Physiological differences in response to di-n-butyl phthalate (DBP) exposure between low- and high-DBP accumulating cultivars of Chinese flowering cabbage (Brassica parachinensis L.)

Evaluation of electrokinetic-assisted phytoremediation efficiency of dibutyl phthalate contaminated soil by maize (Zea mays L.) under different electric field intensities

The excessive accumulation of dibutyl phthalate (DBP) in soil poses a serious threat to soil ecosystems and crop safety production. Electrokinetic-assisted phytoremediation (EKPR) has been considered as a potential technology for remediating organic contaminated soils. In order to investigate the effect of different electric fields on removal efficiency of DBP, three kinds of electric fields were set up in this study (1 V·cm-1, 2 V·cm-1 and 3 V·cm-1). The results showed that 59 % of DBP in soil was removed by maize (Zea mays L.) within 20 d in low-intensity electric field (1 V·cm-1), and the accumulation of DBP in maize tissues decreased significantly compared to the non-electrified treatment group. Interestingly, it could be observed that the low-intensity electric field could maintain ion homeostasis and improve the photosynthetic efficiency of the plant, thereby relieving the inhibition of DBP on plant growth and increasing the chlorophyll content (94.1 %) of maize. However, the removal efficiency of DBP by maize decreased significantly under the medium-intensity (2 V·cm-1) and high-intensity electric field (3 V·cm-1). Moreover, the important roles of soil enzyme and rhizosphere bacterial community in low-electric field were also investigated and discussed. This study provided a new perspective for exploring the mechanism of removing DBP through EKPR.

Root-zone regulation and longitudinal translocation cause intervarietal differences for phthalates accumulation in vegetables

Selecting and cultivating low-accumulating crop varieties (LACVs) is the most effective strategy for the safe utilization of di-(2-ethylhexyl) phthalate (DEHP)-contaminated soils, promoting cleaner agricultural production. However, the adsorption-absorption-translocation mechanisms of DEHP along the root-shoot axis remains a formidable challenge to be solved, especially for the research and application of LACV, which are rarely reported. Here, systematic analyses of the root surface ad/desorption, root apexes longitudinal allocation, uptake and translocation pathway of DEHP in LACV were investigated compared with those in a high-accumulating crop variety (HACV) in terms of the root-shoot axis. Results indicated that DEHP adsorption was enhanced in HACV by root properties, elemental composition and functional groups, but the desorption of DEHP was greater in LACV than HACV. The migration of DEHP across the root surface was controlled by the longitudinal partitioning process mediated by root tips, where more DEHP accumulated in the root cap and meristem of LACV due to greater cell proliferation. Furthermore, the longitudinal translocation of DEHP in LACV was reduced, as evidenced by an increased proportion of DEHP in the root apoplast. The symplastic uptake and xylem translocation of DEHP were suppressed more effectively in LACV than HACV, because DEHP translocation in LACV required more energy, binding sites and transpiration. These results revealed the multifaceted regulation of DEHP accumulation in different choysum (Brassica parachinensis L.) varieties and quantified the pivotal regulatory processes integral to LACV formation.

Low-Arsenic Accumulating Cabbage Possesses Higher Root Activities against Oxidative Stress of Arsenic

Cabbage grown in contaminated soils can accumulate high levels of arsenic (As) in the edible parts, posing serious health risks. The efficiency of As uptake varies drastically among cabbage cultivars, but the underlying mechanisms are not clear. We screened out low (HY, Hangyun 49) and high As accumulating cultivars (GD, Guangdongyizhihua) to comparatively study whether the As accumulation is associated with variations in root physiological properties. Root biomass and length, reactive oxygen species (ROS), protein content, root activity, and ultrastructure of root cells of cabbage under different levels of As stress (0 (control), 1, 5, or 15 mg L^-1) were measured As results, at low concentration (1 mg L^-1), compared to GD, HY reduced As uptake and ROS content, and increased shoot biomass. At a high concentration (15 mg L^-1), the thickened root cell wall and higher protein content in HY reduced arsenic damage to root cell structure and increased shoot biomass compared to GD. In conclusion, our results highlight that higher protein content, higher root activity, and thickened root cell walls result in lower As accumulation properties of HY compared to GD.

