Cd induced generation of free radical species in Brassica juncea is regulated by supplementation of earthworms in the drilosphere

Co-application of earthworms and arbuscular mycorrhizal fungi enhances arsenic tolerance of upland rice and improves soil health

Earthworms and arbuscular mycorrhizal fungi (AMF) are essential soil organisms that interactively shape soil-plant dynamics. This study elucidates the mechanistic basis of their co-inoculation in enhancing arsenic (As) tolerance in upland rice (Oryza sativa L.) and improving soil health in a pot experiment with As-contaminated soil (250.18 mg kg-1). This study revealed that the inoculation effects of co-inoculation on rice biomass, N uptake, and P uptake were 86 %, 109 %, and 177 %, respectively, while reducing As concentration in shoot by 38 %. Physiological analyses revealed a 40.17 % reduction in malondialdehyde (MDA) content and a 6 % increase in superoxide dismutase (SOD) activity, indicating enhanced antioxidant capacity. Subcellular As compartmentalization shifted markedly, with organelle-bound As decreasing by 27 % (roots) and 48 % (leaves), while soluble fraction and cell wall sequestration increased. Soil health metrics improved, evidenced by elevated catalase (38 %), urease (15 %), and acid phosphatase (39 %) activities, alongside a 13 % reduction in bioavailable As fractions (As-F1 and As-F2) due to increased As-F4 stabilization. These findings demonstrate that earthworm-AMF synergy mitigates As toxicity by dual strategies: (1) enhancing plant antioxidant defenses and subcellular As compartmentalization, and (2) promoting plant growth via soil enzyme activation and nutrient cycling. This integrated approach offers a scalable, eco-sustainable strategy for safe rice cultivation in As-contaminated agroecosystems.

Polylactic acid microplastics and earthworms drive cadmium bioaccumulation and toxicity in the soil-radish health community

Recent studies underscored the toxicity of microplastics (MPs) as vectors for cadmium (Cd) in soil-plant systems, yet the driven potential of soil fauna in real-world environments remains overlooked. This study examined the interactive effects of earthworms and polylactic acid (PLA) MPs (0.5 % w/w) on rhizosphere biochemistry and Cd (2 mg/kg)-induced phytotoxicity in radish. The combined treatment of earthworms and PLA MPs significantly increased the soil available Cd (diethylenetriaminepentaacetic acid -extractable Cd) from 0.79 mg/kg to 1.01 mg/kg compared to the Cd treatment (p < 0.05) and enhanced the bacterial network stability. Cd accumulation in radish was significantly elevated under the combined treatment (roots: 2.04 mg/kg; leaves: 12.31 mg/kg) compared to the Cd treatment (roots: 1.59 mg/kg; leaves: 8.82 mg/kg) (p < 0.05). The combined treatment activated the radish antioxidant system. The combined treatment (roots: 6.08 g; leaves: 1.65 g) significantly reduced radish biomass compared to the Cd treatment (roots: 24.41 g; leaves: 4.45 g) (p < 0.05). Metabolic pathways involving lipid and carbohydrate metabolism, membrane transport, and secondary metabolite biosynthesis were disrupted. Structural equation modeling identified rhizosphere soil properties (pH, SOM, and CEC) as well as Cd and antioxidant systems in the leaf as major contributors to radish growth inhibition.

Combined application of earthworms and plant growth promoting rhizobacteria improve metal uptake, photosynthetic efficiency and modulate secondary metabolites levels under chromium metal toxicity in Brassica juncea L

Chromium (Cr) toxicity impairs essential morphological and metabolic activities in plants. The present investigation was carried out to evaluate the beneficial role of plant growth promoting rhizobacterial strains namely Pseudomonas aeruginosa (M1), Burkholderia gladioli (M2) and earthworms (Eisenia fetida) in alleviating Cr toxicity in 10 days old Brassica juncea L. The findings delineated that addition of earthworms and PGPR restored growth, boosted Cr uptake and showed upregulation of metal transporter genes (SULTR 1-4). Supplementation of rhizospheric amendments reinstated Cr induced impairment in photosynthetic attributes. Gaseous exchange attributes, the efficiency of PS II, the content of total phenols, anthocyanin and flavonoids was enhanced with application of earthworms along with PGPR. Confocal imaging of primary photosynthetic pigment (chlorophyll), accessory photosynthetic pigment (carotenoids) and total phenols showed maximum fluorescence with combined inoculation of earthworms and both microbial strains (M1M2). The gene expression analysis revealed that Phyotene synthase (PSY), Photosystem II core protein psb A, psb B were down regulated in Cr stressed seedlings which upon supplementation with earthworms and PGPR were upregulated. Further, Phenylalanine ammonialyase (PAL), chalcone synthase (CHS) were upregulated with addition of earthworms and PGPR. Increased nitric oxide content, enhanced activity and upregulation of nitrate reductase (NR) gene was observed with addition of PGPR and earthworms.

