Phytoextraction of contaminated urban soils by Panicum virgatum L. enhanced with application of a plant growth regulator (BAP) and citric acid

Foliar application of plant growth regulators for enhancing heavy metal phytoextraction efficiency by Sedum alfredii Hance in contaminated soils: Lab to field experiments

The phytoremediation efficiency of plants in removing the heavy metals (HMs) might be influenced by their growth status and accumulation capacity of plants. Herein, we conducted a lab-scale experiment and a field try out to assess the optimal plant growth regulators (PGRs) including indole-3-acetic acid (IAA)/brassinolide (BR)/abscisic acid (ABA) in improving the phytoextraction potential of Sedum alfredii Hance (S. alfredii). The results of pot experiment revealed that application of IAA at 0.2 mg/L, BR at 0.4 mg/L, and ABA at 0.2 mg/L demonstrated notable potential as optimal dosage for Cd/Pb/Zn phytoextraction in S. alfredii. The findings of subcellular level of Cd/Pb/Zn in leaves showed that IAA (0.2 mg/L), BR (0.4 mg/L) or ABA (0.2 mg/L) promoted the HMs storage in the soluble and cell wall fraction, therefore contributing HMs subcellular compartmentation. In addition, application of PGRs notably enhanced the antioxidant system (SOD, CAT, POD, APX activities) while reducing lipid peroxidation (MDA content) in S. alfredii, consequently improving HMs tolerance and growth of S. alfredii. Moreover, the results of field trial showed that application of BR, IAA, or ABA+BR substantially improved the growth of S. alfredii by inducing plants biomass and augmenting the levels of photosynthetic pigment contents. Notably, ABA+BR noticed the highest theoretical biomass by 42.9 %, followed by IAA (41.6 %), and BR (36.4 %), as compared with CK. Additionally, ABA+BR treatment showed effectiveness in removing the Cd by 103.4 %, while BR and IAA led to a significant increase of Pb and Zn removal by 239 % and 116 %, respectively, when compared with CK. Overall, the results of this study highlights that the foliar application of IAA, BR, or ABA+BR can serve as viable strategy to boosting phytoremediation efficiency of S. alfredii in contaminated soil by improving the biomass and metal accumulation in harvestable parts.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

In recent years, the use of plant hormones, such as abscisic acid (ABA) and 6-benzylaminopurine (6-BAP), has gained significant attention for their role in mitigating abiotic stresses across various plant species. These hormones have been shown to play a vital role in enhancing the ascorbate-glutathione cycle and eliciting a wide range of plant growth and biomass, photosynthetic efficiency, oxidative stress and response of antioxidants and other physiological responses. While previous research has been conducted on the individual impact of ABA and 6-BAP in metal stress resistance among various crop species, their combined effects in the context of heavy metal-stressed conditions remain underexplored. The current investigation is to assess the beneficial effects of single and combined ABA (5 and 10 μM L-1) and 6-BAP (5 and 10 μM L-1) applications in rice (Oryza sativa L.) cultivated in chromium (Cr)-contaminated soil (100 μM). Our results showed that the Cr toxicity in the soil showed a significant declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, Cr toxicity significantly increased oxidative stress biomarkers, organic acids, enzymatic and non-enzymatic antioxidants including their gene expression in O. sativa seedlings. Although, the application of ABA and 6-BAP showed a significant increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, And Cr uptake. In addition, individual or combined application of ABA and 6-BAP enhanced the cellular fractionation and decreases the proline metabolism and AsA-GSH cycle in rice plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Effect of citric acid on phytoextraction potential of Cucurbita pepo, Lagenaria siceraria, and Raphanus sativus plants exposed to multi-metal stress

Phytoextraction is a novel technique that involves using plants to remove heavy metals from contaminated soils. An outdoor pot experiment was designed to evaluate the phytoextraction potential of three plant species Cucurbita pepo, Lagenaria siceraria, and Raphanus sativus in soil contaminated with multiple metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) under the application of citric acid. The results showed that Raphanus sativus, out of all the studied plants, had the highest root and shoot dry weight and the capacity to accumulate all heavy metals at higher concentrations except for Cu. The application of citric acid into the polluted soil significantly increased plant growth, biomass, and heavy metal uptake. High bioconcentration values indicate that Raphanus sativus is a promising plant for absorbing and accumulating Cd and Ni from the soil. The maximum values of bioconcentration were also observed by the application of citric acid. The values of metal translocation from the root to the shoot were varied by plant species and the citric acid application. Regarding the biomass, metal content, as well as removal metal percentage values, it became apparent that the Raphanus sativus plant was the most effective crop in removing heavy metals from multi-metal contaminated Soil. Generally, these findings emphasize that the application of citric acid could be a useful approach to assist Cd and Ni phytoextraction by Raphanus sativus plants. When these plants are growing as vegetable crops, more attention should be given to evaluating the heavy metal content in them, especially when adding citric acid to their soil through fertigation systems to avoid food chain contamination.

