Cadmium toxicity in Maize (Zea mays L.): consequences on antioxidative systems, reactive oxygen species and cadmium accumulation

Effects of superoxide radical on photosynthesis and K+ and redox homeostasis in quinoa and spinach

Methyl viologen (MV), also known as paraquat, is a widely used herbicide but has also been reported as highly toxic to different life forms. The mode of its operation is related to superoxide radical (O2.-) production and consequent oxidative damage. However, besides the damage to key macromolecules, reactive oxygen species (ROS; to which O2.- belongs) are also known as regulators of numerous ion transport systems located at cellular membranes. In this study, we used MV as a tool to probe the role of O2.- in regulating membrane-transport activity and systemic acquired tolerance in halophytic Chenopodium quinoa and glycophytic spinach plants. Both plant species showed growth reduction in terms of reduced shoot length, lower shoot fresh and dry weight, photosynthesis rate, and chlorophyll contents; however, quinoa showed less reduction in growth compared with spinach. This whole plant response was further examined by measuring the ion concentration, gene expression of ion transporters, activation of antioxidants, and osmolyte accumulation. We observed that at the mechanistic level, the differences in growth in response to MV were conferred by at least four complementary physiological mechanisms: (1) higher K+ loss from spinach leaves resulted from higher expression of MV-induced plasma membrane-based depolarization-activated K+ efflux GORK channel, (2) higher activation of high-affinity K+ uptake transporter HAK5 in quinoa, (3) higher antioxidant production and osmolyte accumulation in quinoa as compared with spinach, and (4) maintaining a higher rate of photosynthesis due to higher chlorophyll contents, and efficiency of photosystem II and reduced ROS and MDA contents. Obtained results also showed that MV induced O2.- significantly reduced N contents in both species but with more pronounced effects in glycophytic spinach. Taken together this study has shown the role of O2.- in regulating membrane ion transport and N metabolism in the leaves of halophyte vs. glycophyte in the context of oxidative stress tolerance.

Unveiling silicon-mediated cadmium tolerance mechanisms in mungbean (Vigna radiata (L.) Wilczek): Integrative insights from gene expression, antioxidant responses, and metabolomics

Cadmium (Cd), one of the most phytotoxic heavy metals, is a major contributor to yield losses in several crops. Silicon (Si) is recognized for its vital role in mitigating Cd toxicity, however, the specific mechanisms governing this mitigation process are still not fully understood. In the present study, the effect of Si supplementation on mungbean (Vigna radiata (L.) Wilczek) plants grown under Cd stress was investigated to unveil the intricate pathways defining Si derived stress tolerance. Non-invasive leaf imaging technique revealed improved growth, biomass, and photosynthetic efficiency in Si supplemented mungbean plants under Cd stress. Further, physiological and biochemical analysis revealed Si mediated increase in activity of glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT) enzymes involved in reactive oxygen species (ROS) metabolism leading to mitigation of cellular damage and oxidative stress. Untargeted metabolomic analysis using liquid chromatography coupled with mass spectrometry (LC-MS/MS) provided insights into Si mediated changes in metabolites and their respective pathways under Cd stress. Alteration in five different metabolic pathways with major changes in flavanols and flavonoids biosynthesis pathway which is essential for controlling plants antioxidant defense system and oxidative stress management were observed. The information reported here about the effects of Si on photosynthetic efficiency, antioxidant responses, and metabolic changes will be helpful in understanding the Si-mediated resistance to Cd stress in plants.

Redox Regulation by Priming Agents Toward a Sustainable Agriculture

Plants are sessile organisms that are often subjected to a multitude of environmental stresses, with the occurrence of these events being further intensified by global climate change. Crop species therefore require specific adaptations to tolerate climatic variability for sustainable food production. Plant stress results in excess accumulation of reactive oxygen species leading to oxidative stress and loss of cellular redox balance in the plant cells. Moreover, enhancement of cellular oxidation as well as oxidative signals has been recently recognized as crucial players in plant growth regulation under stress conditions. Multiple roles of redox regulation in crop production have been well documented, and major emphasis has focused on key redox-regulated proteins and non-protein molecules, such as NAD(P)H, glutathione, peroxiredoxins, glutaredoxins, ascorbate, thioredoxins and reduced ferredoxin. These have been widely implicated in the regulation of (epi)genetic factors modulating growth and health of crop plants, with an agricultural context. In this regard, priming with the employment of chemical and biological agents has emerged as a fascinating approach to improve plant tolerance against various abiotic and biotic stressors. Priming in plants is a physiological process, where prior exposure to specific stressors induces a state of heightened alertness, enabling a more rapid and effective defense response upon subsequent encounters with similar challenges. Priming is reported to play a crucial role in the modulation of cellular redox homeostasis, maximizing crop productivity under stress conditions and thus achieving yield security. By taking this into consideration, the present review is an up-to-date critical evaluation of promising plant priming technologies and their role in the regulation of redox components toward enhanced plant adaptations to extreme unfavorable environmental conditions. The challenges and opportunities of plant priming are discussed, with an aim of encouraging future research in this field toward effective application of priming in stress management in crops including horticultural species.

6-Benzylaminopurine mediated augmentation of cadmium phytostabilization potential in Strobilanthes alternata

This study unveiled the cadmium phytoremediation potential and its augmentation using 6-Benzylaminopurine in Strobilanthes alternata. Cadmium stress was provided by applying 250 mg/kg cadmium chloride in soil and 25 ppm of 6-BAP (25 ml) was administered to the plants as foliar spray. The results revealed high bioconcentration factor (BCF) (18.82 ± 0.54) and low translocation factor (TF) values (0.055 ± 0.002) for the plant based on which we strongly recommend S. alternata as a promising candidate for Cd phytoremediation. The phytostabilization potential of the plant was further enhanced by applying 6-BAP, which augmented its BCF to 22.09 ± 0.64 and reduced the TF to 0.038 ± 0.001. Cd toxicity caused a reduction of plant growth parameters, root volume, adaxial-abaxial stomatal indices, relative water content, tolerance index, moisture content, membrane stability index, and xylem vessel diameter in S. alternata. However, Cd + 6-BAP treated plants exhibited an increase of the same compared to Cd-treated plants. FTIR analysis of Cd + 6-BAP treated plants revealed increased deposition of hemicellulose, causing enhanced retention of Cd in the root xylem walls, which is largely responsible for increased phytostabilization of Cd. Therefore, 6-BAP application in S. alternata can be exploited to restore Cd-contaminated areas effectively.

Zinc Oxide Nanoparticles Alleviate Salt Stress in Cotton (Gossypium hirsutum L.) by Adjusting Na+/K+ Ratio and Antioxidative Ability

Soil salinization poses a threat to the sustainability of agricultural production and has become a global issue. Cotton is an important cash crop and plays an important role in economic development. Salt stress has been harming the yield and quality of many crops, including cotton, for many years. In recent years, soil salinization has been increasing. It is crucial to study the mechanism of cotton salt tolerance and explore diversified materials and methods to alleviate the salt stress of cotton for the development of the cotton industry. Nanoparticles (NPs) are an effective means to alleviate salt stress. In this study, zinc oxide NPs (ZnO NPs) were sprayed on cotton leaves with the aim of investigating the intrinsic mechanism of NPs to alleviate salt stress in cotton. The results show that the foliar spraying of ZnO NPs significantly alleviated the negative effects of salt stress on hydroponic cotton seedlings, including the improvement of above-ground and root dry and fresh weight, leaf area, seedling height, and stem diameter. In addition, ZnO NPs can significantly improve the salt-induced oxidative stress by reducing the levels of MDA, H2O2, and O2- and increasing the activities of major antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Furthermore, RNA-seq showed that the foliar spraying of ZnO NPs could induce the expressions of CNGC, NHX2, AHA3, HAK17, and other genes, and reduce the expression of SKOR, combined with the CBL-CIPK pathway, which alleviated the toxic effect of excessive Na+ and reduced the loss of excessive K+ so that the Na+/K+ ratio was stabilized. In summary, our results indicate that the foliar application of ZnO NPs can alleviate high salt stress in cotton by adjusting the Na+/K+ ratio and regulating antioxidative ability. This provides a new strategy for alleviating the salt stress of cotton and other crops, which is conducive to the development of agriculture.

Alterations of Photosynthetic and Oxidative Processes Influenced by the Presence of Different Zinc and Cadmium Concentrations in Maize Seedlings: Transition from Essential to Toxic Functions

BACKGROUND

The study examined the impact of varying the concentrations of zinc (Zn) on plant responses, particularly on photosynthetic and oxidative metabolic processes. This investigation aimed to distinguish between the beneficial and harmful effects of Zn on plants, highlighting significant nutrient supply concerns.

