Helping plants to deal with heavy metal stress: the role of nanotechnology and plant growth promoting rhizobacteria in the process of phytoremediation

Ameliorating the detrimental effects of chromium in wheat by silicon nanoparticles and its enriched biochar

Increased anthropogenic activities over the last decades have led to a gradual increase in chromium (Cr) content in the soil, which, due to its high mobility in soil, makes Cr accumulation in plants a serious threat to the health of animals and humans. The present study investigated the ameliorative effect of foliar-applied Si nanoparticles (SiF) and soil-applied SiNPs enriched biochar (SiBc) on the growth of wheat in Cr-polluted soil (CPS). Two levels of CPS were prepared, including 12.5 % and 25 % by adding Cr-polluted wastewater in the soil as soil 1 (S1) and soil 2 (S2), respectively for the pot experiment with a duration of 40 days. Cr stress significantly reduced wheat growth, however, combined application of SiF and SiBc improved root and shoot biomass production under Cr stress by (i) reducing Cr accumulation, (ii) increasing activities of antioxidant enzymes (ascorbate peroxidase and catalase), and (iii) increasing protein and total phenolic contents in both root and shoot respectively. Nonetheless, separate applications of SiF and SiBc effectively reduced Cr toxicity in shoot and root respectively, indicating a tissue-specific regulation of wheat growth under Cr. Later, the Langmuir and Freundlich adsorption isotherm analysis showed a maximum soil Cr adsorption capacity ∼ Q(max) of 40.6 mg g-1 and 59 mg g-1 at S1 and S2 respectively, while the life cycle impact assessment showed scores of -1 mg kg-1 and -211 mg kg-1 for Cr in agricultural soil and - 0.184 and - 38.7 for human health at S1 and S2 respectively in response to combined SiF + SiBC application, thus indicating the environment implication of Si nanoparticles and its biochar in ameliorating Cr toxicity in different environmental perspectives.

Plant growth-promoting rhizobacterial secondary metabolites in augmenting heavy metal(loid) phytoremediation: An integrated green in situ ecorestorative technology

In recent times, increased geogenic and human-centric activities have caused significant heavy metal(loid) (HM) contamination of soil, adversely impacting environmental, plant, and human health. Phytoremediation is an evolving, cost-effective, environment-friendly, in situ technology that employs indigenous/exotic plant species as natural purifiers to remove toxic HM(s) from deteriorated ambient soil. Interestingly, the plant's rhizomicrobiome is pivotal in promoting overall plant nutrition, health, and phytoremediation. Certain secondary metabolites produced by plant growth-promoting rhizobacteria (PGPR) directly participate in HM bioremediation through chelation/mobilization/sequestration/bioadsorption/bioaccumulation, thus altering metal(loid) bioavailability for their uptake, accumulation, and translocation by plants. Moreover, the metallotolerance of the PGPR and the host plant is another critical factor for the successful phytoremediation of metal(loid)-polluted soil. Among the phytotechniques available for HM remediation, phytoextraction/phytoaccumulation (HM mobilization, uptake, and accumulation within the different plant tissues) and phytosequestration/phytostabilization (HM immobilization within the soil) have gained momentum in recent years. Natural metal(loid)-hyperaccumulating plants have the potential to assimilate increased levels of metal(loid)s, and several such species have already been identified as potential candidates for HM phytoremediation. Furthermore, the development of transgenic rhizobacterial and/or plant strains with enhanced environmental adaptability and metal(loid) uptake ability using genetic engineering might open new avenues in PGPR-assisted phytoremediation technologies. With the use of the Geographic Information System (GIS) for identifying metal(loid)-impacted lands and an appropriate combination of normal/transgenic (hyper)accumulator plant(s) and rhizobacterial inoculant(s), it is possible to develop efficient integrated phytobial remediation strategies in boosting the clean-up process over vast regions of HM-contaminated sites and eventually restore ecosystem health.