The effect of combined drought and trace metal elements stress on the physiological response of three Miscanthus hybrids

Drought is a serious threat worldwide and has a significant impact on agricultural production and soil health. It can pose an even greater threat when it involves land contaminated with trace metal element (TMEs). To prevent desertification, such land should be properly managed and growing Miscanthus for energy or raw material purposes could be a solution. The effects of drought and TMEs were studied in a pot experiment on three different Miscanthus hybrids (conventional Miscanthus × giganteus, TV1 and GNT10) considering growth parameters, photosynthetic parameters and elemental composition of roots, rhizomes and shoots. GNT10 was characterised by the weakest gas exchange among the hybrids, which was compensated by the highest number of leaves and biomass. The strongest correlations between the studied parameters were found for TV1, which might indicate a high sensitivity to TME stress. For M × g and GNT10, the main mechanisms for coping with stress seem to be biomass management through number of shoots and leaves and gas exchange. The main factor determining the extent of accumulation of TMEs was the amount of water applied in the experimental treatment, which was related to the location of the plant in the aniso-isohydric continuum. GNT10 was the most resistant plant to combined stress, while it responded similarly to TV1 when drought and trace metal elements were applied separately.

Inoculation of Escherichia coli enriched the key functional bacteria that intensified cadmium accumulation by halophyte Suaeda salsa in saline soils

The enhancement of cadmium (Cd) extraction by plants from contaminated soils associated with phosphate-solubilizing bacteria (PSB) has been widely reported, but the underlying mechanism remains scarcely, especially in Cd-contaminated saline soils. In this study, a green fluorescent protein-labeled PSB, the strain E. coli-10527, was observed to be abundantly colonized in the rhizosphere soils and roots of halophyte Suaeda salsa after inoculation in saline soil pot tests. Cd extraction by plants was significantly promoted. The enhanced Cd phytoextraction by E. coli-10527 was not solely dependent on bacterial efficient colonization, but more significantly, relied on the remodeling of rhizosphere microbiota, as confirmed by soil sterilization test. Taxonomic distribution and co-occurrence network analyses suggested that E. coli-10527 strengthened the interactive effects of keystone taxa in the rhizosphere soils, and enriched the key functional bacteria that involved in plant growth promotion and soil Cd mobilization. Seven enriched rhizospheric taxa (Phyllobacterium, Bacillus, Streptomyces mirabilis, Pseudomonas mirabilis, Rhodospirillale, Clostridium, and Agrobacterium) were obtained from 213 isolated strains, and were verified to produce phytohormone and promote soil Cd mobilization. E. coli-10527 and those enriched taxa could assemble as a simplified synthetic community to strengthen Cd phytoextraction through their synergistic interactions. Therefore, the specific microbiota in rhizosphere soils enriched by the inoculated PSB were also the key to intensifying Cd phytoextraction.

Benzylaminopurine and Abscisic Acid Mitigates Cadmium and Copper Toxicity by Boosting Plant Growth, Antioxidant Capacity, Reducing Metal Accumulation and Translocation in Bamboo [Pleioblastus pygmaeus (Miq.)] Plants

An in vitro experiment was conducted to determine the influence of phytohormones on the enhancement of bamboo resistance to heavy metal exposure (Cd and Cu). To this end, one-year-old bamboo plants (Pleioblastus pygmaeus (Miq.) Nakai.) contaminated by 100 µM Cd and 100 µM Cu both individually and in combination were treated with 10 µM, 6-benzylaminopurine and 10 µM abscisic acid. The results revealed that while 100 µM Cd and 100 µM Cu accelerated plant cell death and decreased plant growth and development, 10 µM 6-benzylaminopurine and 10 µM abscisic acid, both individually and in combination, increased plant growth by boosting antioxidant activities, non-antioxidants indices, tyrosine ammonia-lyase activity (TAL), as well as phenylalanine ammonia-lyase activity (PAL). Moreover, this combination enhanced protein thiol, total thiol, non-protein, glycine betaine (GB), the content of proline (Pro), glutathione (GSH), photosynthetic pigments (Chlorophyll and Carotenoids), fluorescence parameters, dry weight in shoot and root, as well as length of the shoot. It was then concluded that 6-benzyl amino purine and abscisic acid, both individually and in combination, enhanced plant tolerance under Cd and Cu through several key mechanisms, including increased antioxidant activity, improved photosynthesis properties, and decreased metals accumulation and metal translocation from root to shoot.

