Heavy metal mediated phytotoxic impact on winter wheat: oxidative stress and microbial management of toxicity by Bacillus subtilis BM2

Inoculation of multi-metal-resistant Bacillus sp. to a hyperaccumulator plant Sedum alfredii for facilitating phytoextraction of heavy metals from contaminated soil

Co-contamination of soil by multiple heavy metals is a significant global challenge. An effective strategy to address this issue involves using hyperaccumulators such as Sedum alfredii (S. alfredii). The efficiency of phytoremediation can be improved by supplementing with plant growth-promoting bacteria (PGPB). However, bacteria resources of PGPB resistant to multi-heavy metal contamination are still lacking. This study focused nine different strains of Bacillus and screened for resistance to heavy metals including cadmium (Cd), zinc (Zn), copper (Cu), and lead (Pb). A superior strain, Bacillus subtilis PY79 (B. subtilis), showed tolerance for all tested metals. Inoculation with B. subtilis in the rhizosphere of S. alfredii increased the accumulation of Cd, Zn, Cu, and Pb by 88.02%, 58.99%, 90.22%, and 54.97% in the plant shoots after 30 days respectively. B. subtilis application lowered the pH of the rhizosphere soil, thereby increasing the bioavailability of nutrients and heavy metals. Furthermore, B. subtilis helped S. alfredii recruit PGPB and heavy metal-resistant bacteria such as Edaphobacter, Niastella, and Chitinophaga, enhancing the growth and phytoremediation efficiency. Moreover, inoculation with B. subtilis not only upregulated genes of the ABC, HMA, ZIP, and MTP families involved in the translocation and detoxification of heavy metals but also increased the secretion of antioxidants within the cells. These findings indicate that B. subtilis enhances the tolerance, uptake, and translocation of heavy metals in S. alfredii, offering valuable insights for the phytoremediation of multi-metal-contaminated soils.

Characterization of heat, salt, acid, alkaline, and antibiotic stress response in soil isolate Bacillus subtilis strain PSK.A2

Microbes play an essential role in soil fertility by replenishing the nutrients; they encounter various biotic and abiotic stresses disrupting their cellular homeostasis, which expedites activating a conserved signaling pathway for transient over-expression of heat shock proteins (HSPs). In the present study, a versatile soil bacterium Bacillus subtilis strain PSK.A2 was isolated and characterized. Further, the isolated bacterium was exposed with several stresses, viz., heat, salt, acid, alkaline, and antibiotics. Stress-attributed cellular morphological modifications such as swelling, shrinkage, and clump formation were observed under the scanning electron microscope. The comparative protein expression pattern was studied by SDS-PAGE, relative protein stabilization was assessed by protein aggregation assay, and relative survival was mapped by single spot dilution and colony-counting method under control, stressed, lethal, and stressed lethal conditions of the isolate. The findings demonstrated that bacterial stress tolerance was maintained via the activation of various HSPs of molecular weight ranging from 17 to 115 kD to respective stimuli. The treatment of subinhibitory dose of antibiotics not interfering protein synthesis (amoxicillin and ciprofloxacin) resulted in the expression of eight HSPs of molecular weight ranging from 18 to 71 kD. The pre-treatment of short stress dosage showed endured overall tolerance of bacterium to lethal conditions, as evidenced by moderately enhanced total soluble intracellular protein content, better protein stabilization, comparatively over-expressed HSPs, and relatively enhanced cell survival. These findings hold an opportunity for developing novel approaches towards enhancing microbial resilience in a variety of conditions, including industrial bioprocessing, environmental remediation, and infectious disease management.

Bio-stimulating effect of endophytic Aspergillus flavus AUMC 16068 and its respective ex-polysaccharides in lead stress tolerance of Triticum aestivum plant

Heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. As a result, metal-induced phytotoxicity concerns require quick and urgent action to retain and maintain the physiological activities of microorganisms, the nitrogen pool of soils, and the continuous yields of wheat in a constantly worsening environment. The current study was conducted to evaluate the plant growth-promoting endophytic Aspergillus flavus AUMC 16,068 and its EPS for improvement of plant growth, phytoremediation capacity, and physiological consequences on wheat plants (Triticum aestivum) under lead stress. After 60 days of planting, the heading stage of wheat plants, data on growth metrics, physiological properties, minerals content, and lead content in wheat root, shoot, and grains were recorded. Results evoked that lead pollution reduced wheat plants' physiological traits as well as growth at all lead stress concentrations; however, inoculation with lead tolerant endophytic A. flavus AUMC 16,068 and its respective EPS alleviated the detrimental impact of lead on the plants and promoted the growth and physiological characteristics of wheat in lead-contaminated conditions and also lowering oxidative stress through decreasing (CAT, POD, and MDA), in contrast to plants growing in the un-inoculated lead polluted dealings. In conclusion, endophytic A. flavus AUMC 16,068 spores and its EPS are regarded as eco-friendly, safe, and powerful inducers of wheat plants versus contamination with heavy metals, with a view of protecting plant, soil, and human health.

Uncovering the mechanisms of how corn steep liquor and microbial communities minimize cadmium translocation in Chinese cabbage

Corn steep liquor-assisted microbial remediation has been proposed as a promising strategy to remediate cadmium (Cd)-contaminated soil. In this study, we determined Bacillus subtilis (K2) with a high cadmium (Cd) accumulation ability and Cd resistance. However, studies on this strategy used in the Cd uptake of Chinese cabbage are lacking, and the effect of the combined incorporation of corn steep liquor and K2 on the functions and microbial interactions of soil microbiomes is unclear. Here, we study the Cd uptake and transportation in Chinese cabbage by the combination of K2 and corn steep liquor (K2 + C7) in a Cd-contaminated soil and corresponding microbial regulation mechanisms. Results showed that compared to inoculant K2 treatment alone, a reduction of Cd concentration in the shoots by 14.4% and the dry weight biomass of the shoots and the roots in Chinese cabbage increased by 21.6% and 30.8%, respectively, under K2 + C7 treatment. Meanwhile, hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels were decreased by enhancing POD and SOD activity, thereby reversing Cd-induced oxidative damage. Importantly, inoculation of K2 would decrease the diversity of the microbial community while enhancing the abundance of dominant species. These findings provide a promising strategy for reducing the Cd accumulation in Chinese cabbage and recovering soil ecological functions.