Earthworm mucus contributes significantly to the accumulation of soil cadmium in tomato seedlings

Whether earthworm mucus affects Cd transport behavior in soil-plant systems remains uncertain. Consequently, this study thoroughly assessed the impacts of earthworm mucus on plant growth and physiological responses, plant Cd accumulation, translocation, and distribution, as well as soil characteristics and Cd fractionation in a soil-plant (tomato seedling) system. Results demonstrated that the earthworm inoculation considerably enhanced plant Cd uptake and decreased plant Cd translocation, the effects of which were appreciably less significant than those of the earthworm mucus. This suggested that earthworm mucus may play a crucial role in the way earthworms influence plant Cd uptake and translocation. Moreover, the artificial mucus, which contained identical inorganic nitrogen contents to those in earthworm mucus, had no significant effect on plant Cd accumulation or translocation, implying that components other than inorganic nitrogen in the earthworm mucus may have contributed significantly to the overall effects of the mucus. Compared with the control, the earthworm mucus most substantially increased the root Cd content, the Cd accumulation amount of root and whole plant, and root Cd BCF by 93.7 %, 221.3 %, 72.2 %, and 93.7 %, respectively, while notably reducing the Cd TF by 48.2 %, which may be ascribed to the earthworm mucus's significant impacts on tomato seedling growth and physiological indicators, its considerable influences on the subcellular components and chemical species of root Cd, and its substantial effects on the soil characteristics and soil Cd fractionation, as revealed by correlation analysis. Redundancy analysis further suggested that the most prominent impacts of earthworm mucus may have been due to its considerable reduction of soil pH, improvement of soil DOC content, and enhancement of the exchangeable Cd fraction in soil. This work may help better understand how earthworm mucus influences the transport behavior of metals in soil-plant systems.

Phytomelatonin maintained chromium toxicity induced oxidative burst in Brassica juncea L. through improving antioxidant system and gene expression

Chromium (Cr) contamination in soils reduces crop yields and poses a remarkable risk to human and plant system. The main objective of this study was to observe the protective mechanisms of exogenously applied melatonin (Mel- 0.05, 0.1, and 0.15 μM) in seedlings of Brassica juncea L. under Cr (0.2 mM) stress. This was accomplished by analysing the plant's morpho-physiological, biochemical, nuclear, membrane, and cellular characteristics, as well as electrolyte leakage. Superoxide, malondialdehyde, and hydrogen peroxide increased with Cr toxicity. Cr also increased electrolyte leakage. Seedlings under Cr stress had 86.4% more superoxide anion and 27.4% more hydrogen peroxide. Electrolyte leakage increased 35.7% owing to Cr toxicity. B. juncea L. cells with high radical levels had membrane and nuclear damage and decreased viability. Besides this, the activities of the antioxidative enzymes, as POD, APOX, SOD, GST, DHAR, GPOX and GR also elevated in the samples subjected to Cr toxicity. Conversely, the activity of catalase was downregulated due to Cr toxicity. In contrast, Mel reduced oxidative damage and conserved membrane integrity in B. juncea seedlings under Cr stress by suppressing ROS generation. Moreover, the activity of antioxidative enzymes that scavenge reactive oxygen species was substantially upregulated by the exogenous application of Mel. The highest concentration of Mel (Mel c- 0.15 μM) applied showed maximum ameliorative effect on the toxicity caused by Cr. It causes alleviation in the activity of SOD, CAT, POD, GPOX, APOX, DHAR, GST and GR by 51.32%, 114%, 26.44%, 48.91%, 87.51%, 149%, 42.30% and 40.24% respectively. Histochemical investigations showed that Mel increased cell survival and reduced ROS-induced membrane and nuclear damage. The findings showed that Mel treatment upregulated several genes, promoting plant development. Its supplementation decreased RBOH1 gene expression in seedling sunder stress. The results supported the hypothesis that Mel concentrations reduce Cr-induced oxidative burst in B. juncea.

