Arbuscular Mycorrhiza Augments Arsenic Tolerance in Wheat (Triticum aestivum L.) by Strengthening Antioxidant Defense System and Thiol Metabolism

Assessment of rice genotypes through the lens of morpho-physiological and biochemical traits in response to arsenic stress

Rice is a globally important food crop which is sensitive to the presence of a metalloid, arsenic (As). There is limited research pertaining to identifying relevant As-tolerant rice germplasm in adaptive breeding research initiatives, despite the fact that As contamination in rice has long been known. This study served to identify the growth performance of different rice genotypes under high levels of As. Rice seed germination analysis (germination percentage, GP) was performed to categorize the eight different rice genotypes and growing under varying As levels including As25, 25 μM and As50, 50 μM. The Zhenong 41 was identified as the highly tolerant genotypes with lowest decrease in GP by 87 %, plant height (PH) by 26 %, and dry weight (DW) by 16 %; while 9311 was observed to be the most sensitive genotype with highest reduction in GP by 44 %, PH by 48 % and DW by 54 % under As25 stress conditions, compared to control treatment. The higher As50 stress treatment delivered more adverse growth inhibitory effects than the rice plants cultivated under As25. Specifically, the As-sensitive rice genotype 9311 showed significantly higher decrease in foliar chlorophyll contents relative to the other genotypes, especially Zhenong 41 (As-tolerant). During exposure to high As levels, the rice genotype 9311 significantly modulated and augmented the production of MDA and H2O2 by stimulating the activities of POD, SOD, and CAT. This study revealed interesting insights into the responses of rice genotypes to variable As stresses throughout the various growth stages. Overall, the findings of this study could be harnessed to support any ongoing As-tolerant rice breeding agendas for cultivation in As-polluted environments.

Role of arbuscular mycorrhizal fungi in lead translocation from Bidens pilosa L. plants to soil

Bidens pilosa frequently forms a symbiotic association with arbuscular mycorrhizal fungi (AMF). This plant species can grow in Pb-polluted soils, accumulating Pb in its tissues. The aims of the study were to determine whether Pb accumulated in the tissues of B. pilosa can be transferred to the soil through AMF and to compare the role of AMF communities that have a history of exposure to the contaminant with those that have never been exposed. The experiment combined plants with and without Pb accumulated in their tissues, and inoculated with AMF collected from the rhizosphere of B. pilosa in soils contaminated and not contaminated with Pb. The results showed that AMF participate in the removal of Pb that had entered the plant and release it into the soil, as evidenced by the presence of Pb in the AMF spores and in the glomalin produced by AMF. We propose that Pb accumulation in AMF spores would be a protection mechanism that interrupts Pb uptake by the plant; however, that mechanism would not be fully exploited in detoxification, whereas the production of Pb-enriched glomalin could be an important detoxification mechanism to eliminate Pb already taken up by plants. AMF with a history of Pb exposure achieved only higher rates of root colonization, while AMF without previous exposure showed higher Pb concentration in the spores and higher glomalin production, and successfully removed Pb from both the roots and aboveground parts of the plant. The use of AMF communities not adapted to Pb may be a more effective option for microbe-mediated phytoremediation methods in which detoxification mechanisms are desirable.

Application of CuNPs and AMF alleviates arsenic stress by encompassing reduced arsenic uptake through metabolomics and ionomics alterations in Elymus sibiricus

Recent studies have exhibited a very promising role of copper nanoparticles (CuNPs) in mitigation of abiotic stresses in plants. Arbuscular mycorrhizae fungi (AMF) assisted plants to trigger their defense mechanism against abiotic stresses. Arsenic (As) is a non-essential and injurious heavy-metal contaminant. Current research work was designed to elucidate role of CuNPs (100, 200 and 300 mM) and a commercial inoculum of Glomus species (Clonex® Root Maximizer) either alone or in combination (CuNPs + Clonex) on physiology, growth, and stress alleviation mechanisms of E. sibiricus growing in As spiked soils (0, 50, and 100 mg Kg- 1 soil). Arsenic induced oxidative stress, enhanced biosynthesis of hydrogen peroxide, lipid peroxidation and methylglyoxal (MG) in E. sibiricus. Moreover, As-phytotoxicity reduced photosynthetic activities and growth of plants. Results showed that individual and combined treatments, CuNPs (100 mM) as well as soil inoculation of AMF significantly enhanced root growth and shoot growth by declining As content in root tissues and shoot tissues in As polluted soils. E. sibiricus plants treated with CuNPs (100 mM) and/or AMF alleviated As induced phytotoxicity through upregulating the activity of antioxidative enzymes such as catalase (CAT) and superoxide dismutase (SOD) besides the biosynthesis of non-enzymatic antioxidants including phytochelatin (PC) and glutathione (GSH). In brief, supplementation of CuNPs (100 mM) alone or in combination with AMF reduced As uptake and alleviated the As-phytotoxicity in E. sibiricus by inducing stress tolerance mechanism resulting in the improvement of the plant growth parameters.

Sustainable Remediation of Soil and Water Utilizing Arbuscular Mycorrhizal Fungi: A Review

Phytoremediation is recognized as an environmentally friendly technique. However, the low biomass production, high time consumption, and exposure to combined toxic stress from contaminated media weaken the potential of phytoremediation. As a class of plant-beneficial microorganisms, arbuscular mycorrhizal fungi (AMF) can promote plant nutrient uptake, improve plant habitats, and regulate abiotic stresses, and the utilization of AMF to enhance phytoremediation is considered to be an effective way to enhance the remediation efficiency. In this paper, we searched 520 papers published during the period 2000-2023 on the topic of AMF-assisted phytoremediation from the Web of Science core collection database. We analyzed the author co-authorship, country, and keyword co-occurrence clustering by VOSviewer. We summarized the advances in research and proposed prospective studies on AMF-assisted phytoremediation. The bibliometric analyses showed that heavy metal, soil, stress tolerance, and growth promotion were the research hotspots. AMF-plant symbiosis has been used in water and soil in different scenarios for the remediation of heavy metal pollution and organic pollution, among others. The potential mechanisms of pollutant removal in which AMF are directly involved through hyphal exudate binding and stabilization, accumulation in their structures, and nutrient exchange with the host plant are highlighted. In addition, the tolerance strategies of AMF through influencing the subcellular distribution of contaminants as well as chemical form shifts, activation of plant defenses, and induction of differential gene expression in plants are presented. We proposed that future research should screen anaerobic-tolerant AMF strains, examine bacterial interactions with AMF, and utilize AMF for combined pollutant removal to accelerate practical applications.

Transcriptome analysis shows that Glomus versiforme decrease the accumulation and toxicity of cadmium in Ipomoea aquatic Forsk

So far, the physiological and molecular mechanisms of the impact of arbuscular mycorrhizal fungus (AMF) on Cd absorption, transport and detoxification in Ipomoea aquatica (water spinach) are still unclear. In the present study, a pot experiment was performed to investigate the impact of AMF-Glomus versiforme (Gv) on the photosynthetic characteristics, Cd uptake, antioxidative system and transcriptome in water spinach in the soils supplemented with 5 mg Cd kg-1. Gv inoculation improved significantly the photosynthetic characteristics and growth of water spinach. Furthermore, Gv colonization significantly promoted the activities of catalase (CAT), peroxidase (POD) and glutathione reductase (GR), contents of glutathione (GSH) and ascorbic acid (AsA), and the total antioxidant capacity (TCA), but decreased malondialdehyde (MDA) content in water spinach. In addition, Gv inoculation significantly increased pH in rhizosphere soils and decreased the Cd concentrations and uptakes in water spinach. Importantly, 2670 differentially expressed genes (DEGs) were screened in water spinach root colonized with Gv in 5 mg Cd kg-1 soil, of which 2008 DEGs were upregulated and 662 DEGs were downregulated. Especially, the expression levels of POD, CAT, GR, dehydroascorbate reductase 2 (DHAR2), glutathione S-transferase U8 (GSTU8) and glutathione synthetase (GSHS) and cytochrome P450 (Cyt P450) genes were significantly up-regulated in water spinach inoculated with Gv. Meanwhile, the plant cadmium resistance protein 2 (PCR2), metal tolerance protein 4 (MTP4), ATP-binding cassette transporter C family member (ABCC), ABC-yeast cadmium factor 1 (ABC-YCF1) and metallothionein (MT) genes were also up-regulated in mycorrhizal water spinach. Our results firstly elucidated the mechanism by which AMF reduced the uptake and phytotoxicity of Cd in water spinach through a transcriptome analysis.

Zinc oxide application alleviates arsenic-mediated oxidative stress via physio-biochemical mechanism in rice

Arsenic (As) pollution in cultivated soils poses a significant risk to the sustainable growth of agriculture and jeopardizes food security. However, the mechanisms underlying how zinc (Zn) regulates the toxic effects induced by As in plants remain poorly understood. Hence, this study aimed to explore the potential of ZnO as an effective and environmentally friendly amendment to alleviate As toxicity in rice, thereby addressing the significant risk posed by As pollution in cultivated soils. Through a hydroponic experiment, the study assessed the mitigating effects of different ZnO dosages (Zn5, 5 mg L-1; Zn15, 15 mg L-1; Zn30, 30 mg L-1) on rice seedlings exposed to varying levels of As stress (As0, 0 µM L-1; As25, 25 µM L-1). The findings of the study demonstrate significant improvements in plant height and biomass (shoot and root), with a notable increase of 16-40% observed in the Zn15 treatment, and an even more substantial enhancement of 29-53% observed in the Zn30 treatment under As stress, compared to respective control treatment. Furthermore, in the Zn30 treatment, the shoot and root As contents substantially reduced by 47% and 63%, respectively, relative to the control treatment. The elevated Zn contents in shoots and roots enhanced antioxidant enzyme activities (POD, SOD, and CAT), and decreased MDA contents (13-25%) and H2O2 contents (11-27%), indicating the mitigation of oxidative stress. Moreover, the expression of antioxidant-related genes, OsSOD-Cu/Zn, OsCATA, OsCATB, and OsAPX1 was reduced when rice seedlings were exposed to As stress and significantly enhanced after Zn addition. Overall, the research suggests that ZnO application could effectively mitigate As uptake and toxicity in rice plants cultivated in As-contaminated soils, offering potential solutions for sustainable agriculture and food security.

