Effects of diethylphthalate and di-(2-ethyl)hexylphthalate on the physiology and ultrastructure of cucumber seedlings

Toxicity of dibutyl phthalate to pakchoi (Brassica campestris L.): Evaluation through different levels of biological organization

Dibutyl phthalate (DBP) is a typical persistent organic pollutant with a high load in the agricultural soils of vegetable crops. Currently, studies on the toxicity of DBP in vegetable crops are limited. Therefore, in this study, pakchoi (Brassica campestris L.), a typical vegetable crop, was used to evaluate the toxic effects of DBP. Pakchoi was exposed to DBP for 24 d at three doses (2, 20, and 200 mg/kg), and the phenotypic, biochemical, and molecular indicators were determined. The results revealed that DBP could reduce the emergence of pakchoi and inhibit plant height, root length, fresh weight, and leaf area. At the biochemical level, DBP exposure could reduce the content of three typical photosynthetic pigments (chlorophyll a and b and carotenoids). The effects of DBP exposure on the quality of pakchoi were primarily through reduced soluble sugar and increased proline contents. In addition, O₂·^- and H₂O₂ levels increased after DBP stress, and the corresponding antioxidant enzymes (SOD, POD, and CAT) were activated to resist oxidative damage. The dose- and time-dependent toxicities of DBP to pakchoi were demonstrated using an integrated biological response index. Finally, the molecular-level results on Day 24 showed that the three antioxidant enzyme genes (sod, pod, and cat) were significantly downregulated, and the antioxidant enzyme genes were more sensitive biomarkers than the enzyme activities. However, the expression level of enzyme genes was opposite to that of enzyme activity (SOD and POD); thus, DBP might directly interact with these enzymes. Molecular docking showed that DBP could stably bind near the SOD/POD active center through intermolecular interaction forces. This study provides essential information on the risk of DBP toxicity to vegetable crops.

Persistence behavior of chlorpyrifos and biological toxicity mechanism to cucumbers under greenhouse conditions

Chlorpyrifos, a broadly utilized insecticide, inhibits many cellular and physiological processes in plants. Here, the phyto-toxicity of chlorpyrifos on cucumber plants, as well as the dissipation kinetics of chlorpyrifos in leaves, were investigated. Those results showed that chlorpyrifos accumulated primarily in the leaves under normal agrochemical spraying conditions with the half-lives among 2.48-4.59 days. Residues of the primary metabolite, 3,5,6-trichloro-2-pyridinol (TCP), rapidly accumulated in plant tissues and soil with chlorpyrifos degradation. The application amount of chlorpyrifos had a significant effect on the persistence of chlorpyrifos and TCP in both plant and soil environments. Chlorpyrifos generated excessive reactive oxygen species (ROS) and malondialdehyde (MDA), which led to oxidative damage. High chlorpyrifos stress even inhibited antioxidant enzymes. The photosynthetic system and gas exchange were suppressed, which ultimately lead to inefficient light use under chlorpyrifos stress. Morphological results revealed that chlorpyrifos induced membrane damage and harmed organelles such as mitochondria and chloroplast. Noninvasive micro-test technology (NMT) showed that chlorpyrifos promoted intracellular Ca²⁺ influx and efflux of H⁺ and K⁺. The Ca²⁺ influx was significantly stimulated after both high and low chlorpyrifos treatment with the minimum value of - 336.33 pmol·cm^-2·s^-1 at 258 s and - 155.68 pmol·cm^-2·s^-1 at 288 s, respectively. Chlorpyrifos stress reversed the H⁺ influx to an efflux in cucumber mesophyll with the mean value of 0.45 ± 0.03 pmol·cm^-2·s^-1 and 0.19 ± 0.03 pmol·cm^-2·s^-1 in cucumber plants under low and high chlorpyrifos stress. High chlorpyrifos stress dramatically increase K⁺ efflux in cucumber leaves by 13.68 times higher than the control. We suggest that ion homeostasis destruction, accompanied by ROS, resulted in oxidative damage to the mesophyll cell of cucumber seedlings.