Fluorescent labeling and tracing of immobilized efficient degrading bacterium DNB-S1 and its remediation efficiency of DBP contaminated soil

Dibutyl phthalate (DBP) is an organic pollutant frequently detected in soil, and is a reproductive poison that harms animals both before and after birth and has mutagenic, teratogenic, and carcinogenic effects. DBP removal from farmland has been the subject of extensive research in recent years. Efficient DBP degrading bacterial strains were screened in the laboratory. GFP (Green fluorescent protein) labeled degradation strain GFP-DNB-S1 was analyzed for its activity and dynamics. Using sodium alginate (SA) and nano-hydroxyapatite (n-HAP) as carrier materials and CaCl₂ as a cross-linking agent, the immobilized microbial agent n-HAP/SA + DNB-S1 was prepared by embedding cross-linking immobilization technology to study the remediation effect of DBP contaminated soil. The best formation effect of immobilized materials (n-HAP/SA) was found when the SA to n-HAP ratio was 3:2. When compared to single SA immobilized bacteria, n-HAP/SA immobilized bacteria improved the surface roughness and porosity of the microspheres. After 70 days, LED light revealed that the immobilized bacteria's GFP green fluorescent protein expression was stable. At 70 days, the initial DBP concentration of 500 mg ∙ L^-1 degraded at a rate of 69.9%. The degrading bacteria had no effect on DBP degradation before and after being labeled with GFP. The n-HAP/SA immobilized bacteria offered a better living environment for microorganisms due to their rougher surface and a greater number of pores. This protected the microorganisms and increased the efficiency of DBP degradation. When the concentration of DBP in contaminated soil was set to 20 mg ∙ kg^-1 and the n-HAP/SA + DNB-S1 immobilized bacterial agent was applied to the soil, the rate of DBP degradation was determined to be 93.34%. The degradation process followed First-order degradation kinetics, which improved the physical and chemical properties of the soil as well as its fertility.

Phthalates - A family of plasticizers, their health risks, phytotoxic effects, and microbial bioaugmentation approaches

Phthalates are a family of reprotoxicant compounds, predominantly used as a plasticizer to improve the flexibility and longevity of consumable plastic goods. After their use these plastic products find their way to the waste disposal sites where they leach out the hazardous phthalates present within them, into the surrounding environment, contaminating soil, groundwater resources, and the nearby water bodies. Subsequently, phthalates move into the living system through the food chain and exhibit the well-known phenomenon of biological magnification. Phthalates as a primary pollutant have been classified as 1B reprotoxicants and teratogens by different government authorities and they have thus imposed restrictions on their use. Nevertheless, the release of these compounds in the environment is unabated. Bioremediation has been suggested as one of the ways of mitigating this menace, but studies regarding the field applications of phthalate utilizing microbes for this purpose are limited. Through this review, we endeavor to make a deeper understanding of the cause and concern of the problem and to find out a possible solution to it. The review critically emphasizes the various aspects of phthalates toxicity, including their chemical nature, human health risks, phytoaccumulation and entry into the food chain, microbial role in phthalate degradation processes, and future challenges.

Biodegradation of dibutyl phthalate by a novel endophytic Bacillus subtilis strain HB-T2 under in-vitro and in-vivo conditions

