山黧豆根系对H2O2诱导氧化胁迫的生理应答

以水培7d苗龄的山黧豆幼苗为材料,向水培溶液中施加不同浓度H2O2处理山黧豆幼苗24h,分析山黧豆根系受氧化胁迫的程度与抗氧化系统的应答特征,以揭示山黧豆对氧化胁迫的耐受机制。结果显示:(1)随外源H2O2处理浓度的不断增加,山黧豆幼苗侧根的数目无显著变化,而其根的鲜重则显著降低。(2)同时,根系组织的内源H2O2染色范围和程度显著增高,但根尖区域始终保持较低水平的H2O2;相反,O-·2染色范围和程度明显减少,根尖区域却始终保持较高水平的O-·2。(3)同期根系抗坏血酸(ASC)含量及过氧化氢酶(CAT)、过氧化物酶(POD)与抗坏血酸过氧化物酶(APX)的活性均表现出了先升高后降低的趋势,而超氧化物歧化酶(SOD)一直表现为持续上升的趋势。研究表明,在外源H2O2胁迫条件下,山黧豆根系O-·2的积累可能与其生长和活力呈正相关,而根系H2O2的积累则与其受氧化胁迫程度呈正相关;低浓度的H2O2处理可以提高山黧豆抗氧化系统对体内活性氧的清除能力。     

H2O2 at physiological concentrations modulates Leydig cell function inducing oxidative stress and apoptosis

H₂O₂ is one of the active reactive oxygen species secreted by macrophages that are seen closely aligned with Leydig cells in the testicular interstitium. The present study was initiated to investigate the role of H₂O₂ on Leydig cell function in vitro at physiological concentrations. Significant decrease in both testosterone production (p < 0.05) and 3 β-hydroxysteroid dehydrogenase activity (p < 0.05) in adult Leydig cells were observed even with H₂O₂ at low concentrations (30 – 50 μM). H₂O₂ exposure increased oxidative stress in Leydig cells with the rise in lipid peroxidation and fall in the activities of the antioxidant enzymes; superoxide dismutase (SOD), catalase (CAT) & glutathione-s-transferase (GST). There was also a marginal increase (∼8%) in cell apoptosis accompanied by rise in FasL expression and caspase-3 activation. The above findings indicate that H₂O₂ as a bio-molecule modulates Leydig cell function at or below physiological concentrations through a variety of actions like decrease in steroidogenic enzyme activity and increase in oxidative stress and apoptosis.     

Cysteine Suppresses Oxidative Stress-Induced Myofibrillar Proteolysis in Chick Myotubes

The effects of cysteine as an antioxidant nutrient on change in protein modification and myofibrillar proteolysis in chick myotubes by induction of oxidative stress by H₂O₂ treatment were investigated. Myotubes were treated for 1 h with H₂O₂ (1 mM). After this treatment, the H₂O₂ was removed and the cells were cultured in cysteine (0.1 and 1 mM) containing serum-free medium for 24 h. Protein carbonyl content as an index of protein modification and N^τ-methylhistidine release as an index of myofibrillar proteolysis were increased at 24 h after H₂O₂ treatment, and the increment was reduced by cysteine. Calpain, proteasome and cathepsin (B+L and D) activities were increased at 24 h after H₂O₂ treatment, and the increment was also reduced by cysteine. These results indicate that cysteine suppresses protein modification by oxidative stress, resulting in a decrease of protease acitivities, finally resulting in a decrease in myofibrillar proteolysis in chick myotubes.     

