Phytotoxicity and metabolic responses induced by tetrachlorobiphenyl and its hydroxylated and methoxylated derivatives in rice (Oryza sative L.)

Understanding the phytotoxic effects of organic contaminants on rice through predictive modeling with molecular descriptors: A data-driven analysis

The widespread introduction of organic compounds into environments poses significant risks to ecosystems. Assessing the adverse effects of organic contaminants on crops is crucial for ensuring food safety. However, laboratory research is often time-consuming and costly, and machine learning (ML) methods can offer a viable solution to address these challenges. This study aimed at developing a ML model that incorporates chemical descriptors to predict the phytotoxicity of organic contaminants on rice. A dataset was compiled by gathering published experimental data on the phytotoxicity of 60 organic compounds, with a focus on morphological inhibition, photosynthesis perturbation, and oxidative stress. Four ML models (RF, SVM, GBM, ANN) were developed using chemical molecular descriptors (CMD) and the Molecular ACCess System (MACCS) keys. RF-MACCS model demonstrated the highest fitness, achieving an R2 value of 0.79 and an RMSE of 0.14. Feature importance analysis highlighted nAtom, HBA, logKow, and TPSA as the most influential CMDs in our model. Additionally, substructures containing oxygen atoms, carbonyl group and carbon chains with nitrogen and oxygen atoms were identified as significant factors associated with phytotoxicity. This data-driven study could aid in predicting the phytotoxicity of organic contaminants on crops and evaluating the potential risks of emerging contaminants in agroecosystems.

Polybrominated diphenyl ethers (PBDEs) decreased the protein quality of rice grains by disturbing amino acid metabolism

Polybrominated diphenyl ethers (PBDEs) in soils posed potential risks to crop growth and food safety due to their prevalence and persistence. PBDEs were capable of being absorbed and accumulated into crops, impacting their growth, whereas the interference on metabolic components and nutritional composition deserves further elucidation. This study integrated a combined non-targeted and targeted metabolomics method to explore the influences of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) and decabromodiphenyl ether (BDE-209) on the metabolic responses of rice (Oryza sativa). Metabolic pathways, which were associated with sugars, organic acids, and amino acids, were significantly disturbed under PBDE stresses. Particularly, 75% of the marked altered pathways belonged to amino acid metabolism, with alanine/aspartate/glutamate metabolism being commonly enhanced. The degradation of aspartic acid promoted the formation of downstream amino acids, among which the levels of lysine, methionine, isoleucine, and asparagine were increased by 1.31-3.15 folds compared to the control. Thus, the antioxidant capacity in rice plants was enhanced, particularly through the significant promotion of ascorbic acid-glutathione (AsA-GSH) cycle in rice leaves. The amino acids were promoted to resist reactive oxygen species (ROS) efficiently, thus were deficient for nutrient storage. When exposed to 4 μmol/kg PBDEs, the contents of amino acids and proteins in grains decreased by 9.1-32.1% and 8.6-34.8%, respectively. In particular, glutelin level was decreased by 5.6-41.2%, resulting in a decline in nutritional quality. This study demonstrated that PBDEs deteriorated the protein nutrition in rice grains by affecting amino acid metabolism, providing a new perspective for evaluating the ecological risks of PBDEs and securing agricultural products.

Polybrominated diphenyl ethers and polychlorinated biphenyls induced rice "diabetes" by disturbing the transport and decomposition of soluble sugars

Halogenated flame retardants in farmlands were observed to inhibit the growth of exposed crops. This study aimed to elucidate the mechanism of inhibition on rice by employing four representative polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs). The exposure to these contaminants at 200 nM led to a decrease of 0.63-0.95 fold in rice below-ground biomass and 0.49-0.66 fold in yield, and a corresponding 4%-10% increase in soluble sugars in leaves. PBDEs and PCBs were found to significantly disrupt the synthesis, decomposition, and transport of sugars in leaves, the three pivotal determinants of crop growth. Notably, these compounds promoted a 1.41- to 7.60-fold upregulation of the triose phosphate translocator, significantly enhancing soluble sugar synthesis. Conversely, a 0.45-0.97 fold downregulation was observed for sucrose transporters, thus impeding the leaf-to-shoot efflux of soluble sugars. Furthermore, PBDEs and PCBs were favorably bound to fructose-1,6-bisphosphate aldolase (FBA), inducing its substrate-specific dysfunction in fructose-1,6-diphosphate decomposition (3%-14%). Overall, PBDE and PCB exposure promoted a notable intracellular accumulation of soluble sugars in rice leaves, a typical symptom of plant diabetes, since the intensified synthesis of soluble sugars in leaves and the repressed decomposition and transportation of soluble sugars to other storage organs, thus impeding crop growth. This study provided an insightful understanding of the toxic effects and molecular mechanisms of halogenated flame retardants, highlighting their role in abnormal sugar accumulation and growth inhibition in crops and offering vital information for the risk assessment and administration of these compounds to guarantee the safety of agricultural products.

Polychlorinated biphenyls modify Arabidopsis root exudation pattern to accommodate degrading bacteria, showing strain and functional trait specificity

Introduction

The importance of plant rhizodeposition to sustain microbial growth and induce xenobiotic degradation in polluted environments is increasingly recognized.

