EBR预处理对盐胁迫下葡萄幼苗叶片抗氧化物质及酶活性的影响

以2年生葡萄(Vitis vinifera L.)酿酒品种赤霞珠扦插苗为材料,在水培条件下,分别用0、0.05、0.10和0.20mg/L 24-表油菜素内酯(EBR)预处理幼苗,然后进行50mmol/L NaCl胁迫,分别在胁迫6d和12d测定幼苗叶片中超氧阴离子(O_2~)、丙二醛(MDA)、抗氧化物质含量以及相关酶活性,探讨EBR预处理对葡萄幼苗耐盐性的影响。结果表明:与单独盐胁迫处理相比,不同浓度的EBR预处理使盐胁迫葡萄幼苗叶片O_2~和MDA含量显著降低,同时使其抗氧化物质抗坏血酸(AsA)、脱氢抗坏血酸(DHA)、还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量以及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)、超氧化物歧化酶(SOD)活性显著升高;其中,0.10mg/L EBR预处理的表现最佳,在盐胁迫12d时,其葡萄叶O_2~和MDA含量比单独盐胁迫处理分别显著降低30.5%和22.0%,其叶片相应AsA和GSH的含量较单独盐胁迫处理分别显著提高82.8%和27.9%,且GR、APX和SOD活性分别显著提高7.2%、8.5%和24.0%。研究发现,在盐胁迫条件下,适宜浓度的外源BRs预处理能够显著降低葡萄叶片中活性氧含量,提高抗氧化物质含量和抗氧化酶活性,以促进AsA-GSH循环的快速有效运转,有效减轻植株的过氧化伤害,缓解盐胁迫对葡萄幼苗的伤害,提高葡萄的耐盐性。     

Partial oxidative protection by enzymatic and non-enzymatic components in cashew leaves under high salinity

The work evaluated the role of enzymatic and non-enzymatic antioxidants in cashew (Anacardium occidentale) leaves under 0, 50, 100, 150 and 200 mM NaCl. Salt stress increased protein oxidation and decreased the lipid peroxidation, indicating that lipids are less susceptible to oxidative damage. The superoxide dismutase (SOD) activity was not changed, ascorbate peroxidase (APX) activity steadily decreased while the catalase (CAT) activity strongly increased with the increasing NaCl concentration. High salinity also induced alterations in the ascorbate (AsA) and glutathione (GSH) redox state. The salt resistance in cashew may be associated with maintaining of SOD activity and upregulation of CAT activity in concert with the AsA and GSH antioxidants.     

Spermidine pretreatment enhances heat tolerance in rice seedlings through modulating antioxidative and glyoxalase systems

This study was undertaken to investigate the possible involvement of the antioxidant defense and glyoxalase systems in protecting rice seedlings from heat-induced damage in the presence of spermidine (Spd). Hydroponically grown 14-day-old seedlings were subjected to foliar spray with Spd (1 mM, 24 h) prior to heat stress (42 °C, 48 h) followed by subsequent recovery (27 °C, 48 h). Lipoxygenase activity, malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and proline (Pro) content increased significantly whereas fresh weight (FW) and chlorophyll (Chl) content decreased during heat stress and after recovery, indicating unrecoverable damage to rice seedlings. Heat-induced damage was also evident in decreased levels of ascorbate (AsA), glutathione (GSH), and AsA and GSH redox ratios. Superoxide dismutase (SOD) and catalase (CAT) activities increased during heat stress but declined after recovery. Activities of glutathione peroxidase (GPX), ascorbate peroxidase (APX), monodehydroascorbate reductase, dehydroascorbate reductase (DHAR) and glutathione reductase (GR) decreased during heat stress but an opposite trend for most of these enzymes was observed after recovery. Heat stress also resulted in significant increases in the activities of glyoxalase enzymes (Gly I and Gly II). In contrast, exogenous Spd protected rice seedlings from heat-induced damage as marked by lower levels of MDA, H₂O₂, and Pro content coupled with increased levels of AsA, GSH, FW, Chl, and AsA and GSH redox status. After recovery, Spd-pretreated heat-exposed seedlings displayed higher activities of SOD, CAT, GPX, GST APX, DHAR and GR as well as of Gly I and Gly II. In addition, polyamine analysis revealed that exogenously applied Spd significantly elevated the levels of free and soluble conjugated Spd. Therefore, we conclude from our results that heat exposure provoked an oxidative burden while enhancement of the antioxidative and glyoxalase systems by Spd rendered rice seedlings more tolerant to heat stress. Further, co-induction of the antioxidative and glyoxalase systems was closely associated with Spd mediated enhanced level of GSH.     

