Soil Sulfur Sources Differentially Enhance Cadmium Tolerance in Indian Mustard (Brassica juncea L.)

Impact of different sulfur sources on cadmium accumulation and metabolic responses of glutathione and cysteine in peppers

BACKGROUND

Sulfur (S) is essential for life while cadmium (Cd) is known to be both extremely toxic and ubiquitous in natural environments. Interactions between S and Cd from soil to plant could provide insights into the dynamics of environmental contaminants and the mechanisms of regulation. Geological sulfur from pyrite (FeS2) and atmospheric sulfur from coal combustion deposits (H2SO4) significantly affect soil acidification, potentially increasing the bioavailability of Cd. To investigate the influence of different sulfur sources on cadmium (Cd) uptake, transfer, accumulation, and the regulation of physiological responses in pepper, we conducted a controlled pot experiment. The study utilized yellow soil and 'Z2' line pepper (Capsicum spp.) as the test plant. We assessed the fresh weight, Cd concentration in various plant parts, and the levels of reduced glutathione (GSH) and cysteine (Cys) during the fruiting phase under varying concentrations of Cd.

RESULTS

Under Cd stress, supplementation with FeS2 and H2SO4 markedly enhanced pepper growth, increasing biomass by over 30%. Among these, geological sulfur (FeS2) demonstrated a more pronounced effect compared to H2SO4. Overall, the cadmium content of each part of FeS2 treatment was lower than H2SO4 under cadmium-induced stress. And at medium cadmium level, a concentration of 100 mg/kg of FeS2 resulted in a 16.51% relative reduction in fruit Cd content from 2.12 mg/kg in the 1.5 mg/kg Cd treatment to 1.78 mg/kg. Both sulfur sources increased GSH and Cys content, particularly under high Cd stress, with FeS2 raising GSH and Cys levels by 3.33-61.87% and 43.29-71.94%, H2SO4 increased 15.65-66.43% and 48.02-74.58%, respectively (P ≤ 0.05). The highest GSH content occurred in leaves, whereas fruits had the highest Cys content.

CONCLUSION

FeS2 and H2SO4 can promote pepper growth and enhancing the synthesis of GSH and Cys, which mitigates Cd toxicity. On the whole, the cadmium content of each part of FeS2 treatment was lower than H2SO4 under cadmium stress conditions.

Starvation from within: How heavy metals compete with essential nutrients, disrupt metabolism, and impair plant growth

Nutrient starvation is a critical consequence of heavy metal toxicity, severely impacting plant health and productivity. This issue arises from various sources, including industrial activities, mining, agricultural practices, and natural processes, leading to the accumulation of metals such as aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni) in soil and water. Heavy metal exposure disrupts key physiological processes, particularly nutrient uptake and transport, resulting in nutrient imbalances within the plant. Essential nutrients are often unavailable or improperly absorbed due to metal chelation and interference with transporter functions, exacerbating nutrient deficiencies. This nutrient starvation, coupled with oxidative stress induced by heavy metals, manifests in impaired photosynthesis, stunted growth, and reduced crop yields. This review presents important insights into the molecular mechanisms driving nutrient deprivation in plants exposed to heavy metals, emphasizing the roles of transporters, transcription factors, and signaling pathways. It also examines the physiological and biochemical effects, such as chlorosis, necrosis, and altered metabolic activities. Lastly, we explore strategies to mitigate heavy metal-induced nutrient starvation, including phytoremediation, soil amendments, genetic approaches, and microbial interventions, offering insights for enhancing plant resilience in contaminated soils.

