Detoxification of Atrazine by Low Molecular Weight Thiols in Alfalfa (Medicago sativa)

The role of OsBZR4 as a brassinosteroid-signaling component in mediating atrazine and isoproturon degradation in rice

Development of a biotechnological system for rapid degradation of pesticides is important to mitigate the environmental, food security, and health risks that they pose. Degradation of atrazine (ATZ) and isoproturon (IPU) in rice crops promoted by the brassinosteroid (BR) signaling component BRASSINAZOLE RESISTANT4 (OsBZR4) is explored. OsBZR4 is localized in the plasma membrane and nucleus, and is strongly induced by ATZ and IPU exposure. Transgenic rice OsBZR4-overexpression (OE) significantly enhances resistance to ATZ and IPU toxicity, improving growth, and reducing ATZ and IPU accumulation (particularly in grains) in rice crops. Genetic destruction of OsBZR4 (CRISPR/Cas9) increases rice sensitivity and leads to increased accumulation of ATZ and IPU. OE plants promote phase I, II, and III metabolic reactions, and expression of corresponding pesticide degradation genes under ATZ and IPU stress. UPLC-Q-TOF-MS/MS analysis reveals increased relative contents of ATZ and IPU metabolites and conjugates in OE plants, suggesting an increased OsBZR4 expression and consequent detoxification of ATZ and IPU in rice and the environment. The role of OsBZR4 in pesticide degradation is revealed, and its potential application in enhancing plant resistance to pesticides, and facilitating the breakdown of pesticides in rice and the environment, is discussed.

Non-target influence of imidacloprid residues on grape global metabolome and berry quality with the identification of metabolite biomarkers

This paper illustrates the non-target impact of imidacloprid (IM) residues on the grape global metabolome and biomarker identification with high-resolution mass spectrometry. IM was applied at the recommended dose (SD), and ten times SD (10 RD). The global metabolome analysis revealed that 21 metabolites were up- and down-regulated with IM SD treatment. In 10 RD, 9 metabolites were upregulated, and 28 were downregulated. Pathway enrichment analysis revealed the primary and secondary pathway disruption in grapes. Berry quality was affected with decrease in flavonoids by 32.97% in 10 RD; phenols were reduced by 53.93 in SD, 50.8% in 10 RD. The non-target and target study revealed the degradation of IM in grapes to desnitro-IM and IM-urea which were identified as a potential biomarker for IM residues in grapes, which would benefit the authentication of organic product. Overall, imidacloprid showed a significant impact on the grape metabolome and quality.

How could actinobacteria augment the growth and redox homeostasis in barley plants grown in TiO2NPs-contaminated soils? A growth and biochemical study

The increases in titanium dioxide nanoparticles (TiO2-NPs) released into the environment have raised concerns about their toxicity. However, their phytotoxic impact on plants is not well studied. Therefore, this study aimed at a deeper understanding of the TiO2-NPs phytotoxic impact on barley (Hordeum vulgare) growth and stress defense. We also hypothesized that soil inoculation with bioactive Rhodospirillum sp. JY3 strain can be applied as a biological fertilizer to alleviate TiO2-NPs phytotoxicity. At TiO2-NPs phytotoxicity level, photosynthesis was significantly retarded (∼50% reduction) in TiO2-NPs treated-barley plants which accordingly affect the biomass of barley plants. This retardation was accompanied by a remarkable induction of oxidative damage (H2O2, lipid peroxidation) with a concomitant reduction in the antioxidant defense metabolism. At a glance, Rhodospirillum sp. JY3 ameliorated the reduction in growth by enhancing the photosynthetic efficiency in contaminated barley plants. Moreover, Rhodospirillum sp. JY3 inoculation reduced the oxidative damage induced by TiO2-NPs via quenching H2O2 production and lipid peroxidation. Regarding the antioxidant defense arsenal, Rhodospirillum sp. JY3 enhanced both enzymatic (e.g. peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), …. etc.) and non-enzymatic (glutathione (GSH), ascorbate (ASC), polyphenols, flavonoids, tocopherols) antioxidants in shoots and to a greater extent roots of barley plants. Moreover, the inoculation significantly enhanced the heavy metal-detoxifying metabolites (eg. phytochelatins, glutaredoxin, thioredoxin, peroxiredoxin) as well as metal-detoxifying enzymes in barley shoots and more apparently in roots of TiO2-NPs stressed plants. Furthermore, there was an organ-specific response to TiO2-NPs and Rhodospirillum sp. JY3. To this end, this study shed light, for the first time, on the molecular bases underlie TiO2-NPs stress mitigating impact of Rhodospirillum sp. JY3 and it introduced Rhodospirillum sp. JY3 as a promising eco-friendly tool in managing environmental risks to maintain agricultural sustainability.