Biochemical and molecular-level effects of co-exposure to chlorpyrifos and lambda-cyhalothrin on the earthworm (Eisenia fetida)

Farmland soil organisms frequently encounter pesticide mixtures presented in their living environment. However, the underlying toxic mechanisms employed by soil animals to cope with such combined pollution have yet to be explored. This investigation aimed to reveal the changes in cellular and mRNA levels under chlorpyrifos (CPF) and lambda-cyhalothrin (LCT) co-exposures in earthworms (Eisenia fetida). Results exhibited that the combination of CPF and LCT triggered an acute synergistic influence on the animals. Most exposures resulted in significant alterations in the activities of total superoxide dismutase (T-SOD), copper/zinc superoxide dismutase (Cu/Zn-SOD), caspase 3, and carboxylesterase (CarE) compared to the basal level. Moreover, when exposed to chemical mixtures, the transcription levels of four genes [heat shock protein 70 (hsp70), gst, sod, and calreticulin (crt)] also displayed more pronounced changes compared with their individual exposures. These changes in determined parameters indicated the occurrence of oxidative stress, cell death, detoxification dysfunction, and endoplasmic reticulum damage after co-exposure to CPF and LCT in E. fetida. The comprehensive examination of mixture toxicities of CPF and LCT at different endpoints would help to understand the overall toxicity they cause to soil invertebrates. The augmented deleterious effect of these pesticides in a mixture suggested that mixture toxicity assessment was necessary for the safety evaluation and application of pesticide mixtures.

Environmental-related doses of afidopyropen induced toxicity effects in earthworms (Eisenia fetida)

Afidopyropen has high activity against pests. However, it poses potential risks to the soil ecology after entering the environment. The toxicity of afidopyropen to earthworms (Eisenia fetida) was studied for the first time in this study. The results showed that afidopyropen had low level of acute toxicity to E. fetida. Under the stimulation of chronic toxicity, the increase of reactive oxygen species (ROS) level activated the antioxidant and detoxification system, which led to the increase of superoxide dismutase (SOD) and glutathione S-transferase (GST) activities. Lipid peroxidation and DNA damage were characterized by the increase of malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents. Meanwhile, the functional genes SOD, CAT, GST, heat shock protein 70 (HSP70), transcriptionally controlled tumor protein (TCTP), and annetocin (ANN) played a synergistic role in antioxidant defense. However, the comprehensive toxicity of high concentration still increased on the 28th day. In addition, strong histopathological damage in the body wall and intestine was observed, accompanied by weight loss, which indicated that afidopyropen inhibited the growth of E. fetida. The molecular docking revealed that afidopyrene combined with the surface structure of SOD and GST proteins, which made SOD and GST become sensitive biomarkers reflecting the toxicity of afidopyropen to E. fetida. Summing up, afidopyropen destroys the homeostasis of E. fetida through chronic toxic. These results provide theoretical data for evaluating the environmental risk of afidopyropen to soil ecosystem.

The pesticide thiamethoxam induced toxicity in Brassica juncea and its detoxification by Pseudomonas putida through biochemical and molecular modifications

Insecticides are extensively exploited by humans to destroy the pests one such compound thiamethoxam is widely used over crops to offer control over wide-array of sucking insect pests. The present study unravels the detoxification potential of Pseudomonas putida in thiamethoxam exposed B. juncea seedlings. The thiamethoxam application curtailed the fresh weight, dry weight and seedling length by 106.22%, 80.29% and 116.78% while P. putida revived these growth parameters in thiamethoxam exposed B. juncea seedlings by 59.65%, 72.99% and 164.56% respectively. The exogenous supplementation of P. putida resuscitated the photosynthetic efficiency of B. juncea seedlings exposed to thiamethoxam as total chlorophyll, chlorophyll a, chlorophyll b, carotenoid, flavonoid and anthocyanin contents were enhanced by 169.42%, 62.90%, 72.89%, 78.53%, 47.36% and 515.15% respectively in contrast to TMX exposed seedlings. Further, P. putida pre-treatment reinvigorated the osmoprotectant content in B. juncea seedlings grown in thiamethoxam as trehalose, glycine betaine and proline contents were thrusted by 21.20%, 58.98% and 34.26% respectively. The thiamethoxam exposure exorbitated the superoxide anion, hydrogen peroxide and MDA levels by 223.03%, 130.18% and 74.63% while P. putida supplementation slackened these oxidative burst levels by 41.75%, 3.79% and 29.09% respectively in thiamethoxam treated seedlings. Notably, P. putida inoculation in thiamethoxam exposed seedlings upregulated the enzymatic antioxidant and non-enzymatic antioxidant activities as SOD, CAT and glutathione were enhanced by 163.76%, 99.29% and 114.91% respectively in contrast to thiamethoxam treated seedlings. The gene expression analysis exhibited the negative impact of thiamethoxam on B. juncea seedlings as conferred by upregulation of chlorophyllase by 443.86 folds whereas P. putida application in thiamethoxam exposed seedlings downregulated the chlorophyllase expression by 248.73 folds and upregulated CXE, GST, NADH and POD genes by 0.44, 4.07, 1.43 and 0.98 folds respectively suggesting the molecular-level thiamethoxam detoxification efficiency of P. putida.