Methods

Here the "cry-for-help" hypothesis, consisting in root chemistry remodeling upon stress, was investigated in the presence of polychlorinated biphenyls (PCBs), highly recalcitrant and phytotoxic compounds, highlighting its role in reshaping the nutritional and signaling features of the root niche to accommodate PCB-degrading microorganisms.

Results

Arabidopsis exposure to 70 µM PCB-18 triggered plant-detrimental effects, stress-related traits, and PCB-responsive gene expression, reproducing PCB phytotoxicity. The root exudates of plantlets exposed for 2 days to the pollutant were collected and characterized through untargeted metabolomics analysis by liquid chromatography-mass spectrometry. Principal component analysis disclosed a different root exudation fingerprint in PCB-18-exposed plants, potentially contributing to the "cry-for-help" event. To investigate this aspect, the five compounds identified in the exudate metabolomic analysis (i.e., scopoletin, N-hydroxyethyl-β-alanine, hypoxanthine, L-arginyl-L-valine, and L-seryl-L-phenylalanine) were assayed for their influence on the physiology and functionality of the PCB-degrading strains Pseudomonas alcaliphila JAB1, Paraburkholderia xenovorans LB400, and Acinetobacter calcoaceticus P320. Scopoletin, whose relative abundance decreased in PCB-18-stressed plant exudates, hampered the growth and proliferation of strains JAB1 and P320, presumably due to its antimicrobial activity, and reduced the beneficial effect of Acinetobacter P320, which showed a higher degree of growth promotion in the scopoletin-depleted mutant f6'h1 compared to Arabidopsis WT plants exposed to PCB. Nevertheless, scopoletin induced the expression of the bph catabolic operon in strains JAB1 and LB400. The primary metabolites hypoxanthine, L-arginyl-L-valine, and L-seryl-L-phenylalanine, which increased in relative abundance upon PCB-18 stress, were preferentially used as nutrients and growth-stimulating factors by the three degrading strains and showed a variable ability to affect rhizocompetence traits like motility and biofilm formation.

Discussion

These findings expand the knowledge on PCB-triggered "cry-for-help" and its role in steering the PCB-degrading microbiome to boost the holobiont fitness in polluted environments.

Metabolome regulation and restoration mechanism of different varieties of rice (Oryza sativa L.) after lindane stress

There is a lack of studies on the ability of plants to metabolize chlorinated organic pollutants (COPs) and the dynamic expression changes of metabolic molecules during degradation. In this study, hybrid rice Chunyou 927 (CY) and Zhongzheyou 8 (ZZY), traditional rice subsp. Indica Baohan 1 (BH) and Xiangzaoxian 45 (XZX), and subsp. Japonica Yangjing 687 (YJ) and Longjing 31 (LJ) were stressed by a typical COPs of lindane and then transferred to a lindane-free culture to incubate for 9 days. The cumulative concentrations in the roots of BH, XZX, CY, ZZY, YJ and LJ were 71.46, 65.42, 82.06, 80.11, 47.59 and 56.10 mg·kg-1, respectively. And the degradation ratios on day 9 were 87.89 %, 86.92 %, 94.63 %, 95.49 %, 72.04 % and 82.79 %, respectively. On the 0 day after the release of lindane stress, the accumulated lindane inhibited the normal physiological activities of rice by affecting lipid metabolism in subsp. Indica BH, amino acid metabolism and synthesis and nucleotide metabolism in hybrid CY. Carbohydrate metabolism of subsp. Japonica YJ also was inhibited, but with low accumulation of lindane, YJ regulated amino acid metabolism to resist stress. With the degradation of lindane in rice, the amino acid metabolism of BH and CY, which had high degradation ratios on day 9, was activated to compound biomolecules required for the organism to recover from the damage. Amino acid metabolism and carbohydrate metabolism were disturbed and inhibited mainly in YJ with low degradation ratios. This study provides the difference of the metabolic capacity of the metabolic capacity of different rice varieties to lindane, and changes at the molecular level and metabolic response mechanism of rice during the metabolism of lindane.

Tolerance mechanism of rice (Oryza sativa L.) seedings towards polycyclic aromatic hydrocarbons toxicity: The activation of SPX-mediated signal transduction to maintain P homeostasis

Plant tolerance to abiotic stress depends on fast molecular cascades involving stress perception, signal transduction, gene expression alterations, and metabolic rearrangement. This study sheds light on the tolerance mechanism of rice (Oryza sativa L.) towards the toxicity of the polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (Phe), pyrene (Pyr), and benzo[a]pyrene (BaP). Results showed that three PAHs significantly activated the phosphoinositide signaling system involving the phosphorus (P) metabolism and homeostasis in rice roots. This activation increased phytic acid (IP6) levels to over 54.12% of the control (p < 0.05). Molecular docking verified that three PAHs occupied the IP6 binding site in SPX3, a negative regulatory factor of P homeostasis, where ARG229 interacted with PAHs via the van der Waals force. Moreover, the expression of gene encoding SPX3 was significantly downregulated 2.81-, 2.83-, and 2.18-fold under Phe, Pyr, and BaP stress, respectively, relative to the control. Conversely, the expression levels of the gene coding SDEL2 was significantly increased, promoting the degradation of SPX3. Ultimately, P absorption and nucleic acid synthesis were enhanced, alleviating the inhibition effect of PAHs on rice growth. Notably, Pyr demonstrated the strongest binding affinity for SPX3, confirming its critical interference with P homeostasis. These findings provide insight into the molecular mechanisms regulating plant responses to PAHs, and offer guidance for improving crop resistance against organic pollutants and protecting food security.