METHODS

The investigation methods were centered around non-invasive methods, such as biophoton emission (delayed fluorescence-DF, ultra-weak bioluminescence-UWLE), fluorescence induction (Fv/Fm) measurements, chlorophyll content estimation (SPAD) and vegetation index (NDVI) determination. Furthermore, the analytical determination of lipid oxidation (MDA level) and antioxidant capacity (FRAP) as well as gene expression studies of the antioxidative enzymes glutathione reductase (GR), glutathione S-transferase (GST) and lipoxygenase (LOX) for essential Zn and nonessential cadmium (Cd) were also carried out in order to clarify toxic symptoms through different Zn investigation approaches.

RESULTS

It was possible to identify a metabolic enhancement from 1000 µM; however, stress symptoms from the 2000 µM Zn treatment were noted for both the investigated photosynthetic and oxidative processes. The outcomes of this research contribute to the improvement of Zn mineral-supplementation technology, which is essential for maize growth, and the optimization of agricultural practices.

Cadmium and copper-induced metabolic and proteomic changes in the root tip during early maize growth

In this study, the metabolic adjustments performed by maize (Zea mays L.) seminal roots exposed to 25 µM Cd2+ or 25 µM Cu2+ at pre-emergence are compared, focusing on the proteomic changes after metal exposure. Root width was increased, and root length was decreased after 72 h of metal treatment. Both metals induced H2O2 accumulation and lipid peroxidation in the root tip. These changes were accompanied by increases in lipoxygenase activity and 4-hydroxy-2-nonenal content. NMR spectroscopy revealed that the abundance of 38 water-soluble metabolites was significantly modified by Cd and Cu exposure; this set of metabolites comprised carboxylic acids, amino acids, carbohydrates, and unidentified phenolic compounds. Linoleic acid content significantly decreased in Cu-treated samples. The total amount of proteins detected in maize root apexes was 2,171. Gene ontology enrichment analysis of the differentially accumulated proteins was performed to detect pathways probably affected by metal additions. Both metals altered redox homeostasis, up-regulated oxylipins biosynthetic process, and shifted metabolism towards the oxidative pentose-phosphate in the root apexes. However, the methionine salvage pathway appears as a key metabolic module only under Cd stress. The integrative analysis carried out in this study suggests that most molecular features behind the reprogramming of maize root tips to cope with cadmium and copper toxicity are common, but some are not.

Cadmium negatively affects the growth and physiological status and the alleviation effects by exogenous selenium in silage maize (Zea mays L.)

Increasing soil cadmium (Cd) contamination is a serious threat to human food health and safety. In order to reduce Cd uptake and Cd toxicity in silage maize, hydroponic tests were conducted to investigate the effect of exogenous Cd on the toxicity of silage maize in this study. In the study, a combination of Cd (5, 20, 50, 80, and 10 μM) treatments was applied in a hydroponic system. With increasing Cd concentration, Cd significantly inhibited the total root length (RL), root surface area (SA), root volume (RV), root tip number (RT), and branching number (RF) of maize seedlings, which were reduced by 28.1 to 71.3%, 20.2 to 64.9%, 11.2 to 56.5%, 43.7 to 63.4%, and 38.2 to 72.6%, respectively. The excessive Cd accumulation inhibited biomass accumulation and reduced silage maize growth, photosynthesis, and chlorophyll content and activated the antioxidant systems, including increasing lipid peroxidation and stimulating catalase (CAT) and peroxidase (POD), but reduced the activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in the root. Besides, selenium (Se) significantly decreased the Cd concentration of the shoot and root by 27.1% and 35.1% under Cd50, respectively. Our results reveal that exogenously applied Cd reduced silage maize growth and impaired photosynthesis. Whereas silage maize can tolerate Cd by increasing the concentration of ascorbate and glutathione and activating the antioxidant defense system, the application of exogenous selenium significantly reduced the content of Cd in silage maize.

Binding interaction of environmental DNA with typical emerging perfluoroalkyl acids and its impact on bioavailability

As the replacement compounds of perfluoroalkyl acids (PFAAs), emerging PFAAs generally exhibit equal or more hazardous toxicity than legacy PFAAs. Numerous DNA as environmental organic matters coexists with emerging PFAAs, but their interactions and the resulting interaction impacts on the bioavailability of emerging PFAAs remain insufficiently understood. Here, we studied the binding strength and mechanism between DNA and emerging PFAAs (perfluorobutyric acid, perfluorobutylsulfonic acid, and hexafluoropropylene oxide dimer acid) using perfluorooctanoic acid as the control, and further investigated the impacts of DNA binding on the bioavailability of the emerging PFAAs. Isothermal titration calorimetry and quantum chemical calculation found that the emerging PFAAs could bind with DNA bases (main thymine) by van der Waals force and halogen-bond, showing the binding affinities in the range of 7.87 × 104 to L/mol to 6.54 × 106 L/mol. The PFAAs-DNA binding significantly decreased the bioavailability of the PFAAs in both seedlings and plants of pakchoi (Brassica chinensis L.), with little differences in bioavailability change extent among PFAAs. The findings highlight the universality and similarity of the DNA binding effects on PFAAs bioavailability, which can be the natural detoxification mechanism for response to the PFAAs pollution.

Variability in cadmium stress tolerance among four maize genotypes: Impacts on plant physiology, root morphology, and chloroplast microstructure

Cadmium (Cd) is detrimental to both plants and humans. Maize (Zea mays L.) genotypes exhibit variations in Cd accumulations. This study examined variations in Cd accumulation and tolerance among four maize genotypes with contrasting root morphology. The four maize genotypes were cultivated in a semi-hydroponic system with three Cd concentrations (0, 10, 20 μmol L-1). The effects of Cd on plant growth and physiology were assessed 39 days after transplanting. Results showed that root characteristics were positively correlated with root Cd accumulation and the bioconcentration factor under Cd20 treatment. Genotypes Shengrui999 and Zhengdan958 exhibited higher total Cd content than Xundan29 and Zhongke11 under Cd20 conditions. Cd toxicity led to membrane degradation of chloroplast mesophyll cells, loosening and swelling of grana lamella, and reduced starch reserves. The greater tolerance of Shengrui999 and Zhengdan958 was contributed to factors such as root biomass, shallower root depth, higher Cd content, accumulation of osmolyte such as soluble protein, antioxidant activities such as catalase (CAT), and the presence of phytohormone gibberellic acid. The study establishes a link between root morphology, Cd accumulation, and tolerance in maize plants, as demonstrated by the higher Cd accumulation and shallower root system in Cd-tolerant genotypes. This research provides a foundation for breeding maize cultivars better suited for adaptation to moderate Cd-contaminated environments.

Antioxidant defense in cotton under environmental stresses: Unraveling the crucial role of a universal defense regulator for enhanced cotton sustainability

Cotton (Gossypium spp.) is a globally significant crop that provides natural fibers for the textile industry and also an important oil and biopharmaceutical resources. However, the production of cotton faces substantial challenges due to various biotic and abiotic stress factors that can negatively impact cotton growth, yield, and fiber quality. This review offers a comprehensive overview of the effects of biotic stress factors, such as insect pests, bacterial, fungal, and viral pathogens, and nematodes, as well as abiotic stress factors, including extreme hot and cold temperature, drought, toxicity induced by heavy metal and salinity, on the antioxidant systems in cotton. We discuss the crucial antioxidants, such as glutathione, proline, and phenolics, and highlight major antioxidant enzymes, including ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR), and their roles in cotton's response to these stress factors. Furthermore, we explore the potential mechanisms and the crosstalk between different stress factors signaling pathways. We also examine the implications of stress-induced changes in antioxidant levels and enzyme activities for cotton productivity and breeding strategies. Additionally, we shed light on the unanswered questions, research gaps, and future perspectives in this field, paving the way for further investigations to enhance our understanding of cotton's antioxidant defenses and develop novel strategies for improving cotton stress tolerance and yield stability.

Saltbuch extract: a bio-solutionfor cadmium stress sorghum plants in germination and maturation

Cadmium (Cd) is one of the dangerous factors that have negative impacts on plants and human health. Recently, many researchers have been looking for biostimulants to use as bioprotectants that can help or ameliorate plants' tolerance against abiotic stress, including Cd. To test the dangerousness of Cd accumulated in the soil, 200 µM of the latter was applied to sorghum seeds at germination and maturation stages. At the same time, Atriplex halimus water extract (0.1%, 0.25%, 0.5%) was applied to test its efficacy on Cd alleviation in sorghum plants. The obtained results showed that the tested concentrations enhanced the tolerance of sorghum to Cd by enhancing the germination indexes parameters such as germination percentage (GP), seedling vigor index (SVI), and reducing the mean germination time (MGT) of sorghum seeds grown under cadmium stress. On the other hand, the morphological parameters (height and weight) as well as the physiological parameters (chlorophyll and carotenoid) were stimulated in treated maturated sorghum plants under Cd stress. In addition, 0.5% and 0.25% of Atriplex halimus extract (AHE) stimulated the antioxidant enzymes, including superoxide dismutase, catalase, glutathione peroxidase, glutathione-s-transferase, and glutathione reductase. In the same time, an increase in carbon-nitrogen enzymes was recorded in the case of AHE treatment; phosphoenol pyruvate carboxylase, glutamine synthase, glutamate dehydrogenase, and amino acid transferase were all upregulated. These results suggest that using AHE as a biostimulant could be a better strategy to enhance the tolerance of sorghum plants to Cd stress.

