Increased Antioxidant Activity under Elevated Temperatures: A Mechanism of Heat Stress Tolerance in Wheat Genotypes

An experiment was conducted with three wheat (Triticum aestivum L.) genotypes C 306, HD 2285 and HD 2329 (differently susceptible to water and temperature stress) to study the extent of oxidative injury and activities of antioxidant enzymes in relation to heat stress induced by manipulating dates of sowing. Increase in temperature by late sowing significantly decreased leaf relative water content (RWC), ascorbic acid content, and increased H₂O₂ content and lipid peroxidation in all the genotypes at 8 and 23 d after anthesis. Temperature tolerant genotypes C 306, closely followed by HD 2285 were superior to HD 2329 in maintaining high RWC, ascorbic acid content, and lower H₂O₂ content and lipid peroxidation (malondialdehyde content) under high temperature (late sowing) at the two stages. Activities of superoxide dismutase and catalase were highest in HD 2285 followed by C 306 and minimum in HD 2329 while ascorbate peroxidase activity was highest in C 306.     

Drought Induces Oxidative Stress and Enhances the Activities of Antioxidant Enzymes in Growing Rice Seedlings

When rice seedlings grown for 10 and 20 days were subjected to in vitro drought stress of −0.5 and −2.0 MPa for 24 h, an increase in the concentration of superoxide anion (O₂^.−), increased level of lipid peroxidation and a decrease in the concentration of total soluble protein and thiols was observed in stressed seedlings compared to controls. The concentration of H₂O₂ as well as ascorbic acid declined with imposition of drought stress, however glutathione (GSH) concentration declined only under severe drought stress. The activities of total superoxide dismutases (SODs) as well as ascorbate peroxidase (APX) showed consistent increases with increasing levels of drought stress, however catalase activity declined. Mild drought stressed plants had higher guaiacol peroxidase (GPX) and chloroplastic ascorbate peroxidase (c-APX) activity than control grown plants but the activity declined at the higher level of drought stress. The activities of enzymes involved in regeneration of ascorbate i.e. monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were higher in drought stressed plants compared to controls. Results suggest that drought stress induces oxidative stress in rice plants and that besides SOD, the enzymes of ascorbate-glutathione cycle, which have not been studied in detail earlier under stressful conditions, appear to function as important component of antioxidative defense system under drought stress.     

Role of Antioxidant Systems in Wheat Genotypes Tolerance to Water Stress

The role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes. Drought imposed at two different stages after anthesis resulted in an increase in H2O2 accumulation and lipid peroxidation and decrease in ascorbic acid content. Antioxidant enzymes like superoxide dismutase, ascorbate peroxidase and catalase significantly increased under water stress. Drought tolerant genotype C 306 which had highest ascorbate peroxidase and catalase activity and ascorbic acid content also showed lowest H2O2 accumulation and lipid peroxidation (malondialdehyde content) under water stress in comparison to susceptible genotype HD 2329 which showed lowest antioxidant enzyme activity and ascorbic acid content and highest H2O2 content and lipid peroxidation. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Superoxide dismutase activity, however, did not show significant differences among the genotypes under irrigated as well as water stress condition. It seems that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of Hexaploid and Tetraploid Wheat Cultivars in their Responses to Water Stress

We studied the effect of water stress imposed at anthesis and pre-anthesis stages on oxidative stress and antioxidant activity in four wheat cultivars, two hexaploid Triticum aestivum cultivars, drought resistant cv. C 306 and drought susceptible cv. Hira, and two tetraploid cultivars, T. durum cv. A 9-30-1 and T. dicoccum cv. HW 24. Water stress decreased relative water content (RWC), membrane stability index (MSI), and increased H₂O₂ and malondialdehyde (MDA) contents as well as activity of superoxide dismutase (SOD), catalase (Cat) and peroxidase (POX) in all the genotypes at all the stages. Both the tetraploid cultivars showed higher RWC, MSI and SOD activity, and lower H₂O₂ and MDA contents under water stress than hexaploid ones. Cat and POX activities were highest in C 306.     