Evaluation of Chelating Agents Used in Phytoextraction by Switchgrass of Lead Contaminated Soil

Soil lead (Pb) contamination is a recognized environmental and global health problem. Phytoextraction of Pb using switchgrass (Panicum virgatum L.), a second-generation biofuel crop, is typically enhanced by soil chelation. The effectiveness of four different chelating agents, phytic acid (inositol hexaphosphate), citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediaminetetraacetic acid) was examined in pot culture. Plants treated with EDTA (1 mM) showed significantly higher shoot Pb concentrations compared to control plants and plants treated with other chelates. Lead-solubility following phytoextraction was examined by soil washing using 0.01 and 0.05 M acetic acid as an extractant solution revealed no significant differences in Pb concentrations in soil among different chelate treatments and control. Furthermore, the effects of different concentrations (1, 2, 5 and 10 mM) of NTA on Pb phytoextraction of switchgrass were examined. Plants receiving 5 mM and 10 mM NTA had significantly higher foliage concentrations of Pb compared to plants treated with lower levels (1 and 2 mM) of NTA. Moreover, the effect of NTA application alone was significantly improved by a combined application of Triton X-100, an alkyl polyglucoside (APG); the Pb concentration in the foliage of switchgrass was more than doubled when treated with NTA combined with APG. The use of NTA combined with APG has great potential in improving phytoextraction efficiencies of switchgrass on Pb-contaminated soils.

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

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

Roles of exogenous plant growth regulators on phytoextraction of Cd/Pb/Zn by Sedum alfredii Hance in contaminated soils

Plant growth regulators (PGRs) assisted phytoextraction was investigated as a viable phytoremediation technology to increase the phytoextraction efficiency in contaminated soils. This study aimed to evaluate the cadimum (Cd)/lead (Pb)/zinc (Zn) phytoextraction efficiency by a hyperaccumulator Sedum alfredii Hance (S. alfredii) treated with 9 PGRs, including indole-3-acetic acid (IAA), gibberellin (GA₃), cytokinin (CKs), abscisic acid (ABA), ethylene (ETH), brassinosteroid (BR), salicylic acid (SA), strigolactones (SL) and jasmonic acid (JA), in slightly or heavily contaminated (SC and HC, respectively) soil. Results demonstrated that PGRs were able to improve S. alfredii biomass, the most significant increases were observed in GA₃ and SL for HC soil, while for SC soil, IAA and BR exhibited positive effects. The levels of Cd, Pb and Zn in the shoots of S. alfredii treated with ABA and SL were noticeably greater than in the CK treatment in HC soil, while the uptake of metals were increased by IAA and CKs in SC soil. Combined with the results of biomass and metal contents in shoots, we found that ABA showed the highest Cd removal efficiency and the maximum Pb and Zn removal efficiency was observed with GA₃, which was 62.99%, 269.23%, and 41.18%, respectively higher than the control in HC soil. Meanwhile, compared to control, the maximum removal efficiency of Cd by IAA treatment (52.80%), Pb by JA treatment (165.1%), and Zn by BR treatment (44.97%) in the SC soil. Overall, our results suggested that these PGRs, especially, ABA, SL, IAA, BR and GA₃ had great potential in improving phytoremediation efficiency of S. alfredii grown in contaminated soils.

Effects of Herbaspirillum sp. p5-19 assisted with alien soil improvement on the phytoremediation of copper tailings by Vetiveria zizanioides L

Microbial assisted phytoremediation and reclamation are both potential contaminated soil remediation technologies, but little is known about the combined application of the two technologies on real contaminated soils. This study investigated the potential of Herbaspirillum sp. p5-19 (p5-19) assisted with alien soil improvement on improving stress tolerance and enhancing the accumulation of Mn, Cu, Zn, and Cd by Vetiveria zizanioides L. in copper tailings. Phytoremediation potential was evaluated by plant biomass and the ability of plants to absorb and transfer heavy metals. Results showed that the biomass was increased by 19.64-173.81% in p5-19 inoculation treatments with and without alien soil improvement compared with control. Meanwhile, photosynthetic pigment contents were enhanced in co-inoculation treatment (p5-19 with alien soil improvement). In addition, the malondialdehyde (MDA) content was decreased, and the activities of antioxidant enzymes such as ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased in p5-19 treatment, thereby alleviating the oxidative stress. Moreover, co-inoculation significantly (p < 0.05) increased the concentrations of Mn, Cu, Zn, and Cd in the roots and shoots of V. zizanioides. In particular, the highest concentrations of Mn, Zn, and Cd in the shoots (roots) were obtained in covering 10 cm combined with p5-19 inoculation treatment, which were 4.44- (2.71-), 4.73- (3.87-), and 5.93- (4.35-) fold as that of the controls, respectively. These results provided basis for the change of phytoremediation ability of V. zizanioides after inoculation. We concluded that p5-19 assisted with alien soil improvement was a potential strategy for enhancing phytoremediation ability in tailings.

