Uptake and distribution of phenanthrene and pyrene in roots and shoots of maize (Zea mays L.)

Single/joint effects of pyrene and heavy metals in contaminated soils on the growth and physiological response of maize (Zea mays L.)

The widespread presence of polycyclic aromatic hydrocarbons (PAHs) and toxic heavy metals in soils is having harmful effects on food crops and the environment. However, the defense mechanisms and capacity of plants to counteract these substances have not been comprehensively explored, necessitating a systematic categorization of their inhibitory effects. Accordingly, an experimental investigation was conducted to examine the growth and physiological response of maize (Zea mays L.) to different concentrations and combinations of pyrene, copper (Cu), and cadmium (Cd), with an indicator developed to assess the joint stress. The results showed that 57-day culture with contaminations significantly inhibited the plant biomass via causing root cell necrosis, inducing lipid peroxidation, and damaging photosynthesis. Cd (50-100 mg/kg) induced stronger inhibition than Cu (800-1000 mg/kg) under both single and joint stress, and their co-existence further aggravated the adverse effects and generated synergetic inhibition. Although the presence of pyrene at a low concentration (5-50 mg/kg) can somewhat diminish the metal stress, the elevated pollutant concentrations (400-750 mg/kg pyrene, 50-100 mg/kg Cd, and 800-1000 mg/kg Cu) switched the antagonistic effect to additive inhibition on maize growth. A satisfactory tolerance of a low-level pyrene and/or metal stress was determined, associated with a relative stability of chlorophyll-a (Chl-a) content and antioxidant enzymes activity. Nevertheless, the photosynthesis and antioxidant system were significantly damaged with increasing contaminant concentrations, resulting in chlorosis and biomass reduction. These findings could provide valuable knowledge for ensuring crop yield and food quality as well as implementing soil phytoremediation.

Persistent polycyclic aromatic hydrocarbons removal from sewage sludge-amended soil through phytoremediation combined with solid-state ligninolytic fungal cultures

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment, causing increasing concern because of their impact on soil health, food safety and potential health risks. Four bioremediation strategies were examined to assess the dissipation of PAHs in agricultural soil amended with sewage sludge over a period of 120 days: soil-sludge natural attenuation (SS); phytoremediation using maize (Zea mays L.) (PSS); mycoremediation (MR) separately using three white-rot fungi (Pleurotus ostreatus, Phanerochaete chrysosporium and Irpex lacteus); and plant-assisted mycoremediation (PMR) using a combination of maize and fungi. In the time frame of the experiment, mycoremediation using P. chrysosporium (MR-PH) exhibited a significantly higher (P < 0.05) degradation of total PAHs compared to the SS and PSS treatments, achieving a degradation rate of 52 %. Both the SS and PSS treatments demonstrated a lower degradation rate of total PAHs, with removal rates of 18 % and 32 %, respectively. The PMR treatments showed the highest removal rates of total PAHs at the end of the study, with degradation rates of 48-60 %. In the shoots of maize, only low- and medium-molecular-weight PAHs were found in both the PSS and PMR treatments. The calculated translocation and bioconversion factors always showed values < 1. The analysed enzymatic activities were higher in the PMR treatments compared to other treatments, which can be positively related to the higher degradation of PAHs in the soil.

Phenanthrene uptake and translocation by Panicum miliaceum L. tissues: an experimental study in an artificial environment

Polycyclic aromatic hydrocarbons (PAHs), as priority organic pollutants, are capable of accumulation in plants. Phenanthrene (Phe) is one of the most abundant low-molecular-weight PAH in the environment which is commonly used as a model PAH in many phytoremediation studies and as a representative compound for all PAHs group. This paper highlights the uptake, translocation, and accumulation of Phe by growing proso millet (Panicum miliaceum L.) in a pot experiment, subjected to 500, 1000, 1500, and 2000 ppm of Phe treatment after 15 and 30 days. Phe naturally existed in P. miliaceum and its concentration showed a time-dependent reduction in treated plant tissues as well as in perlites. Phe concentration in shoots was higher than in roots. During the aging process, the uptake of Phe was diminished whereas translocation factor (TF) demonstrated an overall increasing trend among treatments. The shoot concentration factor (SCF) values were higher than those of root concentration factor (RCF) on both days 15 and 30 and the highest values for both parameters were achieved in 500 ppm of Phe. Both RCFs and SCFs generally tended to decrease with the increase of perlite Phe concentrations. These results suggested that Phe tended to transfer to the shoots and be metabolized there. The Phe concentration revealed a significant decline in all levels of treatment on both 15 (84 to 96%) and 30 (76 to 94%) days. Therefore, the presence of P. miliaceum was effective in promoting the phytoremediation of Phe polluted perlites.