Variations in microbial assemblage between rhizosphere and root endosphere microbiomes contribute to host plant growth under cadmium stress

IMPORTANCE

In this study, we revealed that the variation in rhizosphere and root endosphere microbial assemblage between host plant ecotypes contribute to their differential abilities to withstand cadmium (Cd) stressors. Furthermore, our study found that phenolic compounds, such as benzenoids and flavonoids, could function as both essential carbon sources and semiochemicals, thereby contributing to the assemblage of rhizosphere microbiome to resist Cd stress. Our findings provide new insights into the mechanisms that drive the differential assemblage of rhizosphere and root endosphere microbiomes to enhance plant growth under abiotic stress.

Metal tolerance and biosorption capacities of bacterial strains isolated from an urban watershed

Rapid industrialization and urbanization have led to widespread metal contamination in aquatic ecosystems. This study explores the metal tolerance and biosorption characteristics of four bacterial strains (Serratia sp. L2, Raoultella sp. L30, Klebsiella sp. R3, and Klebsiella sp. R19) isolated from Saint Clair River sediments. These strains effectively removed various metal cations (As3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Cr6+, and Ni2+) in single and multi-metal solutions. Minimum inhibitory concentration (MIC) assays revealed strain-specific variations in metal tolerance, with L2 and L30 exhibiting higher tolerance. Surprisingly, R3 and R19, despite lower tolerance, demonstrated superior metal removal efficiency, challenging the notion that tolerance dictates removal efficacy. In single-metal solutions, R3 and R19 excelled at extracting various metal ions, while competitive binding in multi-metal solutions hindered removal. However, R3 and R19 retained higher removal efficiencies, possibly due to enhanced flocculation activities facilitating metal-ion contact. Comprehensive Fourier-transform infrared (FTIR) analysis highlighted the strains' metal-binding capabilities, with novel peaks emerging after metal exposure, indicative of extracellular polymeric substance (EPS) production. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed metal accumulation on bacterial surfaces and within cytoplasmic regions and revealed morphological changes and metal adsorption patterns, emphasizing the strains' ability to adapt to metal stress. Scanning transmission microscopy (STEM) and EDX analysis uncovered metal accumulation within bacterial cells, underscoring the complexity of microbial-metal interactions. This study also confirms that the simultaneous presence of an aqueous solution may cause a mutual inhibition in the adsorption of each metal to the EPS resulting in reduced metal uptake, which emphasizes the need to select specific bacterial strains for a given metal-containing effluent. The differences in metal distribution patterns between Klebsiella sp. R19 and Raoultella sp. L30 suggest species-specific metal accumulation strategies driven by environmental conditions and metal availability. The heavy metal-removing capabilities and the ability to grow over a wide range of metal concentrations of the strains used in this study may offer an advantage to employ these organisms for metal remediation in bioreactors or in situ.

Ameliorative effects of Si-SNP synergy to mitigate chromium induced stress in Brassica juncea

Hyperaccumulation of heavy metal in agricultural land has hampered yield of important crops globally. It has consequently deepened concerns regarding the burning issue of food security in the world. Among heavy metals, Chromium (Cr) is not needed for plant growth and found to pose detrimental effects on plants. Present study highlights the role of exogenous application of sodium nitroprusside (SNP, exogenous donor of NO) and silicon (Si) in alleviating detrimental ramification of Cr toxicity in Brassica juncea. The exposure of B. juncea to Cr (100 μM) under hydroponic system hampered the morphological parameters of plant growth like length and biomass and physiological parameters like carotenoid and chlorophyll contents. It also resulted in oxidative stress by disrupting the equilibrium between ROS production and antioxidant quenching leading to accumulation of ROS such as hydrogen peroxide (H2O2) and superoxide (O2•‾) radicle which causes lipid peroxidation. However, application of Si and SNP both individually and in combination counteracted oxidative stress due to Cr by regulating ROS accumulation and enhancing antioxidant metabolism by upregulation of antioxidant genes of DHAR, MDHAR, APX and GR. As the alleviatory effects were more pronounced in plants treated with combined application of Si and SNP; therefore, our findings suggest that dual application of these two alleviators can be used to mitigate Cr stress.

How could actinobacteria augment the growth and redox homeostasis in barley plants grown in TiO2NPs-contaminated soils? A growth and biochemical study

The increases in titanium dioxide nanoparticles (TiO2-NPs) released into the environment have raised concerns about their toxicity. However, their phytotoxic impact on plants is not well studied. Therefore, this study aimed at a deeper understanding of the TiO2-NPs phytotoxic impact on barley (Hordeum vulgare) growth and stress defense. We also hypothesized that soil inoculation with bioactive Rhodospirillum sp. JY3 strain can be applied as a biological fertilizer to alleviate TiO2-NPs phytotoxicity. At TiO2-NPs phytotoxicity level, photosynthesis was significantly retarded (∼50% reduction) in TiO2-NPs treated-barley plants which accordingly affect the biomass of barley plants. This retardation was accompanied by a remarkable induction of oxidative damage (H2O2, lipid peroxidation) with a concomitant reduction in the antioxidant defense metabolism. At a glance, Rhodospirillum sp. JY3 ameliorated the reduction in growth by enhancing the photosynthetic efficiency in contaminated barley plants. Moreover, Rhodospirillum sp. JY3 inoculation reduced the oxidative damage induced by TiO2-NPs via quenching H2O2 production and lipid peroxidation. Regarding the antioxidant defense arsenal, Rhodospirillum sp. JY3 enhanced both enzymatic (e.g. peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), …. etc.) and non-enzymatic (glutathione (GSH), ascorbate (ASC), polyphenols, flavonoids, tocopherols) antioxidants in shoots and to a greater extent roots of barley plants. Moreover, the inoculation significantly enhanced the heavy metal-detoxifying metabolites (eg. phytochelatins, glutaredoxin, thioredoxin, peroxiredoxin) as well as metal-detoxifying enzymes in barley shoots and more apparently in roots of TiO2-NPs stressed plants. Furthermore, there was an organ-specific response to TiO2-NPs and Rhodospirillum sp. JY3. To this end, this study shed light, for the first time, on the molecular bases underlie TiO2-NPs stress mitigating impact of Rhodospirillum sp. JY3 and it introduced Rhodospirillum sp. JY3 as a promising eco-friendly tool in managing environmental risks to maintain agricultural sustainability.