Characterization of <Emphasis Type="Italic">Brassica juncea</Emphasis> antioxidant potential under salinity stress

Present study characterizes the anti-oxidative defense potential of four Brassica juncea varieties, Pusa Jaikisan, Varuna, RLM-198, and CS-52, differing in their ability to withstand salinity stress. 7-day-old seedlings raised in MS medium supplemented with 0, 50, 100, and 150 mM NaCl were used to monitor changes in the growth profile, level of stress marker molecules, and activities of important antioxidant enzymes. Increasing NaCl concentration resulted in a significant (P ≤ 0.05) reduction of shoot fresh and dry mass and vigor index in all the varieties tested. Maximum reduction in growth was recorded for RLM-198 while CS-52 maintained better growth characteristics. Varuna and RLM-198 exhibited a limited increase in superoxide dismutase, ascorbate peroxidase, and total peroxidase activity under increasing salinity. These varieties also recorded maximum salt stress-induced damage in terms of increased lipid peroxidation, H₂O₂ content, and electrolyte leakage. On the other hand, CS-52 recorded maximum proline accumulation with minimum levels of H₂O₂, electrolyte leakage, and malondialdehyde contents. With increasing salinity stress, CS-52 recorded maximal increase in the activity of antioxidant enzymes. However, catalase activity did not correlate with alterations in H₂O₂ levels under stress. Interestingly, a lower superoxide dismutase:ascorbate peroxidase ratio in CS-52 correlated with stress tolerance trait, while a comparatively higher superoxide dismutase:ascorbate peroxidase ratio in RLM-198 marked the susceptible nature of the variety. Our results propose that superoxide dismutase:ascorbate peroxidase ratio is the critical factor, determining the degree of stress tolerance in Brassica juncea.     

The in vivo and in vitro influence of methyl jasmonate on oxidative processes in Arabidopsis thaliana leaves

In Arabidopsis thaliana leaves a strong increase of H₂O₂ content was induced by application of methyl jasmonate (JAMe) through the root system, but the induction only slightly depended on JAMe concentration. The activity of superoxide dismutase and ascorbic acid peroxidase increased at lower JAMe concentrations and decreased at higher ones. Catalase activity decreased proportionally to JAMe concentration (in comparison with control plants). The sum of ascorbic acid and dehydroascorbate content at 10⁻⁶ M JAMe was similar to the control, but at higher concentrations it increased, especially due to a higher ascorbate accumulation. Methyl jasmonate applied directly to the extract of leaves (in vitro experiment) also induced a strong increase in H₂O₂ level, even at a low concentration (10⁻⁸ M). Since lower JAMe concentrations induced weak superoxide dismutase and did not change catalase and peroxidase activity, it is suggested that in this case a high level of hydrogen peroxide was not the result of the activity of the mentioned enzymes. JAMe-induction of H₂O₂ increase at the highest JAMe concentration resulted from SOD activity. Our in vivo and in vitro experiments suggest that jasmonate can influence oxidative stress not only through gene expression but also by its direct effect on enzyme activity.     

外源H_2S对NO_3~-胁迫下番茄幼苗生理生化特性的影响

采用营养液水培方法,通过外源施加H2S供体NaHS(100μmol/L),研究了信号分子H2S对100mmol/L NO3-胁迫下番茄幼苗生理生化特性的影响。结果表明:(1)NO3-胁迫下,随着处理时间的延长,番茄幼苗的株高、根长、鲜重和干重显著降低,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著降低,而胞间CO2浓度以及丙二醛(MDA)、H2O2含量增加,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性显著降低,抗坏血酸(AsA)和还原性谷胱甘肽(GSH)含量显著降低。(2)与NO3-胁迫处理相比,外源NaHS处理1、3、5d后,番茄幼苗的株高、根长、鲜重和干重显著增加,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著升高,而胞间CO2浓度显著降低;MDA和H2O2含量降低,SOD、POD、CAT和APX活性显著增强,AsA和GSH含量显著增加,而且幼苗的硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶的活性显著增强;L-半胱氨酸脱巯基酶活性和内源H2S含量增加。研究认为,外源H2S可能通过提高抗氧化物酶的活性和增加抗氧化物质含量来缓解NO3-对番茄幼苗造成的伤害,从而增强其对NO3-胁迫耐性。     

Hydrogen sulfide alleviated chromium toxicity in wheat

Effects of H₂S on seed germination under chromium (Cr) stress were investigated in wheat (Triticum aestivum L.). Under Cr stress, the percentage of germination of wheat seeds decreased, but this decrease could be alleviated by pretreatment with NaHS, an H₂S donor, in a dose-dependent manner. Furthermore, NaHS significantly enhanced the activities of amylase, esterase, superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase in Cr-stressed germinating seeds, whereas reduced the Cr-induced increase in lipoxygenase activity and over-production of malondialdehyde (MDA) and H₂O₂, and sustained slightly higher content of endogenous H₂S.     

