Selenium mitigates the chromium toxicity in Brassicca napus L. by ameliorating nutrients uptake, amino acids metabolism and antioxidant defense system

Soil Organic Matter and Total Nitrogen Reshaped Root-Associated Bacteria Community and Synergistic Change the Stress Resistance of Codonopsis pilosula

The stress resistance of medicinal plants is essential to the accumulation of pharmacological active ingredients, but the regulation mechanism of biological factors and abiotic factors on medicinal plants is still unclear. To investigate the mechanism of soil nutrient and microecology on the stress resistance of C. pilosula, rhizosphere soil and roots were collected across the four seasons in Minxian, Gansu, and their physicochemical properties, as well as root-associated microorganisms, were examined. The results showed that the bacterial α-diversity indexes increased in the endosphere and rhizosphere from summer to autumn. At the same time, the community composition and function changed considerably. The stability of the endophytic bacterial community was higher than that rhizospheric bacteria, and the complexity of the endophytic bacterial community was lower than rhizospheric bacteria. Soil organic matter (OM), water content (WC), total potassium (TK), and total nitrogen (TN) have been identified as the key factors affecting bacterial community diversity and stress resistance of C. pilosula. WC, TN, and OM showed significant differences from summer to autumn (P < 0.5). Four key soil physiochemical factors changed significantly between seasons (P < 0.01). TN and OM change the stress resistance of C. pilosula mainly by changing the activity of antioxidant enzymes. Changes of OM and endophytic bacterial diversity affect the accumulation of soluble sugars to alter stress resistance. These four key soil physicochemical factors significantly influenced the diversity of endophytic bacteria. WC and OM were identified as the most important factors for endophytic and rhizospheric bacteria, respectively. This study provided the research basis for the scientific planting of C. pilosula.

Effect of selenium and compost on physiological, biochemical, and productivity of chili under chromium stress

In the era of industrialization, chromium (Cr) as a metal poses a substantial threat to the ecosystem. Selenium (Se) is essential for minimizing heavy metal stress in crops and effectively reducing their accumulation in edible plant parts. This research work aimed to evaluate the synergistic effect of compost and Se for alleviation of Cr stress in chili plants. A greenhouse trail was conducted to investigate the individual and combined effects of foliage applied selenium (Na2SeO4 = 3 µM) and soil applied compost (250 mg kg-1, w/w) on the growth, physio-biochemical, antioxidant and of chili grown under varying levels of induced Cr stress (0, 100, and 200 mg kg-1 using K2Cr2O7). Findings revelaed that a significant linear reduction was observed in growth, biomass, and physiological parameters of chili plant with an increasing level of Cr concentrations. Maximum decrease in relative water content (20.04 and 27.21%) and total chlorophyll concentrations (11.73 and 20.57%) and increased in electrolyte leakage (59.14 and 130.52%) was observed at 100 and 200 mg kg-1 of Cr levels in soil in comparison with the control, respectively. Combined application of compost and selenium showed significant increase regardless of Cr concentrations in the soil. Synergistic approach of compost and selenium showed improved growth in comparison with the sole application in limiting the movement and uptake of Cr in the roots and fruits of chili plants. Moreover, improved physiological and antioxidant potential of chili plants helped to cope with higher levels of Cr stress by limiting the lipid peroxidation and membrane damange. The combined use of compost and selenium induces the physio-biochemical defense responses against of the varying levels of Cr stress in chili plants. This promising approach highlights the significant potential for growing chili crop in Cr-contaminated soils to achieve better quality and higher yields.

Impact of iron oxide nanoparticles on cadmium toxicity mitigation in Brassica napus

Cadmium (Cd) contamination greatly hinders plant productivity. Nanotechnology offers a promising solution for Cd phytotoxicity. The novelty of this study lies in the limited research on the effects of nanoiron (Fe3O4NPs) in regulating Cd toxicity in oilseed crops. This study examined how Fe3O4NPs regulated the Cd-exposure in B. napus. Foliar spray of 10 mg L-1 Fe3O4NPs was applied to 50 μM Cd-stressed B. napus seedlings via leaf exposure in hydroponic system. Under Cd stress, Fe3O4NPs decreased the Cd-accumulation (25-37%) due to adsorption followed by more root Cd-immobilization, and increased the plant height (23-31%) and biomass (17-24%). These findings were directly correlated with better photosynthetic activity (chlorophylls, gas exchanges and photosynthetic efficiency), leaf stomata opening and nutrients accumulation (20-29%). Subcellular localization revealed that Fe3O4NPs enhanced the binding capacity of cell wall for Cd to hinder its entry into cell organalles and facilitated vacoular sequestration. Additionally, Fe3O4NPs decreased the oxidative stress (21-33%) and peroxidation of lipids (24-31%) by regulating the genes-associated to superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase, reduced glutathione, phytochelation, chlorophyll synthesis and Cd-transporters. Fe3O4NPs protected plant roots from Cd-induced cell structural damages and cell death. Among studied parameters, ZD 635 exhibited greater tolerance to Cd stress when compared to ZD 622 cultivar. Findings revealed that Fe3O4NPs effectively mitigate Cd toxicity by improving the photosynthesis, antioxidant defense mechanisms, cellular protection, nutrients accumulation and limiting Cd accumulation. This research offers a benchmark for the practical applicability of Fe3O4NPs to enhance the quality of canola production in Cd-contaminated soils.

Positive influence of selenium on the modulation of ascorbate-glutathione cycle in salt stressed Setaria italica L

Soil salinity is a significant abiotic factor affecting crop yield and global distribution, hence selecting salt-tolerant crop species is crucial for food security. Foxtail millet is a resilient crop suitable for hilly, salinity, and drought-prone areas due to its ability to withstand environmental stressors. In this study, foxtail millet was subjected to high NaCl concentrations (150 mM and 200 mM) and selenium (1 μM, 5 μM, and 10 μM) as a stress mitigator. Increased salinity in foxtail plants hampered the growth with decreased pigment levels, increased H₂O₂ levels (153.6%), lipid peroxidation (32.1%), and electrolyte leakage (155.5%). The application of 1 μM Se positively influenced the root-to-shoot ratio (R) (59.2%), photosynthetic pigments, phenolic content (25.1%), flavonoid content (7%) and hence the antioxidant potential of the salt stressed plants there by decreasing the H₂O₂ levels (26.8%) and suggesting a greater ability to scavenge radicals. Both NaCl and Se induced the AsA-GSH pathway. Se supplementation significantly improved AsA-GSH pathway components such as AsA/DHA (40.8%) and GSH/GSSG ratios (39.6%) in salt-stressed foxtail millet, reducing oxidative stress and efficiently neutralizing H₂O₂. Gene expression validation confirmed that SiAPX, SiDHAR, SiMDHAR, and SiGR showed significant upregulation with 1 μM Se application in salt-stressed foxtail millet plants. However, higher Se concentrations (5 μM and 10 μM) led to a reduced fresh weight along with R, increased the MDA and H₂O₂ levels, and did not positively contribute to osmolyte accumulation or improve the AsA/DHA and GSH/GSSG ratios. Elevated Se levels also led to a decreased antioxidant potential. Among the enzymes of the AsA-GSH cycle, higher Se concentrations negatively affected APX, DHAR, MDHAR, and GR activities, indicating stress aggravation rather than mitigation at elevated doses.

Effects of Nanosilica Priming on Rapeseed (Brassica napus) Tolerance to Cadmium and Arsenic Stress by Regulating Cellular Metabolism and Antioxidant Defense

The mechanisms by which seed-primed silicon dioxide nanoparticles (nSi) alleviated arsenic (As) and cadmium (Cd) toxicity in Brassica napus L. remain unclear. A pot study examined the physico-biochemical, cellular, and molecular responses of B. napus exposed to Cd (10 mg/kg soil) and As (50 mg/kg soil) doses with or without nSi priming. The results showed that nSi priming improved photosynthesis, seedling biomass, and metabolite accumulation, and restored the cell structure. Upon Cd and As stress, nSi diminished oxidative stress by downplaying H2O2 (24-32%) and O2•- (29-36%), MDA, and activating antioxidant defenses. Also, nSi relieved Cd and As accumulation (27-36%) by enhancing root-vacuolar sequestration (upregulating BnHMA3, BnPCs, and BnABCC1), cell wall chelation, and downregulating root transporters (BnNRAMP5, BnIRTI, BnHMA2, BnHMA4, BnPHT1.1, and BnPHT1.4). Our findings revealed that nSi priming effectively enhanced canola tolerance to Cd and As toxicity by strengthening multiple oxidative defense mechanisms and limiting their accumulation.

Melatonin: A novel and beneficial substance in sweet potatoes through selenium application

The effects of foliar Se (selenium) fertilizer on melatonin and its biosynthesis in four different colored sweet potatoes were studied. Solutions containing 1.25 mg Se/plant of inorganic selenium (ISe) and organic selenium (OSe) and a control check (CK) were applied three times during the swelling stage. Except for ISe in purple variety, both types of Se applications significantly increased melatonin in four colored varieties. The effect of OSe was greater than that of ISe, mainly because of higher concentration of tryptophan and activities of tryptophan decarboxylase, tryptamine-5 hydroxylase, 5-hydroxytryptamine N-acetyltransferase and N-acetyl-5-hydroxytryptamine methyltransferase. The orange variety had highest melatonin with the application of ISe and OSe, and highest melatonin among all applications was achieved by OSe in orange variety, followed by OSe in purple variety. These findings revealed that melatonin with extremely strong health benefits could be found and significantly increased in sweet potatoes through Se applications.