牛角花齿蓟马为害对紫花苜蓿AsA、GSH含量及相关代谢酶活性的影响

为了明确非酶抗氧化物质抗坏血酸(AsA)、还原型谷胱甘肽(GSH)及相关代谢酶抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)在紫花苜蓿(Medicago sativa L.)对牛角花齿蓟马Odontothrips loti Haliday为害的抗性中的作用,测定了不同牛角花齿蓟马虫口密度下抗、感蓟马苜蓿无性系R-1、I-1的AsA、GSH含量及APX、GR活性的变化。结果表明:受牛角花齿蓟马为害后,R-1无性系在低虫口密度(1、3头/枝条)下,AsA、GSH含量和GR活性均上升,在高虫口密度(5、7头/枝条)下,AsA含量和GR活性先升高后下降,GSH含量上升后保持稳定;I-1无性系的AsA、GSH含量先升高后下降,GR活性在为害后期呈上升趋势;R-1、I-1无性系的APX活性均先上升后下降,但R-1无性系APX活性的上升速率及下降速率小于I-1无性系。说明AsA、GSH含量及APX、GR活性的升高可能是紫花苜蓿对牛角花齿蓟马诱导抗性的一种表现,但I-1无性系对蓟马为害的应激反应滞后于R-1无性系。在牛角花齿蓟马为害后期,R-1无性系体内的AsA、GSH含量及APX、GR活性仍处于较高水平,也说明了R-1无性系对牛角花齿蓟马为害的抗性较I-1无性系强。     

Manganese-excess induces oxidative stress,lowers the pool of antioxidants and elevates activities of key antioxidative enzymes in rice seedlings

Manganese (Mn) is an essential element for plant growth but in excess, specially in acidic soils, it can become phytotoxic. In order to investigate whether oxidative stress is associated with the expression of Mn toxicity during early seedling establishment of rice plants, we examined the changes in the level of reactive oxygen species (ROS), oxidative stress induced an alteration in the level of non-enzymic antioxidants and activities of antioxidative enzymes in rice seedlings grown in sand cultures containing 3 and 6 mM MnCl₂. Mn treatment inhibited growth of rice seedlings, the metal increasingly accumulated in roots and shoots and caused damage to membranes. Mn treated plants showed increased generation of superoxide anion (O₂ ^.−), elevated levels of H₂O₂ and thiobarbituric acid reactive substances (TBARS) and decline in protein thiol. The level of nonprotein thiol, however, increased due to Mn treatment. A decline in contents of reduced ascorbate (AsA) and glutathione (GSH) as well as decline in ratios of their reduced to oxidize forms was observed in Mn-treated seedlings. The activities of antioxidative enzymes superoxide dismutase (SOD) and its isoforms Mn SOD, Cu/Zn SOD, Fe SOD as well as guaiacol peroxidase (GPX) increased in the seedlings due to Mn treatment however, catalase (CAT) activity increased in 10 days old seedlings but it declined by 20 days under Mn treatment. The enzymes of Halliwell-Asada cycle, ascorbate peroxidase (APX) monodehydoascorbate reductase (MDHAR), dehyroascorbate reductase (DHAR) and glutathione reductase (GR) increased significantly in Mn treated seedlings over controls. Results suggest that in rice seedlings excess Mn induces oxidative stress, imbalances the levels of antioxidants and the antioxidative enzymes SOD, GPX, APX and GR appear to play an important role in scavenging ROS and withstanding oxidative stress induced by Mn.     