Phosphorus and selenium compounding mitigates Cr stress in peanut seedlings by enhancing growth homeostasis and antioxidant properties

Peanut is an economically important crop, but it is susceptible to Cr contamination. In this study, we used peanut as experimental material to investigate the effects of exogenous P, Se interacting with Cr on the nutrient growth and antioxidant system of peanut seedlings by simulating Cr (0 μM, 50 μM, and 100 μM) stress environment. The results showed that exogenous P, Se supply could mitigate irreversible damage to peanut seedlings by altering the distribution of Cr in roots and aboveground, changing root conformation, and repairing damaged cells to promote growth. When the Cr concentration is 100 μM, it exhibits the highest toxicity. Compared to the control group P and Se (0 MM), the treatment with simultaneous addition of P + Se (0.5 + 6.0) resulted in a significant increase in root length and root tip number by 248.7% and 127.4%, respectively. Additionally, there was a 46.9% increase in chlorophyll content, a 190.2% increase in total surface area of the seedlings, and a respective increase of 149.1% and 180.3% in soluble protein content in the shoot and roots. In addition, by restricting the absorption of Cr and reducing the synthesis of superoxide dismutase SOD (Superoxide dismutase), CAT (Catalase), POD (Peroxidase), and MDA (Malonaldehyde), it effectively alleviates the oxidative stress on the antioxidant system. Therefore, the exogenous addition of P (0.5 MM) and Se (6.0 MM) prevented the optimal concentration of chromium toxicity to peanuts. Our research provides strong evidence that the exogenous combination of P and Se reduces the risk of peanut poisoning by Cr, while also exploring the optimal concentration of exogenous P and Se under laboratory conditions, providing a basis for further field experiments.

PGPR-Enabled bioremediation of pesticide and heavy metal-contaminated soil: A review of recent advances and emerging challenges

The excessive usage of agrochemicals, including pesticides, along with various reckless human actions, has ensued discriminating prevalence of pesticides and heavy metals (HMs) in crop plants and the environment. The enhanced exposure to these chemicals is a menace to living organisms. The pesticides may get bioaccumulated in the food chain, thereby leading to several deteriorative changes in the ecosystem health and a rise in the cases of some serious human ailments including cancer. Further, both HMs and pesticides cause some major metabolic disturbances in plants, which include oxidative burst, osmotic alterations and reduced levels of photosynthesis, leading to a decline in plant productivity. Moreover, the synergistic interaction between pesticides and HMs has a more serious impact on human and ecosystem health. Various attempts have been made to explore eco-friendly and environmentally sustainable methods of improving plant health under HMs and/or pesticide stress. Among these methods, the employment of PGPR can be a suitable and effective strategy for managing these contaminants and providing a long-term remedy. Although, the application of PGPR alone can alleviate HM-induced phytotoxicities; however, several recent reports advocate using PGPR with other micro- and macro-organisms, biochar, chelating agents, organic acids, plant growth regulators, etc., to further improve their stress ameliorative potential. Further, some PGPR are also capable of assisting in the degradation of pesticides or their sequestration, reducing their harmful effects on plants and the environment. This present review attempts to present the current status of our understanding of PGPR's potential in the remediation of pesticides and HMs-contaminated soil for the researchers working in the area.

Synergistic interactions of nanoparticles and plant growth promoting rhizobacteria enhancing soil-plant systems: a multigenerational perspective

Sustainable food security and safety are major concerns on a global scale, especially in developed nations. Adverse agroclimatic conditions affect the largest agricultural-producing areas, which reduces the production of crops. Achieving sustainable food safety is challenging because of several factors, such as soil flooding/waterlogging, ultraviolet (UV) rays, acidic/sodic soil, hazardous ions, low and high temperatures, and nutritional imbalances. Plant growth-promoting rhizobacteria (PGPR) are widely employed in in-vitro conditions because they are widely recognized as a more environmentally and sustainably friendly approach to increasing crop yield in contaminated and fertile soil. Conversely, the use of nanoparticles (NPs) as an amendment in the soil has recently been proposed as an economical way to enhance the texture of the soil and improving agricultural yields. Nowadays, various research experiments have combined or individually applied with the PGPR and NPs for balancing soil elements and crop yield in response to control and adverse situations, with the expectation that both additives might perform well together. According to several research findings, interactive applications significantly increase sustainable crop yields more than PGPR or NPs alone. The present review summarized the functional and mechanistic basis of the interactive role of PGPR and NPs. However, this article focused on the potential of the research direction to realize the possible interaction of PGPR and NPs at a large scale in the upcoming years.