Overexpression of IlHMA2, from Iris lactea, Improves the Accumulation of and Tolerance to Cadmium in Tobacco

Long-distance transport cadmium (Cd) from roots to shoots is a key factor for Cd phytoremediation. Our previous study indicated that heavy metal P1B2-ATPases, IlHMA2, was involved in improving the accumulation of Cd via mediated long-distance transport Cd, contributing to the phytoremediation in Cd accumulator Iris lactea. However, whether the overexpression of IlHMA2 could enhance the accumulation and tolerance to Cd remains unclear in plants. Here, we generated transgenic tobacco overexpressing IlHMA2 and tested its effect on the translocation and accumulation of Cd and zinc (Zn), as well as the physio-biochemical characteristics under 50 mg/L Cd exposure. The overexpression of IlHMA2 significantly increased Cd concentrations in xylem saps, resulting in enhanced root-to-shoot Cd translocation compared with wild-type. Meanwhile, overexpressing IlHMA2 promoted Zn accumulations, accompanied by elevating proline contents and antioxidant enzyme activity (SOD, POD, and CAT) to diminish the overproduction of ROS in transgenic tobacco. These pieces of evidence suggested that higher Zn concentrations and lower ROS levels could tremendously alleviate Cd toxicity for transgenic tobacco, thereby improving the growth and tolerance. Overall, the overexpression of IlHMA2 could facilitate Cd accumulation and enhance its tolerance in tobacco exposed to Cd contaminations. This would provide a valuable reference for improving Cd phytoremediation efficiency.

Inhibition Roles of Calcium in Cadmium Uptake and Translocation in Rice: A Review

Cadmium (Cd) contamination in rice grains is posing a significant threat to global food security. To restrict the transport of Cd in the soil-rice system, an efficient way is to use the ionomics strategy. Since calcium (Ca) and Cd have similar ionic radii, their uptake and translocation may be linked in multiple aspects in rice. However, the underlying antagonistic mechanisms are still not fully understood. Therefore, we first summarized the current knowledge on the physiological and molecular footprints of Cd translocation in plants and then explored the potential antagonistic points between Ca and Cd in rice, including exchange adsorption on roots, plant cell-wall composition, co-transporter gene expression, and transpiration inhibition. This review provides suggestions for Ca/Cd interaction studies on rice and introduces ionomics research as a means of better controlling the accumulation of Cd in plants.

Nutrient Metabolism Pathways Analysis and Key Candidate Genes Identification Corresponding to Cadmium Stress in Buckwheat through Multiomics Analysis

Fagopylum tatarium (L.) Gaertn (buckwheat) can be used both as medicine and food and is also an important food crop in barren areas and has great economic value. Exploring the molecular mechanisms of the response to cadmium (Cd) stress can provide the theoretical reference for improving the buckwheat yield and quality. In this study, perennial tartary buckwheat DK19 was used as the experimental material, its key metabolic pathways in the response to Cd stress were identified and verified through transcriptomic and metabolomic data analysis. In this investigation, 1798 metabolites were identified through non-targeted metabolomic analysis containing 1091 up-regulated and 984down-regulated metabolites after treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differential metabolites was significantly enriched in galactose metabolism, glycerol metabolism, phenylpropane biosynthesis, glutathione metabolism, starch and sucrose metabolism. Linkage analysis detected 11 differentially expressed genes (DEGs) in the galactose metabolism pathway, 8 candidate DEGs in the lipid metabolism pathway, and 20 candidate DEGs in the glutathione metabolism pathway. The results of our study provided useful clues for genetically improving the resistance to cadmium by analyzing the molecular mechanism of cadmium tolerance in buckwheat.

Antioxidant system of garden cress sprouts for using in bio-monitor of cadmium and lead contamination

Based on garden cress significantly used for phytoremediation, the antioxidant system included antioxidant-phenolic compounds and antioxidant-enzymes of 6-day-garden cress sprouts (GCS) were assessed as potential bio-indicators for cadmium (Cd) and lead (Pb) contamination. Total phenolic and flavonoid contents of GCS germinated under Cd and Pb treatments (25-150 mg kg^-1) gradually increased with increasing concentration of metals and peaked by 2.0, 2.6, and 2.5, 2.3 folds at 150 mg kg^-1, respectively. By using DPPH, ABTS, and PMC antioxidant assays, the total antioxidant activity of phenolic compounds of GCS increased 6.1, 13.0, and 5.8-fold for Cd and 5.9, 14.6, and 8.2-fold for Pb at 150 mg kg^-1, respectively. The antioxidant enzymes of GCS (POD, CAT, GR, and GST) were significantly activated in response to Cd and Pb stress, and two new electrophoretic POD bands were detected. GCS was absorbed 19.0% and 21.3% of Cd and Pb at 150 mg metal kg^-1, respectively. In conclusion, the approaches of the antioxidant defense system of GSC could potentially be used as bio-indicator for monitoring Cd and Pb contamination in a short time of germination process.

Methyl jasmonate and selenium synergistically mitigative cadmium toxicity in hot pepper (Capsicum annuum L.) plants by improving antioxidase activities and reducing Cd accumulation

Methyl jasmonate (MeJA) or selenium (Se)-mediated response to cadmium (Cd) stress in plant has been widely reported, but the combined effects both on plant growth in response to Cd stress and the underlying mechanisms remain obscure. Here, we showed the combined effects of MeJA (2.5 μM) and Se (7 μM) on hot pepper growth under Cd stress (CdCl₂, 5 μM). The results showed Cd suppressed the accumulation of total chlorophyll and carotenoid and reduced the photosynthesis, while it increased the content of endogenous signaling molecules, e.g. nitric oxide (NO) and hydrogen peroxide (H₂O₂), as well as Cd content in leaves. The combined application of MeJA and Se significantly decreased the malondialdehyde (MDA) accumulation and improved the activities of antioxidant enzymes (AOEs, e.g. SOD and CAT) and defense-related enzymes (DREs, POD and PAL). Additionally, the synergistic application of MeJA and Se also obviously improved photosynthesis in hot pepper plants under Cd stress compared with those treated with MeJA or Se respectively or not. Moreover, the treatment of MeJA associated with Se also effectively reduced the Cd accumulation in hot pepper leaves under Cd stress compared with the plants treated with MeJA or Se separately, which implied a potentially synergistic role of MeJA and Se in alleviating Cd toxicity in hot pepper plants. This study provides a theoretical reference for the further analysis of the molecular mechanism of MeJA and Se in jointly mediating the response to heavy metals in plants.

Characteristics of cadmium accumulation and tolerance in apple plants grown in different soils

Cadmium (Cd) is a nonessential element and highly toxic to apple tree. However, Cd accumulation, translocation and tolerance in apple trees planted in different soils remain unknown. To investigate soil Cd bioavailability, plant Cd accumulation, physiological changes as well as gene expression patterns in apple trees grown in five different soils, 'Hanfu' apple seedlings were planted in orchard soils collected from Maliangou village (ML), Desheng village (DS), Xishan village (XS), Kaoshantun village (KS) and Qianertaizi village (QT), and subjected to 500 μM CdCl₂ for 70 d. Results showed that soils of ML and XS had higher content of organic matter (OM), clay and silt, and cation exchange capacity (CEC) but lower sand content than the other soils, thereby reduced Cd bioavailability, which could be reflected by lower concentrations and proportions of acid-soluble Cd but higher concentrations and proportions of reducible and oxidizable Cd. The plants grown in soils of ML and XS had relatively lower Cd accumulation levels and bio-concentration factors than those grown in the other soils. Excess Cd reduced plant biomass, root architecture, and chlorophyll content in all plants but to relatively lesser degree in those grown in soils of ML and XS. The plants grown in soils of ML, XS and QT had comparatively lower reactive oxygen species (ROS) content, less membrane lipid peroxidation, and higher antioxidant content and enzyme activity than those grown in soils of DS and KS. Transcript levels of genes regulating Cd uptake, transport and detoxification such as HA11, VHA4, ZIP6, IRT1, NAS1, MT2, MHX, MTP1, ABCC1, HMA4 and PCR2 displayed significant differences in roots of plants grown in different soils. These results indicate that soil types affect Cd accumulation and tolerance in apple plants, and plants grown in soils with higher OM content, CEC, clay and silt content and lower sand content suffer less Cd toxicity.