Effect of 24-Epibrassinolide on Antioxidative Defence System Against Lead-Induced Oxidative Stress in The Roots of <Emphasis Type="Italic">Brassica juncea</Emphasis> L. Seedlings

Lead (Pb) toxicity causes oxidative stress by increasing the production of reactive oxygen species. The aim of the present study was to investigate the role of 24-epibrassinolide (24-EBL) on the antioxidant defence system as a response to Pb stress in Brassica juncea L. Surface-sterilized seeds were exposed to Pb ion (0 and 2 mM) toxicity in Petri dishes and subsequently, the seeds were sprayed with either (i) deionized water or (ii) different concentrations (10^–12, 10^–10, and 10^–8 M) of 24-EBL on alternate days. After nine days, the roots of the B. juncea seedlings were harvested to analyze the heavy metal content, root length, hydrogen peroxide level, lipid peroxidation, total protein content and activities of the antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, glutathione reductase and glutathione-S-transferase). According to our results, the Pb ions accumulated by the B. juncea roots led to oxidative stress by increasing the level of H₂O₂ and malondialdehyde, and thus, increased the activity of the antioxidative enzymes (except for catalase) and the growth and total protein content decreased. Whereas, the 24-EBL treatment to the roots of Pb stressed seedlings was able to alleviate the Pb-induced oxidative stress. Upon the application of 24-EBL, a reduction in Pb accumulation, H₂O₂ and malondialdehyde levels as well as an increased total protein content and activity of antioxidative enzymes detoxifying hydrogen peroxide (catalase, ascorbate peroxidase and peroxidase) were observed. As a result, the stress protective properties of 24-EBL depending on concentration in B. juncea roots were revealed in this study.     

Transgenic peanut overexpressing <Emphasis Type="Italic">mtlD</Emphasis> gene confers enhanced salinity stress tolerance via mannitol accumulation and differential antioxidative responses

Globally, peanut is an important oilseed crop, which is cultivated under different agro-climatic zones. Soil salinity is one of the major constraints in peanut cultivation. Therefore, to understand the physio-biochemical mechanisms imparting salinity stress, four transgenic peanut lines (cv. GG20) already developed and confirmed by our lab, having bacterial mannitol dehydrogenase gene (mtlD), were subjected to different levels of salinity stresses (1, 2 and 3 dS m^?1) in pots under containment facility. Further, these lines were also characterized for various physio-biochemical parameters at flowering, pegging and pod formation stages. All the transgenic lines recorded significantly higher mannitol dehydrogenase (MTD) activity and mannitol accumulation than the wild type (WT). Under salinity stress, significantly higher levels of superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase activities, while significantly lower levels of H₂O₂ and malondialdehyde contents, were recorded in the transgenics compared to WT. Similarly, significantly higher ascorbic acid and relative water content (RWC) were recorded in transgenic lines. The MTD activity showed positive correlation with various antioxidant enzymes, growth parameters and RWC, while negative correlation was recorded with H₂O₂ and malondialdehyde content at most of the plant growth stages. The mtlD transgenic peanut lines under pot conditions were found maintaining lower oxidative injuries, indicating amelioration of salinity-induced oxidative stress by enhanced protection mechanisms via mannitol accumulation and antioxidative responses. The best lines identified (MTD1 and MTD4) may be used further as pre-breeding source for imparting salinity stress tolerance in peanut. Besides, these lines may also be tested under open-field trials for release as salt-tolerant variety.     

低钾胁迫对番茄叶片活性氧及抗氧化酶系的影响

以2种不同低钾耐性大果番茄(钾敏感型番茄081018和耐低钾型番茄081034)为材料,比较低钾处理下2种番茄叶片中活性氧产生及抗氧化酶系活性和相关基因表达差异,明确植物叶片对低钾胁迫的响应机制.结果显示:(1)钾敏感型番茄在低钾胁迫时,叶片中各种保护酶(SOD及其同工酶、POD、CAT、APX)活性随处理时间延长呈下降趋势,同时活性氧(O2-、H2O2)和MDA含量急剧增加;耐低钾型番茄在低钾胁迫条件下,其各类保护酶活性均比对照水平有所升高,而且O2-、H2O2和MDA的含量增加也较少.(2)钾敏感型番茄在低钾胁迫时叶片内Cu/Zn-SOD、CAT和APX基因的相对表达量均有下降趋势,而同期耐低钾型番茄在低钾胁迫时Cu/Zn-SOD、CAT和APX的表达却明显增加,这与其对应的酶活性变化趋势同步.研究表明,低钾胁迫使耐低钾型番茄具有较高保护酶基因表达量,产生较高的保护酶活性,可降低活性氧的破坏作用,防止膜渗透性增加,使之对低钾的适应性较强,而钾敏感番茄品系则相反.     