Alleviation potential of green-synthesized selenium nanoparticles for cadmium stress in Solanum lycopersicum L: modulation of secondary metabolites and physiochemical attributes

KEY MESSAGE

Selenium nanoparticles reduce cadmium absorption in tomato roots, mitigating heavy metal effects. SeNPs can efficiently help to enhance growth, yield, and biomolecule markers in cadmium-stressed tomato plants. In the present study, the effects of selenium nanoparticles (SeNPs) were investigated on the tomato plants grown in cadmium-contaminated soil. Nanoparticles were synthesized using water extract of Nigella sativa and were characterized for their size and shape. Two application methods (foliar spray and soil drench) with nanoparticle concentrations of 0, 100, and 300 mg/L were used to observe their effects on cadmium-stressed plants. Growth, yield, biochemical, and stress parameters were studied. Results showed that SeNPs positively affected plant growth, mitigating the negative effects of cadmium stress. Shoot length (SL), root length (RL), number of branches (NB), number of leaves per plant (NL), and leaf area (LA) were significantly reduced by cadmium stress but enhanced by 45, 51, 506, 208, and 82%, respectively, by soil drench treatment of SeNPs. Similarly, SeNPs increased the fruit yield (> 100%) and fruit weight (> 100%), and decreased the days to fruit initiation in tomato plants. Pigments were also positively affected by the SeNPs, particularly in foliar treatment. Lycopene content was also enhanced by the addition of NPs (75%). Furthermore, the addition of SeNPs improved the ascorbic acid, protein, phenolic, flavonoid, and proline contents of the tomato plants under cadmium stress, whereas stress enzymes also showed enhanced activities under cadmium stress. It is concluded from the present study that the addition of selenium nanoparticles enhanced the growth and yield of Cd-stressed plants by reducing the absorption of cadmium and increasing the stress management of plants.

The synergistic potential of biochar and nanoparticles in phytoremediation and enhancing cadmium tolerance in plants

Cadmium (Cd) is classified as a heavy metal (HM) and is found into the environment through both natural processes and intensified anthropogenic activities such as industrial operations, mining, disposal of metal-laden waste like batteries, as well as sludge disposal, excessive fertilizer application, and Cd-related product usage. This rising Cd disposal into the environment carries substantial risks to the food chain and human well-being. Inadequate regulatory measures have led to Cd bio-accumulation in plants, which is increasing in an alarming rate and further jeopardizing higher trophic organisms, including humans. In response, an effective Cd decontamination strategy such as phytoremediation emerges as a potent solution, with innovations in nanotechnology like biochar (BC) and nanoparticles (NPs) further augmenting its effectiveness for Cd phytoremediation. BC, derived from biomass pyrolysis, and a variety of NPs, both natural and less toxic, actively engage in Cd removal during phytoremediation, mitigating plant toxicity and associated hazards. This review scrutinizes the application of BC and NPs in Cd phytoremediation, assessing their synergistic mechanism in influencing plant growth, genetic regulations, structural transformations, and phytohormone dynamics. Additionally, the review also underscores the adoption of this sustainable and environmentally friendly strategies for future research in employing BC-NP microaggregates to ameliorate Cd phytoremediation from soil, thereby curbing ecological damage due to Cd toxicity.

