Effects of nicosulfuron on growth, oxidative damage, and the ascorbate-glutathione pathway in paired nearly isogenic lines of waxy maize (Zea mays L.)

Assessing the ecotoxicological risk of nicosulfuron on maize using multi-source phenotype data and hyperspectral imaging

Herbicide-induced toxicity in maize crops poses significant challenges for agricultural management. Traditional assessment methods for herbicide toxicity in crops often show inconsistent accuracy. This study explores rapid and non-invasive techniques for evaluating herbicide toxicity, focusing on the physiological, biochemical, and growth responses of maize varieties subjected to two concentrations of nicosulfuron. We developed a comprehensive toxicity evaluation model to classify samples into three toxicity levels, showing a strong correlation (r = 0.95) with traditional tassel stage toxicity assessments. Additionally, we used hyperspectral imaging coupled with deep learning techniques to predict early toxicity levels in maize following herbicide exposure. After 4 days of herbicide treatment, our ToxicNet model using spectral data achieved an impressive 89.66 % accuracy in predicting nicosulfuron toxicity levels, facilitating early detection. Furthermore, by integrating leaf spectral data, Soil-Plant Analysis Development (SPAD) values and water content, the ToxicNet-MS model achieved a remarkable prediction accuracy of 91.38 %. Notably, this model demonstrated robust generalization across different years and planting seasons, with accuracies of 83.33 % and 89.89 %, respectively. These results significantly outperformed traditional machine learning methods (Support Vector Machine, Random Forest), classical deep learning models (Multilayer Perceptron, AlexNet), and the spectral-based ToxicNet model. This advancement offers a promising, early, and non-invasive solution for assessing herbicide-induced toxicity in maize crops, ultimately benefiting both sustainable agricultural practices and effective crop management.

Metabolomic analyses reveal that graphene oxide alleviates nicosulfuron toxicity in sweet corn

Nicosulfuron can repress the growth and quality of sweet corn (Zea mays), and graphene oxide has been used for sustainable agriculture. However, the underlying mechanism of the toxicity of nicosulfuron that is mediated in sweet corn remains elusive. To explore the potential mechanism of GO-mediated nicosulfuron toxicity in sweet corn in this study, we investigated the effects of graphene oxide on nicosulfuron stress in the sweet corn sister inbred lines of H01 and H20. Furthermore, we performed a metabolomics analysis for the H01 and H20 under different treatments. The results showed that nicosulfuron severely affected the rate of survival, physiological parameters, photosynthetic indicators, and chlorophyll fluorescence parameters of corn seedlings, whereas foliar spraying with graphene oxide promoted the rate of survival under nicosulfuron toxicity. The metabolomics analysis showed that 70 and 90 metabolites differentially accumulated in the H01 and H20 inbred lines under nicosulfuron treatment, respectively. Graphene oxide restored 59 metabolites in the H01 seedlings and 56 metabolites to normal levels in the H20 seedlings, thereby promoting the rate of survival of the sweet corn seedlings. Compared with nicosulfuron treatment alone, graphene oxide resulted in 108 and 66 differential metabolites in the H01 and H20 inbred lines, respectively. A correlation analysis revealed that metabolites, such as doronine and (R)-2-hydroxy-2-hydroxylase-1,4-benzoxazin-3(4-hydroxylase)-1, were significantly correlated with the rate of survival, photosynthetic parameters and chlorophyll fluorescence parameters. Furthermore, metabolites related to the detoxification of graphene oxide were enriched in the flavonoid metabolic pathways. These results collectively indicate that graphene oxide can be used as a regulator of corn growth and provide insights into their use to improve crops in areas that are contaminated with nicosulfuron.