Mitigation of atrazine-induced oxidative stress on soybean seedlings after co-inoculation with atrazine-degrading bacterium Arthrobacter sp. DNS10 and inorganic phosphorus-solubilizing bacterium Enterobacter sp. P1

Atrazine toxicity is one of the limiting factors inhibiting sensitive plant growth. Previous studies showed that atrazine-degrading bacteria could alleviate atrazine toxicity. However, there is limited information on how atrazine-degrading bacteria and plant growth-promote bacteria alleviate atrazine toxicity in soybeans. Therefore, the current study aimed to explore the atrazine removal, phosphorus utilization, and the oxidative stress alleviation of atrazine-degrading bacterium Arthrobacter sp. DNS10 and/or inorganic phosphorus-solubilizing bacterium Enterobacter sp. P1 in the reduction of atrazine toxicity in soybean. The results showed that atrazine exposure to soybean seedlings led to significant inhibition in growth, atrazine removal, and phosphorus utilization. However, the co-inoculatied strains significantly increased seedlings biomass, chlorophyll a/b contents, and total phosphorus in leaves accompanied by great reduction of the atrazine-induced antioxidant enzymes activities and malonaldehyde (MDA) contents, as well as atrazine contents in soil and soybeans under atrazine stress. Furthermore, transcriptome analysis highlighted that co-inoculated strains increased the expression levels of genes related to photosynthetic-antenna proteins, carbohydrate metabolism, and fatty acid degradation in leaves. All the results suggest that the co-inoculation mitigates atrazine-induced oxidative stress on soybean by accelerating atrazine removal from soil and phosphorus accumulation in leaves, enhancing the chlorophyll contents, and regulating plant transcriptome. It may be suggested that co-inoculation of atrazine-degrading bacteria and inorganic phosphorus-solubilizing bacteria can be used as a potential method to alleviate atrazine toxicity to the sensitive crops.

Rhodospirillum sp. JY3: An innovative tool to mitigate the phytotoxic impact of galaxolide on wheat (Triticum aestivum) and faba bean (Vicia faba) plants

To date, several studies have considered the phytotoxic impact of cosmetics and personal care products on crop plants. Nonetheless, data are scarce about the toxic impact of galaxolide [hexahydro-hexamethyl cyclopentabenzopyran (HHCB)] on the growth, physiology, and biochemistry of plants from different functional groups. To this end, the impact of HHCB on biomass, photosynthetic efficiency, antioxidant production, and detoxification metabolism of grass (wheat) and legume (faba bean) plants has been investigated. On the other hand, plant growth-promoting bacteria (PGPB) can be effectively applied to reduce HHCB phytotoxicity. HHCB significantly reduced the biomass accumulation and the photosynthetic machinery of both crops, but to more extent for wheat. This growth reduction was concomitant with induced oxidative damage and decreased antioxidant defense system. To mitigate HHCB toxicity, a bioactive strain of diazotrophic plant growth-promoting Rhodospirillum sp. JY3 was isolated from heavy metal-contaminated soil in Jazan, Kingdom of Saudi Arabia, and applied to both crops. Overall, Rhodospirillum mitigated HHCB-induced stress by differently modulating the oxidative burst [malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and protein oxidation] in both wheat and faba beans. This alleviation was coincident with improvement in plant biomass and photosynthetic efficiency, particularly in wheat crops. Considering the antioxidant defense system, JY3 augmented the antioxidants in both wheat and faba beans and the detoxification metabolism under HHCB stress conditions. More interestingly, inoculation with JY3 further enhanced the tolerance level of both wheat and faba beans against contamination with HHCB via quenching the lignin metabolism. Overall, this study advanced our understanding of the physiological and biochemical mechanisms underlying HHCB stress and mitigating its impact using Rhodospirillum sp. JY3, which may strikingly reduce the environmental risks on agriculture sustainability.