Antioxidant Effects of Rhodoxanthin from Potamogeton crispus L. on H2O2-Induced RAW264.7 Macrophages Cells

Potamogeton crispus L. (P. crispus) is the type of a widely distributed perennial herbs, which is rich in rhodoxanthin. In this research work, five antioxidant indexes in vitro were selected to study the antioxidant activity of rhodoxanthin from P. crispus (RPC). A model of hydrogen peroxide (H₂O₂) -induced oxidative damage in RAW264.7 cells was established to analyze the antioxidant effect and potential mechanism of RPC. The levels of ROS, MDA and the activities of oxidation related enzymes by H₂O₂ were determined by enzyme linked immunosorbent assay (ELISA). The mRNA expression of Nrf-2, HO-1, SOD1 and SOD2 was measured by qRT-PCR assay. According to the results, RPC had free radical scavenging ability for 2, 2-diphenyl-1-trinitrohydrazine (DPPH), 2,2’-azinobis(3-ethylbenzo-thiazoline-6-sulfonic acid radical ion) (ABTS), hydroxyl radical and superoxide anion. RPC significantly decreased the level of MDA and ROS and LDH activity, while increased GSH level and activities of SOD, GSH−Px and CAT. It was showed that RPC could increase the mRNA expression of Nrf-2, HO-1, SOD1 and SOD2 in RAW264.7 cells in a dose-dependently manner. In summary, RPC treatment could effectively attenuate the H₂O₂-induced cell damage rate, and the mechanism is related to the reduction of H₂O₂ induced oxidative stress and the activation of Nrf-2 pathway.     

Prevention of hyperhydricity in micropropagated carnation shoots by bottom cooling: implications of oxidative stress

Carnation shoot cultures were micropropagated in two different agar concentrations (0.58 and 0.85%) and placed in a bottom cooling system or control conditions. During the culture period of 28 days, it was observed that relative humidity, hyperhydricity, dry weight, multiplication rate, and the activity of the antioxidant enzymatic system changed in relation to the agar concentration used and the application of bottom cooling. The percentage of hyperhydric shoots also showed a significant decrease under bottom cooling conditions for both agar concentrations. Lipid peroxidation was always lower in shoots cultured with bottom cooling. All the antioxidant enzymatic activities were lower in bottom cooling treatments compared to controls. These results show that the normalization of the environmental conditions in vitro via bottom cooling can prevent the onset of different simultaneous stress reactions concomitant with hyperhydricity. The present work provides for the first time , direct evidence of a reduced H₂O₂ generation in the tissues cultured in bottom cooling able to reduce oxidative stress.     

Nanoparticle-mediated catalase delivery protects human neurons from oxidative stress

Several neurodegenerative diseases and brain injury involve reactive oxygen species and implicate oxidative stress in disease mechanisms. Hydrogen peroxide (H₂O₂) formation due to mitochondrial superoxide leakage perpetuates oxidative stress in neuronal injury. Catalase, an H₂O₂-degrading enzyme, thus remains an important antioxidant therapy target. However, catalase therapy is restricted by its labile nature and inadequate delivery. Here, a nanotechnology approach was evaluated using catalase-loaded, poly(lactic co-glycolic acid) nanoparticles (NPs) in human neuronal protection against oxidative damage. This study showed highly efficient catalase encapsulation capable of retaining∼99% enzymatic activity. NPs released catalase rapidly, and antioxidant activity was sustained for over a month. NP uptake in human neurons was rapid and nontoxic. Although human neurons were highly sensitive to H₂O₂, NP-mediated catalase delivery successfully protected cultured neurons from H₂O₂-induced oxidative stress. Catalase-loaded NPs significantly reduced H₂O₂-induced protein oxidation, DNA damage, mitochondrial membrane transition pore opening and loss of cell membrane integrity and restored neuronal morphology, neurite network and microtubule-associated protein-2 levels. Further, catalase-loaded NPs improved neuronal recovery from H₂O₂ pre-exposure better than free catalase, suggesting possible applications in ameliorating stroke-relevant oxidative stress. Brain targeting of catalase-loaded NPs may find wide therapeutic applications for oxidative stress-associated acute and chronic neurodegenerative disorders.     

