The symbiosis between Nicotiana tabacum and the endomycorrhizal fungus Funneliformis mosseae increases the plant glutathione level and decreases leaf cadmium and root arsenic contents

The coexistence of arbuscular mycorrhizal fungi and dark septate endophytes synergistically enhanced the cadmium tolerance of maize

Introduction

Arbuscular mycorrhizal fungi (AMF) and dark septate endophytic fungi (DSEs) generally coexist in the roots of plants. However, our understanding of the effects of their coexistence on plant growth and stress resistance is limited.

Methods

In the present study, the effects of single and dual inoculation of AMF and DSE on the growth, photosynthetic physiology, glutathione (GSH) metabolism, endogenous hormones, and cadmium (Cd) content of maize under 25 mg•kg-1 Cd stress were investigated.

Results

Compared with that after the non-inoculation treatment, AMF+DSE co-inoculation significantly increased the photosynthetic rate (Pn) of maize leaves; promoted root GSH metabolism; increased the root GSH concentration and activity of γ-glutamyl cysteine synthase (γ-GCS), ATP sulfatase (ATPS) and sulfite reductase (SIR) by 215%, 117%, 50%, and 36%, respectively; and increased the concentration of endogenous hormones in roots, with increases in zeatin (ZR), indole-3 acetic acid (IAA), and abscisic acid (ABA) by 81%, 209%, and 72%, respectively. AMF inoculation, DSE inoculation and AMF+DSE co-inoculation significantly increased maize biomass, and single inoculation with AMF or DSE increased the Cd concentration in roots by 104% or 120%, respectively. Moreover, significant or highly significant positive correlations were observed between the contents of ZR, IAA, and ABA and the activities of γ-GCS, ATPS, and SIR and the glutathione (GSH) content. There were significant or highly significant positive interactions between AMF and DSE on the Pn of leaves, root GSH metabolism, and endogenous hormone contents according to two-way analysis of variance. Therefore, the coexistence of AMF and DSE synergistically enhanced the Cd tolerance of maize.

Mitigating heavy metal accumulation in tobacco: Strategies, mechanisms, and global initiatives

The threat of heavy metal (HM) pollution looms large over plant growth and human health, with tobacco emerging as a highly vulnerable plant due to its exceptional absorption capacity. The widespread cultivation of tobacco intensifies these concerns, posing increased risks to human health as HMs become more pervasive in tobacco-growing soils globally. The absorption of these metals not only impedes tobacco growth and quality but also amplifies health hazards through smoking. Implementing proactive strategies to minimize HM absorption in tobacco is of paramount importance. Various approaches, encompassing chemical immobilization, transgenic modification, agronomic adjustments, and microbial interventions, have proven effective in curbing HM accumulation and mitigating associated adverse effects. However, a comprehensive review elucidating these control strategies and their mechanisms remains notably absent. This paper seeks to fill this void by examining the deleterious effects of HM exposure on tobacco plants and human health through tobacco consumption. Additionally, it provides a thorough exploration of the mechanisms responsible for reducing HM content in tobacco. The review consolidates and synthesizes recent domestic and international initiatives aimed at mitigating HM content in tobacco, delivering a comprehensive overview of their current status, benefits, and limitations.

Beneficial Interactive Effects Provided by an Arbuscular Mycorrhizal Fungi and Yeast on the Growth of Oenothera picensis Established on Cu Mine Tailings

