy metals in plant tissues. Because of their beneficial effects on plants, some studies have identified bacterial communities associated with the roots of Typha species growing in the presence of heavy metals. This review describes in detail the phytoremediation process and highlights the application of Typha species. Then, it describes bacterial communities associated with roots of Typha growing in natural ecosystems and wetlands contaminated with heavy metals. Data indicated that bacteria from the phylum Proteobacteria are the primary colonizers of the rhizosphere and root-endosphere of Typha species growing in contaminated and non-contaminated environments. Proteobacteria include bacteria that can grow in different environments due to their ability to use various carbon sources. Some bacterial species exert biochemical activities that contribute to plant growth and tolerance to heavy metals and enhance phytoremediation.

State-of-art advances on removal, degradation and electrochemical monitoring of 4-aminophenol pollutants in real samples: A review

p_Aminophenol, namely 4-aminophenol (4-AP), is an aromatic compound including hydroxyl and amino groups contiguous together on the benzene ring, which are suitable chemically reactive, amphoteric, and alleviating agents in nature. Amino phenols are appropriate precursors for synthesizing oxazoles and oxazines. However, since the toxicity of aniline and phenol can harm human and herbal organs, it is essential to improve a reliable technique for the determination of even a trace amount of amino phenols, as well as elimination or (bio)degradation/photodegradation of it to protect both the environment and people's health. For this purpose, various analytical methods have been suggested up till now, including spectrophotometry, liquid chromatography, spectrofluorometric and capillary electrophoresis, etc. However, some drawbacks such as the requirement of complex instruments, high costs, not being portable, slow response time, low sensitivity, etc. prevent them to be employed in a wide range and swift in-situ applications. In this regard, besides the efforts such as (bio)degradation/photodegradation or removal of 4-AP pollutants from real samples, electroanalytical techniques have become a promising alternative for monitoring them with high sensitivity. In this review, it was aimed to emphasize and summarize the recent advances, challenges, and opportunities for removal, degradation, and electrochemical sensing 4-AP in real samples. Electroanalytical monitoring of amino phenols was reviewed in detail and explored the various types of electrochemical sensors applied for detecting and monitoring in real samples. Furthermore, the various technique of removal and degradation of 4-AP in industrial and urban wastes were also deliberated. Moreover, deep criticism of multifunctional nanomaterials to be utilized as a catalyst, adsorbent/biosorbent, and electroactive material for the fabrication of electrochemical sensors was covered along with their unique properties. Future perspectives and conclusions were also criticized to pave the way for further studies in the field of application of up-and-coming nanostructures in environmental applications.

Interaction of Lead and Cadmium Reduced Cadmium Toxicity in Ficus parvifolia Seedlings

Potentially toxic elements (PTEs) pollution occurs widely in soils due to various anthropogenic activities. Lead (Pb) and cadmium (Cd) coexist in soil frequently, threatening plant growth. To explore the interaction effect between Pb and Cd in Ficus parvifolia and the response of plant physiological characteristics to Pb and Cd stress, we designed a soil culture experiment. The experiment demonstrated that Pb stress improved leaf photosynthesis ability, while Cd stress inhibited it. Furthermore, Pb or Cd stress increased malonaldehyde (MDA) content, but plants were able to reduce it by increasing antioxidant enzyme activities. The presence of Pb could alleviate Cd phytotoxicity in plants by inhibiting Cd uptake and accumulation as well as increasing leaf photosynthesis and antioxidant ability. Pearson correlation analysis illustrated that the variability of Cd uptake and accumulation between Pb and Cd stress was related to plant biomass and antioxidant enzyme activities. This research will offer a new perspective on alleviating Cd phytotoxicity in plants.

A Green Approach Used for Heavy Metals 'Phytoremediation' Via Invasive Plant Species to Mitigate Environmental Pollution: A Review

Heavy metals (HMs) normally occur in nature and are rapidly released into ecosystems by anthropogenic activities, leading to a series of threats to plant productivity as well as human health. Phytoremediation is a clean, eco-friendly, and cost-effective method for reducing soil toxicity, particularly in weedy plants (invasive plant species (IPS)). This method provides a favorable tool for HM hyperaccumulation using invasive plants. Improving the phytoremediation strategy requires a profound knowledge of HM uptake and translocation as well as the development of resistance or tolerance to HMs. This review describes a comprehensive mechanism of uptake and translocation of HMs and their subsequent detoxification with the IPS via phytoremediation. Additionally, the improvement of phytoremediation through advanced biotechnological strategies, including genetic engineering, nanoparticles, microorganisms, CRISPR-Cas9, and protein basis, is discussed. In summary, this appraisal will provide a new platform for the uptake, translocation, and detoxification of HMs via the phytoremediation process of the IPS.

