Phytoremediation of Cadmium Contaminated Soil Using Brassica juncea: Influence on PSII Activity, Leaf Gaseous Exchange, Carbohydrate Metabolism, Redox and Elemental Status

Growth and metabolic functions of Schizolobium amazonicum subjected to nickel doses

Anthropic activities such as industries, agriculture and mining has generated public concern for its numerous irregular disposals of its waste, the incorrect deposition of heavy metals such as nickel (Ni) has caused the degradation and contamination of groundwater and water. Studies that point out cheap and efficient solutions have been an obstacle to the advancement of solutions for degraded area recovery programs. For this, a vegetable home experiment was developed, with an entirely randomized design with 5 treatments being a control (no metal) and 4 nickel concentrations (200 μM/L; 400 μM/L; 600 μM/L and 800 μM/L) with 6 repetitions. The variables analyzed were growth and biochemical activity. Plant height and diameter were not affected by increasing nickel concentrations and this response was due to the low leaf and leaflet production capacity of the species under these conditions, consequently reducing biomass production. Metabolic parameters such as sucrose, carbohydrates, proline and glycine increase under stressful conditions, which does not occur for nutritional configurations that decrease with increasing nickel stress.

Similarities and differences in physiological adaptation to cadmium interactions with nitrogen levels between two aquatic iris life forms in urban wetlands

Plants play a key role in the ecological restoration of urban wetlands. Previous studies have shown that heavy-metal accumulation capacities and adaptation strategies of wetland plants may be related to their life forms. In this study, pot experiments were conducted to investigate the effects of nitrogen (N) on the adaptation strategies of two evergreen and deciduous aquatic iris life forms under cadmium (Cd) stress. Our results showed that Cd stress decreased the gas exchange parameters and biomass in both evergreen and deciduous irises. However, the interactions between N and Cd reversed this effect. Specifically, for deciduous irises, the shoot mass (SM) and root-to-shoot ratio (S/R) increased with higher N concentrations, whereas in evergreen irises, these parameters initially increased and then decreased as N levels increased, suggesting that the two life forms have different efficiencies in utilizing N. Additionally, under the combined stress of N and Cd, evergreen irises exhibited higher malondialdehyde (MDA) content and antioxidant enzyme activity than deciduous irises, whereas deciduous irises had higher chlorophyll content and aboveground biomass. These findings suggest that evergreen and deciduous irises employ distinct adaptive strategies to Cd toxicity; evergreen irises mitigate oxidative stress through enhanced reactive oxygen species (ROS) scavenging, whereas deciduous irises dilute Cd toxicity by increasing biomass. These results provide valuable insight into the use of different aquatic iris life forms for heavy-metal pollution remediation in wetlands.

Combined effects of heatwaves and atmospheric CO₂ levels on Brassica juncea phytoremediation

Heatwaves, expected to become more frequent, pose a significant threat to plant biomass production. This experiment was designed to estimate heatwave influence on Brassica juncea phytoremediation when superimposed on different CO2 levels. A 7-day heatwave was generated during the species flowering stage. Heatwaves decreased all B. juncea dry weights. The lowest species dry weight was recorded when the heatwave was accompanied by 250 ppm CO2, in which the biomass significantly decreased by 40.0% relative to that of no heatwave under the same atmospheric CO2 conditions. Heatwave superposition with 250 ppm CO2 reduced the Cd content in B. juncea aerial parts by 28.1% relative to that of identical environmental conditions without heatwave, whereas the opposite result was observed under 550 ppm CO2 conditions. The heatwave caused oxidative damage to B. juncea under all CO2 conditions, as manifested by increased malondialdehyde levels in the plant shoots. With heatwave superposition, antioxidant enzyme activity was enhanced by exposure to 400 and 550 ppm CO2. Considering biomass yield generation and Cd uptake capacity, heatwave superposition decreased the B. juncea phytoremediation effects, and high atmospheric CO2 conditions could alleviate detrimental effects to a certain extent. This study uniquely examines the combined effects of heatwaves and varying CO2 levels on phytoremediation, providing microscopic insights into oxidative damage and enzyme activity, highlighting the potential for CO2 enrichment to mitigate heatwave impacts, and offering comprehensive analysis for future agricultural practices and environmental management.