The environmental prevalence and potential toxicity of dibutyl phthalate (DBP) motivate the attempt to develop feasible strategies to deal with DBP contamination. In this study, a strain of endphytic bacteria HB-T2 was isolated from sorrel roots and identified as Bacillus sp. by analysing its morphology, physiology, biochemistry and 16S rDNA sequence. The degradation efficiency of DBP by HB-T2 was almost identical under the temperature of 30∼40°C, but was significantly enhanced as the culture pH and inoculum size increases from 6.0 to 8.0, and 1% to 5% respectively. The degradation kinetics of DBP could be well described by the first-order kinetic model, with the degradation half-life ranging from 1.59 to 7.61 h when the initial concentrations of DBP were in the range of 5-20 mg/L. LC-MS analysis of the culture samples taken at varying intervals revealed monobutyl phthalate, phthalic acid and protocatechuic acid as the major metabolic intermediates during the degradation process. HB-T2 exhibited an excellent capability to degrade a wide range of phthalate esters (PAEs), especially butyl benzyl phthalate (BBP), dipentyl phthalate (DPP), and diisobutyl phthalate (DIBP). Inoculation of HB-T2 into Chinese cabbage (Brassica chinensis L.) growing in DBP-contaminated soils could significantly reduce the DBP levels in plant tissues and relieve the phytotoxic effects of DBP. Results of this study highlighted the great potential of this novel endophytic Bacillus subtilis strain HB-T2 for bioremediation of PAEs contamination and improvement of agricultural product safety by reducing PAEs accumulation in edible crops.

Ecotoxicological and genotoxic effects of dimethyl phthalate (DMP) on Lemna minor L. and Spirodela polyrhiza (L.) Schleid. plants under a short-term laboratory assay

The environmental occurrence of phthalates (PAE) is of great concern for the ecosystem and human health. Despite of their recognized toxicity on biota, a lack of knowledge is still present about the effects of PAE on plants. In this scenario, the effects of dimethyl phthalate (DMP) on duckweed plants (Lemna minor L. and Spirodela polyrhiza (L.) Schleid.), two model plant species for ecotoxicological and trophic studies, were investigated. Under a 7-day lab assay, morphological (biometric indicators), physiological (pigment content and photosynthetic performance) and molecular (DNA damage) parameters were studied. No effects were observed at growth and physiological level in both plants at 3 and 30 mg/L DMP. On the contrary, at 600 mg/L DMP, a concentration used for plant acute toxicity studies, a remarkable growth inhibition and pigment content and photosynthetic parameters reduction compared to control were observed in both plants species, particularly in Spirodela. Alkaline Comet assay in 24 h-treated plants revealed a genotoxic damage induced by DMP, particularly relevant in Spirodela. These results described for the first time the adverse effects exerted by DMP on aquatic plants, contributing to highlight the environmental risk associated to the presence of this compound in the aquatic ecosystem.

Links between microbial compositions and metabolites during aerobic composting under amoxicillin stress was evaluated by 16S rRNA sequencing and gas chromatography-mass spectrometry: Benefit for the plant growth

The purpose of this study was to identify the relationship between core bacteria and metabolites during aerobic composting and analyze the effects of metabolites on plant growth. The results revealed that amoxicillin might affect the generation and transformation of metabolites by reconstructs the bacterial communities. The peak area ratios (PAR) of esters and fatty acids (FAs) were increased, while sterols decreased during composting. Furthermore, the correlation analysis showed that the production of FAs, esters and sterols is strongly correlated with Oceanobacillus, Corynebacterium, Psychrobacter, Xanthomonadaceae, Pusillimonas and Gracilibacillus. Moreover, 36 key metabolites were screened out, the PAR of the propanoic acid ethyl ester and oleic acid that benefit plant growth were increased in amoxicillin groups. However, the PAR of environmental pollutants, such as n-hexadecanoic acid and 3β, 5β-Cholestan-3-ol is the opposite. Therefore, composting can eliminate the environmental risks caused by antibiotic residues in feces and promote plant growth.

Variety-Selective Rhizospheric Activation, Uptake, and Subcellular Distribution of Perfluorooctanesulfonate (PFOS) in Lettuce (Lactuca sativa L.)