Biodegradation of Di-n-butyl phthalate in rhizosphere and growth-promoting effect of Cucumis sativus Linn. by a novel Pseudomonas sp. DNB-S1

Plant associated-bacteria can facilitate the host plant in overcoming contaminant-induced stress responses as well as improve plant development and growth. In this study, a successful approach was reported to reduce the Dibutyl phthalate (DBP) levels of polluted soil and, consequently, to improve cucumber growth. DBP suppressed development of cucumber seedings significantly, damage sub-cellular of root, especially the biomembrane system, and affected the microbial community structures of the soil. When DBP was applied at a concentration of 5 mg/kg to cucumber seedlings inoculated with degrading strain DNB-S1, the DBP residue in roots was very low. When the cucumber plants were exposed to DBP stress over 20 and 40 mg/kg DBP, the DBP residues in the roots inoculated with degrading strain DNB-S1 were reduced by 36.5% and 40.42% respectively, compared with the non-inoculation group. Moreover, DBP dissipation in rhizosphere soil is accelerated through inoculation with DNB-S1 which could effectively relieve the pressure of DBP stress on plant. The dry weight of cucumber roots inoculated with DBP-degrading bacterium was higher than that of non-inoculated seedlings. According to ultrastructural micrographs, the DBP-degrading bacteria could considerably alleviate the damaging effect of DBP on cucumber root cell organs. The application of strain DNB-S1 could efficiently alleviated the stress of DBP on the microbial community structure.

Simultaneous anaerobic decolorization/degradation of Reactive Black-5 azo dye and chromium(VI) removal by Bacillus cereus strain MS038EH followed by UV-C/H2O2 post-treatment for detoxification of biotransformed products

The existence of synthetic dyes and heavy metals in textile wastewater is a serious problem. These compounds should be removed before discharge into the environment by an appropriate method. The present study was conducted for the characterization of efficient multi-functional strain Bacillus cereus MS038EH for the simultaneous removal of Reactive Black-5 and Chromium(VI). Maximum decolorization efficiency of 94.74% was achieved at pH 7, 35 °C, and 4% inoculum size for 900 mg/L of Reactive Black-5. Also, 94.10% efficiency was observed in the presence of 8 g/L of yeast extract as an optimum nitrogen source, while carbon sources had no significant effect on decolorization. It should be pointed out that the decolorization efficiency was decreased from 94 to 64% by increasing NaCl concentrations from 0 to 50 g/L, respectively. Bacillus cereus strain MS038EH could decolorize 94.31% of Reactive Black-5 (900 mg/L) and remove 87.31% of chromium(VI) (30 mg/L) within 36 h. Results of Gas chromatography-mass spectrometry and Fourier transform-infrared spectroscopy proved that Reactive Black-5 was cleaved into the lower molecular weight products without any azo bonds. However, the phyto-toxicity analysis showed that Reactive Black-5 was not toxic for Triticum aestivum and Maize, while biologically treated Reactive Black-5 was toxic for seeds. Therefore, ultraviolet-C/H₂O₂ was applied for the detoxification of biotransformed products. When ultraviolet-C/H₂O₂ was applied as post-treatment, the seeds were germinated completely. It is demonstrated that the application of ultraviolet-C/H₂O₂ after anaerobic treatment is effective for toxicity reduction of textile wastewater.

Elucidating physiological and biochemical alterations in giant duckweed (Spirodela polyrhiza L. Schleiden) under diethyl phthalate stress: insights into antioxidant defence system

Background

The emollient properties of phthalates have led to their extensive production and intense use in plastic products. Owing to their weak covalent bonding with the plastic polymers, phthalates enter into the environment during their manufacturing, processing, disposal, consequently found their way directly into water sources, soil, and sediments.

Methods

The present study envisaged the toxic effects of diethyl phthalate (DEP) on physiological and biochemical attributes of Spirodela polyrhiza, when exposed to various concentrations of DEP (0, 10, 20, 40, 80, 100, 200, and 400 ppm) for short term exposure period of seven days.