Methyl Jasmonate Was Involved in Hydrogen Sulfide-Alleviated Cadmium Stress in Cucumber Plants Through ROS Homeostasis and Chlorophyll Metabolism

Cadmium (Cd), as one of the most toxic nonessential elements, severely prohibits plant growth and development. Hydrogen sulfide (H2S) and methyl jasmonate (MeJA) play essential roles in plant response to abiotic stress. However, the potential mechanism of H2S and MeJA in alleviating Cd stress in plants remains unclear. In the current study, the importance and crosstalk of H2S and MeJA in the Cd tolerance of cucumber seedlings have been investigated. Our results revealed that Cd stress obviously prohibited the growth of cucumber seedlings. Optimal concentrations of H2S donor sodium hydrosulfide (NaHS) or MeJA treatment, respectively, or in combination, significantly enhanced seedling growth under Cd stress. However, the positive effects of H2S during seedling growth were obviously reversed by the application of MeJA biosynthesis inhibitors, which implied that MeJA might be involved in the H2S-improved growth of cucumber seedlings under Cd stress. Moreover, Cd stress resulted in the increase in hydrogen peroxide (H2O2), superoxide radical (O2·-) accumulation, and impaired the functioning of the ascorbate-glutathione cycle. Both H2S and MeJA decreased the reactive oxygen species (ROS) level and ameliorated the negative effects of Cd stress through significantly increasing the ratio of ascorbate (AsA)/dehydroascorbic acid (DHA) and reduced glutathione (GSH)/oxidized glutathione (GSSG). Besides that, the expression level of ROS scavenge genes was significantly upregulated by the application of exogenous H2S or MeJA treatment. Moreover, H2S and MeJA significantly enhanced the chlorophyll concentration and inhibited chlorophyll degradation through decreasing the expression levels of chlorophyll catabolic enzymes. Additionally, exogenous H2S and MeJA obviously enhanced the chlorophyll fluorescence. However, MeJA biosynthesis inhibitors significantly suppressed the positive role of H2S. The above results suggested MeJA is involved in H2S-induced Cd stress alleviation in cucumber seedlings through enhancing ROS-scavenge capacity and improving the photosynthesis system.

Exploring mercury detoxification in fish: The role of selenium from tuna byproduct diets for sustainable aquaculture

Exposure to mercury (Hg) through fish consumption poses significant environmental and public health risks, given its status as one of the top ten hazardous chemicals. Aquaculture is expanding, driving a surge in demand for sustainable aquafeeds. Tuna byproducts, which are rich in protein, offer potential for aquafeed production, yet their use is challenged by the high content of heavy metals, particularly Hg. However, these byproducts also contain elevated levels of selenium (Se), which may counteract Hg adverse effects. This study examines the fate of dietary Hg and Se in an aquaculture model fish. Biomolecular speciation analyses through hyphenated analytical approaches were conducted on the water-soluble protein fraction of key organs of juvenile rainbow trout (Oncorhynchus mykiss) exposed to various combinations of Hg and Se species, including diets containing tuna byproducts, over a six-month period. The findings shed light on the dynamics of Hg and Se compounds in fish revealing potential Hg detoxification mechanisms through complexation with Hg-biomolecules, such as cysteine, glutathione, and metallothionein. Furthermore, the trophic transfer of selenoneine is demonstrated, revealing novel opportunities for sustainable aquafeed production. Understanding the interactions between Hg and Se in aquaculture systems is crucial for optimizing feed formulations and mitigating environmental risks. This research contributes to the broader goal of advancing sustainable practices in aquaculture while addressing food security challenges.

Ameliorating the detrimental effects of chromium in wheat by silicon nanoparticles and its enriched biochar

Increased anthropogenic activities over the last decades have led to a gradual increase in chromium (Cr) content in the soil, which, due to its high mobility in soil, makes Cr accumulation in plants a serious threat to the health of animals and humans. The present study investigated the ameliorative effect of foliar-applied Si nanoparticles (SiF) and soil-applied SiNPs enriched biochar (SiBc) on the growth of wheat in Cr-polluted soil (CPS). Two levels of CPS were prepared, including 12.5 % and 25 % by adding Cr-polluted wastewater in the soil as soil 1 (S1) and soil 2 (S2), respectively for the pot experiment with a duration of 40 days. Cr stress significantly reduced wheat growth, however, combined application of SiF and SiBc improved root and shoot biomass production under Cr stress by (i) reducing Cr accumulation, (ii) increasing activities of antioxidant enzymes (ascorbate peroxidase and catalase), and (iii) increasing protein and total phenolic contents in both root and shoot respectively. Nonetheless, separate applications of SiF and SiBc effectively reduced Cr toxicity in shoot and root respectively, indicating a tissue-specific regulation of wheat growth under Cr. Later, the Langmuir and Freundlich adsorption isotherm analysis showed a maximum soil Cr adsorption capacity ∼ Q(max) of 40.6 mg g-1 and 59 mg g-1 at S1 and S2 respectively, while the life cycle impact assessment showed scores of -1 mg kg-1 and -211 mg kg-1 for Cr in agricultural soil and - 0.184 and - 38.7 for human health at S1 and S2 respectively in response to combined SiF + SiBC application, thus indicating the environment implication of Si nanoparticles and its biochar in ameliorating Cr toxicity in different environmental perspectives.

Biochar solutions: Slow and fast pyrolysis effects on chromium stress in rapeseed roots

Chromium (Cr) contamination in agricultural soils, largely due to industrial activities, poses a significant threat to plant growth and productivity. This study examines the effects of Cr stress at concentrations of 100 and 200 mg of K2Cr2O7 per kg soil on rapeseed (Brassica napus) roots and evaluates the mitigating potential of biochar. Biochar, produced through both slow and fast pyrolysis and applied at 30 g per kg soil, was investigated for its ability to neutralize Cr toxicity. Our findings indicate that Cr stress significantly decreased the growth and physiological functions of rapeseed roots. However, biochar application improved soil pH, cation exchange capacity, and the uptake of essential nutrients such as nitrogen, phosphorus, potassium, calcium, and magnesium. Additionally, biochar enhanced the production of osmotic regulators like glycine betaine and soluble proteins, as well as indole acetic acid, promoting better root growth and water uptake under Cr stress. Notably, biochar reduced Cr availability and absorption in rapeseed roots, leading to lower levels of stress-related hormones such as abscisic acid, salicylic acid, and jasmonic acid. Among the biochars tested, slow pyrolysis biochar was more effective than fast pyrolysis biochar in mitigating Cr toxicity. These results highlight the potential of slow pyrolysis biochar as a sustainable strategy to alleviate Cr pollution and enhance plant resilience in contaminated soils.

Harnessing the potential of copper-based nanoparticles in mitigating abiotic and biotic stresses in crops

The demand for crops production continues to intensify with the rapid increase in population. Agricultural crops continue to encounter abiotic and biotic stresses, which can substantially hamper their productivity. Numerous strategies have been focused to tackle the abiotic and biotic stress factors in various plants. Nanotechnology has displayed great potential to minimize the phytotoxic impacts of these environmental constraints. Copper (Cu)-based nanoparticles (NPs) have displayed beneficial effects on plant growth and stress tolerance. Cu-based NPs alone or in combination with plant growth hormones or microorganisms have been documented to induce plant tolerance and mitigate abiotic or biotic stresses in different plants. In this review, we have comprehensively discussed the uptake and translocation of Cu-based NPs in plants, and beneficial roles in improving the plant growth and development at various growth stages. Moreover, we have discussed how Cu-based NPs mechanistically modulate the physiological, biochemical, metabolic, cellular, and metabolic functions to enhance plant tolerance against both biotic (viruses, bacterial and fungal diseases, etc.) and abiotic stresses (heavy metals or metalloids, salt, and drought stress, etc.). We elucidated recent advancements, knowledge gaps, and recommendations for future research. This review would help plant and soil scientists to adapt Cu-based novel strategies such as nanofertilizers and nanopesticides to detoxify the abiotic or biotic stresses. These outcomes may contribute to the promotion of healthy food production and food security, thus providing new avenues for sustainable agriculture production.

Melatonin and copper oxide nanoparticles synergistically mitigate clubroot disease and enhance growth dynamics in Brassica rapa

Clubroot, a devastating soil borne disease affecting 30%∼50% of Brassicaceae crops worldwide, lacks effective control measures. In the present study, we explored the potential of melatonin (MT) and copper oxide nanoparticle (CuO-NPs) in mitigating clubroot severity in the Brassica rapa ssp. pekinensis. Following 18 h priming with MT, CuO-NPs, or both seeds were grown in controlled environment using synthetic potting mix. Inoculated with Plasmodiophora brassicae spores on 5th day, followed by a soil drench phyto-nano treatment with a week interval. Plants were assessed for various health and growth indices including disease, biometrics, photosynthesis, reactive oxygen species (ROS), antioxidant enzyme activity, hormones and genes expression at onset of secondary clubroot infection using established protocols. Statistical analysis employed ANOVA with Fisher's LSD for significance assessment (P < 0.05). Our results revealed that seed priming with both MT (50 μMol/L) and CuO-NPs (200 mg/L), followed by soil drenching significantly reduced clubroot incidence (38%) and disease index (57%), compared to control treatments. This synergistic effect was associated with enhanced plant growth (shoots: 48% and roots: 59%). Plants treated with both MT and CuO-NPs showed robust antioxidant defenses, significantly increased superoxide dismutase (SOD (25/29%)), catalase (CAT (83/55%)), and ascorbate peroxidase (APX (83/46%)) activity in both shoots/roots, respectively, compared to infected control. Notably, salicylic acid and jasmonic acid levels doubled in treated plants, while stress hormone abscisic acid (ABA) decreased by 80% in roots and 21% in shoots. Gene expression analysis corroborated these findings, showing that the combined treatment activated antioxidant defense genes (SOD, APX and CAT) by 1.9-7.2-fold and upregulated hormone signaling genes JAZ1 (7.8-fold), MYC2 (3.9-fold) and SABP2 (36-fold). Conversely, ABA biosynthesis genes (ABA1 and NCED1) were downregulated up to 7.2-fold, while plant resistance genes NPR1, PRB1 and PDF1.2 were dramatically increased by up to 6.3-fold compared to infected plants. Overall, our combined treatment approach significantly reduces clubroot severity in B. rapa via enhanced antioxidant defenses, improved ROS scavenging, coordinated hormonal regulation and increased pathogen response genes. This study offers promising strategy for developing effective control measures against clubroot in susceptible cruciferous crops.