Comparison of resistance to drought of three bean cultivars

The aim of the present work was to evaluate oxidative stress and plant antioxidant system of three contrasting bean (Phaseolus vulgaris L.) genotypes in the response to drought. Drought was imposed 14 d after emergence, by withholding water, until leaf relative water content reached 65 %. Water stress increased lipid peroxidation (LPO), membrane injury index, H₂O₂ and OH^⋅ production in leaves of stressed plants. Activities of the antioxidative enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APOX) increased significantly under water stress in all the studied cultivars, while catalase (CAT) increased in cvs. Plovdiv 10 and Prelom, but decreased in cv. Dobrudjanski ran. Furthermore cv. Plovdiv 10 which had the highest APOX and CAT activities also showed the lowest increase in H₂O₂ and OH^⋅ production and LPO while cv. Dobrudjanski ran showed the lowest increases (and often the lowest values) in the antioxidant enzyme activities and the highest increases of H₂O₂ and OH^⋅ production, and LPO. On the basis of the data obtained we could specify cv. Plovdiv 10 and cv. Prelom as drought tolerant and cv. Dobrudjanski ran as a drought sensitive.     

Ferulic acid (FA) protects human retinal pigment epithelial cells from H2O2‐induced oxidative injuries

The aim of present study is to investigate whether Ferulic acid (FA), a natural polyphenol antioxidant, was able to protect ARPE‑19 cells from hydrogen peroxide (H₂O₂)‑induced damage, and elucidate the underlying mechanisms. Our results revealed that FA pre‐treatment for 24 hours can reverse cell loss of H₂O₂‐induced ARPE‐19 cells via the promotion of cell proliferation and prevention of apoptosis, as evidenced by 5‐ethynyl‐2′‐deoxyuridine (EdU) incorporation and terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labelling (TUNEL) assay, respectively. Moreover, the addition of FA (5 mM) can decrease Bax and cleaved caspase‐3 protein expression, but increase Bcl‐2 protein expression in ARPE‐19 cells. Furthermore, H₂O₂‐induced oxidative stress in ARPE‐19 cells was significantly alleviated by FA, illustrated by reduced levels of ROS and MDA. In addition, the attenuated antioxidant enzymes activities of (SOD, CAT and GPX) and GSH level were reversed almost to the normal base level by the pre‐addition of FA for 24 hours. In all assays, FA itself did not exert any effect on the change of the above parameters. These novel findings indicated that FA effectively protected human ARPE‐19 cells from H₂O₂‐induced oxidative damage through its pro‐proliferation, anti‐apoptosis and antioxidant activity, suggesting that FA has a therapeutic potential in the prevention and treatment of AMD.     

Differential domain structure stability of the severe acute respiratory syndrome coronavirus papain-like protease

Recent studies from our laboratory have showed that resveratrol, a polyphenol found predominantly in grapes rendered strong cardioprotection in animal models of heart disease. The cardioprotection which was observed was primarily associated with the ability of resveratrol to reduce oxidative stress in these models. The aim of the current study was to corroborate the role of resveratrol as an inhibitor of oxidative stress and explore the underlying mechanisms of its action in heart disease. For this purpose, we used a cell model of oxidative stress, the hydrogen peroxide (H₂O₂) exposed adult rat cardiomyocytes, which was treated with and without resveratrol (30 μM); cardiomyocytes which were not exposed to resveratrol served as controls. Cell injury, cell death and oxidative stress measurements as well as the activities of the major endogenous antioxidants superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were carried out in control and H₂O₂ exposed cardiomyocytes, treated with and without resveratrol. Pharmacological blockade using specific blockers of the antioxidant enzymes were used to confirm their role in mediating resveratrol action in H₂O₂ exposed cardiomyocytes. The status of H₂O₂ and antioxidant enzymes in serum samples from spontaneously hypertensive rats (SHR) treated with and without resveratrol (2.5 mg/kg body weight) was also examined.Our results showed significant cell injury and death in H₂O₂ exposed cardiomyocytes which was prevented upon resveratrol treatment. SOD and CAT activities were decreased in H₂O₂ exposed adult rat cardiomyocytes; treatment with resveratrol significantly prevented this reduction. However, GPx activity was not altered in the H₂O₂ exposed cardiomyocytes in comparison to controls. Pharmacological blockade of SOD and/or CAT prevented the beneficial effect of resveratrol. In SHR, H₂O₂ levels were increased, but CAT activity was decreased, while SOD remained unchanged, when compared to WKY rats; resveratrol treatment significantly prevented the increase in H₂O₂ levels and the decrease in CAT activities in SHR.Based on our results, we conclude that treatment with resveratrol prevents oxidative stress induced cardiomyocyte injury mainly by preserving the activities of critical antioxidant enzymes. This may be a crucial mechanism by which resveratrol confers cardioprotection.     