Perfluorooctanesulfonate (PFOS) as an accumulative emerging persistent organic pollutant in crops poses severe threats to human health. Lettuce varieties that accumulate a lower amount of PFOS (low-accumulating crop variety, LACV) have been identified, but the regarding mechanisms remain unsolved. Here, rhizospheric activation, uptake, translocation, and compartmentalization of PFOS in LACV were investigated in comparison with those of high-accumulating crop variety (HACV) in terms of rhizospheric forms, transporters, and subcellular distributions of PFOS. The enhanced PFOS desorption from the rhizosphere soils by dissolved organic matter from root exudates was observed with weaker effect in LACV than in HACV. PFOS root uptake was controlled by a transporter-mediated passive process in which low activities of aquaporins and rapid-type anion channels were corrected with low expression levels of PIPs (PIP1-1 and PIP2-2) and ALMTs (ALMT10 and ALMT13) genes in LACV roots. Higher PFOS proportions in root cell walls and trophoplasts caused lower root-to-shoot transport in LACV. The ability to cope with PFOS toxicity to shoot cells was poorer in LACV relative to HACV since PFOS proportions were higher in chloroplasts but lower in vacuoles. Our findings provide novel insights into PFOS accumulation in lettuce and further understanding of multiprocess mechanisms of LACV.

A Visual Leaf Zymography Technique for the In Situ Examination of Plant Enzyme Activity under the Stress of Environmental Pollution

This study established a high-efficiency fluorescence quenching approach for the in situ visualization and modeling of the spatial distribution of xylanase, β-glucosidase, and phosphatase activities in plant leaves under pollution stress (namely, the leaf zymography technique, LZT). In the LZT, a membrane saturated with an enzyme-specific fluorescent substrate on the leaf surface was incubated and the fluorescence image generated on the membrane under ultraviolet light was recorded. An image-based modeling method for restoring the morphological traits of the true image by reducing noise was developed to ensure the accurate estimation of enzyme activities. The LZT could simultaneously measure 48 samples within 2 h, with good reproducibility. The results obtained by the LZT were comparable to those obtained by a conventional biochemical analysis method and presented low-cost and convenient advantages. This paper explains the theoretical basis required to investigate the realistic application of the LZT for assessing ecotoxicity in large-scale monitoring.

Improving yield and quality of vegetable grown in PAEs-contaminated soils by using novel bioorganic fertilizer

Phthalate acid esters (PAEs) are ubiquitous pollutants in agricultural soils. Application of bioorganic fertilizer (BOF) containing beneficial microbes represents a promising approach to improve the yield and quality of crops grown in contaminated soils. In the present study, a novel multifunctional bioorganic fertilizer N-BOF was developed by using compost of sewage sludge and agricultural waste and inoculating with PAEs-degrading B. megaterium YJB3 and phosphate solubilizing B. megaterium YLYP1. Its feasibility of improving the yield and quality of vegetable grown in PAEs (including DBP and DEHP) contaminated soil was evaluated by pot experiments. The N-BOF could effectively promote plant growth, with biomass increasing by 4-66.9% and 19-110% compared to chemical (CF) and no fertilizer (CK), respectively. The concentrations of DBP and DEHP in shoots of chemically fertilised vegetable ranged 1.23-3.12 mg/kg (dry weight, DW) and 1.63-3.89 mg/kg (DW), respectively. Their concentrations were significantly decreased (p < 0.05) when N-BOF was applied (1%, 2%, 5% amendment), especially at higher application rate ranging 0.11-0.3 mg/kg (DW) and 0.16-0.32 mg/kg (DW), respectively. Meanwhile, vegetable quality attributes were also significantly improved when 2% N-BOF was applied, with increase in the contents of vitamin C, vitamin B1, total protein, and starch, and decrease in the contents of nitrite and nitrate. In this case, the human health risk from consumption of the vegetable grown in PAEs-contaminated soil could be significantly reduced. Thus, our study is expected to provide an efficient way of high-value utilization of organic substrates by producing low-cost but high quality N-BOF. Future studies on the effects of N-BOF in terms of fertilizer regimes on yield and quality of the vegetable are needed, and further field studies for assessing the long-term efficacy and reliability of this promising N-BOF are also warranted.

Uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid and perfluorooctane sulfonic acid by wetland plant Alisma orientale

Perfluoroalkyl substances (PFASs) are of particular environmental concern due to their environmental persistence and potential toxicity. Phytoremediation may be used to remove PFASs from wastewater. Here we investigated the uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS) in the wetland plant Alisma orientale by using a series of hydroponic experiments. Active uptake facilitated by water transporters and anion channels was involved in the uptake of PFASs by plant roots. PFOA and PFOS were mainly distributed in the water-soluble fraction (46.2-70.8%) and in cell walls (45.6-58.4%), respectively. The uptake process was proposed as follows: PFOS and PFOA were first distributed in the soluble fraction; a proportion of PFOS and PFOA were adsorbed gradually by the cell wall, and a proportion of PFOS and PFOA in the cell wall passed through the cell wall and plasmalemma and bind with organelles. PFOS and PFOA were transported from the external solution to the vascular bundle of the plant root through both symplastic and apoplastic routes.

Bioaccumulation and Phytotoxicity and Human Health Risk from Microcystin-LR under Various Treatments: A Pot Study

Microcystin-LR (MC-LR) is prevalent in water and can be translocated into soil-crop ecosystem via irrigation, overflow (pollution accident), and cyanobacterial manure applications, threatening agricultural production and human health. However, the effects of various input pathways on the bioaccumulation and toxicity of MCs in terrestrial plants have been hardly reported so far. In the present study, pot experiments were performed to compare the bioaccumulation, toxicity, and health risk of MC-LR as well as its degradation in soils among various treatments with the same total amount of added MC-LR (150 μg/kg). The treatments included irrigation with polluted water (IPW), cultivation with polluted soil (CPS), and application of cyanobacterial manure (ACM). Three common leaf-vegetables in southern China were used in the pot experiments, including Ipomoea batatas L., Brassica juncea L., and Brassica alboglabra L. All leaf vegetables could bioaccumulate MC-LR under the three treatments, with much higher MC-LR bioaccumulation, especially root bioconcentration observed in ACM treatment than IPW and CPS treatments. An opposite trend in MC-LR degradation in soils of these treatments indicated that ACM could limit MC-LR degradation in soils and thus promote its bioaccumulation in the vegetables. MC-LR bioaccumulation could cause toxicity to the vegetables, with the highest toxic effects observed in ACM treatment. Similarly, bioaccumulation of MC-LR in the edible parts of the leaf-vegetables posed 1.1~4.8 fold higher human health risks in ACM treatment than in IPW and CPS treatments. The findings of this study highlighted a great concern on applications of cyanobacterial manure.

Populus alba dioctyl phthalate uptake from contaminated water

Phthalates are micro-pollutants of great concern due to their negative effects on ecosystem functioning and human health. Thanks to its capability in uptake and accumulation of organic pollutants, Populus alba L. "Villafranca" clone could be a good candidate for reducing the impacts derived by the persistence of such compounds in the environment. We investigated plant response and uptake of dioctyl phthalate (DOP) by poplar, grown in hydroponics condition, for 21 days with 0, 40, and 400 μg L^-1 of d₄-DOP. Treated plants, after 21 days of 400 μg L^-1 d₄-DOP, showed an increase in root dry biomass (+ 29%) at the expense of aerial parts (- 8%) compared with control. The root development could be sustained by the increase of Mg uptake by poplar. LC-MS/MS analysis demonstrated the uptake and accumulation in roots of d₄-DOP starting from day one (3.5 ± 3.29 and 7.1 ± 3.28 in 40 and 400 μg L^-1 d₄-DOP respectively), despite volatilization of d₄-DOP was observed from nutritive solution. The chemical interaction between d₄-DOP and Zn occurred in roots of plants treated with the high d₄-DOP concentration, without limiting the Zn concentration in leaves. Results confirm the high tolerance of "Villafranca" clone to xenobiotic and suggest the poplar capability in d₄-DOP uptake and accumulation at root level.