Transcriptome analysis of Gossypium reveals the molecular mechanisms of Ca2+ signaling pathway on arsenic tolerance induced by arbuscular mycorrhizal fungi

Introduction

Arbuscular mycorrhizal fungi (AMF) have been demonstrated their ability to enhance the arsenic (As) tolerance of host plants, and making the utilization of mycorrhizal plants a promising and practical approach for remediating As-contaminated soils. However, comprehensive transcriptome analysis to reveal the molecular mechanism of As tolerance in the symbiotic process between AMF and host plants is still limited.

Methods

In this study, transcriptomic analysis of Gossypium seedlings was conducted with four treatments: non-inoculated Gossypium under non-As stress (CK0), non-inoculated Gossypium under As stress (CK100), F. mosseae-inoculated Gossypium under non-As stress (FM0), and F. mosseae-inoculated Gossypium under As stress (FM100).

Results

Our results showed that inoculation with F. mosseae led to a reduction in net fluxes of Ca2+, while increasing Ca2+ contents in the roots and leaves of Gossypium under the same As level in soil. Notably, 199 and 3129 differentially expressed genes (DEGs) were specially regulated by F. mosseae inoculation under As stress and non-As stress, respectively. Through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation and enrichment analyses, we found that under As stress, F. mosseae inoculation up-regulated a significant number of genes related to the Ca2+ signaling pathway genes, involved in cellular process, membrane part, and signal transduction. This suggests a potential role in mitigating As tolerance in Gossypium seedlings. Furthermore, our analysis identified specific DEGs in transcription factor families, including ERF, MYB, NAC, and WRKY, that were upregulated by F. mosseae inoculation. Conversely, MYB and HB-other were down-regulated. The ERF and MYB families exhibited the highest number of up- and down-regulated DEGs, respectively, which were speculated to play an important role in alleviating the As toxicity of Gossypium.

Discussion

Our findings provided valuable insights into the molecular theoretical basis of the Ca2+ signaling pathway in improving As tolerance of mycorrhizal plants in the future.

Nutrient and mycoremediation of a global menace 'arsenic': exploring the prospects of phosphorus and Serendipita indica-based mitigation strategies in rice and other crops

KEY MESSAGE

Serendipita indica induced metabolic reprogramming in colonized plants complements phosphorus-management in improving their tolerance to arsenic stress on multifaceted biological fronts. Restoration of the anthropic damage done to our environment is inextricably linked to devising strategies that are not only economically sound but are self-renewing and ecologically conscious. The dilemma of heavy metal (HM) dietary ingestion, especially arsenic (As), faced by humans and animals alike, necessitates the exploitation of such technologies and the cultivation of healthy and abundant crops. The remarkable symbiotic alliance between plants and 'mycorrhizas' has evolved across eons, benefiting growth/yield aspects as well as imparting abiotic/biotic stress tolerance. The intricate interdependence of Serendipita indica (S. indica) and rice plant reportedly reduce As accumulation, accentuating the interest of microbiologists, agriculturists, and ecotoxicological scientists apropos of the remediation mechanisms of As in the soil-AMF-rice system. Nutrient management, particularly of phosphorus (P), is also praised for mitigating As phytotoxicity by deterring the uptake of As molecules due to the rhizospheric cationic competition. Taking into consideration the reasonable prospects of success in minimizing As acquisition by rice plants, this review focuses on the physiological, metabolic, and transcriptional alterations underlying S. indica symbiosis, recuperation of As stress together with nutritional management of P by gathering case studies and presenting successful paradigms. Weaving together a volume of literature, we assess the chemical forms of As and related transport pathways, discuss As-P-rice interaction and the significance of fungi in As toxicity mitigation, predominantly the role of mycorrhiza, as well as survey of the multifaceted impacts of S. indica on plants. A potential strategy for simultaneous S. indica + P administration in paddy fields is proposed, followed by future research orientation to expand theoretic comprehension and encourage field-based implementation.

Hesperidin and chlorogenic acid mitigate arsenic-induced oxidative stress via redox regulation, photosystems-related gene expression, and antioxidant efficiency in the chloroplasts of Zea mays

The ubiquitous metalloid arsenic (As), which is not essential, can be found extensively in the soil and subterranean water of numerous nations, raising substantial apprehensions due to its impact on both agricultural productivity and sustainability. Plants exposed to As often display morphological, physiological, and growth-related abnormalities, collectively leading to reduced productivity. Polyphenols, operating as secondary messengers within the intricate signaling networks of plants, assume integral functions in the acquisition of resistance to diverse environmental stressors, including but not limited to drought, salinity, and exposure to heavy metals. The pivotal roles played by polyphenols in these adaptive processes underscore their profound significance in plant biology. This study aims to elucidate the impact of hesperidin (HP) and chlorogenic acid (CA), recognized as potent bioactive compounds, on maize plants exposed to As. To achieve this objective, the study examined the physiological and biochemical impacts, including growth parameters, photosynthesis, and chloroplastic antioxidants, of HP (100 μM) and CA (50 μM) on Zea mays plants exposed to arsenate stress (AsV, 100 μM - Na2HAsO4⋅7H2O). As toxicity led to reductions in fresh weight (FW) and dry weight (DW) by 33% and 26%, respectively. However, the application of As+HP and As + CA increased FW by 22% and 40% and DW by 14% and 17%, respectively, alleviating the effects of As stress. As toxicity resulted in the up-regulation of PSII genes (psbA and psbD) and PSI genes (psaA and psaB), indicating a potential response to the re-formation of degraded regions, likely driven by the heightened demand for photosynthesis. Exogenous HP or/and CA treatments effectively counteracted the adverse effects of As toxicity on the photochemical quantum efficiency of PSII (Fv/Fm). H2O2 content showed a 23% increase under As stress, and this increase was evident in guard cells when examining confocal microscopy images. In the presence of As toxicity, the chloroplastic antioxidant capacity can exhibit varying trends, with either a decrease or increase observed. After the application of CA and/or HP, a significant increase was observed in the activity of GR, APX, GST, and GPX enzymes, resulting in decreased levels of H2O2 and MDA. Additionally, the enhanced functions of MDHAR and DHAR have modulated the redox status of ascorbic acid (AsA) and glutathione (GSH). The HP or CA-mediated elevated levels of AsA and GSH content further contributed to the preservation of redox homeostasis in chloroplasts facing stress induced by As. In summary, the inclusion of HP and CA in the growth medium sustained plant performance in the presence of As toxicity by regulating physiological and biochemical characteristics, chloroplastic antioxidant enzymes, the AsA-GSH cycle and photosynthesis processes, thereby demonstrating their significant potential to confer resistance to maize through the mitigation of As-induced oxidative damage and the safeguarding of photosynthetic mechanisms.

Arbuscular mycorrhizae reduced arsenic induced oxidative stress by coordinating nutrient uptake and proline-glutathione levels in Cicer arietinum L. (chickpea)

Accumulation of Arsenic (As) generates oxidative stress by reducing nutrients availability in plants. Arbuscular mycorrhizal (AM) symbiosis can impart metalloid tolerance in plants by enhancing the synthesis of sulfur (S)-rich peptides (glutathione- GSH) and low-molecular-weight nitrogenous (N) osmolytes (proline- Pro). The present study, therefore investigated the efficiency of 3 AM fungal species (Rhizoglomus intraradices-Ri, Funneliformis mosseae -Fm and Claroideoglomus claroideum- Cc) in imparting As (arsenate-AsV -40 at 60 mg kg-1 and arsenite- AsIII at 5 and 10 mg kg-1) tolerance in two Cicer arietinum (chickpea) genotypes (HC 3 and C 235). As induced significantly higher negative impacts in roots than shoots, which was in accordance with proportionately higher reactive oxygen species (ROS) in the former, with AsIII more toxic than AsV. Mycorrhizal symbiosis overcame oxidative stress by providing the host plants with necessary nutrients (P, N, and S) through enhanced microbial enzyme activities (MEAs) in soil, which increased the synthesis of Pro and GSH and established a redox balance in the two genotypes. This coordination between nutrient status, Pro-GSH levels, and antioxidant defense was stronger in HC 3 than C 235 due to its higher responsiveness to the three AM species. However, Ri was most beneficial in inducing redox homeostasis, followed by Fm and Cc, since the Cicer arietinum-Ri combination displayed the maximum ability to boost antioxidant defense mechanisms and establish a coordination with Pro synthesis. Thus, the results highlighted the importance of selecting specific chickpea genotypes having an ability to establish effective mycorrhizal symbiosis for imparting As stress tolerance.