Characterization and bioactivities of exopolysaccharide produced from Azotobacter salinestris EPS-AZ-6

This study involved the extraction of an exopolysaccharide (EPS) from Azotobacter salinestris AZ-6, which was isolated from soil cultivated with leguminous plants. In a medium devoid of nitrogen, the AZ-6 strain displayed a maximum EPS yield of 1.1 g/l and the highest relative viscosity value of 3.4. The homogeneity of the polymer was demonstrated by the average molecular weight of 1.61 × 106 Da and a retention time of 17.211 min for levan. The presence of characteristic functional groups and structural units of carbohydrate polymers has been confirmed through spectroscopic analyses utilizing Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) revealed a noteworthy decrease in weight (74 %) in the temperature range spanning from 260 to 350 °C. X-ray diffraction (XRD) was utilized to verify the crystalline and amorphous characteristics of EPS-AZ-6. The EPS-AZ-6 exhibited significant cytotoxicity against the MCF-7 tumor cell line, as evidenced by an IC50 value of 6.39 ± 0.05 μg/ml. It also demonstrated a moderate degree of cytotoxicity towards HepG-2 cell line, as indicated by an IC50 value of 29.79 ± 0.41 μg/ml. EPS-AZ-6 exhibited potent antioxidant and in vitro antibacterial properties. These characteristics suggest the potential application value of EPS-AZ-6 in the food industry and pharmaceutical applications.

Understanding the phytotoxic impact of Al3+, nano-size, and bulk Al2O3 on growth and physiology of maize (Zea mays L.) in aqueous and soil media

The release and accumulation of metal-oxide nanoparticles in soils have threatened terrestrial plants. However, limited knowledge is available on the accumulation of nano-Al₂O₃ (22 nm), bulk-Al₂O₃ (167 nm), and Al³⁺ by maize plants and the subsequent impact on its physiology and growth in agar (0.7% w/v), hydroponic (1X), and soil. Maize plants were cultivated with 0.05-2 mg g^-1 or ml^-1 of three Al types and their biological attributes, oxidative status, Al bioaccumulation, and translocation were measured. The ICP-MS results revealed a dose-dependent increase (P ≤ 0.05 or ≤0.01) in Al content in maize tissues following nano-Al₂O₃ and Al³⁺ exposure, however, plants exposed to bulk-Al₂O₃ showed no significant uptake of Al. Atomic mapping by EDX during SEM analysis and TEM revealed varied distributions of nano-Al₂O₃ from roots to aerial parts and intracellular transportation. Al deposition in tissues followed the order: Al³⁺ > nano-Al₂O₃ > bulk-Al₂O₃ and therefore, a similar trend of toxicity was observed for seed germination, the emergence of plant organs, length, biomass accumulation, total chlorophyll, phosphorus content, and total soluble protein. Oxidative stress was profoundly induced dose-dependently and was highest at 2 mg ml^-1 or g^-1 of Al³⁺ and nano-Al₂O₃ when superoxide radical formation, proline induction, activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (GPX), and glutathione reductase (GR) and membrane lipid peroxidation were measured. Aluminum toxicity was found higher in hydroponically grown maize compared to soil-grown maize. Forty days exposure in soil showed greater inhibition of maize growth compared to 20 days exposure. This study is significant in understanding the maize response to different Al types in soil and soil-free media.

The potential of Bacillus subtilis and phosphorus in improving the growth of wheat under chromium stress

AIM

Hexavalent chromium (Cr⁺⁶ ) is one of the most toxic heavy metals that have deteriorating effects on the growth and quality of the end product of wheat. Consequently, this research was designed to evaluate the role of Bacillus subtilis and phosphorus fertilizer on wheat facing Cr⁺⁶ stress.

METHODS AND RESULTS

The soil was incubated with Bacillus subtilis and phosphorus fertilizer before sowing. The statistical analysis of the data showed that the co-application of B. subtilis and phosphorus yielded considerably more significant (p < 0.05) results compared with an individual application of the respective treatments. The co-treatment improved the morphological, physiological and biochemical parameters of plants compared with untreated controls. The increase in shoot length, root length, shoot fresh weight and root fresh weight was 38.17%, 29.31%, 47.89% and 45.85%, respectively, compared with untreated stress-facing plants. The application of B. subtilis and phosphorus enhanced osmolytes content (proline 39.98% and sugar 41.30%), relative water content and stability maintenance of proteins (86.65%) and cell membranes (66.66%). Furthermore, augmented production of antioxidants by 67.71% (superoxide dismutase), 95.39% (ascorbate peroxidase) and 60.88% (catalase), respectively, were observed in the Cr⁺⁶ - stressed plants after co-application of B. subtilis and phosphorus.

CONCLUSION

It was observed that the accumulation of Cr⁺⁶ was reduced by 54.24%, 59.19% and 90.26% in the shoot, root and wheat grains, respectively. Thus, the combined application of B. subtilis and phosphorus has the potential to reduce the heavy metal toxicity in crops.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study explored the usefulness of Bacillus subtilis and phosphorus application on wheat in heavy metal stress. It is a step toward the combinatorial use of plant growth-promoting rhizobacteria with nutrients to improve the ecosystems' health.

Understanding the Phytoremediation Mechanisms of Potentially Toxic Elements: A Proteomic Overview of Recent Advances

Potentially toxic elements (PTEs) such as cadmium (Cd), lead (Pb), chromium (Cr), and arsenic (As), polluting the environment, pose a significant risk and cause a wide array of adverse changes in plant physiology. Above threshold accumulation of PTEs is alarming which makes them prone to ascend along the food chain, making their environmental prevention a critical intervention. On a global scale, current initiatives to remove the PTEs are costly and might lead to more pollution. An emerging technology that may help in the removal of PTEs is phytoremediation. Compared to traditional methods, phytoremediation is eco-friendly and less expensive. While many studies have reported several plants with high PTEs tolerance, uptake, and then storage capacity in their roots, stem, and leaves. However, the wide application of such a promising strategy still needs to be achieved, partly due to a poor understanding of the molecular mechanism at the proteome level controlling the phytoremediation process to optimize the plant's performance. The present study aims to discuss the detailed mechanism and proteomic response, which play pivotal roles in the uptake of PTEs from the environment into the plant's body, then scavenge/detoxify, and finally bioaccumulate the PTEs in different plant organs. In this review, the following aspects are highlighted as: (i) PTE's stress and phytoremediation strategies adopted by plants and (ii) PTEs induced expressional changes in the plant proteome more specifically with arsenic, cadmium, copper, chromium, mercury, and lead with models describing the metal uptake and plant proteome response. Recently, interest in the comparative proteomics study of plants exposed to PTEs toxicity results in appreciable progress in this area. This article overviews the proteomics approach to elucidate the mechanisms underlying plant's PTEs tolerance and bioaccumulation for optimized phytoremediation of polluted environments.