Chromium uptake and its impact on antioxidant level, photosynthetic machinery, and related gene expression in Brassica napus cultivars

The development of heavy metals, particularly chromium (Cr)-tolerant crop cultivars, is hampered due to lack of understanding of the mechanisms behind Cr stress tolerance. In this study, two Brassica napus cultivars, ZS758 and ZD622, were compared for Cr stress resistance by using the chlorophyll a fluorescence technique and biochemical characteristics. In both cultivars, Cr stress dramatically decreased PSII and PSI efficiency, biomass accumulation, and antioxidant enzyme levels. Although, cultivar ZS758 showed reduction in oxidative stress by decreasing the production of reactive oxygen species (ROS) in terms of reduced H2O2 and MDA content and increased enzymatic activities of key antioxidants enzymes including SOD, APX, CAT, and POD activities that play a crucial role in the regulation of numerous transcriptional pathways involved in oxidative stress responses. Higher non-photochemical quenching (NPQ) and QY were found in tolerant ZS758 cultivar under Cr stress, indicating that tolerant cultivar had a greater capacity to preserve PSII activity under Cr stress by enhancing heat dissipation as a photo-protective component of NPQ. Lower PSI activity and electron transfer from PSII were confirmed by lower PSI efficiency and higher donor end limitation of PSI in both rapeseed cultivars. The Cr concentration was greater in the ZD622 as compared to ZS758, which affected the mineral nutrients profile and damaged the cellular ultrastructure and related gene expression levels. However, current study suggest that cultivar ZS758 is more resistant to Cr stress than ZD622 due to improved metabolism and structural integrity and Cr stress tolerance that is linked with the increased PSII activity, NPQ, and antioxidant potential; these physiological characteristics can be exploited to select cultivars for Cr stress tolerance.

Selenium alleviates chromium stress and promotes chromium uptake in As-hyperaccumulator Pteris vittata: Cr reduction and cellar distribution

Arsenic-hyperaccumulator Pteris vittata exhibits remarkable absorption ability for chromium (Cr) while beneficial element selenium (Se) helps to reduce Cr-induced stress in plants. However, the effects of Se on the Cr uptake and the associated mechanisms in P. vittata are unclear, which were investigated in this study. P. vittata plants were grown for 14 days in 0.2-strength Hoagland solution containing 10 (Cr10) or 100 μM (Cr100) chromate (CrVI) and 1 μM selenate (Se1). The plant biomass, malondialdehyde contents, total Cr and Se contents, Cr speciation, expression of genes associated with Cr uptake, and Cr subcellular distribution in P. vittata were determined. P. vittata effectively accumulated Cr by concentrating 96-99% in the roots under Cr100 treatment. Further, Se substantially increased its Cr contents by 98% to 11,596 mg kg-1 in the roots, which may result from Se's role in reducing its oxidative stress as supported by 27-62% reduction in the malondialdehyde contents. Though supplied with CrVI, up to 98% of the Cr in the roots was reduced to insoluble chromite (CrIII), with 83-89% being distributed on root cell walls. Neither Cr nor Se upregulated the expression of sulfate transporters PvSultr1;1-1;2 or phosphate transporter PvPht1;4, indicating their limited role in Cr uptake. P. vittata effectively accumulates Cr in the roots mainly as CrIII on cell walls and Se effectively enhances its Cr uptake by reducing its oxidative stress. Our study suggests that Se can be used to enhance P. vittata Cr uptake and reduce its oxidative stress, which may have application in phytostabilization of Cr-contaminated soils.

Application of selenium to reduce heavy metal(loid)s in plants based on meta-analysis

Agricultural soils are currently at risk of pollution from toxic heavy metal(loid)s (HMs) due to human activities, resulting in the excessive accumulation of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), lead (Pb) and zinc (Zn) in food plants. This poses significant risks to human health. Exogenous selenium (Se) has been proposed as a potential solution to reduce HMs accumulation in plants. However, there is currently a lack of comprehensive quantitative overview regarding its influence on the accumulation of HMs in plants. This study utilized meta-analysis to consolidate the existing knowledge on the impact of Se amendments on plant HMs accumulation from contaminated soil media. The present study conducted a comprehensive meta-analysis on literature published prior to December 2023, investigating the effects of different factors on HMs accumulation by meta-subgroup analysis and meta-regression model. Se application showed an inhibitory effect on plant uptake of Hg (28.9%), Cr (25.5%), Cd (25.2%), Pb (22.0%), As (18.3%) and Cu (6.00%) concentration. There was a significant difference in the levels of HMs between treatments with Se application and those without Se application in various plant organs. The percentage changes in the HMs contents of the organs varied from -13.0% to -22.0%. Compared with alkaline soil (pH > 8), Se application can reduce more HMs contents in plants in acidic soil (pH < 5.5) and neutral soil (pH = 5.5-8). For daily food plants(e.g. rice, wheat and corn), Se application can reduce HMs contents in Oryza sp., Triticum sp. and Zea sp., ranging from 14.0-20.0%. Our study emphasizes that the impact of Se on reducing HMs depends on the single or combined effects of Se concentration, plant organs, plant genera and soil pH condition.

Integrative approach to mitigate chromium toxicity in soil and enhance antioxidant activities in rice (Oryza sativa L.) using magnesium-iron nanocomposite and Staphylococcus aureus strains

Pollutants in soil, particularly chromium (Cr), pose high environmental and health risks due to their persistence, bioavailability, and potential for causing toxicity. Cr impairment in plants act as a deleterious environmental pollutant that enters the food chain and eventually disturbs human health. Current study demonstrated the potential of integrative foliar application of magnesium-iron (Mg + Fe) nanocomposite with Staphylococcus aureus strains to alleviate Cr toxicity in rice (Oryza sativa) crops by improving yield and defense system. Growth and yield traits such as shoot length (15%), root length (17%), shoot fresh weight (14%), shoot dry weight (9%), root fresh weight (23%), root dry weight (7%), number of tillers (33%), number of grains (10%) and spike length (13%) improved by combined application of Mg + Fe (20 mg L-1) nanocomposite and S. aureus strains with Cr (110 mg kg-1), compared to when applied alone. Mutual Mg + Fe and S. aureus strains application augmented the SPAD value (9%), total chlorophyll (11%), a (12%), b (17%), and carotenoids (32%), with Cr (110 mg kg-1), compared to alone. Malondialdehyde (13%), hydrogen peroxide (H2O2) (11%), and electrolyte leakage (7%) were significantly regulated in shoots with combined Mg + Fe and S. aureus strains application with Cr (110 mg kg-1) contrasted to alone. Peroxidase (20%), superoxide dismutase (17%), ascorbate peroxidase (18%), and catalase (20%) were increased in shoots with combined Mg + Fe and S. aureus strains application with Cr (110 mg kg-1) in comparison to alone. The combined application of Mg + Fe (20 mgL-1) nanocomposite and S. aureus strains with Cr (110 mg kg-1) enhanced the macro-micronutrients in shoots compared to alone. Cr accumulation in roots (21%), shoots (25%), and grains (47%) were significantly reduced under Cr (110 mg kg-1) with combined Mg + Fe and S. aureus strains application, compared to alone. Subsequently, applying combined Mg + Fe and S. aureus strains is a sustainable solution to boost crop production under Cr toxicity.

Insights into trehalose mediated physiological and biochemical mechanisms in Zea mays L. under chromium stress

BACKGROUND

Chromium (Cr) toxicity significantly threatens agricultural ecosystems worldwide, adversely affecting plant growth and development and reducing crop productivity. Trehalose, a non-reducing sugar has been identified as a mitigator of toxic effects induced by abiotic stressors such as drought, salinity, and heavy metals. The primary objective of this study was to investigate the influence of exogenously applied trehalose on maize plants exposed to Cr stress.

RESULTS

Two maize varieties, FH-1046 and FH-1453, were subjected to two different Cr concentrations (0.3 mM, and 0.5 mM). The results revealed significant variations in growth and biochemical parameters for both maize varieties under Cr-induced stress conditions as compared to the control group. Foliar application of trehalose at a concentration of 30 mM was administered to both maize varieties, leading to a noteworthy reduction in the detrimental effects of Cr stress. Notably, the Cr (0.5 mM) stress more adversely affected the shoot length more than 0.3mM of Cr stress. Cr stress (0.5 mM) significantly reduced the shoot length by 12.4% in FH-1046 and 24.5% in FH-1453 while Trehalose increased shoot length by 30.19% and 4.75% in FH-1046 and FH-1453 respectively. Cr stress significantly constrained growth and biochemical processes, whereas trehalose notably improved plant growth by reducing Cr uptake and minimizing oxidative stress caused by Cr. This reduction in oxidative stress was evidenced by decreased production of proline, SOD, POD, MDA, H2O2, catalase, and APX. Trehalose also enhanced photosynthetic activities under Cr stress, as indicated by increased values of chlorophyll a, b, and carotenoids. Furthermore, the ameliorative potential of trehalose was demonstrated by increased contents of proteins and carbohydrates and a decrease in Cr uptake.

CONCLUSIONS

The study demonstrates that trehalose application substantially improved growth and enhanced photosynthetic activities in both maize varieties. Trehalose (30 mM) significantly increased the plant biomass, reduced ROS production and enhanced resilience to Cr stress even at 0.5 mM.

Insights into the combined toxicity and mechanisms of BDE-47 and PFOA in marine blue mussel: An integrated study at the physiochemical and molecular levels

The coexistence of multiple emerging contaminants imposes a substantial burden on the ecophysiological functions in organisms. The combined toxicity and underlying mechanism requires in-depth understanding. Here, marine blue mussel (Mytilus galloprovincialis L.) was selected and exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and perfluorooctanoic acid (PFOA) individually and in combination at environmental related concentrations to elucidate differences in stress responses and potential toxicological mechanisms. Characterization and comparison of accumulation, biomarkers, histopathology, transcriptomics and metabolomics were performed. Co-exposure resulted in differential accumulation patterns, exacerbated histopathological alterations, and different responses in oxidative stress and biomarkers for xenobiotic transportation. Moreover, the identified differentially expressed genes (DEGs) and differential metabolites (DEMs) in mussels were found to be annotated to different metabolic pathways. Correlation analyses further indicated that DEGs and DEMs were significantly correlated with the above biomarkers. BDE-47 and PFOA altered the genes and metabolites related to amino acid metabolism, energy and purine metabolism, ABC transporters, and glutathione metabolism to varying degrees, subsequently inducing accumulation differences and combined toxicity. Furthermore, the present work highlighted the pivotal role of Nrf2-keap1 detoxification pathway in the acclimation of M. galloprovincialis to reactive oxygen species (ROS) stress induced by BDE-47 and PFOA. This study enabled more comprehensive understanding of combined toxic mechanism of multi emerging contaminants pollution.