Effects of Exogenous Application of Plant Growth Regulators (SNP and GA3) on Phytoextraction by Switchgrass (Panicum virgatum L.) Grown in Lead (Pb) Contaminated Soil

Soil lead (Pb) contamination is a major environmental and public health risk. Switchgrass (Panicum virgatum), a second-generation biofuel crop, is potentially useful for the long-term phytoremediation and phytoextraction of Pb contaminated soils. We evaluated the efficacy of a coordinated foliar application of plant growth regulators and soil fungicide and a chelator in order to optimize phytoextraction. Plants were grown in soil culture under controlled conditions. First, three exogenous nitric oxide (NO) donors were evaluated at multiple concentrations: (1) S-nitroso-N-acetylpenicillamine (SNAP); (2) sodium nitroprusside (SNP); and (3) S-nitrosoglutathione (GSNO). Second, the effect of SNP (0.5 μM) was examined further with the model chelate EDTA and the soil fungicide propicanazole. Third, a combined foliar application of SNP and gibberellic acid (GA3) was examined with EDTA and propicanazole. The soil application of propiconazole (a broad-spectrum fungicides) reduced AMF colonization and allowed greater Pb phytoextraction. The foliar application of SNP resulted in similar concentrations of Pb (roots and foliage) to plants that were challenged with chelates and soil fungicides. The combined foliar application of SNP and GA3 resulted in significantly greater average Pb concentration (243 mg kg−1) in plant foliage in comparison to control plants (182 mg kg−1) and plants treated with GA3 alone (202 mg kg−1). The combined foliar application of SNP and GA3 resulted in the greatest phytoextraction efficiency and could therefore potentially improve phytoextraction by switchgrass grown in Pb contaminated soils.

Application of abscisic acid and 6-benzylaminopurine modulated morpho-physiological and antioxidative defense responses of tomato (Solanum lycopersicum L.) by minimizing cobalt uptake

A hydroponic study was conducted to determine the effects of single and/or combined application of different doses (0, 5 and 10 μM L^-1) of abscisic acid (ABA) and 6-benzylaminopurine (BAP) on cobalt (Co) accumulation, morpho-physiological and antioxidative defense attributes of tomato (Solanum lycopersicum L.) exposed to severe Co stress (400 μM L^-1). The single Co treatment (T1), prominently decreased tomato growth, relative water contents, photosynthetic pigments (chlorophyll a and chlorophyll b), whereas enhanced oxidative stress and Co accumulation in shoot and root tissues. Nonetheless, the supplementation of ABA and 6-BAP via nutrient media significantly (P < 0.05) enhanced plant biomass, root morphology and chlorophyll contents of tomato, compared to only Co treatment (T1). Moreover, the oxidative stress indicators such as malondialdehyde, proline and H₂O₂ contents were ameliorated through activation of enzymatic antioxidant activities i.e. ascorbate peroxidase, superoxide dismutase, catalase, and peroxidase, in growth modulator treatments in comparison to T1. The Co uptake, translocation (TF) and bioaccumulation factor (BAF) by shoot and root tissues of tomato were significantly reduced under all the treatments than that of T1. The supply of 6-BAP alone or in combination with ABA at 10 μM L^-1 application (T7) rate was found the most effective to reduce Co accumulation in the roots and shoots by 48.4% and 70.2% respectively than T1 treatment. It can be concluded that two plant growth modulators could improve the stress tolerance by inhibition of Co uptake in tomato plants.