Unraveling the mechanisms behind sodium persulphate-induced changes in petroleum-contaminated aquifers' biogeochemical parameters and microbial communities

Sodium persulphate (PS) is a highly effective oxidising agent widely used in groundwater remediation and wastewater treatment. Although numerous studies have examined the impact of PS with respect to the removal efficiency of organic pollutants, the residual effects of PS exposure on the biogeochemical parameters and microbial ecosystems of contaminated aquifers are not well understood. This study investigates the effects of exposure to different concentrations of PS on the biogeochemical parameters of petroleum-contaminated aquifers using microcosm batch experiments. The results demonstrate that PS exposure increases the oxidation-reduction potential (ORP) and electrical conductivity (EC), while decreasing total organic carbon (TOC), dehydrogenase (DE), and polyphenol oxidase (PO) in the aquifer. Three-dimensional excitation-emission matrix (3D-EEM) analysis indicates PS is effective at reducing fulvic acid-like and humic acid-like substances and promoting microbial metabolic activity. In addition, PS exposure reduces the abundance of bacterial community species and the diversity index of evolutionary distance, with a more pronounced effect at high PS concentrations (31.25 mmol/L). Long-term (90 d) PS exposure results in an increase in the abundance of microorganisms with environmental resistance, organic matter degradation, and the ability to promote functional genes related to biological processes such as basal metabolism, transmission of genetic information, and cell motility of microorganisms. Structural equation modeling (SEM) further confirms that ORP and TOC are important drivers of change in the abundance of dominant phyla and functional genes. These results suggest exposure to different concentrations of PS has both direct and indirect effects on the dominant phyla and functional genes by influencing the geochemical parameters and enzymatic activity of the aquifer. This study provides a valuable reference for the application of PS in ecological engineering.

Phytoaccumulation of cadmium by Pelargonium × hortorum - tolerance and metal recovery

The main aim of the present study was to assess the removal of cadmium (Cd) from contaminated soil by using Pelargonium × hortorum - an ornamental plant. Furthermore, the genotoxic impacts of Cd on plant was evaluated, and accumulated Cd in shoots were recovered as Cd-nanoparticles. For this purpose, a pot experiment was carried out with Cd (0-150 mg/kg) spiked soil. P. hortorum was grown for 24 weeks in a greenhouse. Subsequently, harvested root/shoot biomass and Cd concentration in root/shoot were determined. The micronucleus assay was performed to assess the genotoxicity of Cd within the selected plant. Accumulated Cd in shoots was recovered as Cd-nanoparticles and was characterized by SEM and XRD. Exposure to Cd exhibited a phytotoxic impact by reducing the plant biomass, but plant survived at higher Cd concentrations and the tolerance index was greater than 60% at a higher Cd level (150 mg/kg). Moreover, 257 mg/kg of Cd in aerial parts was observed, and maximum Cd uptake (120 mg plant^-1) by P. hortorum was found at 150 mg/kg Cd. Plants exposed to Cd exhibited genotoxic impact by increasing the number of micronuclei by 59% at a higher Cd level (150 mg/kg) and the mitotic index was reduced by 20%. Furthermore, recovered nanoparticles were spherically shaped with an average size of 36.2-355 nm. The plant has potential for the removal of Cd and has exhibited good tolerance.

Cadmium phytoremediation potential of Brassica genotypes grown in Cd spiked Loamy sand soils: Accumulation and tolerance

Phytoremediation acts as an efficient methodology for management of toxic elements spiked soils. The accumulation and tolerance potential of hyper-accumulator plants for toxic elements act as an index for in-situ removal of toxic elements. Extraction of cadmium (Cd) through its accumulation in harvestable parts of plants has attracted attention as the economic and environment friendly technique. Brassica genotypes have greater potential to accumulate Cd when grown in Cd spiked soils. Therefore, for evaluation of comparative efficiency of three Brassica genotypes (B. juncea, B. campestris and B. napus) in phytoremediation of Cd spiked soils, a pot study was carried out in Cd contaminated soil with 6 levels as 0, 5, 10, 20, 40, and 80 mg kg^-1 soil. Results indicated that dry biomass production of Brassica genotypes declined with the enhanced Cd contamination in soil. The reduction in grain and shoot yield varied from 2.87 to 1.85 and 11.85 to 8.00 g pot^-1 with increased Cd contamination from 5 to 80 mg kg^-1 soil. Similarly, increased levels of Cd contamination resulted in enhanced concentration and accumulation in grains as well as shoots of all Brassica genotypes. Among Brassica genotypes, B. juncea recorded the highest production of dry biomass (12.8 g pot^-1), Cd accumulation (736.0 μg pot^-1). Also, the bioaccumulation coefficient and tolerance index indicated that B. juncea is the most tolerant genotype to Cd contamination in soil. Therefore, B. juncea could act as the most potential genotypes for decontamination of Cd spiked soils by preventing its entry into food chain.