Interactive effect of glycine, alanine, and calcium nitrate Ca(NO3)2 on wheat (Triticum aestivum L.) under lead (Pb) stress

Aim of this study was to evaluate the interactive effects of glycine, alanine, calcium nitrate [Ca(NO₃)₂], and their mixture on the growth of two wheat (Triticum aestivum L.) varieties, i.e., var. Punjab-2011 and var. Anaj-2017 under lead [0.5 mM Pb(NO₃)₂] stress. A pot experiment was conducted for this purpose. Pre-sowing seed treatment with 1 mM glycine, alanine, and calcium nitrate [Ca(NO₃)₂] was applied under two levels of lead nitrate [Pb(NO₃)₂] stress, i.e., control and 0.5 mM Pb(NO₃)₂. Lead (0.5 mM) stress significantly decreased root and shoot lengths, fresh and dry weights of root and shoot, and chlorophyll contents, while it increased activities of antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and peroxidase (POD) in both wheat varieties. Lead (0.5 mM) stress increased the accumulation of free proline, glycinebetaine, total free amino acids, and total soluble protein contents. Although var. Punjab-2011 was higher in root fresh and dry weights, shoot length, and total leaf area per plant, however, var. Anaj-2017 showed less reduction in shoot dry weight, root fresh weight, and shoot length under lead stress. Under lead stress, Punjab-2011 was higher in grain yield and number of grain plant^-1, chlorophyll a contents, membrane permeability (%), POD activity, total free amino acids, and glycinebetaine (GB) contents as compared to Anaj-2017. Pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) increased shoot dry weight, number of grains per plants, 100-grain weight, number of spikes, and chlorophyll a contents under normal and lead-stressed conditions. Wheat var. Anaj-2017 showed higher growth and yield attributes as compared to var. Punjab-2011. Results of the current study have shown that pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) can overcome the harmful effects of lead (Pb) stress in wheat plants.

Efficacy of citric acid chelate and Bacillus sp. in amelioration of cadmium and chromium toxicity in wheat

Heavy metals contamination in agricultural soil is a major issue having drastic effects on plants and human health. To solve this issue, we have formulated and tested a new approach of fusion of inorganic (citric acid chelate) and organic (Bacillus sp.) amelioration methods for heavy metals. The Bacillus sp. was heavy metal tolerant and showed plant growth-promoting characteristics including phosphate solubilization, siderophore production, hydrogen cyanide production, indole acetic acid production, and 1-Aminocyclopropane-1-carboxylate deaminase production. The analysis of data showed that plants receiving the combined application of citric acid (CA) chelate and Bacillus sp. mitigated heavy metal toxicity. They augmented the biomass production and amount of photosynthetic pigments in plant cells. They suppressed the negative effects of Cadmium (Cd) and Chromium (Cr) on plants' metabolic systems. A considerable increase was also observed in the activity of enzymatic and non-enzymatic antioxidants which reduced the damaging effects of reactive oxygen species and maintained internal structures of cells. The decrease in the content of Cr and Cd in wheat grains by the treatment of CA chelate and Bacillus sp. was 51%, and 27% respectively. The bioaccumulation of metals was also reduced to 49% (Cr) and 57% (Cd). This approach can be tested and applied in field conditions for soils with heavy metals contamination.

Potential use of a novel actinobacterial species to ameliorate tungsten nanoparticles induced oxidative damage in cereal crops

Tungsten nanoparticles (WNPs) could induce hazard impact on plant growth and development; however, no study investigated their phytotoxicity. On the other hand, plant growth-promoting bacteria (PGPB) can effectively reduce WNPs toxicity. To this end, Nocardiopsis sp. was isolated and employed to mitigate the phytotoxic effect of WNPs on three crops (wheat, barley, and oat). Soil contamination with WPNs induced the W accumulation in all tested crops, inhibited both growth and photosynthesis and induced oxidative damage. On the other hand, pre-inoculation with Nocardiopsis sp. significantly reduced W level in treated plants. Concomitantly, Nocardiopsis sp. strikingly mitigated the inhibitory effect of WNPs by augmenting both growth and reactive oxygen species (ROS) homeostasis. To cope with heavy metal stress, all the tested species orchestrated their antioxidant homeostasis through enhancing the production of antioxidant metabolites (e.g., phenolics, flavonoids and tocopherols) and elevated the activities of ROS-scavenging enzymes (e.g., APX, POX, CAT, as well as the enzymes involved in AsA/GSH cycle). Moreover, pre-inoculation with Nocardiopsis sp. improved the detoxification metabolism by enhancing the accumulation of phytochelatins (PCs), metallothionein (MTC) and glutathione-S-transferase (GST) in grasses grown in WNPs-contaminated soils. Overall, restrained ROS homeostasis and improved WNPs detoxification systems were the bases underlie the WNPs stress mitigating impact of Nocardiopsis sp treatment.

Wheat Microbiome: Structure, Dynamics, and Role in Improving Performance Under Stress Environments

Wheat is an important cereal crop species consumed globally. The growing global population demands a rapid and sustainable growth of agricultural systems. The development of genetically efficient wheat varieties has solved the global demand for wheat to a greater extent. The use of chemical substances for pathogen control and chemical fertilizers for enhanced agronomic traits also proved advantageous but at the cost of environmental health. An efficient alternative environment-friendly strategy would be the use of beneficial microorganisms growing on plants, which have the potential of controlling plant pathogens as well as enhancing the host plant's water and mineral availability and absorption along with conferring tolerance to different stresses. Therefore, a thorough understanding of plant-microbe interaction, identification of beneficial microbes and their roles, and finally harnessing their beneficial functions to enhance sustainable agriculture without altering the environmental quality is appealing. The wheat microbiome shows prominent variations with the developmental stage, tissue type, environmental conditions, genotype, and age of the plant. A diverse array of bacterial and fungal classes, genera, and species was found to be associated with stems, leaves, roots, seeds, spikes, and rhizospheres, etc., which play a beneficial role in wheat. Harnessing the beneficial aspect of these microbes is a promising method for enhancing the performance of wheat under different environmental stresses. This review focuses on the microbiomes associated with wheat, their spatio-temporal dynamics, and their involvement in mitigating biotic and abiotic stresses.