Microplastics reduced bioavailability and altered toxicity of phenanthrene to maize (Zea mays L.) through modulating rhizosphere microbial community and maize growth

Due to its large specific surface area and great hydrophobicity, microplastics can adsorb polycyclic aromatic hydrocarbons (PAHs), affecting the bioavailability and the toxicity of PAHs to plants. This study aimed to evaluate the effects of D550 and D250 (with diameters of 550 μm and 250 μm) microplastics on phenanthrene (PHE) removal from soil and PHE accumulation in maize (Zea mays L.). Moreover, the effects of microplastics on rhizosphere microbial community of maize grown in PHE-contaminated soil would also be determined. The results showed that D550 and D250 microplastics decreased the removal of PHE from soil by 6.5% and 2.7% and significantly reduced the accumulation of PHE in maize leaves by 64.9% and 88.5%. Interestingly, D550 microplastics promoted the growth of maize and enhanced the activities of soil protease and alkaline phosphatase, while D250 microplastics significantly inhibited the growth of maize and decreased the activities of soil invertase, alkaline phosphatase and catalase, in comparison with PHE treatment. In addition, microplastics changed the rhizosphere soil microbial community and reduced the relative abundance of PAHs degrading bacteria (Pseudomonas, Massilia, Proteobacteria), which might further inhibit the removal of PHE from soil. This study provided a new perspective for evaluating the role of microplastics on the bioavailability of PHE to plants and revealing the combined toxicity of microplastics and PHE to soil microcosm and plant growth.

Absorption, metabolism and distribution of carbosulfan in maize plants (Zea mays L.)

BACKGROUND

The insecticide carbosulfan is usually applied as a soil treatment or seed-coating agent, and so may be absorbed by crops and pose dietary risks. Understanding the uptake, metabolism and translocation of carbosulfan in crops is conducive to its safe application. In this study, we investigated the distribution of carbosulfan and its toxic metabolites in maize plants at both the tissue and subcellular levels, and explored the uptake and translocation mechanism of carbosulfan.

RESULTS

Carbosulfan was mainly taken up by maize roots via the apoplast pathway, was preferentially distributed in cell walls (51.2%-57.0%) and most (85.0%) accumulated in roots with only weak upward translocation. Carbofuran, the main metabolite of carbosulfan in maize plants, was primarily stored in roots. However, carbofuran could be upwardly translocated to shoots and leaves because of its greater distribution in root-soluble components (24.4%-28.5%) compared with carbosulfan (9.7%-14.5%). This resulted from its greater solubility compared with its parent compound. The metabolite 3-hydroxycarbofuran was found in shoots and leaves.

CONCLUSION

Carbosulfan could be passively absorbed by maize roots, mainly via the apoplastic pathway, and transformed into carbofuran and 3-hydroxycarbofuran. Although carbosulfan mostly accumulated in roots, its toxic metabolites carbofuran and 3-hydroxycarbofuran could be detected in shoots and leaves. This implies that there is a risk in the use of carbosulfan as a soil treatment or seed coating. © 2023 Society of Chemical Industry.

Exogenous IAA application affects the specific characteristics of fluoranthene distribution in Arabidopsis