Variation in metabolism and degradation of di-n-butyl phthalate (DBP) by high- and low-DBP accumulating cultivars of rice (Oryza sativa L.) and crude enzyme extracts

Crops can take up and accumulate di-n-butyl phthalate (DBP), an extensively used plasticizer with endocrine disrupting effect, which poses potential risk to human health. Our previous study found the genotype variation in accumulation of DBP by different cultivars of rice (Oryza sativa L.). Nevertheless, the effect of DBP metabolism in vivo on the accumulation variation among different plant cultivars remains unknown. In this study, metabolism variation of DBP by low (Fengyousimiao) and high (Peizataifeng) DBP-accumulating cultivars of rice and the key enzymes involving in DBP metabolism in rice plants were investigated using in vivo exposure of rice plants and in vitro exposure of root crude enzyme extracts. Both mono-n-butyl phthalate (MBP) and phthalic acid (PA) were detected as DBP metabolites in all rice tissues (i.e., roots, stems, leaves) and crude enzyme extracts with MBP predominance. DBP metabolism occurred simultaneously when DBP uptake with the highest metabolism in roots in vivo. Degradation of DBP in root crude enzyme extracts fitted well with the first order kinetics (R² = 0.49-0.76, P < 0.05). The activity of carboxylesterase (CXE) in root crude enzyme extracts was significantly positively correlated with DBP degradation rates. CXE played an important role in DBP metabolism of rice plants, confirming by the fact that triphenyl phosphate of CXE inhibitor could inhibit DBP metabolism of in vivo and in vitro exposure. This result was further confirmed by in vitro degradation of DBP with the commercial pure CXE. The crude enzyme solution from roots of Fengyousimiao with higher CXE activity had significantly higher DBP degradation rates than that of Peizataifeng. However, Fengyousimiao with lower tolerance to DBP stress and higher inhibition by triphenyl phosphate displayed lower DBP metabolism ability in vivo than Peizataifeng.

Effects of β-cyclodextrin on phytoremediation of soil co-contaminated with Cd and BDE-209 by arbuscular mycorrhizal amaranth

Pot experiments were conducted to investigate the effects of a series of β-cyclodextrin (β-CD) on phytoremediation of soil co-contaminated with Cd and BDE-209 by amaranth (Amaranthus hypochondriacus L.) inoculated with arbuscular mycorrhizal fungus (AMF) - Rhizophagus intraradices. Results showed that the combination of mycorrhizal amaranth and 0.4% β-CD (RI+β_0.4) significantly enhanced Cd concentrations and contents in shoots, total PBDEs concentration in roots, and BDE-209 dissipation in soil. Moreover, the RI+β_0.4 treatment exerted the highest removal efficiency of both Cd and BDE-209. On the contrary, the xylem area, shoot Cd and BDE-209 concentrations and contents, and removal efficiency of Cd were markedly reduced in mycorrhizal amaranth with 0.8% or 1.2% β-CD treatments (RI+β_0.8, RI+β_1.2), compared with single inoculation treatment. The well-organized chloroplast and well-defined root anatomical structure were also observed in the treatment of RI+β_0.4. Positive correlation was found between shoot biomass and chlorophyll concentrations. Shoot Cd or BDE-209 concentrations were positively correlated with xylem areas. In conclusion, mycorrhizal amaranth added with 0.4% β-CD could be used for the decontamination of soil polluted with mixture of Cd and BDE-209 due to the higher chlorophyll concentration and the larger xylem area.

Dibutyl phthalate contamination remolded the fungal community in agro-environmental system

Dibutyl phthalate (DBP) is a typical soil contaminant that is widely used as plasticizer in modern agricultural production. In this study, an experiment was conducted to evaluate fungal community succession in a soil-vegetable ecosystem under different DBP concentrations. By using high-throughput sequencing of the ribosomal internal transcribed spacer (ITS) region, it was shown that DBP contamination caused significant changes to the soil fungal community, in terms of both α and β diversities. The largest changes in fungal α and β diversities were detected under 50 mg/kg DBP concentration at the first day of addition. The bulk soils, rhizosphere soils and the phyllosphere harbored different fungal communities, while the abundance of saprotrophs and plant pathogens in the phyllosphere have been increased under DBP contamination. From correlation analysis and partial Mantel test, the change in fungal community α diversity was the result of multiple factors (DBP concentration, bacterial community and soil properties) while the β diversity of fungal community was mainly co-varied with the bacterial community after DBP contamination. Moreover, molecular ecological network analysis demonstrated that DBP contamination was detrimental to mutualistic relationships among fungal species and destabilized the network structure. Overall, the fungal communities in soils and around vegetables were largely remolded by DBP contamination that provides new insight into DBP contamination impacts on agricultural ecosystems.