Effects of short-term heat stress on oxidative damage and responses of antioxidant system in Lilium longiflorum

This paper aims to determine the changes in reactive oxygen species (ROS) and the responses of the lily (Lilium longiflorum L.) antioxidant system to short-term high temperatures. Plants were exposed to three levels of heat stress (37°C, 42°C, 47°C) for 10 h when hydrogen peroxide (H₂O₂) and superoxide (O₂⁻) production rate along with membrane injury indexes, and changes in antioxidants were measured. Compared with the control (20°C), electrolyte leakage and MDA concentration varied slightly after 10 h at 37°C and 42°C, while increased significantly at 47°C. During 10 h at 37°C and 42°C, antioxidant enzyme activities, such as SOD, POD, CAT, APX and GR, were stimulated and antioxidants (AsA and GSH concentrations) maintained high levels, which resulted in low levels of O₂⁻ and H₂O₂ concentration. However, after 10 h at 47°C, SOD, APX, GR activities and GSH concentration were similar to the controls, while POD, CAT activities and AsA concentration decreased significantly as compared with the control, concomitant with significant increase in O₂⁻ and H₂O₂ concentrations. In addition, such heat-induced effects on antioxidant enzymes were also confirmed by SOD and POD isoform, as Cu/ZnSOD maintained high stability under heat stress and the intensity of POD isoforms reduced with the duration of heat stress, especially at 47°C. It is concluded that in lily plants, the oxidative damage induced by heat stress was related to the changes in antioxidant enzyme activities and antioxidants.     

Aluminum-induced changes in reactive oxygen species accumulation, lipid peroxidation and antioxidant capacity in wheat root tips

The present study investigated the effects of aluminum on lipid peroxidation, accumulation of reactive oxygen species and antioxidative defense systems in root tips of wheat (Triticum aestivum L.) seedlings. Exposure to 30 μM Al increased contents of malondialdehyde, H₂O₂, suproxide radical and Evans blue uptake in both genotypes, with increases being greater in Al-sensitive genotype Yangmai-5 than in Al-tolerant genotype Jian-864. In addition, Al treatment increased the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione reductase (GR) and glutathione peroxidase (GPX), as well as the contents of ascorbate (AsA) and glutathione (GSH) in both genotypes. The increased activities SOD and POD were greater in Yangmai-5 than in Jian-864, whereas the opposite was true for the activities of CAT, APX, MDHAR, GR and GPX and the contents of AsA and GSH. Consequently, the antioxidant capacity in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH)-radical scavenging activity and ferric reducing/antioxidant power (FRAP) was greater in Jian-864 than in Yangmai-5.     

Selenium Pretreatment Upregulates the Antioxidant Defense and Methylglyoxal Detoxification System and Confers Enhanced Tolerance to Drought Stress in Rapeseed Seedlings