Indole-3-acetic acid (IAA) is a crucial growth regulator involved in the accumulation of polycyclic aromatic hydrocarbons (PAHs). However, the precise physiological and molecular mechanisms underlying IAA-mediated plant growth and PAH accumulation are not yet fully understood. In this study, two distinct IAA-sensitive genotypes of Arabidopsis thaliana (wild type and Axr5 mutant) were chosen to investigate the mechanisms of fluoranthene (Flu) uptake and accumulation in plant tissues (roots and leaves) through physiological and molecular analyses. The results revealed that the Flu concentration in Axr5 leaves was significantly higher than that in wild-type (WT) leaves. In roots, the Flu content decreased significantly with increasing IAA treatment, while no significant changes were observed with lower IAA treatment. Principal component analysis demonstrated that Flu accumulation in Arabidopsis roots was associated with IAA concentrations, whereas Flu accumulation in leaves was dependent on the genotype. Moreover, Flu accumulation showed a positive correlation with the activity of glutathione S-transferase (GST) and root length and a positive correlation with catalase (CAT) and peroxidase (POD) activity in the leaves. Transcriptome analysis confirmed that the expression of the ethylene-related gene ATERF6 and GST-related genes ATGSTF14 and ATGSTU27 in roots, as well as the POD-related genes AtPRX9 and AtPRX25 and CAT-related gene AtCAT3 in leaves, played a role in Flu accumulation. Furthermore, WRKY transcription factors (TFs) in roots and NAC TFs in leaves were identified as important regulators of Flu accumulation. Understanding the mechanisms of Flu uptake and accumulation in A. thaliana provides valuable insights for regulating PAH accumulation in plants.

Evaluation of Azolla filiculoides potential in pyrene and phenanthrene accumulation and phytoremediation in contaminated waters

Polycyclic aromatic hydrocarbons (PAHs) are a serious threat to the health of the environment. This study investigated the potential of Azolla filiculoides for the uptake, accumulation, and biodegradation of phenanthrene and pyrene. A- filiculoides plants were treated with 10 and 30 mg L-1 concentrations of phenanthrene and pyrene for the experimental duration of ten days. Phenanthrene and pyrene concentrations were measured using the high-performance liquid chromatography (HPLC) technique. Identification of the intermediate by-products resulting from the biological degradation of PAHs was performed by gas chromatography-mass spectrometry (GC/MS). The quantities of phenanthrene and pyrene in the ten-day treatments with 10 and 30 mg L-1 were 0.007 and 0.011 mg g-1 FW, and 0.048 and 0.079 mg g-1 FW, respectively. The growth parameters in the plants such as fresh weight, dry weight and RFN as well as the content of photosynthetic pigment of the plant decreased significantly compared to the control sample (p < 0.05). Ten compounds were identified from the plant tissue during the decomposition of pyrene and phenanthrene, and none of the PAHs were identified in the aquatic environment. Therefore, the use of A-filiculoides for phytoremediation of water resources contaminated with PAHs is an effective and promising method.

Enhancement of electrokinetic-phytoremediation by Ophiopogon japonicus: stimulation of electrokinetic on root system and improvement of polycyclic aromatic hydrocarbon degradation

Root systems are sensitive to voltage and tend to improve the degradation of organic pollutants by promoting the root exudates and increasing microbial enzyme activity in the rhizosphere under the effect of electrokinetic. In this study, electrokinetic-assisted phytoremediation (EKPR) was applied for the remediation of soil containing phenanthrene (PHE) and pyrene (PYR). Direct current (DC) voltage (1 V cm-1) was applied across the soils for 30 days following 3 treatment schedules (0 h, 4 h, and 12 h per day), referred to as treatments EK0, EK4, and EK12. Electrokinetic assistance improved phytoremediation. Compared to EK0, the removal of PHE and PYR increased by 51.79% and 45.07% for EK4 and by 43.18% and 38.75% for EK12. The applied voltage promoted root growth, stimulated the root exudate release, and increased accumulation of PHE and PYR by plants, and the effect was most pronounced in treatment EK4. Catalase and urease activities in rhizosphere soil also increased, by respective increments of 44.51% and 40.86% for EK4 and by 28.53% and 21.24% for EK12. In this study, we demonstrated that a low voltage applied for an appropriate duration (4 h per day) improves removal of PAHs by stimulating root growth, promoting the root exudate release and enhancing enzyme activity in the microbiome of rhizosphere soil.