Deposition of sulfur by Spartina alterniflora promoted its ecological adaptability in cadmium-polluted coastal wetlands

Invasive Spartina alterniflora poses a significant threat to coastal wetland ecosystems. This study investigated the role of sulfur (S) in facilitating the invasion of S. alterniflora in cadmium (Cd)-contaminated coastal wetlands by greenhouse-control-experiment. Results demonstrate that increased S deposition significantly enhanced the formation of acid-volatile sulfur in sediments, thereby reducing the bioavailability of Cd to plants by 41%. Additionally, S supplementation improved plant nutrient uptake and stress tolerance by increasing the C/N ratio and the concentrations of essential mineral elements. These physiological and biochemical changes, including enhanced photosynthesis, increased carbohydrate storage, and improved antioxidant capacity, ultimately contributed to increased shoot and root biomass production by 15% and 31% respectively, and the competitive ability of S. alterniflora. The findings of this study highlight the critical role of S in promoting the invasion of S. alterniflora. Effective strategies can be developed to control the spread of S. alterniflora and protect coastal ecosystems.

Toxicity of copper oxide nanoparticles in barley: induction of oxidative stress, hormonal imbalance, and systemic resistances

BACKGROUND

Over the years, nanoparticles have emerged as a promising approach for improving crop growth, yield, and overall agricultural sustainability. However, there has been growing concern about the potential adverse effects of nanoparticles in the agricultural sector and the environment. The present study aimed to investigate the detrimental effects of high (1000 mg L-1) concentrations of copper oxide nanoparticles (CuO NPs) on barley seedlings. The equivalent concentrations of CuO bulk and the ionic form of copper were also used in the experiments for comparative analysis. CuO NPs were characterized by Field Emission-Scanning Electron Microscopy, Dynamic Light Scattering, Zeta Potential analysis, and X-ray Diffraction prior to the application. Barley seedlings were subjected to the foliar application of CuO NP, CuO bulk, ionic Cu, and control group. The presence of CuO NPs in barley leaves was confirmed 72 hours after treatment by energy-dispersive X-ray analysis.

RESULTS

The results showed a CuO NPs treatment led to an impairment of nutrient balance in barley leaves. An increase in hydrogen peroxide content followed by the higher specific activity of catalase and ascorbate peroxidase was also observed in response to CuO NPs, CuO bulk, and Cu2+ ions. The profile of phytohormones including auxins (IAA and IBA), Gibberellins (GA1, GA4, and GA9), abscisic acid (ABA), ethylene (ET), and jasmonic acid (JA) significantly affected by CuO NPs, CuO bulk, and Cu2+ ions. The transcripts of the PR1 gene involved in systemic acquired resistance (SAR) and LOX-1 and PAL involved in induced systemic resistance (ISR) were significantly upregulated in response to CuO NPs treatment.

CONCLUSION

Our findings suggest that the systemic resistances in barley seedlings were induced by higher accumulation of ABA, ET, and JA under CuO NPs treatment. The activation of systemic resistances indicated the involvement of both SAR and SAR pathways in the response to CuO NPs in barley.

Time series analysis of uptake and translocation of Cd and expression of transporter genes in nine Andrographis paniculata accessions

Cadmium is a non-essential and toxic metal. Its presence in plants can have hazardous effects not only on the plants themselves but also on human health after consumption. A time-dependent experiment was conducted on nine accessions of A. paniculata (AP1, AP2, AP3, AP8, AP11, AP12, AP21, AP25, and CIM) in Cd-contaminated soil to understand the variability of Cd accumulation. The study examined the Cd uptake, translocation, antioxidant stress enzymes, ionic composition of root exudates, Cd bioavailability, and expression of transporter genes PCR, NRAMP, ABCC, HMA, and HIPP. Results demonstrated the lowest bio-concentration factor for Cd in AP1 and CIM (0.34-1.04). A significant increase in bio-concentration (6-37%), bioaccumulation (25-80%), and translocation (6-52%) of Cd was observed in nine accessions with time. However, AP1, AP8, AP11, and CIM demonstrated a significant decrease in bio-concentration (7-38%), bioaccumulation (14-50%), and translocation (8-45%) of Cd with time. The differential Cd uptake among the accessions was major associated with antioxidant enzyme activities, root exudates, Cd bioavailability, and biomass. The differential expression of Cd influx (ApNRAMP3 and ApNRAMP5) and efflux (ApPCR2, ApPCR6, ApPCR8, and ApPCR11) transporter genes was observed with time. According to the results, low accumulating accessions AP1, AP8, AP11, and CIM had higher biomass (10-46%) and lower Cd uptake (7-38%) than high accumulating accessions. These accessions also had minimal stress enzyme activities and a prevalence of cations in root exudates, which impeded Cd bioavailability (8-26%) and increased microbial biomass carbon (7-31%). The upregulation of ApPCR2, ApPCR6, ApPCR8, ApPCR11, ApHMA3, ApABCC3, ApABCC5, ApHIPP3.1, and ApHIPP3.2 while downregulation of ApNRAMP3, ApNRAMP5, and ApHMA1 genes further modulated Cd uptake and tolerance in low accumulating accessions.