Effect of natural soil nanocolloids on the fate and toxicity of cadmium to rice (Oryza sativa L.) roots

Toxic heavy metals are common contaminants and will most likely interact with ubiquitous natural nanocolloids (Ncs) in the soil environment. However, the effect of soil Ncs on the fate and health risk of cadmium (Cd) have not been well addressed. Here, the interaction between Ncs and Cd is investigated using two-dimensional correlation spectroscopy (2DCOS) combined with synchronous fluorescence and Fourier transform infrared spectroscopy. Our results reveal that Cd binding to the soil Ncs surface is mainly driven through strong hydrophilic effects and π - π interactions, which contribute to a high adsorption capacity (366-612 mg/g) and strong affinity (K_L = 4.3-9.7 L/mg) of Cd to soil Ncs. Interestingly, soil Ncs and Cd coexposure can significantly mediate the phytotoxicity (e.g., uptake, root growth, and oxidative stress) of Cd to rice (Oryza sativa L.) roots after 7 days of exposure. At the molecular level, metabolomic analysis reveals that the downregulated metabolic pathways (e.g., isoquinoline alkaloid and aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism) may contribute to the above adverse phytotoxicity. This study provides new insight into the effect of natural Ncs on the fate and health risks of toxic heavy metals in soil environments.

Metabolomic analysis reveals the impact of ketoprofen on carbon and nitrogen metabolism in rice (Oryza sativa L.) seedling leaves

Pharmacologically active compounds (PACs) are becoming common pollutants in the natural environment, posing potential risks to crop quality; however, the toxic effects and metabolic changes that they cause in agricultural plants remain unclear. Here, we investigated the effects of ketoprofen on respiration rate, ATP synthesis, carbon and nitrogen metabolism, and metabolomics in rice seedling leaves. The results showed that ketoprofen treatment adversely affected the respiration rate, ATP content, H⁺-ATPase activity and induced changes in the contents of carbon assimilation products (soluble sugar, reducing sugar, sucrose, and starch) and the activities of key enzymes in carbon metabolism (sucrose synthase (SS), sucrose phosphate synthase (SPS), and sucrose invertase (InV)). The contents of nitrate, ammonium, and free amino acids, and the activities of key enzymes involved in nitrogen metabolism (nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH)) were also affected in a concentration-dependent manner. Metabolomics analysis showed that ketoprofen disturbed the type and content of metabolites (amino acids, carbohydrates, and secondary metabolites) to varying degrees and perturbed key metabolic pathways (substance synthesis and energy metabolism), ultimately resulting in the reduction of rice seedling biomass. This study provides important information and a useful reference for the accurate assessment of the environmental risks of PACs.

Biotransformation of Organophosphate Esters by Rice and Rhizosphere Microbiome: Multiple Metabolic Pathways, Mechanism, and Toxicity Assessment

The biotransformation behavior and toxicity of organophosphate esters (OPEs) in rice and rhizosphere microbiomes were comprehensively studied by hydroponic experiments. OPEs with lower hydrophobicity were liable to be translocated acropetally, and rhizosphere microbiome could reduce the uptake and translocation of OPEs in rice tissues. New metabolites were successfully identified in rice and rhizosphere microbiome, including hydrolysis, hydroxylated, methylated, and glutathione-, glucuronide-, and sulfate-conjugated products. Rhizobacteria and plants could cooperate to form a complex ecological interaction web for OPE elimination. Furthermore, active members of the rhizosphere microbiome during OPE degradation were revealed and the metagenomic analysis indicated that most of these active populations contained OPE-degrading genes. The results of metabolomics analyses for phytotoxicity assessment implied that several key function metabolic pathways of the rice plant were found perturbed by metabolites, such as diphenyl phosphate and monophenyl phosphate. In addition, the involved metabolism mechanisms, such as the carbohydrate metabolism, amino acid metabolism and synthesis, and nucleotide metabolism in Escherichia coli, were significantly altered after exposure to the products mixture of OPEs generated by rhizosphere microbiome. This work for the first time gives a comprehensive understanding of the entire metabolism of OPEs in plants and associated microbiome, and provides support for the ongoing risk assessment of emerging contaminants and, most critically, their transformation products.

β-Glucosidases as dominant dose-dependent regulators of Oryza sativa L. in response to typical organic pollutant exposures