Assessment of the capability of cadmium accumulation and translocation among 31 willows: four patterns of willow biomass variation response to cadmium

Cadmium (Cd) pollution threatens food security and the environment. Willow species (Salix, Salicaceae) exhibit a remarkable potential to restore Cd-polluted sites due to their high biomass production and high Cd accumulation capacities. This study examined the Cd accumulation and tolerance in 31 genotypes of shrub willow in hydroponic conditions at varying Cd levels (0 μM Cd, 5 μM Cd, and 20 μM Cd). The root, stem, and leaf biomass of 31 shrub willow genotypes showed significant differences to Cd exposure. Among 31 willow genotypes, four patterns of biomass variation response to Cd were identified: insensitive to Cd; growth inhibition due to excessive Cd supply (high Cd inhibition); low Cd causing inhibited growth, whereas high Cd leading to increased biomass (U-shape); and growth increment with excessive Cd exposure (high Cd induction). The genotypes belonging to the "insensitive to Cd" and/or "high Cd induction" were candidates for the utilization of phytoremediation. Based on the analysis of Cd accumulation of 31 shrub willow genotypes at high and low Cd levels, genotypes 2372, 51-3, and 1052 obtained from a cross between S. albertii and S. argyracea grew well and accumulated relatively more Cd levels than other genotypes. In addition, for Cd-treated seedlings, root Cd accumulation was positively correlated with shoot Cd accumulation and total Cd uptake, demonstrating that Cd accumulation in roots could serve as a biomarker for evaluating the Cd extraction capacity of willows, especially in hydroponics screening. The results of this study screened out willow genotypes with high Cd uptake and translocation capacities, which will provide valuable approaches for restoring Cd-contaminated soils with willows.

Alleviating the toxic effects of Cd and Co on the seed germination and seedling biochemistry of wheat (Triticum aestivum L.) using Azolla pinnata

One of the most significant environmental challenges in the twenty-first century is heavy metal pollution. The potential use of fresh Azolla pinnata to alleviate the toxic effects of Cd and Co on the germination measurements of wheat seeds (Triticum aestivum L.) and the biochemistry of seedlings was studied. Two concentrations (80 and 100 mg L^-1 solutions) of CdNO₃ and CoCl₂ were used before and after treatment with A. pinnata. The highest removal efficiency (RE) by A. pinnata was obtained on the fifth day, with a Cd RE = 55.9 and 49.9% at 80 and 100 mg L^-1, respectively. Cadmium and cobalt solutions reduced the germination percentage, and the measured variables of wheat seeds meanwhile increased the radicle phytotoxicity. In contrast, the presence of A. pinnata in the germination medium increased all the measured variables and decreased radicle phytotoxicity. At 80 and 100 mg L^-1, Cd significantly reduced the fresh and dry biomass, and height of wheat seedlings after 21 days of cultivation compared to Co. Cadmium and high concentrations of cobalt increased the contents of H₂O₂, proline, MDA, phenolic, and flavonoid compounds. The application of treated Cd and Co solutions by A. pinnata showed a decrease in H₂O₂, proline, phenolic, and flavonoid compounds levels accompanied by a reduction in catalase and peroxidase activities compared to the control. This study showed the positive role of A. pinnata in alleviating the metal impacts, particularly Cd, on the seedling growth of wheat and its germination.

Effects of α-Fe2O3 nanoparticles and biochar on plant growth and fruit quality of muskmelon under cadmium stress

Cadmium pollution in farmland has become a global environmental problem, threatening ecological security and human health. Biochar is effective in remediation of soil pollution. However, high concentrations of biochar can inhibit plant growth, and low concentrations of biochar have limited mitigation effect on cadmium toxicity. Therefore, the combination of low-concentration biochar and other amendments is a promising approach to alleviate cadmium toxicity in plants and improve the safety of edible parts. In this study, muskmelon was selected as the research object, and different concentrations of α-Fe₂O₃ nanoparticles were used alone or combined with biochar to explore the effects of different treatments on muskmelon plants in cadmium-contaminated soil. The results showed that the combined application of 250 mg/kg α-Fe₂O₃ nanoparticles and biochar had a good effect on the repair of cadmium toxicity in muskmelon plants. Compared with cadmium treatment, its application increased plant height by 32.53%, cadmium transport factor from root to stem decreased by 32.95%, chlorophyll content of muskmelon plants increased by 14.27%, and cadmium content in muskmelon flesh decreased by 18.83%. Moreover, after plant harvest, soil available cadmium content in 250 mg/kg α-Fe₂O₃ nanoparticles and biochar combined treatment decreased by 31.18% compared with cadmium treatment. The results of this study provide an effective reference for the composite application of different exogenous amendments and a feasible idea for soil heavy metal remediation and mitigation of cadmium pollution in farmland.

Proteomic analysis reveals differential responsive mechanisms in Solanum nigrum exposed to low and high dose of cadmium

Cadmium (Cd) contamination is becoming a widespread environmental problem. However, the differential responsive mechanisms of Cd hyperaccumulator Solanum nigrum to low or high dose of Cd are not well documented. In this study, phenotypic and physiological analysis firstly suggested that the seedlings of S. nigrum showed slight leaf chlorosis symptoms under 25 μM Cd and severe inhibition on growth and photosynthesis under 100 μM Cd. Further proteomic analysis identified 105 differentially expressed proteins (DEPs) in the Cd-treated leaves. Under low dose of Cd stress, 47 DEPs are mainly involved in primary metabolic processes, while under high dose of Cd stress, 92 DEPs are mainly involved in photosynthesis, energy metabolism, production of phytochelatin and reactive oxygen species (ROS). Protein-protein interaction (PPI) network analysis of DEPs support above differential responses in the leaves of S. nigrum to low and high dose of Cd treatments. This work provides the differential responsive mechanisms in S. nigrum to low and high dose of Cd, and the theoretical foundation for the application of hyperaccumulating plants in the phytoremediation of Cd-contaminated soils.

Influence of ionic cerium and cerium oxide nanoparticles on Zea mays seedlings grown with and without cadmium

Cerium (Ce⁴⁺) and cerium oxide nanoparticles (CeO₂-NPs) have diversified reported effects on plants. Once dispersed in the environment their fate is not well understood, especially in co-existence with other pollutants like cadmium (Cd). The effect of co-application of Ce and Cd are reported in various studies, but the role of Ce source (ionic or bulk) and nanoparticle size is still unknown in cereal plants like maize (Zea mays). To better understand the synergistic effects of Ce and Cd, 500 mg kg^-1 Ce coming from ionic (Ce⁴⁺ as CeSO₄) and CeO₂ nano sources (10 nm, 50 nm, and 100 nm) alone and in combination with 0.5 mg Cd kg^-1 sand were applied to maize seedlings. Growth, physiology, root structure, anatomy, and ionic homeostasis in maize were measured. The results revealed that Ce⁴⁺ resulted in overall decrease in seedling growth, biomass and resulted in higher heavy metal (in control sets) and Cd (in Cd spiked sets) uptake in maize seedlings' root and shoot. The effects of CeO₂-NPs were found to be dependent on particle size; in fact, under Cd-0 (non-Cd spiked sets) CeO₂-100 nm showed beneficial effects compared to the control. While under co-application with Cd, CeO₂-50 nm showed net beneficial effects on maize seedling growth parameters. The Ce alone, and in combination with Cd, altered the root suberin barrier formation. Both ionic and nano Ce sources alone and in co-existence with Cd behaved differently for tissue elemental concentrations (Ce, Cd, micronutrients like B, Mn, Ni, Cu, Zn, Mo, Fe and elements Co, Si) suggesting a strong influence of Cd-Ce coexistence on the element's uptake and translocation in maize.

Primary plant nutrients modulate the reactive oxygen species metabolism and mitigate the impact of cold stress in overseeded perennial ryegrass

Overseeded perennial ryegrass (Lolium perenne L.) turf on dormant bermudagrass (Cynodon dactylon Pers. L) in transitional climatic zones (TCZ) experience a severe reduction in its growth due to cold stress. Primary plant nutrients play an important role in the cold stress tolerance of plants. To better understand the cold stress tolerance of overseeded perennial ryegrass under TCZ, a three-factor and five-level central composite rotatable design (CCRD) with a regression model was used to study the interactive effects of nitrogen (N), phosphorus (P), and potassium (K) fertilization on lipid peroxidation, electrolyte leakage, reactive oxygen species (ROS) production, and their detoxification by the photosynthetic pigments, enzymatic and non-enzymatic antioxidants. The study demonstrated substantial effects of N, P, and K fertilization on ROS production and their detoxification through enzymatic and non-enzymatic pathways in overseeded perennial ryegrass under cold stress. Our results demonstrated that the cold stress significantly enhanced malondialdehyde, electrolyte leakage, and hydrogen peroxide contents, while simultaneously decreasing ROS-scavenging enzymes, antioxidants, and photosynthetic pigments in overseeded perennial ryegrass. However, N, P, and K application mitigated cold stress-provoked adversities by enhancing soluble protein, superoxide dismutase, peroxide dismutase, catalase, and proline contents as compared to the control conditions. Moreover, N, P, and, K application enhanced chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids in overseeded perennial ryegrass under cold stress as compared to the control treatments. Collectively, this 2-years study indicated that N, P, and K fertilization mitigated cold stress by activating enzymatic and non-enzymatic antioxidants defense systems, thereby concluding that efficient nutrient management is the key to enhanced cold stress tolerance of overseeded perennial ryegrass in a transitional climate. These findings revealed that turfgrass management will not only rely on breeding new varieties but also on the development of nutrient management strategies for coping cold stress.