Protection against oxidative stress by vitamin D in cone cells

Photoreceptor degeneration (PD) refers to a group of heterogeneous outer retinal dystrophies characterized by the death of photoreceptors. Both oxidative stress and inflammation are involved in the pathogenesis of PD. We investigate whether vitamin D has a potential for the treatment of PD by evaluating the anti‐oxidative stress and anti‐inflammatory properties of the active form of vitamin D₃, 1,α, 25‐dihydroxyvitamin D₃, in a mouse cone cell line, 661W. Mouse cone cells were treated with H₂O₂ or a mixture of H₂O₂ and vitamin D; cell viability was determined. The production of reactive oxygen species (ROS) in treated and untreated cells was measured. The expression of key anti‐oxidative stress and inflammatory genes in treated and untreated cells was determined. Treatment with vitamin D significantly increased cell viability and decreased ROS production in 661W cells under oxidative stress induced by H₂O₂. H₂O₂ treatment in 661W cells can significantly down‐regulate the expression of antioxidant genes and up‐regulate the expression of neurotoxic cytokines. Vitamin D treatment significantly reversed these effects and restored the expression of antioxidant genes. Vitamin D treatment also can block H₂O₂ induced oxidative damages. The data suggested that vitamin D may offer a therapeutic potential for patients with PD.     

On the relationship between isoprene emission and thermotolerance in Phragmites australis leaves exposed to high temperatures and during the recovery from a heat stress

Thermotolerance induced by isoprene has been assessed during heat bursts but there is little information on the ability of endogenous isoprene to confer thermotolerance under naturally elevated temperature, on the interaction between isoprene-induced thermotolerance and light stress, and on the persistence of this protection in leaves recovering at lower temperatures. Moderately high temperature treatment (38 °C for 1.5 h) reduced photosynthesis, stomatal conductance, and photochemical efficiency of photosystem II in isoprene-emitting, but to a significantly lower extent than in isoprene-inhibited Phragmites australis leaves. Isoprene inhibition and high temperature independently, as well as together, induced lipid peroxidation, increased level of H₂O₂, and increased catalase and peroxidase activities. However, leaves in which isoprene emission was previously inhibited developed stronger oxidative stress under high temperature with respect to isoprene-emitting leaves. The heaviest photosynthetic stress was observed in isoprene-inhibited leaves exposed to the brightest illumination (1500 µmol m⁻² s⁻¹) and, in general, there was also a clear additive effect of light excess on the formation of reactive oxygen species, antioxidant enzymes, and membrane damage. The increased thermotolerance capability of isoprene-emitting leaves may be due to isoprene ability to stabilize membranes or to scavenge reactive oxygen species. Irrespective of the mechanism by which isoprene reduces thermal stress, isoprene-emitting leaves are able to quickly recover after the stress. This may be an important feature for plants coping with frequent and transient temperature changes in nature.     