Understanding the metabolic defense and compensation to maintain homeostasis is crucial for assessing the potential health risk of organic pollutants in crops. Currently, limited understanding is available regarding the targeted metabolic pathways and response mechanism under contaminant stress. This study showed that ciprofloxacin (CIP) at the environmental concentrations (1, 5, 25, 50 mg/L) did not significantly inhibit growth or cause severe oxidative damage to rice (Oryza sativa L.). Instead, the increment in CIP concentration induced a series of sequential metabolic disorders, which were characterized predominantly by primary and secondary metabolic disturbances, including phenylpropanoid biosynthesis, the carbohydrate, lipid and amino acid metabolism. After CIP in vivo exceeded a certain threshold level (>0.29 mg/g dry weight), β-glucosidases (BGLUs) mediated the transition from the activation of the genes related to phenylpropanoid biosynthesis to the inhibition of the genes related to carbohydrate metabolism in rice. In particular, starch and sucrose metabolism showed the most profound perturbation stressed by environmental concentrations of CIP (5 mg/L) and other tested organic pollutants (10 μg/L of tricyclazole, thiamethoxam, polybrominated diphenyl ethers, and polychlorinated biphenyls). Besides, the key genes encoding endoglucanase and BGLU were significantly downregulated (|log₂FC| > 3.0) under 100 μg/L of other tested organic pollutants, supporting the transition from the activation of secondary defense metabolism to the disruption of primary energy metabolism. Thus, in addition to bioaccumulation, changes in BGLU activity and starch and sucrose metabolism can reflect the potential adverse effects of pollutants on rice. This study explained the stepwise metabolic and transcriptional responses of rice to organic pollutants, which provided a new reference for the comprehensive evaluation of their environmental risks.

In vivo phytotoxic effect of yttrium-oxide nanoparticles on the growth, uptake and translocation of tomato seedlings (Lycopersicon esculentum)

The potential toxicity and ecological risks of rare-earth nanoparticles in the environment have become a concern due to their widespread application and inevitable releases. The integration of hydroponics experiments, partial least squares structural equation modeling (PLS-SEM), and Transmission Electron Microscopy (TEM) were utilized to investigate the physiological toxicity, uptake and translocation of yttrium oxide nanoparticles (Y₂O₃ NPs) under different hydroponic treatments (1, 5, 10, 20, 50 and 100 mg·L^-1 of Y₂O₃ NPs, 19.2 mg·L^-1 Y(NO₃)₃ and control) in tomato (Lycopersicon esculentum) seedlings. The results indicated that Y₂O₃ NPs had a phytotoxic effect on tomato seedlings' germination, morphology, physiology, and oxidative stress. The Y₂O₃ NPs and soluble Y^III reduced the root elongation, bud elongation, root activity, chlorophyll, soluble protein content and superoxide dismutase and accelerated the proline and malondialdehyde in the plant with increasing concentrations. The phytotoxic effects of Y₂O₃ NPs on tomato seedlings had a higher phytotoxic effect than soluble Y^III under the all treatments. The inhibition rates of different levels of Y₂O₃ NPs in shoot and root biomass ranged from 0.2% to 6.3% and 1.0-11.3%, respectively. The bioaccumulation and translocation factors were less than 1, which suggested that Y₂O₃ NPs significantly suppressed shoot and root biomass of tomato seedlings and easily bioaccumulated in the root. The observations were consistent with the process of concentration-dependent uptake and translocation factor and confirmed by TEM. Y₂O₃ NPs penetrate the epidermis, enter the cell wall, and exist in the intercellular space and cytoplasm of mesophyll cells of tomato seedlings by endocytic pathway. Moreover, PLS-SEM revealed that the concentration of NPs significantly negatively affects the morphology and physiology, leading to the change in biomass of plants. This study demonstrated the possible pathway of Y₂O₃ NPs in uptake, phytotoxicity and translocation of Y₂O₃ NPs in tomato seedlings.

Photosynthetic, antioxidative, and metabolic adjustments of a crop plant to elevated levels of La and Ce exposure

Rare earth elements (REEs) have been widely applied as fertilizers in farmland of China for decades to improve the yield and quality of crops. Unfortunately, adverse effects on plants have been observed due to overdosing with REEs. Until now, the toxicology of REEs was mainly evaluated based on phenotypic responses, but knowledge gaps still exist concerning their metabolic effects. Here, the physiological responses and nontargeted metabolomics studies were combined to systematically explore the potential effects of La and Ce on a crop plant, wheat Triticum aestivum. It was observed that REEs accumulated in the shoots of wheat, with significant reduction of the shoot biomass at higher exposure doses. The disturbance of photosynthesis and induced oxidative stress were identified by analyzing indicators of the photosynthetic (chlorophyll a/b, carotenoid and rubisco) and antioxidant systems (POD, CAT, SOD, GSH and MDA). Furthermore, the global metabolic profiles of REEs treatment groups and the non-exposed control group were screened and compared, and the metabolomic disturbance of REEs was dose-dependent. A high overlap of significantly changed metabolites and matched disturbed biological pathways was found between La and Ce treatments, indicating similarity of their toxicity mechanism in wheat shoots. Generally, the perturbed metabolomic pathways were mainly related to carbohydrate, amino acid and nucleotide/side metabolism, suggesting a disturbance of carbon and nitrogen metabolism, which finally affected the growth of wheat. We thus proved the potential adverse effect of inappropriate application of REEs in crop plants and postulated metabolomics as a feasible tool to identify the underlying toxicological mechanisms.