Results

Plants of S. polyrhiza accumulated significant amount of DEP (112 mg kg⁻¹ fw) when exposed to various concentrations of DEP for seven days. Results depicted that DEP toxicity significantly (p ≤ 0.05) affected growth parameters and pigments in treated S. polyrhiza as compared to control. Further, high doses of DEP (400 ppm) caused significant decrement in carbohydrate (86%), protein (76%) and elevation in MDA content (42%). Meanwhile, DEP altered the activities of antioxidant enzymes (SOD, CAT, APX, GPX and GR) along with the induction of enhanced levels of proline, electrolyte leakage and phenolic content. Scanning electron microscopic and confocal studies also confirmed oxidative stress in plants under DEP stress.

Conclusions

Present findings will help understand the accumulation, tolerance, and detoxification mechanisms of DEP by S. polyrhiza to counteract the effects of reactive oxygen species (ROS), along with the evaluation of environmental threat for aquatic plants in aquatic ecosystems.

Accumulation, morpho-physiological and oxidative stress induction by single and binary treatments of fluoride and low molecular weight phthalates in Spirodela polyrhiza L. Schleiden

The present study examined the interactive effects of fluoride and phthalates on their uptake, generation of reactive oxygen species and activation of antioxidative defence responses in Spirodela polyrhiza L. Schleiden. A hydroponic study was conducted in which S. polyrhiza cultured in Hoagland’s nutrient medium, was exposed to fluoride (50 ppm) and different concentrations viz., 75, 150 300 ppm of diethyl phthalate (DEP) and diallyl phthalate (DAP) individually as well as in combination for the time period of 24, 72, 120 and 168 h respectively. A significant decline in fresh weight, dry to fresh weight ratio, total chlorophyll, carotenoid content and increased anthocyanin content was observed. Fluoride and phthalates was found to be readily accumulated by S. polyrhiza in all the exposure periods. Interestingly, when binary treatments were given in nutrient medium, uptake of both fluoride and phthalate was found to be influenced by each other. In combined treatments, DEP stimulated fluoride uptake, while its own uptake was restricted by fluoride. In contrary to this, fluoride stimulated DAP uptake. Moreover, combined stress further caused significant decrement in carbohydrate, protein content and increment in MDA levels, phenolic content and electrolyte leakage. Nevertheless, phthalates showed more pronounced oxidative stress and growth inhibition compared to fluoride. To cope up with the oxidative damage, enhanced level of antioxidant enzymatic activities was observed in S. polyrhiza under both fluoride and phthalate stress as compared to control. Scanning electron microscope imaging of leaf stomata revealed that combined stress of fluoride with phthalates caused distortion in the shape of guard cells. Confocal micrographs confirmed the generation of reactive oxygen species, cell damage, disruption in membrane integrity, and enhanced levels of glutathione in plant cells. This study focussed on ecotoxicological and interactive significance of fluoride led phthalate uptake or vice versa which was also assumed to confer tolerance attributes.

Phytotoxicity and oxidative effects of typical quaternary ammonium compounds on wheat (Triticum aestivum L.) seedlings

The large-scale use of quaternary ammonium compounds (QACs) in medicines or disinfectants can lead to their release into the environment, posing a potential risk to organisms. This study examined the effects of three typical QACs, dodecyltrimethylammonium chloride (DTAC), dodecyldimethylbenzylammonium chloride (DBAC), and didodecyldimethylammonium chloride (DDAC), on hydroponically cultured wheat seedlings. After 14 days of exposure, both hormesis and phytotoxicity were observed in the wheat seedlings. The shoot and root fresh weight gradually increased as QAC concentrations rose from 0.05 to 0.8 mg L^-1. However, higher QAC concentrations severely inhibited plant growth by decreasing shoot and root fresh weight, total root length, and photosynthetic pigment content. Moreover, the increase in malondialdehyde and O₂^.- contents, as well as root membrane permeability, reflected an oxidative burst and membrane lipid peroxidation caused by QACs. However, the effects of QACs on the levels of these oxidative stress markers were compound-specific, and the changes in superoxide dismutase, peroxidases, and catalase activity were partly related to reactive oxygen species levels. Considering the order of median effective concentration values (EC₅₀) and the levels of oxidative stress induced by the three tested QACs, their phytotoxicities in wheat seedlings increased in the following order: DDAC < DTAC < DBAC, which mainly depended on their characteristics and applied concentrations. These results, which illustrated the complexity of QAC toxicity to plants, could potentially be used to assess the risk posed by these compounds in the environment.