Alfalfa's response to atrazine stress and its secreted atrazine metabolites

Although listed as endocrine disruptor compounds, atrazine (ATZ) is still used in large quantities in agricultural production. Here, alfalfa seedling was cultivated in hydroponic media to investigate the toxic effects of ATZ on alfalfa and accumulation of ATZ in tissues of different plant parts. Alfalfa had a strong upward translocation ability to ATZ. The stress response of alfalfa under ATZ stress was studied using metabolomic and transcriptomic techniques. S-adenosylmethionine, glutathione, 3-mercaptopyruvic acid, ornithine, and aminopropylcadaverine were significantly increased by ATZ in pathways mtr00270 and mtr00480. Several genes of cysteine synthase and spermidine synthase were significantly up-regulated by ATZ induction. They may be markers and genes with potential physiological functions of alfalfa in response to ATZ stress. In addition, using high resolution mass spectrometry, a total of five ATZ metabolites secreted from alfalfa roots were detected. Among them, acetylated deisopropylated ATZ was discovered for the first time. Hydroxylated ATZ and acetylated deethylated ATZ were more readily excreted by the root system. This study not only provides potential genes for the construction of engineering plants to remediate ATZ-contaminated soil, but also provides monitoring objects for the ecological research of ATZ metabolites.

Residues of Reduced Herbicides Terbuthylazine, Ametryn, and Atrazine and Toxicology to Maize and the Environment through Salicylic Acid

Terbuthylazine (TBA), ametryn (AME), and atrazine (ATZ) are triazine family herbicides. They are dominantly used in the field of cereal crops like wheat and maize for prevention of upland from annual gramineous and broad-leaved weeds, with attributes of weed efficiency broad spectrum and good market performance. Salicylic acid (SA) is a kind of natural plant growth regulator existing widely in the plant kingdom and participating in many physiological and defense processes. In this study, the effects of SA on the detoxification and degradation of herbicides TBA, AME, and ATZ in maize were investigated. When maize plants were exposed to 6 mg kg^-1 of the triazine herbicides, the growth and chlorophyll concentration were reduced, while the membrane permeability increased. After maize was sprayed with 5 mg kg^-1 SA, the herbicide-induced phytotoxicity was significantly assuaged, with the increased content of chlorophyll and decreased cellular damage in plants. Activities of several biomarker enzymes such as SOD, POD, and GST were repressed in the presence of SA. The concentration of the triazine herbicides in maize and the soil determined by high-performance liquid chromatography was drastically reduced by spraying SA. Using LC/Q-TOF-MS/MS, six metabolites and nine conjugates of AME in maize and soil were characterized. The relative contents of AME metabolites and conjugates in maize with SA were higher than those without SA. These results suggest that SA is able to promote the detoxification and decay of these triazine herbicides in maize and soil.

Endophytic bacterium CIMAP-A7 mediated amelioration of atrazine induced phyto-toxicity in Andrographis paniculata

The presence of atrazine, a triazine herbicide, and its residues in agriculture soil poses a serious threat to human health and environment through accumulation in edible plant parts. Hence, the present study focused on atrazine induced stress amelioration of Andrographis paniculata, an important medicinal plant, by a plant growth promoting and atrazine degrading endophytic bacterium CIMAP-A7 inoculation. Atrazine has a non-significant effect at a lower dose while at a higher dose (lower: 25 and higher: 50 mg kg^-1) 22 and 36% decrease in secondary metabolite content and plant dry weight of A. paniculata was recorded, respectively. Endophyte CIMAP-A7 inoculation significantly reduced atrazine soil content, by 78 and 51% at lower and a higher doses respectively, than their respective control treatments. Inoculation of CIMAP-A7 exhibited better plant growth in terms of increased total chlorophyll, carotenoid, protein, and metabolite content with reduced atrazine content under both atrazine contaminated and un-contaminated treatments. Atrazine induced oxidative stress in A. paniculata was also ameliorated by CIMAP-A7 by reducing stress enzymes, proline, and malondialdehyde accumulation under contaminated soil conditions than un-inoculated treatments. Furthermore, the presence of atrazine metabolites deisopropylatrazine (DIA) and desethylatrazine (DEA) strongly suggests a role of CIMAP-A7 in mineralization however, the absence of these metabolites in uninoculated soil and all plant samples were recorded. These findings advocate that the amelioration of atrazine induced stress with no/least pesticide content in plant tissues by plant-endophyte co-interactions would be efficient in the remediation of atrazine contaminated soils and ensure safe crop produce.