GO promotes detoxification of nicosulfuron in sweet corn by enhancing photosynthesis, chlorophyll fluorescence parameters, and antioxidant enzyme activity

Although graphene oxide (GO) has extensive recognized application prospects in slow-release fertilizer, plant pest control, and plant growth regulation, the incorporation of GO into nano herbicides is still in its early stages of development. This study selected a pair of sweet corn sister lines, nicosulfuron (NIF)-resistant HK301 and NIF-sensitive HK320, and sprayed them both with 80 mg kg-1 of GO-NIF, with clean water as a control, to study the effect of GO-NIF on sweet corn seedling growth, photosynthesis, chlorophyll fluorescence, and antioxidant system enzyme activity. Compared to spraying water and GO alone, spraying GO-NIF was able to effectively reduce the toxic effect of NIF on sweet corn seedlings. Compared with NIF treatment, 10 days after of spraying GO-NIF, the net photosynthetic rate (A), stomatal conductance (Gs), transpiration rate (E), photosystem II photochemical maximum quantum yield (Fv/Fm), photochemical quenching coefficient (qP), and photosynthetic electron transfer rate (ETR) of GO-NIF treatment were significantly increased by 328.31%, 132.44%, 574.39%, 73.53%, 152.41%, and 140.72%, respectively, compared to HK320. Compared to the imbalance of redox reactions continuously induced by NIF in HK320, GO-NIF effectively alleviated the observed oxidative pressure. Furthermore, compared to NIF treatment alone, GO-NIF treatment effectively increased the activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both lines, indicating GO induced resistance to the damage caused by NIF to sweet corn seedlings. This study will provides an empirical basis for understanding the detoxification promoting effect of GO in NIF and analyzing the mechanism of GO induced allogeneic detoxification in cells.

Crop Safety and Weed Control of Foliar Application of Penoxsulam in Foxtail Millet

Grass damage has become an important factor restricting foxtail millet production; chemical weeding can help resolve this issue. However, special herbicides in foxtail millet fields are lacking. Penoxsulam has a broad weed control spectrum and a good control effect. In this project, Jingu 21 was used as the test material, and five different concentrations of penoxsulam were used for spraying test in the three-five leaf stage. In this experiment, the effects on the growth of foxtail millet were discussed by measuring the agronomic characters and antioxidant capacity of foxtail millet after spraying penoxsulam. The results showed that: (1) penoxsulam is particularly effective in controlling Amaranthus retroflexus L. (A. retroflexus) and Echinochloa crus-galli (L.) Beauv. (E. crus-galli), but is ineffective in controlling Chenopodium album L. (C. album) and Digitaria sanguinalis (L.) Scop. (D. sanguinalis); (2) the stem diameter, fresh weight, and dry weight of the above-ground parts decreased with the increase in spraying amount; (3) as the spraying dosage increased, the superoxide (SOD), peroxidase (POD), and catalase (CAT) activities in the foxtail millet initially increased and subsequently decreased; the malonaldehyde (MDA) content increased. Our experiment found that 1/2X and 1X spraying dosages had certain application value in controlling gramineous weeds in foxtail millet field. Other spraying dosages are not recommended as they may harm the crops. Our findings provide reference for identifying new herbicides in the foxtail millet field.

Early detection of nicosulfuron toxicity and physiological prediction in maize using multi-branch deep learning models and hyperspectral imaging

The misuse of herbicides in fields can cause severe toxicity in maize, resulting in significant reductions in both yield and quality. Therefore, it is crucial to develop early and efficient methods for assessing herbicide toxicity, protecting maize production, and maintaining the field environment. In this study, we utilized maize crops treated with the widely used nicosulfuron herbicide and their hyperspectral images to develop the HerbiNet model. After 4 d of nicosulfuron treatment, the model achieved an accuracy of 91.37 % in predicting toxicity levels, with correlation coefficient R² values of 0.82 and 0.73 for soil plant analysis development (SPAD) and water content, respectively. Additionally, the model exhibited higher generalizability across datasets from different years and seasons, which significantly surpassed support vector machines, AlexNet, and partial least squares regression models. A lightweight model, HerbiNet-Lite, exhibited significantly low complexity using 18 spectral wavelengths. After 4 d of nicosulfuron treatment, the HerbiNet-Lite model achieved an accuracy of 87.93 % for toxicity prediction and R² values of 0.80 and 0.71 for SPAD and water content, respectively, while significantly reducing overfitting. Overall, this study provides an innovative approach for the early and accurate detection of nicosulfuron toxicity within maize fields.