Effect of Cadmium Ions on Antioxidant Defense System in Sunflower Cotyledons

Sunflower (Helianthus annuus L.) seeds were germinated and grown in the presence of 50, 100 and 200 μM CdCl₂. The lower concentration (50 μM) of Cd² ions produced slight decrease in reduced glutathione (GSH) content and overall increase (except superoxide dismutase) in antioxidant enzyme activities, and in H₂O₂ concentration. Chlorophyll content, lipid peroxidation and protein oxidation were not affected under 50 μM CdCl₂. GSH content was diminished under 100 and 200 μM CdCl₂, and except for superoxide dismutase, which activity remained unaltered, overall decreases in the antioxidant enzyme activities (catalase, ascorbate peroxidase, dehydroascorbate peroxidase, glutathione reductase) and in guaiacol peroxidase were observed. These Cd² concentrations caused a decrease in chlorophyll content as well as an increase in lipid peroxidation, protein oxidation and H₂O₂ concentration. All the observed effects were more evident with the highest concentration of cadmium chloride used. This revised version was published online in July 2006 with corrections to the Cover Date.     

(-)-Epigallocatechin-3-gallate and hydroxytyrosol improved antioxidative and anti-inflammatory responses in bovine mammary epithelial cells

(-)-Epigallocatechin-3-gallate (EGCG), the major phenolic compound of green tea, and hydroxytyrosol (HTyr), a phenol found in olive oil, have received attention due to their wide-ranging health benefits. To date, there are no studies that report their effect in bovine mammary gland. Therefore, the aim of this study was to evaluate the anti-oxidative and anti-inflammatory effects of EGCG and HTyr in bovine mammary epithelial cell line (BME-UV1) and to compare their antioxidant and anti-inflammatory in vitro efficacy. Sample of EGCG was obtained from a commercially available green tea extract while pure HTyr was synthetized in our laboratories. The mammary oxidative stress and inflammatory responses were assessed by measuring the oxidative stress biomarkers and the gene expression of inflammatory cytokines. To evaluate the cellular antioxidant response, glutathione (GSH/GSSH), γ-glutamylcysteine ligase activity, reactive oxygen species and malondialdehyde (MDA) production were measured after 48-h incubation of 50 µM EGCG or 50 µM of HTyr. Reactive oxygen species production after 3 h of hydrogen peroxide (50 µM H₂O₂) or lipopolysaccharide (20 µM LPS) exposure was quantified to evaluate and to compare the potential protection of EGCG and HTyr against H₂O₂-induced oxidative stress and LPS-induced inflammation. The anti-inflammatory activity of EGCG and HTyr was investigated by the evaluation of pro and anti-inflammatory interleukins (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-10) messenger RNA abundance after treatment of cells for 3 h with 20 µM of LPS. Data were analyzed by one-way ANOVA. (-)-Epigallocatechin-3-gallate or HTyr treatments induced higher concentrations of intracellular GSH compared to control cells, matched by an increase of γ-glutamylcysteine ligase activity mainly in cells treated with HTyr. Interestingly, EGCG and HTyr prevented oxidative lipid damage in the BME-UV1 cells by a reduction of intracellular MDA levels. (-)-Epigallocatechin-3-gallate and HTyr were able to enhance cell resistance against H₂O₂-induced oxidative stress. It was found that EGCG and HTyr elicited a reduction of the three inflammatory cytokines TNF-α, IL-1β, IL-6 and an increase of the anti-inflammatory cytokine IL-10. Hydroxytyrosol has proved to be a strong antioxidant compound, and EGCG has shown mainly an anti-inflammatory profile. These results indicated that EGCG and HTyr may provide dual protection because they were able to attenuate oxidative stress and inflammatory responses, suggesting that these phenolic compounds are potential natural alternatives to be used in dairy cattle as feed supplement for reducing the development of oxidative and inflammatory processes related to parturition or as topical treatments for the control of bovine intramammary inflammation.     