Phytoremediation, an environmentally friendly and sustainable approach for addressing Cu-contaminated environments, remains underutilized in mine tailings. Arbuscular mycorrhizal fungi (AMF) play a vital role in reducing Cu levels in plants through various mechanisms, including glomalin stabilization, immobilization within fungal structures, and enhancing plant tolerance to oxidative stress. Yeasts also contribute to plant growth and metal tolerance by producing phytohormones, solubilizing phosphates, generating exopolysaccharides, and facilitating AMF colonization. This study aimed to assess the impact of AMF and yeast inoculation on the growth and antioxidant response of Oenothera picensis plants growing in Cu mine tailings amended with compost. Plants were either non-inoculated (NY) or inoculated with Meyerozyma guilliermondii (MG), Rhodotorula mucilaginosa (RM), or a combination of both (MIX). Plants were also inoculated with Claroideoglomus claroideum (CC), while others remained non-AMF inoculated (NM). The results indicated significantly higher shoot biomass in the MG-NM treatment, showing a 3.4-fold increase compared to the NY-NM treatment. The MG-CC treatment exhibited the most substantial increase in root biomass, reaching 5-fold that in the NY-NM treatment. Co-inoculation of AMF and yeast influenced antioxidant activity, particularly catalase and ascorbate peroxidase. Furthermore, AMF and yeast inoculation individually led to a 2-fold decrease in total phenols in the roots. Yeast inoculation notably reduced non-enzymatic antioxidant activity in the ABTS and CUPRAC assays. Both AMF and yeast inoculation promoted the production of photosynthetic pigments, further emphasizing their importance in phytoremediation programs for mine tailings.

Arbuscular mycorrhizal fungi alleviates salt stress in Xanthoceras sorbifolium through improved osmotic tolerance, antioxidant activity, and photosynthesis

Mycorrhizal inoculation was widely reported to alleviate the damage resulting from NaCl by various physiological ways. However, the symbiotic benefit under distant NaCl concentrations and the relationship among different responsive physiological processes were elusive. In this study, saline resistant plant Xanthoceras sorbifolium was selected as the experimental material and five concentrations of NaCl in the presence or absence of Arbuscular Mycorrhiza Fungi (AMF) were conducted, in order to understand the differences and similarities on the photosynthesis, antioxidant activity, and osmotic adjustment between arbuscular mycorrhizal (AM) plants and non-arbuscular mycorrhizal (NM) plants. Under low salt stress, X. sorbifolium can adapt to salinity by accumulating osmotic adjustment substances, such as soluble protein and proline, increasing superoxide dismutase (SOD), catalase (CAT) activity, and glutathione (GSH). However, under high concentrations of NaCl [240 and 320 mM (mmol·L−1)], the resistant ability of the plants significantly decreased, as evidenced by the significant downregulation of photosynthetic capacity and biomass compared with the control plants in both AM and NM groups. This demonstrates that the regulatory capacity of X. sorbifolium was limiting, and it played a crucial role mainly under the conditions of 0–160 mM NaCl. After inoculation of AMF, the concentration of Na+ in roots was apparently lower than that of NM plants, while Gs (Stomatal conductance) and Ci (Intercellular CO2 concentration) increased, leading to increases in Pn (Net photosynthetic rate) as well. Moreover, under high salt stress, proline, soluble protein, GSH, and reduced ascorbic acid (ASA) in AM plants are higher in comparison with NM plants, revealing that mycorrhizal symbiotic benefits are more crucial against severe salinity toxicity. Meanwhile, X. sorbifolium itself has relatively high tolerance to salinity, and AMF inoculation can significantly increase the resistant ability against NaCl, whose function was more important under high concentrations.

Reconditioning of plant metabolism by arbuscular mycorrhizal networks in cadmium contaminated soils: Recent perspectives

Cadmium (Cd) is one of the most perilous nonessential heavy metal for plants, owing to its high water solubility and obstruction with various physiological and biochemical processes. It enters food chain via plant uptake from contaminated soil, posing a grave menace to ecosystem and mankind. Green remediation comprises approaches intended at prudent use of natural resources for increasing profits to humans and environment. Arbuscular mycorrhizal (AM) fungi are considered a promising green technological tool for remedial of Cd-polluted soils. They are naturally associated with root system of plants in Cd-contaminated soils, evidencing their tolerance to Cd. AM can decrease Cd uptake by plants broadly through two strategies: (1) extracellular mechanisms involving Cd chelation by root exudates, binding to fungal cell wall/structures or to the glycoprotein glomalin; (2) intracellular means involving transfer via hyphal network, detoxification and vacuolar sequestration mediated by complexation of Cd with glutathione (GSH), phytochelatins (PCs), metallothioneins (MTs) and polyphosphate granules. Additionally, mycorrhizal symbiosis facilitates reconditioning of plants' metabolism primarily through dilution effect, increased water and mineral uptake. Recently, AM-induced remodelling of root cell wall synthesis has been reported to improve plant vigor and survival under Cd stressed environments. The present article highlights Cd impacts on AM growth, its diversity in Cd contaminated soils, and variations among diverse AM fungal species for imparting plant Cd tolerance. The most recent perspectives on AM-mediated Cd tolerance mechanisms in plants, including cellular and molecular studies have also been reviewed for successful utilization of these beneficial microbes in sustainable agriculture.

Regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi

Endophytic fungi exist widely in plants and play an important role in the growth and adaptation of plants. They could be used in phytoremediation techniques against heavy metal contaminated soil since beneficial microbial symbionts can endow plants with resistance to external heavy metal stresses. This review summarized the regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi. Potential endophytic fungi in enhancing plant's adaption to heavy metal stresses include arbuscular mycorrhizal fungi, dark septate endophytic fungi, plant growth promoting endophytic fungi. The mechanisms involve coevolution strategy, immune regulation and detoxification transport to improve the ability of plants to adapt to heavy metal stress. They can increase the synthesis of host hormones and maintaining the balance of endogenous hormones, strengthen osmotic regulation, regulate carbon and nitrogen metabolism, and increase immune activity, antioxidant enzyme and glutathione activity. They also help to improve the detoxification transport and heavy metal emission capacity of the host by significantly producing iron carrier, metallothionein and 1-aminocyclopropane-1-carboxylic acid deaminase. The combination of endophytic fungi and hyperaccumulation plants provides a promising technology for the ecological restoration of heavy metal contaminated soil. Endophytic fungi reserves further development on enhancing host plant's adaptability to heavy metal stresses.

Root symbionts alter herbivore-induced indirect defenses of tomato plants by enhancing predator attraction

Beneficial root microbes are among the most frequently used biocontrol agents in cropping systems, since they have been shown to promote plant growth and crop yield. Moreover, they are able to enhance protection against pathogens and insect herbivores by activating plant resistance mechanisms. Plant defense responses against herbivorous insects include the induction of metabolic pathways involved in the synthesis of defense-related metabolites. These metabolites include volatile organic compounds (VOCs), which attract natural enemies of the herbivores as a form of indirect resistance. Considering that beneficial root microbes may affect direct herbivore resistance, we hypothesized that also indirect resistance may be affected. We tested this hypothesis in a study system composed of tomato, the arbuscular mycorrhizal fungus Rhizophagus irregularis, the growth-promoting fungus Trichoderma harzianum, the generalist chewing herbivore Spodoptera exigua and the omnivorous predator Macrolophus pygmaeus. Using a Y-tube olfactometer we found that M. pygmaeus preferred plants with S. exigua herbivory, but microbe-inoculated plants more than non-inoculated ones. We used a targeted GC-MS approach to assess the impact of beneficial microbes on the emission of volatiles 24 h after herbivory to explain the choice of M. pygmaeus. We observed that the volatile composition of the herbivore-infested plants differed from that of the non-infested plants, which was driven by the higher emission of green leaf volatile compounds, methyl salicylate, and several monoterpenes and sesquiterpenes. Inoculation with microbes had only a marginal effect on the emission of some terpenoids in our experiment. Gene expression analysis showed that the marker genes involved in the jasmonic and salicylic acid pathways were differentially expressed in the microbe-inoculated plants after herbivory. Our results pinpoint the role of root symbionts in determining plant-microbe-insect interactions up to the third trophic level, and elucidates their potential to be used in plant protection.