Identification of 2,2',4,5,5'-Pentachlorobiphenyl (PCB101) metabolites and their transmission characteristics in silver crucian carp (Carassius auratus gibelio)

Polychlorinated biphenyls (PCBs) have been attracting global concern due to their persistence and toxicity. However, the study on the metabolites of PCBs in freshwater fish is limited. In this study, the metabolites of 2,2',4,5,5'-Pentachlorobiphenyl (PCB101) in silver crucian carp (Carassius auratus gibelio) were identified for the first time. After intraperitoneal injection of PCB101 (2 mg/kg), the results showed that it could be metabolized to at least three types of metabolites, including hydroxylated (OH-), methoxylated (MeO-) and methyl sulfonated (MeSO₂-) PCB101. The OH- metabolites identified in most tissues were 3-OH-PCB101and 4-OH-PCB101, such as liver, gallbladder, blood and muscle. MeSO₂- metabolites identified in gallbladder, blood and brain were 3-MeSO₂-PCB101 and 4-MeSO₂-PCB101. Meanwhile, the MeO- metabolite identified in liver, gallbladder, blood and spleen of silver crucian carp was 4-MeO-PCB101. The investigation of the types and structures of PCB101 and its metabolites, as well as the tissue distribution and accumulation characteristics in silver crucian carp are beneficial to understand the transformation and metabolic mechanisms of PCBs in aquatic organisms. It is of great significance to identify potential pollution hazards of precursor compounds and their metabolites on aquatic products and ensure the quality and safety of aquatic products.

Uptake and accumulation of erythromycin in leafy vegetables and induced phytotoxicity and dietary risks

Erythromycin (ERY), a widely used macrolide antibiotic, is omnipresent in soil and aquatic environments, which may potentially contaminate food crops but remains to be explored. Two leafy vegetables, pakchoi (Brassica rapa subsp. chinensis) and water spinach (Ipomoea aquatica Forsk.), were grown in laboratory-constructed soil or hydroponic systems to investigate the dynamic accumulation of ERY in edible plants. Results indicate ¹⁴C-ERY could be absorbed by water spinach and pakchoi in both systems. Autoradiographic imaging and concentration data of plant tissues suggested that ERY had limited translocation from roots to shoots in these two vegetables. The accumulation level of ERY was similar between the two vegetables in the soil system; but in the hydroponic system, pakchoi had a higher ERY accumulation than water spinach, with the bioconcentration factor of 2.74-25.98 and 3.65-11.67 L kg^-1, respectively. The ERY intake via vegetable consumption was 0.01-2.17 ng kg^-1 day^-1, which was much lower than the maximum acceptable daily intake (700 ng kg^-1 day^-1), indicating negligible risks of consuming vegetables with roots exposed to ERY at environmentally relevant levels. In addition, ERY was found to cause growth inhibition and oxidative stress to pakchoi, even at low concentrations (7 and 22 μg L^-1). This work contributes to a better understanding of plant uptake and translocation of ERY in soils and water, and has important implications for the reasonable evaluation of the implied risks of ERY to vegetables and human health.

Molecular Mechanism of Organic Pollutant-Induced Reduction of Carbon Fixation and Biomass Yield in Oryza sativa L

Photosynthetic carbon fixation is fundamental for plant growth and is a key process driving the global carbon cycle. This study explored the mechanism of disturbed carbon fixation in Oryza sativa L. by organic pollutants 2,3,4,5-tetrachlorobiphenyl (CB 61), 4'-hydroxy-2,3,4,5-tetrachlorobiphenyl (4'-OH-CB 61), 2,2',4,4'-tetrabromo diphenyl ether (BDE 47), tricyclazole (TRI), and pyrene. The biomass of rice exposed to 4'-OH-CB 61, TRI, and BDE 47 was on average 80.63% of that of the control (p < 0.05), and the inhibition of net photosynthetic rate was 59.15% by 4'-OH-CB 61. Proteomics confirmed that 4'-OH-CB 61 significantly downregulated the enzymes in the photosynthetic carbon fixation pathway, which was attributed to the decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the rate-limiting enzyme in the Calvin cycle. In detail, decreased Rubisco activity (6.96-33.44%) and downregulated OsRBCS2-5 encoding small Rubisco subunits (-6.80 < log₂FC < -2.13) by 4'-OH-CB 61, TRI, and BDE 47 were in line with biomass yield reduction. Molecular docking and dynamic simulation suggested that the three pollutants potentially competed with CO₂ for binding to the active sites in Rubisco, leading to reduced CO₂ capture efficiency. These results revealed the molecular mechanism of organic pollution-induced rice yield reduction, contributing to improving the understanding of crop growth and carbon sequestration capacity of organics-contaminated soils globally.

Simulation experiment on OH-PCB being ingested through daily diet: Accumulation, transformation and distribution of hydroxylated-2, 2', 4, 5, 5'-pentachlorobiphenyl (OH-PCB101) in mice

Animals exposure to polychlorinated biphenyls (PCBs) may result in retention of hydroxylated PCBs (OH-PCBs). OH-PCBs can be accumulated in animals, including humans, through the transmission of food chain. However, there are few studies on the accumulation and metabolism of OH-PCBs exposed to the body through daily diet. Therefore, this study was conducted to investigate the fate of OH-PCBs after being ingested through dietary intake. By adding 3-OH-PCB101 and 4-OH-PCB101 to the edible tissue of crucian carp, which were used as raw materials to prepare mouse feed, with an exposure concentration of 2.5 μg/kg ww. The exposure experiment lasted for a total of 80 days. The blood, feces and 11 tissues of mice at different times were analyzed qualitatively and quantitatively. It was found that major OH-PCB101 were accumulated in intestine or excreted with feces. A small part was accumulated in heart, lung and spleen. For the first time that the conversion from OH-PCB101 to PCB101 in mice was discovered, which shows from another perspective that persistent organic pollutants are difficult to be completely degraded in the environment. 4-MeO-PCB101, 3-MeSO₂-PCB101, and 4-MeSO₂-PCB101 were also found in various tissues. The results of this study show that after OH-PCBs accumulated in animals re-enter the organism through the food chain, they can be metabolized again and may be reversely transformed into the parent compounds. The present research shed new light on simulating the metabolic transformation process of OH-PCBs exposed to mammals through ingestion of fish. Available data show that second-generation persistent organic pollutants in the environment still need to be continuously concerned.