Phosphorus and selenium compounding mitigates Cr stress in peanut seedlings by enhancing growth homeostasis and antioxidant properties

Peanut is an economically important crop, but it is susceptible to Cr contamination. In this study, we used peanut as experimental material to investigate the effects of exogenous P, Se interacting with Cr on the nutrient growth and antioxidant system of peanut seedlings by simulating Cr (0 μM, 50 μM, and 100 μM) stress environment. The results showed that exogenous P, Se supply could mitigate irreversible damage to peanut seedlings by altering the distribution of Cr in roots and aboveground, changing root conformation, and repairing damaged cells to promote growth. When the Cr concentration is 100 μM, it exhibits the highest toxicity. Compared to the control group P and Se (0 MM), the treatment with simultaneous addition of P + Se (0.5 + 6.0) resulted in a significant increase in root length and root tip number by 248.7% and 127.4%, respectively. Additionally, there was a 46.9% increase in chlorophyll content, a 190.2% increase in total surface area of the seedlings, and a respective increase of 149.1% and 180.3% in soluble protein content in the shoot and roots. In addition, by restricting the absorption of Cr and reducing the synthesis of superoxide dismutase SOD (Superoxide dismutase), CAT (Catalase), POD (Peroxidase), and MDA (Malonaldehyde), it effectively alleviates the oxidative stress on the antioxidant system. Therefore, the exogenous addition of P (0.5 MM) and Se (6.0 MM) prevented the optimal concentration of chromium toxicity to peanuts. Our research provides strong evidence that the exogenous combination of P and Se reduces the risk of peanut poisoning by Cr, while also exploring the optimal concentration of exogenous P and Se under laboratory conditions, providing a basis for further field experiments.

Nano-Selenium and Glutathione Enhance Cucumber Resistance to Botrytis cinerea by Promoting Jasmonic Acid-Mediated Cucurbitacin Biosynthesis

Nano-selenium (Nano-Se), as a biological stimulant, promotes plant growth and development, as well as defense against biotic and abiotic stresses. Glutathione (GSH) is a crucial antioxidant and is also involved in the plant defense response to various stresses. In this study, the efficacy of combined treatment of Nano-Se and GSH (SeG) on the resistance of cucumber plants to Botrytis cinerea was investigated in terms of the plant phenotype, gene expression, and levels of accumulated metabolites using transcriptomic and metabolomic analyses. The exogenous application of SeG significantly enhanced plant growth and increased photosynthetic pigment contents and capacity. Notably, B. cinerea infection was reduced markedly by 41.9% after SeG treatment. At the molecular level, the SeG treatment activated the alpha-linolenic acid metabolic pathway and upregulated the expression of genes responsible for jasmonic acid (JA) synthesis, including LOX (210%), LOX4 (430%), AOS1 (100%), and AOC2 (120%), therefore promoting JA accumulation in cucumber. Intriguingly, the level of cucurbitacin, an important phytoalexin in cucurbitaceous plants, was found to be increased in SeG-treated cucumber plants, as was the expression of cucurbitacin biosynthesis-related genes OSC (107.5%), P450 (440.8%,31.6%), and ACT (414.0%). These genes were also upregulated by JA treatment, suggesting that JA may be an upstream regulator of cucurbitacin biosynthesis. Taken together, this study demonstrated that pretreatment of cucumber plants with SeG could activate the JA signaling pathway and promote cucurbitacin biosynthesis to enhance the resistance of the plants to B. cinerea infection. The findings also indicate that SeG is a promising biostimulant for protecting cucumber plants from B. cinerea infection without growth loss.

Dynamic interplay of reactive oxygen and nitrogen species (ROS and RNS) in plant resilience: unveiling the signaling pathways and metabolic responses to biotic and abiotic stresses

KEY MESSAGE

Plants respond to environmental challenges by producing reactive species such as ROS and RNS, which play critical roles in signaling pathways that lead to adaptation and survival strategies. Understanding these pathways, as well as their detection methods and effects on plant development and metabolism, provides insight into increasing crop tolerance to combined stresses. Plants encounter various environmental stresses (abiotic and biotic) that affect plant growth and development. Plants sense biotic and abiotic stresses by producing different molecules, including reactive species, that act as signaling molecules and stimulate secondary messengers and subsequent gene transcription. Reactive oxygen and nitrogen species (ROS and RNS) are produced in both physiological and pathological conditions in the plasma membranes, chloroplasts, mitochondria, and endoplasmic reticulum. Various techniques, including spectroscopy, chromatography, and fluorescence methods, are used to detect highly reactive, short-half-life ROS and RNS either directly or indirectly. In this review, we highlight the roles of ROS and RNS in seed germination, root development, senescence, mineral nutrition, and post-harvest control. In addition, we provide information on the specialized metabolism involved in plant growth and development. Secondary metabolites, including alkaloids, flavonoids, and terpenoids, are produced in low concentrations in plants for signaling and metabolism. Strategies for improving crop performance under combined drought and pathogen stress conditions are discussed in this review.

Efficient reduction of Cr(VI) by guava (Psidium guajava) leaf extract and its mitigation effect on Cr toxicity in rice seedlings

Hexavalent chromium (Cr(VI)) is a toxic element that has negative impacts on crop growth and yield. Using plant extracts to convert toxic Cr(VI) into less toxic Cr(III) may be a more favorable option compared to chemical reducing agents. In this study, the potential effects and mechanisms of using an aqueous extract of Psidium guajava L. leaves (AEP) in reducing Cr(VI) toxicity in rice were comprehensively studied. Firstly, the reducing power of AEP for Cr(VI) was confirmed by the cyclic voltammetry combined with X-ray photoelectron spectroscopy (XPS) assays. The highest Cr(VI) reduction efficiency reached approximately 78% under 1.5 mg gallic acid equivalent (GAE)/mL of AEP and 10 mg/L Cr(VI) condition. Additionally, Cr(VI) stress had a significant inhibitory effect on rice growth. However, the exogenous application of AEP alleviated the growth inhibition and oxidative damage of rice under Cr(VI) stress by increasing the activity and level of enzymatic and non-enzymatic antioxidants. Furthermore, the addition of AEP restored the ultrastructure of root cells, promoted Cr adsorption onto root cell walls, and limited the translocation Cr to shoots. In shoots, AEP application also triggered the expression of specific genes involved in Cr defense and detoxification response, including photosynthesis pathways, antioxidant systems, flavonoids biosynthesis, and plant hormone signal transduction. These results suggest that AEP is an efficient reduction agent for Cr(VI), and exogenous application of AEP may be a promising strategy to mitigate the harm of Cr(VI) on rice, ultimately contributing to improved crop yield in Cr-contaminated environments.

Combined transcriptome and metabolome analyses reveal the effects of selenium on the growth and quality of Lilium lancifolium

Lilium lancifolium Thunb (L. lancifolium) is an important medicinal and edible plant with outstanding functionality for selenium (Se) biofortification. However, the molecular response of L. lancifolium to exogenous Se has not been fully elucidated. In this study, the effects of different levels of Se on L. lancifolium growth and quality were explored by transcriptome, metabolome and biochemical analyses. The results showed that the total Se and organic Se content in L. lancifolium bulbs increased with increasing Se dosage (0-8.0 mmol/L). Moreover, Se stimulated the growth of L. lancifolium at low level (2.0 mmol/L) but showed an inhibitory effect at high levels (≥4.0 mmol/L). Metabolomic and biochemical analyses revealed that the bulb weight and the content of amino acid, soluble sugar, and soluble protein were significantly increased in the 2.0 mmol/L Se treatment compared with those in the control (0 mmol/L Se). Transcriptome and metabolome analyses revealed that the significant upregulation of the GPD1, GPAT and ADPRM genes promoted glycerophospholipid accumulation. Additionally, the significantly upregulated glyA and downregulated asnB, nadB, thrA and SAT genes coordinate to the regulation of amino acid biosynthesis. The significantly upregulated SUS, bgl B, BAM, and SGA1 genes were involved in soluble sugar accumulation under Se treatment. In summary, this study identified the optimal Se concentration (2.0 mmol/L), which significantly improved the growth and nutritional quality of L. lancifolium and contributed to understanding the combined effects of Se treatment on the expression of genes and the accumulation of metabolites in L. lancifolium bulbs.

Seed pretreatment with brassinosteroids stimulates sunflower immunity against parasitic weed (Orobanche cumana) infection

Broomrape (Orobanche cumana) negatively affects sunflower, causing severe yield losses, and thus, there is a need to control O. cumana infestation. Brassinosteroids (BRs) play key roles in plant growth and provide resilience to weed infection. This study aims to evaluate the mechanisms by which BRs ameliorate O. cumana infection in sunflower (Helianthus annuus). Seeds were pretreated with BRs (1, 10, and 100 nM) and O. cumana inoculation for 4 weeks under soil conditions. O. cumana infection significantly reduced plant growth traits, photosynthesis, endogenous BRs and regulated the plant defence (POX, GST), BRs signalling (BAK1, BSK1 to BSK4) and synthesis (BRI1, BR6OX2) genes. O. cumana also elevated the levels of malondialdehyde (MDA), hydroxyl radical (OH-), hydrogen peroxide (H2O2) and superoxide (O2 •-) in leaves/roots by 77/112, 63/103, 56/97 and 54/89%, as well as caused ultrastructural cellular damages in both leaves and roots. In response, plants activated a few enzymes, superoxide dismutase (SOD), peroxidase (POD) and reduced glutathione but were unable to stimulate the activity of ascorbate peroxidase (APX) and catalase (CAT) enzymes. The addition of BRs (especially at 10 nM) notably recovered the ultrastructural cellular damages, lowered the production of oxidative stress, activated the key enzymatic antioxidants and induced the phenolic and lignin contents. The downregulation in the particular genes by BRs is attributed to the increased resilience of sunflower via a susceptible reaction. In a nutshell, BRs notably enhanced the sunflower resistance to O. cumana infection by escalating the plant immunity responses, inducing systemic acquired resistance, reducing oxidative or cellular damages, and modulating the expression of BR synthesis or signalling genes.