Unraveling the effects of arbuscular mycorrhizal fungi on cadmium uptake and detoxification mechanisms in perennial ryegrass (Lolium perenne)

Cadmium (Cd) is a major environmental pollutant and one of the most toxic metals in the environment. Arbuscular mycorrhizal fungi (AMF) assisted phytoremediation can be used to remove Cd from polluted soils but the role of AMF, which mediate in Cd accumulation and tolerance, remains poorly understood. Here we inoculated Lolium perenne with two different AMF species (Glomus etunicatum and Glomus mosseae). Mycorrhizal L. perenne and non-mycorrhizal controls were exposed to Cd stress and we tested the effects of AMF mycorrhization on Cd uptake and subsequent tolerance, as well as the underlying mechanisms. Mycorrhizal infection increased root Cd²⁺ uptake and we observed that net Cd²⁺ influx was coupled with net Ca²⁺ influx. The inactivation of Ca²⁺ transporter channels decreased Cd²⁺ uptake in non-inoculated roots to a greater extent than in inoculated roots, indicating that AMF activates additional ion transport channels. In consequence, inoculated plants exhibited higher Cd accumulation in both roots and shoots than non-inoculated controls. However, AMF-inoculated plants showed higher chlorophyll concentrations, photosynthesis, and growth under Cd, indicating lower Cd toxicity in AMF-inoculated plants, despite the increase in Cd uptake. We observed that AMF-inoculated favored the isolation of Cd within cell walls and vacuoles, and had higher concentrations of superoxide dismutase activity and glutathione concentration in roots than non-inoculated plants, consequently experiencing less stress upon Cd exposure. Our results highlight the potential and mechanism of AMF for enhancing phytoremediation of L. perenne in heavy metal contaminated environments.

Native AMF Communities in an Italian Vineyard at Two Different Phenological Stages of Vitis vinifera

Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms that can establish symbiotic associations with Vitis vinifera roots, resulting in positive effects on grapevine performance, both in terms of water use efficiency, nutrient uptake, and replant success. Grapevine is an important perennial crop cultivated worldwide, especially in Mediterranean countries. In Italy, Piedmont is one of the regions with the longest winemaking tradition. In the present study, we characterized the AMF communities of the soil associated or not with the roots of V. vinifera cv. Pinot Noir cultivated in a vineyard subjected to conventional management using 454 Roche sequencing technology. Samplings were performed at two plant phenological stages (flowering and early fruit development). The AMF community was dominated by members of the family Glomeraceae, with a prevalence of the genus Glomus and the species Rhizophagus intraradices and Rhizophagus irregularis. On the contrary, the genus Archaeospora was the only one belonging to the family Archaeosporaceae. Since different AMF communities occur in the two considered soils, independently from the plant phenological stage, a probable role of V. vinifera in determining the AMF populations associated to its roots has been highlighted.

Arbuscular Mycorrhizal Fungi as Potential Agents in Ameliorating Heavy Metal Stress in Plants

Heavy metal accumulation in plants is a severe environmental problem, rising at an expeditious rate. Heavy metals such as cadmium, arsenic, mercury and lead are known environmental pollutants that exert noxious effects on the morpho-physiological and biological attributes of a plant. Due to their mobile nature, they have become an extended part of the food chain and affect human health. Arbuscular mycorrhizal fungi ameliorate metal toxicity as they intensify the plant’s ability to tolerate metal stress. Mycorrhizal fungi have vesicles, which are analogous to fungal vacuoles and accumulate massive amount of heavy metals in them. With the help of a pervasive hyphal network, arbuscular mycorrhizal fungi help in the uptake of water and nutrients, thereby abating the use of chemical fertilizers on the plants. They also promote resistance parameters in the plants, secrete a glycoprotein named glomalin that reduces the metal uptake in plants by forming glycoprotein–metal complexes, and improve the quality of the soil. They also assist plants in phytoremediation by increasing the absorptive area, increase the antioxidant response, chelate heavy metals and stimulate genes for protein synthesis that reduce the damage caused by free radicals. The current manuscript focuses on the uptake of heavy metals, accumulation, and arbuscular mycorrhizal impact in ameliorating heavy metal stress in plants.