Vermi-cyanobacterial remediation of cadmium-contaminated soil with rice husk biochar: An eco-friendly approach

Present study is aimed to evaluate the influence of earthworm (Eisenia fetida), Cyanobacteria (Cylindrospermum stagnale), and rice husk biochar (BC) on cadmium (Cd) detoxification in artificially contaminated soil. The Cd content was kept at 10 mg/kg in factorial design I, coupled with 2% and 0% BC. E. fetida and C. stagnale un-inoculated and inoculated experiments were maintained respectively as negative and positive controls. In factorial design II, E. fetida and C. stagnale were inoculated, along with BC (0% and 2%, denoted as B), without BC (WB), along with four different Cd concentrations (Cd-0, Cd-5, Cd-10, and Cd-20 mg/kg). Results suggest a substantial amount of Cd removal in BC-assisted treatments when compared to negative control-1. Cd (mg/g) in E. fetida tissue ranged from 0.019 (WB2) to 0.0985 (B4). C. stagnale of WB4 (0.036) bioaccumulated the most Cd (mg/g), while B2 showed the least (0.018). The maximum quantity of metallothionein (5.34 μM/mg) was detected in E. fetida of B4 (factorial design - II) and the minimum was claimed in WB1 (0.48 μM/mg) at the end. Earthworm metallothionein protein is a key component in Cd removal from soil by playing an important role in detoxification process. Microbial communities and humic substances were observed in BC-assisted treatments, which aided in Cd-contaminated soil remediation. The present findings suggest that BC (2%) + earthworms + algae could be a suitable remediation strategy for Cd contaminated soil. BC + earthworm + algal-based investigation on heavy metal remediation will be a valuable platform for detoxifying harmful metals in soils.

The impact of tritium phytoremediation on plant health as measured by fluorescence

Phytoremediation, using plants for soil, sediment, or water contaminant clean-up, is an established technology dependent on plant health. Tritium (3H), a radioactive isotope of hydrogen that is generally found in the environment as tritiated water (HTO), is a low-level beta emitter with a half-life of 12.32 years. Chlorophyll fluorescence (CF) for monitoring risk assessment of tritium to plant health was conducted at the Tritium Irrigation Facility (TIF) located on the US Department of Energy's Savannah River Site (SRS) near Aiken, SC. Two fluorometers were evaluated in conjunction with phytoremediation at the 25 -acre TIF where tritiated groundwater is being spray-irrigated on a mixed coniferous/deciduous forested watershed as a means of reducing tritium release to a nearby stream that serves as a tributary to the Savannah River. Tritium activity in irrigated water averaged 104 + 42 pCi mL-1 during the 2003 project. Fluorescence parameters measured by the two fluorometers were well correlated with each other (p < 0.0001). Tritium in water respired from oak leaves ranged up to 1845.13 pCi ml-1 and 2138.22 pCi ml-1 in pine needles. Trees in both the test and control sites were approximately 15 years old. Here we demonstrated that fluorescence parameters provide an effective way to estimate the impact of HTO on plant health in a noninvasive, extremely rapid, and cost-effective manner. In the current study applying fluorometry, plants within the TIF phytoremediation site exposed to the site tritiated water were not significantly impacted by the tritium phytoremediation based on CF parameters as compared to the control, a nascent non-irrigated site.

Anticancer and Free Radical Scavenging Competence of Zinc Oxide Nanoparticles Synthesized by Aqueous Leaf Extract of Phyllanthus acidus

The purpose of this study was aimed to investigate the zinc oxide nanoparticles (ZnONPs) synthesizing efficiency of aqueous leaf extract of Phyllanthus acidus. Furthermore, the antioxidant and anticancer activities of synthesized ZnONPs were also investigated through the in-vitro approach. The obtained results show that the aqueous extract of P. acidus can synthesize ZnONPs, as evidenced by a sharp absorbance peak at 375 nm. The Fourier transform infrared spectroscopy (FTIR) analysis confirmed that the aqueous extract contained significant numbers of functional groups, which were involved in reducing zinc nitrate into ZnONPs. Also, they participate in the capping and stabilization of synthesized ZnONPs and their size ranged from 27.14-35.74 nm with a spherical shape . The results obtained in ABTS radical scavenging activity 1, 1-diphenyl-2-picryl-hydroxyl (DPPH), hydrogen peroxide (H2O2), and 2,2'-Azino-Bis(3-ethylbenzene thiazoline-6-sulfonic acid) (ABTS) assays declared has excellent in-vitro radicals scavenging activity with reasonable IC50 values. Interestingly, these green synthesized ZnONPs have an excellent anticancer activity against human epidermoid carcinoma (Hep3) cell line in an in-vitro approach. These findings imply that an aqueous leaf extract of P. acidus can be used to synthesize pharmaceutically valuable ZnONPs. To consider such nanomaterials as potential therapeutic agents, optimization and in-vivo biomedical studies are required.