Interconversion between methoxylated, hydroxylated and sulfated metabolites of PCB 3 in whole poplar plants

Methoxylated polychlorinated biphenyls (MeO-PCBs) are overlooked metabolites of PCBs. In general, they are more toxic to plants than their parent congeners. However, information on the fate of MeO-PCBs and the relationship between methoxylated, hydroxylated and sulfated metabolites of PCBs in plants is scarce. In this work, poplar plants (Populus deltoides × nigra, DN34) were hydroponically and separately exposed to 4'-methoxy-4-monochlorobiphenyl (4'-MeO-PCB 3) and 4'-PCB 3 sulfate for 10 days to investigate the uptake, translocation and metabolism of MeO-PCBs and the relationship between methoxy-PCBs, hydroxyl-PCBs and PCB sulfates within plants. Results showed that 4'-MeO-PCB 3 and 4'-PCB 3 sulfate were taken up by the roots of poplar plants and translocated from roots to shoots and leaves. 4'-OH-PCB 3 and 4'-PCB 3 sulfate were identified as the hydroxylated metabolite and sulfate metabolite of 4'-MeO-PCB 3 in poplar, respectively. In the backward reaction, 4'-OH-PCB 3 and 4'-MeO-PCB 3 were found as metabolites of 4'-PCB 3 sulfate. For exposure groups, the yields of 4'-OH-PCB 3 produced from 4'-MeO-PCB 3 and 4'-PCB 3 sulfate were 1.29% and 0.13% respectively. The yield of 4'-PCB 3 sulfate which originated from 4'-MeO-PCB 3 in wood and root samples of exposure groups was only 0.02%. Only 0.04% of the initial mass of 4'-PCB 3 sulfate was transformed to 4'-MeO-PCB 3 in the exposure groups. The sulfation yield of 4'-OH-PCB 3 was higher than hydrolysis yield of 4'-PCB 3 sulfate, indicating that formation of PCB sulfates was predominant over the reverse reaction, the formation of hydroxy-PCBs. These results provide new perspective on the transport, metabolism, and fate of MeO-PCBs, and also help to better understand sources of OH-PCBs and PCB sulfates in the environment. This study provides the first evidence of interconversion of sulfate metabolites from methoxy-PCBs and methoxy-PCBs from PCB sulfates.

Disturbed phospholipid metabolism by three polycyclic aromatic hydrocarbons in Oryza sativa

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in soils that can be readily absorbed by crops, affecting growth and development. Phospholipids (PLs) are essential components of cell membrane and can indicate cellular responses to various organic pollutants. However, the detailed molecular mechanism of phospholipid metabolism based regulation employed by crops in response to PAHs stresses remains elusive. This study characterized the accumulation patterns of representative PAHs, namely phenanthrene (PHEN), pyrene (PY), and benzo[a]pyrene (BaP) in rice (Oryza sativa). Crop's responses to PAHs via the regulation of phospholipid metabolism were also explored. PHEN exhibited the highest accumulation in both roots and shoots, followed by PY and BaP, despite PY exhibited much greater phytotoxicity than the other two PAHs. The exposure to 10-500 μg/L PY resulted in downregulations of the phospholipase A₂ genes PLA₂-3, PLA₂-4, and PLA₂-6 (to 19% of the control without exposure) and phospholipase C genes PLC-1, PLC-2, and PLC-4 (to 50% of the control), consistent with the changes in phospholipase activity. The contents of typical PLs, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidic acid also decreased to a greater extent than those in the PHEN- and BaP-exposed groups. These were the major reasons for the relatively high phytotoxicity of PY, in terms of growth inhibition and cell membrane damage. These findings provide a more comprehensive understanding of crop responses to PAHs and provide insights into risk assessment of soil PAH contamination, which hold potentials in improving food safety and quality worldwide.

Phytotoxicity of tris-(1-chloro-2-propyl) phosphate in soil and its uptake and accumulation by pakchoi (Brassica chinensis L. cv. SuZhou)

This study investigated physiological and biochemical changes in pakchoi at different growth stages (25 and 50 d) under different tris-(1-chloro-2-propyl) phosphate (TCIPP) treatments (10, 100, 500, and 1000 μg kg^-1). The uptake and accumulation of TCIPP by pakchoi and variation of TCIPP speciation in soil were also determined. TCIPP decreased the length and fresh weight of pakchoi root compared with those in blank controls, and this effect was significant when the concentration of TCIPP was higher than 100 μg kg^-1. The fresh weight of pakchoi stems and leaves, the chlorophyll content, and the activities of superoxide dismutase, peroxidase, and catalase in the leaves first increased and then decreased with increasing TCIPP concentration. The inflection point of the variation in these indices was 100 μg kg^-1 TCIPP in soil. The contents of proline and malondialdehyde increased continuously with increasing TCIPP concentration. The uptake of TCIPP by pakchoi increased linearly with increasing TCIPP concentration, and the highest TCIPP concentrations in the roots, stems, and leaves were 275.9, 80.0, and 2126.3 μg kg^-1, respectively. TCIPP was easily transferred from the roots to leaves of pakchoi, with translocation factor of up to 12.6. The content of bioavailable TCIPP in soil was high, accounting for 46.5%. Planting pakchoi could significantly reduce the content of bioavailable TCIPP, with removal rate of 39.9%-54.1%. After 50 d of planting pakchoi, the removal rate of TCIPP in soil (10.4%-18.6%) was significantly higher than that in the control without plant, but the contribution of phytoextraction was small, accounting for 2.62%-26.6%.

