Effect of herbicides in the oxidative stress in crop winter species

In vitro immunotoxic evaluation of herbicides in RAW 264.7 cells

Weeds are a concern in agriculture and the use of herbicides constitutes an effective, efficient, and economical way to control their growth. Recent discoveries of herbicides are promising for the management of resistant weeds. However, there is a gap in the knowledge of the toxic effects of some herbicides previously reported on immune cells. The present study aimed to examine cellular immunotoxicity of three herbicides (clomazone, glyphosate, and sulfentrazone) after 96 hr incubation utilizing RAW 264.7 BALB/c mouse monocyte/macrophage-like cell line to elucidate the role of some toxicological pathways. Data demonstrated the herbicides clomazone, glyphosate, and sulfentrazone initiated a cytotoxic effect as evidenced by EC50 values of 429.2; 53.7; 866.6 mg/L, respectively. Clomazone and sulfentrazone, at all concentrations, induced excess production of reactive oxygen (ROS) and reactive nitrogen (RNS) free radicals. An immunosuppression was observed in RAW 264.7 cells after incubation with 50 or 100 mg/L glyphosate and 500 or 1000 mg/L sulfentrazone. In addition, all herbicides produced mitochondrial depolarization and decreased tumor necrosis factor-α (TNF-α) levels. This constitutes the first report of the effects of clomazone and sulfentrazone on RAW 264.7 cells, including reduced TNF-α levels, indicating the adverse influence of herbicides on the immune system.

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.

Redox status upon herbicides application in the control of Lolium multiflorum (2n and 4n) as weed

Lolium multiflorum Lam. is a winter weed of difficult control found as diploid (2n) and tetraploid plants (4n). Our study aimed to evaluate the responses of antioxidant enzymes and lipid peroxidation, in both diploid and tetraploid ryegrass varieties. Treatments consisted of control plants (without any herbicide application), and four herbicides with different mechanisms of action. Leaf material was collected 36 h after treatment imposition to determine the lipid peroxidation by ferrous oxidation-xylenol (FOX) content, and the activity of the enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione-S-transferase (GST), and δ-aminolevulinic acid dehydratase (ALAD). Both ryegrass varieties showed oxidative stress mainly due to a downregulated decreased (>31%) in SOD activity and an increase (>32%) in lipid peroxidation (FOX), mainly in ryegrass genotypes exposed to haloxyfop, glyphosate, and iodosulfuron. On the other hand, clethodim-treated plants had an increase in SOD and APX activities, associated with a reduced ALAD activity in both 2n (32%) and 4n (11%) genotypes. In general, the 2n genotype was more affected than the 4n genotype.

Effect of New Pre-Emergence Herbicides on Quality and Yield of Potato and Its Associated Weeds

Potato is an economically important vegetable crop in Egypt. Weed infestation, especially broad-leafed, during the vegetative growth stage substantially affects both crop yield and tuber quality. In the current study, the impact of new ready-mix pre-emergent herbicides on broadleaf weeds, tuber yield, and quality was evaluated. The two-year field experiment comprised the following treatments: (1) Un-weeded control, (2) Hand hoeing, (3) Sencor, (4) Ecopart, (5) Zeus, (6) Kroki, and (7) Flomex. The results showed that weed control treatments significantly reduced the weed density compared to un-weeded control and the herbicides efficacy reached over 90%. The herbicidal treatments also significantly increased the activity of antioxidant enzymes peroxidases (POX) and catalase (CAT) and improved the non-enzymatic antioxidant (carotenoids) compared to un-weeded control. Conversely, the higher content of malondialdehyde (MDA) in potato leaves was obtained for un-weeded control. Moreover, weed control treatments caused significant enhancement in plant growth parameters, yield, and its components in addition to tuber quality of potato. Compared to the un-weeded control, maximum tuber yield was observed in Flomex followed by Ecopart, Kroki, Zeus, and Sencor, respectively. The higher number of tubers and total yield were recorded in plants treated with Flomex plus compared to all the other treatments. Higher content of total soluble sugar, total soluble protein, and total starch content was observed in weed control treatments compared with un-weeded control. Based on Pearson’s correlation and heatmap analysis, the changes in agro-physiological parameters data are linked to the herbicidal treatments. The results indicate that the applied herbicides could be alternative products for Sencor and an option for controlling broadleaved weeds. However, further studies are needed to ensure their efficacy and safety under other conditions.

Selectivity of metsulfuron applied to soybean before sowing in different intervals and soils

This work aimed to evaluate the selectivity of the herbicide metsulfuron applied at different times on the development of soybeans grown in soils with different characteristics. The experiment was conducted in a randomized block design, in a factorial scheme (4 x 4), with four replicates. Factor A was application time (0, 15, 30, and 45 days before sowing, DBS) and factor B was soil type (Erechim, Itaqui, Piratini, and Santa Maria). Soybean plants cultivated in the Erechim soil showed moderate phytotoxicity, with greater damage to the leaf area and plant dry matter, mainly after application at 30 DBS. Those cultivated in Itaqui soil showed gradual phytotoxicity between 14 and 28 days after emergence (DAE). Soybean plants grown in the Piratini and Santa Maria soils showed the highest phytotoxicity and photosynthetic reduction, mainly at 15 and 0 DBS. Metsulfuron application at 45 DBS caused reduced plant growth by up to 40%, and reduced shoot development (30%) in soybean plants grown in Piratini and Santa Maria soils, respectively. There were gradual changes in phytotoxicity and the morphophysiological traits of soybean plants exposed to the residual effect of metsulfuron in different soils, which indicates that soybeans should be sown more than 45 days after the application of metsulfuron, regardless of soil characteristics.

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

Effect of fomesafen on the embryonic development of zebrafish

Fomesafen is widely used in agriculture and can be detected in the environment and agricultural products. Research on the developmental toxicity of fomesafen in animals is currently very limited. Here, we used zebrafish as an animal model to evaluate the toxicity of fomesafen in developing aquatic vertebrates and higher animals. From 6h to 72h following fertilization, exposure of zebrafish embryos to 5, 10 and 20 mg/L of fomesafen resulted in pericardial edema, a reduction in heart rate, shortening of body length, and yolk sac edema. Fomesafen reduced the number of immune cells such as neutrophils and macrophages, increased the expression of a number of inflammatory factors, induced the up-regulation of the oxidative stress response and apoptosis, and disrupted the activity of enzymes related to nerve development, which affected the motility of the embryos. In conclusion, the results provide new evidence for the comprehensive assessment of fomesafen toxicity in aquatic vertebrates.

Effect of pH on the Hydrolytic Transformation of a New Mixture Formulation of Fomesafen and Quizalofop-ethyl in Water

A hydrolytic transformation study was conducted in water of pH 4.0, 7.0 and 9.2 to evaluate the effect of pH on persistence of a new readymix formulation of fomesafen and quizalofop-ethyl. The water samples were fortified at 0.5 and 1 µg mL^-1 levels and analysed at 0 (2 h), 1, 3, 7, 15, 30, 60, 90, 120, 150 days interval. Both the analytical methods were validated following SANTE guideline and found accurate based on average recovery of 80-100%, Relative standard deviation (RSD) < 20% and Coefficient of Determination (R²) 0.99. The dissipation of both the molecules was pH dependent and followed first order kinetics. Higher persistence of fomesafen was observed in alkaline pH as compared to neutral and acidic pH with half-life of 41.56-63.24 days, whereas higher stability of quizalofop-ethyl was observed in the water of acidic pH followed by neutral and alkaline pH with half-life of 1.26-8.09 days.