Drought Tolerant Enterobacter sp./Leclercia adecarboxylata Secretes Indole-3-acetic Acid and Other Biomolecules and Enhances the Biological Attributes of Vigna radiata (L.) R. Wilczek in Water Deficit Conditions

Drought or water stress is a limiting factor that hampers the growth and yield of edible crops. Drought-tolerant plant growth-promoting rhizobacteria (PGPR) can mitigate water stress in crops by synthesizing multiple bioactive molecules. Here, strain PAB19 recovered from rhizospheric soil was biochemically and molecularly characterized, and identified as Enterobacter sp./Leclercia adecarboxylata (MT672579.1). Strain PAB19 tolerated an exceptionally high level of drought (18% PEG-6000) and produced indole-3-acetic acid (176.2 ± 5.6 µg mL-1), ACC deaminase (56.6 ± 5.0 µg mL-1), salicylic acid (42.5 ± 3.0 µg mL-1), 2,3-dihydroxy benzoic acid (DHBA) (44.3 ± 2.3 µg mL-1), exopolysaccharide (204 ± 14.7 µg mL-1), alginate (82.3 ± 6.5 µg mL-1), and solubilized tricalcium phosphate (98.3 ± 3.5 µg mL-1), in the presence of 15% polyethylene glycol. Furthermore, strain PAB19 alleviated water stress and significantly (p ≤ 0.05) improved the overall growth and biochemical attributes of Vigna radiata (L.) R. Wilczek. For instance, at 2% PEG stress, PAB19 inoculation maximally increased germination, root dry biomass, leaf carotenoid content, nodule biomass, leghaemoglobin (LHb) content, leaf water potential (ΨL), membrane stability index (MSI), and pod yield by 10%, 7%, 14%, 38%, 9%, 17%, 11%, and 11%, respectively, over un-inoculated plants. Additionally, PAB19 inoculation reduced two stressor metabolites, proline and malondialdehyde, and antioxidant enzymes (POD, SOD, CAT, and GR) levels in V. radiata foliage in water stress conditions. Following inoculation of strain PAB19 with 15% PEG in soil, stomatal conductance, intercellular CO2 concentration, transpiration rate, water vapor deficit, intrinsic water use efficiency, and photosynthetic rate were significantly improved by 12%, 8%, 42%, 10%, 9% and 16%, respectively. Rhizospheric CFU counts of PAB19 were 2.33 and 2.11 log CFU g-1 after treatment with 15% PEG solution and 8.46 and 6.67 log CFU g-1 for untreated controls at 40 and 80 DAS, respectively. Conclusively, this study suggests the potential of Enterobacter sp./L. adecarboxylata PAB19 to alleviate water stress by improving the biological and biochemical features and of V. radiata under water-deficit conditions.

Epiphytic PGPB Bacillus megaterium AFI1 and Paenibacillus nicotianae AFI2 Improve Wheat Growth and Antioxidant Status under Ni Stress

The present study demonstrates the Ni toxicity-ameliorating and growth-promoting abilities of two different bacterial isolates when applied to wheat (Triticum aestivum L.) as the host plant. Two bacterial strains tolerant to Ni stress were isolated from wheat seeds and selected based on their ability to improve the germination of wheat plants; they were identified as Bacillus megaterium AFI1 and Paenibacillus nicotianae AFI2. The protective effects of these epiphytic bacteria against Ni stress were studied in model experiments with two wheat cultivars: Ni stress-tolerant Leningradskaya 6 and susceptible Chinese spring. When these isolates were used as the inoculants applied to Ni-treated wheat plants, the growth parameters and the levels of photosynthetic pigments of the two wheat cultivars both under normal and Ni-stress conditions were increased, though B. megaterium AFI1 had a more pronounced ameliorative effect on the Ni contents in plant tissues due to its synthesis of siderophores. Over the 10 days of Ni exposure, the plant growth promotion bacteria (PGPB) significantly reduced the lipid peroxidation (LPO), ascorbate peroxidase (APX), superoxide dismutase (SOD) activities and proline content in the leaves of both wheat cultivars. The PGPB also increased peroxidase (POX) activity and the levels of chlorophyll a, chlorophyll b, and carotenoids in the wheat leaves. It was concluded that B. megaterium AFI1 is an ideal candidate for bioremediation and wheat growth promotion against Ni-induced oxidative stress, as it increases photosynthetic pigment contents, induces the antioxidant defense system, and lowers Ni metal uptake.

Nickel stress-tolerance in plant-bacterial associations

Nickel (Ni) is an essential element for plant growth and is a constituent of several metalloenzymes, such as urease, Ni-Fe hydrogenase, Ni-superoxide dismutase. However, in high concentrations, Ni is toxic and hazardous to plants, humans and animals. High levels of Ni inhibit plant germination, reduce chlorophyll content, and cause osmotic imbalance and oxidative stress. Sustainable plant-bacterial native associations are formed under Ni-stress, such as Ni hyperaccumulator plants and rhizobacteria showed tolerance to high levels of Ni. Both partners (plants and bacteria) are capable to reduce the Ni toxicity and developed different mechanisms and strategies which they manifest in plant-bacterial associations. In addition to physical barriers, such as plants cell walls, thick cuticles and trichomes, which reduce the elevated levels of Ni entrance, plants are mitigating the Ni toxicity using their own antioxidant defense mechanisms including enzymes and other antioxidants. Bacteria in its turn effectively protect plants from Ni stress and can be used in phytoremediation. PGPR (plant growth promotion rhizobacteria) possess various mechanisms of biological protection of plants at both whole population and single cell levels. In this review, we highlighted the current understanding of the bacterial induced protective mechanisms in plant-bacterial associations under Ni stress.