Responses of antioxidant enzymes to cold and high light are not correlated to freezing tolerance in natural accessions of Arabidopsis thaliana

Low temperatures and high light cause imbalances in primary and secondary reactions of photosynthesis, and thus can result in oxidative stress. Plants employ a range of low‐molecular weight antioxidants and antioxidant enzymes to prevent oxidative damage, and antioxidant defence is considered an important component of stress tolerance. To figure out whether oxidative stress and antioxidant defence are key factors defining the different cold acclimation capacities of natural accessions of the model plant Arabidopsis thaliana, we investigated hydrogen peroxide (H₂O₂) production, antioxidant enzyme activity and lipid peroxidation during a time course of cold treatment and exposure to high light in four differentially cold‐tolerant natural accessions of Arabidopsis (C24, Nd, Rsch, Te) that span the European distribution range of the species. All accessions except Rsch (from Russia) had elevated H₂O₂ in the cold, indicating that production of reactive oxygen species is part of the cold response in Arabidopsis. Glutathione reductase activity increased in all but Rsch, while ascorbate peroxidase and superoxide dismutase were unchanged and catalase decreased in all but Rsch. Under high light, the Scandinavian accession Te had elevated levels of H₂O₂. Te appeared most sensitive to oxidative stress, having higher malondialdehyde (MDA) levels in the cold and under high light, while only high light caused elevated MDA in the other accessions. Although the most freezing‐tolerant, Te had the highest sensitivity to oxidative stress. No correlation was found between freezing tolerance and activity of antioxidant enzymes in the four accessions investigated, arguing against a key role for antioxidant defence in the differential cold acclimation capacities of Arabidopsis accessions.     

水稻磷脂氢谷胱甘肽过氧化物酶在蛋白质水平上的组织和诱导表达特征

蛋白质是生命活动的主要承担分子,了解蛋白质在有机体中的时空分布对于正确解析蛋白质的功能十分重要．磷脂氢谷胱甘肽过氧化物酶 (PHGPx) 是目前发现的唯一能够直接还原膜上脂类过氧化物的抗氧化酶,在保护生物膜免受过氧化损伤方面有着重要作用．采用Western blot技术,分析了水稻PHGPx (OsPHGPx) 在水稻不同组织以及多种胁迫条件下的蛋白质表达特征．结果表明,OsPHGPx在成熟水稻植株内主要分布于叶组织中,以旗叶中含量最高,而在水稻幼苗中则在茎及叶组织中均检测到较强的杂交信号．OsPHGPx在幼苗中的表达受到H₂O₂和NaCl的强烈诱导,但植物激素对其表达的影响较弱．H₂O₂和NaCl的诱导效果呈现出时间及剂量的相关性,当用0.5 mmol/L H₂O₂处理12 h或用500 mmol/L NaCl处理24 h,此时OsPHGPx表达量达到最大值．对H₂O₂清除剂二甲基硫脲处理的水稻幼苗,外源H₂O₂的再处理并不能诱导OsPHGPx的表达,而NaCl的诱导效果并不受影响,说明H₂O₂可能并不介导NaCl诱导OsPHGPx的表达．这些结果为进一步研究OsPHGPx在水稻中生物学功能奠定了基础．     

Effects of exogenous nitric oxide on photosynthesis,antioxidative ability,and mineral element contents of perennial ryegrass under copper stress

A hydroponics experiment was conducted to test the effects of sodium nitroprusside (SNP, a donor of NO) supplied with different concentrations on copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.). Excess Cu (200 µM) reduced chlorophyll content, resulting a decrease in photosynthesis. Cu stress induced the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^{? ?}), leading to malondialdehyde (MDA) accumulation. Furthermore, activities of antioxidant enzymes in Cu-treated seedlings such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were decreased. In addition, Cu stress inhibited the uptake of K, Mg, Fe, and Zn and increased Ca content in roots. Moreover, in leaves of Cu-stressed seedlings, K, Fe, and Zn contents were decreased and the contents of Ca and Mg were not affected significantly. In Cu-treated seedlings, Cu concentration in roots was higher than in leaves. Addition of 50, 100, 200 µM SNP in Cu-mediated solutions increased chlorophyll content and photosynthesis, improved antioxidant enzyme activities, reduced Cu-induced oxidative damages, kept intracellular ion equilibrium under Cu stress, increased Cu concentration in roots and inhibited Cu accumulation in leaves. In particular, addition of 100 µM SNP had the best effect on promoting growth of ryegrass seedlings under Cu stress. However, the application of 400 µM SNP had no obvious alleviating effect on Cu toxicity in ryegrass seedlings.     