Ethylene Is Crucial in Abscisic Acid-Mediated Modulation of Seed Vigor, Growth, and Photosynthesis of Salt-Treated Mustard

The current study explored the differential interaction between ethylene (ET) and abscisic acid (ABA) in relation to salt stress in mustard (Brassica juncea L.) plants. Significant reductions in seed germination, growth, and photosynthesis were observed with 100 mmol NaCl. Among the cultivars tested, the Pusa Vijay cultivar was noted as ET-sensitive. Pusa Vijay responded maximally to an application of 2.0 mmol ethephon (Eth; 2-chloethyl phosphonic acid-ethylene source), and exhibited the greatest growth, photosynthesis, activity of 1-aminocyclopropane carboxylic acid (ACC) synthase (ACS), and ET evolution. Notably, Eth (2.0 mmol) more significantly improved the seed germination percentage, germination and vigor index, amylase activity, and reduced H2O2 content under salt stress, while ABA (25 µmol) had negative effects. Moreover, the individual application of Eth and ABA on Pusa Vijay under both optimal and salt-stressed conditions increased the growth and photosynthetic attributes, nitrogen (N) and sulfur (S) assimilation, and antioxidant defense machinery. The addition of aminoethoxyvinylglycine (0.01 µmol AVG, ET biosynthesis inhibitor) to ABA + NaCl-treated plants further added to the effects of ABA on parameters related to seed germination and resulted in less effectiveness of growth and photosynthesis. In contrast, the effects of Eth were seen with the addition of fluoridone (25 µmol Flu, ABA biosynthesis inhibitor) to Eth + NaCl. Thus, it can be suggested that ET is crucial for alleviating salt-induced inhibition in seed germination, growth, and photosynthesis, while ABA collaborated with ET to offer protection by regulating nutrient assimilation and enhancing antioxidant metabolism. These findings provide insight into the complex regulatory processes involved in ET-ABA interaction, enhancing our understanding of plant growth and development and the mitigation of salt stress in mustard. It opens pathways for developing hormonal-based strategies to improve crop productivity and resilience, ultimately benefiting agricultural practices amidst a challenging environment.

The effect of sulphur supplementation on cadmium phytotoxicity in wheat and lettuce: changes in physiochemical properties of roots and accumulation of phytochelatins