AMF communities associated to Vitis vinifera in an Italian vineyard subjected to integrated pest management at two different phenological stages

Vitis vinifera L. is an economically important crop that can be influenced by soil microorganisms, including arbuscular mycorrhizal fungi (AMF), that establish symbiotic associations with its roots. AMF have beneficial effects on grapevine performance improving water use efficiency and replant success. Most grapevine varieties are susceptible to various diseases, and integrated pest management (IPM) is one of the emerging approaches to perform pest control. In the present study, we examined the AMF communities present in the soil associated to the roots of V. vinifera cv. Pinot Noir (comparing them to those present in a soil not affected by grapevine roots), in a vineyard subjected to IPM at two different phenological stages, using 454 Roche sequencing technology. We proposed a new approach to analyze sequencing data. Most of the taxa were included in the family Glomeraceae. In particular, Glomus sp. Rhizophagus sp. and Septoglomus viscosum were present. The family Archeosporaceae was represented only by the genus Archeospora sp. Different AMF communities were found in the two soils and the importance of the phenological stage in regulating AMF biodiversity was assessed.

Bioremediation of arsenic by soil methylating fungi: Role of Humicola sp. strain 2WS1 in amelioration of arsenic phytotoxicity in Bacopa monnieri L

Fungi mediated arsenic (As) stress modulation has emerged as an important strategy for the mitigation of As mediated stress management in plants for reducing As contamination to the food chain. In the present study, total of 45 fungal strains were isolated from the three As contaminated sites of West Bengal, India. These strains were morphologically different and inhibited variable As tolerance (10 to 5000 mg l^-1As). Total 21 fungal isolates, tolerant up to 5000 mg l^-1 AsV, were investigated for As removal (10 mg l^-1 As) after 21 d of cultivation under laboratory conditions. The As bioaccumulation in fungal biomass ranged between 0.146 to 11.36 g kg^-1 biomass. Range of volatilized As was between 0.05 to 53.39 mg kg^-1 biomass. Most promising bioaccumulation and biovolatilization potential were observed in strains viz., 2WS1, 3WS1 and 2WS9. Strain 2WS1 showed highest As biovolatilization (53.39 mg kg^-1 biomass) and was identified as Humicola sp. using ITS/5.8S rDNA gene sequencing. This is the first report of Humicola sp. having As biomethylation property. Best first 8 As biomethylating fungal strains were further tested for their As remediation and PGP potential in Bacopa monnieri plant grown in As contaminated soil (20 mg kg^-1) in a pot experiment under greenhouse conditions. The highest leaf stem ratio and lowest As content in leaf tissues were observed in 2WS1 inoculated Bacopa monnieri plants. The presence of arsM gene in 2WS1 strain suggests As biovolatilization as possible bioremediation and As stress mitigation strategy of 2WS1. Therefore, application of this strain of Humicola sp. strain 2WS1 in As contaminated soils could be a potential and realistic mitigation strategy for reducing As contamination to cropping system coupled with enhanced productivity.

Arsenic toxicity and its mitigation in ectomycorrhizal fungus Hebeloma cylindrosporum through glutathione biosynthesis

Arsenic (As) contamination is one of the most daunting environmental problem bothering the whole world. Exploring a suitable bioremediation technique is an urgent need of the hour. The present study focusses on scrutinizing the ectomycorrhizal (ECM) fungus for its potential role in As detoxification and understanding the molecular mechanisms responsible for its tolerance. When exposed to increasing concentrations of external As, the ECM fungus H. cylindrosporum accumulated the metalloid intracellularly, inducing the glutathione biosynthesis pathway. The genes coding for GSH biosynthesis enzymes, γ-glutamylcysteine synthetase (Hcγ-GCS) and glutathione synthetase (HcGS) were highly regulated by As stress. Arsenic coordinately upregulated the expression of both Hcγ-GCS and HcGS genes, thus resulting in increased Hcγ-GCS and HcGS protein expressions and enzyme activities, with substantial increase in intracellular GSH. Functional complementation of the two genes (Hcγ-GCS and HcGS) in their respective yeast mutants (gsh1^Δ and gsh2^Δ) further validated the role of both enzymes in mitigating As toxicity. These findings clearly highlight the potential importance of GSH antioxidant defense system in regulating the As induced responses and its detoxification in ECM fungus H. cylindrosporum.