Farmland phytoremediation in bibliometric analysis

Phytoremediation is an environmentally friendly, economical, and sustainable technique for restoring farmland. It can remove heavy metals and organic pollutants from the soil through the implementation of hyperaccumulator plants. In recent years, it has garnered significant interest from academic and industrial sectors. This article screened 368 research papers from the Web of Science core collection database related to farmland phytoremediation and conducted a bibliometric analysis of the domain based on CiteSpace. The paper intuitively demonstrates the most influential countries, the most productive institutions, the most contributing groups of authors, and the primary sources of farmland phytoremediation research domain. The findings additionally indicate that the research hotspots include: (1) mechanisms and principles of phytoremediation, (2) the improvement of restoration efficiency, (3) the economic, ecological, and sustainable development of phytoremediation. The exploration of plants with potential to accumulate heavy metals and produce large amounts of biomass is the research frontier within the field of farmland phytoremediation. Additionally, this bibliometric analysis can help scholars willing to work in this research field by concisely understanding the overall research field and frontiers. With the continuous improvement of phytoremediation and its combination with other remediation technologies, the future of farmland remediation will have a promising prospect.

Arsenic pollution cycle, toxicity and sustainable remediation technologies: A comprehensive review and bibliometric analysis

Arsenic pollution and its allied impacts on health are widely reported and have gained global attention in the last few decades. Although the natural distribution of arsenic is limited, anthropogenic activities have increased its mobility to distant locations, thereby increasing the number of people affected by arsenic pollution. Arsenic has a complex biogeochemical cycle which has a significant role in pollution. Therefore, this review paper has comprehensively analysed the biogeochemical cycle of arsenic which can dictate the occurrence of arsenic pollution. Considering the toxicity and nature of arsenic, the present work has also analysed the current status of arsenic pollution around the world. It is noted that the south of Asia, West-central Africa, west of Europe and Latin America are major hot spots of arsenic pollution. Bibliometric analysis was performed by using scopus database with specific search for keywords such as arsenic pollution, health hazards to obtain the relevant data. Scopus database was searched for the period of 20 years from year 2003-2023 and total of 1839 articles were finally selected for further analysis using VOS viewer. Bibliometric analysis of arsenic pollution and its health hazards has revealed that arsenic pollution is primarily caused by anthropogenic sources and the key sources of arsenic exposure are drinking water, sea food and agricultural produces. Arsenic pollution was found to be associated with severe health hazards such as cancer and other health issues. Thus considering the severity of the issue, few sustainable remediation technologies such as adsorption using microbes, biological waste material, nanomaterial, constructed wetland, phytoremediation and microorganism bioremediation are proposed for treating arsenic pollution. These approaches are environmentally friendly and highly sustainable, thus making them suitable for the current scenario of environmental crisis.

Unveiling the Potential of Bioinoculants and Nanoparticles in Sustainable Agriculture for Enhanced Plant Growth and Food Security

The increasing public concern over the negative impacts of chemical fertilizers and pesticides on food security and sustainability has led to exploring innovative methods that offer both environmental and agricultural benefits. One such innovative approach is using plant-growth-promoting bioinoculants that involve bacteria, fungi, and algae. These living microorganisms are applied to soil, seeds, or plant surfaces and can enhance plant development by increasing nutrient availability and defense against plant pathogens. However, the application of biofertilizers in the field faced many challenges and required conjunction with innovative delivering approaches. Nanotechnology has gained significant attention in recent years due to its numerous applications in various fields, such as medicine, drug development, catalysis, energy, and materials. Nanoparticles with small sizes and large surface areas (1-100 nm) have numerous potential functions. In sustainable agriculture, the development of nanochemicals has shown promise as agents for plant growth, fertilizers, and pesticides. The use of nanomaterials is being considered as a solution to control plant pests, including insects, fungi, and weeds. In the food industry, nanoparticles are used as antimicrobial agents in food packaging, with silver nanomaterials being particularly interesting. However, many nanoparticles (Ag, Fe, Cu, Si, Al, Zn, ZnO, TiO2, CeO2, Al2O3, and carbon nanotubes) have been reported to negatively affect plant growth. This review focuses on the effects of nanoparticles on beneficial plant bacteria and their ability to promote plant growth. Implementing novel sustainable strategies in agriculture, biofertilizers, and nanoparticles could be a promising solution to achieve sustainable food production while reducing the negative environmental impacts.