Intensive sulphur fertilisation has been reported to improve the nutrient balance and growth of Cd-exposed plants, but the reasons of this phenomenon and the role of sulphur compounds in the resistance to cadmium are unclear. We investigated sulphur supplementation-induced changes in the surface properties of roots and the level of thiol peptides (PCs) in Cd-stressed Triticum aestivum L. (monocots clade) and Lactuca sativa L. (dicots clade) grown in nutrient solution. The combination of three sulphur (2 mM S-basic level, 6 or 9 mM S-elevated levels) and four cadmium (0, 0.0002, 0.02 or 0.04 mM Cd) concentrations was used. The physicochemical parameters of the roots were determined based on the apparent surface area (Sr), total variable surface charge (Q), cation exchange capacity (CEC) and surface charge density (SCD). In Cd-exposed plants supplied with sulphur, a different character and trend in the physicochemical changes (adsorption and ion exchange) of roots were noted. At the increased sulphur levels, as a rule, the Sr, CEC, Q and SCD values clearly increased in the lettuce but decreased in the wheat in the entire range of the Cd concentrations, except the enhanced Sr of wheat supplied with 6 mM S together with elevated (0.0002 mM) and unchanged (0.02, 0.04 mM Cd) value of this parameter at 9 mM S. This indicates a clade-specific and/or species-specific plant reaction. The 6 mM S appears to be more effective than 9 mM S in alleviation of the cadmium's toxic effects on roots. It was found that at 0.02 and 0.04 mM Cd, the use of 6 mM S limits the Cd accumulation in the roots of both species in comparison with the basic S fertilisation. Moreover, PC accumulation was much more efficient in wheat than in lettuce, and intensive sulphur nutrition generally induced biosynthesis of these chelating compounds. Physicochemical parameters together with quantitative and qualitative assessment of thiol peptides can be important indicators of the efficiency of root system functioning under cadmium stress. The differences between the species and the multidirectional character of the changes are a result of the involvement of a number of multi-level mechanisms engaged in the defence against metal toxicity.

Exogenously-Sourced Salicylic Acid Imparts Resilience towards Arsenic Stress by Modulating Photosynthesis, Antioxidant Potential and Arsenic Sequestration in Brassica napus Plants

In the current study, salicylic acid (SA) assesses the physiological and biochemical responses in overcoming the potential deleterious impacts of arsenic (As) on Brassica napus cultivar Neelam. The toxicity caused by As significantly reduced the observed growth and photosynthetic attributes and accelerated the reactive oxygen species (ROS). Plants subjected to As stress revealed a significant (p ≤ 0.05) reduction in the plant growth and photosynthetic parameters, which accounts for decreased carbon (C) and sulfur (S) assimilation. Foliar spray of SA lowered the oxidative burden in terms of hydrogen peroxide (H2O2), superoxide anion (O2•-), and lipid peroxidation in As-affected plants. Application of SA in two levels (250 and 500 mM) protected the Brassica napus cultivar from As stress by enhancing the antioxidant capacity of the plant by lowering oxidative stress. Among the two doses, 500 mM SA was most effective in mitigating the adverse effects of As on the Brassica napus cultivar. It was found that SA application to the Brassica napus cultivar alleviated the stress by lowering the accumulation of As in roots and leaves due to the participation of metal chelators like phytochelatins, enhancing the S-assimilatory pathway, carbohydrate metabolism, higher cell viability in roots, activity of ribulose 1, 5-bisphosphate carboxylase (Rubisco), and proline metabolism through the active participation of γ-glutamyl kinase (GK) and proline oxidase (PROX) enzyme. The current study shows that SA has the capability to enhance the growth and productivity of B. napus plants cultivated in agricultural soil polluted with As and perhaps other heavy metals.

Protective mechanisms of sulfur against arsenic phytotoxicity in Brassica napus by regulating thiol biosynthesis, sulfur-assimilation, photosynthesis, and antioxidant response

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S⁰) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg^-1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26-11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26-11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S⁰, 100 or 200 mg S kg^-1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S⁰ also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O₂^•-) and H₂O₂, hydrogen peroxide, in As affected plants. In general, S⁰ at 200 mg kg^-1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S⁰ at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H₂S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H₂S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S⁰ as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils.

Perspective of Melatonin-Mediated Stress Resilience and Cu Remediation Efficiency of Brassica juncea in Cu-Contaminated Soils

