Non-enzymatic Reactive Oxygen Species Scavenging Research Articles

Control of postharvest soft rot of green peppers by Bacillus subtilis through regulating ROS metabolism

Soft rot caused by Pectobacterium carotovorum is one of the most serious postharvest bacterial diseases of green peppers. The present research aimed to determine the biocontrol effect of Bacillus subtilis on postharvest soft rot of green peppers and to further delve into biocontrol mechanisms by analyzing the metabolism of reactive oxygen species (ROS) in green peppers. As key results, soft rot occurrence of green peppers was alleviated with the increase of the concentration of B. subtilis, and the disease incidence and index of the fruits treated with 1 × 109 CFU/mL of B. subtilis for 4 d were 28.3% and 12.7%, respectively, which were significantly decreased compared with that of the control. B. subtilis could significantly increase NADPH oxidase (NOX) activity in green peppers to trigger ROS outbreaks, which induced defense response of the fruits. Furthermore, it promoted the enzymatic activities of the ROS scavenging system, including antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), ascorbic acid-glutathione (AsA-GSH) cycle-related enzymes (ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR)), glutathione peroxidase (GPX) cycle-related enzymes (GPX, GR and glutathione-s-transferase (GST)). Besides, B. subtilis increased the non-enzymatic ROS scavenging system contents, including ascorbate (AsA) and glutathione (GSH) in green peppers. Importantly, the levels of O2−·, H2O2 and malondialdehyde (MDA) in green peppers were reduced, thereby enhancing green pepper disease resistance. This study offers novel insights to advanced strategies in preventing and controlling postharvest soft rot in green peppers.

Monascus pigment prevent the oxidative cytotoxicity in myotube derived hydrogen peroxide.

The amounts of Reactive oxygen species (ROS) become higher by strenuous exercises which consume larger amounts of oxygen in active muscles. Since these ROS directly injured muscles, the high ROS concentration involves muscle fatigue. Thus, an immediate ROS scavenging system in the muscle is desired. Since Monascus pigment (MP) involves physiologically active substances which scavenge ROS, it may be a clue to save the muscle injury. However, there are no reports examining MP effects on oxidative stress in skeletal muscle. In this study, we investigated the effect and mechanism of MP on skeletal muscle cells damaged by oxidative stress. The ability to directly eliminate ROS was evaluated by mixing MP solutions with •OH and O2 •-, a type of ROS. The effect of peroxidation in C2C12 cells was evaluated by cell viability assay and Western blotting. MP scavenges •OH and O2 •-. MP treatment increases the survival rate under oxidative stress. At that time, the expression of catalase was increased: the enzyme change H2O2 into H2O to rescue the cells under oxidative stress. We conclude that monascus pigment suppressed myotube damage under oxidative stress by both non-enzymatic ROS scavenging and up-regulation of catalase expression.

Oxidative Stress Under Macronutrient Deficiency in Plants

Mineral nutrients play crucial functions in the growth and development of plants as they are intimately involved in the plant cell organization and metabolic functions. The mineral nutrients are either structural/functional constituents of enzymes or act as activators or regulators of various enzyme activities. The macronutrients like N (nitrogen) and P (phosphorus) form structural constituents of building block materials, and some of them [K (potassium), Ca (calcium), and Mg (magnesium)] are regulator or activator of enzymes. Deficiencies of macronutrient affect various physiological or metabolic activities including increased production of reactive oxygen species (ROS) in the organisms. Excess production of ROS causes oxidative stress in the plants. To counter with the oxidative stress, plants have evolved both enzymatic and non-enzymatic ROS scavenging system for protection of cellular components against deleterious ROS. Antioxidant machinery is comprised of various antioxidant enzymes such as peroxidases (POD), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), and non-enzyme molecules such as ascorbate (AA), glutathione (GSH), carotenoids and α-tocopherols. Reactive oxygen species can attack cellular structures such as cell membranes and various biomolecules including proteins and nucleic acids and causes lipid peroxidation and protein damage. In this review, we summarize recent developments on oxidative stress and antioxidant responses of plants induced by macronutrient deficiency. Further, we discuss possible ROS signaling events involved in oxidative stress and antioxidant responses induced due to different macronutrient deficiency.