Low concentration of exogenous abscisic acid increases lead tolerance in rice seedlings

The effects of exogenous abscisic acid (ABA) on lead tolerance in rice (Oryza sativa L.) seedlings were investigated. Pre-treatment with 0.1 g m³ ABA for 2 d restricted amount of Pb translocated from roots to shoots, decreased malondialdehyde and H₂O₂ contents in leaves, and alleviated Pb-induced decrease in plant growth and leaf chlorophyll content. Further, ABA pre-treatment adjusted leaf antioxidative enzyme activities (increased ascorbate peroxidase and catalase activities while decreased superoxide dismutase activity) and so alleviated oxidative stress.     

Exogenous Hydrogen Peroxide Changes Antioxidant Enzyme Activity and Protects Ultrastructure in Leaves of Two Cucumber Ecotypes Under Osmotic Stress

Cucumber (Cucumis sativus L.) varieties cv. Jinchun no. 4 (a North China ecotype) and cv. Lvfeng no. 6 (a South China ecotype) were cultivated to explore the effects of osmotic stress on the ultrastructure of chloroplasts and mitochondria, as well as to assess the possible protective effect of exogenous hydrogen peroxide (H₂O₂). Under osmotic stress induced by 10% polyethylene glycol 6000, 84.3% of the chloroplasts in Jinchun no. 4 were abnormal, whereas 88.6% were abnormal in Lvfeng no. 6. Abnormal mitochondria occurred in these two strains at rates of 78.5 and 87.1%, respectively. The stress condition disintegrated the membranes of most chloroplasts and mitochondria in the leaf cells of both cucumber ecotypes, and it also increased the malondialdehyde (MDA) content. We subjected the two cultivars to a combined treatment with H₂O₂ and osmotic stress and made the following observations: (1) Abnormal chloroplasts occurred at rates of 25.7 and 28.6%, and abnormal mitochondria were observed at rates of 22.9 and 32.8%, respectively. (2) Most of the investigated membranes were well organized in leaves of Jinchun no. 4 and Lvfeng no. 6, and the levels of endogenous H₂O₂, superoxide anion, and MDA were lower. Osmotic stress and exogenous H₂O₂ both increased the activities of antioxidative enzymes such as manganese superoxide dismutase, glutathione peroxidase, catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, dehydroascorbate reductase, and the antioxidants ascorbate and reduced glutathione. The combined effect of osmotic stress and exogenous H₂O₂ resulted in the highest antioxidant activities in both cucumber ecotypes. We propose that exogenous H₂O₂ increases antioxidant activity in cucumber leaves and thereby decreases lipid peroxidation to some extent, thus protecting the ultrastructure of most chloroplasts and mitochondria under osmotic stress.     

Induction of Betalain Pigmentation in Hairy Roots of Red Beet under Different Radiation Sources

The effects of aluminum on lipid peroxidation and activities of antioxidative enzymes were investigated in detached rice leaves treated with 0 to 5 mM AlCl₃ at pH 4.0 in the light. AlCl₃ enhanced the content of malondialdehyde but not the content of H₂O₂. Superoxide dismutase activity was reduced by AlCl₃, while catalase and glutathione reductase activities were increased. Peroxidase and ascorbate peroxidase activities were increased only after prolonged treatment, when toxicity occurred. The results give evidence that Al treatment caused oxidative stress and in turn, it caused lipid peroxidation.     

Exogenous progesterone alleviates heat and high light stress-induced inactivation of photosystem II in wheat by enhancing antioxidant defense and D1 protein stability

This experiment was conducted to test the effects of foliar application of progesterone on the photochemical efficiency of photosystem II (PSII) and photosynthetic rate in wheat flag leaves subjected to cross-stress of heat and high light during grain-filling stage. The results showed that progesterone pretreatment increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, and the contents of ascorbic acid and glutathione under the cross-stress. Meanwhile, the rate of O₂ ^? production, hydrogen peroxide (H₂O₂) and malondialdehyde contents in progesterone pretreated leaves were significantly lower under heat and high light stress. In parallel with the alleviation of oxidative stress, higher content of D1 protein in PSII reactive center was observed in progesterone pretreated leaves, resulting in a significant increase in the potential (Fv/Fm) and actual (ΦPS II) photochemical efficiency of PSII, and the net photosynthetic rate. In summary, this study suggested that foliar application of progesterone might protect the PSII complex from heat and high light stress-induced damage through enhancing antioxidant defense system and further facilitating D1 protein stability in the wheat leaves.     