Integrative application of biochar and arbuscular mycorrhizal fungi for enhanced chromium resistance in Medicago sativa

Soil chromium (Cr) contamination has become an environmental problem of global concern. However, the joint effects of combined utilization of biochar and arbuscular mycorrhizal (AM) fungal inoculum, which are considered as two promising remediation strategies of soil heavy metal pollutions, on plant Cr resistance are still poorly understood. In this study, a two-factor pot experiment was conducted to investigate how biochar and AM fungus Rhizophagus irregularis regulate Medicago sativa growth, physiological trait, nutrient and Cr uptake, relevant gene expressions, soil properties, and Cr speciation, independently or synergistically. The results showed that biochar notably decreased AM colonization, while biochar and AM fungus could simultaneously increase plant dry biomass. The greatest growth promotion was observed in mycorrhizal shoots at the highest biochar level (50 g kg-1 soil) by 91 times. Both biochar application and AM fungal inoculation enhanced plant photosynthesis and P nutrition, but the promoting effects of AM fungus on them were significantly greater than that of biochar. In addition, the combined application of biochar and AM fungus dramatically reduced shoot and root Cr concentrations by up to 92 % and 78 %, respectively, compared to the non-amended treatment. Meanwhile, down-regulated expressions were observed for metal chelating-related genes. Furthermore, Cr translocation from roots to shoots was reduced by both two soil amendments. Transcriptional levels of genes involved in reactive oxygen species and proline metabolisms were also regulated by biochar application and AM fungal colonization, leading to alleviation of Cr phytotoxicity. Furthermore, AM fungal inoculation slightly elevated soil pH but decreased plant-available soil P, which was, by contrast, lifted by biochar addition. The combined application reduced soil acid-extractable Cr concentration by 40 %. This study provides new insights into comprehensively understanding of the mechanisms of biochar and AM fungi combination on improving plant Cr tolerance.

Soil microbiome engineering for sustainability in a changing environment

Recent advances in microbial ecology and synthetic biology have the potential to mitigate damage caused by anthropogenic activities that are deleteriously impacting Earth's soil ecosystems. Here, we discuss challenges and opportunities for harnessing natural and synthetic soil microbial communities, focusing on plant growth promotion under different scenarios. We explore current needs for microbial solutions in soil ecosystems, how these solutions are being developed and applied, and the potential for new biotechnology breakthroughs to tailor and target microbial products for specific applications. We highlight several scientific and technological advances in soil microbiome engineering, including characterization of microbes that impact soil ecosystems, directing how microbes assemble to interact in soil environments, and the developing suite of gene-engineering approaches. This Review underscores the need for an interdisciplinary approach to understand the composition, dynamics and deployment of beneficial soil microbiomes to drive efforts to mitigate or reverse environmental damage by restoring and protecting healthy soil ecosystems.

Mycorrhized wheat and bean plants tolerate bismuth contaminated soil via improved metal detoxification and antioxidant defense systems

Contamination of agricultural fields with bismuth (Bi) reduces crop yield and quality. Arbuscular mycorrhizal fungi (AMF) are known to enhance plant growth and crop production, even under stressful conditions such as soil contamination with heavy metals. The objective of this study was to investigate the effect of AMF on the mitigation of Bi-phytotoxicity in wheat (Triticum aestivum) and beans (Phaseolus vulgaris) and to provide a comprehensive evaluation of the physiological and biochemical basis for the growth and development of AMF-induced plants under Bi stress conditions. Wheat and bean were treated by Bi and AMF individually and in combination. Then the physiological and biochemical responses in the shoot and roots of the two crop species were studied. Evident retardations in plant growth and key photosynthesis-related parameters and accumulation of MDA, H2O2, as markers of oxidative stress, were observed in plants subjected to Bi. AMF colonization reduced the uptake and translocation of Bi in the plant organs by enhancing the exudation of polyphenols and organic acids into the rhizospheric soil. Mycorrhized wheat and bean plants were able to attenuate the effects of Bi by improving metal detoxification (phytochelatins, metallothionein, total glutathione, and glutathione-S-transferase activity) and antioxidant defense systems (both enzymatic and non-enzymatic) and maintaining C assimilation and nutrient status. The current results suggest the manipulation of AMF as a powerful approach to alleviate the phytotoxicity of Bi in legumes and grasses.

Arbuscular mycorrhiza augments aluminum tolerance in white clover (Trifoliumrepens L.) by strengthening the ascorbate-glutathione cycle and phosphorus acquisition

The ascorbate-glutathione (AsA-GSH) cycle is essential for detoxifying reactive oxygen species (ROS) under environmental stresses. The toxicity of aluminum (Al) limits the growth and performance of cultivated plants in acidic soil. However, there is limited information available on the relationship between arbuscular mycorrhizal symbiosis and the AsA-GSH cycle in host plants under Al stress. This study aimed to examine the impact of arbuscular mycorrhizal fungi (AMF), specifically Funneliformis mosseae, on the growth, antioxidant enzymes, components of the AsA-GSH cycle, and stress response gene expressions in white clover (Trifolium repens L.) under Al stress. Our findings demonstrate that AMF inoculation significantly reduced Al accumulation and increased phosphorus (P) content in the roots of white clover, thereby promoting plant biomass accumulation and mycorrhizal colonization under Al stress. AMF effectively scavenged Al-induced ROS (H2O2 and O2-) by enhancing the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as the components of the AsA-GSH cycle (e.g., enzymes and antioxidants) in the leaves and roots of white clover plants. Additionally, the mitigating effect of AMF was associated with the upregulation of genes involved in P transport (PHO1-2 and PHT1-7), the AsA-GSH pathway (GST-2 and APX-2), and Al stress (ALMT1) in white clover roots compared to control plants. Principal component analysis revealed that 65.9% of the total variance was explained by the first principal component. Dry mass showed a positive correlation with POD and P content, while exhibiting a highly negative correlation with ROS, antioxidant physiology index, Al content, and the expression of related genes in white clover. Overall, this study suggests that AMF enhances the tolerance of white clover to Al stress by improving P uptake and strengthening the AsA-GSH cycle.

Graphical Abstract

Insight into the plant-associated bacterial interactions: Role for plant arsenic extraction and carbon fixation

This study investigated the interactions between rhizosphere and endosphere bacteria during phytoextraction and how the interactions affect arsenic (As) extraction and carbon (C) fixation of plants. Pot experiments, high-throughput sequencing, metabonomics, and network analysis were integrated. Results showed that positive correlations dominated the interconnections within modules (>95 %), among modules (100 %), and among keystone taxa (>72 %) in the bacterial networks of plant rhizosphere, root endosphere, and shoot endosphere. This confirmed that cooperative interactions occurred between bacteria in the rhizosphere and endosphere during phytoextraction. Modules and keystone taxa positively correlating with plant As extraction and C fixation were identified, indicating that modules and keystone taxa promoted plant As extraction and C fixation simultaneously. This is mainly because modules and keystone taxa in plant rhizosphere, root endosphere, and shoot endosphere carried arsenate reduction and C fixation genes. Meanwhile, they up-regulated the significant metabolites related to plant As tolerance. Additionally, shoot C fixation increased peroxidase activity and biomass thereby facilitating plant As extraction was confirmed. This study revealed the mechanisms of plant-associated bacterial interactions contributing to plant As extraction and C fixation. More importantly, this study provided a new angle of view that phytoextraction can be applied to achieve multiple environmental goals, such as simultaneous soil remediation and C neutrality.

Zinc oxide nanoparticles mitigated the arsenic induced oxidative stress through modulation of physio-biochemical aspects and nutritional ions homeostasis in rice (Oryza sativa L.)

Zinc oxide nanoparticles (nZn) have emerged as vital agents in combating arsenic (As) stress in plants. However, their role in mitigation of As induced oxidative stress is less studied. Therefore, this study aimed to assess the comparative role of nZn and ZnO in alleviating As toxicity in rice genotype "9311". The results of this study revealed that nZn demonstrated superior efficacy compared to ZnO in mitigating As toxicity. This superiority can be attributed to the unique size and structure of nZn, which enhances its ability to alleviate As toxicity. Exposure to As at a concentration of 25 μM L-1 led to significant reductions in shoot length, root length, shoot dry weight, and root dry weight by 39%, 51%, 30%, and 46%, respectively, while the accumulation of essential nutrients such as magnesium (Mg), potassium (K), iron (Fe), manganese (Mn), and zinc (Zn) decreased by 25%-47% compared to the control plants. Additionally, As exposure resulted in stomatal closure and structural damage to vital cellular components such as grana thylakoids (GT), starch granules (SG), and the nucleolus. However, the application of nZn at a concentration of 30 mg L-1 exhibited significant alleviation of As toxicity, resulting in a reduction of As accumulation by 54% in shoots and 62% in roots of rice seedlings. Furthermore, nZn demonstrated the ability to scavenge reactive oxygen species (ROS) like hydrogen peroxide (H2O2) and superoxide anion (O2.-), while significantly promoted the gas exchange parameters, chlorophyll content (SPAD value), fluorescence efficiency (Fv/m) and antioxidant enzyme activities under As-induced stress. These findings highlight the potential of nZn in mitigating the adverse impacts of As contamination in rice plants. However, further research is necessary to fully comprehend the underlying mechanisms responsible for the protective effects of nZn and to determine the optimal conditions for their application in real-world agricultural settings.

Improvements in the biochemical responses and Pb and Ni phytoremediation of lavender (Lavandula angustifolia L.) plants through Funneliformis mosseae inoculation

BACKGROUND

Heavy metals (HMs) phytoremediation is a well-recognized protocol to remove toxic elements from the soil. As known, arbuscular mycorrhizal fungi (AMF) enhance the plants' growth responses. The idea of the present study was to assay the response of lavender plants to HMs stress under AMF inoculation. We hypothesized that mycorrhiza will enhance the phytoremediation and simultaneously reduce the harmful effects of heavy HMs. So, lavender (Lavandula angustifolia L.) plants were inoculated with AMF (0 and 5 g Kg^-1 soil) under Pb [150 and 225 mg kg^-1 soil from Pb (NO₃)₂] and Ni [220 and 330 mg kg^-1 soil from Ni (NO₃)₂] pollution, in the greenhouse conditions. The control treatment was plants not treated with AMF and HMs. Doing this, the root colonization, HMs uptake, enzymatic and non-enzymatic antioxidants pool, MDA, proline, total phenolics (TPC), flavonoids (TFC), anthocyanins, and essential oil (EO) components were evaluated.