Fine mapping and functional validation of the maize nicosulfuron-resistance gene CYP81A9

Nicosulfuron, a widely utilized herbicide, is detrimental to some maize varieties due to their sensitivity. Developing tolerant varieties with resistance genes is an economical and effective way to alleviate phytotoxicity. In this study, map-based cloning revealed that the maize resistance gene to nicosulfuron is Zm00001eb214410 (CYP81A9), which encodes a cytochrome P450 monooxygenase. qRT- PCR results showed that CYP81A9 expression in the susceptible line JS188 was significantly reduced compared to the resistant line B73 during 0-192 hours following 80 mg/L nicosulfuron spraying. Meanwhile, a CYP81A9 overexpression line exhibited normal growth under a 20-fold nicosulfuron concentration (1600 mg/L), while the transgenic acceptor background material Zong31 did not survive. Correspondingly, silencing CYP81A9 through CRISPR/Cas9 mutagenesis and premature transcription termination mutant EMS4-06e182 resulted in the loss of nicosulfuron resistance in maize. Acetolactate Synthase (ALS), the target enzyme of nicosulfuron, exhibited significantly reduced activity in the roots, stems, and leaves of susceptible maize post-nicosulfuron spraying. The CYP81A9 expression in the susceptible material was positively correlated with ALS activity in vivo. Therefore, this study identified CYP81A9 as the key gene regulating nicosulfuron resistance in maize and discovered three distinct haplotypes of CYP81A9, thereby laying a solid foundation for further exploration of the underlying resistance mechanisms.

What can reactive oxygen species (ROS) tell us about the action mechanism of herbicides and other phytotoxins?

Reactive oxygen species (ROS) are formed in plant cells continuously. When ROS production exceeds the antioxidant capacity of the cells, oxidative stress develops which causes damage of cell components and may even lead to the induction of programmed cell death (PCD). The levels of ROS production increase upon abiotic stress, but also during pathogen attack in response to elicitors, and upon application of toxic compounds such as synthetic herbicides or natural phytotoxins. The commercial value of many synthetic herbicides is based on weed death as result of oxidative stress, and for a number of them, the site and the mechanism of ROS production have been characterized. This review summarizes the current knowledge on ROS production in plants subjected to different groups of synthetic herbicides and natural phytotoxins. We suggest that the use of ROS-specific fluorescent probes and of ROS-specific marker genes can provide important information on the mechanism of action of these toxins. Furthermore, we propose that, apart from oxidative damage, elicitation of ROS-induced PCD is emerging as one of the important processes underlying the action of herbicides and phytotoxins.

Design, Synthesis, and Biological Evaluation of Novel Purine Derivatives as Herbicide Safeners

Mesosulfuron-methyl, an inhibitor of acetolactate synthase (ALS), has been extensively used in wheats. However, it can damage wheat (Triticum aestivum) and even lead to crop death. Herbicide safeners selectively shield crops from such damage without compromising weed control. To mitigate the phytotoxicity of mesosulfuron-methyl in crops, several purine derivatives were developed based on active substructure splicing. The synthesized title compounds underwent thorough characterization using infrared spectroscopy, 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry. We evaluated chlorophyll and glutathione contents as well as various enzyme activities to evaluate the safer activity of these compounds. Compounds III-3 and III-7 exhibited superior activity compared with the safener mefenpyr-diethyl. Molecular structure analysis, along with predictions of absorption, distribution, metabolism, excretion, and toxicity, indicated that compound III-7 shared pharmacokinetic traits with the commercial safener mefenpyr-diethyl. Molecular docking simulations revealed that compound III-7 competitively bound to the ALS active site with mesosulfuron-methyl, elucidating the protective mechanism of the safeners. Overall, this study highlights purine derivatives as potential candidates for novel safener development.