Current Status of Biotechnological Approaches to Enhance the Phytoremediation of Heavy Metals in India-A Review

Rising waste construction, agricultural actions, and manufacturing sewages all contribute to heavy metal accumulation in water resources. Humans consume heavy metals-contaminated substances to make sustenance, which equally ends up in the food circle. Cleaning of these vital properties, along with the prevention of new pollution, has long been required to evade negative strength consequences. Most wastewater treatment techniques are widely acknowledged to be costly and out of the grasp of governments and small pollution mitigation businesses. Utilizing hyper-accumulator plants that are extremely resilient to heavy metals in the environment/soil, phytoremediation is a practical and promising method for eliminating heavy metals from contaminated environments. This method extracts, degrades, or detoxifies harmful metals using green plants. The three phytoremediation techniques of phytostabilization, phytoextraction, and phytovolatilization have been used extensively for soil remediation. Regarding their ability to be used on a wide scale, conventional phytoremediation methods have significant limitations. Hence, biotechnological attempts to change plants for heavy metal phytoremediation methods are extensively investigated in order to increase plant effectiveness and possible use of improved phytoremediation approaches in the country of India. This review focuses on the advances and significance of phytoremediation accompanied by the removal of various harmful heavy metal contaminants. Similarly, sources, heavy metals status in India, impacts on nature and human health, and variables influencing the phytoremediation of heavy metals have all been covered.

Alleviation of cadmium and drought stress in wheat by improving growth and chlorophyll contents amended with GA3 enriched deashed biochar

Drought and cadmium (Cd) stress are both major issues that significantly affect the growth and development of wheat plants. Both drought stress and Cd toxicity disrupt physiological processes i.e., nutrient uptake, cell expansion, and enzymatic reactions resulting in poor crop growth. To overcome these issues, the use of activated carbon and gibberellic acid (GA3) are considered valuable amendments. However, the current study aimed to add value using GA3-enriched biochar (GA3-BC). That's why, a lab experiment was conducted on wheat to assess the effectiveness of GA3-BC against Cd and drought stress. For GA3 enrichment in biochar, 10 µg GA3/g biochar was mixed. There were 3 levels of GA3-BC i.e., 0, 0.6 (GA3-BC1), and 0.9% (GA3-BC). All levels were applied in 3 replicates under no stress (0Cd + no drought), drought stress (DS), and 6 mg Cd/ kg soil (6Cd). Results showed that GA3-BC2 caused a significant improvement in shoot length (44.99%), root length (99.73%), seedling length (60.13%) and shoot fresh weight (63.59%) over control at 6Cd + drought stress. A significant improvement in chlorophyll a, chlorophyll b, and total chlorophyll while a decrease in electrolyte leakage and regulation of antioxidants i.e., lipid peroxidation, SOD, CAT, APx, GR, GPx, GST, and DPHH also signified the effectiveness of GA3-BC2 compared to control at 6Cd + drought stress. In conclusion, GA3-BC2 is an efficacious amendment for simultaneously alleviating drought and Cd stress in wheat. More investigations are recommended at the field level on different cereal crops cultivated in different soil textures to declare GA3-BC2 as the best treatment for mitigation of drought stress and Cd toxicity.

Plant growth promoting rhizobacteria modulates the antioxidant defense and the expression of stress-responsive genes providing Pb accumulation and tolerance of grass pea