Differences in Root Physiological and Proteomic Responses to Dibutyl Phthalate Exposure between Low- and High-DBP-Accumulation Cultivars of Brassica parachinensis

Di- n-butyl phthalate (DBP), as an endocrine-disrupting chemical that tends to be accumulated in crops, poses great risks to human health through the food chain. To identify the molecular mechanism underlying differences in their DBP accumulation, the root physiological and proteomic responses to DBP stress of two Brassica parachinensis cultivars, a high-DBP accumulator (Huaguan) and a low-DBP accumulator (Lvbao), were investigated. Root damage of greater severity and significantly greater ( p < 0.05) decreases in root protein content and root activity were detected in Lvbao than in Huaguan, suggesting that Lvbao had lower tolerance to DBP. In total, 52 DBP-responsive proteins were identified by two-dimensional electrophoresis and MALDI-TOF mass spectrometry. More proteins involved in basic metabolic processes, such as protein synthesis and energy metabolism, were downregulated in Lvbao, possibly explaining its lower tolerance and root damage. Several proteins involved in starch metabolism, cell-wall biosynthesis and modification, and stress response were activated in Huaguan, suggesting greater tolerance to DBP. Overall, differences in root proteome between the two cultivars might be responsible for the genotype-dependent DBP tolerance and accumulation in B. parachinensis.

Cultivar-Dependent Accumulation and Translocation of Perfluorooctanesulfonate among Lettuce ( Lactuca sativa L.) Cultivars Grown on Perfluorooctanesulfonate-Contaminated Soil

Perfluorooctanesulfonate (PFOS) is a toxic and persistent organic pollutant that can be widely detected in agricultural soils. In this study, two lettuce cultivars with low PFOS accumulation were screened out to reduce the exposure of PFOS to the human body via vegetable consumption. The screened low-PFOS cultivars may help to ensure food safety, despite planting in highly PFOS-polluted soils (1.0 mg/kg), due to their high tolerance to PFOS and 4.4-5.7 times lower shoot PFOS concentration than the high-PFOS cultivars. Protein content and protein-mediated transpiration played key roles in regulating PFOS accumulation in the lettuce cultivars tested. Lower protein content, lower stomatal conductance, and lower transpiration rate resulted in low PFOS accumulation. This study reveals the mechanism of forming low-PFOS accumulation of lettuce cultivars at physiological and biochemical levels and lays a foundation for developing a cost-effective and safe approach to grow vegetables in PFOS-polluted soils.

Genotypic variation and mechanism in uptake and translocation of perfluorooctanoic acid (PFOA) in lettuce (Lactuca sativa L.) cultivars grown in PFOA-polluted soils

The cultivation of crop cultivars with low pollutant accumulation is an important strategy to reduce the potential health risks of food produced from polluted soils. In this study, we identified three loose-leaf lettuce cultivars with low accumulation of perfluorooctanoic acid (PFOA), a highly toxic and persistent organic pollutant. PFOA concentrations in the shoots of low-PFOA cultivars were 3.7-5.5-fold lower than those of high-PFOA cultivars. The identification of low-PFOA cultivars could contribute to ensuring food safety despite cultivation in highly polluted soils (1 mg/kg) based on the tolerable daily PFOA intake (1.5 μg/kg/d). We detected lower desorbing fractions of PFOA in rhizosphere soil, lower bioconcentration factors, and higher distribution in the cell walls and organelles of roots in low-PFOA cultivars, all of which are key factors in limiting PFOA uptake and translocation from soil to shoots, than in high-PFOA cultivars. This study reveals the mechanism of PFOA uptake from soil to crop and lays a foundation for establishing a cost-effective strategy to plant crops in polluted soil and reduce exposure risk due to persistent organic pollutants in crops.