Auxin regulates growth, photosynthetic efficiency and mitigates copper induced toxicity via modulation of nutrient status, sugar metabolism and antioxidant potential in Brassica juncea

The involvement of auxin (IAA) in growth and development of plants is well known, but its role in the mitigation of metal stress, especially copper (Cu), is not fully understood; therefore, it is time to explore its involvement in minimizing the stress. A pot experiment was conducted to assess the protective function of IAA, applied to the foliage, on photosynthetic machinery, carbohydrate metabolism, and growth of Brassica juncea, grown with Cu (30 or 60 mg kg^-1 of soil). Among the different concentrations (10^-10, 10^-8, or 10^-6 M), 10^-8 M of IAA alone enhanced the photosynthetic characteristics, sugar accumulation and vegetative growth with minimal cellular oxidative stress level. Moreover, the same concentration of auxin was most effective in decreasing the stress levels generated by Cu and maintained it nearly to that of the control in terms of photosynthetic attributes, gas exchange parameters, PSII activity, electron transport rate, and growth attributes. Auxin also maintained the membrane stability and ultrastructure of chloroplast, stomatal morphology with a reduction in malondialdehyde (MDA), electrolyte leakage (EL) and cell death in test plants even under Cu stress. IAA also improved the translocation of Cu from root to the aerial parts, thus enhanced the Cu-reclamation in metal contaminated soils. Our findings suggest that the application of 10^-8 M of IAA maintains the overall growth of plants and may be used as an effective agent to improve growth, photosynthesis and phyto-remediation potential of B. juncea in Cu contaminated soil.

The elemental defense effect of cadmium on Alternaria brassicicola in Brassica juncea

BACKGROUND

The elemental defense hypothesis states a new defensive strategy that hyperaccumulators defense against herbivores or pathogens attacks by accumulating heavy metals. Brassica juncea has an excellent ability of cadmium (Cd) accumulation. However, the elemental defense effect and its regulation mechanism in B. juncea remain unclear.

RESULTS

In this study, we profiled the elemental defense effect and the molecular regulatory mechanism in Cd-accumulated B. juncea after Alternaria brassicicola infection. B. juncea treated with 180 mg Kg^- 1 DW CdCl₂ 2.5H₂O exhibited obvious elemental defense effect after 72 h of infection with A. brassicicola. The expression of some defense-related genes including BjNPR1, BjPR12, BjPR2, and stress-related miRNAs (miR156, miR397, miR398a, miR398b/c, miR408, miR395a, miR395b, miR396a, and miR396b) were remarkably elevated during elemental defense in B. juncea.

CONCLUSIONS

The results indicate that Cd-accumulated B. juncea may defend against pathogens by coordinating salicylic acid (SA) and jasmonic acid (JA) mediated systemic acquired resistance (SAR) and elemental defense in a synergistic joint effect. Furthermore, the expression of miRNAs related to heavy metal stress response and disease resistance may regulate the balance between pathogen defense and heavy metal stress-responsive in B. juncea. The findings provide experimental evidence for the elemental defense hypothesis in plants from the perspectives of phytohormones, defense-related genes, and miRNAs.

Activation of antioxidative and detoxificative systems in Brassica juncea L. plants against the toxicity of heavy metals

Plant metal hyperaccumulators, to which Brassica juncea belongs, must have very efficient defence mechanisms that enable growth and development in an environment polluted with various heavy metals. B. juncea (Indiana mustard) v. Małopolska was exposed to the activity of trace elements such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in combinations: CuPb, CuCd, CuZn, PbCd, PbZn, and ZnCd in a concentration of 25 μM each for 96 h during control cultivation. We observed a clear tendency for metal uptake and accumulation in above-ground parts which is characteristic of hyperaccumulators. The combinations of CuCd, CuZn, and PbCd inhibited the development of the seedlings the most. The used metal combinations increased the levels of reactive oxygen species (ROS) such as: hydrogen peroxide (H₂O₂), superoxide anion (O₂^.-) and oxidized proteins in B. juncea organs, generating oxidative stress conditions in the cells. We determined the level of transcription of the respective defence proteins of the detoxification and antioxidant systems. We have shown that in the first 24 h of stress condiction, activation of glutamylcysteine-γ synthetase (yECS) and glutathione reductase (GR1) enzymes related to the detoxification of heavy metals is important for B. juncea plants. In addition, the data provide important information on how plants respond to the presence of heavy metals in the first days of stress conditions.