Effects of various seed priming on morphological, physiological, and biochemical traits of rice under chilling stress

INTRODUCTION/BACKGROUND

Direct-seeded rice is exceptionally vulnerable to chilling stress, especially at the seed germination and seedling growth stages in the early season of the double cropping system.

METHODS

Therefore, we conducted two experiments to evaluate the role of various seed primings and their different concentrations of plant growth regulators [experiment 1-abscisic acid (ABA), gibberellin (GA₃), salicylic acid (SA), brassinolide (BR), paclobutrazol, uniconazole (UN), melatonin (MT), and jasmonic acid (JA)] and osmopriming substances (chitosan, polyethylene glycol 6000 (PEG6000), and CaCl₂) and experiment 2-GA, BR (two best), CaCl₂ (worst), and control (CK)] on rice seedlings under low temperature condition.

RESULTS

Results showed that the maximum germination rate of 98% was recorded in GA₃ (10 mgL^-1) and BR (0.3 mgL^-1) among treatments. Compared to CK, root and shoot length were improved in ABA (0.5 mgL^-1) and GA₃ (100 mgL^-1) by 64% and 68%, respectively. At the same time, root and shoot weights (fresh and dry) were enhanced in Paclobutrazol (300 mgL^-1) and GA3 among treatments. Furthermore, the average root volume, average root diameter, and total root surface area were increased by 27%, 38%, and 33% in Paclobutrazol (300 mgL^-1), Paclobutrazol (200 mgL^-1) and JA (1 mgL^-1) treatments, respectively compared to CK. In the second experiment, a respective increase of 26%, 19%, 38%, and 59% was noted in SOD, POD, CAT, and APX enzyme activities in GA treatment compared to CK. Similarly, proline, soluble sugar, soluble protein, and GA content were also improved by 42%, 25.74%, 27%, and 19%, respectively, in GA treatment compared to CK. However, a respective reduction of 21% and 18% was noted in MDA and ABA content in GA treatment compared to CK. Our finding highlighted that better germination of primed-rice seedlings was associated with fresh and dry weights of the roots and shoots and the average root volume of the seedlings.

DISCUSSION

Our results suggested that GA₃ (10 mg L^-1) and BR (0.3 mg L^-1) seed priming prevent rice seedlings from chilling-induced oxidative stress by regulating antioxidant enzyme activities and maintaining ABA, GA, MDA, soluble sugar, and protein content. However, further studies (transcriptome and proteome) are needed to explore the molecular mechanisms involved in seed priming-induced chilling tolerance under field conditions.

Foliar application of nanoceria attenuated cadmium stress in okra (Abelmoschus esculentus L.)

Foliar application of nanoparticles (NPs) as a means for ameliorating abiotic stress is increasingly employed in crop production. In this study, the potential of CeO₂-NPs as stress suppressants for cadmium (Cd)-stressed okra (Abelmoschus esculentus) plants was investigated, using two cycles of foliar application of CeO₂-NPs at 200, 400, and 600 mg/l. Compared to untreated stressed plants, Cd-stressed plants treated with CeO₂-NPs presented higher pigments (chlorophyll a and carotenoids). In contrast, foliar applications did not alter Cd root uptake and leaf bioaccumulation. Foliar CeO₂-NPs application modulated stress enzymes (APX, SOD, and GPx) in both roots and leaves of Cd-stressed plants, and led to decreases in Cd toxicity in plant's tissues. In addition, foliar application of CeO₂-NPs in Cd-stressed okra plants decreased fruit Cd contents, and improved fruit mineral elements and bioactive compounds. The infrared spectroscopic analysis of fruit tissues showed that foliar-applied CeO₂-NPs treatments did not induce chemical changes but induced conformational changes in fruit macromolecules. Additionally, CeO₂-NPs applications did not alter the eating quality indicator (Mg/K ratio) of okra fruits. Conclusively, the present study demonstrated that foliar application of CeO₂-NPs has the potential to ameliorate Cd toxicity in tissues and improve fruits of okra plants.

Efficacy of marigold (Tagetes erecta L.) for the treatment of tannery and surgical industry wastewater under citric acid amendment: a lab scale study

Contamination of land and aquatic ecosystems with heavy metals (HMs) is a global issue having the persistent potential to damage the quality of food and water. In the present study, Tagetes erecta L. plants were used to assess their potential to uptake HMs from wastewater. Plants were grown in soil for 20 days and then transplanted in hydroponic system containing Hoagland nutrient solution. After more than 15 days of growth, plants were then subjected to wastewater from tannery and surgical industries in different concentrations ranging from 25 to 100% in combination of citric acid (5 and 10 mM). After 6 weeks of treatment, plants were collected and segmented into roots, stem, and leaves for characterizing the morphological properties including plant height, roots length, fresh and dry mass of roots, stem, and leaves. For evaluation of the effect of wastewater on the plants, photosynthetic pigments; soluble proteins; reactive oxygen species (ROS); antioxidant enzymes SOD, POD, CAT, and APX; and metal accumulation were analyzed. Application of industrial wastewater revealed a significant effect on plant morphology under wastewater treatments. Overall growth and physiological attributes of plant decreased, and metal accumulation enhanced with increasing concentration of wastewater. Similarly, the production of ROS and antioxidant enzymes were also increased. Chlorophyll, protein content, and enzyme production enhanced with CA (5 and 10 mM) mediation; however, ROS production and EL were reduced. Metals analysis showed that the maximum accumulation of Pb was in roots, while Cr and Ni in the stem which further increased under CA mediation. Overall, the metal accumulation ability was in the order of Pb > Ni > Cr under CA.

Crop Wild Relatives: A Valuable Source of Tolerance to Various Abiotic Stresses

Global climate change is one of the major constraints limiting plant growth, production, and sustainability worldwide. Moreover, breeding efforts in the past years have focused on improving certain favorable crop traits, leading to genetic bottlenecks. The use of crop wild relatives (CWRs) to expand genetic diversity and improve crop adaptability seems to be a promising and sustainable approach for crop improvement in the context of the ongoing climate challenges. In this review, we present the progress that has been achieved towards CWRs exploitation for enhanced resilience against major abiotic stressors (e.g., water deficiency, increased salinity, and extreme temperatures) in crops of high nutritional and economic value, such as tomato, legumes, and several woody perennial crops. The advances in -omics technologies have facilitated the elucidation of the molecular mechanisms that may underlie abiotic stress tolerance. Comparative analyses of whole genome sequencing (WGS) and transcriptomic profiling (RNA-seq) data between crops and their wild relative counterparts have unraveled important information with respect to the molecular basis of tolerance to abiotic stressors. These studies have uncovered genomic regions, specific stress-responsive genes, gene networks, and biochemical pathways associated with resilience to adverse conditions, such as heat, cold, drought, and salinity, and provide useful tools for the development of molecular markers to be used in breeding programs. CWRs constitute a highly valuable resource of genetic diversity, and by exploiting the full potential of this extended allele pool, new traits conferring abiotic-stress tolerance may be introgressed into cultivated varieties leading to superior and resilient genotypes. Future breeding programs may greatly benefit from CWRs utilization for overcoming crop production challenges arising from extreme environmental conditions.

Moringa oleifera smoke induced positive changes in biochemical, metabolic, and antioxidant profile of rice seedling under cadmium stress

Cadmium as a heavy metal contaminates the agricultural soil and effect plant growth due to rapid increases in industrialization and anthropogenic activities. Smoke water of Moringa oleifera was used in the current study to alleviate the effect of cadmium on the physiological, biochemical, metabolic, and antioxidant profile of Basmati 385 and Shaheen Basmati seedling. Cadmium stress of 100, 200, and 400 µM were given to 28 days-old seedlings along with smoke water (1:1,000) for one week in hydroponic culture. As a result, Cd⁺² toxicity negatively affects the seedling length, fresh and dry weight, photosynthetic pigment, and electrolytes leakage, while the application of smoke water alleviated those effects. Furthermore, Cd⁺² content, cell injury, metabolic parameters (proline, total soluble sugar), and antioxidants (peroxidase, catalase) were increased with increasing Cd⁺² concentration while smoke water-treated seedlings showed reduction at high concentration. From present study, it can be concluded that smoke water had some regulatory compound which could reduce the Cd⁺² stress level in rice seedlings and improve plant growth.