Effect of biochars on the bioavailability of cadmium and di-(2-ethylhexyl) phthalate to Brassica chinensis L. in contaminated soils

Soil co-contamination of potentially toxic elements (PTEs) and phthalate esters has become prominent due to its potential adverse effect on human food supply. There is limited information on using wood- and animal-derived biochars for the remediation of co-contaminated soils. Therefore, a pot experiment was conducted using Brassica chinensis L. as a bio-indicator plant to investigate the effect of P. orientalis biochar and pig biochar application on the bioavailability of cadmium (Cd) and di-(2-ethylhexyl) phthalate (DEHP) and on plant physiological parameters (malondialdehyde, proline and soluble sugars). Biochar materials were applied to two soils containing low (LOC) and high (HOC) organic carbon content at rates of 0, 0.5, 1, 2, and 4%. To better understand the influence of biochar, physicochemical properties and X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), Fourier transform-infrared spectrometry (FTIR), scanning electron microscopy (SEM) were characterized. Biochar application increased soil pH, organic carbon content, and available phosphorus content. Increasing biochar application rates decreased DTPA-extractable Cd and extractable DEHP concentrations in both soils. Biochar application reduced the plant uptake of both Cd and DEHP from co-contaminated soils; the maximum reduction of Cd (92.7%) and DEHP (52.0%) was observed in 2% pig biochar-treated LOC soil. The responses of plant physiological parameters to increased biochar applications indicated that less Cd and DEHP were taken up by plants. Pig biochar was more effective (P < 0.05) at reducing the bioavailability of Cd and DEHP in both soils than P. orientalis biochar; therefore, pig biochar had greater potential for improving the quality of the crop. However, the highest application rate (4%) of pig biochar restricted plant seed germination. Key factors influencing the bioavailability of Cd and DEHP in soils were soil organic carbon content, biochar properties (such as surface alkalinity, available phosphorus content and ash content) and biochar application rates.

Phthalic acid esters disturbed the genetic information processing and improved the carbon metabolism in black soils

Phthalic acid esters (PAEs), such as dimethyl phthalate (DMP) and dibutyl phthalate (DBP), are widely distributed as environmental pollutants. In this study, the effects of these chemicals were investigated in black soils using a metagenomics approach. The results clearly showed that DMP or DBP increased the abundance of genes involved in transcription, replication and repair in black soils. In addition, the abundances of genes associated with metabolic functions was improved following treatment with DMP or DBP, including those involved in lipid transport and metabolism, carbohydrate transport and metabolism, and energy production and conversion. There could be many reasons for these observed changes. First, the DMP or DBP treatments increased the abundances of genes associated with the LuxR family, the UvrABC repair system, DNA replication pathways, the RNA polymerase complex and base excision repair. Second, the abundances of genes associated with isocitrate lyase regulator (IclR) family transcriptional regulators, lipid metabolism and carbohydrate active enzymes (CAZys) were altered by the DMP or DBP treatments. Finally, the DMP or DBP treatments also increased the emission load of CO₂ and altered the fluorescence intensity of humic acid. Therefore, the results of this study suggested that DMP and DBP contamination altered the abundances of genes associated with genetic information processing and improved the carbon metabolism in black soils.

