Early Abscisic Acid Accumulation Regulates Ascorbate and Glutathione Metabolism in Soybean Leaves Under Progressive Water Stress

Ascorbate (AsA) and glutathione (GSH) play an important role in improving the tolerance of plants to water stress. The objective of this study was to investigate the effect of early abscisic acid (ABA) accumulation on AsA and GSH metabolism in soybean plants after 24 h of exposure to progressive water stress. The results showed that AsA, total AsA, GSH and total GSH content, and ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), GSH reductase (GR), GSH peroxidase (GPX), l-galactono-1,4-lactone dehydrogenase (GLDH), and γ-glutamylcysteine synthetase (γ-GCS) activities were increased by progressive water stress. The above increases, except for total GSH content and the activities of GLDH and γ-GCS, were blocked by pretreatment with tungstate, an ABA biosynthesis inhibitor, which significantly suppressed the early increase in ABA and reactive oxygen species (ROS) in stressed plants. Application of ABA reversed the effects of tungstate. Pretreatments with several ROS scavengers, such as Tiron and dimethylthiourea (DMTU), and an inhibitor of NADPH oxidase, diphenyleneiodonium (DPI), significantly arrested the early accumulation of ROS but not ABA in stressed plants. Furthermore, the above-mentioned pretreatments remarkably prevented any increase in APX, MDHAR, DHAR, GR, and GPX activities, as well as AsA, total AsA and GSH levels in stressed plants. Our results indicated that early ABA accumulation caused by progressive water stress triggers an early rise in ROS levels, which, in turn, leads to regulation of AsA and GSH metabolism.

     

外源α-萘乙酸对花期长期干旱大豆叶片抗氧化系统的影响

以不同耐旱型品种‘南农99-6’和‘科丰1号’大豆为材料,2012年在南京农业大学牌楼试验站进行为期110 d的盆栽试验,研究大豆花期叶面喷施α-萘乙酸(NAA)对长期干旱条件下大豆植株抗氧化系统的影响.结果表明: 干旱胁迫显著降低了大豆地上部干物质量,叶片中丙二醛(MDA)含量及活性氧(ROS)水平显著升高,同时,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)、单脱氢抗坏血酸还原酶（MDHAR）、谷胱甘肽还原酶(GR)和谷胱甘肽过氧化物酶(GPX)活性,还原型抗坏血酸(AsA)、还原型谷胱甘肽(GSH)含量及AsA/DHA(双脱氢抗坏血酸)和GSH/GSSG(氧化型谷胱甘肽)比值显著升高,其中‘科丰1号’大豆的抗氧化能力更高,从而维持较低的ROS水平和MDA含量.NAA可显著提高叶片中的APX、POD、CAT、MDHAR活性及AsA/DHA、GSH/GSSG比值,其中‘科丰1号’大豆叶片的脱氢抗坏血栓还原酶（DHAR）活性和AsA含量极显著增加.     

Exogenous salicylic acid regulates reactive oxygen species metabolism and ascorbate–glutathione cycle in <Emphasis Type="Italic">Nitraria tangutorum</Emphasis> Bobr. under salinity stress

The effect of 0.5–1.5 mM salicylic acid (SA) on modulating reactive oxygen species metabolism and ascorbate–glutathione cycle in NaCl-stressed Nitraria tangutorum seedlings was investigated. The individual plant fresh weight (PFW) and plant dry weight (PDW) significantly increased under 100 mM NaCl while remained unchanged or decreased under 200–400 mM NaCl compared to the control. Superoxide anion (O ₂ ^·? ), hydrogen peroxide (H₂O₂), thiobarbituric acid reactive substances (TBARS), reduced ascorbate (AsA), dehydroascorbate (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) increased whereas the ratios of AsA/DHA and GSH/GSSG decreased under varied NaCl treatments. Ascorbate peroxidase (APX) and glutathione reductase (GR) activities were enhanced while dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities remained unvaried under 100–400 mM NaCl stresses. In addition, exogenous SA further increased PFW, PDW and root/shoot ratio. SA effectively diminished O ₂ ^·? accumulation. H₂O₂ and TBARS decreased under 0.5 and 1.0 mM SA treatments compared to those without SA. 0.5 mM of SA increased while 1.0 and 1.5 mM SA decreased APX activities. DHAR activities were elevated by 0.5 and 1.0 mM SA but not by 1.5 mM SA. MDHAR and GR activities kept constant or significantly increased at varying SA concentrations. Under SA treatments, AsA and GSH contents further increased, DHA and GSSG levels remained unaltered, while the decreases in AsA/DHA and GSH/GSSG ratios were inhibited. The above results demonstrated that the enhanced tolerance of N. tangutorum seedlings conferred by SA could be attributed mainly to the elevated GR and DHAR activities as well as the increased AsA/DHA and GSH/GSSG ratios.     