Molecular Defensive Mechanism of Echinacea purpurea (L.) Moench against PAH Contaminations

The understanding of the molecular defensive mechanism of Echinacea purpurea (L.) Moench against polycyclic aromatic hydrocarbon (PAH) contamination plays a key role in the further improvement of phytoremediation efficiency. Here, the responses of E. purpurea to a defined mixture of phenanthrene (PHE) and pyrene (PYR) at different concentrations or a natural mixture from an oilfield site with a history of several decades were studied based on transcriptomics sequencing and widely targeted metabolomics approaches. The results showed that upon 60-day PAH exposure, the growth of E. purpurea in terms of biomass (p < 0.01) and leaf area per plant (p < 0.05) was negatively correlated with total PAH concentration and significantly reduced at high PAH level. The majority of genes were switched on and metabolites were accumulated after exposure to PHE + PYR, but a larger set of genes (3964) or metabolites (208) showed a response to a natural PAH mixture in E. purpurea. The expression of genes involved in the pathways, such as chlorophyll cycle and degradation, circadian rhythm, jasmonic acid signaling, and starch and sucrose metabolism, was remarkably regulated, enhancing the ability of E. purpurea to adapt to PAH exposure. Tightly associated with transcriptional regulation, metabolites mainly including sugars and secondary metabolites, especially those produced via the phenylpropanoid pathway, such as coumarins, flavonoids, and their derivatives, were increased to fortify the adaptation of E. purpurea to PAH contamination. These results suggest that E. purpurea has a positive defense mechanism against PAHs, which opens new avenues for the research of phytoremediation mechanism and improvement of phytoremediation efficiency via a mechanism-based strategy.

Comparative analysis of remediation efficiency and ultrastructural translocalization of polycyclic aromatic hydrocarbons in Medicago sativa, Helianthus annuus, and Tagetes erecta

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile anthropogenic contaminants that can damage soil fertility and threaten the environment due to their hazardous effects on various ecological parameters. The experimental objective was divided into two parts because PAHs are always present in mixtures. The toxicity of anthracene, phenanthrene, pyrene, and fluoranthene was examined and investigated the potential of three phytoremediator plants species viz Tagetes erecta, Helianthus annuus, and Medicago sativa for remediation and translocation of individual PAH. PAHs were shown to have inhibitory or stimulating effects on growth, antioxidant properties, and impact on the structure of plant cells. The result showed that M. sativa significantly enhances the removal rate of PAHs in the soil. The dissipation rate reached 96.2% in M. sativa planted soil, followed by H. annuus and T. erecta. Among the plant species, M. sativa exhibited the highest root and shoot concentrations (314.37 and 169.55 mg kg-1), while the lowest concentration was 187.56 and 76.60 mg kg-1 in T. erecta. SEM-EDX and fluorescence micrographs confirmed that pyrene altered plant tissue's ultrastructure and cell viability and was found to be the most toxic and resistant. M. sativa was proven to be the most effective plant for the mitigation of PAHs.

Levels, sources, and risk assessment of PAHs residues in soil and plants in urban parks of Northwest China

Polycyclic aromatic hydrocarbons (PAHs) will be ingested by people through different ways to threaten their health during play, so the environmental quality of the park directly affects the health of tourists and residents. Using eight typical parks in Urumqi in Northwest China as the study area, we used GC-MS to detect the PAHs content in the park surface soil and 10 common plants in the park in different seasons. The results showed that the content of PAHs in park soil in the summer was 5-6 times that in the winter, and the monomer PAHs in some park soil sampling points were higher than the soil pollution risk screening value. And the contamination level at these sampling sites was also higher compared to other sampling sites. In summer, the plants with high PAHs content in leaves are short herbs, while in winter, they are tall arbors. The PAHs of the park soil are mainly composed of high-cyclic aromatic hydrocarbons, and are mainly of traffic origin. The proportion of low-ring aromatic hydrocarbons in the winter was significantly higher than that in the summer. The source of PAHs in plants in summer is similar to that in soil, but the source of PAHs in plants in winter is more complex. The toxicity equivalent concentration method values of soil PAHs in South Park, Zhiwu Park, Shihua Park and Toutunhe Park were higher than that in other parks. The lifetime carcinogenic risk (ILCRs) values of some sampling points in these four parks in the summer were relatively high. The average ILCRs of adults and children in all parks reached a low-risk level in summer. The carcinogenic risk in children is much higher than that of adults.