'Cry-for-help' in contaminated soil: a dialogue among plants and soil microbiome to survive in hostile conditions

An open question in environmental ecology regards the mechanisms triggered by root chemistry to drive the assembly and functionality of a beneficial microbiome to rapidly adapt to stress conditions. This phenomenon, originally described in plant defence against pathogens and predators, is encompassed in the ‘cry‐for‐help’ hypothesis. Evidence suggests that this mechanism may be part of the adaptation strategy to ensure the holobiont fitness in polluted environments. Polychlorinated biphenyls (PCBs) were considered as model pollutants due to their toxicity, recalcitrance and poor phyto‐extraction potential, which lead to a plethora of phytotoxic effects and rise environmental safety concerns. Plants have inefficient detoxification processes to catabolize PCBs, even leading to by‐products with a higher toxicity. We propose that the ‘cry‐for‐help’ mechanism could drive the exudation‐mediated recruitment and sustainment of the microbial services for PCBs removal, exerted by an array of anaerobic and aerobic microbial degrading populations working in a complex metabolic network. Through this synergistic interaction, the holobiont copes with the soil contamination, releasing the plant from the pollutant stress by the ecological services provided by the boosted metabolism of PCBs microbial degraders. Improving knowledge of root chemistry under PCBs stress is, therefore, advocated to design rhizoremediation strategies based on plant microbiome engineering.

Metabolomics reveals the inhibition on phosphorus assimilation in Chlorella vulgaris F1068 exposed to AgNPs

Phosphorus removal by algae-based biotechnology can be achieved through algal assimilation, surface adsorption, or abiotic precipitation. However, there are still unavailable how these phosphorus removal processes were affected by nanoparticles in wastewater. Here, we employed a non-targeted metabolomic approach to reveal the impact of silver nanoparticles (AgNPs) on the phosphorus assimilation by a unicellular green alga Chlorella vulgaris F1068 (C. vulgaris F1068). Results showed that AgNPs mostly inhibited total phosphorus (TP) removal by the algal assimilation, with TP removal efficiency being reduced by 66.2% (with 0.20 mg/L AgNPs) of the control (without AgNPs). Metabolomics analysis also indicated that AgNPs disturbed metabolic responses related to phosphorus assimilation. AgNPs inhibited phospholipid metabolism which included inositol phosphate metabolism and phosphatidylinositol signaling system (downregulation of glycerol-3-phosphate and myo-inositol, as well as upregulation of serine). Metabolites related to phosphorus assimilation products were impacted through downregulation of guanine, glutamine, alanine, and aspartic acid, as well as upregulation of succinic acid, thereby impeding the algal assimilation of phosphorus. Moreover, perturbation of glutathione metabolism induced by oxidative stress stimulated the alteration of membrane state (upregulation of glycine). These findings contribute to a molecular-scale perspective of nanoparticles on algae-based biotechnology in phosphorus removal.

Multistage Defense System Activated by Tetrachlorobiphenyl and its Hydroxylated and Methoxylated Derivatives in Oryza sativa

Crops can initiate various defense responses to environmental stresses. The process is often accompanied by extensive transcriptional and metabolic changes to reallocate metabolites. However, it remains unclear how organic pollutants activate the defense systems to reallocate metabolites in crops. The current study demonstrates that three defense systems, including the cytochrome P450s (CYP450s), glutathione S-transferases (GSTs), and phenylpropanoid biosynthesis, were sequentially activated after Oryza sativa was exposed to 2,3,4,5-tetrachlorobipheny l (PCB 61) and its derivatives 4'-hydroxy-2,3,4,5-tetrachlorobiphenyl (OH-PCB 61) and 4'-methoxy-2,3,4,5-tetrachlorobiphenyl (MeO-PCB 61), respectively. Genes encoding CYP76Ms and CYP72As were significantly upregulated after 0.5 h of exposure, followed by the GST-coding gene GSTU48, suggesting that the biotransformation and detoxification of PCB 61, OH-PCB 61, and MeO-PCB 61 occurred. Subsequently, CCR1 and CCR10 involved in phenylpropanoid biosynthesis were activated after 12 h, potentially reducing the oxidative stress induced by PCB 61 and its derivatives. Furthermore, β-d-glucan exohydrolase involved in both phenylpropanoid biosynthesis and starch and sucrose metabolism was significantly downregulated by 7.04-fold in the OH-PCB 61-treated group, potentially contributing to the inhibition of sugar hydrolysis. These findings provide insights into increasing rice adaptability to organic pollutants by reinforcing the enzyme-mediated defense systems, characterizing a novel and critical strategy that enables augmented crop outputs and quality in environments stressed by organic contaminants.