A Review on Practical Application and Potentials of Phytohormone-Producing Plant Growth-Promoting Rhizobacteria for Inducing Heavy Metal Tolerance in Crops

Water scarcity and high input costs have compelled farmers to use untreated wastewater and industrial effluents to increase profitability of their farms. Normally, these effluents improve crop productivity by serving as carbon source for microbes, providing nutrients to plants and microbes, and improving soil physicochemical and biological properties. They, however, may also contain significant concentrations of potential heavy metals, the main inorganic pollutants affecting plant systems, in addition to soil deterioration. The continuous use of untreated industrial wastes and agrochemicals may lead to accumulation of phytotoxic concentration of heavy metals in soils. Phytotoxic concentration of heavy metals in soils has been reported in Pakistan along the road sides and around metropolitan areas, which may cause its higher accumulation in edible plant parts. A number of bacterial that can induce heavy metal tolerance in plants due to their ability to produce phytohormones strains have been reported. Inoculation of crop plants with these microbes can help to improve their growth and productivity under normal, as well as stressed, conditions. This review reports the recent developments in heavy metal pollution as one of the major inorganic sources, the response of plants to these contaminants, and heavy metal stress mitigation strategies. We have also summarized the exogenous application of phytohormones and, more importantly, the use of phytohormone-producing, heavy metal-tolerant rhizobacteria as one of the recent tools to deal with heavy metal contamination and improvement in productivity of agricultural systems.

Cd heavy metal and plants, rather than soil nutrient conditions, affect soil arbuscular mycorrhizal fungal diversity in green spaces during urbanization

Urbanization accelerates pollution and habitat fragmentation, and the mechanism that shapes the arbuscular mycorrhizal (AM) fungal community in urban ecosystem still remains poorly understood. In this study, soil samples from 23 sites (from rural to urban), belonging to 4 green space types (country park, Co; urban park, Pa; roadside green space1, RoP1; and roadside green space2, RoP2), were collected to assess the effects of the urbanization on the AM fungal diversity. Using 454 pyrosequencing, a total of 79 AM fungal OTUs were uncovered. We found that urbanization showed a neutral effect on Shannon diversity, Simpson diversity, Pielou diversity, and community composition of the AM fungi. Within urban areas, the composition of AM fungal community was significantly different between RoP1 and RoP2. The db-RDA analysis of RoP1 and RoP2 revealed that the soil Cd accounted for the largest community composition variation, with an explanation rate of 20.5%, followed by the SOC (15.1%). Across 23 sites, Cd may have an obvious ecological toxicity on AM fungi, with significantly negative correlations between the soil Cd content and the AM fungal species richness and evenness. The AM fungal community also indicated significantly Mantel correlation with the soil Cd contents. Additionally, high herbaceous richness promoted rich AM fungi. The herbaceous composition, not the richness, has a significant impact on the AM fungal community composition. This study suggests that the toxicity of Cd from traffic should receive more attention during urban green space construction and management, and reasonable plant configuration contributed to the maintenance of the AM fungal community.

Potential of Panicum aquanticum Poir. (Poaceae) for the phytoremediation of aquatic environments contaminated by lead

Aquatic environments contaminated by lead (Pb) are a problem in many regions of world. Since Pb has high toxicity, the identification of species for phytoremediation is important for the recovery of these areas. Thus, the phytoremediation potential of Panicum aquaticum Poir. (Poaceae) was evaluated. The anatomical and physiological responses of P. aquaticum were assessed under different concentrations of Pb [0.0, 0.5, 1.0, 2.0, 4.0, and 8.0 mM of Pb(NO₃)₂]. Plant growth, anatomy of roots and leaves, root uptake, root to shoot translocation, and the concentration and accumulation of Pb in organs were analyzed. Regarding leaf anatomy, Pb treatment led to changes in epidermis thickness, stomatal density, stomatal diameter, and sclerenchymal area. Endoderm thickness was increased at the highest concentrations of Pb, which may be related to reduced translocation and shoot accumulation. The roots of P. aquaticum presented increased absorption (2279 μg g^-1 DW^-1 of Pb). In conclusion, P. aquaticum was found to have potential for the phytoremediation of areas contaminated with Pb.

Effect of Citric Acid on Growth, Ecophysiology, Chloroplast Ultrastructure, and Phytoremediation Potential of Jute (Corchorus capsularis L.) Seedlings Exposed to Copper Stress

Soil and water contamination from heavy metals and metalloids is one of the most discussed and caused adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. A hydroponic investigation was executed to evaluate the influence of citric acid (CA) on copper (Cu) phytoextraction potential of jute (Corchorus capsularis L.). Three-weeks-old seedlings of C. capsularis were exposed to different Cu concentrations (0, 50, and 100 μM) with or without the application of CA (2 mM) in a nutrient growth medium. The results revealed that exposure of various levels of Cu by 50 and 100 μM significantly (p < 0.05) reduced plant growth, biomass, chlorophyll contents, gaseous exchange attributes, and damaged ultra-structure of chloroplast in C. capsularis seedlings. Furthermore, Cu toxicity also enhanced the production of malondialdehyde (MDA) which indicated the Cu-induced oxidative damage in the leaves of C. capsularis seedlings. Increasing the level of Cu in the nutrient solution significantly increased Cu uptake by the roots and shoots of C. capsularis seedlings. The application of CA into the nutrient medium significantly alleviated Cu phytotoxicity effects on C. capsularis seedlings as seen by plant growth and biomass, chlorophyll contents, gaseous exchange attributes, and ultra-structure of chloroplast. Moreover, CA supplementation also alleviated Cu-induced oxidative stress by reducing the contents of MDA. In addition, application of CA is helpful in increasing phytoremediation potential of the plant by increasing Cu concentration in the roots and shoots of the plants which is manifested by increasing the values of bioaccumulation (BAF) and translocation factors (TF) also. These observations depicted that application of CA could be a useful approach to assist Cu phytoextraction and stress tolerance against Cu in C. capsularis seedlings grown in Cu contaminated sites.