The association between phenanthrene and nutrients uptake in lotus cultivar 'Zhongguo Hong Beijing'

It has been well documented that polycyclic aromatic hydrocarbon (PAHs) can be taken up from the environment by the plants and translocated into the shoots. However, the mechanisms underlying this process are poorly understood. Nelumbo nucifera L. (lotus) is a highly ornamental aquatic plant known to possess strong phytoremediation capability. In the present study, the association between phenanthrene (Phe) and nutrients, including nitrogen (N) and phosphorus (P), in lotus was investigated. Over 2 years, all eight lotus cultivars tested accumulated Phe to various degrees when grown in PAH-polluted sediment (0.46 mg/kg Phe). Cluster analysis showed N. nucifera 'Zhongguo Hong Beijing (ZHB)' was the one with the highest Phe levels in the leaves and petals in 2 years. The Phe concentrations in the tissues of 'ZHB' were 3.14 mg/kg and 1.63 mg/kg on average in the first and second year, respectively. Interestingly, 'ZHB' was also the cultivar with the lowest N and P levels considering 2 years and tissues. Hydroponic studies further revealed a negative association between the concentrations of Phe and those of N and P in the aerial tissues under 0.5 and 1.0 mg/L Phe treatments in 'ZHB'. Furthermore, the significant reductions of the roots number (72.6%), longest root length (75.8%), and petiolar height (34.6%) in 'ZHB' seedlings exposed to 1.0 mg/L Phe were observed, indicating that Phe retarded the growth of lotus. These results provide a new understanding of the accumulation of Phe in plants and the association with nutrients and enrich the basis of phytoremediation to the contaminated environment.

Elevated urbanization-driven plant accumulation and human intake risks of polycyclic aromatic hydrocarbons in crops of peri-urban farmlands

As an ubiquitous carcinogen, polycyclic aromatic hydrocarbons (PAHs) are closely related to anthropogenic activities. The process of urbanization leads to the spatial interlacing of farmlands and urbanized zones. However, field evidence on the influence of urbanization on the accumulation of PAHs in crops of peri-urban farmlands is lacking. This study comparatively investigated the urbanization-driven levels, compositions, and sources of PAHs in 120 paired plant and soil samples collected from the Yangtze River Delta in China and their species-specific human intake risks. The concentrations of PAHs in crops and soils in the peri-urban areas were 2407.92 ng g^-1 and 546.64 ng g^-1, respectively, which are significantly higher than those in the rural areas. The PAHs in the root were highly relevant to those in the soils (R² = 0.63, p < 0.01), and the root bioconcentration factors were higher than 1.0, implying the contributions of root uptake to plant accumulations. However, the translocation factors in the peri-urban areas (1.57 ± 0.33) were higher than those in the rural areas (1.19 ± 0.14), indicating the enhanced influence through gaseous absorption. For the congeners, the 2- to 3-ring PAHs showed a higher plant accumulation potential than the 4- to 6-ring PAHs. Principal component analysis show that the PAHs in the peri-urban plants predominantly resulted from urbanization parameters, such as coal combustion, vehicle emissions, and biomass burning. The mean values of estimated dietary intake of PAHs from the consumption of peri-urban and rural crops were 9116 ng day^-1 and 6601.83 ng day^-1, respectively. The intake risks of different crops followed the order rice > cabbage > carrot > pea. Given the significant input of PAHs from urban to farmland, the influence of many anthropogenic pollutants arising from rapid urbanization should be considered when assessing the agricultural food safety.

Pyrene remediation by Trametes maxima: an insight into secretome response and degradation pathway

The rapid pace of economic development has resulted in the release of several polycyclic aromatic hydrocarbons (PAHs) into the environment. Microbial degradation using white-rot fungi is a promising method for the removal of PAHs from the environment. In the present study, biodegradation of recalcitrant PAH by a white-rot fungus, Trametes maxima IIPLC-32, was investigated using pyrene. The pyrene concentration decreased by 79.80%, 65.37%, and 56.37% within 16 days from the initial levels of 10 mg L^-1, 25 mg L^-1, and 50 mg L^-1, respectively. Gas chromatographic-mass spectrometric identification of prominent metabolites 1-hydroxypyrene, 2-methyl-1-naphthyl acetic acid, di-n-butyl phthalate, and diethyl phthalate helped in determining the pyrene degradation pathway. The presence of 81 extracellular proteins was revealed by secretome analysis. The identified proteins up-regulated in response to pyrene degradation were classified into detoxification proteins (6.12%), redox proteins (6.12%), stress proteins (4.08%), metabolic-related proteins (26.53%), translation and transcriptional proteins (49%), catalytic proteins (49%), and other proteins (8.16%). Knowledge of secretome analysis in pyrene degradation helped to understand the degradation mechanism of pyrene. Also, the study suggests that T. maxima IIPLC-32 has the potential to be used in the bioremediation of PAH contaminated aquatic environment.