Di (2-ethylhexyl) phthalate-induced reproductive toxicity involved in dna damage-dependent oocyte apoptosis and oxidative stress in Caenorhabditis elegans

Di-(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer with a high environmental exposure level. As a persistent organic pollutant, DEHP causes reproductive and developmental toxicity in mammals. In this paper, the reproductive toxicity of DEHP was discussed using the model organism Caenorhabditis elegans to determine the sensitivity indices for evaluating the ecotoxicological effects of DEHP. L4 C. elegans larvae to evaluate the LC50 of DEHP and the changes in brood size and generation time, we found that the LC50 of DEHP to C. elegans exceeded 100 mg/L. And 10 mg/L DEHP exposure significantly reduced the brood sizes but not the generation time. Results of oocyte and distal-tip cell (DTC) counting suggested that the number of oocytes were decreased and apoptotic cells that from the unilateral gonad arm were increased in the 1 mg/L and 10 mg/L DEHP exposed groups. In contrast, there was no significant difference in the fluorescence intensity of DTC. Fluorescence analysis of HUS-1 showed that HUS-1 protein was overexpressed after DEHP exposure. The H₂O₂ level and DNA damage were measured by Bradford protein assay and AP staining respectively. The results showed that there was no significant difference in H₂O₂ level after DEHP exposure, in contrast, DNA damage was increased significantly. Moreover, 10 mg/L concentration DEHP exposure significantly increased the expression levels of apoptosis-related genes cep-1, egl-1, ced-4, and ced-3 and decreased the expression levels of ced-9. It suggested that cep-1, egl-1, ced-4, and ced-3 genes promote apoptosis and the ced-9 gene inhibits apoptosis. Meanwhile, 10 mg/L concentration DEHP exposure decreased the expression of oxidative stress-related genes mev-1 and gas-1. The mev-1 and gas-1 are mainly involved in the inhibition of oxidative stress in nematodes. In short, the decreased oocyte numbers and increased apoptosis oocyte numbers in C. elegans when exposed to DEHP, which may involve in the DNA damage induced by oxidative stress.

Applying β-cyclodextrin to amaranth inoculated with white-rot fungus for more efficient remediation of soil co-contaminated with Cd and BDE-209

A pot experiment was conducted to investigate the effect of a series of β-cyclodextrin (β-CD) concentrations on bioremediation of soil co-contaminated with Cd and BDE-209 using amaranth and the white-rot fungus Phanerochaete chrysosporium, with BDE-209 degrading ability. Results showed that the white-rot fungus was beneficial to the growth of amaranth, Cd uptake and BDE-209 degradation. Addition of β-CD further increased biomass of both shoots and roots, shoot Cd concentrations and contents, chlorophyll concentrations and soil manganese peroxidase (MnP) activities. Furthermore, well-organized mesophyll cells were observed in β-CD treatments, implying that the combination of white-rot fungus and β-CD can alleviate the stresses of Cd and BDE-209 to mesophyll cells. The BDE-209 degradation rate was positively correlated to β-CD concentration and MnP activity in soil. Our results also revealed that RF+β_0.8 treatment possessed the greatest Cd removal efficiency due to its well-configured mesophyll cells and the highest shoot biomass, chlorophyll concentration, and shoot Cd concentration. Considering simultaneous removal of Cd and BDE-209 from soil, using 0.8% β-CD to amaranth inoculated with white-rot fungus is a promising way forward for the phytoremediation of soil co-contaminated with Cd and BDE-209. A high percentage of mono-BDE was detected in inoculated amaranth, suggesting that BDE-209 was debrominated into low brominated PBDEs by the fungus in soil, which were then absorbed and further debrominated into mono-BDE in the plant.

Toxicological sensitivity of Pennisetum americanum (L.) K. Schum to atrazine exposure

The tolerance of Pennisetum americanum (L.) K Schum (P. americanum) to the herbicide atrazine, as well as the atrazine accumulation in exposed plants, was investigated in this study. The germination of P. americanum seeds was not significantly inhibited by exposure to atrazine at concentrations below 100 mg·L^-1. The roots of the seedlings were much more sensitive to atrazine than the shoots were, as shown by observations that shoot and root elongation were significantly inhibited by treatment with 100 and 50 mg·kg^-1 of atrazine, respectively. In addition, significant differences were found in the dry weights of the seedling shoots and roots after exposure to 50 and 20 mg·kg^-1 of atrazine, respectively. Atrazine accumulated readily in the roots of exposed seedlings, and the root ultrastructure was visibly damaged by exposure to lower levels of atrazine compared to the ultrastructure of the shoot. The contents of chlorophyll a and chlorophyll b and the transcription of psbA were inhibited by exposure to atrazine at concentrations above 20 mg·kg^-1. Finally, the tolerance threshold of P. americanum to atrazine was about 20 mg·kg^-1, indicating that the test plant exhibited some atrazine tolerance.