Phytoremediation of cadmium (Cd) and uranium (U) contaminated soils by Brassica juncea L. enhanced with exogenous application of plant growth regulators

This investigation was made to examine the role of indole-3-acetic acid (IAA), gibberellin A3 (GA₃), 6-Benzylaminopurine (6-BA), and 24-epibrassinolide (EBL) in improving stress tolerance and phytoremediation of the cadmium (Cd) and uranium (U) by mustard (Brassica juncea L.). The optimum concentrations of IAA, GA₃, 6-BA, and EBL were determined based on plant biomass production, metal uptake, translocation, and removal efficiency. The biomass and total chlorophyll content decreased under Cd and U stress. Nevertheless, the application of IAA, GA₃, and 6-BA significantly (p < 0.05) increased the growth and total chlorophyll content of mustard. The malondialdehyde (MDA) and H₂O₂ content of mustard were enhanced under Cd and U stress, but they were significantly (p < 0.05) decreased in plant growth regulators (PGRs) treatments (except for EBL). PGRs treatments increased activities of antioxidant enzymes such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, thus reducing the oxidative stress. Furthermore, the shoot uptake of Cd and U of IAA and EBL treatments was significantly (p < 0.05) higher than that of other treatments. IAA and EBL also have more significant effects on the translocation and remediation of Cd and U compared to GA₃ and 6-BA. The removal efficiency of Cd and U reached the maximum in the 500 mg L^-1 IAA treatment, which was 330.77% and 118.61% greater than that in the control (CK), respectively. These results suggested that PGRs could improve the stress tolerance and efficiency of phytoremediation using B. juncea in Cd- and U- contaminated soils.

Citric Acid Enhances Plant Growth, Photosynthesis, and Phytoextraction of Lead by Alleviating the Oxidative Stress in Castor Beans

Lead (Pb) toxicity has a great impact in terms of toxicity towards living organisms as it severely affects crop growth, yield, and food security; thus, warranting appropriate measures for the remediation of Pb polluted soils. Phytoextraction of heavy metals (HMs) using tolerant plants along with organic chelators has gained global attention. Thus, this study examines the possible influence of citric acid (CA) on unveiling the potential phytoextraction of Pb by using castor beans. For this purpose, different levels of Pb (0, 300, 600 mg kg^-1 of soil) and CA (0, 2.5, and 5 mM) were supplied alone and in all possible combinations. The results indicate that elevated levels of Pb (especially 600 mg kg^-1 soil) induce oxidative stress, including hydrogen peroxide (H₂O₂) and malanodialdehyde (MDA) production in plants. The Pb stress reduces the photosynthetic traits (chlorophyll and gas exchange parameters) in the tissues of plants (leaves and roots), which ultimately lead to a reduction in growth as well as biomass. Enzyme activities such as guaiacol peroxidase, superoxide dismutase, ascorbate peroxidase, and catalase are also linearly increased in a dose-dependent manner under Pb stress. The exogenous application of CA reduced the Pb toxicity in plants by improving photosynthesis and, ultimately, plant growth. The upsurge in antioxidants against oxidative stress shows the potential of CA-treated castor beans plants to counteract stress injuries by lowering H₂O₂ and MDA levels. From the results of this study, it can be concluded that CA treatments play a promising role in increasing the uptake of Pb and reducing its phytotoxicity. These outcomes recommend that CA application could be an effective approach for the phytoextraction of Pb from polluted soils by growing castor beans.