In order to observe the possible regulatory role of selenium (Se) in relation to the changes in ascorbate (AsA) glutathione (GSH) levels and to the activities of antioxidant and glyoxalase pathway enzymes, rapeseed (Brassica napus) seedlings were grown in Petri dishes. A set of 10-day-old seedlings was pretreated with 25 μM Se (Sodium selenate) for 48 h. Two levels of drought stress (10% and 20% PEG) were imposed separately as well as on Se-pretreated seedlings, which were grown for another 48 h. Drought stress, at any level, caused a significant increase in GSH and glutathione disulfide (GSSG) content; however, the AsA content increased only under mild stress. The activity of ascorbate peroxidase (APX) was not affected by drought stress. The monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) activity increased only under mild stress (10% PEG). The activity of dehydroascorbate reductase (DHAR), glutathione S-transferase (GST), glutathione peroxidase (GPX), and glyoxalase I (Gly I) activity significantly increased under any level of drought stress, while catalase (CAT) and glyoxalase II (Gly II) activity decreased. A sharp increase in hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA content) was induced by drought stress. On the other hand, Se-pretreated seedlings exposed to drought stress showed a rise in AsA and GSH content, maintained a high GSH/GSSG ratio, and evidenced increased activities of APX, DHAR, MDHAR, GR, GST, GPX, CAT, Gly I, and Gly II as compared with the drought-stressed plants without Se. These seedlings showed a concomitant decrease in GSSG content, H₂O₂, and the level of lipid peroxidation. The results indicate that the exogenous application of Se increased the tolerance of the plants to drought-induced oxidative damage by enhancing their antioxidant defense and methylglyoxal detoxification systems.     

Polyamines as antioxidant protectors against paraquat damage in radish (Raphanus sativus L.) cotyledons

Pretreatment of radish cotyledons with polyamines (PAs; especially 1 mM spermidine) significantly improved their tolerance to subsequent 50 μM paraquat (PQ)-induced oxidative damage. Symptoms in the cotyledons, e.g., large accumulations of H₂O₂, and losses of fresh weight, chlorophyll, and proteins, were remarkably alleviated. Likewise, analysis of several enzymes belonging to the Superoxide dismutase (SOD)/ascorbate-glutathione cycle showed that pretreatment with PAs prevented typical PQ-induced declines in the total activities of SOD, ascorbate peroxidase (APX), and glutathione reductase (GR). Dehydroascorbate reductase (DHAR) activity, which normally decreases sharply under prolonged PQ exposure, was also highly maintained by PA treatment. In a native gel assay, two SOD isozymes (FeSOD and Cu/ZnSODI), two APX isozymes (APX1 and APX2), and two GSSG-specific isozymes (GR1 and GR2) proved to be more responsible for PQ tolerance, as manifested by the strong increases in their activities by spermidine (Spd) pretreatment. In addition, experiments with protein synthesis inhibitors (actinomycin D and cycloheximide) indicated that Spd could stimulatede novo synthesis of SOD and APX at the translational level. We can conclude that PAs may function as antioxidant protectors by invoking an efficient SOD/ascorbate-glutathione cycle in radish cotyledons exposed to PQ.     

The responses of the enzymes related with ascorbate–glutathione cycle during drought stress in apple leaves

To explore the significance of the ascorbate–glutathione cycle under drought stress, the leaves of 2-year-old potted apple (Malus domestica Borkh.) plants were used to investigate the changes of each component of the ascorbate–glutathione cycle as well as the gene expression of dehydroascorbate reductase (DHAR, EC 1.8.5.1), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) under drought stress. The results showed that the malondialdehyde (MDA) and H₂O₂ concentrations in apple leaves increased during drought stress and began to decrease after re-watering. The contents of total ascorbate, reduced ascorbic acid (AsA), total glutathione and glutathione (GSH) were obviously upregulated in apple leaves when the soil water content was 40–45%. With further increase of the drought level, the contents of the antioxidants and especially redox state of AsA and GSH declined. However, levels of them increased again after re-watering. Moreover, drought stress induced significant increase of the activities of enzymes such as APX, scavenging H₂O₂, and also of monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), DHAR and GR used to regenerate AsA and GSH, especially when the soil water content was above 40–45%. During severe drought stress, activities of the enzymes were decreased and after re-watering increased again. Gene expression of cytoplasmic DHAR, cytoplasmic APX and cytoplasmic GR showed similar changes as the enzyme activities, respectively. The results suggest that the ascorbate–glutathione cycle is up-regulated in response to drought stress, but cannot be regulated at severe drought stress conditions.     

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content and superoxide anion (O₂) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.     