Opportunities and challenges in the remediation of metal-contaminated soils by using tobacco (Nicotiana tabacum L.): a critical review

The successful phytoextraction of potentially toxic elements (PTEs) from polluted soils can be achieved by growing non-food and industrial crops. Tobacco (Nicotiana tabacum L.) is one of the main industrial crops and is widely grown in many countries. Tobacco can uptake high concentrations of PTEs especially in aboveground biomass without suffering from toxicity. This review highlighted the potential of tobacco for the phytoextraction of heavy metals and tolerance mechanisms under metal stress. Different management practices have been discussed which can enhance the potential of this plant for metal extraction. Finally, suitable options for the management/disposal of biomass enriched in excess metal have been elaborated to prevent secondary pollution.

Effects of arbuscular mycorrhizal fungi on the growth and heavy metal accumulation of bermudagrass [Cynodon dactylon (L.) Pers.] grown in a lead-zinc mine wasteland

A pot experiment was conducted to investigate the potential influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Diversispora spurcum, on the growth and nutrient (P and S) and heavy metal (HMs) (Pb, Zn, and Cd) content of bermudagrass [Cynodon dactylon (L.) Pers.] in a lead-zinc mine wasteland. The D. spurcum inoculation significantly increased the bermudagrass growth, whereas the F. mosseae inoculation did not. The AMF inoculation significantly increased the soil pH and uptake of P, S, and HMs by bermudagrass, decreased the contents of available Pb and Zn in soils and Pb in shoots, reduced the translocation factor (TF) and translocation capacity factor (TF') of Pb and Cd in bermudagrass and increased the TF and TF' of Zn in bermudagrass. A significant negative correlation was found between pH and available HMs in soil, whereas a significant positive correlation was noted between the HMs content and nutrient content in bermudagrass shoots. Experiment results provide evidence of the potential role of AMF in improving bermudagrass performance for the vegetation restoration of metalliferous mine wastelands.

Arbuscular mycorrhizal fungi enhance antioxidant defense in the leaves and the retention of heavy metals in the roots of maize

In this study, we investigated the effects of the arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae and Diversispora spurcum on the growth, antioxidant physiology, and uptake of phosphorus (P), sulfur (S), lead (Pb), zinc (Zn), cadmium (Cd), and arsenic (As) by maize (Zea mays L.) grown in heavy metal-polluted soils though a potted plant experiment. F. mosseae significantly increased the plant chlorophyll a content, height, and biomass; decreased the H₂O₂ and malondialdehyde (MDA) contents; and enhanced the superoxide dismutase (SOD) and catalase (CAT) activities and the total antioxidant capacity (T-AOC) in maize leaves; this effect was not observed with D. spurcum. Both F. mosseae and D. spurcum promoted the retention of heavy metals in roots and increased the uptake of Pb, Zn, Cd, and As, and both fungi restricted heavy metal transfer, resulting in decreased Pb, Zn, and Cd contents in shoots. Therefore, the fungi reduced the translocation factors for heavy metal content (TF) and uptake (TF') in maize. Additionally, F. mosseae promoted P and S uptake by shoots, and D. spurcum increased P and S uptake by roots. Moreover, highly significant negative correlations were found between antioxidant capacity and the H₂O₂, MDA, and heavy metal contents, and there was a positive correlation with the biomass of maize leaves. These results suggested that AMF alleviated plant toxicity and that this effect was closely related to antioxidant activation in the maize leaves and increased retention of heavy metals in the roots.

Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects

Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.