Cytokinin and indole-3-acetic acid crosstalk is indispensable for silicon mediated chromium stress tolerance in roots of wheat seedlings

The rising heavy metal contamination of soils imposes toxic impacts on plants as well as other life forms. One such highly toxic and carcinogenic heavy metal is hexavalent chromium [Cr(VI)] that has been reported to prominently retard the plant growth. The present study investigated the potential of silicon (Si, 10 µM) to alleviate the toxicity of Cr(VI) (25 µM) on roots of wheat (Triticum aestivum L.) seedlings. Application of Si to Cr(VI)-stressed wheat seedlings improved their overall growth parameters. This study also reveals the involvement of two phytohormones, namely auxin and cytokinin and their crosstalk in Si-mediated mitigation of the toxic impacts of Cr(VI) in wheat seedlings. The application of cytokinin alone to wheat seedlings under Cr(VI) stress reduced the intensity of toxic effects of Cr(VI). In combination with Si, cytokinin application to Cr(VI)-stressed wheat seedlings significantly minimized the decrease induced by Cr(VI) in different parameters such as root-shoot length (10.8% and 13%, respectively), root-shoot fresh mass (11.3% and 10.1%, respectively), and total chlorophyll and carotenoids content (13.4% and 6.8%, respectively) with respect to the control. This treatment also maintained the regulation of proline metabolism (proline content, and P5CS and PDH activities), ascorbate-glutathione (AsA-GSH) cycle and nutrient homeostasis. The protective effect of Si and cytokinin against Cr(VI) stress was minimized upon supplementation of an inhibitor of polar auxin transport- 2,3,5-triiodobenzoic acid (TIBA) which suggested a potential involvement of auxin in Si and cytokinin-mediated mitigation of Cr(VI) toxicity. The exogenous addition of a natural auxin - indole-3-acetic acid (IAA) confirmed auxin is an active member of a signaling cascade along with cytokinin that aids in Si-mediated Cr(VI) toxicity alleviation as IAA application reversed the negative impacts of TIBA on wheat roots treated with Cr(VI), cytokinin and Si. The results of this research are also confirmed by the gene expression analysis conducted for nutrient transporters (Lsi1, CCaMK, MHX, SULT1 and ZIP1) and enzymes involved in the AsA-GSH cycle (APX, GR, DHAR and MDHAR). The overall results of this research indicate towards possible induction of a crosstalk between cytokinin and IAA upon Si supplementation which in turn stimulates physiological, biochemical and molecular changes to exhibit protective effects against Cr(VI) stress. Further, the information obtained suggests probable employment of Si, cytokinin and IAA alone or combined in agriculture to maintain plant productivity under Cr(VI) stress and data regarding expression of key genes can be used to develop new crop varieties with enhanced resistance against Cr(VI) stress together with its reduced load in seedlings.

Selenium increases antimony uptake in ramie (Boehmeria nivea L.) by enhancing the physiological, antioxidative, and ionomic mechanisms

Ramie (Boehmeria nivea L.) is a promising phytoremediation candidate due to its high tolerance and enrichment capacity for antimony (Sb). However, challenges arise as Sb accumulated mainly in roots, complicating soil extraction. Under severe Sb contamination, the growth of ramie may be inhibited. Strategies are needed to enhance Sb accumulation in ramie's aboveground parts and improve tolerance to Sb stress. Considering the beneficial effects of selenium (Se) on plant growth and enhancing resistance to abiotic stresses, this study aimed to investigate the potential use of Se in enhancing Sb uptake by ramie. We investigated the effects of Se (0.5, 1, 2, 5, or 10 μM) on ramie growth, Sb uptake and speciation, antioxidant responses, and ionomic profiling in ramie under 10 mg/L of SbIII or antimonate (SbV) stresses. Results revealed that the addition of 0.5 μM Se significantly increased shoot biomass by 75.73% under SbIII stress but showed minimal effects on shoot and root length in both SbIII and SbV treatments. Under SbIII stress, 2 μM Se significantly enhanced Sb concentrations by 48.42% in roots and 62.88% in leaves. In the case of SbV exposure, 10 μM Se increased Sb content in roots by 42.57%, and 1 μM Se led to a 91.74% increase in leaves. The speciation analysis suggested that Se promoted the oxidation of SbIII to less toxic SbV to mitigate Sb toxicity. Additionally, Se addition effectively minimized the excess reactive oxygen species produced by Sb exposure, with the lowest malondialdehyde (MDA) content at 0.5 μM Se under SbIII and 2 μM Se under SbV, by activating antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione peroxidase. Ionomic analysis revealed that Se helped in maintaining the homeostasis of certain nutrient elements, including magnesium, potassium (K), calcium (Ca), iron (Fe), and copper (Cu) in the SbIII-treated roots and K and manganese (Mg) in the SbV-treated roots. The results suggest that low concentrations of Se can be employed to enhance the phytoremediation of Sb-contaminated soils using ramie.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

Effect of riboflavin on redox balance, osmolyte accumulation, methylglyoxal generation and nutrient acquisition in indian squash (Praecitrullus fistulosus L.) under chromium toxicity

The presence of high chromium (Cr) levels induces the buildup of reactive oxygen species (ROS), resulting in hindered plant development. Riboflavin (vitamin B2) is produced by plants, fungi, and microbes. It serves as a precursor to the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which play a crucial role in cellular metabolism. The objective of this work was to clarify the underlying mechanisms by which riboflavin alleviates Cr stress in Praecitrullus fistulosus L. Further, the role of riboflavin in growth, ions homeostasis, methylglyoxal detoxification, and antioxidant defense mechanism are not well documented in plants under Cr toxicity. We found greater biomass and minimal production of ROS in plants pretreated with riboflavin under Cr stress. Results manifested a clear abridge in growth, chlorophyll content, and nutrient uptake in Indian squash plants exposed to Cr stress. Findings displayed that Cr stress visibly enhanced oxidative injury reflected as higher malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide radical (O2•‒), methylglyoxal (MG) levels alongside vivid lipoxygenase activity. Riboflavin strengthened antioxidant system, enhanced osmolyte production and improved membrane integrity. Riboflavin diminished Cr accumulation in aerial parts that led to improved nutrient acquisition. Taken together, riboflavin abridged Cr phytotoxic effects by improving redox balance because plants treated with riboflavin had strong antioxidant system that carried out effective ROS detoxification. Riboflavin protected membrane integrity that, in turn, improved nutrient uptake in plants.

Differential responses of Brassica napus cultivars to dual effects of magnesium oxide nanoparticles

Magnesium oxide nanoparticles (MgO NPs) have great potential to enhance the crop productivity and sustainability of agriculture. Still, a thorough understanding is lacking about its essentiality or toxicity and precise dose for the safe cultivation of oilseed crops. Thus, we assessed the dual effects of MgO NPs (control, 5, 10, 20, 40, 80, and 200 mg/L) on the seed germination, growth performance, photosynthesis, total soluble protein, total carbohydrates, oxidative stress markers (hydrogen peroxide as H2O2 and superoxide anion as O2•‒), lipid peroxidation as MDA, and antioxidant defence machinery (SOD, CAT, APX, and GR activities, and GSH levels) of seven different oilseeds (Brassica napus L.) cultivars (ZY 758, ZD 649, ZD 635, ZD 619, GY 605, ZD 622, and ZD 630). Our findings revealed that low doses of MgO NPs (mainly at 10 mg/L) markedly boosted the seed germination, plant growth (shoot and root lengths) (15‒22%), and biomass (fresh and dry) (11‒19%) by improving the levels of photosynthetic pigments (14‒27%), net photosynthetic rate, stomatal conductance, photosynthetic efficiency (Fv/Fm), total soluble protein and total carbohydrates (16‒36%), antioxidant defence, and reducing the oxidative stress in B. napus tissues. Among all B. napus cultivars, these beneficial effects of MgO NPs were pronounced in ZD 635. ile, elevated levels of MgO NPs (particularly at 200 mg/L) induced oxidative stress, impaired antioxidant scavenging potential, photosynthetic inhibition, protein oxidation, and carbohydrate degradation and lead to inhibit the plant growth attributes. These inhibitory effects were more pronounced in ZD 622. Collectively, low-dose MgO NPs reinforced the Mg contents, protected the plant growth, photosynthesis, total soluble carbohydrates, enzyme activities, and minimized the oxidative stress. While, the excessive MgO NP levels impaired the above-reported traits. Overall, ZD 622 was highly susceptible to MgO NP toxicity and ZD 635 was found most tolerant to MgO NP toxicity.

Selenium-molybdenum interactions reduce chromium toxicity in Nicotiana tabacum L. by promoting chromium chelation on the cell wall

Chromium (Cr) is a hazardous heavy metal that negatively affects animals and plants. The micronutrients selenium (Se) and molybdenum (Mo) have been widely shown to alleviate heavy metal toxicity in plants. However, the molecular mechanism of Cr chelation on the cell wall by combined treatment with Se and Mo has not been reported. Therefore, this study aimed to explore the effects of Se-Mo interactions on the subcellular distribution of Cr (50 µM) and on cell wall composition, structure, functional groups and Cr content, in addition to performing a comprehensive analysis of the transcriptome. Our results showed that the cell walls of shoots and roots accumulated 51.0% and 65.0% of the Cr, respectively. Furthermore, pectin in the cell wall bound 69.5%/90.2% of the Cr in the shoots/roots. Se-Mo interactions upregulated the expression levels of related genes encoding galacturonosyltransferase (GAUT), UTP-glucose-1-phosphate uridylyltransferase (UGP), and UDP-glucose-4-epimerase (GALE), involved in polysaccharide biosynthesis, thereby increasing pectin and cellulose levels. Moreover, combined treatment with Se and Mo increased the lignin content and cell wall thickness by upregulating the expression levels of genes encoding cinnamyl alcohol dehydrogenase (CAD), peroxidase (POX) and phenylalanine amino-lyase (PAL), involved in lignin biosynthesis. Fourier-transform infrared (FTIR) spectroscopy results showed that Se + Mo treatment (in combination) increased the number of carboxylic acid groups (-COOH) groups, thereby enhancing the Cr chelation ability. The results not only elucidate the molecular mechanism of action of Se-Mo interactions in mitigating Cr toxicity but also provide new insights for phytoremediation and food safety.