Comparison of In Vitro and In Planta Heavy Metal Tolerance and Accumulation Potential of Different Armeria maritima Accessions from a Dry Coastal Meadow

The aim of the present study was to compare the tolerance to several heavy metals and their accumulation potential of Armeria maritima subsp. elongata accessions from relatively dry sandy soil habitats in the Baltic Sea region using both in vitro cultivated shoot explants and long-term soil-cultivated plants at the flowering stage as model systems. The hypothesis that was tested was that all accessions will show a relatively high heavy metal tolerance and a reasonable metal accumulation potential, but possibly to varying degrees. Under the conditions of the tissue culture, the explants accumulated extremely high concentration of Cd and Cu, leading to growth inhibition and eventual necrosis, but the accumulation of Pb in their tissues was limited. When grown in soil, the plants from different accessions showed a very high heavy metal tolerance, as the total biomass was not negatively affected by any of the treatments. The accumulation potential for heavy metals in soil-grown plants was high, with several significant accession- and metal-related differences. In general, the heavy metal accumulation potential in roots and older leaves was similar, except for Mn, which accumulated more in older leaves. The absolute higher values of the heavy metal concentrations reached in the leaves of soil-grown A. maritima plants (500 mg Cd kg^-1, 600 mg Cu kg^-1, 12,000 mg Mn kg^-1, 1500 mg Pb kg^-1, and 15,000 mg Zn kg^-1) exceeded the respective threshold values for hyperaccumulation. In conclusion, A. maritima can be characterized by a species-wide heavy metal tolerance and accumulation potential, but with a relatively high intraspecies diversity.

Advances in biological methods for the sequestration of heavy metals from water bodies: A review

Pollution is a major concern of the modern era as it affects all the principal aspects of the environment, especially the hydrosphere. Pollution with heavy metals has unequivocally threatened aquatic bodies and organisms as these metals are persistent, non-biodegradable, and toxic. Heavy metals tend to accumulate in the environment and eventually in humans, which makes their efficient removal a topic of paramount importance. Treatment of metal-contaminated water can be done both via chemical and biological methods. Where remediation through conventional methods is expensive and generates a large amount of sludge, biological methods are favoured over older and prevalent chemical purification processes because they are cheaper and environment friendly. The present review attempts to summarise effective methods for the remediation of water contaminated with heavy metals. We concluded that in biological techniques, bio-sorption is among the most employed and successful mechanisms because of its high efficacy and eco-friendly nature.

Plant Growth-Promoting Bacteria (PGPB) integrated phytotechnology: A sustainable approach for remediation of marginal lands

Land that has little to no utility for agriculture or industry is considered marginal land. This kind of terrain is frequently found on the edge of deserts or other arid regions. The amount of land that can be used for agriculture continues to be constrained by increasing desertification, which is being caused by climate change and the deterioration of agriculturally marginal areas. Plants and associated microorganisms are used to remediate and enhance the soil quality of marginal land. They represent a low-cost and usually long-term solution for restoring soil fertility. Among various phytoremediation processes (viz., phytodegradation, phytoextraction, phytostabilization, phytovolatilization, phytofiltration, phytostimulation, and phytodesalination), the employment of a specific mechanism is determined by the state of the soil, the presence and concentration of contaminants, and the plant species involved. This review focuses on the key economically important plants used for phytoremediation, as well as the challenges to plant growth and phytoremediation capability with emphasis on the advantages and limits of plant growth in marginal land soil. Plant growth-promoting bacteria (PGPB) boost plant development and promote soil bioremediation by secreting a variety of metabolites and hormones, through nitrogen fixation, and by increasing other nutrients' bioavailability through mineral solubilization. This review also emphasizes the role of PGPB under different abiotic stresses, including heavy-metal-contaminated land, high salinity environments, and organic contaminants. In our opinion, the improved soil fertility of marginal lands using PGPB with economically significant plants (e.g., Miscanthus) in dual precession technology will result in the reclamation of general agriculture as well as the restoration of native vegetation.