A simple method for the extraction and identification of light density microplastics from soil

This article introduces a simple and cost-saving method developed to extract, distinguish and quantify light density microplastics of polyethylene (PE) and polypropylene (PP) in soil. A floatation method using distilled water was used to extract the light density microplastics from soil samples. Microplastics and impurities were identified using a heating method (3-5s at 130°C). The number and size of particles were determined using a camera (Leica DFC 425) connected to a microscope (Leica wild M3C, Type S, simple light, 6.4×). Quantification of the microplastics was conducted using a developed model. Results showed that the floatation method was effective in extracting microplastics from soils, with recovery rates of approximately 90%. After being exposed to heat, the microplastics in the soil samples melted and were transformed into circular transparent particles while other impurities, such as organic matter and silicates were not changed by the heat. Regression analysis of microplastics weight and particle volume (a calculation based on image J software analysis) after heating showed the best fit (y=1.14x+0.46, R²=99%, p<0.001). Recovery rates based on the empirical model method were >80%. Results from field samples collected from North-western China prove that our method of repetitive floatation and heating can be used to extract, distinguish and quantify light density polyethylene microplastics in soils. Microplastics mass can be evaluated using the empirical model.

Effect of di-n-butyl phthalate (DBP) on the fruit quality of cucumber and the health risk

Di-n-butyl phthalate (DBP) widely used as plastic films' plasticizer, can cause agricultural pollution which is of increasing concern because of the food safety issues. Cucumber ( Cucumis sativus Linn.), commonly cultured in greenhouse, was exposed to DBP stress to gain more information about the ecological risk of DBP in this study. Changes of DBP residues and fruit quality of cucumber at different DBP concentrations (0, 5, 10, 20, 40 mg/kg of dry soil) were investigated in pot experiments using an agricultural soil under greenhouse condition, respectively. DBP residue in cucumber fruits ranged from 0.5326 to 1.8938 mg/kg, and the quality of cucumber fruits (organic acids, vitamin C, soluble protein, and soluble sugar) were influenced by DBP stress. Moreover, the health risk assessment was evaluated by estimate daily intakes (EDI) and the target hazard quotient (THQ) was analyzed. Under 40 mg/kg DBP condition, the highest value of EDI was 2.49 μg/kg bw/day and the THQ ranged from 0.000700 to 0.0249. Although the risk of DBP in cucumber fruits was lower than the threshold limit value of risk, the potential health risk was not a negligible issue.

Effect of dimethyl phthalate (DMP) on germination, antioxidant system, and chloroplast ultrastructure in Cucumis sativus L

Pollution of agricultural soils caused by widely employed plastic products, such as phthalic acid esters (PAEs), are becoming widespread in China, and they have become a threat to human health and the environment. However, little information is available on the influence of PAEs on vegetable crops. In this study, effects of different dimethyl phthalate (DMP) treatments (0, 30, 50, 100, and 200 mg L(-1)) on seed germination and growth of cucumber seedlings were investigated. Although germination rate showed no significant difference compared to control, seed germination time was significantly delayed at DMP greater than 50 mg L(-1). Concentrations of DMP greater than 30 mg L(-1) reduced cucumber lateral root length and number. The measurement of five physiological indexes in cucumber leaves with increasing DMP concentration revealed a decrease in leaf chlorophyll content, while proline and H2O2 contents increased. Peroxidase (POD) and catalase (CAT) activities increased in cucumber plants under 30 and 50 mg L(-1) DMP treatments compared to control; while after a 7-day treatment, these activities were seriously reduced under 100 and 200 mg L(-1) DMP treatments. According to transmission electron microscopy (TEM) micrographic images, the control and 30 mg L(-1) DMP treatments caused no change to leaf chloroplast shape with well-structured thylakoid membrane and parallel pattern of lamellae. At concentrations higher than 30 mg L(-1), DMP altered the ultrastructure of chloroplast, damaged membrane structure, disordered the lamellae, and increased the number and volume of starch grains. Moreover, the envelope of starch grains began to degrade under 200 mg L(-1) DMP treatment.