Impact of metal-oxide nanoparticles on growth, physiology and yield of tomato (Solanum lycopersicum L.) modulated by Azotobacter salinestris strain ASM

The current study for the first time demonstrates the interference of a free-living, N₂-fixing, and nanoparticle (NP) tolerant Azotobacter salinestris strain ASM recovered from metal-polluted soil with tomato plant-metal oxide NPs (ZnO, CuO, Al₂O_3, and TiO₂) interactions in a sandy clay loam soil system with bulk materials as control. Tomato plants were grown till full maturity in soils amended with 20-2000 mg kg^-1 of each metal-oxide NP with and without seed biopriming and root-inoculation of A. salinestris. A. salinestris was found metabolically active, producing considerably high amounts of bioactive indole-3-acetic-acid, morphologically unaffected, and with low alteration of cell membrane permeability under 125-1500 μgml^-1 of NPs. However, ZnO-NPs slightly alter bacterial membrane permeability. Besides, A. salinestris secreted significantly higher amounts of extracellular polymeric substance (EPS) even under NP exposure, which could entrap the NPs and form metal-EPS complex as revealed and quantified by SEM-EDX. NPs were also found adsorbed on bacterial biomass. EPS stabilized the NPs and provided negative zeta potential to NPs. Following soil application, A. salinestris improved the plant performance and augmented the yield of tomato fruits and lycopene content even in NPs stressed soils. Interestingly, A. salinestris inoculation enhanced photosynthetic pigment formation, flower attributes, plant and fruit biomass, and reduced proline level. Bacterial inoculation also reduced the NP's uptake and accumulation significantly in vegetative organs and fruits. The organ wise order of NP's internalization was roots > shoots > fruits. Conclusively, A. salinestris inoculation could be an alternative to increase the production of tomato in metal-oxide NPs contaminated soils.

Physiological disruption, structural deformation and low grain yield induced by neonicotinoid insecticides in chickpea: A long term phytotoxicity investigation

Arbitrary use of insecticides in agricultural practices cause severe environmental hazard that adversely affects the growth and productivity of edible crops. Considering theses, the aim of the present study was to evaluate the toxicological potential of two neonicotinoid insecticides, imidacloprid (IMID) and thiamethoxam (THIA) using chickpea as a test crop. Application of insecticides at three varying doses revealed a gradual decrease in biological performance of chickpea plants which however, varied noticeably among insecticides and their doses. Significant (P ≤ 0.05) decline in germination efficiency, length of plant organs under in vitro condition was observed in a dose related manner. Among insecticides, 300 μgIMIDkg^-1 (3X dose) maximally and significantly (P ≤ 0.05) inhibited germination efficiency, vigor index, length, dry matter accumulation, photosynthetic pigment formation, nodule volume and mass, nutrient uptake, grain yield and protein over untreated control. In contrast, 75 μgTHIAkg^-1 (3X dose) considerably declined the leghaemoglobin content, shoot phosphorus and root nitrogen. Enhanced expression of stress biomarkers including proline, malondialdehyde (MDA), and antioxidant defence enzymes was noticed in the presence of insecticides. For instance, at 3X IMID, shoot proline, MDA, ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and peroxidase (POD) were increased significantly (P ≤ 0.05) by 66%, 81%, 36% and 35%, respectively. Additionally, electrolyte leakage was maximally (77%) increased at 3X dose of IMID, whereas, H₂O₂ in foliage was maximally accumulated (0.0156 μ moles min^-1 g^-1 fw) at 3X dose of THIA which was 58% greater than untreated foliage. A clear distortion/damage in tip and surface of roots and ultrastructural deformation in xylem and phloem of plant tissues as indication of insecticidal phytotoxicity was observed under scanning electron microscope (SEM). For oxidative stress and cytotoxicity assessment, root tips were stained with a combination of acridine orange and propidium iodide, and Evan blue dyes and examined. Confocal laser scanning microscopic (CLSM) images of roots revealed a 10-fold and 13.5-fold increase in red and blue fluorescence when 3X IMID treated roots were assessed quantitatively. Conclusively, the present investigation recommends that a careful and protected approach should be adopted before the application of insecticides in agricultural ecosystems.

Biosorption of heavy metals by dry biomass of metal tolerant bacterial biosorbents: an efficient metal clean-up strategy

Heavy metals discharge at an unrestrained rate from various industries into the environment pose serious human health problems. Considering this, the present study aimed at exploring the metal biosorbing potentials of bacterial strains recovered from polluted soils. The bacterial strains (CPSB1, BM2 and CAZ3) belonging to genera Pseudomonas, Bacillus and Azotobacter expressing multi-metal tolerance ability were identified to species level as P. aeruginosa, B. subtilis and A. chroococcum, respectively, by 16S rRNA partial gene sequence analysis. The biosorption of cadmium, chromium, copper, nickel, lead and zinc by three dead bacterial genera were studied as a function of metal concentration, variable pH of the medium and reaction (contact) time. The three bacterial strains exhibited a tremendous metal removal ability which continued even at the highest tested concentration of some metals. Later, a decline in the percentage of biosorbed metals was recorded as the metal concentration was increased with the simultaneous generation of a driving force to overcome mass transfer resistance for movement of metal ions between the solution and the surface of adsorbent. Among test bacteria, B. subtilis biosorbed a maximum of 96% chromium at 25 μg mL^-1 while the maximum percentage (91%) of biosorbed metals recorded at 400 μg Cd mL^-1 was observed for P. aeruginosa. The sorption of metal ions by dead biomass of three bacterial genera at optimum conditions followed the order-(i) B. subtilis BM2: Pb > Cu > Ni > Cd > Cr, (ii) A. chroococcum CAZ3: Cr > Cd > Cu > Ni > Pb and (iii) P. aeruginosa CPSB1: Cd > Cr > Ni > Cu > Pb > Zn. It was found that the optimum pH for metal adsorption ranged between pH 8 and 9 which, however, declined substantially at pH 5.0 for all three bacterial strains. In general, the biosorption of Cd, Cr, Cu, Ni and Pb by B. subtilis and A. chroococcum and such metals along with Zn by P. aeruginosa occurred maximally up to 60 min of bacterial growth. The adsorption data with regard to five metals provide an outstanding fit to the Langmuir and Freundlich isotherms. The biosorptive ability of three bacterial genera correlated strongly (r² > 0.9) with each metal. The bacteria belonging to two Gram-negative genera Pseudomonas (P. aeruginosa) and Azotobacter (A. chroococcum) and one Gram-positive genus Bacillus (B. subtilis) demonstrated exceptional metal removal efficiency and, hence, provides a comprehensive understanding of metal-bacteria sorption process which in effect paves the way for detoxifying/removing metals from contaminated environment.