Insights into heavy metal tolerance mechanisms of Brassica species: physiological, biochemical, and molecular interventions

Heavy metal (HM) contamination of soil due to anthropogenic activities has led to bioaccumulation and biomagnification, posing toxic effects on plants by interacting with vital cellular biomolecules such as DNA and proteins. Brassica species have developed complex physiological, biochemical, and molecular mechanisms for adaptability, tolerance, and survival under these conditions. This review summarizes the HM tolerance strategies of Brassica species, covering the role of root exudates, microorganisms, cell walls, cell membranes, and organelle-specific proteins. The first line of defence against HM stress in Brassica species is the avoidance strategy, which involves metal ion precipitation, root sorption, and metal exclusion. The use of plant growth-promoting microbes, Pseudomonas, Psychrobacter, and Rhizobium species effectively immobilizes HMs and reduces their uptake by Brassica roots. The roots of Brassica species efficiently detoxify metals, particularly by flavonoid glycoside exudation. The composition of the cell wall and callose deposition also plays a crucial role in enhancing HMs resistance in Brassica species. Furthermore, plasma membrane-associated transporters, BjCET, BjPCR, BjYSL, and BnMTP, reduce HM concentration by stimulating the efflux mechanism. Brassica species also respond to stress by up-regulating existing protein pools or synthesizing novel proteins associated with HM stress tolerance. This review provides new insights into the HM tolerance mechanisms of Brassica species, which are necessary for future development of HM-resistant crops.

Ecotoxicological Differences of Antimony (III) and Antimony (V) on Earthworms Eisenia fetida (Savingy)

In this study, we assessed the acute and chronic toxic effects of Sb (III) and Sb (V) on Eisenia fetida (Savingy) (E. fetida) by applying the filter paper contact method, aged soil treatment, and avoidance test experiment. In the acute filter paper contact test, the LC50 values for Sb (III) were 2581 mg/L (24 h), 1427 mg/L (48 h), and 666 mg/L (72 h), which were lower than Sb (V). In the chronic aged soil exposure experiment, when the Sb (III)-contaminated soil was aged 10 d, 30 d, and 60 d after exposure for 7 d, the LC50 value of E. fetida was 370, 613, and >4800 mg/kg, respectively. Compared to Sb (V) spiked soils aged only for 10 d, the concentrations causing 50% mortality significantly increased by 7.17-fold after 14 days of exposure in soil aged for 60 d. The results show that Sb (III) and Sb (V) could cause death and directly affect the avoidance behavior of E. fetida; yet, the toxicity of Sb (III) was higher than that of Sb (V). Consistent with the decrease in water-soluble Sb, the toxicity of Sb to E. fetida was greatly reduced with time. Therefore, in order to avoid overestimating the ecological risk of Sb with varying oxidative states, it is important to consider the forms and bioavailability of Sb. This study accumulated and supplemented the toxicity data, and provided a more comprehensive basis for the ecological risk assessment of Sb.