Comprehensive exploration of the ultraviolet degradation of polychlorinated biphenyls in different media

As one of the most important natural transformation processes, photodegradation deserves more attention and research. In the current work, we comprehensively explored the photochemical behaviors of polychlorinated biphenyls (PCBs) in n-hexane (Hex), methanol/water, and silica gel under UV-irradiation. Photodegradation rates were found to be faster in methanol/water than in Hex. All of the three photochemical systems generated sigmatropic rearrangement products. The dominant photodegradation pathways were dechlorination, dechlorination/methoxylation/hydroxylation, and hydroxylation in Hex, methanol/water, and silica gel systems, respectively. Furthermore, some new photodegradation products, such as polychlorinated biphenyl ethers, polychlorinated dibenzofurans, polychlorinated biphenylenes, and methylated polychlorinated biphenyls, are reported for the first time. These findings would provide deeper insight into the phototransformation behaviors of PCBs.

An inadvertent issue of human retina exposure to endocrine disrupting chemicals: A safety assessment

Endocrine disrupting chemicals (EDCs) are a group of chemical compounds that present a considerable public health problem due to their pervasiveness and associations with chronic diseases. EDCs can interrupt the endocrine system and interfere with hormone homeostasis, leading to abnormalities in human physiology. Much attention has been focused on the adverse effects EDCs have on the reproductive system, neurogenesis, neuroendocrine system, and thyroid dysfunction. The eye is usually directly exposed to the surrounding environment; however, the influences of EDCs on the eye have received comparatively little attention. Ocular diseases, such as ocular surface diseases and retinal diseases, have been implicated in hormone deficiency or excess. Epidemiologic studies have shown that EDC exposure not only causes ocular surface disorders, such as dry eye, but also associates with visual deficits and retinopathy. EDCs can pass through the human blood-retinal barrier and enter the neural retina, and can then accumulate in the retina. The retina is an embryologic extension of the central nervous system, and is extremely sensitive and vulnerable to EDCs that could be passed across the placenta during critical periods of retinal development. Subtle alterations in the retinal development process usually result in profound immediate, long-term, and delayed effects late in life. This review, based on extensive literature survey, briefly summarizes the current knowledge about the impact of representative manufactured EDCs on retinal toxicity, including retinal structure alterations and dysfunction. We also highlight the potential mechanism of action of EDCs on the retina, and the predictive retinal models of EDC exposure.

Biochemical and molecular responses of maize (Zea mays L.) to 1,2-dibromo-4-(1,2 dibromoethyl) cyclohexane (TBECH) diastereomers: Oxidative stress, DNA damage, antioxidant enzyme gene expression and diversity of root exudates

The phytotoxicities of TBECH diastereomers to plants at the biochemical and molecular levels were investigated in a hydroponic study by using maize as a model plant. The results showed that TBECH could induce the production of two species of reactive oxygen species (ROS), O₂^•- and H₂O₂, in maize tissues. The accumulation of ROS was the highest when maize was exposed to β-TBECH. TBECH enhanced the phosphorylation of plant histone, and the contents of γ-H2AX in maize followed the order β-TBECH > αβ-TBECH > γδ-TBECH > γ-TBECH. Transcriptome profiling revealed that antioxidant enzyme genes (AEGs) were over-expressed in maize when stressed by technical grade TBECH. The RT-PCR detection further validated that three typical AEGs, including CAT, SOD, and POD genes, were time-dependent and selectively expressed under the influence of TBECH diastereomers. Molecular compositions of maize root exudates characterized by FT-ICR-MS were significantly different among the four groups of TBECH diastereomer treatments. TBECH diastereomers specifically affected the chemical diversity and abundance of root exudates. New insights into the biochemical effects of TBECH on plants are provided in this work, which is helpful to deepening the understanding of their stereo-selectivity.

Bacillus velezensis CLA178-Induced Systemic Resistance of Rosa multiflora Against Crown Gall Disease

Plant growth-promoting rhizobacteria (PGPRs) are able to activate induced systemic resistance (ISR) of the plants against phytopathogens. However, whether and how ISR can be activated by PGPRs in plants of the Rosa genus is unclear. The effects of PGPR Bacillus velezensis CLA178 and the pathogen Agrobacterium tumefaciens C58 on the growth, plant defense-related genes, hormones, and reactive oxygen species (ROS) in the rose plants were compared. Pretreatment with CLA178 significantly reduced crown gall tumor biomass and relieved the negative effects of the C58 pathogen on plant biomass, chlorophyll content, and photosynthesis of roses. Pretreatment of the roots with CLA178 activated ISR and significantly reduced disease severity. Pretreatment with CLA178 enhanced plant defense response to C58, including the accumulation of ROS, antioxidants, and plant hormones. Moreover, pretreatment with CLA178 enhanced C58-dependent induction of the expression of the genes related to the salicylic acid (SA) or ethylene (ET) signaling pathways. This result suggested that SA- and ET-signaling may participate in CLA178-mediated ISR in roses. Additional experiments in the Arabidopsis mutants showed that CLA178 triggered ISR against C58 in the pad4 and jar1 mutants and not in the etr1 and npr1 mutants. The ISR phenotypes of the Arabidopsis mutants indicated that CLA178-mediated ISR is dependent on the ET-signaling pathway in an NPR1-dependent manner. Overall, this study provides useful information to expand the application of PGPRs to protect the plants of the Rosa genus from phytopathogens.