Cardiotoxicity of forchlorfenuron (CPPU) in zebrafish (Danio rerio) and H9c2 cardiomyocytes

Forchlorfenuron (CPPU), as a plant growth regulator or herbicide/pesticide, is widely used in agriculture worldwide. It is adopted by most farmers due to its high efficacy for boosting size and improving the quality of fruit. However, CPPU was implicated in, and gained notoriety due to an incident of exploding watermelon that occurred in 2011. Subsequently, the wider community became aware of the potential risks it posed to living organisms and the ecosystem. In this study, we evaluated the effects of CPPU on the survival, cardiac morphology and function, as well as hematopoietic system, of zebrafish (Danio rerio). Notably, CPPU (2.5-12.5 μg/ml) induced cardiac morphology deformation, cardiac contractile dysfunction and erythrocyte reduction in zebrafish. Consistently, the mRNA expression levels of several cardiac and hematopoietic gene markers (myl7, gata4, mef2c, amhc, vmhc and gata1) were altered by CPPU treatment. In addition, CPPU caused cytotoxicity, cytoskeleton destruction and reduced corresponding proteins (Myl7, Gata4 and Mef2c) expression in H9c2 cardiomyocytes in vitro. Taken together, this study has identified the cardiotoxicity of CPPU in different experimental models and enhanced our understanding on the mechanism underlying the toxicity of CPPU to living organisms.

Heavy Metal Pollutions: State of the Art and Innovation in Phytoremediation

Mineral nutrition of plants greatly depends on both environmental conditions, particularly of soils, and the genetic background of the plant itself. Being sessile, plants adopted a range of strategies for sensing and responding to nutrient availability to optimize development and growth, as well as to protect their metabolisms from heavy metal toxicity. Such mechanisms, together with the soil environment, meaning the soil microorganisms and their interaction with plant roots, have been extensively studied with the goal of exploiting them to reclaim polluted lands; this approach, defined phytoremediation, will be the subject of this review. The main aspects and innovations in this field are considered, in particular with respect to the selection of efficient plant genotypes, the application of improved cultural strategies, and the symbiotic interaction with soil microorganisms, to manage heavy metal polluted soils.

Biostimulants application for bacterial metabolic activity promotion and sodium dodecyl sulfate degradation under copper stress

In this study, the metabolic activity (adenosine triphosphate, ATP; electron transfer system, ETS; and dehydrogenase activity, DHA) response of a sodium dodecyl sulfate (SDS) degrading bacterium Pseudomonas sp. SDS-N2 to copper stress conditions were investigated. Results showed that the ATP content, ETS activity, and DHA activity of strain SDS-N2 were significantly correlated with substrate removal efficiency and bacterial growth under copper stress conditions. Based on the metabolic response patterns of strain SDS-N2, biostimulants citric acid, proline as well as FeSO₄ were used to promote the metabolic activity of strain SDS-N2 at 0.8 mg L^-1 copper stress condition. Plackett-Burman design and analysis proved that citric acid and FeSO₄ were significant factors for enhanced SDS removal; and the optimum biostimulation conditions (FeSO₄ 72 mg L^-1 and citric acid 100 mg L^-1) for SDS removal were obtained by using steepest ascent experiment and central composite design. Under the optimum biostimulation conditions, ATP, ETS, DHA activity as well as bacterial growth were 14.1, 45.5, 0.5 and 2.3-fold higher than that of the control (without FeSO₄ and citric acid addition) after 12.5 h biodegradation, and the substrate removal efficiency was increase by 37.6%.

Cultivation of C4 perennial energy grasses on heavy metal contaminated arable land: Impact on soil, biomass, and photosynthetic traits

The objective of this study was to evaluate the potential of three C4 perennial grasses (Miscanthus x giganteus, Panicum virgatum and Spartina pectinata) for biomass production on arable land unsuitable for food crop cultivation due to Pb, Cd and Zn contamination. We assessed soil properties, biomass yield, metal concentrations, and the photosynthetic performance of each species. Physico-chemical and elemental analyses were performed on soil samples before plantation establishment (2014) and after three years of cultivation (2016), when leaf area index, plant height, yield and heavy metal content of biomass were also determined. Physiological measurements (gas exchange, pigment content, chlorophyll a fluorescence) were recorded monthly between June and September on mature plants in 2016. Cultivation of investigated plants resulted in increased pH, nitrogen, and organic matter (OM) content in soil, although OM increase (13%) was significant only for S. pectinata plots. During the most productive months, maximal quantum yield values of primary photochemistry (F_v/F_m) and gas exchange parameter values reflected literature data of those plants grown on uncontaminated sites. Biomass yields of M. x giganteus (15.0 ± 0.4 t d.m. ha^-1) and S. pectinata (12.6 ± 1.2 t d.m. ha^-1) were also equivalent to data published from uncontaminated land. P. virgatum performed poorly (4.1 ± 0.4 t d.m. ha^-1), probably due to unfavourable climatic conditions, although metal uptake in this species was the highest (3.6 times that of M. x giganteus for Pb). Yield and physiological measurements indicated that M. x giganteus and S. pectinata were unaffected by the levels of contamination and therefore offer alternatives for areas where food production is prohibited. The broad cultivatable latitudinal range of these species suggests these results are widely relevant for development of the bioeconomy. We recommend multi-location trials under diverse contaminant and environmental regimes to determine the full potential of these species.