Effect of di-n-butyl phthalate on root physiology and rhizosphere microbial community of cucumber seedlings

The authors investigated the effects of di-n-butyl phthalate (DBP) on root physiology and rhizosphere microbial communities of cucumber seedlings (sativus L. cv Jinyan No. 4). Root protein content and root activity were observed to decrease. From the ultrastructural micrographs, visible impact on the mitochondria, endoplasmic reticulum and vacuole were detected. Moreover, the number of starch grains increased, and some were adhered to other cell components which might be the most direct evidence of DBP causing cellular damage. Results of PCR-DGGE (denaturing gradient gel electrophoresis) indicated that DBP significantly changed the abundance, structure and composition of rhizosphere bacteria when the concentration was higher than 50 mg L(-1). The relative abundances of Firmicutes increased while that of Bacteroidetes decreased. Bacillus was detected as the dominant bacteria in DBP contaminated cucumber rhizospheric soil. The amount of Actinobacteridae and Pseudomonas decreased until it disappeared in the rhizosphere soil when exposed to DBP concentrations higher than 50 mg L(-1).

Physical and chemical indices of cucumber seedling leaves under dibutyl phthalate stress

Phthalic acid ester (PAE) pollution to soil can lead to phytotoxicity in plants and potential health risks to human being. Dibutyl phthalate (DBP) as a kind of PAE has a large usage amount and large residues in soil. To analyze antioxidant responses of plants to DBP stress, effects of varying DBP concentrations on cucumber seedlings growth had been investigated. Malonaldehyde (MDA), hydrogen peroxide (H2O2), chlorophyll, proline, glutathione (GSH), and oxidized glutathione (GSSH) contents and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) were studied. The results showed that H2O2 content increased in cucumber seedlings with the increase of DBP concentration. The chlorophyll content in the higher DBP significantly declined compared to the control. In the present study, a disturbance of the GSH redox balance was evidenced by a marked decrease in GSH/GSSG ratio in cucumber seedlings subjected DBP stress. Our results indicated that DBP treatment not only inhibited antioxidant capacity and antioxidant enzyme activity in seedlings' leaves but might also induce chlorophyll degradation or reduce the synthesis of chlorophyll. Moreover, it could also enhance the accumulation of reactive oxygen species (ROS) which induced membrane lipid peroxidation. DBP also altered the ultrastructure of mesophyll cells, damaged membrane structure of chloroplast and mitochondrion, and increased the number and size of starch grains in chloroplasts reducing the photosynthetic capacity.

Effects of di-n-butyl phthalate on the physiology and ultrastructure of cucumber seedling roots

Agricultural pollution caused by the use of plastic sheetings has been documented to be a widespread problem in most of the major crop-planting regions of the world. In order to better understand the phytotoxic mechanisms induced by phthalic acid esters involved with this problem, Cucumber sativus L. cv Jinyan No. 4 were sown in pots to the three-leaf-stage in the presence of di-n-butyl phthalate (DBP; 0, 30, 50, 100, and 200 mg L(-1)) for 1, 3, 5, or 7 days. Physiology, biochemistry, and ultrastructure of seedling roots were examined. The results indicated that activities of three antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)) were stimulated at low-DBP treatments and decreased under higher levels (>100 mg L(-1)) compared to the controls. On the other hand, SOD and POD provided a better defense against DBP-induced oxidative damage in the roots of cucumber seeding, compared to CAT. The productions of both malondialdehyde (MDA) and proline (Pro) were promoted under DBP stress. Visible impact on the cytoderm, mitochondrion, and vacuole was detected, possibly as a consequence of free radical generation. These results suggested that activation of the antioxidant system by DBP led to the formation of reactive oxygen species that resulted in cellular damage.