Exogenous acetone O-(4-chlorophenylsulfonyl) oxime alleviates Cd stress-induced photosynthetic damage and oxidative stress by regulating the antioxidant defense mechanism in Zea mays

Cadmium (Cd) toxicity in leaves decreases their photosynthetic efficiency by degrading photosynthetic pigments, reducing the activity of gas exchange parameters and photosystem II (PSII), and producing reactive oxygen species. Although acetone O-(4-chlorophenylsulfonyl) oxime (AO) alleviates stress due to heavy metals in plants, its effects on the photosynthetic apparatus and redox balance under Cd stress are not clear. Herein, the role of AO in modulating the relationship between the antioxidant defense system and photosynthetic performance including chlorophyll fluorescence and gas exchange in mitigating the stress damage caused by Cd in maize seedlings was investigated. Three-week-old maize seedlings were pre-treated with AO (0.66 mM) and exposed to 100 µM Cd stress. Our findings indicated that AO application increased Cd accumulation, thiobarbituric acid-reactive substances (TBARS), photosynthetic rate, hydrogen peroxide (H2O2), total chlorophyll and carotenoid, transpiration, stomatal conductance, maximum photochemical efficiency of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), intercellular CO2 concentration, photochemical quenching (qP), superoxide dismutase, electron transport rate, proline, ascorbate peroxidase, catalase, guaiacol peroxidase, 4-hydroxybenzoic acid, catechol, and cinnamic acid in maize seedling under Cd stress. Conversely, AO significantly reduced oxidative damage levels (H2O2, TBARS). It was concluded that exogenous AO can overcome Cd-mediated oxidative damage and hence protect the photosynthetic machinery by providing stress tolerance and regulating the antioxidant defense mechanism, which includes proline, phenolic compounds, and antioxidant enzyme activities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01258-5.

The role of auxins and auxin-producing bacteria in the tolerance and accumulation of cadmium by plants

Cadmium (Cd) is one of the most toxic heavy metals for plant physiology and development. This review discusses Cd effects on auxin biosynthesis and homeostasis, and the strategies for restoring plant growth based on exogenous auxin application. First, the two well-characterized auxin biosynthesis pathways in plants are described, as well as the effect of exogenous auxin application on plant growth. Then, review describes the impacts of Cd on the content, biosynthesis, conjugation, and oxidation of endogenous auxins, which are related to a decrease in root development, photosynthesis, and biomass production. Finally, compelling evidence of the beneficial effects of auxin-producing rhizobacteria in plants exposed to Cd is showed, focusing on photosynthesis, oxidative stress, and production of antioxidant compounds and osmolytes that counteract Cd toxicity, favoring plant growth and improve phytoremediation efficiency. Expanding our understanding of the positive effects of exogenous auxins application and the interactions between bacteria and plants growing in Cd-polluted environments will allow us to propose phytoremediation strategies for restoring environments contaminated with this metal.

Impacts of Cd Pollution on the Vitality, Anatomy and Physiology of Two Morphologically Different Lichen Species of the Genera Parmotrema and Usnea, Evaluated under Experimental Conditions

The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers.

Application of phytoremediation on soil polluted by heavy metals from sewage sludge

Soil pollution by heavy metals (HM) has become a problem in Algeria, in particular that caused by the discharge of untreated sewage sludge due to the lack of means at the level of sewage treatment plants (WWTP). The objective of our work was to study the possibility of reducing HM pollution of the soil of the WWTP site of Reghaia (Algeria) by phytoremediation. The results obtained showed the decrease in plant growth parameters (maize, rapeseed and alfalfa) grown on the polluted soil. However, on polluted soil amended with fertilizer, improved growth of these plants was noted. It has also been observed that the cultivation of plants in polluted soils (amended and unamended) made it possible to have attenuation rates for HMs (Cd, Zn and Cr) higher than those obtained in the absence of plant cultivation. However, these rates were not very high (less than 40%), and the fertilizer amendment did not increase these rates, despite the improvement in the production of plant biomass. This would be mainly due to the decrease in the bioavailability of HMs for plants. It was concluded that the tested plants do not allow the phytoextraction of HM but their phytostabilization in the polluted soil of the Reghaia WWTP site.

Exogenous Hemin alleviated cadmium stress in maize (Zea mays L.) by enhancing leaf photosynthesis, AsA-GSH cycle and polyamine metabolism

Cadmium (Cd) stress is one of the principal abiotic stresses that inhibit maize growth. The research was to explore (hemin chloride) Hemin (100 μmol L^-1) on photosynthesis, ascorbic acid (AsA)-glutathione (GSH) cycle system, and polyamine metabolism of maize under Cd stress (85 mg L^-1) using nutrient solution hydroponics, with Tiannong 9 (Cd tolerant) and Fenghe 6 (Cd sensitive) as experimental materials. The results showed that Hemin can increase leaf photosynthetic pigment content and ameliorate the ratio of Chlorophyll a/chlorophyll b (Chla/Chlb) under Cd stress. The values of ribose 1, 5-diphosphate carboxylase/oxygenase (RuBPcase) and phosphoenolpyruvate carboxylase (PEPCase), and total xanthophyll cycle pool [(violoxanthin (V), antiflavin (A) and zeaxanthin (Z)] increased, which enhancing xanthophyll cycle (DEPS) de-epoxidation, and alleviating stomatal and non-stomatal limitation of leaf photosynthesis. Hemin significantly increased net photosynthetic rate (P_n ), stomatal conductance (g_s ), transpiration rate (T_r ), photochemical quenching coefficient (qP), PSII maximum photochemical efficiency (F_v/F_m ), and electron transfer rate (ETR), which contributed to the improvement of the PSII photosynthetic system. Compared with Cd stress, Hemin can reduce thiobartolic acid reactant (TBARS) content, superoxide anion radical (O₂ ^-) production rate, hydrogen peroxide (H₂O₂) accumulation, and the extent of electrolyte leakage (EL); decreased the level of malondialdehyde (MDA) content and increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT); slowed the decrease in dehydroascorbic acid reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activity and the increase in glutathione reductase (GR) and ascorbate peroxidase (APX) activity in leaves; promoted the increase in AsA and GSH content, decreased dehydroascorbic acid (DHA) and oxidized glutathione (GSSG), and increased AsA/DHA and GSH/GSSG ratios under Cd stress. Hemin promoted the increase of conjugated and bound polyamine content, and the conversion process speed of free putrescine (Put) to free spermine (Spm) and spermidine (Spd) in maize; decreased polyamine oxidase (PAO) activity and increased diamine oxidase (DAO), arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) enzyme activities in leaves under Cd stress.

Evaluating the Accumulation of Antioxidant and Macro- and Trace Elements in Vaccinium myrtillus L

This study was conducted in order to characterise the accumulation ability of Vaccinium myrtillus L for trace elements such as Al, Cd, Cu, Fe, Mn, Pb and Zn and selected macroelements Ca, K, Mg, Na and P. The accumulation of nutrient elements and trace elements (ANE and ATE) and changes in the ecophysiological responses in bilberry in differently polluted areas were compared. The accumulation of the elements in the roots, stems and leaves of bilberry from four sites (in the nearest vicinity of a zinc smelter, a Mining and Metallurgical Plant, a main road with a high traffic volume and an unprotected natural forest community) were measured using optical emission spectrometry with excitation using inductively coupled argon plasma after wet acid digestion. The highest Cd, Cu, Pb and Zn concentrations were found in the V. myrtillus samples that were growing under the influence of the emissions from the zinc smelter. Moreover, the level of the total accumulated trace metals (ATE-17.09 mmolc kg-1) was also highest for the bilberry at this site. However, in the same area, the sum of the accumulated macronutrients (ANE-296.92 mmolc kg-1) was lower than at the other sampling sites. An EF > 2 was found for Cd, Pb, Zn and Mn, which suggests that bilberries may be enriched in these metals. According to the translocation factor, V. myrtillus was an accumulator of Cd, Zn and Mn. An analysis of the ecophysiological responses showed that the greatest concentration of ascorbic acid was found in the leaves of V. myrtillus at the most contaminated site (3.32 mg g-1 fresh weight). There were no significant differences in the total phenols between the contaminated and non-contaminated sites. However, the lowest value of the total phenolic content (490.77 mg g-1 dry weight) was recorded at the site where the highest Fe concentration was detected in the leaves. A significantly positive correlation between the Cd, Pb and Zn concentrations and a strong negative correlation between the Mn concentration and ascorbic acid content in the leaves of bilberry was also observed. The results provide evidence that the ANE method, which is used to interpret the chemical composition of bilberry has made determining the impact of toxic trace metals on the mineral composition of V. myrtillus significantly easier and also that a non-enzymatic antioxidant such as ascorbic acid can be a good biomarker for determining the oxidative stress that is caused by toxic trace metals.