Role of glutathione S-transferases in the mode of action of herbicides that inhibit amino acid synthesis in Amaranthus palmeri

Acetolactate synthase inhibitors (ALS inhibitors) and glyphosate are two classes of herbicides that act by inhibiting an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. Besides amino acid synthesis inhibition, both herbicides trigger similar physiological effects in plants. The main aim of this study was to evaluate the role of glutathione metabolism, with special emphasis on glutathione S-transferases (GSTs), in the mode of action of glyphosate and ALS inhibitors in Amaranthus palmeri. For that purpose, plants belonging to a glyphosate-sensitive (GLS) and a glyphosate-resistant (GLR) population were treated with different doses of glyphosate, and plants belonging to an ALS-inhibitor sensitive (AIS) and an ALS-inhibitor resistant (AIR) population were treated with different doses of the ALS inhibitor nicosulfuron. Glutathione-related contents, GST activity, and related gene expressions (glutamate-cysteine ligase, glutathione reductase, Phi GST and Tau GST) were analysed in leaves. According to the results of the analytical determinations, there were virtually no basal differences between GLS and GLR plants or between AIS and AIR plants. Glutathione synthesis and turnover did not follow a clear pattern in response to herbicides, but GST activity and gene expression (especially Phi GSTs) increased with both herbicides in treated sensitive plants, possibly related to the rocketing H2O2 accumulation. As GSTs offered the clearest results, these were further investigated with a multiple resistant (MR) population, compressing target-site resistance to both glyphosate and the ALS inhibitor pyrithiobac. As in single-resistant plants, measured parameters in the MR population were unaffected by herbicides, meaning that the increase in GST activity and expression occurs due to herbicide interactions with the target enzymes.

Research on phytotoxicity assessment and photosynthetic characteristics of nicosulfuron residues on Beta vulgaris L

Nicosulfuron is a common herbicide used to control weeds in maize fields. In northeast China, sugar beet is often grown as a subsequent crop after maize, and its frequently suffers from soil nicosulfuron residue damage, but the related toxicity evaluation and photosynthetic physiological mechanisms are not clear. Therefore, we experimented to evaluate the impacts of nicosulfuron residues on beet growth, photochemical properties, and antioxidant defense system. The results showed that when the nicosulfuron residue content reached 0.3 μg kg-1, it inhibited the growth of sugar beet. When it reached 36 μg kg-1 (GR50), the growth stagnated. Compared to the control group, a nicosulfuron residue of 36 μg kg-1 significantly decreased beet plant height (70.93 %), leaf area (91.85 %), dry weights of shoot (70.34 %) and root (32.70 %). It also notably reduced the potential photochemical activity (Fv/Fo) by 12.41 %, the light energy absorption performance index (PIabs) by 46.09 %, and light energy absorption (ABS/CSm) by 6.56 %. It decreased the capture (TRo/CSm) by 9.30 % and transferred energy (ETo/CSm) by 16.13 % per unit leaf cross-section while increasing the energy flux of heat dissipation (DIo/CSm) by 22.85 %. This ultimately impaired the photochemical capabilities of PSI and PSII, leading to a reduction in photosynthetic performance. Furthermore, nicosulfuron increased malondialdehyde (MDA) content while decreasing superoxide dismutase (SOD) and catalase (CAT) activities. In conclusion, this research clarified the toxicity risk level, lethal dose, and harm mechanism of the herbicide nicosulfuron residue. It provides a theoretical foundation for the rational use of herbicides in agricultural production and sugar beet planting management.