RESULTS

According to the findings, the AMF inoculation enhanced shoot and root Pb and Ni content, antioxidant enzymes activity, the total antioxidant activity by DPPH and FRAP methods, TPC, TFC, anthocyanins, and H₂O₂ content in the lavender plants subjected to Pb and Ni stress. Moreover, the highest (28.91%) and the least (15.81%) percentages of borneol were identified in the lavender plants subjected to AMF under 150 mg kg^-1 of Pb and the control plants without AMF application, respectively. Furthermore, the top 1,8-cineole (12.75%) content was recorded in AMF-inoculated plants.

CONCLUSIONS

The overall results verify that AMF inoculation can be a reliable methodology to enhance the phytoremediation of Pb and Ni by lavender plants while maintaining reliable growth potential. The treatments improved the main EO constituents content, especially under moderate HMs stress conditions. With more detailed studies, the results will be advisable for the extension section for the phytoremediation of polluted soils.

The function and community structure of arbuscular mycorrhizal fungi in ecological floating beds used for remediation of Pb contaminated wastewater

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to be ubiquitous in aquatic ecosystems. However, their distributions and ecological functions are rarely studied. To date, a few studies have combined sewage treatment facilities with AMF to improve removal efficiency, but appropriate and highly tolerant AMF strains have not been explored, and the purification mechanisms remain unclear. In this study, three ecological floating-bed (EFB) installations inoculated with different AMF inocula (mine AMF inoculum, commercial AMF inoculum and non-AMF inoculated) were constructed to investigate their removal efficiency for Pb-contaminated wastewater. The AMF community structure shifts in the roots of Canna indica inhabiting EFBs during the three phases (pot culture phase, hydroponic phase and hydroponic phase with Pb stress) were tracked utilizing quantitative real-time polymerase chain reaction and Illumina sequencing techniques. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to detect the Pb location in mycorrhizal structures. The results showed that AMF could promote host plant growth and enhance the Pb removal efficiency of the EFBs. The higher the AMF abundance, the better the effect of the AMF on Pb purification by EFBs. Both flooding and Pb stress decreased the AMF diversity but did not significantly inhibit the abundance. The three inoculation treatments showed different community compositions with different dominant AMF taxa in different phases, and an uncultured Paraglomus species (Paraglomus sp. LC516188.1) was found to be the most dominant (99.65 %) AMF in the hydroponic phase with Pb stress. The TEM and EDS analysis results showed that the Paraglomus sp. could accumulate Pb in plant roots through their fungal structures (intercellular mycelium, intracellular mycelium, etc.), which alleviated the toxic effect of Pb on plant cells and limited Pb translocation. The new findings provide a theoretical basis for the application of AMF in plant-based bioremediation of wastewater and polluted waterbodies.

Arbuscular mycorrhiza fungus alleviates arsenic mediated disturbances in tricarboxylic acid cycle and nitrogen metabolism in Triticum aestivum L

Utilization of arbuscular mycorrhizal (AM) fungi (AMF) as a sustainable strategy in redeeming arsenic (As) toxicity in plants is a promising approach. Low As accumulation, restoration of physiological processes, and As tolerance by AMF have been documented in crop plants. However, to comprehend AM-mediated As tolerance in plants, understanding the biochemical responses of host to the symbiont is crucial. The study evaluated the effect of an AM fungus, Rhizophagus intraradices on tricarboxylic acid cycle (TCA) and nitrogen metabolism of Triticum aestivum under three As concentrations (0, 25, and 50 mg As kg^-1 soil). Results showed that TCA cycle and nitrogen metabolism were severely impaired by As that resulted into a higher C/N ratio. However, colonization by R. intraradices attenuated As mediated alterations in TCA cycle by augmenting the activity of pyruvate dehydrogenase that provided sufficient substrate for the TCA cycle. Furthermore, mycorrhizal (M) plants reinstated the activities of isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase even under high As level. Although citrate synthase and oxoglutarate dehydrogenase activities declined upon As exposure in M-plants, these were nevertheless higher than their non-mycorrhizal (NM) counterparts, ensuring higher levels of citric acid and succinic acid in M-plants. AM colonization also moderated the As-mediated disturbances in nitrogen assimilation by augmenting the activity of nitrate reductase, nitrite reductase, glutamine synthase, and glutamine-2-oxoglutarate amino transferase. Overall findings of the study point out that colonization by R. intraradices favourably regulated the TCA cycle and nitrogen metabolism and confronted As-mediated alterations in C/N ratio.

Microbial remediation and plant-microbe interaction under arsenic pollution

Arsenic contamination in aquatic and terrestrial ecosystem is a serious environmental issue. Both natural and anthropogenic processes can introduce it into the environment. The speciation of the As determine the level of its toxicity. Among the four oxidation states of As (-3, 0, +3, and + 5), As(III) and As(V) are the common species found in the environment, As(III) being the more toxic with adverse impact on the plants and animals including human health. Therefore, it is very necessary to remediate arsenic from the polluted water and soil. Different physicochemical as well as biological strategies can be used for the amelioration of arsenic polluted soil. Among the microbial approaches, oxidation of arsenite, methylation of arsenic, biosorption, bioprecipitation and bioaccumulation are the promising transformation activities in arsenic remediation. The purpose of this review is to discuss the significance of the microorganisms in As toxicity amelioration in soil, factors affecting the microbial remediation, interaction of the plants with As resistant bacteria, and the effect of microorganisms on plant arsenic tolerance mechanism. In addition, the exploration of genetic engineering of the bacteria has a huge importance in bioremediation strategies, as the engineered microbes are more potent in terms of remediation activity along with quick adaptively in As polluted sites.

Interactive Effect of Arbuscular Mycorrhizal Fungi (AMF) and Olive Solid Waste on Wheat under Arsenite Toxicity

Heavy metal such as arsenite (As^III) is a threat worldwide. Thus, to mitigate As^III toxicity on plants, we investigated the interactive effect of olive solid waste (OSW) and arbuscular mycorrhizal fungi (AMF) on wheat plants under As^III stress. To this end, wheat seeds were grown in soils treated with OSW (4% w/w), AMF-inoculation, and/or As^III treated soil (100 mg/kg soil). AMF colonization is reduced by As^III but to a lesser extent under As^III + OSW. AMF and OSW interactive effects also improved soil fertility and increased wheat plants' growth, particularly under As^III stress. The interactions between OSW and AMF treatments reduced As^III-induced H₂O₂ accumulation. Less H₂O₂ production consequently reduced As^III-related oxidative damages i.e., lipid peroxidation (malondialdehyde, MDA) (58%), compared to As stress. This can be explained by the increase in wheat's antioxidant defense system. OSW and AMF increased total antioxidant content, phenol, flavonoids, and α-tocopherol by approximately 34%, 63%, 118%, 232%, and 93%, respectively, compared to As stress. The combined effect also significantly induced anthocyanins accumulation. The combination of OSW+AMF improved antioxidants enzymes activity, where superoxide dismutase (SOD, catalase (CAT), peroxidase (POX), glutathione reductase (GR), and glutathione peroxidase (GPX) were increased by 98%, 121%, 105%, 129%, and 110.29%, respectively, compared to As^III stress. This can be explained by induced anthocyanin percussors phenylalanine, cinamic acid and naringenin, and biosynthesic enzymes (phenylalanine aminolayse (PAL) and chalcone synthase (CHS)). Overall, this study suggested the effectiveness of OSW and AMF as a promising approach to mitigate As^III toxicity on wheat growth, physiology, and biochemistry.

Involvement of exogenous arsenic-reducing bacteria in root surface biofilm formation promoted phytoextraction of arsenic

Root surface biofilm (RSB) is the last window for pollutants entering plant roots and thus plays a critical role in the phytoextraction of pollutants. Exogenous arsenic-reducing bacteria (EARB) have been adopted to enhance the phytoextraction of arsenic (As). However, whether EARB would be involved in RSB formation together with indigenous bacteria and the role of EARB involvement in As phytoextraction are still unknown. Herein, two EARB strains and two phytoextractors (wheat and maize) were selected to investigate the involvement of EARB in RSB formation and its role in As phytoextraction. Results showed that EARB successfully participated in RSB formation together with indigenous bacteria, attributing to their strong chemotaxis and biofilm formation abilities induced by root exudates. The involvement of EARB in RSB formation significantly enhanced As accumulation in plant roots, since more arsenite (As(III)) caused by arsenate (As(V)) reduction in RSB was absorbed by roots. Its underlying mechanism was further elucidated. EARB involvement increased phylum Proteobacteria to produce more siderophores in RSB. Siderophores then improved photosynthesis by increasing catalase and peroxidase activities and decreasing the malondialdehyde of plants. These actions further raised the shoot fresh weight to enhance As accumulation in plant roots. Moreover, mesophyll cell in wheat has a stronger As(V) reduction ability than that in maize, resulting in opposite distribution patterns of As(III) and As(V) in wheat and maize shoots. This study provides a new understanding of phytoextraction enhanced by exogenous bacteria and fills the gap in the role of EARB in As phytoextraction from the perspective of the RSB microregion.