Silicon and arbuscular mycorrhizal fungi alleviate chromium toxicity in Brassica rapa by regulating Cr uptake, antioxidant defense expression, the glyoxalase system, and secondary metabolites

The potential contribution of silicon (Si) (300 mg kg-1 potash silica) or arbuscular mycorrhizal fungi (AMF) (Rhizophagus irregularis) to reduce chromium toxicity (Cr; 0 and 300 mg kg-1) in Brassica rapa was examined in this work. Under Cr stress, Si and AMF were used separately and in combination (no Si, or AMF, Si, AMF, and Si + AMF). Brassica rapa growth, colonization, photosynthesis, and physio-biochemical characteristics decreased under Cr stress. Oxidative stress was a side effect of Cr stress and was associated with high levels of methylglyoxal (MG), hydrogen peroxide (H2O2), lipid peroxidation (MDA), and maximum lipoxygenase activity (LOX). On the other hand, quantitative real-time PCR analyses of gene expression showed that under Cr stress, the expression of genes for secondary metabolites and antioxidant enzymes was higher than that under the control. The co-application of Si and AMF activated the plant defense system by improving the antioxidative enzymes activities, the potassium citrate and glutathione pool, the glyoxalase system, metabolites, and genes encoding these enzymes under Cr stress. Under the influence of Cr stress, oxidative stress was reduced by the coordinated control of the antioxidant and glyoxalase systems. However, the restricted Cr uptake and root and shoot accumulation of Si and AMF co-applied to only Cr-stressed plants was more significant. In summary, Si and AMF applied together successfully counteract the deleterious effects of Cr stress and restore growth and physio-biochemical characteristics. As a result, the beneficial effects of the combined Si and AMF application may be attributed to mycorrhizae-mediated enhanced Si absorption and metal resistance.

Modulation of plant photosynthetic processes during metal and metalloid stress, and strategies for manipulating photosynthesis-related traits

Metals constitute vital elements for plant metabolism and survival, acting as essential co-factors in cellular processes which are indispensable for plant growth and survival. Excess or deficient provision of metal/metalloids puts plant's life and survival at risk, thus considered a potent stress for plants. Chloroplasts as an organelle with a high metal demand form a pivotal site within the metal homeostasis network. Therefore, the metal-mediated electron transport chain (ETC) in chloroplasts is a primary target site of metal/metalloid-induced stresses. Both excess and deficient availability of metal/metalloids threatens plant's photosynthesis in several ways. Energy demands from the photosynthetic carbon reactions should be in balance with energy output of ETC. Malfunctioning of ETC components as a result of metal/metalloid stress initiates photoinhiition. A feedback inhibition from carbon fixation process also impedes the ETC. Metal stress impairs antioxidant enzyme activity, pigment biosynthesis, and stomatal function. However, genetic manipulations, nutrient management, keeping photostasis, and application of phytohormones are among strategies for coping with metal stress. Consequently, a comprehensive understanding of the underlying mechanisms of metal/metalloid stress, as well as the exploration of potential strategies to mitigate its impact on plants are imperative. This review offers a mechanistic insight into the disruption of photosynthesis regulation by metal/metalloids and highlights adaptive approaches to ameliorate their effects on plants. Focus was made on photostasis, nutrient interactions, phytohormones, and genetic interventions for mitigating metal/metalloid stresses.

Melatonin alleviated cadmium accumulation and toxicity by modulating phytohormonal balance and antioxidant metabolism in rice

Cadmium (Cd) contamination is an eminent dilemma that jeopardizes global food safety and security, especially through its phytotoxicity in rice; one of the most edible crops. Melatonin (MET) has emerged as a protective phytohormone in stress conditions, but the defensive role and underlying mechanisms of MET against Cd toxicity in rice still remain unclear. To fulfill this knowledge gap, the present study is to uncover the key mechanisms for MET-mediated Cd-stress tolerance in rice. Cd toxicity significantly reduced growth by hindering the process of photosynthesis, cellular redox homeostasis, phytohormonal imbalance, and ultrastructural damages. Contrarily, MET supplementation considerably improved growth attributes, photosynthetic efficiency, and cellular ultrastructure as measured by gas exchange elements, chlorophyll content, reduced Cd accumulation, and ultrastructural analysis via transmission electron microscopy (TEM). MET treatment significantly reduced Cd accumulation (39.25%/31.58%), MDA (25.87%/19.45%), H2O2 (17.93%/9.56%), and O2 (29.11%/27.14%) levels in shoot/root tissues, respectively, when compared with Cd treatment. More importantly, MET manifested association with stress responsive phytohormones (ABA and IAA) and boosted the defense mechanisms of plant by enhancing the activities of ROS-scavenging antioxidant enzymes (SOD; superoxide dismutase, POD; peroxidase, CAT; catalase, APX; ascorbate peroxidase) and as well as regulating the key stress-responsive genes (OsSOD1, OsPOD1, OsCAT2, OsAPX1), thereby reinstate cellular membrane integrity and confer tolerance to ultrastructural damages under Cd-induced phytotoxicity. Overall, our findings emphasized the potential of MET as a long-term and cost-effective approach to Cd remediation in paddy soils, which can pave the way for a healthier and more environmentally conscious agricultural sector.

Application of magnesium oxide nanoparticles as a novel sustainable approach to enhance crop tolerance to abiotic and biotic stresses

Abiotic stresses (heavy metals, drought, salinity, etc.) or biotic pathogens (bacteria, fungi, nematodes, etc.) contribute to major losses in crop yields.

Crinum bulbispermum, a Medicinal Geophyte with Phytostabilization Properties in Metal-Enriched Mine Tailings

Ancient grasslands are lost through transformation to agriculture, mining, and urban expansion. Land-use change leads to ecosystem degradation and a subsequent loss of biodiversity. Globally, degraded grasslands have become a priority for restoration efforts to recover lost ecosystem services. Although the ecological and social benefits of woody species and grasses are well documented, limited research has considered the use of forbs for restoration purposes despite their benefits (e.g., C sequestration and medicinal uses). The aim of this study was to determine if Crinum bulbispermum (Burm.f.) Milne-Redh. & Schweick., a medicinal geophyte, could form part of restoration initiatives to restore mine soils in grasslands of the South African Highveld. A pot experiment was conducted to assess the performance of C. bulbispermum in a random design, with three soil treatments varying in level of degradation and metal contamination. The plants were monitored for 12 months, and the morphological characters were measured monthly to assess performance and survival. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the soil and plant tissue concentration of potentially toxic metals. The results indicated that mine tailings negatively affected the growth and development of C. bulbispermum. Although the survival rates indicated that it could survive on tailings, its below-par productivity indicated that the species is not ideal for restoration purposes unless the tailings are ameliorated with topsoil. Although there was root accumulation of metals (Co, Cd, Cu, Mo, and Zn), there was no translocation to the bulbs and leaves, which makes C. bulbispermum suitable for medicinal use even when grown on metal-enriched soil. This species may not be viable for phytoremediation but is a contender to be used in phytostabilization due to its ecological advantages and the fact that it does not accumulate or store metals. These findings underscore the importance of considering geophytes in grassland restoration strategies, expanding their ecological and societal benefits beyond conventional approaches.

Progress in phytoremediation of chromium from the environment

As chromium (Cr) in ecosystems affects human health through food chain exposure, phytoremediation is an environmentally friendly and efficient way to reduce chromium pollution in the environment. Here, we review the mechanism of absorption, translocation, storage, detoxification, and regulation of Cr in plants. The Cr(VI) form is more soluble, mobile, and toxic than Cr(III), reflecting how various valence states of Cr affect environmental risk characteristics, physicochemical properties, toxicity, and plant uptake. Plant root's response to Cr exposure leads to reactive oxygen species (ROS) generation and apoptosis. Cell wall immobilization, vacuole compartmentation, interaction of defense proteins and organic ligand with Cr, and removal of reactive oxygen species by antioxidants continue plant life. In addition, the combined application of microorganisms, genetic engineering, and the addition of organic acids, nanoparticles, fertilization, soil amendments, and other metals could accelerate the phytoremediation process. This review provides efficient methods to investigate and understand the complex changes of Cr metabolism in plants. Preferably, fast-growing, abundantly available biomass species should be modified to mitigate Cr pollution in the environment as these green and efficient remediation technologies are necessary for the protection of soil and water ecology.

Selenium foliar application contributes to decrease ratio of water-soluble fluoride and improve physio-biochemical components in tea leaves

The tea plant accumulates elevated levels of fluoride (F) from environmental sources. Drinking tea containing high F levels poses a potential threat to human health. Selenium (Se) was applied by foliar spray to investigate its effects on F accumulation and physiology in tea plant. Foliar application of different forms of Se, i.e., Na2SeO3, Kappa-selenocarrageenan, Selenomethionine and Nanoselenium, reduced F content in tea leaves by 10.17 %-44.28 %, 16.12 %-35.41 %, 22.19 %-45.99 % and 22.24 %-43.82 %, respectively. Foliar spraying Se could increase F accumulation in pectin through increasing pectin content and pectin demethylesterification to bind more F in the cell wall, which decreased the proportion of water-soluble fluoride in tea leaves. Application of Se significantly decreased the contents of chromium (39.6 %-72.0 %), cadmium (48.3 %-84.4 %), lead (2.2 %-44.4 %) and copper (14.1 %-44.6 %) in tea leaves. Foliar spraying various forms of Se dramatically increased the Se content and was efficiently transformed into organic Se accounting for more than 80 % in tea leaves. All Se compounds increased peroxidase activity by 3.3 %-35.5 % and catalase activity by 2.6 %-99.4 %, reduced malondialdehyde content by 5.6 %-37.1 %, and increased the contents of chlorophyll by 0.65 %-31.8 %, carotenoids by 0.24 %-27.1 %, total catechins by 1.6 %-21.0 %, EGCG by 4.4 %-17.6 % and caffeine by 9.1 %-28.6 %. These results indicated that Se application could be served as a potential efficient and safe strategy diminishing the concentration of F in tea leaves.

