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

Nitric oxide application alleviates fungicide and ampicillin co-exposure induced phytotoxicity by regulating antioxidant defense, detoxification system, and secondary metabolism in wheat seedlings

Pesticides and antibiotics usually sink into soil, posing serious phytotoxic effects on plants. However, studies are elusive regarding the phytotoxic effects of fungicide Consento (CON) and antibiotic ampicillin (AMP) co-exposure. Nitric oxide (NO) is an important plant signaling molecule known for abiotic stress tolerance in plants. This study investigated the phytotoxic effects of CON and/or AMP on the growth and antioxidant activities of wheat (Triticum aestivum L.) seedlings and unveiled the underlying mechanisms induced by the application of NO as sodium nitroprusside (SNP; 100 μM) in wheat seedlings exposed to CON and/or AMP in a hydroponic culture. Results revealed that application of CON, AMP, and CON + AMP significantly reduced the shoot length (21, 27, & 42%), root length (49, 41, & 51%), shoot biomass (30, 27, & 35%), root biomass (51, 36, & 56%), Chl-a (24, 19, & 29%), Chl-b (42, 48, & 54%), and carotenoid contents (35, 33, & 35%), respectively, due to significantly higher hydrogen peroxide (231, 151, & 157%) and malondialdehyde production (97, 60, & 148%) in wheat seedlings compared to control plants. However, the application of NO significantly enhanced wheat lengths (38%), biomass (60%), and photosynthetic pigments (67%) on co-exposure to CON + AMP. Moreover, NO treatment significantly lowered hydrogen peroxide (36%) and malondialdehyde contents (35%) in wheat seedlings exposed to CON + AMP stress, indicating the protective role of NO in scavenging reactive oxygen species. Wheat seedlings exposed to the combined stress of CON and AMP regulated antioxidant defense, xenobiotic detoxification, and the phenylpropanoid pathway to combat stress conditions. However, NO application significantly increased CAT (44%), proline (60%), total phenolic (41%), nitrate reductase (53%), and polyphenol oxidase activities (31%) to mitigate CON + AMP stress. These findings suggest NO application as an effective and environmentally friendly approach for detoxification of CON + AMP stress through biosynthesis of secondary metabolic enzymes and regulation of antioxidants for boosting wheat crop resilience under pesticide and antibiotic co-contamination.

Deciphering the role of nitric oxide in mitigation of systemic fungicide induced growth inhibition and oxidative damage in wheat

Consento (CON) poses a significant environmental hazard as a systemic fungicide, adversely affecting the health of non-target organisms. Nitric oxide (NO), a signaling molecule, is known to play a crucial role in plant physiology and abiotic stress tolerance. However, whether NO plays any role to enhance fungicide CON tolerance in wheat seedlings is yet unclear. Therefore, we conducted a hydroponic experiment i) to investigate the morpho-physio-biochemical changes of wheat seedlings to fungicide CON stress, and ii) to examine the effects of NO and fungicide CON treatments on oxidative damage, antioxidant system, secondary metabolism and detoxification of systemic fungicide in wheat seedlings. The results showed that CON fungicide at the highest (4X) concentration significantly decreased wheat seedlings fresh weight (46.89%), shoot length (40.26%), root length (56.11%) and total chlorophyll contents (67.44%) in a dose response relationship. Moreover, CON significantly increased hydrogen peroxide, malondialdehyde, catalase, ascorbate peroxidase, glutathione-S-transferase, and peroxidase activities while decreased reduced glutathione (GSH) content. This ultimately impaired the redox homeostasis of cells, leading to oxidative damage in cell membrane. Under fungicide treatment, the addition of NO reduced the fungicide phytotoxicity, with an increase of over 60% in seedling growth. The NO application mitigated CON phytotoxicity as reflected by significantly increased chlorophyll pigments (69.88%) and decreased oxidative damage in wheat leaves. Indeed, the NO alleviatory effect was able to increase the tolerance of seedlings to fungicide, which resulted increments in antioxidant and detoxification enzymes activity, with the enhanced GSH level (78.54%). Interestingly, NO alleviated CON phytotoxicity through the phenylpropanoid pathway by enhancing the activity of secondary metabolism enzymes such as phenylalanine ammonia-lyase (47.28%), polyphenol oxidase (9%), and associated metabolites such as phenolic acids (77.62%), flavonoids (34.33%) in wheat leaves. Our study has provided evidence that NO plays a key role in the metabolism and detoxification of systemic fungicide in wheat through enhanced activity of antioxidants, detoxifications and secondary metabolic enzymes.

Degradation Characteristics of Nicosulfuron in Water and Soil by MnO2 Nano-Immobilized Laccase

As a typical sulfonylurea herbicide, nicosulfuron is mainly used to control grass weeds and some broadleaf weeds in corn fields. However, as the amount of use continues to increase, it accumulates in the environment and eventually becomes harmful to the ecosystem. In the present study, a new metallic nanomaterial, δ-MnO2, was prepared, which not only has a similar catalytic mechanism as laccase but also has a significant effect on pesticide degradation. Therefore, the bicatalytic property of MnO2 can be utilized to improve the remediation of nicosulfuron contamination. Firstly, MnO2 nanomaterials were prepared by controlling the hydrothermal reaction conditions, and immobilized laccase was prepared by the adsorption method. Next, we investigate the effects of different influencing factors on the effect of immobilized laccase, MnO2, and free laccase on the degradation of nicosulfuron in water and soil. In addition, we also analyze the metabolic pathway of nicosulfuron degradation in immobilized laccase and the bicatalytic mechanism of MnO2. The results demonstrated that the degradation rate of nicosulfuron in water by immobilized laccase was 88.7%, and the optimal conditions were 50 mg/L, 25 h, 50 °C, and pH 5. For nicosulfuron in soil, the optimal conditions for the degradation by immobilized laccase were found to be 151.1 mg/kg, 46 °C, and pH 5.9; under these conditions, a degradation rate of 90.1% was attained. The findings of this study provide a theoretical reference for the immobilized laccase treatment of sulfonylurea herbicide contamination in water and soil.

Biodegradation of atrazine and nicosulfuron by Streptomyces nigra LM01: Performance, degradative pathway, and possible genes involved

Microbial herbicide degradation is an efficient bioremediation method. In this study, a strain of Streptomyces nigra, LM01, which efficiently degrades atrazine and nicosulfuron, was isolated from a corn field using a direct isolation method. The degradation effects of the identified strain on two herbicides were investigated and optimized using an artificial neural network. The maximum degradation rates of S. nigra LM01 were 58.09 % and 42.97 % for atrazine and nicosulfuron, respectively. The degradation rate of atrazine in the soil reached 67.94 % when the concentration was 108 CFU/g after 5 d and was less effective than that of nicosulfuron. Whole genome sequencing of strain LM01 helped elucidate the possible degradation pathways of atrazine and nicosulfuron. The protein sequences of strain LM01 were aligned with the sequences of the degraded proteins of the two herbicides by using the National Center for Biotechnology Information platform. The sequence (GE005358, GE001556, GE004212, GE005218, GE004846, GE002487) with the highest query cover was retained and docked with the small-molecule ligands of the herbicides. The results revealed a binding energy of - 6.23 kcal/mol between GE005358 and the atrazine ligand and - 6.66 kcal/mol between GE002487 and the nicosulfuron ligand.