Physio-Biochemical and Transcriptomic Features of Arbuscular Mycorrhizal Fungi Relieving Cadmium Stress in Wheat

Arbuscular mycorrhizal fungi (AMF) can improve plant cadmium (Cd) tolerance, but the tolerance mechanism in wheat is not fully understood. This study aimed to examine the physiological properties and transcriptome changes in wheat inoculated with or without Glomus mosseae (GM) under Cd stress (0, 5, and 10 mg·kg^-1 CdCl₂) to understand its role in wheat Cd tolerance. The results showed that the Cd content in shoots decreased while the Cd accumulation in roots increased under AMF symbiosis compared to the non-inoculation group and that AMF significantly promoted the growth of wheat seedlings and reduced Cd-induced oxidative damage. This alleviative effect of AMF on wheat under Cd stress was mainly attributed to the fact that AMF accelerated the ascorbate-glutathione (AsA-GSH) cycle, promoted the production of GSH and metallothionein (MTs), improved the degradation of methylglyoxal (MG), and induced GRSP (glomalin-related soil protein) secretion. Furthermore, a comparative analysis of the transcriptomes of the symbiotic group and the non-symbiotic group revealed multiple differentially expressed genes (DEGs) in the 'metal ion transport', 'glutathione metabolism', 'cysteine and methionine metabolism', and 'plant hormone signal transduction' terms. The expression changes of these DEGs were basically consistent with the changes in physio-biochemical characteristics. Overall, AMF alleviated Cd stress in wheat mainly by promoting immobilization and sequestration of Cd, reducing ROS production and accelerating their scavenging, in which the rapid metabolism of GSH may play an important role.

Consequences of Arsenic Contamination on Plants and Mycoremediation-Mediated Arsenic Stress Tolerance for Sustainable Agriculture

Arsenic contamination in water and soil is becoming a severe problem. It is toxic to the environment and human health. It is usually found in small quantities in rock, soil, air, and water which increase due to natural and anthropogenic activities. Arsenic exposure leads to several diseases such as vascular disease, including stroke, ischemic heart disease, and peripheral vascular disease, and also increases the risk of liver, lungs, kidneys, and bladder tumors. Arsenic leads to oxidative stress that causes an imbalance in the redox system. Mycoremediation approaches can potentially reduce the As level near the contaminated sites and are procuring popularity as being eco-friendly and cost-effective. Many fungi have specific metal-binding metallothionein proteins, which are used for immobilizing the As concentration from the soil, thereby removing the accumulated As in crops. Some fungi also have other mechanisms to reduce the As contamination, such as biosynthesis of glutathione, cell surface precipitation, bioaugmentation, biostimulation, biosorption, bioaccumulation, biovolatilization, methylation, and chelation of As. Arsenic-resistant fungi and recombinant yeast have a significant potential for better elimination of As from contaminated areas. This review discusses the relationship between As exposure, oxidative stress, and signaling pathways. We also explain how to overcome the detrimental effects of As contamination through mycoremediation, unraveling the mechanism of As-induced toxicity.

Integrated metabolomic and transcriptomic profiling revealed coping mechanisms of the edible and medicinal homologous plant Plantago asiatica L. cadmium resistance

Rapidly increasing cadmium (Cd) pollution led to the increase in contamination in farmland. The study explained the Cd resistance mechanisms of Plantago asiatica L. via physiological, metabolomic, and transcriptomic analyses. The results showed that as soil Cd level increased, proline content declined and then increased significantly. In contrast to the H2O2 content change trend, contents of soluble protein and malondialdehyde (MDA) first decreased, then increased, and finally, declined. Leaf Cd concentration was positively related to soluble protein content and negatively to both MDA content and activities of superoxide dismutase (SOD) and catalase (CAT). Most of the top 50 differential metabolites belonged to organic acids and sugars. Besides combining metabolome and transcriptome data, in the metabolic network involving the target metabolic pathways (e.g., ascorbate and aldarate metabolism, glutathione metabolism, galactose metabolism, and glyoxylate and dicarboxylate metabolism), dehydroascorbate (DHA), regulated by l-ascorbate peroxidase (APX) and l-gulonolactone oxidase (GULO), was significantly up-regulated. This illuminated that, in P. asiatica, CAT and SOD played vital roles in Cd resistance, and soluble protein and MDA acted as the main indexes to characterize Cd damage. It also suggested that DHA functioned effectively in Cd resistance, and the function was regulated by APX and GULO.

Novel Mycorrhiza-Specific P Transporter PvPht1;6 Contributes to As Accumulation at the Symbiotic Interface of As-Hyperaccumulator Pteris vittata

Arsenic (As) is toxic and ubiquitous in the environment, posing a growing threat to human health. As-hyperaccumulator Pteris vittata has been used for phytoremediation of As-contaminated soil. Symbiosis with arbuscular mycorrhizal fungi (AMF) enhances As accumulation by P. vittata, which is different from As inhibition in typical plants. In this study, P. vittata seedlings inoculated with or without AMF were cultivated in As-contaminated soils for 2 months. AMF-root symbiosis enhanced plant growth, with 64.5% greater As contents in the fronds. After exposure to AsV for 2 h, the arsenate (AsV) and arsenite (AsIII) contents in AMF-roots increased by 1.8- and 3.6-fold, suggesting more efficient As uptake by P. vittata with AMF-roots. Plants take up and transport AsV via phosphate transporters (Phts). Here, for the first time, we identified a novel mycorrhiza-specific Pht transporter, PvPht1;6, from P. vittata. The transcripts of PvPht1;6 were strongly induced in AMF-roots, which were localized to the plasma membrane of arbuscule-containing cells. By complementing a yeast mutant lacking 5-Phts, we confirmed PvPht1;6's transport activity for both P and AsV. In contrast to typical AMF-inducible phosphate transporter LePT4 from tomato, PvPht1;6 showed greater AsV transport capacity. The results suggest that PvPht1;6 is probably critical for AsV transport at the periarbuscular membrane of P. vittata root cells, revealing the underlying mechanism of efficient As accumulation in P. vittata with AMF-roots.

Claroideoglomus etunicatum affects the structural and functional genes of the rhizosphere microbial community to help maize resist Cd and La stresses

Arbuscular mycorrhizal fungi (AMF) and plant rhizosphere microbes reportedly enhance plant tolerance to abiotic stresses and promote plant growth in contaminated soils. The co-contamination of soil by heavy metals (e.g., Cd) and rare earth elements (e.g., La) represents a severe environmental problem. Although the influence of AMF in the phytoremediation of contaminated soils is well documented, the underlying interactive mechanisms between AMF and rhizosphere microbes are still unclear. We conducted a greenhouse pot experiment to evaluate the effects of AMF (Claroideoglomus etunicatum) on maize growth, nutrient and metal uptake, rhizosphere microbial community, and functional genes in soils with separate and combined applications of Cd and La. The purpose of this experiment was to explore the mechanism of AMF affecting plant growth and metal uptake via interactions with rhizosphere microbes. We found that C. etunicatum (i) significantly enhanced plant nutritional level and biomass and decreased metal concentration in the co-contaminated soil; (ii) significantly altered the structure of maize rhizosphere bacterial and fungal communities; (iii) strongly enriched the abundance of carbohydrate metabolism genes, ammonia and nitrate production genes, IAA (indole-3-acetic acid) and ACC deaminase (1-aminocyclopropane-1-carboxylate) genes, and slightly altered the abundance of P-related functional genes; (iv) regulated the abundance of microbial quorum sensing system and metal membrane transporter genes, thereby improving the stability and adaptability of the rhizosphere microbial community. This study provides evidence of AMF improving plant growth and resistance to Cd and La stresses by regulating plant rhizosphere microbial communities and aids our understanding of the underlying mechanisms.

Increasing atmospheric CO2 differentially supports arsenite stress mitigating impact of arbuscular mycorrhizal fungi in wheat and soybean plants

Arbuscular mycorrhizal fungi (AMF) are beneficial for the plant growth under heavy metal stress. Such beneficial effect is improved by elevated CO2 (eCO2). However, the mechanisms by which eCO2 improves AMF symbiotic associations under arsenite (AsIII) toxicity are hardly studied. Herein, we compared these regulatory mechanisms in species from two agronomical important plant families - grasses (wheat) and legumes (soybean). AsIII decreased plant growth (i.e., 53.75 and 60.29% of wheat and soybean, respectively) and photosynthesis. It also increased photorespiration and oxidative injury in both species, but soybean was more sensitive to oxidative stress as indicated by higher H2O2 accumulation and oxidation of protein and lipid. eCO2 significantly improved AMF colonization by increasing auxin levels, which induced high carotenoid cleavage dioxygenase (CCDs) activity, particularly in soybean roots. The improved sugar metabolism in plant shoots by co-application of eCO2 and AsIII allocated more sugars to roots sequentially. Sugar accumulation in plant roots is further induced by AMF, resulting in more C skeletons to produce organic acids, which are effectively exudated into the soil to reduce AsIII uptake. Exposure to eCO2 reduced oxidative damage and this mitigation was stronger in soybean. This could be attributed to a greater reduction in photorespiration as well as a stronger antioxidant and detoxification defence systems. The grass/legume-specificity was supported by principal component analysis, which revealed that soybean was more affected by AsIII stress and more responsive to AMF and eCO2. This study provided a mechanistic understanding of the impact of AMF, eCO2 and their interaction on As-stressed grass and legume plants, allowing better practical strategies to mitigate AsIII phytotoxicity.