Proline is a quencher of singlet oxygen and superoxide both in in vitro systems and isolated thylakoids.

Proline is a versatile plant metabolite, which is produced in large amounts in plants exposed to osmotic and oxidative stress. Proline has been shown to provide protection against various reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals. On the other hand, its protective effect against singlet oxygen has been debated, and it is considered ineffective against superoxide. Here we used various methods for the detection of singlet oxygen (electron paramagnetic resonance, EPR, spin trapping by 2,2,6,6-tetramethyl-4-piperidone, fluorescence probing by singlet oxygen sensor green, SOSG, and oxygen uptake due to chemical trapping) and superoxide (oxygen uptake due to oxygen reduction) in vitro and in isolated thylakoids. We demonstrated that proline does quench both singlet oxygen and superoxide in vitro. By comparing the effects of chemical scavengers and physical quenchers, we concluded that proline eliminates singlet oxygen via a physical mechanism, with a bimolecular quenching rate of ca. 1.5-4 106 M-1 s-1 . Our data also show that proline can eliminate superoxide in vitro in a process that is likely to proceed via an electron transfer reaction. We could also show that proline does quench both singlet oxygen and superoxide produced in isolated thylakoids. The scavenging efficiency of proline is relatively small on a molar basis, but considering its presence in high amounts in plant cells under stress conditions it may provide a physiologically relevant contribution to ROS scavenging, supplementing other nonenzymatic ROS scavengers of plant cells.

Improvement of ionizing gamma irradiation tolerance of Chlorella vulgaris by pretreatment with polyethylene glycol

Purpose: To evaluate the effects of polyethylene glycol (PEG) 6000 pretreatment on growth and physiological responses of eukaryotic microalga Chlorella vulgaris exposed to ionizing irradiation.Materials and methods: The microalgal cells pretreated with different PEG concentrations (0, 5, 10 and 20%) and then exposed to 300 Gray gamma irradiation at a dose rate of 0.5 Gy s−1. The various growth and physiological parameters including algal growth, cell size, the degree of electrolyte leakage (EL) and lipid peroxidation, the content of pigments and proline and the activity of antioxidant enzymes under gamma-free or 300 Gray gamma irradiation conditions were examined.Results: The results showed that PEG stimulated a higher growth and cell size under both stress-free and gamma-stress conditions. The maximum growth and cell size was reported when the algae was pretreated with 10% PEG. A relative increase of catalase activity was observed in all samples after exposing to gamma irradiation. However, the highest value was recorded for the gamma-radiated algae pretreated with 10% PEG. In the absence of PEG, gamma irradiation induced a significant reduction in ascorbate peroxidase activity, but with PEG pretreatment, the enzyme activity remained constant or even increased after gamma irradiation. On the other hand, although gamma irradiation stress generally suppressed the activity of superoxide dismutase in all cells, pretreating the algae with PEG could diminish this suppressing effect at all applied concentrations. Compared to the PEG-free controls, a lower rate of chlorophylls and membrane integrity loss was shown in the PEG-treated algae when exposed to gamma stress. Total carotenoid content in PEG-treated algae was also similar under both gamma-free and gamma-radiated conditions. A PEG-independent increase in proline accumulation was reported under gamma-irradiation treatment.Conclusions: Overall, the results suggested that PEG pretreatment could improve gamma-irradiation tolerance in C. vulgaris probably by stimulating a range of enzymatic and non-enzymatic reactive oxygen species scavenging systems. The microalgae may also consume PEG to break down and use it as an alternative source of carbon during stress which should be further studied in detail.

Metabolomics Studies on Cytoplasmic Male Sterility during Flower Bud Development in Soybean.