Effect of Plant Growth-Promoting Bacteria on Antioxidant Status, Acetolactate Synthase Activity, and Growth of Common Wheat and Canola Exposed to Metsulfuron-Methyl

Metsulfuron-methyl, a widely used herbicide, could cause damage to the sensitive plants in crop-rotation systems at extremely low levels in the soil. The potential of plant growth-promoting bacteria (PGPB) for enhancing the resistance of plants against herbicide stress has been discovered recently. Therefore, it is poorly understood how physiological processes occur in plants, while PGPB reduce the phytotoxicity of herbicides for agricultural crops. In greenhouse studies, the effect of strains Pseudomonas protegens DA1.2 and Pseudomonas chlororaphis 4CH on oxidative damage, acetolactate synthase (ALS), enzymatic and non-enzymatic antioxidants in canola (Brassica napus L.), and wheat (Triticum aestivum L.) were investigated under two levels (0.05 and 0.25 mg∙kg-1) of metsulfuron-methyl using spectrophotometric assays. The inoculation of herbicide-exposed wheat with bacteria significantly increased the shoots fresh weight (24-28%), amount of glutathione GSH (60-73%), and flavonoids (5-14%), as well as activity of ascorbate peroxidase (129-140%), superoxide dismutase SOD (35-49%), and ALS (50-57%). Bacterial treatment stimulated the activity of SOD (37-94%), ALS (65-73%), glutathione reductase (19-20%), and the accumulation of GSH (61-261%), flavonoids (17-22%), and shoots weight (27-33%) in herbicide-exposed canola. Simultaneous inoculation prevented lipid peroxidation induced by metsulfuron-methyl in sensitive plants. Based on the findings, it is possible that the protective role of bacterial strains against metsulfuron-metil is linked to antioxidant system activation.

Design, Synthesis, and Structure-Activity Relationship of Novel Aryl-Substituted Formyl Oxazolidine Derivatives as Herbicide Safeners

Nicosulfuron is the leading herbicide in the global sulfonylurea (SU) herbicide market; it was jointly developed by DuPont and Ishihara. Recently, the widespread use of nicosulfuron has led to increasingly prominent agricultural production hazards, such as environmental harm and influence on subsequent crops. The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of existing herbicides. A series of novel aryl-substituted formyl oxazolidine derivatives were designed using the active group combination method. Title compounds were synthesized using an efficient one-pot method and characterized by infrared (IR) spectrometry, ¹H and ¹³C nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS). The chemical structure of compound V-25 was further identified by X-ray single crystallography. The bioactivity assay and structure-activity relationship proved that nicosulfuron phytotoxicity to maize could be reduced by most title compounds. The glutathione S-transferase (GST) activity and acetolactate synthase (ALS) in vivo were determined, and compound V-12 showed inspiring activity comparable to that of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound V-12 competed with nicosulfuron for the acetolactate synthase active site and that this is the protective mechanism of safeners. Absorption, distribution, metabolism, excretion, and toxicity (ADMET) predictions demonstrated that compound V-12 exhibited superior pharmacokinetic properties to the commercialized safener isoxadifen-ethyl. The target compound V-12 shows strong herbicide safener activity in maize; thus, it may be a potential candidate compound that can help further protect maize from herbicide damage.

Role of oxidative stress in the physiology of sensitive and resistant Amaranthus palmeri populations treated with herbicides inhibiting acetolactate synthase

The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H₂O₂, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H₂O₂ content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress.

Effects of nicosulfuron on plant growth and sugar metabolism in sweet maize (Zea mays L.)

The sulfonylurea herbicide nicosulfuron is efficient, harmless and selective at low doses and has been widely used in maize cultivation. In this study, a pair of corn sister lines, HK301 (nicosulfuron-tolerence, NT) and HK320 (nicosulfuron-sensitive, NS), was chosen to study the effect of nicosulfuron on plant growth and sugar metabolism in sweet maize (Zea mays L.) seedlings. All the experimental samples were subjected to treatment with water or 80 mg kg^–1 of nicosulfuron when the sweet maize seedlings grew to the four-leaf stage. Nicosulfuron significantly inhibited the growth of NS line. The content of sucrose and the activities of sucrose phosphate synthase and sucrose synthase in the two inbred lines increased differentially under nicosulfuron stress compared with the respective control treatment. After nicosulfuron treatment, the activities of hexokinase and 6-phosphofructokinase and the contents of pyruvic acid and citric acid in NS line decreased significantly compared with those of NT line, while the content of sucrose and activities of sucrose phosphate synthase and sucrose synthase increased significantly. The disruption of sugar metabolism in NS line led to a lower supply of energy for growth. This study showed that the glycolysis pathway and the tricarboxylic acid cycle were enhanced in nicosulfuron-tolerant line under nicosulfuron stress in enhancing the adaptability of sweet maize.