Uptake, translocation and subcellular distribution of chlorantraniliprole and tetrachlorantraniliprole in maize

This study aimed to investigate the uptake, translocation, and subcellular distribution of chlorantraniliprole (Cap) and tetrachlorantraniliprole (Tca) in maize (Zea mays L.) plants using a hydroponic experiment. Tca mainly accumulated in the roots and stems, while Cap showed better acropetal translocation capacity than Tca. The uptake of Cap was positively correlated with Tca uptake, particularly at the effect of plant transpiration force. Transpiration inhibitor treatments significantly reduced the acropetal translocation of Cap and Tca. The absorption of Cap and Tca in the dead and fresh roots showed a good linear relationship and mainly occurred via the apoplastic pathway. Regarding subcellular distribution, the cell wall was the dominant storage compartment for Cap and Tca. In the protoplast, Cap mainly accumulated in cell soluble fractions, while Tca accumulated in the organelles. This study provides information for the accurate application of maize pest management and is of great significance to environmental risk and food safety assessments.

Detoxification of phenanthrene in Arabidopsis thaliana involves a Dioxygenase For Auxin Oxidation 1 (AtDAO1)

Polycyclic aromatic hydrocarbon (PAH) contamination has a negative impact on ecosystems. PAHs are a large group of toxins with two or more benzene rings that are persistent in the environment. Some PAHs can be cytotoxic, teratogenic, and/or carcinogenic. In the bacterium Pseudomonas, PAHs can be modified by dioxygenases, which increase the reactivity of PAHs. We hypothesize that some plant dioxygenases are capable of PAH biodegradation. Herein, we investigate the involvement of Arabidopsis thaliana At1g14130 in the degradation of phenanthrene, our model PAH. The At1g14130 gene encodes Dioxygenase For Auxin Oxidation 1 (AtDAO1), an enzyme involved in the oxidative inactivation of the hormone auxin. Expression analysis using a β-glucuronidase (GUS) reporter revealed that At1g14130 is prominently expressed in new leaves of plants exposed to media with phenanthrene. Analysis of the oxidative state of gain-of-function mutants showed elevated levels of H₂O₂ after phenanthrene treatments, probably due to an increase in the oxidation of phenanthrene by AtDAO1. Biochemical assays with purified AtDAO1 and phenanthrene suggest an enzymatic activity towards the PAH. Thus, data presented in this study support the hypothesis that an auxin dioxygenase, AtDAO1, from Arabidopsis thaliana contributes to the degradation of phenanthrene and that there is possible toxic metabolite accumulation after PAH exposure.

Interactions between pyrene and heavy metals and their fates in a soil-maize (Zea mays L.) system: Perspectives from the root physiological functions and rhizosphere microbial community

The co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in agricultural soils has become a worldwide food crop security concern. Pot experiments, rhizosphere microbial metagenomic sequencing, and root metatranscriptomic sequencing were performed to investigate the interactions among pyrene, Cu, and Cd in a soil-maize (Zea mays L.) system. This study provided direct evidence that the co-presence of PAHs and heavy metals changed the root physiological functions and the rhizosphere microbial community, which subsequently influenced the fate of the contaminants. Co-contamination at low levels tended to enhance the uptake potential and biodegradation performance of the plant, whereas increased contaminant concentrations produced opposite effects. The co-presence of 1000 mg/kg Cu decreased the abundance of Mycobacterium in the rhizosphere and reduced pyrene degradation by 12%-16%. The presence of 400-750 mg/kg pyrene altered the metabolic processes, molecular binding functions, and catalytic activity of enzymes in the maize roots, thus impeding the phytoextraction of Cu and Cd. Competitive absorption between Cu and Cd was observed for the 800-1000 mg/kg Cu and 50-100 mg/kg Cd co-treatment, in which Cu showed a competitive advantage, enhancing its root-to-shoot translocation. These findings provide important information for the production of safe crops and for the development of phytoremediation technologies.