Harnessing plant microbiome for mitigating arsenic toxicity in sustainable agriculture

Heavy metal toxicity has become an impediment to agricultural productivity, which presents major human health concerns in terms of food safety. Among them, arsenic (As) a non-essential heavy metal has gained worldwide attention because of its noxious effects on agriculture and public health. The increasing rate of global warming and anthropogenic activities have promptly exacerbated As levels in the agricultural soil, thereby causing adverse effects to crop genetic and phenotypic traits and rendering them vulnerable to other stresses. Conventional breeding and transgenic approaches have been widely adapted for producing heavy metal resilient crops; however, they are time-consuming and labor-intensive. Hence, finding new mitigation strategies for As toxicity would be a game-changer for sustainable agriculture. One such promising approach is harnessing plant microbiome in the era of 'omics' which is gaining prominence in recent years. The use of plant microbiome and their cocktails to combat As metal toxicity has gained widespread attention, because of their ability to metabolize toxic elements and offer an array of perquisites to host plants such as increased nutrient availability, stress resilience, soil fertility, and yield. A comprehensive understanding of below-ground plant-microbiome interactions and their underlying molecular mechanisms in exhibiting resilience towards As toxicity will help in identifying elite microbial communities for As mitigation. In this review, we have discussed the effect of As, their accumulation, transportation, signaling, and detoxification in plants. We have also discussed the role of the plant microbiome in mitigating As toxicity which has become an intriguing research frontier in phytoremediation. This review also provides insights on the advancements in constructing the beneficial synthetic microbial communities (SynComs) using microbiome engineering that will facilitate the development of the most advanced As remedial tool kit in sustainable agriculture.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Antioxidants as modulators of arsenic-induced oxidative stress tolerance in plants: An overview

Arsenic (As) is a highly toxic contaminant in the environment. Although both inorganic and organic types of arsenic exist in the environment, the most common inorganic forms of As that adversely affect plants are arsenite (As III) and arsenate (As V). Despite no evidence for As being essential for plant growth, exposure of roots to this element can cause its uptake primarily via transporters responsible for the transport of essential mineral nutrients. Arsenic exposure even at low concentrations disturbs the plant normal functioning via excessive generation of reactive oxygen species, a condition known as oxidative stress leading to an imbalance in the redox system of the plant. This is associated with considerable damage to the cell components thereby impairing normal cellular functions and activation of several cell survival and cell death pathways. To counteract this oxidative disorder, plants possess natural defense mechanisms such as chemical species and enzymatic antioxidants. This review considers how different types of antioxidants participate in the oxidative defense mechanism to alleviate As stress in plants. Since the underlying phenomena of oxidative stress tolerance are not yet fully elucidated, the potential for "Omics" technologies to uncover molecular mechanisms are discussed. Various strategies to improve As-induced oxidative tolerance in plants such as exogenous supplementation of effective growth regulators, protectant chemicals, transgenic approaches, and genome editing are also discussed thoroughly in this review.

Endophytic fungus Serendipita indica reduces arsenic mobilization from root to fruit in colonized tomato plant

The accumulation of arsenic in crop plants has become a worldwide concern that affects millions of people. The major source of arsenic in crop plants is irrigation water and soil. In this study, Serendipita indica, an endophytic fungus, was used to investigate the protection against arsenic and its accumulation in the tomato plant. We found that inoculation of S. indica recovers seed germination, plant growth and improves overall plant health under arsenic stress. A hyper-colonization of fungus in the plant root was observed under arsenic stress, which results in reduced oxidative stress via modulation of antioxidative enzymes, glutathione, and proline levels. Furthermore, fungal colonization restricts arsenic mobilization from root to shoot and fruit by accumulating it exclusively in the root. We observed that fungal colonization enhances the arsenic bioaccumulation factor 1.48 times in root and reduces the arsenic translocation factor by 2.96 times from root to shoot and 13.6 times from root to fruit compared to non colonized plants. Further, investigation suggests that S. indica can tolerate arsenic by immobilizing it on the cell wall and accumulating it in the vacuole. This study shows that S. indica may be helpful for the reduction of arsenic accumulation in crops grown in arsenic-contaminated agriculture fields.

Plant-Mycorrhizal Fungi Interactions in Phytoremediation of Geogenic Contaminated Soils

Soil contamination by geogenic contaminants (GCs) represents an imperative environmental problem. Various soil remediation methods have been successfully employed to ameliorate the health risks associated with GCs. Phytoremediation is considered as an eco-friendly and economical approach to revegetate GC-contaminated soils. However, it is a very slow process, as plants take a considerable amount of time to gain biomass. Also, the process is limited only to the depth and surface area of the root. Inoculation of arbuscular mycorrhizal fungi (AMF) with remediating plants has been found to accelerate the phytoremediation process by enhancing plant biomass and their metal accumulation potential while improving the soil physicochemical and biological characteristics. Progress in the field application is hindered by a lack of understanding of complex interactions between host plant and AMF that contribute to metal detoxification/(im)mobilization/accumulation/translocation. Thus, this review is an attempt to reveal the underlying mechanisms of plant-AMF interactions in phytoremediation.

Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

Cadmium (Cd) is a major environmental contaminant due to its widespread industrial use. Cd contamination of soil and water is rather classical but has emerged as a recent problem. Cd toxicity causes a range of damages to plants ranging from germination to yield suppression. Plant physiological functions, i.e., water interactions, essential mineral uptake, and photosynthesis, are also harmed by Cd. Plants have also shown metabolic changes because of Cd exposure either as direct impact on enzymes or other metabolites, or because of its propensity to produce reactive oxygen species, which can induce oxidative stress. In recent years, there has been increased interest in the potential of plants with ability to accumulate or stabilize Cd compounds for bioremediation of Cd pollution. Here, we critically review the chemistry of Cd and its dynamics in soil and the rhizosphere, toxic effects on plant growth, and yield formation. To conserve the environment and resources, chemical/biological remediation processes for Cd and their efficacy have been summarized in this review. Modulation of plant growth regulators such as cytokinins, ethylene, gibberellins, auxins, abscisic acid, polyamines, jasmonic acid, brassinosteroids, and nitric oxide has been highlighted. Development of plant genotypes with restricted Cd uptake and reduced accumulation in edible portions by conventional and marker-assisted breeding are also presented. In this regard, use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics to enhance the adverse impacts of Cd in plants may be quite helpful. The review's results should aid in the development of novel and suitable solutions for limiting Cd bioavailability and toxicity, as well as the long-term management of Cd-polluted soils, therefore reducing environmental and human health hazards.

Rhizophagus intraradices improves arsenic tolerance in Sophora viciifolia Hance

Purpose

Arbuscular mycorrhizal fungi (AMF) are capable of protecting host plants against heavy metal toxicity, whereas rare knowledge has been acquired on the underlying effects of AMF on woody leguminous species under arsenic (As) stress. This study was aimed that whether AMF inoculation improves the As tolerance in Sophora viciifolia (a king of leguminous shrub).

Methods

S. viciifolia seedlings were inoculated with AMF Rhizophagus intraradices, and then the seedlings were grown at three levels (0, 50, and 100 mg As kg−1 soil) of As-polluted soil by performing the potted experiments. The plant growth, photosynthetic parameter, oxidative damage, antioxidant enzyme activities and gene expression of phytochelatin synthase in R. intraradices- and non-inoculated S. davidii seedlings under the different levels of As stress were analyzed.

Result

Compared with non-inoculated S. viciifolia at the identical As level, R. intraradices-inoculated S. viciifolia were higher in the shoot and root dry weight, plant height, root length, photosynthetic rate, stomatal conductance, transpiration rate, maximal photochemical efficiency of PSII photochemistry, actual quantum yield, and photochemical quenching values, while the intercellular CO2 concentration and non-photochemical quenching values were lower. As-induced oxidative stress generating malondialdehyde, hydrogen peroxide and superoxide in the S. viciifolia leaves and roots reduced significantly by R. intraradices inoculation, whereas the activities of antioxidative enzymes (e.g., superoxide dismutase, peroxidase, and catalase) in S. viciifolia leaves and roots were increased by R. intraradices inoculation. Notably, R. intraradices inoculation up-regulated the gene expression of S. viciifolia phytochelatins in the leaves and roots.

Conclusion

These results demonstrated that R. intraradices inoculation enhanced the As tolerance in S. viciifolia seedlings by improving the plant growth, gas exchange, chlorophyll fluorescence, reactive oxygen species, antioxidant enzymes and gene expression of S. viciifolia phytochelatins. The present study verified a multifarious positive role of AMF for woody leguminous species under As stress.

Tandem application of endophytic fungus Serendipita indica and phosphorus synergistically recuperate arsenic induced stress in rice

In the context of eco-sustainable acquisition of food security, arsenic (As) acts as a deterring factor, which easily infiltrates our food chain via plant uptake. Therefore, devising climate-smart strategies becomes exigent for minimizing the imposed risks. Pertinently, Serendipita indica (S. indica) is well reputed for its post-symbiotic stress alleviatory and phyto-promotive potential. Management of phosphorus (P) is acclaimed for mitigating arsenic toxicity in plants by inhibiting the uptake of As molecules due to the competitive cationic exchange in the rhizosphere. The current study was designed to investigate the tandem effects of S. indica and P in combating As toxicity employing two rice genotypes, i.e., Guodao-6 (GD-6; As-sensitive genotype) and Zhongzhe You-1 (ZZY-1; As-tolerant genotype). After successful fungal colonization, alone and combined arsenic (10  μ M L^-1) and phosphorus (50  μ M L^-1) treatments were applied. Results displayed that the recuperating effects of combined S. indica and P treatment were indeed much profound than their alone treatments; however, most of the beneficial influences were harnessed by ZZY-1 in comparison with GD-6. Distinct genotypic differences were observed for antioxidant enzyme activities, which were induced slightly higher in S. indica-colonized ZZY-1 plants, with or without additional P, as compared to GD-6. Ultrastructure images of root and shoot exhibited ravages of As in the form of chloroplasts-, nuclei-and cell wall-damage with enlarged vacuole area, mellowed mostly by the combined treatment of S. indica and P in both genotypes. Gene expression of PHTs family transporters was regulated at different levels in almost all treatments across genotypes. Conclusively, the results of this study validated the promising role of S. indica and additional P in mitigating As stress, albeit corroborated that the extent of relevant benefit exploitation is highly genotype-dependent. Verily, unlocking the potential of nature-friendly solutions will mend the anthropogenic damage already been done to our environment.