Heavy metal and metalloid toxicity in horticultural plants: Tolerance mechanism and remediation strategies

Heavy metal/metalloids (HMs) are among the primary soil pollutants that limit crop production worldwide. Plants grown in HM contaminated soils exhibit reduced growth and development, resulting in a decrease in crop production. The exposure to HMs induces plant oxidative stress due to the formation of free radicals, which alter plant morphophysiological and biochemical mechanisms at cellular and tissue levels. When exposed to HM toxicity, plants evolve sophisticated physiological and cellular defense strategies, such as sequestration and transportation of metals, to ensure their survival. Plants also have developed efficient strategies by activating signaling pathways, which induce the expression of HM transporters. Plants either avoid the uptake of HMs from the soil or activate the detoxifying mechanism to tolerate HM stress, which involves the production of antioxidants (enzymatic and non-enzymatic) for the scavenging of reactive oxygen species. The metal-binding proteins including phytochelatins and metallothioneins also participate in metal detoxification. Furthermore, phytohormones and their signaling pathways also help to regulate cellular activities to counteract HM stress. The excessive levels of HMs in the soil can contribute to plant morpho-physiological, biochemical, and molecular alterations, which have a detrimental effect on the quality and productivity of crops. To maintain the commercial value of fruits and vegetables, various measures should be considered to remove HMs from the metal-polluted soils. Bioremediation is a promising approach that involves the use of tolerant microorganisms and plants to manage HMs pollution. The understanding of HM toxicity, signaling pathways, and tolerance mechanisms will facilitate the development of new crop varieties that help in improving phytoremediation.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

The involvement of nitric oxide and ethylene on the formation of endodermal barriers in response to Cd in hyperaccumulator Sedum alfredii

Nitric oxide (NO) and ethylene are both important signaling molecules which participate in numerous plant development processes and environmental stress resistance. Here, we investigate whether and how NO interacts with ethylene during the development of endodermal barriers that have major consequences for the apoplastic uptake of cadmium (Cd) in the hyperaccumulator Sedum alfredii. In response to Cd, an increased NO accumulation, while a decrease in ethylene production was observed in the roots of S. alfredii. Exogenous supplementation of NO donor SNP (sodium nitroprusside) decreased the ethylene production in roots, while NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) had the opposite effect. The exogenous addition of NO affected the ethylene production through regulating the expression of genes related to ethylene synthesis. However, upon exogenous ethylene addition, roots retained their NO accumulation. The abovementioned results suggest that ethylene is downstream of the NO signaling pathway in S. alfredii. Regardless of Cd, addition of SNP promoted the deposition of endodermal barriers via regulating the genes related to Casparian strips deposition and suberization. Correlation analyses indicate that NO positively modifies the formation of endodermal barriers via the NO-ethylene signaling pathway, Cd-induced NO accumulation interferes with the synthesis of ethylene, leading to a deposition of endodermal barriers in S. alfredii.

Integral effects of brassinosteroids and timber waste biochar enhances the drought tolerance capacity of wheat plant

Drought stress is among the major threats that affect negatively crop productivity in arid and semi-arid regions. Probably, application of some additives such as biochar and/or brassinosteroids could mitigate this stress; however, the mechanism beyond the interaction of these two applications is not well inspected. Accordingly, a greenhouse experiment was conducted on wheat (a strategic crop) grown under deficit irrigation levels (factor A) i.e., 35% of the water holding capacity (WHC) versus 75% of WHC for 35 days while considering the following additives, i.e., (1) biochar [BC, factor B, 0, 2%] and (2) the foliar application of 24-epibrassinolide [BR, factor C, 0 (control treatment, C), 1 (BR1) or 3 (BR2) μmol)]. All treatments were replicated trice and the obtained results were statistically analyzed via the analyses of variance. Also, heat-map conceits between measured variables were calculated using the Python software. Key results indicate that drought stress led to significant reductions in all studied vegetative growth parameters (root and shoot biomasses) and photosynthetic pigments (chlorophyll a, b and total contents) while raised the levels of oxidative stress indicators. However, with the application of BC and/or BR, significance increases occurred in the growth attributes of wheat plants, its photosynthetic pigments, especially the combined additions. They also upraised the levels of enzymatic and non-enzymatic antioxidants while decreased stress indicators. Furthermore, they increased calcium (Ca), phosphorus (P) and potassium (K) content within plants. It can therefore be deduced that the integral application of BR and BC is essential to mitigate drought stress in plants.

Effect of Qiangdi 863 Nanosynergids Treated Water, Nitrogen, Phosphorous and Potassium Fertilizers on Rice Growth Physiology and Grain Quality

Nanotechnology is an emerging technique that helps in solving the biotic and abiotic agricultural issues leading to enhance crop productivity. Therefore, it was hypothesized to check the effect of Qiangdi 863 nano synergids biological-assisted growth apparatus and nitrogen, phosphorous, and potassium (NPK) fertilizers improving rice germination, early growth, physiology, and yield. An experiment was performed on five rice varieties for three consecutive years (2017-2019). The nanosynergids-treated water (NTW) significantly improved the speed of germination (25.3, 35.6, and 32.3%), final emergence percentage (100%) and seed emergence energy percentage (80, 95, and 90%), radical (1.25, 1.7, and 2.35 cm) and plumule growth (1.29, 1.24, and 1.66 cm), soil plant analysis development (46, 45, and 47), antioxidant enzymatic activities, such as catalase activity (34,376 μg-1FW h-1, 33,264 μg-1FW h-1, and 34,453 μg-1F W h-1), superoxide dismutase (18,456 μg-1F W h-1, 19,445 μg-1F W h-1, and 19,954 μg-1F W h-1), peroxide (745 Ug-1F W, 734 Ug-1F W, and 752 Ug-1F W), production and declined malondialdehyde (4.5 μmolg-1F W, 5.1 μmolg-1F W, and 4.2 μmolg-1F W) for all years respectively in KSK 133. The application of nano-treated irrigated water enriched the biomass of rice seedlings. The overall nano synergid treatments successfully enhanced the endogenous hormones as salicylic acid (6,016.27 p mol/L, 5823.22 p mol/L, and 5922.12 p mol/L), jasmonates (JA) (5,175.6 p mol/L, 4231 p mol/L, and 5014.21 p mol/L) brassinosteroids (BR) (618.2 p mol/L, 546.83 p mol/L, and 582.1 p mol/L) quantification and yield 1000 grain weight (22.3, 22, and 23.2 g) of KSK 133. Hence, the overall results proved that NTW could effectively enhance the early growth and yield of rice varieties.

Hydrogen sulphide alleviates cadmium stress in Trigonella foenum-graecum by modulating antioxidant enzymes and polyamine content

Cadmium (Cd) toxicity reduces growth and yield of crops grown in metal-polluted sites. Research was conducted to estimate the potential of hydrogen sulphide (H₂ S) to mitigate toxicity caused by Cd in fenugreek seedlings (Trigonella foenum-graecum L.). Different concentrations of CdCl₂ (Cd1-1 mM, Cd2-1.5 mM, Cd3-2mM) and H₂ S (HS1-100 µM, HS2-150 µM, HS3-200 µM) were assessed. Seeds of fenugreek were primed with sodium hydrosulphide (NaHS), as H₂ S donor. Seedlings growing in Cd-spiked media treated with H₂ S were harvested after 2 weeks. Cd stress affected growth of fenugreek seedlings. Cd toxicity decreased leaf relative water content (LRWC), intercellular CO₂ concentration, net photosynthesis, stomatal conductance and transpiration. However, application of H₂ S significantly improved seedling morphological attributes by increasing the activity of antioxidant enzymes, i.e. APX, CAT and SOD, in Cd-contaminated soil. H₂ S treatment also regulated phenolic and flavonoid content. H₂ S-induced biosynthesis of spermidine (Spd) and putrescine (Put) could account for the enhancement of growth and physiological performance of fenugreek seedlings under Cd stress. H₂ S treatment also reduced H₂ O₂ production (38%) and electrolyte leakage (EL, 51%) in seedlings grown in different concentrations of Cd. It is recommended to evaluate the efficacy of H₂ S in alleviating Cd toxicity in other crop plants.