Reducing phenanthrene uptake and translocation, and accumulation in the seeds by overexpressing OsNRT2.3b in rice

The uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops have gained much attention due to their toxicity to humans. Nitrogen (N) is an essential element for plant growth and has also been implicated in the acquisition and acropetal translocation of PAHs. OsNRT2.3b encodes a nitrate (NO₃^-) transporter that is involved in the acquisition and mobilization of N in rice. Here, we investigated whether overexpression of OsNRT2.3b would exert any mitigating influence on the uptake and translocation of phenanthrene (Phe, a model PAH) in transgenic rice (Oryza sativa). The wild-type seedlings exhibited a reduction in plant height, primary root length, and shoot biomass when grown hydroponically in a medium supplemented with Phe. Acquisition of Phe by the roots and its subsequent translocation to shoots increased concomitantly with an increase in Phe concentration in the medium and duration of the treatment. OsNRT2.3b-overexpressing lines (Ox-6 and Ox-8) were generated independently. Compared with the wild-type, the concentration of Phe in Ox-6 and Ox-8 were significantly lower in the roots (47%-54%) and shoots (22%-31%) grown hydroponically with Phe (1 mg/L). Further, the wild-type and Ox lines were grown to maturity in a pot soil under Phe conditions and the concentrations of Phe and total N were assayed in the culms and flag leaves. Compared with the wild-type, in Ox lines the concentration of total N significantly increased in the culms (288%-366%) and flag leaves (12%-25%), while that of Phe significantly reduced in the culms (25%-28%) and flag leaves (18%-21%). The results revealed an antagonistic correlation between the concentration of total N and Phe. The concentration of Phe was also significantly lower (29%-38%) in the seeds of Ox lines than the wild-type. The study highlighted the efficacy of overexpressing OsNRT2.3b in mitigating the Phe toxicity by attenuating its acquisition, mobilization, and allocation to the seeds.

Biotreatment of pyrene and Cr(VI) combined water pollution by mixed bacteria

Pyrene and chromium (Cr(VI)) are persistent pollutants and cause serious environmental problems because they are toxic to organisms and difficult to remediate. The toxicity of pyrene and Cr(VI) to three crops (cotton, soybean and maize) was confirmed by the significant decrease in root and shoot biomass during growth in pyrene/Cr(VI) contaminated hydroponic solution. Two bacterial strains capable of simultaneous pyrene biodegradation and Cr(VI) reduction were isolated and identified as Serratia sp. and Arthrobacter sp. A mixture of the isolated strains at a ratio of 1:1 was more efficient for biotreatment of pyrene and Cr(VI) than either strain alone; the mixture effectively carried out bioremediation of contaminated water in a hydroponic system mainly through pyrene biodegradation and Cr(VI) reduction. Application of these isolates shows potential for practical microbial remediation of pyrene and Cr(VI) combined water pollution.

The effect of residual hydrocarbons in soil following oil spillages on the growth of Zea mays plants

Liquid hydrocarbon pipeline accidents, including leaks due to the illegal or unauthorized collection of petroleum from oil pipelines, are a widespread phenomenon that can lead to pollution that may negatively affect soil quality and plant growth. The aim of this study is to evaluate hydrocarbon uptake and accumulation in Zea mays plants grown on soil affected by spills of fossil fuels. The experiments were conducted in microcosm, mesocosm and field tests. The potential transfer of contaminants from soil to plant and their effects on plant growth were investigated. The results from both the laboratory and field experiments showed that the plants grew better in the uncontaminated soil than in the soil polluted by hydrocarbons. Despite their significantly lower aerial biomass, plants grown in contaminated soil did not show any significant differences in C > 12 concentration, either in shoots or roots, compared to the control plants. Thus, the decrease in plant yield might not be attributed to hydrocarbons accumulation in the plant tissues and may rather be due to a reduced soil fertility, which negatively affected plant growth. Under our experimental conditions, the hydrocarbons present in the contaminated soil were not absorbed by the plants and did not accumulate in plant tissue or in grains, thus avoiding the risk of them entering the food chain.