Arbuscular mycorrhizae and silicon alleviate arsenic toxicity by enhancing soil nutrient availability, starch degradation and productivity in Cajanus cajan (L.) Millsp

Arsenic (As) pollution of soil reduces the growth and reproductive potential of plants. Silicon (Si) and arbuscular mycorrhizal (AM) fungi play significant roles in alleviating adverse effects of As stress. However, studies are scant regarding alleviative effects of Si in pigeonpea (Cajanus cajan L. Millsp.) because legumes are considered low Si-accumulators. We investigated the individual as well as synergistic potential of Si with two AM species (M1-Claroideoglomus etunicatum and M2-Rhizoglomus intraradices) in modulating soil properties, thereby improving growth and productivity of pigeonpea genotype Pusa 2001 grown in AsV and AsIII challenged soils. Both As species hampered the establishment of AM symbiosis, thus, reducing nutrient uptake, growth and yield, with AsIII more toxic than AsV. Exogenously applied Si and AM species enhanced soil glomalin and phosphatases activity, hence decreased metal bioavailability in soil, increased plant nutrient acquisition, biomass and chlorophylls; with maximum benefits provided by M2, closely followed by Si and least by M1. These amendments boosted the activities of starch hydrolytic enzymes (α-, β-amylase, starch phosphorylase) in plants, along with a simultaneous increase in total soluble sugars (TSS). This enhanced sugar accumulation directly led to improved reproductive attributes, more efficiently by M2 and Si than by M1. Moreover, there was a substantial increase in proline biosynthesis due to significantly enhanced activities of its biosynthetic enzymes. Additionally, combined applications of Si and AM, especially +Si+M2, complemented each other where AM enhanced Si uptake, while Si induced mycorrhization, suggesting their mutual and beneficial roles in ameliorating metal(loid) toxicity and achieving sustainability in pigeonpea production under As stress.

Arsenic acquisition, toxicity and tolerance in plants - From physiology to remediation: A review

Globally, environmental contamination by potentially noxious metalloids like arsenic is becoming a critical concern to the living organisms. Arsenic is a non-essential metalloid for plants and can be acclimatised in plants to toxic levels. Arsenic acquisition by plants poses serious health risks in human due to its entry in the food chain. High arsenic regimes disturb plant water relations, promote the generation of reactive oxygen species (ROS) and induce oxidative outburst in plants. This review evidences a conceivable tie-up among arsenic levels, speciation, its availability, uptake, acquisition, transport, phytotoxicity and arsenic detoxification in plants. The role of different antioxidant enzymes to confer plant tolerance towards the enhanced arsenic distress has also been summed up. Additionally, the mechanisms involved in the modulation of different genes coupled with arsenic tolerance have been thoroughly discussed. This review is intended to present an overview to rationalise the contemporary progressions on the recent advances in phytoremediation approaches to overcome ecosystem contamination by arsenic.

Assessment of the Role of PAL in Lignin Accumulation in Wheat (Tríticum aestívum L.) at the Early Stage of Ontogenesis

The current study evaluates the role of phenylalanine ammonia-lyase (PAL) and the associated metabolic complex in the accumulation of lignin in common wheat plants (Tríticum aestívum L.) at the early stages of ontogenesis. The data analysis was performed using plant samples that had reached Phases 4 and 5 on the Feekes scale—these phases are characterized by a transition to the formation of axial (stem) structures in cereal plants. We have shown that the substrate stimulation of PAL with key substrates, such as L-phenylalanine and L-tyrosine, leads to a significant increase in lignin by an average of 20% in experimental plants compared to control plants. In addition, the presence of these compounds in the nutrient medium led to an increase in the number of gene transcripts associated with lignin synthesis (PAL6, C4H1, 4CL1, C3H1). Inhibition was the main tool of the study. Potential competitive inhibitors of PAL were used: the optical isomer of L-phenylalanine—D-phenylalanine—and the hydroxylamine equivalent of phenylalanine—O-Benzylhydroxylamine. As a result, plants incubated on a medium supplemented with O-Benzylhydroxylamine were characterized by reduced PAL activity (almost one third). The lignin content of the cell wall in plants treated with O-Benzylhydroxylamine was almost halved. In contrast, D-phenylalanine did not lead to significant changes in the lignin-associated metabolic complex, and its effect was similar to that of specific substrates.

Fate of arsenic in living systems: Implications for sustainable and safe food chains

Arsenic, a group 1 carcinogen for humans, is abundant as compared to other trace elements in the environment and is present mainly in the Earth's crust and soil. The arsenic distributions in different geographical regions are dependent on their geological histories. Anthropogenic activities also contribute significantly to arsenic release into the environment. Arsenic presents several complications to humans, animals, and plants. The physiology of plants and their growth and development are affected by arsenic. Arsenic is known to cause cancer and several types of organ toxicity, such as cardiotoxicity, nephrotoxicity, and hepatotoxicity. In the environment, arsenic exists in variable forms both as inorganic and organic species. From arsenic containing compartments, plants can absorb and accumulate arsenic. Crops grown on these contaminated soils pose several-fold higher toxicity to humans compared with drinking water if arsenic enters the food chain. Information regarding arsenic transfer at different trophic levels in food chains has not been summarized until now. The present review focuses on the food chain perspective of arsenic, which affects all components of the food chain during its course. The circumstances that facilitate arsenic accumulation in flora and fauna, as components of the food chain, are outlined in this review.

An actinomycete strain of Nocardiopsis lucentensis reduces arsenic toxicity in barley and maize

Accumulation of arsenic in plant tissues poses a substantial threat to global crop yields. The use of plant growth-promoting bacterial strains to mitigate heavy metal toxicity has been illustrated before. However, its potential to reduce plant arsenic uptake and toxicity has not been investigated to date. Here, we describe the identification and characterization of a Nocardiopsis lucentensis strain isolated from heavy metal contaminated soil. Inoculation with this bioactive actinomycete strain decreased arsenic root and shoot bioaccumulation in both C3 and C4 crop species namely barley and maize. Upon arsenate treatment, N. lucentensis S5 stimulated root citric acid production and the plant's innate detoxification capacity in a species-specific manner. In addition, this specific strain promoted biomass gain, despite substantial tissue arsenic levels. Detoxification (metallothionein, phytochelatin, glutathione-S-transferase levels) was upregulated in arsenate-exposed shoot and roots, and this response was further enhanced upon S5 supplementation, particularly in barley and maize roots. Compared to barley, maize plants were more tolerant to arsenate-induced oxidative stress (less H₂O₂ and lipid peroxidation levels). However, barley plants invested more in antioxidative capacity induction (ascorbate-glutathione turnover) to mitigate arsenic oxidative stress, which was strongly enhanced by S5. We quantify and mechanistically discuss the physiological and biochemical basis of N. lucentensis-mediated plant biomass recovery on arsenate polluted soils. Our findings substantiate the potential applicability of a bactoremediation strategy to mitigate arsenic-induced yield loss in crops.

Arsenic Remediation through Sustainable Phytoremediation Approaches

Arsenic contamination of the environment is a serious problem threatening the health of millions of people exposed to arsenic (As) via drinking water and crops grown in contaminated areas. The remediation of As-contaminated soil and water bodies needs to be sustainable, low-cost and feasible to apply in the most affected low-to-middle income countries, like India and Bangladesh. Phytoremediation is an aesthetically appreciable and successful approach that can be used for As decontamination with use of the best approach(es) and the most promising plant(s). However, phytoremediation lacks the required speed and sometimes the stress caused by As could diminish plants’ potential for remediation. To tackle these demerits, we need augment plants’ potential with appropriate technological methods including microbial and nanoparticles applications and genetic modification of plants to alleviate the As stress and enhance As accumulation in phytoremediator plants. The present review discusses the As phytoremediation prospects of soil and water bodies and the usefulness of various plant systems in terms of high biomass, high As accumulation, bioenergy potential, and economic utility. The potential and prospects of assisted phytoremediation approaches are also presented.