H_2S对干旱胁迫下白三叶幼苗抗氧化防御能力的影响

以‘拉丁诺’白三叶(Trifolium repens cv.‘Ladino’)为试验材料,研究外源H2S处理对PEG6 000(聚乙二醇)模拟干旱胁迫下白三叶叶片相对含水量(RWC)、膜脂过氧化、活性氧成分、抗氧化酶、抗坏血酸-谷胱甘肽循环代谢和非酶抗氧化物质的影响,以揭示H_2S调控白三叶抗旱性的生理机制。结果显示:(1)0.2 mmol/L的外源NaHS(H_2S供体)能显著提高干旱胁迫下白三叶的叶片相对含水量,维持显著较低的电解质渗透率(EL)和丙二醛(MDA)含量。(2)与直接干旱胁迫相比,干旱胁迫下外源添加NaHS处理的白三叶叶片内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性显著增强,抗坏血酸-谷胱甘肽循环代谢中关键酶抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、单脱水抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性及其抗氧化中间产物抗坏血酸(AsA)、谷胱甘肽(GSH)含量也显著提高。(3)叶片类黄酮、总酚和原花青素的含量在一定的胁迫时间范围内亦显著增加,并伴随着活性氧成分O_2~(-·)产生速率和H_2O_2水平降低。研究认为,外源H2S能通过促进干旱胁迫下白三叶体内的多重抗氧化防御能力来提高其幼苗的抗旱性。     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

不同海拔青海云杉与祁连圆柏叶片抗氧化系统

以祁连山寺大隆林区连续海拔梯度(2 665~3 365 m)上青海云杉(Picea crassifolia)和祁连圆柏(Sabina przewalskii)为材料, 测定叶片中抗氧化保护系统的变化, 探讨常绿木本植物抗氧化系统对高山极端环境的适应机制。结果显示, 祁连圆柏和青海云杉叶片中丙二醛(MDA)含量均与海拔高度呈正相关, 相同海拔上青海云杉MDA含量极显著高于祁连圆柏(p＜0.01)。随海拔升高, 两树种抗氧化保护酶超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性和非酶促抗氧化剂脯氨酸(Pro)、抗坏血酸(AsA)、还原性谷胱甘肽(GSH)含量均呈明显增加趋势。青海云杉叶片的AsA水平高于祁连圆柏, 但对海拔变化的敏感性较低; 祁连圆柏的GSH、Pro水平及其对海拔变化的敏感性均高于青海云杉。结果表明, 研究区青海云杉所受过氧化伤害较祁连圆柏更严重, 但两树种清除O₂^-·的能力相当而主要负责分解H₂O₂的酶种有所不同: 祁连圆柏中为POD, 青海云杉中则为CAT、APX和GR, AsA-GSH循环系统在青海云杉活性氧清除中的作用强于在祁连圆柏中, 祁连圆柏的活性氧清除物质可能以Pro为主。     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Investigations on the antioxidative defence responses to NaCl stress in a mangrove, Bruguiera parviflora: Differential regulations of isoforms of some antioxidative enzymes