ZnO Nanoparticle-Mediated Seed Priming Induces Biochemical and Antioxidant Changes in Chickpea to Alleviate Fusarium Wilt

Chickpea (Cicer arietinum L.) is one of the main pulse crops of Pakistan. The yield of chickpea is affected by a variety of biotic and abiotic factors. Due to their environmentally friendly nature, different nanoparticles are being synthesized and applied to economically important crops. In the present study, Trichoderma harzianum has been used as a stabilizing and reducing agent for the mycosynthesis of zinc oxide nanoparticles (ZnO NPs). Before their application to control Fusarium wilt of chickpea, synthesized ZnO NPs were characterized. X-ray diffraction (XRD) analysis revealed the average size (13 nm) of ZnO NPs. Scanning electron microscopy (SEM) indicated their spherical structure, and energy dispersive X-ray analysis (EDX) confirmed the oxide formation of ZnO NPs. Transmission electron microscopy (TEM) described the size and shape of nanoparticles, and Fourier transform infrared (FTIR) spectroscopy displayed the presence of reducing and stabilizing chemical compounds (alcohol, carboxylic acid, amines, and alkyl halide). Successfully characterized ZnO NPs exhibited significant mycelial growth inhibition of Fusarium oxysporum, in vitro. In a greenhouse pot experiment, the priming of chickpea seeds with ZnO NPs significantly increased the antioxidant activity of germinated plants and they displayed 90% less disease incidence than the control. Seed priming with ZnO NPs helped plants to accumulate higher quantities of sugars, phenol, total proteins, and superoxide dismutase (SOD) to create resistance against wilt pathogen. These nanofungicides were produced in powder form and they can easily be transferred and used in the field to control Fusarium wilt of chickpea.

Assessment of bioremediation potential of metal contaminated soils (Cu, Cd, Pb and Zn) by earthworms from their tolerance, accumulation and impact on metal activation and soil quality: A case study in South China

This study was aimed to evaluate the potential of four earthworm species commonly found in South China for the bioremediation of soils contaminated by Cu, Cd, Pb and Zn. Survival rates and metal accumulation of Eisenia fetida, Amynthas morrisi, A. robustus and A. corticis and changes in soil physico-chemical properties were investigated in a 60-day incubation experiment with a metal-polluted soil. At the end of the experiment, the survival rates of E. fetida, A. morrisi and A. robustus were significantly higher than that of A. corticis. Principal component analysis showed that earthworm activity improved soil quality with the averaging soil quality index being 0.66, 0.64, 0.56, 0.53, and 0.12 for the A. corticis, A. morrisi, A. robustus, E. fetida, and control treatments, respectively. The highest total available Cd, Cu, and Pb in casts were found in the treatment with A. morrisi, and this species accumulated the smallest amount of metals. Results indicate that A. morrisi may be the best candidate for earthworm-assisted bioremediation of metal contaminated soils in South China.

Amelioration of Chromium-Induced Oxidative Stress by Combined Treatment of Selected Plant-Growth-Promoting Rhizobacteria and Earthworms via Modulating the Expression of Genes Related to Reactive Oxygen Species Metabolism in Brassica juncea

Chromium (Cr) toxicity leads to the enhanced production of reactive oxygen species (ROS), which are extremely toxic to the plant and must be minimized to protect the plant from oxidative stress. The potential of plant-growth-promoting rhizobacteria (PGPR) and earthworms in plant growth and development has been extensively studied. The present study was aimed at investigating the effect of two PGPR (Pseudomonas aeruginosa and Burkholderia gladioli) along with earthworms (Eisenia fetida) on the antioxidant defense system in Brassica juncea seedlings under Cr stress. The Cr toxicity reduced the fresh and dry weights of seedlings, enhanced the levels of superoxide anion (O₂•^-), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL), which lead to membrane as well as the nuclear damage and reduced cellular viability in B. juncea seedlings. The activities of the antioxidant enzymes, viz., superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate peroxidase (APOX), glutathione peroxidase (GPOX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were increased; however, a reduction was observed in the activity of catalase (CAT) in the seedlings under Cr stress. Inoculation of the PGPR and the addition of earthworms enhanced the activities of all other antioxidant enzymes except GPOX, in which a reduction of the activity was observed. For total lipid- and water-soluble antioxidants and the non-enzymatic antioxidants, viz., ascorbic acid and glutathione, an enhance accumulation was observed upon the inoculation with PGPR and earthworms. The supplementation of PGPR with earthworms (combined treatment) reduced both the reactive oxygen species (ROS) and the MDA content by modulating the defense system of the plant. The histochemical studies also corroborated that the combined application of PGPR and earthworms reduced O₂•^-, H₂O₂, lipid peroxidation, and membrane and nuclear damage and improved cell viability. The expression of key antioxidant enzyme genes, viz., SOD, CAT, POD, APOX, GR, DHAR, and GST showed the upregulation of these genes at post-transcriptional level upon the combined treatment of the PGPR and earthworms, thereby corresponding to the improved plant biomass. However, a reduced expression of RBOH1 gene was noticed in seedlings supplemented under the effect of PGPR and earthworms grown under Cr stress. The results provided sufficient evidence regarding the role of PGPR and earthworms in the amelioration of Cr-induced oxidative stress in B. juncea.