Global Picture of Protein Regulation in Response to Dibutyl Phthalate (DBP) Stress of Two Brassica parachinensis Cultivars Differing in DBP Accumulation

iTRAQ analysis was used to map the proteomes of two Brassica parachinensis cultivars that differed in dibutyl phthalate (DBP) accumulation. A total of 5699 proteins were identified to obtain 152 differentially regulated proteins, of which 64 and 48 were specific to a high- and a low-DBP-accumulation cultivar, respectively. Genotype-specific biological processes were involved in coping with DBP stress, accounting for the variation in DBP tolerance and accumulation. Formation of high DBP accumulation in B. parachinensis might attribute to the more effective regulation of protein expression in physiology and metabolism, including (a) enhanced cell wall biosynthesis and modification, (b) better maintenance of photosynthesis and energy balance, (c) greatly improved total capacity for antioxidation and detoxification, and (d) enhanced cellular transport and signal transduction. Our novel findings contribute to a global picture of DBP-induced alterations of protein profiles in crops and provide valuable information for the development of molecular-assisted breeds of low-accumulation cultivars.

Intraspecific variability of ciprofloxacin accumulation, tolerance, and metabolism in Chinese flowering cabbage (Brassica parachinensis)

To investigate the mechanism of genotype differences in ciprofloxacin (CIP) accumulation, this study was designed to compare the tolerance and metabolic responses to CIP exposure between low (Cutai) and high (Sijiu) CIP-accumulation cultivars of Brassica parachinensis. Decreases in biomass and chlorophyll content were significantly greater (p < 0.05) and toxicities were more severe within cell ultrastructures of Cutai compared to Sijiu. A sequential growth test also revealed that Sijiu was more tolerant to CIP stress compared to Cutai. Meanwhile, significantly higher (p < 0.05) root parameters and higher areas of the stele and xylem may be responsible for the increased uptake and transport of CIP in Sijiu. Ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis revealed that CIP was metabolized to three major metabolites by the hydroxylation and breakdown of the piperazinyl substituent in the CIP molecule. The enhanced metabolic transformation of CIP in Sijiu indicated a more efficient capacity to detoxify, which in turn favored an increased accumulation of CIP in this cultivar. Thus, the present study demonstrated that the stronger tolerance and metabolism of Sijiu to CIP were responsible for its high CIP accumulation, suggesting an evolutionary mechanism for adaptation to environmental stress.

Carboxylesterase-involved metabolism of di-n-butyl phthalate in pumpkin (Cucurbita moschata) seedlings

Uptake and accumulation by plants is a significant pathway in the migration and transformation of phthalate esters (PAEs) in the environment. However, limited information is available on the mechanisms of PAE metabolism in plants. Here, we investigated the metabolism of di-n-butyl phthalate (DnBP), one of the most frequently detected PAEs, in pumpkin (Cucurbita moschata) seedlings via a series of hydroponic experiments with an initial concentration of 10 mg L^-1. DnBP hydrolysis occurred primarily in the root, and two of its metabolites, mono-n-butyl phthalate (MnBP) and phthalic acid (PA), were detected in all plant tissues. The MnBP concentration was an order of magnitude higher than that of PA in shoots, which indicated MnBP was more readily transported to the shoot than was PA because of the former's dual hydrophilic and lipophilic characteristics. More than 80% of MnBP and PA were located in the cell water-soluble component except that 96% of MnBP was distributed into the two solid cellular fractions (i.e., cell wall and organelles) at 96 h. A 13-20% and 29-54% increase of carboxylesterase (CXE) activity shown in time-dependent and concentration-dependent experiments, respectively, indicated the involvement of CXEs in plant metabolism of DnBP. The level of CXE activity in root subcellular fractions was in the order: the cell water-soluble component (88-94%) >> cell wall (3-7%) > cell organelles (3-4%), suggesting that the cell water-soluble component is the dominant locus of CXE activity and also the domain of CXE-catalyzed hydrolysis of DnBP. The addition of triphenyl phosphate, a CXE inhibitor, led to 43-56% inhibition of CXE activity and 16-25% increase of DnBP content, which demonstrated the involvement of CXEs in plant metabolism of DnBP. This study contributes to our understanding of enzymitic mechanisms of PAE transformation in plants.