Abnormal reactive oxygen species (ROS) may mediate cytoplasmic male sterility (CMS). To observe the effect of ROS on soybean CMS, metabolite content and antioxidant enzyme activity in the flower buds between soybean N8855-derived CMS line and its maintainer were compared. Of the 612 metabolites identified, a total of 74 metabolites were significantly differentiated in flower buds between CMS line and its maintainer. The differential metabolites involved 32 differential flavonoids, 13 differential phenolamides, and 1 differential oxidized glutathione (GSSG) belonging to a non-enzymatic ROS scavenging system. We observed lower levels of flavonoids and antioxidant enzyme activities in flower buds of the CMS line than in its maintainer. Our results suggest that deficiencies of enzymatic and non-enzymatic ROS scavenging systems in soybean CMS line cannot eliminate ROS in anthers effectively, excessive accumulation of ROS triggered programmed cell death and ultimately resulted in pollen abortion of soybean CMS line.

Response of Ornamental Pepper to High-Temperature Stress and Role of Exogenous Salicylic Acid in Mitigating High Temperature

Ornamental pepper (Capsicum annuum L.) is an important economic decorative plant well known for its abundant genetic diversity. However, high-temperature (HT) stress seriously affects its aesthetic and commercial value. In this work, we analyzed the effects of exogenous salicylic acid (SA) on seed germination and seedling growth of ornamental pepper under HT stress. The inherent physiological and biochemical basis of the alleviating effect of salicylic acid was further analyzed. The findings revealed SA with 0.01 mM and 0.1 mM was most effective in enhancing thermotolerance in seeds and seedlings, respectively. SA treatment increased the germination rate and germination potential, and reduced the oxidative damage of seeds under HT stress. For seedlings, spraying SA with 0.1 mM significantly alleviated yellow leaves and dwarfing under HT stress. SA could maintain high root vigor, inhibit water loss, and maintain the integrity of cell structure by regulating osmotic substance content under HT. SA-induced thermotolerance development involved in the activation of antioxidant defense system. SA decreased the production of reactive oxygen species (ROS), increased the activity of protective enzymes, and the content of non-enzymatic ROS scavengers in plants under HT. The changes of chlorophyll fluorescence parameters showed that SA was beneficial to maintain a high level of photosynthetic capacity of ornamental pepper seedlings under HT stress. Moreover, recovery also showed a mitigatory effect on injuries induced by HT stress. Taken together, this study provided evidence for the ability of exogenous SA application to moderate the detrimental effects by HT stress.

Enhanced oxidative stress in the jasmonic acid-deficient tomato mutant def-1 exposed to NaCl stress

Jasmonic acid (JA) has been mostly studied in responses to biotic stresses, such as herbivore attack and pathogenic infection. More recently, the involvement of JA in abiotic stresses including salinity was highlighted; yet, its role in salt stress remained unclear. In the current study, we compared the physiological and biochemical responses of wild-type (WT) tomato (Solanum lycopersicum) cv Castlemart and its JA-deficient mutant defenseless-1 (def-1) under salt stress to investigate the role of JA. Plant growth, photosynthetic pigment content, ion accumulation, oxidative stress-related parameters, proline accumulation and total phenolic compounds, in addition to both enzymatic and non-enzymatic antioxidant activities, were measured in both genotypes after 14 days of 100 mM NaCl treatment. Although we observed in both genotypes similar growth pattern and sodium, calcium and potassium levels in leaves under salt stress, def-1 plants exhibited a more pronounced decrease of nitrogen content in both leaves and roots and a slightly higher level of sodium in roots compared to WT plants. In addition, def-1 plants exposed to salt stress showed reactive oxygen species (ROS)-associated injury phenotypes. These oxidative stress symptoms in def-1 were associated with lower activity of both enzymatic antioxidants and non-enzymatic antioxidants. Furthermore, the levels of the non-enzymatic ROS scavengers proline and total phenolic compounds increased in both genotypes exposed to salt stress, with a higher amount of proline in the WT plants. Overall the results of this study suggest that endogenous JA mainly enhanced tomato salt tolerance by maintaining ROS homeostasis.