Arbuscular Mycorrhiza-Mediated Regulation of Polyamines and Aquaporins During Abiotic Stress: Deep Insights on the Recondite Players

Environmental stresses of (a)biotic origin induce the production of multitudinous compounds (metabolites and proteins) as protective defense mechanisms in plants. On account of the regulation of some of these compounds, arbuscular mycorrhizal fungi (AMF) reinforce the inherent tolerance of plants toward the stress of different origins and kind. This article reviews two specific fundamental mechanisms that are categorically associated with mycorrhiza in alleviating major abiotic stresses, salt, drought, and heavy metal (HM) toxicity. It puts emphasis on aquaporins (AQPs), the conduits of water and stress signals; and polyamines (PAs), the primordial stress molecules, which are regulated by AMF to assure water, nutrient, ion, and redox homeostasis. Under stressful conditions, AMF-mediated host AQP responses register distinct patterns: an upregulation to encourage water and nutrient uptake; a downregulation to restrict water loss and HM uptake; or no alterations. The patterns thereof are apparently an integrative outcome of the duration, intensity, and type of stress, AMF species, the interaction of fungal AQPs with that of plants, and the host type. However, the cellular and molecular bases of mycorrhizal influence on host AQPs are largely unexplored. The roles of PAs in augmenting the antioxidant defense system and improving the tolerance against oxidative stress are well-evident. However, the precise mechanism by which mycorrhiza accords stress tolerance by influencing the PA metabolism per se is abstruse and broadly variable under different stresses and plant species. This review comprehensively analyzes the current state-of-art of the involvement of AMF in "PA and AQP modulation" under abiotic stress and identifies the lesser-explored landscapes, gaps in understanding, and the accompanying challenges. Finally, this review outlines the prospects of AMF in realizing sustainable agriculture and provides insights into potential thrust areas of research on AMF and abiotic stress.

Iron oxide nanoparticles alleviate arsenic phytotoxicity in rice by improving iron uptake, oxidative stress tolerance and diminishing arsenic accumulation

The food chain contaminated with arsenic (As) has developed a hazardous threat to the growth and development of plants, animals and humans. The present study was conducted to examine the application of iron oxide nanoparticles (FeNPs) on biochemical and molecular traits of roots and leaves of rice plants under As phytotoxicity. The results showed that As reduced the accumulation of Fe in roots and leaves and thus reduced photosynthetic pigments and growth of rice plants. As stress enhanced the accumulation of hydrogen peroxide, superoxide anion and methylglyoxal by increasing the accumulation of As in roots and leaves, resulting in damage to membrane lipids and raised electrolyte leakage (EL). However, FeNPs strengthen the glyoxalase system and antioxidant enzymes, thereby alleviating oxidative stress and reducing EL. FeNPs protected plant cells from As phytotoxicity by enhancing the accumulation of chelating agents (proline, glutathione and phytochelatins) and the sequestration and immobilization of As in the vacuoles and the cell walls. FeNPs downregulated the expression of genes involved in As uptake and translocation (Lsi1 and Lsi2) and, consequently, reduced As accumulation in the roots and leaves of As-stressed plants. FeNPs also improved the accumulation of Fe in the roots and leaves by modulating the expression of genes that regulate Fe uptake and its transport to leaves (IRT1, IRT2, YSL2, YSL13, FRDL1, DMAS1, NAS2 and NAS3), resulting in the restoration of photosynthetic pigments and the growth of As-stressed plants. Our findings authenticate the role of FeNPs in diminishing As phytotoxicity on rice.

Metalloid hazards: From plant molecular evolution to mitigation strategies

Metalloids such as boron and silicon are key elements for plant growth and crop productivity. However, toxic metalloids such as arsenic are increasing in the environment due to inputs from natural sources and human activities. These hazardous metalloids can cause serious health risks to humans and animals if they enter the food chain. Plants have developed highly regulated mechanisms to alleviate the toxicity of metalloids during their 500 million years of evolution. A better understanding the molecular mechanisms underlying the transport and detoxification of toxic metalloids in plants will shed light on developing mitigation strategies. Key transporters and regulatory proteins responsive to toxic metalloids have been identified through evolutionary and molecular analyses. Moreover, knowledge of the regulatory proteins and their pathways can be used in the breeding of crops with lower accumulation of metalloids. These findings can also assist phytoremediation by the exploration of plants such as fern species that hyperaccumulate metalloids from soils and water, and can be used to engineer plants with elevated uptake and storage capacity of toxic metalloids. In summary, there are solutions to remediate contamination due to toxic metalloids by combining the research advances and industrial technologies with agricultural and environmental practices.

Unravelling the role of arbuscular mycorrhizal fungi in mitigating the oxidative burst of plants under drought stress

With continued climate changes, soil drought stress has become the main limiting factor for crop growth in arid and semi-arid regions. A typical characteristic of drought stress is the burst of reactive oxygen species (ROS), causing oxidative damage. Plant-associated microbes, such as arbuscular mycorrhizal fungi (AMF), can regulate physiological and molecular responses to tolerate drought stress, and they have a strong ability to cope with drought-induced oxidative damage via enhanced antioxidant defence systems. AMF produce a limited oxidative burst in the arbuscule-containing root cortical cells. Similar to plants, AMF modulate a fungal network in enzymatic (e.g. GmarCuZnSOD and GintSOD1) and non-enzymatic (e.g. GintMT1, GinPDX1 and GintGRX1) antioxidant defence systems to scavenge ROS. Plants also respond to mycorrhization to enhance stress tolerance via metabolites and the induction of genes. The present review provides an overview of the network of plant - arbuscular mycorrhizal fungus dialogue in mitigating oxidative stress. Future studies should involve identifying genes and transcription factors from both AMF and host plants in response to drought stress, and utilize transcriptomics, proteomics and metabolomics to clarify a clear dialogue mechanism between plants and AMF in mitigating oxidative burst.

Arbuscular Mycorrhiza Improves Photosynthesis and Restores Alteration in Sugar Metabolism in Triticum aestivum L. Grown in Arsenic Contaminated Soil

Contamination of agricultural soil by arsenic (As) is a serious menace to environmental safety and global food security. Symbiotic plant-microbe interaction, such as arbuscular mycorrhiza (AM), is a promising approach to minimize hazards of As contamination in agricultural soil. Even though the potential of AM fungi (AMF) in redeeming As tolerance and improving growth is well recognized, the detailed metabolic and physiological mechanisms behind such beneficial effects are far from being completely unraveled. The present study investigated the ability of an AM fungus, Rhizophagus intraradices, in mitigating As-mediated negative effects on photosynthesis and sugar metabolism in wheat (Triticum aestivum) subjected to three levels of As, viz., 0, 25, and 50 mg As kg-1 of soil, supplied as sodium arsenate. As exposure caused significant decrease in photosynthetic pigments, Hill reaction activity, and gas exchange parameters such as net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. In addition, As exposure also altered the activities of starch-hydrolyzing, sucrose-synthesizing, and sucrose-degrading enzymes in leaves. Colonization by R. intraradices not only promoted plant growth but also restored As-mediated impairments in plant physiology. The symbiosis augmented the concentration of photosynthetic pigments, enhanced Hill reaction activity, and improved leaf gas exchange parameters and water use efficiency of T. aestivum even at high dose of 50 mg As kg-1 of soil. Furthermore, inoculation with R. intraradices also restored As-mediated alteration in sugar metabolism by modulating the activities of starch phosphorylase, α-amylase, β-amylase, acid invertase, sucrose synthase, and sucrose-phosphate synthase in leaves. This ensured improved sugar and starch levels in mycorrhizal plants. Overall, the study advocates the potential of R. intraradices in bio-amelioration of As-induced physiological disturbances in wheat plant.

Piriformospora indica augments arsenic tolerance in rice (Oryza sativa) by immobilizing arsenic in roots and improving iron translocation to shoots

Arsenic (As) toxicity can be a hazardous threat to sustainable agriculture and human health. Piriformospora indica (P. indica), as a beneficial endophytic fungus, is involved in the plant tolerance to stressful conditions. Here, the biochemical and molecular responses of rice plants to As (50 μM) phytotoxicity and P. indica inoculation as well as the role of P. indica in improving rice adaptation to As stress were evaluated. The results showed that As stress reduced chlorophylls content, chlorophyll fluorescence yield (Fv/Fm), electron transport rate (ETR) and growth. However, P. indica restored chlorophyll content and growth. P. indica decreased the contents of methylglyoxal and malondialdehyde by improving the activity of enzymes involved in the glyoxalase pathway and modulating the redox state of the ascorbic acid-glutathione cycle, and consequently, increased the plant tolerance to As toxicity. P. indica, by downregulating Lsi2 expression (involved in As translocation to the shoot) and upregulating PCS1 and PCS2 expression (involved in As sequestration in vacuoles), immobilized As in the roots and reduced damage to photosynthetic organs. P. indica increased iron (Fe) accumulation in the shoot under As toxicity by upregulating the expression of IRO2, YSL2 and FRDL1 genes. The results of the present study augmented our knowledge in using P. indica symbiosis in improving the tolerance of rice plants against As toxicity for sustainable agriculture.

Arbuscular mycorrhizal fungi-induced mitigation of heavy metal phytotoxicity in metal contaminated soils: A critical review

The heavy metal pollution is a worldwide problem and has received a serious concern for the ecosystem and human health. In the last decade, remediation of the agricultural polluted soil has attracted great attention. Phytoremediation is one of the technologies that effectively alleviate heavy metal toxicity, however, this technique is limited to many factors contributing to low plant growth rate and nature of metal toxicities. Arbuscular mycorrhizal fungi (AMF) assisted alleviation of heavy metal phytotoxicity is a cost-effective and environment-friendly strategy. AMF have a symbiotic relationship with the host plant. The bidirectional exchange of resources is a hallmark and also a functional necessity in mycorrhizal symbiosis. During the last few years, a significant progress in both physiological and molecular mechanisms regarding roles of AMF in the alleviation of heavy metals (HMs) toxicities in plants, acquisition of nutrients, and improving plant performance under toxic conditions of HMs has been well studied. This review summarized the current knowledge regarding AMF assisted remediation of heavy metals and some of the strategies used by mycorrhizal fungi to cope with stressful environments. Moreover, this review provides the information of both molecular and physiological responses of mycorrhizal plants as well as AMF to heavy metal stress which could be helpful for exploring new insight into the mechanisms of HMs remediation by utilizing AMF.