Metabolism and detoxification of pesticides in plants

Pesticides make indispensable contributions to agricultural productivity. However, the residues after their excessive use may be harmful to crop production, food safety and human health. Although the ability of plants (especially crops) to accumulate and metabolize pesticides has been intensively investigated, data describing the chemical and metabolic processes in plants are limited. Understanding how pesticides are metabolized is a key step toward developing cleaner crops with minimal pesticides in crops, creating new green pesticides (or safeners), and building up the engineered plants for environmental remediation. In this review, we describe the recently discovered mechanistic insights into pesticide metabolic pathways, and development of improved plant genotypes that break down pesticides more effectively. We highlight the identification of biological features and functions of major pesticide-metabolized enzymes such as laccases, glycosyltransferases, methyltransferases and ATP binding cassette (ABC) transporters, and discuss their chemical reactions involved in diverse pathways including the formation of pesticide S-conjugates. The recent findings for some signal molecules (phytohomormes) like salicylic acid, jasmonic acid and brassinosteroids involved in metabolism and detoxification of pesticides are summarized. In particular, the emerging research on the epigenetic mechanisms such DNA methylation and histone modification for pesticide metabolism is emphasized. The review would broaden our understanding of the regulatory networks of the pesticide metabolic pathways in higher plants.

Mechanism of growth amelioration of triclosan-stressed tobacco (Nicotiana tabacum) by endogenous salicylic acid

Among emerging organic contaminants (EOCs), triclosan (TCS) is an antibacterial agent and frequently detected in sludge. In this study, RNA sequencing (RNA-seq) was used to obtain the first transcriptomic profile of tobacco with TCS treatment in comparison with control. The results of transcriptome profiling indicated that salicylic acid (SA) signalling pathway actively participated in the tobacco's response to TCS treatment. The accumulation of endogenous SA in transgene tobacco lines transformed with a homologous gene of SA binding protein (LcSABP) was significantly enhanced. The resistance of transgenic tobacco lines to TCS was markedly enhanced revealed by morphological and physiological indexes while the total Chl level and Pn of transgenic individuals showed about 180% and 250% higher than that of WT on average, and the accumulation of H2O2 and O2- induced by TCS in SABP overexpressing tobacco was 35.3%-37.3% and 53.0%-56.0% lower than that of WT. In order to further explore the mechanism of TCS tolerance in transgenic plants, RNA-seq was then performed to obtain the second transcriptomic profile between wild type and transgenic samples with TCS exposure. The results indicated that differentially expressed genes (DEGs) were most highly enriched in MAPK signalling pathway, amino acid synthesis pathway and plant hormone transduction pathway. Especially, genes encoding key proteins such as cytochrome P450, laccase, peroxidase, glycosyl transferase, glutathione S-transferase and ATP-binding cassette were considered to be related to the increased tolerance ability of transgenic tobacco to the treatment of TCS stress. This research will likely provide novel insights into the molecular mechanism of SA-mediated amelioration of TCS stress on tobacco.

Phytotoxic evaluation of neonicotinoid imidacloprid and cadmium alone and in combination on tomato (Solanum lycopersicum L.)