Citric acid and hydrogen sulfide cooperate to mitigate chromium stress in tomato plants by modulating the ascorbate-glutathione cycle, chromium sequestration, and subcellular allocation of chromium

The study aimed to investigate the role of hydrogen sulfide (H2S) in regulating chromium stress (Cr-S) tolerance of tomato plants treated with citric acid (CA). Prior to the Cr treatment, tomato plants were foliar-fed with CA (100 μM) daily for 3 days. Subsequently, the plants were grown for another ten days in a hydroponic system in a 50 μM Cr (VI) solution. Chromium treatment reduced photosynthetic pigments and plant biomass, but boosted the levels of hydrogen peroxide (H2O2) malondialdehyde (MDA), H2S, phytochelatins (PCs), and glutathione (GSH), electrolyte leakage (EL), and antioxidant enzyme activity in tomato plants. However, the foliar spray of CA mitigated the levels of H2O2, MDA, and EL, promoted plant growth and chlorophyll content, enhanced antioxidant enzymes' activities, and increased H2S production in Cr-S-tomato plants. CA also increased the levels of GSH and PCs, potentially reducing the toxicity of Cr through regulated sequestration. Additionally, the application of sodium hydrogen sulfide (NaHS), a donor of H2S, improved CA-induced Cr stress tolerance. The addition of CA promoted Cr accumulation in root cell wall and leaf vacuoles to suppress its toxicity. To assess the involvement of H2S in CA-mediated Cr-S tolerance, 0.1 mM hypotaurine (HT), an H2S scavenger, was provided to the control and Cr-S-plants along with CA and CA + NaHS. HT reduced the beneficial effects of CA by decreasing H2S production in tomato plants. However, the NaHS addition with CA + HT inverted the adverse impacts of HT, indicating that H2S is required for CA-induced Cr-S tolerance in tomato plants.

In Vitro Culture Studies for the Mitigation of Heavy Metal Stress in Plants

Heavy metals are among the most common and dangerous contaminants; their action on plants, as well as the possibility for plants to effectively absorb and translocate them, have been studied for several years, mainly for exploitation in phytoremediation, an environmentally friendly and potentially effective technology proposed and studied for the recovery of contaminated soils and waters. In this work, the analysis has focused on the studies developed using in vitro techniques on the possibilities of mitigating, in plants, the stress due to the presence of heavy metals and/or improving their absorption. These objectives can be pursued with the use of different substances and organisms, which have been examined in detail. The following are therefore presented in this review: an analysis of the role of metals and metalloids; the use of several plant growth regulators, with their mechanisms of action in different physiological phases of the plant; the activity of bacteria and fungi; and the role of other effective compounds, such as ascorbic acid and glutathione.

Seed priming with nano-silica effectively ameliorates chromium toxicity in Brassica napus

Plant yield is severely hampered by chromium (Cr) toxicity, affirming the urgent need to develop strategies to suppress its phyto-accumulation. Silicon dioxide nanoparticles (SiO2 NPs) have emerged as a provider of sustainable crop production and resistance to abiotic stress. But, the mechanisms by which seed-primed SiO2 NPs palliate Cr-accumulation and its toxic impacts in Brassica napus L. tissues remains poorly understood. To address this gap, present study examined the protective efficacy of seed priming with SiO2 NPs (400 mg/L) in relieving the Cr (200 µM) phytotoxicity mainly in B. napus seedlings. Results delineated that SiO2 NPs significantly declined the accumulation of Cr (38.7/35.9%), MDA (25.9/29.1%), H2O2 (27.04/36.9%) and O2• (30.02/34.7%) contents in leaves/roots, enhanced the nutrients acquisition, leading to improved photosynthetic performance and better plant growth. SiO2 NPs boosted the plant immunity by upregulating the transcripts of antioxidant (SOD, CAT, APX, GR) or defense-related genes (PAL, CAD, PPO, PAO and MT-1), GSH (assists Cr-vacuolar sequestration), and modifying the subcellular distribution (enhances Cr-proportion in cell wall), thereby confer tolerance to ultrastructural damages under Cr stress. Our first evidence to establish the Cr-detoxification by seed-primed SiO2 NPs in B. napus, indicated the potential of SiO2 NPs as stress-reducing agent for crops grown in Cr-contaminated areas.

Novel Finding on How Melatonin and Nanoselenium Alleviate 2,4-D Butylate Stress in Wheat Plants

Nanoselenium (nano-Se) or melatonin (MT) foliar spray reduces pesticide stress by stimulating plant secondary metabolism and antioxidant capacity. However, the effects of nano-Se and MT biofortification on the interaction between plant secondary metabolic pathways and rhizosphere microbes in mitigating 2,4-D butyrate stress remain unknown. Compared to nano-Se or MT treatment alone, nano-Se and MT combined application increased the antioxidant enzyme activities and decreased the MDA (25.0%) and H2O2 (39.3%) contents with 2,4-D butylate exposure. Importantly, they enhance the soil enzymes (S-FDA by 53.1%), allelochemicals (luteolin by 164.1% and tricin by 147.3%), as well as plant secondary metabolites (JA by 63.3% and 193.3% in leaves and roots) levels. It also improved the beneficial microbial abundance of Comamonadaceae, Sphingomonadaceae, and Rhodobacteraceae in the rhizosphere soil. In conclusion, nano-Se and MT alleviate 2,4-D butylate stress in wheat plants by enabling the interaction between rhizosphere microorganisms, allelopathic substances, and secondary metabolites.

Coumarin regulated redox homeostasis to facilitate phytoremediation of saline and alkaline soils by bitter gourd (Momordica charantia L.)

The use of coumarin (COU) to alleviate the phytotoxic effects of salinity has great potential in improving the phytoremediation of saline and alkaline soils. 30-day bitter gourd plants were exposed to 15 dS m‒1 salinity of neutral (NaCl and Na2SO4) and alkaline (Na2CO3 and NaHCO3) salts. 60-day plants were harvested to record different growth, physiological and biochemical attributes. Salinity significantly subsided plant growth, chlorophyll, photosynthesis, and nutrient acquisition. Salinity induced notable oxidative damage in plants that displayed higher relative membrane permeability (RMP), accumulated elevated ROS (H2O2 and O2•‒) and MDA levels alongside intensified lipoxygenase (LOX) activity. The production of cytotoxic methylglyoxal was also significantly higher in plants under salinity. COU seed priming (50, 100 and 150 mg L‒1) promoted plant growth by circumventing oxidative injury and intensifying oxidative defense. Further, COU maintained the intricate balance between reduced (GSH) and oxidized (GSSG) glutathione to diminish ion excess toxicity, thereby facilitating the phytoremediation of saline soils. The lower doses of COU promoted methylglyoxal and ROS detoxification systems that, in turn, lessened the phytotoxic effects of salinity. COU restored ions homeostasis by augmenting osmotic adjustment in plants under salinity.

Effect of different levels of EDTA on phytoextraction of heavy metal and growth of Brassica juncea L

Heavy metal pollution of soil is a major concern due to its non-biodegradable nature, bioaccumulation, and persistence in the environment. To explore the probable function of EDTA in ameliorating heavy metal toxicity and achieve the sustainable development goal (SDG), Brassica juncea L. seedlings were treated with different concentrations of EDTA (0, 1.0, 2.0, 3.0, and 4.0 mM Kg-1) in heavy metal-polluted soil. Plant samples were collected 60 days after sowing; photosynthetic pigments, H2O2, monoaldehyde (MDA), antioxidant enzymes, and ascorbic acid content, as well as plant biomass, were estimated in plants. Soil and plant samples were also examined for the concentrations of Cd, Cr, Pb, and Hg. Moreover, values of the phytoremediation factor were utilized to assess the accumulation capacity of heavy metals by B. juncea under EDTA treatments. In the absence of EDTA, B. juncea seedlings accrued heavy metals in their roots and shoots in a concentration-dependent manner. However, the highest biomass of plants (roots and shoots) was recorded with the application of 2 mM kg-1 EDTA. Moreover, high levels (above 3 mM kg-1) of EDTA concentration have reduced the biomass of plants (roots and shoots), photosynthetic area, and chlorophyll content. The effect of EDTA levels on photosynthetic pigments (chlorophyll a and b) revealed that with an increment in EDTA concentration, accumulation of heavy metals was also increased in the plant, subsequently decreasing the chlorophyll a and b concentration in the plant. TLF was found to be in the order Pb> Hg> Zn> and >Ni, while TF was found to be in the order Hg>Zn>Ni>Pb, and the best dose was 3 mM kg-1 EDTA for Hg and 4 mM kg-1 for Pb, Ni, and Zn. Furthermore, hyperaccumulation of heavy metals enhanced the generation of hydrogen peroxide (H2O2), superoxide anions (O2•-), and lipid peroxidation. It also interrupts mechanisms of the antioxidant defense system. Furthermore, heavy metal stress reduced plant growth, biomass, and chlorophyll (chl) content. These findings suggest that the exogenous addition of EDTA to the heavy metal-treated seedlings increases the bioavailability of heavy metals for phytoextraction and decreases heavy metal-induced oxidative injuries by restricting heavy metal uptake and components of their antioxidant defense systems.

Selenium enhances ROS scavenging systems and sugar metabolism increasing growth of sugarcane plants

Selenium (Se) beneficial effect on plants is related to an increase in nitrogen (N) assimilation and its role as an abiotic stress mitigator by reactive oxygen species (ROS) scavenging enhanced by antioxidant metabolism. This study aimed to evaluate sugarcane (Saccharum spp.) growth, photosynthetic and antioxidant responses, and sugar accumulation in response to Se supply. The experimental design was a factorial scheme 2 × 4: two sugarcane varieties (RB96 6928 and RB86 7515) and four Se application rates (0; 5; 10 and 20 μmol L-1) applied as sodium selenate in the nutrient solution. Leaf Se concentration increased under Se application in both varieties. The enzymes SOD (EC 1.15.1.1) and APX (EC 1.11.1.11) showed increase activities under Se application on variety RB96 6928. Nitrate reductase activity increased in both varieties resulting in the conversion of nitrate into higher total amino acids concentration indicating an enhanced N assimilation. This led to an increased concentration of chlorophylls and carotenoids, increased CO2 assimilation rate, stomatal conductance, and internal CO2 concentration. Selenium provided higher starch accumulation and sugar profiles in leaves boosting plant growth. This study shows valuable information regarding the role of Se on growth, photosynthetic process, and sugar accumulation in sugarcane leaves, which could be used for further field experiments. The application rate of 10 μmol Se L-1 was the most adequate for both varieties studied considering the sugar concentration and plant growth.