He-Ne laser irradiation ameliorates cadmium toxicity in wheat by modulating cadmium accumulation, nutrient uptake and antioxidant defense system

Cadmium (Cd) is one of the most hazardous heavy metals that negatively affect the growth and yield of wheat. He-Ne laser irradiation is known to ameliorate cadmium (Cd) stress in wheat. However, the underlying mechanism of He-Ne laser irradiation on protecting wheat against Cd stress is not well recognized. In present study, Cd-treated wheat showed significant reduction in growth, root morphology and total chlorophyll content, but notably increase of Cd accumulation in both roots and shoots. However, He-Ne laser irradiation dramatically reduced concentrations of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and increased total chlorophyll content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) in roots of wheat plants under Cd stress. Further, He-Ne laser irradiation significantly upregulated the transcripts of TaGR (glutathione reductase) and TaGST (glutathione-S-transferase) genes along with the increased activities of GR and GST and glutathione (GSH) concentration in roots of wheat seedlings under Cd stress. In addition, He-Ne laser irradiation enhanced the uptake of mineral elements (N, P, Mg, Fe, Zn and Cu), and significantly decreased Cd uptake and transport mainly through down-regulating the expressions of Cd transport genes (TaHMA2 and TaHMA3) in roots of wheat seedlings under Cd stress. Overall, these findings suggested that He-Ne laser irradiation alleviated the adverse effects of Cd on wheat growth by enhancing antioxidant defense system, improving mineral nutrient status, and decreasing the Cd uptake and transport. This study provides new insights into the roles of He-Ne laser irradiation in the amelioration of Cd stress in wheat and indicates the potential application of this irradiation in crop breeding and growth under Cd stress conditions.

Cadmium Stabilization and Redox Transformation Mechanism in Maize Using Nanoscale Zerovalent-Iron-Enriched Biochar in Cadmium-Contaminated Soil

Cadmium (Cd) is a readily available metal in the soil matrix, which obnoxiously affects plants and microbiota; thus, its removal has become a global concern. For this purpose, a multifunctional nanoscale zerovalent-iron enriched biochar (nZVI/BC) was used to alleviate the Cd-toxicity in maize. Results revealed that the nZVI/BC application significantly enhanced the plant growth (57%), chlorophyll contents (65%), intracellular permeability (61%), and biomass production index (76%) by restraining Cd uptake relative to Cd control. A Cd stabilization mechanism was proposed, suggesting that high dispersion of organic functional groups (C-O, C-N, Fe-O) over the surface of nZVI/BC might induce complex formations with cadmium by the ion exchange process. Besides this, the regular distribution and deep insertion of Fe particles in nZVI/BC prevent self-oxidation and over-accumulation of free radicals, which regulate the redox transformation by alleviating Cd/Fe⁺ translations in the plant. Current findings have exposed the diverse functions of nanoscale zerovalent-iron-enriched biochar on plant health and suggest that nZVI/BC is a competent material, feasible to control Cd hazards and improve crop growth and productivity in Cd-contaminated soil.

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

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

Exogenous Caffeine (1,3,7-Trimethylxanthine) Application Diminishes Cadmium Toxicity by Modulating Physio-Biochemical Attributes and Improving the Growth of Spinach (Spinacia oleracea L.)

Leafy vegetables usually absorb and retain heavy metals more readily than most of the other crop plants, and thus contribute ≥70% of the total cadmium (Cd) intake of humans. Caffeine mediates plant growth and has proved to be beneficial against pathogens and insects. Therefore, it was hypothesized that foliar applications of caffeine could alter metabolism and reduce Cd toxicity in spinach (Spinacia oleracea L.). Seven-day old spinach seedlings were provided with Cd (0, 50, and 100 µM) stress. Caffeine (0, 5, or 10 mM) foliar spray was given twice at after 20 days of seeds germination with an interval of one week. In results, Cd stress reduced photosynthetic pigments biosynthesis, increased oxidative stress, imbalanced nutrient retention, and inhibited plant growth. On the other hand, the caffeine-treated spinach plants showed better growth owing to the enhanced biosynthesis of chlorophylls, better oxidative defense systems, and lower accumulation and transport of Cd within the plant tissues. Furthermore, caffeine application enhanced the accumulation of the proline and ascorbic acid, but reduced MDA and H2O2 contents and Cd in plant leaves, and ultimately improved mineral nutrition of spinach plants exposed to different Cd regimes. In conclusion, exogenous application of caffeine significantly diminishes Cd stress by modulating physiological, biochemical, and growth attributes of spinach (Spinacia oleracea L.)

Combined Effect of Microplastics and Cd Alters the Enzymatic Activity of Soil and the Productivity of Strawberry Plants

The synergistic effect between heavy metals and microplastics can affect soil properties as well as plant performance and yield. The objective of this study was to evaluate the combined effect of microplastics and cadmium on a soil-plant system. Specifically, we proposed to explore changes in soil microbiological activity, the growth and yield parameters of strawberry plants, and to evaluate the accumulation of these pollutants in the soil and root system. Plants were planted in clay pots under greenhouse conditions. The experiment was set up as a completely randomized design, with four treatments (Control; MPs; Cd; and Cd + MPs) and five replicates. The results showed that MPs and/or Cd affected plant growth, plant biomass, the number of fruits, root characteristics, dehydrogenase activity, acid phosphatase, and microbial biomass, and increased the accumulation of Cd in the roots and soil. The increased bioavailability of Cd, due to the presence of microplastics, could explain the observed negative effects on soil properties and the performance of strawberry plants.

Biochar application for the remediation of trace metals in contaminated soils: Implications for stress tolerance and crop production

In modern agriculture and globalization, the release of trace metals from manufacturing effluents hinders crop productivity by polluting the atmosphere and degrading food quality. Sustaining food safety in polluted soils is critical to ensure global food demands. This review describes the negative effects of trace metals stress on plant growth, physiology, and yield. Furthermore, also explains the potential of biochar in the remediation of trace metal's contaminations in plants by adoption of various mechanisms such as reduction, ion exchange, electrostatic forces of attraction, precipitation, and complexation. Biochar application enhances the overall productivity, accumulation of biomass, and photosynthetic activity of plants through the regulation of various biochemical and physiological mechanisms of plants cultivated under trace metals contaminated soil. Moreover, biochar scavenges the formation of reactive oxygen species, by activating antioxidant enzyme production i.e., ascorbate peroxidase, catalase, superoxide dismutase, peroxidase, etc. The application of biochar also improves the synthesis of stressed proteins and proline contents in plants thus maintaining the osmoprotectant and osmotic potential of the plant under contaminates stress. Integrated application of biochar with other amendments i.e., microorganisms and plant nutrients to improve trace metal remediation potential of biochar and improving crop production was also highlighted in this review. Moreover, future research needs regarding the application of biochar have also been addressed.

A scoping review on biochar-based fertilizers: enrichment techniques and agro-environmental application

Biochar is a carbonized biomass that can be used as a soil amendment. However, the exclusive use of biochar may present some limitations, such as the lack of nutrients. Thus, biochar enrichment techniques have made it possible to obtain biochar-based fertilizers (BCFs), with great potential to improve soil fertility. Nevertheless, there is still a lack of information about the description, advantages, and limitations of the methods used for biochar enrichment. This review provides a comprehensive overview of the production methods of enriched biochar and its performance in agriculture as a soil amendment. Studies demonstrate that the application of BCF is more effective in improving soil properties and crop yields than the exclusive application of pure biochar or other fertilizers. The post-pyrolysis method is the most used technique for enriching biochar. Future studies should focus on understanding the mechanisms of the long-term application of BCFs.

Differences in Cadmium Accumulation, Detoxification and Antioxidant Defenses between Contrasting Maize Cultivars Implicate a Role of Superoxide Dismutase in Cd Tolerance

Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, 12 Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and we determined their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd-tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. A principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd-tolerance, we studied the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT). Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology, antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd-tolerance.

Application of sewage sludge combined with thiourea improves the growth and yield attributes of wheat (Triticum aestivum L.) genotypes under arsenic-contaminated soil

Arsenic (As) contamination is a serious threat to agriculture and human health worldwide. It can adversely affect the growth attributes of food crops. On the other hand, using thiourea (TU) to ameliorate As stress is an economically consistent approach. However, there is a knowledge gap regarding the combined use of TU and Sewage sludge (SS). SS is considered important, unutilized biomass. It can be used as a fertilizer that has high organic matter and nutrients. Therefore, the current study was performed to evaluate TU and SS sole and combined responses under As toxicity on two wheat genotypes (Markaz 19 and Ujala 16). There were four treatments control (As 50 mg kg^-1), SS (30 g kg⁻¹)+TU (6.5 mM)+As, TU+As and SS+As applied with four replications. Results revealed that SS+TU performed significantly better over SS, TU and control for improvement in root and shoot fresh and dry weight of wheat varieties Markaz 19 and Ujala 16 under As toxicity. A significant decrease in POD, SOD and APX of Markaz 19 and Ujala 16 also validated the effective functioning of SS+TU over control. The maximum increase of 71 and 77% was noted in phosphorus, where SS+TU was applied over control in Markaz 19 and Ujala 16, respectively. In conclusion, SS+TU is a better approach than the sole application of SS and TU under As contamination for improvement in wheat growth attributes. More investigations are recommended at the field level under different As contamination and agro-climatic zones to declare SS+TU an effective amendment to mitigate As toxicity in wheat.