Improved physiological defense responses by application of sodium nitroprusside in Isatis cappadocica Desv. under cadmium stress

Isatis cappadocica is a well-known arsenic-hyperaccumulator, but there are no reports of its responses to cadmium (Cd). Nitric oxide (NO) is a signaling molecule, which induces cross-stress tolerance and mediates several physio-biochemical processes related to heavy metal toxicity. In this study, the effects of Cd and sodium nitroprusside (SNP as NO donor) on the growth, defense responses and Cd accumulation in I. cappadocica were investigated. When I. cappadocica was treated with 100 and 200 μM Cd, there was an insignificant inhibition of shoot growth. However, Cd stress at Cd400 treatment decreased significantly the dry weight of root and shoot by 73 and 38%, respectively, as compared to control. The application of SNP significantly improved the growth parameters and mitigated Cd toxicity. In addition, SNP decreased reactive oxygen species (ROS) production induced by Cd. The increased total thiol and glutathione (GSH) concentrations after SNP application may play a decisive role in maintaining cellular redox homeostasis, thereby protecting plants against oxidative damage under Cd stress. Bovine hemoglobin (Hb as NO scavenger) reduced the protective role of SNP, suggesting a major role of NO in the defensive effect of SNP. Furthermore, the reduction in shoot growth and the increase of oxidative damage were more severe after the addition of Hb, which confirms the protective role of NO against Cd-induced oxidative stress. The protective role of SNP in decreasing Cd-induced oxidative stress may be related to NO production, which can lead to stimulation of the thiols synthesis and improve defense system.

Earthworm and arbuscular mycorrhiza interactions: Strategies to motivate antioxidant responses and improve soil functionality

Earthworms and arbuscular mycorrhizal fungi (AMF) act synergistically in the rhizosphere and may increase host plant tolerance to Cd. However, mechanisms by which earthworm-AMF-plant partnerships counteract Cd phytotoxicity are unknown. Thus, we evaluated individual and interactive effects of these soil organisms on photosynthesis, antioxidant capacity, and essential nutrient uptake by Solanum nigrum, as well as on soil quality following Cd exposure (0-120 mg kg^-1). Decreases in biomass and photosynthetic activity, as well as nutrient imbalances were observed in Cd-stressed plants; however, the addition of AMF and earthworms reversed these effects. Cd exposure increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, whereas inoculation with Rhizophagus intraradices decreased those. Soil enzymatic activity decreased by 15-60% with increasing Cd concentrations. However, Cd-mediated toxicity was partially reversed by soil organisms. Earthworms and AMF ameliorated soil quality based on soil enzyme activity. At 120 mg kg^-1 Cd, the urease, catalase, and acid phosphatase activities were 1.6-, 1.4-, and 1.2-fold higher, respectively, in soils co-incubated with earthworms and AMF than in uninoculated soil. Cd inhibited shoot Fe and Ca phytoaccumulation, whereas AMF and earthworms normalized the status of essential elements in plants. Cd detoxification by earthworm-AMF-S. nigrum symbiosis was manifested by increases in plant biomass accumulation (22-117%), chlorophyll content (17-63%), antioxidant levels (SOD 10-18%, POD 9-25%, total polyphenols 17-22%, flavonoids 15-29%, and glutathione 7-61%). It also ameliorated the photosynthetic capacity, and macro- and micronutrient statuses of plants; markedly reduced the levels of malondialdehyde (20-27%), superoxide anion (29-36%), and hydrogen peroxide (19-30%); and upregulated the transcription level of FeSOD. Thus, the combined action of earthworms and AMF feasibly enhances metal tolerance of hyperaccumulating plants and improves the quality of polluted soil.

Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Characterization of mechanisms involved in tolerance and accumulation of Cd in Biscutella auriculata L

Biscutella auriculata L. is one of the rare species that is able to grow in a very contaminated mining area in Villamayor de Calatrava (Ciudad Real, Spain). In an effort to understand the mechanisms involved in the tolerance of this plant to high metal concentrations, we grew B. auriculata in the presence of 125 μM Cd(NO₃)₂ for 15 days and analysed different parameters associated with plant growth, nitric oxide and reactive oxygen species metabolism, metal uptake and translocation, photosynthesis rate and biothiol (glutathione and phytochelatins) content. Treatment with Cd led to growth inhibition in both the leaves and the roots, as well as a reduction of photosynthetic parameters, transpiration and stomatal conductance. The metal was mainly accumulated in the roots and in the vascular tissue, although most Cd was detected in areas surrounding their epidermal cells, while in the leaves the metal accumulated mainly in spongy mesophyll, stomata and trichrome. Based on the Cd bioaccumulation (5.93) and translocation (0.15) factors, this species denoted enrichment of the metal in the roots and its low translocation to the upper tissues. Biothiol analysis showed a Cd-dependent increase of reduced glutathione (GSH) as well as the phytochelatins (PC2 and PC3) in both roots and leaves. Cd-promoted oxidative damage occurred mainly in the leaves due to disturbances in enzymatic and nonenzymatic antioxidants, while the roots did not show significant damage as a result of induction of antioxidant defences. It can be concluded that B. auriculata is a new Cd-tolerant plant with an ability to activate efficient metal-sequestering mechanisms in the root surface and leaves and to induce PCs, as well as antioxidative defences in roots.

Earthworm Eisenia andrei modulates oxidative stress in bean plants Vicia faba irrigated with treated wastewater

With respect to reducing the pressure on freshwater resources, treated wastewater (TWW) irrigation represents a sustainable alternative in agriculture. Due to their low quality and variable composition, TWW could entail harmful consequences for living organisms in terrestrial ecosystems. This study aims to evaluate how earthworm (Eisenia andrei) can modulate oxidative stress in bean plants (Vicia faba) that are irrigated over a course of 60 days with two doses of TWW (50 and 100%) in addition to a control condition (0%) irrigated with distilled water. This is achieved by measuring glutathione-S-transferase (GST) activity and malondialdehyde accumulation (MDA) in plants. Furthermore, catalase (CAT), GST, MDA, and acetylcholinesterase (AChE) activities of the earthworms are also assessed. Our results show that growth and physiological parameters are modified when applying TWW irrigation. Moreover, oxidative stress apprehended by GST activity and MDA accumulation is exacerbated in V. faba plants after exposure to increased TWW doses. Similarly, TWW irrigation enhances oxidative stress parameters in earthworms with a crucial decrease in AChE activity. In addition, the presence of earthworms increases growth and physiological parameters; it also results in a significant reduction in GST activity and MDA rate in V. faba plants. Our results provide new insights into the impact of TWW irrigation on soil organisms and the importance of earthworms in the reduction of oxidative stress in plants.

Microcystin-LR-induced changes of hepatopancreatic transcriptome, intestinal microbiota, and histopathology of freshwater crayfish (Procambarus clarkii)

As a hepatotoxin, microcystin-LR (MC-LR) poses a great threat to aquatic organisms. In this research, the hepatopancreatic transcriptome, intestinal microbiota, and histopathology of Procambarus clarkii (P. clarkii) in response to acute MC-LR exposure were studied. RNA-seq analysis of hepatopancreas identified 372 and 781 differentially expressed genes (DEGs) after treatment with 10 and 40 μg/L MC-LR, respectively. Among the DEGs, 23 genes were immune-related and 21 genes were redox-related. GO functional enrichment analysis revealed that MC-LR could impact nuclear-transcribed mRNA catabolic process, cobalamin- and heme-related processes, and sirohydrochlorin cobaltochelatase activity of P. clarkii. In addition, the only significantly enriched KEGG pathway induced by MC-LR was galactose metabolism pathway. Meanwhile, sequencing of the bacterial 16S rRNA gene demonstrated that MC-LR decreased bacterial richness and diversity, and altered the intestinal microbiota composition. At the phylum level, after 96 h, the abundance of Verrucomicrobia decreased after treatment with 10 and 40 μg/L MC-LR, while Firmicutes increased in the 40 μg/L MC-LR-treated group. At the genus level, the abundances of 15 genera were significantly altered after exposure to MC-LR. Our research demonstrated that MC-LR exposure caused histological alterations such as structural damage of hepatopancreas and intestines. This research provides an insight into the mechanisms associated with MC-LR toxicity in aquatic crustaceans.