Neonicotinoids and heavy metals pollution exist simultaneously in agro ecosystem. However, little is known about their combined ecotoxicological effects on non-target crop plants. We have selected imidacloprid (IMI) and cadmium (Cd), applied alone and in combination, to evaluate their effect on growth, physiological and biochemical parameters of tomato. Results showed that the single application of contaminants (IMI and/or Cd) adversely affected both the growth and chlorophyll pigment, and Cd alone application was more phytotoxic than IMI. However, their combined action aggravated the inhibitory effect and indicate a synergistic effect, but it exerted antagonistic effects on chlorophyll pigment inhibition compared with IMI and Cd alone treatments. Both chemicals increased hydrogen peroxide level and generated lipid peroxidation, and the co-contamination exacerbates oxidative stress by their synergistic effect. Those results implicate that disturbance of cellular redox status is the plausible mechanism for IMI and Cd induced toxicity. In conclusion, the single or combined IMI and Cd cause negative effects on tomatoes.

Advance in Methodology and Strategies To Unveil Metabolic Mechanisms of Pesticide Residues in Food Crops

Pesticide residues are a food safety concern. A good detection method is critical for rapid and accurate determination of pesticide metabolites in crops and studying metabolism. The pretreatment methods have mainly been ultrasonic extraction-solid-phase extraction and QuEChERS, while detection methods have been radio-chromatography, nuclear magnetic resonance, and mass spectrometry. This perspective briefed the progress of analytical methods used for studying pesticide transformation in crops over the past decade. With the combination of the characteristics of the pesticide molecular structure and the transformation principles of pesticides in crops, we presented specific methods for elucidating new metabolites and the approaches to identify metabolites using multi-high-resolution mass spectrometry.

Comprehensive analyses of degradative enzymes associated with mesotrione-degraded process in rice for declining environmental risks

Mesotrione (MTR) is a highly effective pesticide widely used for weeding in farmland. Overload of MTR in agricultural soils may result in environmental problems. To evaluate the potential contamination of MTR in environments, a better understanding of the MTR degradation process and mechanisms in crops is required. This study investigated the impact of MTR on growth and toxicological responses in rice (Oryza sativa). The growth of rice tissues was significantly compromised with increasing MTR concentrations. RNA-sequencing combined with HRLC-Q-TOF-MS/MS analysis identified many transcriptional components responsible for MTR degradation. Four libraries composed of root and shoot tissues exposed to MTR were RNA-sequenced in biological triplicate. Compared to -MTR, treatment with environmentally realistic MTR concentration upregulated 1995 genes in roots and 326 genes in shoots. Gene enrichment revealed many MTR-degradative enzymes functioning in resistance to environmental stress and molecular metabolism of xenobiotics. Specifically, many differentially expressed genes are critical enzymes like cytochrome P450, glycosyltransferases, methyltransferase, glutathione S-transferases and acetyltransferase involved in the process. To evidence MTR degradative metabolisms, HRLC-Q-TOF-MS/MS was used to characterize eight metabolites and five conjugates in the pathways involving hydrolysis, reduction, glycosylation, methylation or acetylation. The precise association between the specific MTR-degraded products and enhanced activities of its corresponding enzymes was established. This study advanced our understanding of the detailed MTR degradative mechanisms and pathways, which may help engineer genotypes to facilitate MTR degradation in the paddy crop.

Identification of a novel function of a component in the jasmonate signaling pathway for intensive pesticide degradation in rice and environment through an epigenetic mechanism

Developing a biotechnical system with rapid degradation of pesticide is critical for reducing environmental, food security and health risks. Here, we investigated a novel epigenetic mechanism responsible for the degradation of the pesticide atrazine (ATZ) in rice crops mediated by the key component CORONATINE INSENSITIVE 1a (OsCOI1a) in the jasmonate-signaling pathway. OsCOI1a protein was localized to the nucleus and strongly induced by ATZ exposure. Overexpression of OsCOI1a (OE) significantly conferred resistance to ATZ toxicity, leading to the improved growth and reduced ATZ accumulation (particularly in grains) in rice crops. HPLC/Q-TOF-MS/MS analysis revealed increased ATZ-degraded products in the OE plants, suggesting the occurrence of vigorous ATZ catabolism. Bisulfite-sequencing and chromatin immunoprecipitation assays showed that ATZ exposure drastically reduced DNA methylation at CpG context and histone H3K9me2 marks in the upstream of OsCOI1a. The causal relationships between the DNA demethylation (hypomethylatioin), OsCOI1a expression and subsequent detoxification and degradation of ATZ in rice and environment were well established by several lines of biological, genetic and chemical evidence. Our work uncovered a novel regulatory mechanism implicated in the defense linked to the epigenetic modification and jasmonate signaling pathway. It also provided a modus operandi that can be used for metabolic engineering of rice to minimize amounts of ATZ in the crop and environment.