Lipid Peroxidation and Peroxide-Scavenging Enzymes in Cotton Seeds Under Natural Ageing

The present study was carried out to contribute to our knowledge of the mechanism of seed deterioration in two cotton (Gossypium hirsutum L.) cultivars (HS6 and H1098) during natural ageing. The seeds were sealed in polythene bags and stored at 25 ± 1 °C for 3, 6, 9, 12 and 18 months. In both the cultivars, germinability decreased whereas membrane deterioration assayed as electrical conductivity of the seed leachates increased with storage period. The decrease in germinability was well correlated with increased accumulation of H₂O₂ and malondialdehyde content. The activities of peroxidase, catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase decreased with ageing. Seeds of cv. H1098 were more susceptible to ageing than HS6. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cadmium toxicity and translocation in rice seedlings are reduced by hydrogen peroxide pretreatment

A hydroponic experiment was carried out to study the role of hydrogen peroxide (H₂O₂) in enhancing tolerance and reducing translocation of cadmium (Cd) in rice seedlings. Plant growth (length and biomass of shoot and root) was significantly repressed by Cd exposure. However, pretreatment with 100 μM H₂O₂ for 1d mitigated Cd stress by inducing enzyme activities for antioxidation (e.g., superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX)) and detoxification (e.g., glutathione S-transferase (GST)) as well as by elevating contents of reduced glutathione (GSH) and ascorbic acid (AsA). As a result, H₂O₂ and malondialdehyde (MDA) content decreased in plants and the seedling growth was less inhibited. On the other hand, H₂O₂ pretreatment decreased Cd concentration in shoots, thus lowered the ratio of Cd concentration in shoots and roots (S/R), indicating that H₂O₂ may affect Cd distribution in rice seedlings. The improved Cd tolerance is partly due to an enhanced antioxidative system that efficiently prevents the accumulation of H₂O₂ during Cd stress. Increased Cd sequestration in rice roots may contribute to the decline of Cd translocation.     

Cadmium-induced oxidative damage in rice leaves is reduced by polyamines

The protective effect of polyamines against Cd toxicity of rice (Oryza sativa) leaves was investigated. Cd toxicity to rice leaves was determined by the decrease in protein content. CdCl₂ treatment results in (1) increased Cd content, (2) induction of Cd toxicity, (3) increase in H₂O₂ and malondialdehyde (MDA) contents, (4) decrease in ascorbic acid (ASC) and reduced glutathione (GSH) contents, and (5) increase in the activities of antioxidative enzymes (superoxide dismutase, glutathione reductase, ascorbate peroxidase, catalase, and peroxidase). Spermidine (Spd) and spermine (Spm), but not putrescine (Put), were effective in reducing CdCl₂-induced toxicity. Spd and Spm prevented CdCl₂-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of ASC and GSH, and increase in the activities of antioxidative enzymes. Spd and Spm pretreatments resulted in a decrease in Cd content when compared with H₂O pretreatment, indicating that Spd and Spm may reduce the uptake of Cd. Results of the present study suggest that Spd and Spm are able to protect Cd-induced oxidative damage and this protection is most likely related to the avoidance of H₂O₂ generation and the reduction of Cd uptake.     

Antioxidant Enzyme Responses to NaCl Stress in Cassia angustifolia

Seeds of Cassia angustifolia Vahl. were subjected to 0, 20, 50, 100 mM NaCl for 7 d in order to study the effect of salt stress on growth parameters, endogenous Na⁺ and Cl^– concentrations, antioxidant system, lipid peroxidation, hydrogen peroxide, and proline contents. Salinity affected all of the considered parameters and caused a great reduction in plant biomass. The root and shoot length, fresh and dry mass and germination percentage were inhibited by NaCl treatments. These changes were associated with an increase in the Na⁺ and Cl^– contents in the seedlings and increased activities of superoxide dismutase, catalase, peroxidase, and polyphenol oxidase. The increased enzyme activity coincided with decreased ascorbate content and enhanced H₂O₂ and proline content.     

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。