Endophytic Paecilomyces formosus LHL10 Augments Glycine max L. Adaptation to Ni-Contamination through Affecting Endogenous Phytohormones and Oxidative Stress

This study investigated the Ni-removal efficiency of phytohormone-producing endophytic fungi Penicillium janthinellum, Paecilomyces formosus, Exophiala sp., and Preussia sp. Among four different endophytes, P. formosus LHL10 was able to tolerate up to 1 mM Ni in contaminated media as compared to copper and cadmium. P. formosus LHL10 was further assessed for its potential to enhance the phytoremediation of Glycine max (soybean) in response to dose-dependent increases in soil Ni (0.5, 1.0, and 5.0 mM). Inoculation with P. formosus LHL10 significantly increased plant biomass and growth attributes as compared to non-inoculated control plants with or without Ni contamination. LHL10 enhanced the translocation of Ni from the root to the shoot as compared to the control. In addition, P. formosus LHL10 modulated the physio-chemical apparatus of soybean plants during Ni-contamination by reducing lipid peroxidation and the accumulation of linolenic acid, glutathione, peroxidase, polyphenol oxidase, catalase, and superoxide dismutase. Stress-responsive phytohormones such as abscisic acid and jasmonic acid were significantly down-regulated in fungal-inoculated soybean plants under Ni stress. LHL10 Ni-remediation potential can be attributed to its phytohormonal synthesis related genetic makeup. RT-PCR analysis showed the expression of indole-3-acetamide hydrolase, aldehyde dehydrogenase for indole-acetic acid and geranylgeranyl-diphosphate synthase, ent-kaurene oxidase (P450-4), C13-oxidase (P450-3) for gibberellins synthesis. In conclusion, the inoculation of P. formosus can significantly improve plant growth in Ni-polluted soils, and assist in improving the phytoremediation abilities of economically important crops.

The heavy metal paradox in arbuscular mycorrhizas: from mechanisms to biotechnological applications

Arbuscular mycorrhizal symbioses that involve most plants and Glomeromycota fungi are integral and functional parts of plant roots. In these associations, the fungi not only colonize the root cortex but also maintain an extensive network of hyphae that extend out of the root into the surrounding environment. These external hyphae contribute to plant uptake of low mobility nutrients, such as P, Zn, and Cu. Besides improving plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal (HM) toxicity to their host plants. HMs, such as Cu, Zn, Fe, and Mn, play essential roles in many biological processes but are toxic when present in excess. This makes their transport and homeostatic control of particular importance to all living organisms. AMF play an important role in modulating plant HM acquisition in a wide range of soil metal concentrations and have been considered to be a key element in the improvement of micronutrient concentrations in crops and in the phytoremediation of polluted soils. In the present review, we provide an overview of the contribution of AMF to plant HM acquisition and performance under deficient and toxic HM conditions, and summarize current knowledge of metal homeostasis mechanisms in arbuscular mycorrhizas.

The arbuscular mycorrhizal fungus Rhizophagus irregularis differentially regulates the copper response of two maize cultivars differing in copper tolerance

Arbuscular mycorrhiza can increase plant tolerance to heavy metals. The effects of arbuscular mycorrhiza on plant metal tolerance vary depending on the fungal and plant species involved. Here, we report the effect of the arbuscular mycorrhizal fungus Rhizophagus irregularis on the physiological and biochemical responses to Cu of two maize genotypes differing in Cu tolerance, the Cu-sensitive cv. Orense and the Cu-tolerant cv. Oropesa. Development of the symbiosis confers an increased Cu tolerance to cv. Orense. Root and shoot Cu concentrations were lower in mycorrhizal than in non-mycorrhizal plants of both cultivars. Shoot lipid peroxidation increased with soil Cu content only in non-mycorrhizal plants of the Cu-sensitive cultivar. Root lipid peroxidation increased with soil Cu content, except in mycorrhizal plants grown at 250mg Cu kg^-1soil. In shoots of mycorrhizal plants of both cultivars, superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase activities were not affected by soil Cu content. In Cu-supplemented soils, total phytochelatin content increased in shoots of mycorrhizal cv. Orense but decreased in cv. Oropesa. Overall, these data suggest that the increased Cu tolerance of mycorrhizal plants of cv. Orense could be due to an increased induction of shoot phytochelatin biosynthesis by the symbiosis in this cultivar.