Integrated proteomics, metabolomics and physiological analyses for dissecting the toxic effects of halosulfuron-methyl on soybean seedlings (Glycine max merr.)

Halosulfuron methyl (HSM) is a herbicide widely used to control sedge and broad-leaved weeds during crop production, but its environmental residue may damage non-target crops. Here, proteomics and metabolomics methods were used to explore the phytotoxicity mechanisms of HSM against soybean (Glycine max Merr.). Soybean seedlings were exposed to 0.01, 0.05 and 0.5 mg/L HSM for 8 d. The HSM applications significantly reduced chlorophyll and carotenoid contents in HSM-treated seedlings. Additionally, chlorophyll a fluorescence was seriously affected. The glutathione, hydrogen peroxide and malondialdehyde contents, as well as antioxidant enzyme activities, significantly increased in seedlings exposed to HSM. Furthermore, five enzymes involved in the tricarboxylic acid (TCA) cycle, α-ketoglutarate dehydrogenase, isocitrate dehydrogenase, aconitase, malic dehydrogenase and succinate dehydrogenase, were inhibited to varying degrees in HSM-treated seedlings compared with controls. Proteomics results showed multiple differentially abundant proteins involved in chlorophyll synthesis, photosystem processes and chloroplast ATP synthetase were down-regulated. Metabolomics analyses revealed that metabolites involved in the TCA cycle decreased significantly. Moreover, metabolites and proteins related to reactive oxygen species detoxification accumulated. In conclusion, the phytotoxicity mechanisms of HSM against soybean mainly act by damaging the photosynthetic machinery, inhibiting chlorophyll synthesis, interrupting the TCA cycle and causing oxidative stress. These results provide new insights into the toxicity mechanisms of sulfonylurea herbicides against non-target crops.

Uptake of atrazine in a paddy crop activates an epigenetic mechanism for degrading the pesticide in plants and environment

There is a rising public concern on accumulation of harmful pesticides in environment and crops. Epigenetic alteration caused by environmental contaminants is one of the key factors in the etiology of environmentally-associated diseases. Growing evidence shows that harmful pesticide atrazine (ATZ) has a profound effect on DNA methylation in human genome, however, little is known about the epigenetic mechanism underlying ATZ accumulation and degradation in plants, particularly in edible plants growing in the ATZ-contaminated areas. This study investigated the atrazine elimination that was mediated by DNA methylation and histone modification in the food crop rice. Studies with two mutant Osmet1-1/2 defective in the genomic CG DNA methylation show significantly lower accumulation of atrazine than its wild-types. Profiling methylome and transcriptome of ATZ-exposed Osmet1 and wild-type identified many differentially methylated loci (≥2 fold change, p < 0.05), which were associated with activation of genes responsible for atrazine degradation in plants. Three demethylated loci OsGTF, OsHPL1 and OsGLH were expressed in eukaryotic yeast cells and found to eliminate a marked proportion of ATZ in growth environments by 48%, 43% and 32%, respectively, whereas the increased ATZ-degraded products were characterized using UPLC/Q-TOF-MS/MS. These results suggest that activation of the loci mediated by ATZ-induced hypomethylation could be responsible for the removal of ATZ in rice. Our work helps understand a new regulatory mechanism underlying the atrazine degradation in crops which may potentially reduce the environmental risks to human health through food chain.