The alleviating effects and underlying mechanisms of exogenous selenium on both Sb(III) and Sb(V) toxicity in rice seedlings (Oryza sativa L.)

Selenium (Se) has been used to detoxify various heavy metals in plants. However, the effects and underlying mechanisms of exogenous Se application on the toxicity of antimonite [Sb(III)] and antimonate [Sb(V)] in crops are still poorly understood. Therefore, the potential alleviating roles of Se on the plant growth, antioxidant system, uptake and subcellular distribution of Sb, and expression of Sb-related genes were comprehensively investigated in rice seedlings (Oryza sativa L.) under both Sb(III) and Sb(V) stress conditions. The results showed that high concentrations of Sb(III) (100 µM) and Sb(V) (300 µM) caused a significant decrease in plant growth parameters, photosynthetic pigments and relative water content in rice seedlings. In contrast, the addition of Se (20 or 2 µM) improved rice growth, decreased Sb accumulation, and reduced oxidative stress in rice seedlings when exposed to 100 µM Sb(III) and 300 µM Sb(V), respectively. Furthermore, Se application could effectively improve the physiological adaptability of rice seedlings under Sb(III) and Sb(V) stress by regulating enzymatic and non-enzymatic antioxidant systems, Sb subcellular distribution and transcription levels of Sb-related genes, including in antioxidant response (OsCuZnSOD2, OsCATA and OsGSH1), detoxification (OsPCS1, OsPCS2 and OsABCC1) and Sb transport and sequestration (OsLsi1 and OsWAK11). Moreover, we also discovered that the mitigation effect of Se was dose-dependent and depended on Sb valence states. Thus, these findings contribute to our understanding of the mechanisms underlying Se-Sb antagonism in rice, offering a potentially useful method for producing both safe and Se-rich crops.

Allantoin alleviates chromium phytotoxic effects on wheat by regulating osmolyte accumulation, secondary metabolism, ROS homeostasis and nutrient acquisition

Allantoin is a nitrogen metabolite with significant potential to mediate plant defense responses under salinity. However, the impact of allantoin on ions homeostasis and ROS metabolism has yet to be established in plants under Cr toxicity. In the current study, chromium (Cr) notably diminished growth, photosynthetic pigments, and nutrient acquisition in two wheat cultivars (Galaxy-2013 and Anaj-2017). Plants subjected to Cr toxicity displayed excessive Cr accumulation. Chromium produced substantial oxidative stress reflected as higher levels of O₂^•, H₂O₂, MDA, methylglyoxal (MG) and lipoxygenase activity. Plants manifested marginally raised antioxidant enzyme activities due to Cr stress. Further, reduced glutathione (GSH) levels diminished with a concurrent rise in oxidized glutathione levels (GSSG). Plants exhibited a considerable abridge in GSH:GSSG due to Cr toxicity. Allantoin (200 and 300 mg L¹) subsided metal phytotoxic effects by strengthening the activities of antioxidant enzymes and levels of antioxidant compounds. Plants administered allantoin displayed a considerable rise in endogenous H₂S and nitric oxide (NO) levels that, in turn, lessened oxidative injury in Cr-stressed plants. Allantoin diminished membrane damage and improved nutrient acquisition under Cr stress. Allantoin markedly regulated the uptake and distribution of Cr in wheat plants, abridging the degree of metal phytotoxic effect.

Hydrogen sulfide alleviates chromium toxicity by promoting chromium sequestration and re-establishing redox homeostasis in Zea mays L

Hydrogen sulfide (H₂S) is a multifunctional gaseous signaling molecule involved in the regulation of Cr stress responses. In the present study, we combined transcriptomic and physiological analyses to elucidate the mechanism underlying the mitigation of Cr toxicity by H₂S in maize (Zea mays L.). We showed that treatment with sodium hydrosulfide (NaHS, a donor of H₂S) partially alleviated Cr-induced growth inhibition. However, Cr uptake was not affected. RNA sequencing suggested that H₂S regulates the expression of many genes involved in pectin biosynthesis, glutathione metabolism, and redox homeostasis. Under Cr stress, NaHS treatment significantly increased pectin content and pectin methylesterase activity; thus, more Cr was retained in the cell wall. NaHS application also increased the content of glutathione and phytochelatin, which chelate Cr and transport it into vacuoles for sequestration. Furthermore, NaHS treatment mitigated Cr-induced oxidative stress by enhancing the capacity of enzymatic and non-enzymatic antioxidants. Overall, our results strongly support that H₂S alleviates Cr toxicity in maize by promoting Cr sequestration and re-establishing redox homeostasis rather than by reducing Cr uptake from the environment.

Detoxification mechanisms of biochar on plants in chromium contaminated soil: Chromium chemical forms and subcellular distribution

The complete pathway of chromium (Cr) transfer from soil to plant tissues and subcellular components under biochar amendment remains to be quantified, as well as the involved diverse detoxification processes in roots and stems respectively. Pot experiments and quantitative analysis were conducted to investigate Cr fixation in soil amended with Enteromorpha prolifera-derived biochar and subsequent phytoprocesses (Cr uptake, transfer, and phytotoxicity) in cultivated Secale cereale L. (rye). The results indicated that adding 5-30 g kg^-1 of biochar increased the residual form of Cr (B4) in soil by 8-21% and decreased the bioavailable form of Cr (B1) by 9-29%. For Cr transferred to rye, Cr in the rye was mainly present in the low-toxicity bound state, with the acetic acid-extracted Cr (F4) (45-54%) in roots and the NaCl-extracted Cr (F3) (37-47%) in stems. The subcellular distribution of Cr in both roots and stems was predominantly in the cell wall and residues (T1), followed by the cytoplasm (T4). Partial least squares path model (PLS-PM) was used for quantifying the effect of biochar on the form changes and subcellular detoxification of Cr from soil to roots and stems to sub-cells. In soils, biochar reduced the bioavailability of Cr and decreased the transfer of Cr to rye. In plant roots, Cr was distributed mainly as low-toxicity phosphate complexes in cell walls and vacuoles in sub-cells (with the largest path coefficients of 0.90 and -0.91, respectively). In the stems, Cr was distributed mainly as proteins integrated into the cell walls and vacuoles. This was due to the difference in subcellular compartmentalization of detoxification in the roots and stems. These PLS-PM results provide new insights into the entire process of pollutant detoxification in complex environments.

Exogenous hydrogen sulfide alleviates chromium toxicity by modulating chromium, nutrients and reactive oxygen species accumulation, and antioxidant defence system in mungbean (Vigna radiata L.) seedlings

Chromium (Cr), a highly toxic redox-active metal cation in soil, seriously threatens global agriculture by affecting nutrient uptake and disturbing various physio-biochemical processes in plants, thereby reducing yields. Here, we examined the effects of different concentrations of Cr alone and in combination with hydrogen sulfide (H₂S) application on the growth and physio-biochemical performance of two mungbeans (Vigna radiata L.) varieties, viz. Pusa Vishal (PV; Cr tolerant) and Pusa Ratna (PR; Cr sensitive), growing in a pot in hydroponics. Plants were grown in the pot experiment to examine their growth, enzymatic and non-enzymatic antioxidant levels, electrolyte balance, and plasma membrane (PM) H⁺-ATPase activity. Furthermore, root anatomy and cell death were analysed 15 days after sowing both varieties in hydroponic systems. The Cr-induced accumulation of reactive oxygen species caused cell death and affected the root anatomy and growth of both varieties. However, the extent of alteration in anatomical features was less in PV than in PR. Exogenous application of H₂S promoted plant growth, thereby improving plant antioxidant activities and reducing cell death by suppressing Cr accumulation and translocation. Seedlings of both cultivars treated with H₂S exhibited enhanced photosynthesis, ion uptake, glutathione, and proline levels and reduced oxidative stress. Interestingly, H₂S restricted the translocation of Cr to aerial parts of plants by improving the nutrient profile and viability of root cells, thereby relieving plants from oxidative bursts by activating the antioxidant machinery through triggering the ascorbate-glutathione cycle. Overall, H₂S application improved the nutrient profile and ionic homeostasis of Cr-stressed mungbean plants. These results highlight the importance of H₂S application in protecting crops against Cr toxicity. Our findings can be utilised to develop management strategies to improve heavy metal tolerance among crops.

Biogeochemical behaviour and toxicology of chromium in the soil-water-human nexus: A review

Chromium (Cr) affects human health if it accumulates in organs to elevated concentrations. The toxicity risk of Cr in the ecosphere depends upon the dominant Cr species and their bioavailability in the lithosphere, hydrosphere, and biosphere. However, the soil-water-human nexus that controls the biogeochemical behaviour of Cr and its potential toxicity is not fully understood. This paper synthesizes information on different dimensions of Cr ecotoxicological hazards in the soil and water and their subsequent effects on human health. The various routes of environmental exposure of Cr to humans and other organisms are also discussed. Human exposure to Cr(VI) causes both carcinogenic and non-carcinogenic health effects via complicated reactions that include oxidative stress, chromosomal and DNA damage, and mutagenesis. Chromium (VI) inhalation can cause lung cancer; however, incidences of other types of cancer following Cr(VI) exposure are low but probable. The non-carcinogenic health consequences of Cr(VI) exposure are primarily respiratory and cutaneous. Research on the biogeochemical behaviour of Cr and its toxicological hazards on human and other biological routes is therefore urgently needed to develop a holistic approach to understanding the soil-water-human nexus that controls the toxicological hazards of Cr and its detoxification.