Alleviation of Cd phytotoxicity and enhancement of rape seedling growth by plant growth-promoting bacterium Enterobacter sp. Zm-123

The present study aims to investigate the impact of a metal-tolerant bacterium on metal detoxification and rape seedling growth promotion under Cd stress. The results showed that the isolated bacterium Enterobacter sp. Zm-123 has capability to resist Cd (200 mg/L), produce IAA (26.67 mg/L) and siderophores (82.34%), and solubilize phosphate (137.5 mg/L), etc. Zm-123 inoculation significantly enhanced the fresh weight of rape seedlings from 9.47 to 19.98% and the root length from 10.42 to 57.05% compared with non-inoculation group under different concentrations of Cd (0, 0.5, 1, 3, 5 mg/L) (p < 0.05). It also significantly increased the content of chlorophyll, soluble sugar, soluble protein, and proline (p < 0.05) in rape seedlings. Moreover, a significant elevation in catalase (CAT) and peroxidase (POD) activities and a significant reduction in malondialdehyde (MDA), electrolyte leakage (EL), and Cd content in rape seedlings were detected owing to Zm-123 inoculation (p < 0.05). The combined results imply that strain Zm-123 can alleviate the Cd phytotoxicity and promote the rape seedling growth by improving the physiological activity and antioxidant level, which can be potentially applied to protect plants from Cd toxicity.

Cadmium mediated phytotoxic impacts in Brassica napus: Managing growth, physiological and oxidative disturbances through combined use of biochar and Enterobacter sp. MN17

Cadmium (Cd) is a toxic heavy metal with unknown biological role. Interactive effect of Enterobacter sp. MN17 and biochar was studied on the growth, physiology and antioxidant defense system of Brassica napus under Cd contaminated soil. A multi-metal tolerant endophytic bacterium, Enterobacter sp. MN17, was able to grow in tryptic soy agar (TSA) medium with up to 160, 200, 300, 700, 160 and 400 μg mL^-1 of Cd, Cu, Cr, Pb, Ni and Zn, respectively. Paper and pulp waste biochar was prepared at 450 °C and applied to pots (7 kg soil) at a rate of 1% (w/w), while Cd was spiked at 80 mg kg^-1 soil. Application of Enterobacter sp. MN17 and biochar, alone or combined, was found effective in the amelioration of Cd stress. Combined application of Enterobacter sp. MN17 and biochar caused the maximum appraisal in shoot and root length (52.5 and 76.5%), fresh and dry weights of shoot (77.1 and 70.7%) and root (81.2 and 57.9%), photosynthetic and transpiration rate (120.2 and 106.6%), stomatal and sub-stomatal conductance (81.3 and 75.5%), chlorophyll content and relative water content (RWC) (78.4 and 102.9%) than control. Their combined use showed a significant decrease in electrolyte leakage (EL), proline, malondialdehyde (MDA), catalase (CAT), glutathione peroxidase (GPX), glutathione S transferase (GST) and superoxide dismutase (SOD) by 39.3, 39.4, 39.5, 37.0, 39.0 42.1 and 30.8%, respectively, relative to control. Likewise, the combined application of bacterial strain MN17 and biochar reduced Cd in soil by 45.6%, thereby decreasing its uptake in root and shoot by 40.1 and 38.2%, respectively in Cd contaminated soil. The application of biochar supported the maximum colonization of strain MN17 in the rhizosphere soil, root and shoot tissues. These results reflected that inoculation with Enterobacter sp. MN17 could be an effective approach to accelerate biochar-mediated remediation of Cd contaminated soil for sustainable production of crops.

Enhancing Cadmium Tolerance and Pea Plant Health through Enterobacter sp. MN17 Inoculation Together with Biochar and Gravel Sand

Contamination of soils with heavy metals, particularly cadmium (Cd), is an increasingly alarming environmental issue around the world. Application of organic and inorganic immobilizing amendments such as biochar and gravel sand in combination with metal-tolerant microbes has the potential to minimize the bioavailability of Cd to plants. The present study was designed to identify the possible additive effects of the application of Enterobacter sp. MN17 as well as biochar and gravel sand on the reduction of Cd stress in plants and improvement of growth and nutritional quality of pea (Pisum sativum) plants through the reduction of Cd uptake. Pea seeds were surface sterilized then non-inoculated seeds and seeds inoculated with Enterobacter sp. MN17 were planted in artificially Cd-polluted soil, amended with the immobilizing agents biochar and gravel sand. Application of biochar and gravel sand alone and in combination not only improved the growth and nutritional quality of pea plants by in situ immobilization but also reduced the uptake of Cd by plant roots and its transport to shoots. However, microbial inoculation further enhanced the overall plant health as well as alleviated the toxic effects of Cd on the pea plants. These soil treatments also improved rates of photosynthesis and transpiration. The combined use of biochar and gravel sand with bacterial inoculation resulted in an increase in plant height (47%), shoot dry weight (42%), root dry weight (57%), and 100 seeds weight (49%) as compared to control plants in Cd contaminated soil. Likewise, biochemical constituents of pea seeds (protein, fat, fiber, and ash) were significantly increased up to 41%, 74%, 32%, and 72%, respectively, with the combined use of these immobilizing agents and bacterium. Overall, this study demonstrated that the combined application of biochar and gravel sand, particularly in combination with Enterobacter sp. MN17, could be an efficient strategy for the remediation of Cd contaminated soil. It could support better growth and nutritional quality of pea plants.

Burkholderia phytofirmans PsJN and tree twigs derived biochar together retrieved Pb-induced growth, physiological and biochemical disturbances by minimizing its uptake and translocation in mung bean (Vigna radiata L.)