Targeting Cd coping mechanisms for stress tolerance in Brassica napus under spiked-substrate system: from physiology to remediation perspective

Cadmium (Cd) is a prevalent, non-essential, carcinogenic, and hazardous heavy metal that reduces plant productivity and capacity of arable land area around the globe. In the present substrate-based pot study, seedlings of Brassica napus 180015 were grown equidistantly in the spiked-substrate medium for 60 days under increasing concentrations of Cd (0, 10, 20, 30, 40, 50 mg kg^-1). Following harvest, the morpho-physio-biochemical, antioxidative, and Cd-induced tolerance responses were evaluated in B. napus under an increasing Cd stress regime. Additionally, these parameters were also investigated to select the plant's threshold tolerance limit for Cd under the spiked-substrate system. B. napus showed dynamic behavior regarding morpho-physio-biochemical attributes, including agronomic features, biomass, photosynthetic pigments, relative water content under increased Cd toxicity. Cd stress-induced hydrogen peroxide (H₂O₂) production with high MDA contents and passive EL, followed by the orchestration of both enzymatic (SOD, POD, APX, CAT, and GR) and non-enzymatic antioxidants (flavonoids, TPC, TPA, proline, and total soluble protein) up to a certain limit. In addition, Cd-induced stress upregulated transcriptional levels of antioxidative enzyme SOD, POD, APX, GR, and MT encoded genes in B. napus. The increasing trend of Cd accumulation in different tissues at the highest Cd concentration was as follows: root > leaf > stem. In spiked substrate system, B. napus demonstrated improved metal extractability performance and a high potential for phyto-management of low to moderate Cd contamination, implying that this study could be used for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.Novelty statementThis study provides an insight into Cd-coping mechanisms of oilseed rape involved in alleviating toxicity and simultaneous phyto-management of increasing Cd concentration under spiked substrate system. The current study is the first scientific evidence of using a Cd-spiked soilless substrate medium. The present study will further strengthen our understanding of Cd-instigated positive responses in B. napus. Furthermore, it will provide a useful basis for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.

Photosynthesis, lipid peroxidation, and antioxidative responses of Helianthus annuus L. against chromium (VI) accumulation

The present study was performed to address how Cr(VI) posed its toxicities on photosynthesis, lipid peroxidation, and its retaliation by antioxidative system of Helianthus annuus L. during Cr(VI) accumulation. For this, a pot experiment was performed wherein three different concentrations viz, 15, 30, and 60 mg Cr(VI) kg-1 soil were applied to Helianthus annuus L. at the time of seeds sowing. The results revealed that Cr(VI) accumulation was two to three folds higher in roots than in shoots which suggests that root is the major site for Cr(VI) accumulation. It was observed that with increasing doses of Cr(VI), growth indices hampered significantly, along with closure of stomata and damaged guard and epidermal cells. Photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), leaf gaseous exchange parameters (A, E, GH2O), and PSII efficiency (Fv/Fm) worsened under Cr(VI) toxicity in dose dependent manner. Cr(VI) accumulation intensified the lipid peroxidation, too by triggering the MDA and H2O2 production, however, the plant responded well against the lipid peroxidation by enhancing the coordinated action of enzymatic (SOD, APX, GR) and non-enzymatic (GSH, AsA) antioxidants. In a nutshell, Helianthus annuus L. could be used as a potential Cr(VI) accumulator because of its good tolerance strategies against Cr(VI) toxicities.NOVELTY STATEMENT The results revealed that Cr(VI) accumulation was two to three folds higher in roots than in shoots which suggests that root is the major site for Cr(VI) accumulation. Photosynthetic pigments, leaf gaseous exchange parameters, and Fv/Fm worsened under Cr(VI) toxicity. Cr(VI) accumulation intensified lipid peroxidation by triggering MDA and H2O2 production, however, the plant responded well against the lipid peroxidation by enhancing the coordinated action of enzymatic and non-enzymatic antioxidants. In a nutshell, Helianthus annuus L. could be used as a potential Cr(VI) accumulator because of its good tolerance strategies against Cr(VI) toxicities.

Phytoremediation of Cadmium Contaminated Soil: Impacts on Morphological Traits, Proline Content and Stomata Parameters of Sweet Sorghum Seedlings

Phytoremediation is a green, simple, eco-friendly, sustainable, and cost-effective remediation technology to remove and degrade contaminants from soil. In this study, a germination experiment and a pot experiment were performed in greenhouse to evaluate cadmium toxicity and phytoremediation capacity. The results showed that there was the highest membership function value of cadmium (MFVC) in KFJT-3 than that of KFJT-CK and KFJT-1, the value being 0.473, 0.456 and 0.413, respectively. Furthermore, the highest biomass was discovered in KFJT-3 compared to the other genotypes under 50 mg/kg cadmium stress. Physiological analysis showed that proline content significantly increased in KFJT-3, the value being 31.88%. In addition, Bioaccumulation factor (BAF) and Translocation factor (TF) value were 3.80 and 1.02 for KFJT-3, respectively. In conclusion, BAF and TF values showed that the cadmium tolerance of KFJT-1 and KFJT-3 could be higher than that of KFJT-CK, which could be the genotype for phytoremediation of cadmium contaminated soil.