The present study evaluated the influence of melatonin (MEL) on copper toxicity in terms of morphophysiological, microscopic, histochemical, and stress resilience responses in Brassica juncea. Different levels of Cu (0, 30, and 60 mg kg-1) were given in air-dried soil, and 25 days after sowing (DAS), plants were sprayed with 30, 40, or 50 μM of MEL. The results demonstrated that under Cu stress, a significant amount of Cu accumulated in plant tissues, particularly in roots than in upper ground tissues, thereby suppressing the overall growth as evidenced by decrease in tolerance index and photosynthesis and increase in oxidative stress biomarkers (reactive oxygen species, malondialdehyde, and electrolyte leakage content) and cell death. Interestingly, the follow-up treatment of MEL, mainly 40 μM, efficiently improved the physio-biochemical and growth parameters, sugar accumulation, and metabolism. The potential of MEL in modulating Cu stress is attributed to its involvement in enriching the level of nutrient and improving chloroplast and stomatal organization besides lowering oxidative stress via enhanced levels of antioxidants. MEL improved the Cu reclamation potential in plants by enhancing Cu uptake and its translocation to aerial tissues. Principal component analysis showed that most of the morphophysiological and growth attributes were positively linked with MEL and negatively related to Cu levels, whereas all the stress-enhancing attributes showed a strong relationship with excessive Cu levels in soils. The present study suggested that MEL has the potential to improve growth and photosynthesis resulting in improved stress resilience under Cu stress along with increased remediation capability of mustard for remediation of Cu-contaminated soils.

Ethylene-nitrogen synergism induces tolerance to copper stress by modulating antioxidant system and nitrogen metabolism and improves photosynthetic capacity in mustard

This study aimed to test the efficiency of ethylene (Eth; 200 µL L^-1 ethephon) in presence or absence of nitrogen (N; 80 mg N kg^-1 soil) in protecting photosynthetic apparatus from copper (Cu; 100 mg Cu kg^-1 soil) stress in mustard (Brassica juncea L.) and to elucidate the physio-biochemical modulation for Eth plus N-induced Cu tolerance. Elevated Cu-accrued reductions in photosynthesis and growth were accompanied by significantly higher Cu accumulation in leaves and oxidative stress with reduced assimilation of N and sulfur (S). Ethylene in coordination with N considerably reduced Cu accumulation, lowered lipid peroxidation, lignin accumulation, and contents of reactive oxygen species (hydrogen peroxide, H₂O₂, and superoxide anion, O₂^•-), and mitigated the negative effect of Cu on N and S assimilation, accumulation of non-protein thiols and phytochelatins, enzymatic, and non-enzymatic antioxidants (activity of ascorbate peroxidase, APX, and glutathione reductase, GR; content of reduced glutathione, GSH, and ascorbate, AsA), cell viability, photosynthesis, and growth. Overall, the effect of ethylene-nitrogen synergism was evident on prominently mitigating Cu stress and protecting photosynthesis. The approach of supplementing ethylene with N may be used as a potential tool to restrain Cu stress, and protect photosynthesis and growth of mustard plants.

Phytoextraction of Heavy Metals by Various Vegetable Crops Cultivated on Different Textured Soils Irrigated with City Wastewater

A challenging task in urban or suburban agriculture is the sustainability of soil health when utilizing city wastewater, or its dilutes, for growing crops. A two-year field experiment was conducted to evaluate the comparative vegetable transfer factors (VTF) for four effluent-irrigated vegetable crops (brinjal, spinach, cauliflower, and lettuce) grown on six study sites (1 acre each), equally divided into two soil textures (sandy loam and clay loam). Comparisons of the VTF factors showed spinach was a significant and the best phytoextractant, having the highest heavy metal values (Zn = 20.2, Cu = 12.3, Fe = 17.1, Mn = 30.3, Cd = 6.1, Cr = 7.6, Ni = 9.2, and Pb = 6.9), followed by cauliflower and brinjal, while lettuce extracted the lowest heavy metal contents (VTF: lettuce: Zn = 8.9, Cu = 4.2, Fe = 9.6, Mn = 6.6, Cd = 4.7, Cr = 2.9, Ni = 5.5, and Pb = 2.5) in response to the main (site and vegetable) or interactive (site * vegetable) effects. We suggest that, while vegetables irrigated with sewage water may extract toxic heavy metals and remediate soil, seriously hazardous/toxic contents in the vegetables may be a significant source of soil and environmental pollution.