To ensure the success of phytoremediation, it is important to consider the appropriate combination of plants and microorganisms. This study was conducted to get a better insight into the underlying molecular and biochemical mechanism of grass pea (Lathyrus sativus L.) induced by plant growth promoting rhizobacteria (PGPR), when exposed for 3, 6, 9, and 14 days to 1 mM Pb in a hydroponic system. The significant positive effect of bacterial inoculation was reproduced in various parameters. Results indicated that inoculation of PGPR significantly increased the accumulation of Pb by 20%, 66%, 43%, and 36% in roots and by 46%, 55%, 37%, and 46% in shoots, respectively after 3, 6, 9, and 14 days of metal exposure compared to the uninoculated plants. The metal accumulation in grass pea plants triggered a significant elevation in the synthesis of non-protein thiols (NPT), particularly in inoculated plant leaves where it was about 3 and 2-fold higher than the uninoculated set on the 6th and the 9th day. Nevertheless, Pb treatment significantly increased oxidative stress and membrane damage in leaves with the highest hydrogen peroxide (H2O2) production and tissue malondialdehyde (MDA) concentration recorded in uninoculated plants. Furthermore, the PGPR inoculation alleviated the oxidative stress, improved significantly plant tolerance, and modulated the activities of antioxidant enzymes (SOD, CAT, APX, GR, DHAR, and MDHAR). Similarly, the expression patterns of LsPCS, LsGCN, LsCNGC, LsGR, and LsGST through qRT-PCR demonstrated that bacterial inoculation significantly induced gene expression levels in leaves 6 days after Pb treatment, indicating that PGPR act as regulators of stress-responsive genes. The findings suggest the key role of PGPR (R. leguminosarum (M5) + Pseudomonas fluorescens (K23) + Luteibacter sp. + Variovorax sp.) in enhancing Pb accumulation, reducing metal toxicity, strengthening of the antioxidant system, and conferring higher Pb tolerance to grass pea plants. Hence, the association Lathyrus sativus-PGPR is an effective tool to achieve the goal of remediation of Pb contaminated sites.

Recent advances in bioremediation of heavy metals and persistent organic pollutants: A review

Heavy metals and persistent organic pollutants are causing detrimental effects on the environment. The seepage of heavy metals through untreated industrial waste destroys the crops and lands. Moreover, incineration and combustion of several products are responsible for primary and secondary emissions of pollutants. This review has gathered the remediation strategies, current bioremediation technologies, and their primary use in both in situ and ex situ methods, followed by a detailed explanation for bioremediation over other techniques. However, an amalgam of bioremediation techniques and nanotechnology could be a breakthrough in cleaning the environment by degrading heavy metals and persistant organic pollutants.

Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil

In the present scenario, the uncontrolled and irrational use of pesticides is affecting the environment, agriculture and livelihood worldwide. The excessive application of pesticides for better production of crops and to maintain sufficient food production is leading to cause many serious environmental issues such as soil pollution, water pollution and also affecting the food chain. The efficient management of pesticide use and remediation of pesticide-contaminated soil is one of the most significant challenges to overcome. The efficiency of the current methods of biodegradation of pesticides using different microbes and enzymes depends on the various physical and chemical conditions of the soil and they have certain limitations. Hence, a novel strategy is the need of the hour to safeguard the ecosystem from the serious environmental hazard. In recent years, the application of nanomaterials has drawn attention in many areas due to their unique properties of small size and increased surface area. Nanotechnology is considered to be a promising and effective technology in various bioremediation processes and provides many significant benefits for improving the environmental technologies using nanomaterials with efficient performance. The present article focuses on and discusses the role, application and importance of nano-bioremediation of pesticides and toxic pollutants to explore the potential of nanomaterials in the bioremediation of hazardous compounds from the environment.

Evaluation of Selected Heavy Metals Contaminants in the Fruits and Leaves of Organic, Conventional and Wild Raspberry (Rubus idaeus L.)

Chemical pollutants contaminate the air, soil and then plants, which are the main source of xenobiotics for humans. Many consumers perceive that organically grown foods are of better quality, healthier and more nutritious than conventionally grown foods. The aim of the study was to analyse raspberry fruits and leaves from organic, conventional and wild crops in Poland for two years, independently of climatic and agrotechnical conditions. The metal contents (Al, B, Cu, Mn and Zn) were determined using the validated Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and by Inductively Coupled Plasma Mass Spectrometry (ICP-MS/MS) (As, Cd, Pb, Cr, Co, Mo, V, Sr, Sb, Ti and Tl). The raspberry fruits from organic farming contained more (p ≤ 0.05) Cd, Zn, Mn and V compared to those from conventional cultivation. Fruits of wild-growing raspberry had more Cd, Zn, Co and Mn compared to other crops. Wild-growing raspberry leaves had more Cd, Pb, Zn, Mn and Tl than the other leaves. The raspberry leaves from organic cultivation had more Cr, Cd and Pb compared to leaves from conventional cultivation. The leaves and fruits of wild-growing raspberry are characterized by a significantly higher content of heavy metals.