Protective Responses Induced by Chiral 3-Dichloroacetyl Oxazolidine Safeners in Maize (Zea mays L.) and the Detoxification Mechanism

Herbicide safeners selectively protect crops from herbicide injury while maintaining the herbicidal effect on the target weed. To some extent, the detoxification of herbicides is related to the effect of herbicide safeners on the level and activity of herbicide target enzymes. In this work, the expression of the detoxifying enzyme glutathione S-transferase (GST) and antioxidant enzyme activities in maize seedlings were studied in the presence of three potential herbicide safeners: 3-dichloroacetyl oxazolidine and its two optical isomers. Further, the protective effect of chiral herbicide safeners on detoxifying chlorsulfuron in maize was evaluated. All safeners increased the expression levels of herbicide detoxifying enzymes, including GST, catalase (CAT), and peroxidase (POD) to reduce sulfonylurea herbicide phytotoxicity in maize seedlings. Our results indicate that the R-isomer of 3-(dichloroacetyl)-2,2,5-trimethyl-1,3-oxazolidine can induce glutathione (GSH) production, GST activity, and the ability of GST to react with the substrate 1-chloro-2,4-dinitrobenzene (CDNB) in maize, meaning that the R-isomer can protect maize from damage by chlorsulfuron. Information about antioxidative enzyme activity was obtained to determine the role of chiral safeners in overcoming the oxidative stress in maize attributed to herbicides. The interaction of safeners and active target sites of acetolactate synthase (ALS) was demonstrated by molecular docking modeling, which indicated that both isomers could form a good interaction with ALS. Our findings suggest that the detoxification mechanism of chiral safeners might involve the induction of the activity of herbicide detoxifying enzymes as well as the completion of the target active site between the safener and chlorsulfuron.

Isoproturon-Induced Salicylic Acid Confers Arabidopsis Resistance to Isoproturon Phytotoxicity and Degradation in Plants

This study identified the effect of salicylic acid on degradation of isoproturon in Arabidopsis. Three T-DNA insertion mutant lines pal1- 1, pal1- 2, and eps1- 1 defective in salicylic acid synthesis were tested, which showed higher isoproturon accumulation and a toxic symptom in the mutants. When treated with 5 mg/L salicylic acid, these lines displayed a lower level of isoproturon and showed an attenuated toxic symptom. An RNA-sequencing study identified 2651 (1421 up and 1230 down) differentially expressed genes (DEGs) in eps1- 1 and 2211 (1556 up and 655 down) in pal1- 2 mutant plants (>2.0 fold change, p < 0.05). Some of the DEGs covered Phase I-III reaction components, like glycosyltransferases (GTs) and ATP-binding cassette transporters (ABCs). Using ultra performance liquid chromatography-time-of-flight-tandem-mass spectrometer/mass spectrometer (UPLC/Q-TOF-MS/MS), 13 Phase I and four Phase II metabolites were characterized. Of these, two metabolites 1-OH-isopropyl-benzene-O-glucoside and 4-isopropylphenol-S-2-methylbutanoyl-serine, have been identified and reported for the first time.

Reduced phytotoxicity of propazine on wheat, maize and rapeseed by salicylic acid

Propazine belongs to the triazine herbicide family and widely used in the farmland for crop production. Recent studies have shown that the residue of propazine in environment is accumulative. This inevitably results in accumulation of propazine in crops. Therefore, reduction of propazine toxicity and accumulation in crops is critically important. In this study, the growth of wheat, maize and rapeseed was significantly inhibited by 2, 8 and 0.4 mg kg^-1 propazine in soils. The chlorophyll content of the three crops also showed significant decrease, while the electrolyte permeability, a biomarker of cellular damage, increased in the plant cells. However, when plants were sprayed with 5 mg L^-1 of salicylic acid (SA), the propazine phytotoxicity of the crops was relieved, with increased chlorophyll content and reduced electrolyte permeability of all crops. Meanwhile, the activities of peroxidase (POD) and glutathione transferase (GST) remained lower. The propazine accumulation in the crops and the residues in the soil were determined by high performance liquid chromatography. The concentration of propazine in plants and soils treated by SA was less than that of the untreated control. Six propazine degraded products (derivatives) in rhizosphere of wheat were characterized using ultraperformance liquid chromatography with a quadrupole-time-of-flight tandem mass spectrometer. Our work indicates that the improved growth of crops was possibly due to the acceleration of propazine degradation by salicylic acid.