Responses of photosynthesis, antioxidant enzymes, and related gene expression to nicosulfuron stress in sweet maize (Zea mays L.)

Weed control in maize (Zea mays L.) crops is usually undertaken using the postemergence herbicide nicosulfuron. The toxicity of nicosulfuron on maize, especially sweet maize, has been widely reported. In order to examine the effect of nicosulfuron on seedling photosynthetic characteristics, chlorophyll fluorescence, reactive oxygen species production, antioxidant enzyme activities, and gene expressions on sweet maize, nicosulfuron-tolerant "HK310" and nicosulfuron-sensitive "HK320" were studied. All experiment samples were subjected to a water or 80 mg kg^-1 of nicosulfuron treatment when sweet maize seedlings grow to the stage of four leaves. After treatment with nicosulfuron, results for HK301 were significantly higher than those for HK320 for net photosynthetic rate, transpiration rate, stomatal conductance, leaf maximum photochemical efficiency of PSII, photochemical quenching of chlorophyll fluorescence, and the electron transport rate. These results were contrary to nonphotochemical quenching and intercellular CO₂ concentration. As exposure time increased, associated effects also increased. Both O₂^·- and H₂O₂ detoxification is modulated by antioxidant enzymes. Compared to HK301, SOD, POD, and CAT activities of HK320 were significantly reduced as exposure time increase. Compared to HK320, the gene expression for the majority of SOD genes, except for SOD2, increased due to inducement by nicosulfuron, and it significantly upregulated the gene expression of CAT in HK301. Results from this study indicate that plants can improve photosynthesis, scavenging capabilities of ROS, and protective mechanisms to alleviate phytotoxic effect of nicosulfuron. Future research is needed to further elucidate the important role antioxidant systems and gene regulation play in herbicide detoxification in sweet maize.

Inuloxin A Inhibits Seedling Growth and Affects Redox System of Lycopersicon esculentum Mill. and Lepidium sativum L

Allelochemicals are considered an environment-friendly and promising alternative for weed management, although much effort is still needed for understanding their mode of action and then promoting their use in plant allelopathy management practices. Here, we report that Inuloxin A (InA), an allelochemical isolated from Dittrichia viscosa, inhibited root elongation and growth of seedlings of Lycopersicon esculentum and Lepidium sativum at the highest concentrations tested. InA-induced antioxidant responses in the seedlings were investigated by analysing the contents of glutathione (GSH) and ascorbate (ASC), and their oxidized forms, dehydroascorbate (DHA), and glutathione disulphide (GSSG), as well as the redox state of thiol-containing proteins. An increase in ASC, DHA, and GSH levels at high concentrations of InA, after 3 and 6 days, were observed. Moreover, the ASC/DHA + ASC and GSH/GSSG + GSH ratios showed a shift towards the oxidized form. Our study provides the first insight into how the cell redox system responds and adapts to InA phytotoxicity, providing a framework for further molecular studies.