Two-month-old healthy seedlings of a true mangrove, Bruguiera parviflora, raised from propagules in normal nursery conditions were subjected to varying concentrations of NaCl for 45 d under hydroponic culture conditions to investigate the defence potentials of antioxidative enzymes against NaCl stress imposed oxidative stress. Changes in the activities of the antioxidative enzymes catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POX), glutathione reductase (GR) and superoxide dismutase (SOD) were assayed in leaves to monitor the temporal regulation. Among the oxidative stress triggered chemicals, the level of H₂O₂ was significantly increased while total ascorbate and total glutathione content decreased. The ratio of reduced to oxidized glutathiones, however, increased due to decreased levels of oxidized glutathione in the leaf tissue. Among the five antioxidative enzymes monitored, the APX, POX, GR and SOD specific activities were significantly enhanced at high concentration (400 mM NaCl), while the catalase activities declined, suggesting both up and downregulations of antioxidative enzymes occurred due to NaCl imposed osmotic and ionic stress. Analysis of the stress induced alterations in the isoforms of CAT, APX, POX, GR and SOD revealed differential regulations of the isoforms of these enzymes. In B. parviflora one isoform of each of Mn-SOD and Cu/Zn-SOD while three isoforms of Fe-SOD were observed by activity staining gel. Of these, only Mn-SOD and Fe-SOD2 content was preferentially elevated by NaCl treatment, whereas isoforms of Cu/Zn-SOD, Fe-SOD1 and Fe-SOD3 remained unchanged. Similarly, out of the six isoforms of POX, the POX-1,-2,-3 and -6 were enhanced due to salt stress but the levels of POX-4 and -5 remained same as in control plants suggesting preferential upregulation of selective POX isoforms. Activity staining gel revealed only one prominent band of APX and this band increased with increased salt concentration. Similarly, two isoforms of GR (GR1 and GR2) were visualized on activity staining gel and both these isoforms increased upon salt stress. In this mangrove four CAT-isoforms were identified, among which the prominent CAT-2 isoform level was maximally reduced again suggesting differential downregulation of CAT isoforms by NaCl stress. The results presented in this communication are the first report on the resolutions of isoforms APX, POX and GR out of five antioxidative enzymes studied in the leaf tissue of a true mangrove. The differential changes in the levels of the isoforms due to NaCl stress may be useful as markers for recognizing salt tolerance in mangroves. Further, detailed analysis of the isoforms of these antioxidative enzymes is required for using the various isoforms as salt stress markers. Our results indicate that the overproduction of H₂O₂ by NaCl treatment functions as a signal of salt stress and causes upregulation of APX, POX, GR and deactivations of CAT in B. parviflora. The concentrations of malondialdehyde, a product of lipid peroxidation and lipoxygenase activity remained unchanged in leaves treated with different concentrations of NaCl, which again suggests that the elevated levels of the antioxidant enzymes protect the plants against the activated oxygen species thus avoiding lipid peroxidation during salt stress.     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明：外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L^-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L^-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

Nickel-induced oxidative stress and the role of antioxidant defence in rice seedlings

Seedlings of rice (Oryza sativa L.) cv. Pant-12 grown in sand cultures containing 200 and 400 μM NiSO₄, showed a decrease in length and fresh weight of roots and shoots. Nickel was readily taken up by rice seedlings and the concentration was higher in roots than shoots. Nickel-treated seedlings showed increased rates of superoxide anion (O₂ ^•− ) production, elevated levels of H₂O₂ and thiobarbituric acid reactive substances (TBARS) demonstrating enhanced lipid peroxidation, and a decline in protein thiol levels indicative of increased protein oxidation compared to controls. With progressively higher Ni concentrations, non-protein thiol and ascorbate (AsA) increased, whereas the level of low-molecular-weight thiols (such as glutathione and hydroxyl-methyl glutathione), the ratio of these thiols to their corresponding disulphides, and the ratio of AsA to dehydroascorbic acid declined in the seedlings. Among the antioxidant enzymes studied, the activities of all isoforms of superoxide dismutase (Cu-Zn SOD, Mn SOD and Fe SOD), guaiacol peroxidases (GPX) and ascorbate peroxidase (APX) increased in Ni-treated seedlings, while no clear alteration in catalase activity was evident. Activity of the ascorbate-glutathione cycle enzymes monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR)—significantly increased in Ni-treated seedlings. However such increase was apparently insufficient to maintain the intracellular redox balance. Results suggest that Ni induces oxidative stress in rice plants, resulting in enhanced lipid peroxidation and decline in protein thiol levels, and that (hydroxyl-methyl) glutathione and AsA in conjunction with Cu-Zn SOD, GPX and APX are involved in stress response.