Response of ROS-Scavenging Systems to Salinity Stress in Two Different Wheat (Triticum aestivum L.) Cultivars

Salinity leads to oxidative stress in plant cells due to increased production of reactive oxygen species. The response of two wheat (Triticum aestivum L.) cultivars, salt sensitive (‘Darab2’) and salt-tolerant (‘Arta’) were studied to salinity-induced oxidative stress (0, 75 and 150 mM NaCl). Increasing of lipid peroxidation caused oxidative stress in both sensitive and tolerant cultivars. The result showed that reactive oxygen species (ROS) viz., superoxide and hydrogen peroxide increased in leaves of ‘Darab2’ under salinity stress. Under salinity stress, the salt-tolerant cv. ‘Arta’ showed higher activity of the ROS scavenging enzymes like ascorbate peroxidase and peroxidases than ‘Darab2’. Furthermore, in sensitive cv. ‘Darab2’ the activities of these enzymes in leaves were unable to prevent the scavenging of H2O2. Unlike ‘Arta’, there were no significant differences in superoxide dismutases and glutathione reductase activities in sensitive cv. ‘Darab2’ under salinity stress. The amount of reduced glutathione, reduced/oxidized glutathione ratio in leaves of ‘Darab2’ was lower than ‘Arta’ under saline conditions. It seems that in salt tolerant cultivars like ‘Arta’, both enzymatic and non-enzymatic ROS scavenging machineries is critical point to overcome salinity-induced oxidative stress.

Pre-storage cold acclimation maintained quality of cold-stored cucumber through differentially and orderly activating ROS scavengers

Cucumber fruit are susceptible to chilling injury (CI) during storage and shipping at temperatures below 7–10°C. Pre-storage cold acclimation (PsCA) is a promising postharvest method for reducing CI and maintaining quality, but the reported duration of PsCA varies greatly, partly because no method so far has been developed for evaluating the chilling tolerance induced by PsCA at an early time. Following PsCA at 10°C for 6h, 12h, 24h, 48h and 72h, CI, secondary diseases and relative electrolyte leakage of cucumbers stored at 5°C decreased with PsCA duration, indicating PsCA-induced chilling tolerance in cucumber was positively correlated with the length of exposure to PsCA. Meanwhile, PsCA increased soluble solids and ascorbic acid, and reduced malondialdehyde, O2− and H2O2, suggesting that PsCA improved quality by inhibiting reactive oxygen species (ROS) and maintaining cell membrane integrity. In addition, PsCA enhanced gene expression and activities of four enzymatic ROS scavengers, superoxide dismutase, peroxidase, ascorbate peroxidase, catalase and two non-enzymatic ROS scavengers, AsA and glutathione. However, different ROS scavengers had variable transition points before they were consistently activated, suggesting that ROS scavengers were differentially activated in an orderly way and that the chilling tolerance is positively correlated with the number of activated ROS scavengers, but require enough number of ROS scavengers to be effective. This study provides possibility for early evaluation of PsCA-induced chilling tolerance and for timely arrangement of marketing and processing to reduce losses.

Water relations, gas exchange, photochemical efficiency, and peroxidative stress of four plant species in the Heihe drainage basin of northern China

Haloxylon ammodendron, Calligonum mongolicum, Elaeagnus angustifolia, and Populus hosiensis had different adaptations to limited water availability, high temperature, and high irradiance. C. mongolicum used water more efficiently than did the other species. Because of low transpiration rate (E) and low water potential, H. ammodendron had low water loss suitable for desert conditions. Water use efficiency (WUE) was high in E. angustifolia, but high E and larger leaf area made this species more suitable for mesic habitats; consequently, this species is important in tree shelterbelts. P. hosiensis had low WUE, E, and photosynthesis rates, and therefore, does not prosper in arid areas without irrigation. High irradiances caused photoinhibition of the four plants. The decrease of photochemical efficiency was a possible non-stomata factor for the midday depression of C. mongolicum. However, the species exhibited different protective mechanisms against high irradiance under drought stress. H. ammodendron and C. mongolicum possessed a more effective antioxidant defence system than E. angustifolia. These three species showed different means of coping with oxidative stress. Hence an enzymatic balance is maintained in these plants under adverse stress conditions, and the concerted action of both enzymatic and non-enzymatic reactive oxygen species scavenging mechanisms is vital to survive adverse conditions.