Effect of Pyrazosulfuron-Methyl on the Photosynthetic Characteristics and Antioxidant Systems of Foxtail Millet

Foxtail millet (Setaria Italica L.) plays a principal role in food security in Africa and Asia, but it is sensitive to a variety of herbicides. This study was performed to clarify whether pyrazosulfuron-methyl can be used in foxtail millet fields and the effect of pyrazosulfuron-methyl on the photosynthetic performance of foxtail millet. Two foxtail millet varieties (Jingu 21 and Zhangzagu 10) were subjected to five doses (0, 15, 30, 60, and 120 g ai ha-1) of pyrazosulfuron-methyl in pot and field experiments. The plant height, leaf area, stem diameter, photosynthetic pigment contents, gas exchange parameters, chlorophyll fluorescence parameters, antioxidant enzyme activities, and antioxidant contents at 7 and 15 days after pyrazosulfuron-methyl application, and the yield of foxtail millet were measured. The results suggested that pyrazosulfuron-methyl inhibited the growth of foxtail millet and reduced the photosynthetic pigment contents, photosynthetic rate, and photosynthetic system II activity. Similarly, pyrazosulfuron-methyl decreased the antioxidant enzyme activities and antioxidant contents. These results also indicated that the toxicity of pyrazosulfuron-methyl to foxtail millet was decreased gradually with the extension of time after application; however, the foxtail millet yield was still significantly reduced. Therefore, pyrazosulfuron-methyl is not recommended for application in foxtail millet fields.

Protective efficacy of phenoxyacetyl oxazolidine derivatives as safeners against nicosulfuron toxicity in maize

BACKGROUND

Herbicide safeners mitigate crop damage without reducing herbicide efficacy. Here, the protective effects of phenoxyacetyl oxazolidine derivatives as potential safeners were evaluated with a view toward reducing injury caused by sulfonylurea herbicide nicosulfuron to sensitive maize varieties.

RESULTS

Growth indices demonstrated that the bioactivity of compound 9 (N-phenoxyacety-2-methyl-2,4-diethyl-1,3-oxazolidine) was superior to that of R-28725 and all other compounds tested. Compound 9 induced endogenous glutathione and upregulated glutathione-S-transferase (GST) in maize. Thus, it could enhance maize tolerance to nicosulfuron. Compared with the untreated water control group, the maximum reaction rate of GST was increased by 37.62%, while the maximum velocity of GST was decreased by 61.93% after treatment with compound 9. Acetolactate synthase relative activity was significantly enhanced in the case of treatment with compound 9, indicating the excellent protective effects of compound 9 against nicosulfuron in maize.

CONCLUSIONS

The present work demonstrates that phenoxyacetyl oxazolidine derivatives are potentially efficacious as herbicide safeners and merit further investigation.

Silicon tackles butachlor toxicity in rice seedlings by regulating anatomical characteristics, ascorbate-glutathione cycle, proline metabolism and levels of nutrients

Reckless use of herbicides like butachlor (Buta) in the fields represents a serious threat to crop plants, and hence to their productivity. Silicon (Si) is well known for its implication in the alleviation of the effects of abiotic stresses; however, its role in mitigating Buta toxicity is not yet known. Therefore, this study was carried out to explore the role of Si (10 µM) in regulating Buta (4 µM) toxicity in rice seedlings. Buta reduced growth and photosynthesis, altered nitric oxide (NO) level and leaf and root anatomy, inhibited enzyme activities of the ascorbate-glutathione cycle (while transcripts of associated enzymes, increased except OsMDHAR), as well as its metabolites (ascorbate and glutathione) and uptake of nutrients (Mg, P, K, S, Ca, Fe, etc. except Na), while addition of Si reversed Buta-induced alterations. Buta stimulated the expression of Si channel and efflux transporter genes- Lsi1 and Lsi2 while the addition of Si further greatly induced their expression under Buta toxicity. Buta increased free proline accumulation by inducing the activity of Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and decreasing proline dehydrogenase (PDH) activity, while Si reversed these effects caused by Buta. Our results suggest that Si-governed mitigation of Buta toxicity is linked with favorable modifications in energy flux parameters of photosynthesis and leaf and root anatomy, up-regulation of Si channel and transporter genes, ascorbate-glutathione cycle and nutrient uptake, and lowering in oxidative stress. We additionally demonstrate that NO might have a crucial role in these responses.