Effects of methylglyoxal and pyridoxamine in rat brain mitochondria bioenergetics and oxidative status

Advanced glycation end products (AGEs) and methylglyoxal (MG), an important intermediate in AGEs synthesis, are thought to contribute to protein aging and to the pathogenesis of age-and diabetes-associated complications. This study was intended to investigate brain mitochondria bioenergetics and oxidative status of rats previously exposed to chronic treatment with MG and/or with pyridoxamine (PM), a glycation inhibitor. Brain mitochondrial fractions were obtained and several parameters were analyzed: respiratory chain [states 3 and 4 of respiration, respiratory control ratio (RCR), and ADP/O index] and phosphorylation system [transmembrane potential (ΔΨ_m), ADP-induced depolarization, repolarization lag phase, and ATP levels]; hydrogen peroxide (H₂O₂) production levels, mitochondrial aconitase activity, and malondialdehyde levels as well as non-enzymatic antioxidant defenses (vitamin E and glutathione levels) and enzymatic antioxidant defenses (glutathione disulfide reductase (GR), glutathione peroxidase (GPx), and manganese superoxide dismutase (MnSOD) activities). MG treatment induced a statistical significant decrease in RCR, aconitase and GR activities, and an increase in H₂O₂ production levels. The administration of PM did not counteract MG-induced effects and caused a significant decrease in ΔΨ_m. In mitochondria from control animals, PM caused an adaptive mechanism characterized by a decrease in aconitase and GR activities as well as an increase in both α-tocopherol levels and GPx and MnSOD activities. Altogether our results show that high levels of MG promote brain mitochondrial impairment and PM is not able to reverse MG-induced effects.     

Effects of Different Treatments of Salicylic Acid on Heat Tolerance, Chlorophyll Fluorescence, and Antioxidant Enzyme Activity in Seedlings of Cucumis sativa L.

The effects of different treatments of salicylic acid (SA) on lipid peroxidation, chlorophyll fluorescence and antioxidant enzyme activity in seedlings of Cucumis sativa L. were studied before heat stress treatment, 36 h after heat stress and 24 h after recovery. Compared with the controls (foliar spray of distilled water), a foliar spray of 1 mM SA (SSA treatment) decreased electrolyte leakage and the concentration of H₂O₂ and thiobarbituric acid reactive substances (TBARS). SSA treatment also enhanced maximum yield of photosystem II photochemical reactions (Fv/Fm) and the quantum yield of the photosystem II electron transport (ΦPSII) after both heat stress and recovery; however, adding 1 mM SA to the nutrient solution (ASA treatment) or both adding 1 mM SA to the nutrient solution and foliar spray of 1 mM SA as well (SSA + ASA treatment) had the opposite effects. SOD activity was stimulated by all SA treatments. CAT activity was stimulated by SSA treatment and inhibited by ASA and SSA + ASA treatments after heat stress and recovery. This suggest that SSA treatment can efficiently remove H₂O₂ and decrease heat stress, and CAT plays a key role in removing H₂O₂ in cucumber seedlings under heat stress, while more H₂O₂ accumulates in ASA and SSA + ASA treatments and therefore induces serious oxidative stress. GPX, APX and GR showed higher activities in all SA treatments under heat stress, however, it appears that they were not key enzymes in removing H₂O₂ in cucumber subject to heat stress.