Insight into citric acid-induced chromium detoxification in rice (Oryza sativa. L)

High content of chromium in plants hampers plants' metabolism, disrupts plant growth and development. Therefore, improving plants' tolerance to Cr toxicity is very essential. In our present study, we investigated the role of citric acid (CA) on chromium detoxification in terms of stress tolerance in rice. Application of CA under Cr stress restore the growth parameters, total protein content and membrane stability confirming that CA plays important role in Cr detoxification in rice. However, supplementation of CA under Cr stress caused no significant change in root Cr content but increased shoot Cr concentration (97 µg/g) compare with Cr stressed plant (24 µg/gm), suggesting that CA alleviates Cr toxicity by its chelating properties. Moreover, Fe content showed no significant changes due to CA supplementation under Cr stress, implying that Fe regulation is not involved with CA-mediated mitigation of Cr toxicity in rice. Furthermore, increased CAT, POD, and GR activity along with raised metabolites (glutathione and proline) indicates active participation in ROS scavenging and palliate the Cr toxicity in rice.

Phytoextraction of heavy metals from a multiply contaminated dredged sediment by chicory (Cichorium intybus L.) and castor bean (Ricinus communis L.) enhanced with EDTA, NTA, and citric acid application

The remediation of contaminated dredged sediments is necessary to eliminate the risk towards human beings or the environment when there is disposal on land. A greenhouse experiment was carried out to evaluate the chemically assisted phytoextraction to clean up dredged sediment contaminated with Cr, Cu, Pb, and Zn. The ability of castor bean and chicory to absorb, translocate, and accumulate metals from sediment to root and shoot was evaluated by applying EDTA (5 mM), NTA (5 mM), and citric acid (60 mM) to sediment, before the harvest. Citric acid 60 mM was the most effective treatment in increasing Cr, Cu, and Pb in castor bean and chicory shoot. Chicory could accumulate 1730 mg Cr kg-1 in shoot, and had greater values than one for the bioaccumulation and translocation factors when citric acid was added to the sediment. But, the Cr percentages removed per harvest of chicory were 0.05% and were lower for Cu, Pb, and Zn due to low biomass obtained. Citric acid-assisted phytoextraction with chicory can be a promising short time solution to reduce Cr concentration in sediment and reach the Cr level guide for industrial land use only if suitable agronomic practices could be implemented to increase crop yield.

Citric acid assisted phytoextraction of chromium by sunflower; morpho-physiological and biochemical alterations in plants

Soil and water contamination from heavy metals and metalloids is one of the most discussed and burning global issues due to its potential to cause the scarcity of healthy food and safe water. The scientific community is proposing a range of lab and field based physical, chemical and biological solutions to remedy metals and metalloids contaminated soils and water. The present study finds out a possibility of Chromium (Cr) extraction by sunflower from spiked soil under chelating role of citric acid (CA). The sunflower plants were grown under different concentrations of Cr (0, 5, 10 & 20mgkg^-1) and CA (0, 2.5 & 5mM). Growth, biomass, gas exchange, photosynthesis, electrolyte leakage (EL), reactive oxygen species (ROS; malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and the activities of antioxidant enzymes such as, superoxide dismutase (SOD), guaiacole values peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT) were measured. The results depicted a clear decline in plant height, root length, leaf area, number of leaves and flowers per plant along with fresh and dry biomass of all parts of plant with increasing concentration of Cr in soil. Similar reduction was observed in chlorophyll a and b, total chlorophyll, carotenoids, soluble protein, gas exchange attributes and SPAD. The increasing concentration of Cr also enhanced the Cr uptake and accumulation in plant roots, stem and leaves along with the production of ROS and EL. The activities of antioxidant enzymes increased with increasing Cr concentration from 0 to 10mg, but decreased at 20mgkg^-1 soil. The CA application significantly alleviated Cr-induced inhibition of plant growth, biomass, photosynthesis, gas exchange, soluble proteins and SPAD value. Presence of CA also enhanced the activities of all antioxidant enzymes and reduced the production of ROS and EL. The chelating potential of CA increased the concentration and accumulation of Cr in plant roots, stem and leaves. It is concluded that the sunflower can be a potential candidate for the remediation of Cr under CA treatment, while the possibility may vary with genotype, Cr level and CA concentration.