Toxicity of the herbicides used on herbicide-tolerant crops, and societal consequences of their use in France

In France, the implementation of mutant herbicide-tolerant crops and the use of the related herbicides - sulfonylureas and imidazolinones - have triggered a strong societal reaction illustrated by the intervening actions of environmentalist groups illegally mowing such crops. Trials are in progress, and therefore should be addressed the questions of the environmental risks and the toxicity of these herbicides for the animals and humans consuming the products derived from these plants. Regulatory authorities have allowed these mutant and herbicide-tolerant plants arguing that the herbicides against which they resist only target an enzyme found in 'weeds' (the acetolactate synthase, ALS), and that therefore all organisms lacking this enzyme would be endowed with immunity to these herbicides. The toxicological literature does not match with this argument: 1) Even in organisms displaying the enzyme ALS, these herbicides impact other molecular targets than ALS; 2) These herbicides are toxic for animals, organisms that do not possess the enzyme ALS, and especially invertebrates, amphibians and fish. In humans, epidemiological studies have shown that the use and handling of these toxins are associated with a significantly increased risk of colon and bladder cancers, and miscarriages. In agricultural soils, these herbicides have a persistence of up to several months, and water samples have concentrations of some of these herbicides above the limit value in drinking water.

Design, Synthesis, and Biological Activity of Novel Diazabicyclo Derivatives as Safeners

Herbicide safeners selectively protect crops from herbicide damage without reducing the herbicidal efficiency on target weed species. The title compounds were designed by the intermediate derivatization approach and fragment splicing to exploit novel potential safeners. A total of 31 novel diazabicyclo derivatives were synthesized by the microwave-assistant method using isoxazole-4-carbonyl chloride and diazabicyclo derivatives. All synthetic compounds were confirmed by infrared, ¹H and ¹³C nuclear magnetic resonance, and high-resolution mass spectrometry. The bioassay results demonstrated that most of the title compounds could reduce the nicosulfuron phytotoxicity on maize. The glutathione S-transferase (GST) activity in vivo was assayed, and compound 4(S15) revealed an inspiring safener activity comparable to commercialized safeners isoxadifen-ethyl and BAS-145138. The molecular docking model exhibited that the competition at the active sites of target enzymes between compound 4(S15) and nicosulfuron was investigated with respect to herbicide detoxification. The current work not only provided a powerful supplement to the intermediate derivatization approach and fragment splicing in design pesticide bioactive molecules but also assisted safener development and optimization.

Rapid identification of a candidate nicosulfuron sensitivity gene (Nss) in maize (Zea mays L.) via combining bulked segregant analysis and RNA-seq

A candidate nicosulfuron sensitivity gene Nss was identified by combining bulked segregant analysis and RNA-seq. Multiple mutations of this gene were discovered in nicosulfuron-sensitive maize compared with the tolerant. It has been demonstrated that variabilities exist in maize response to nicosulfuron. Two nicosulfuron-sensitive inbred lines (HB39, HB41) and two tolerant inbred lines (HB05, HB09) were identified via greenhouse and field trials. Genetic analysis indicated that the sensitivity to nicosulfuron in maize was controlled by a single, recessive gene. To precisely and rapidly map the nicosulfuron sensitivity gene (Nss), two independent F₂ segregating populations, Population A (HB41 × HB09) and Population B (HB39 × HB05), were constructed. By applying bulked segregant RNA-Seq (BSR-Seq), the Nss gene was, respectively, mapped on the short arm of chromosome 5 (chr5: 1.1-15.3 Mb) and (chr5: 0.5-18.2 Mb) using two populations, with 14.2 Mb region in common. Further analysis revealed that there were 43 and 119 differentially expressed genes in the mapping intervals, with 18 genes in common. Gene annotation results showed that a cytochrome P450 gene (CYP81A9) appeared to be the candidate gene of Nss associated with nicosulfuron sensitivity in maize. Sequence analysis demonstrated that two common deletion mutations existed in the sensitive maize, which might lead to the nicosulfuron sensitivity in maize. The results will make valuable contributions to the understanding of molecular mechanism of herbicide sensitivity in maize.