Nitric oxide-mediated regulation of oxidative stress in plants under metal stress: a review on molecular and biochemical aspects

Given their sessile nature, plants continuously face unfavorable conditions throughout their life cycle, including water scarcity, extreme temperatures and soil pollution. Among all, metal(loid)s are one of the main classes of contaminants worldwide, posing a serious threat to plant growth and development. When in excess, metals which include both essential and non-essential elements, quickly become phytotoxic, inducing the occurrence of oxidative stress. In this way, in order to ensure food production and safety, attempts to enhance plant tolerance to metal(loid)s are urgently needed. Nitric oxide (NO) is recognized as a signaling molecule, highly involved in multiple physiological events, like the response of plants to abiotic stress. Thus, substantial efforts have been made to assess NO potential in alleviating metal-induced oxidative stress in plants. In this review, an updated overview of NO-mediated protection against metal toxicity is provided. After carefully reviewing NO biosynthetic pathways, focus was given to the interaction between NO and the redox homeostasis followed by photosynthetic performance of plants under metal excess.

Melatonin Stimulates Activities and Expression Level of Antioxidant Enzymes and Preserves Functionality of Photosynthetic Apparatus in Hickory Plants (Carya cathayensis Sarg.) under PEG-Promoted Drought

Nowadays, drought is one of the major abiotic factors which negatively affects growth and development of several fruit tree species, including Chinese hickory plants (Carya cathayensis Sarg.). The present investigation was conducted to study the possible positive effects of melatonin in drought resistance of C. cathayensis plants along with associated mechanisms. It was observed that melatonin pre-treatment applied before limited water availability significantly contrasted drought-promoted negative effects in terms of plant growth and physiological responses. Significant improvement was observed in key biological parameters like relative water content, net photosynthetic rate, stomatal conductance, transpiration rate, maximum photosynthetic efficiency of photosystem II (PSII), and PSII electron transport rate. Antioxidant apparatus was also stimulated by melatonin and enhanced activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were noticed along with higher accumulation of proline. Gene expression studies herein revealed that melatonin promoted the up-regulation of the expression of SOD (70.7%), CAT (32.7%), and APX (66.5%) genes. As a consequence, accumulation of malondialdehyde by-products and leaf symptoms were reduced in melatonin-treated plants. All these observations offer the clear evidence that pre-treatment with melatonin ameliorate the performance of Chinese hickory plants against drought stress.

Editorial of the VSI "Antibiotics and heavy metals in the environment: Facing the challenge"

The Virtual Special Issue (VSI) "Antibiotics and Heavy Metals in the Environment: Facing the Challenge" received more than 100 submissions from research teams around the world. Finally, more than 50 papers were accepted and published. These very interesting research papers allow going ahead in the knowledge of different aspects which determine the fate of antibiotics and heavy metals in the environmental. The success of the VSI, as well as reports from scientific databases, indicate that this field of research is clearly growing, which is expected to continue, especially considering emerging pollutants as a whole.

Modulation of the Functional Components of Growth, Photosynthesis, and Anti-Oxidant Stress Markers in Cadmium Exposed Brassica juncea L

Abstract: Heavy metals (including Cadmium) are being entered into the environment through various sources and cause toxicity to plants. Response of Brassica juncea L. var. RLC-1 was evaluated after exposing them to different concentration of cadmium (Cd) for seven days. Seeds of B. juncea were treated with different concentrations of Cd like 0.2-0.6 mM for 7 days, allowing them to grow in Petri-dishes, and seedlings were examined for different physiological responses. Following exposure to Cd, in the seedlings of B. juncea, growth parameters (root and shoot length), stress markers (lipid peroxidation and H2O2 content), secondary metabolites, photosynthetic pigments, and ion analysis, were estimated along with enzymatic and non-enzymatic antioxidants. We observed a significant reduction in root and shoot length after Cd treatment as compared to control seedlings. Malondialdehyde and H2O2 contents were increased accompanied by enhanced Cd uptake. Activities of antioxidative enzymes were also significantly altered following Cd exposure to the seedlings of B. juncea. Conclusively, we suggest that Cd exposure to the seedlings triggered an induction of several defense responses in B. juncea including major metabolites.