Anthropogenic activities like industrial mining, refining and smelting release substantial amounts of lead (Pb) into the soil causing potential ecological menaces to environment, soil productivity and food security. Present pot scale study was undertaken to investigate the effects of tree twigs-derived biochar and a bacterium Burkholderia phytofirmans PsJN on Pb accumulation, growth, physiological, biochemical and antioxidative defense responses of mung bean grown in Pb spiked soil. The original soil was spiked with Pb (600 mg kg^-1) and amended with biochar (1% w/w). Upon screening in laboratory, B. phytofirmans PsJN exhibited high Pb tolerance and was able to grow at high Pb concentrations. Surface-disinfected seeds of mung bean were inoculated with B. phytofirmans PsJN and sown in pots along with un-inoculated seeds. Data were collected for various growth, physiological and biochemical parameters from fully matured harvested plants. Application of biochar and B. phytofirmans PsJN ameliorated Pb induced negative impacts in mung bean both individually and in combination, but better growth, physiological and seed quality responses were observed with their combined use. Compared with respective controls, their combined use increased the following parameters in normal and Pb spiked soils, respectively: plant height (69% and 159%), root dry weight (97% and 130%), shoot dry weight (42% and 104%), number of pods (70% and 210%), grains weight (58% and 194%) and number of root nodules (71% and 255%). Moreover, combined use increased chlorophyll contents (27% and 37%), photosynthetic rate (93% and 204%), transpiration rate (42% and 132%), stomatal conductance (70% and 218%), sub-stomatal conductance (93% and 148%) and water use efficiency (35% and 43%). In addition, combined application of biochar and B. phytofirmans PsJN retarded Pb-induced oxidative stress by intensifying antioxidant enzyme activities and reducing activities of reactive oxygen species. Similarly, considerable reduction in Pb uptake, translocation and bioaccumulation in mung bean was noticed in Pb spiked soil due to applied amendments. Furthermore, their combined use resulted in considerable increase in grain quality parameters (protein, fat, ash) both in normal and Pb-spiked soils. Therefore, it can be inferred that interactive use of biochar and B. phytofirmans PsJN provides an efficient innovative strategy to repossess Pb induced growth, physiological, biochemical and oxidative disturbances in mung bean.

Heavy metal induced stress on wheat: phytotoxicity and microbiological management

Among many soil problems, heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. Due to these problems, soil biologists/agronomists in recent times have also raised concerns over heavy metal pollution, which indeed are unpleasantly affecting agro-ecosystems and crop production. The toxic heavy metals once deposited beyond certain permissible limits, obnoxiously affect the density, composition and physiological activities of microbiota, dynamics and fertility of soil leading eventually to reduction in wheat production and via food chain, human and animal health. Therefore, the metal induced phytotoxicity problems warrant urgent and immediate attention so that the physiological activities of microbes, nutrient pool of soils and concurrently the production of wheat are preserved and maintained in a constantly deteriorating environment. To mitigate the magnitude of metal induced changes, certain microorganisms have been identified, especially those belonging to the plant growth promoting rhizobacteria (PGPR) group endowed with the distinctive property of heavy metal tolerance and exhibiting unique plant growth promoting potentials. When applied, such metal-tolerant PGPR have shown variable positive impact on wheat production, even in soils contaminated with metals, by supplying macro and micro nutrients and secreting active biomolecules like EPS, melanins and metallothionein (MTs). Despite some reports here and there, the phytotoxicity of metals to wheat and how wheat production in metal-stressed soil can be enhanced is poorly explained. Thus, an attempt is made in this review to better understand the mechanistic basis of metal toxicity to wheat, and how such phytotoxicity can be mitigated by incorporating microbiological remediation strategies in wheat cultivation practices. The information provided here is likely to benefit wheat growers and consequently optimize wheat production inexpensively under stressed soils.

Among many soil problems, heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety.

Lead toxicity induced phytotoxic effects on mung bean can be relegated by lead tolerant Bacillus subtilis (PbRB3)

Being a primary toxic heavy metal, lead (Pb) contamination presents an imposing environmental and public health concern worldwide. A Bacillus subtilis PbRB3, displaying higher Pb tolerance, was isolated from the textile effluent. The bacterial culture was able to remove >80% of Pb from culture solution. Upon screening in the presence of Pb, PbRB3 strain exhibited significant plant growth promoting potential. A 3 weeks long pot experiment was established to examine the capability of PbRB3 strain for physiological and biochemical traits, and Pb accumulation tendency of mung bean at 250 and 500 mg kg^-1 of Pb toxicity, respectively. With respect to control treatments, photosynthetic pigments, protein synthesis, net assimilation rate, transpiration rate and stomatal conductance were significantly constrained by Pb toxicity levels. Intrinsic and instantaneous water use efficiencies were considerably improved in inoculated plants under Pb toxicity. Compared to inoculated control, significantly higher superoxide dismutase activity in both Pb toxicity treatments, while higher malondialdehyde contents only at Pb500 treatment was recorded with PbRB3 inoculation. Catalase activity between Pb250 and Pb500 treatments was comparable at both inoculation level. Moreover, PbRB3 inoculation led to significantly higher peroxidase activity under Pb toxicity treatments compared to inoculated control. The PbRB3 inoculation led to comparable differences in root Pb content between Pb250 and Pb500 treatments. These results suggest that inoculation of Pb tolerant, Bacillus subtilis PbRB3, could be employed to improve mung bean growth potential and adaptation against Pb toxicity, and thereby accelerated Pb rhizoaccumulation from metal contaminated environment.

Application of Rice Grain Husk Derived Biochar in Ameliorating Toxicity Impacts of Cu and Zn on Growth, Physiology and Enzymatic Functioning of Wheat Seedlings

Livestock and poultry manure containing high levels of copper and zinc have led to contamination of farmland and products which could have an impact on human health. Biochar is an inexpensive and efficient heavy metal absorbent. In the present study, we have used biochar to mitigate the effects of heavy metals on the growth of wheat seedlings. The study showed that the effects of heavy metals on wheat seedlings growth were mitigated by increasing exposure to biochar. Compared to the control group, the germination potential, germination rate, germination index and vigor index of wheat seedlings with supplemented biochar increased significantly. Moreover, the specific activity of catalase, peroxidase, superoxide dismutase decreased and chlorophyll contents increased, which promote wheat growth and suggests that the addition of biochar could reduce the effects of heavy metals on wheat seedlings.