Copper affects the enzymes of the ascorbate-glutathione cycle and its related metabolites in the roots of Phaseolus vulgaris

The involvement of the ascorbate-glutathione cycle in the defence against Cu-induced oxidative stress was studied in the roots of Phaseolus vulgaris L. cv. Limburgse vroege. All the enzymes of this cycle [ascorbate peroxidase (APOD), EC 1.11.1.11; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; dehydroascorbate reductase (DHAR), EC 1.8.5.1; glutathione reductase (GR), EC 1.6.4.2] were increased, and the total ascorbate and glutathione pools rose after a 15 μ M root Cu treatment. In the first hours after the start of the experiment, the accumulation of dehydroascorbate (DHA), formed as a result of a Cu-mediated direct oxidation of ascorbate (AA), was limited by a non-enzymatic reduction using glutathione (GSH) as the reductant. At 24 h, the enzyme capacities of both DHAR and GR were increased to maintain the redox status of the AA and GSH pools. After 72 h of Cu application, the DHAR capacity was inhibited and MDHAR was responsible for maintaining the AA pool in its reduced form. Although the GR capacity was enhanced after 72 h in the treated plants, the GSSG/GSH ratio was increased. This could be due to direct participation of GSH in the detoxification of Cu through reduction and complexation.     

Exogenous 5-aminolevulinic acid pretreatment ameliorates oxidative stress triggered by low-temperature stress of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis>

Low temperature is an important limiting factor in tomato production in early spring and winter. 5-Aminolevulinic acid (ALA) protects crops against varied abiotic stresses. However, the methodology to precisely use ALA to increase the cold tolerance in tomatoes is still not fully known. We therefore explored the effects of ALA concentration, application period, and dose on membrane lipid peroxidation, antioxidation, photosynthesis, and plant growth in different tomato cultivars (Zhongza No. 9, ZZ and Jinpeng No. 1, JP) at low-temperature stress. Results revealed that low temperature caused plants oxidative damage and growth inhibition in both ZZ and JP plants. The ROS (hydrogen peroxide and superoxide anion) accumulation and membrane lipid peroxidation (malondialdehyde content and the relative electrical conductivity) were more remarkable in JP plants than ZZ plants under low temperature. The catalase (CAT) and ascorbate–glutathione cycle (AsA–GSH) induced by ALA reliably eliminated excessive ROS to maintain the redox balance in both tomato cultivars under low-temperature stress. In AsA–GSH cycle, AsA regeneration was mainly catalyzed by dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR), from dehydroascorbate (DHA) to AsA and monodehydroascorbate (MDA) to AsA in ZZ plants, while AsA regeneration in JP plants was mostly catalyzed by DHAR, from DHA to AsA. The ALA optimum concentration was 25 mg L^?1. The tomato plants with five true leaves pretreated with 6 mL ALA were more effective than spraying after cold occurred. In conclusion, the two tomato varieties illustrated different capacities to bear low-temperature stress. And ZZ plants were more tolerant to low temperature than JP plants. Precise ALA pretreatment observably alleviated low temperature induced-damage via CAT and AsA–GSH cycle in both cultivars. The regeneration of AsA in AsA–GSH cycle may be more comprehensive in ZZ plants than JP plants, to better tolerate low-temperature stress.     

Co-expression of monodehydroascorbate reductase and dehydroascorbate reductase from Brassica rapa effectively confers tolerance to freezing-induced oxidative stress

Plants are exposed to various environmental stresses and have therefore developed antioxidant enzymes and molecules to protect their cellular components against toxicity derived from reactive oxygen species (ROS). Ascorbate is a very important antioxidant molecule in plants, and monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) and dehydroascorbate reductase (DHAR; EC 1.8.5.1) are essential to regeneration of ascorbate for maintenance of ROS scavenging ability. The MDHAR and DHAR genes from Brassica rapa were cloned, transgenic plants overexpressing either BrMDHAR and BrDHAR were established, and then, each transgenic plant was hybridized to examine the effects of co-expression of both genes conferring tolerance to freezing. Transgenic plants co-overexpressing BrMDHAR and BrDHAR showed activated expression of relative antioxidant enzymes, and enhanced levels of glutathione and phenolics under freezing condition. Then, these alteration caused by co-expression led to alleviated redox status and lipid peroxidation and consequently conferred improved tolerance against severe freezing stress compared to transgenic plants overexpressing single gene. The results of this study suggested that although each expression of BrMDHAR or BrDHAR was available to according tolerance to freezing, the simultaneous expression of two genes generated synergistic effects conferring improved tolerance more effectively even severe freezing.     

Modulation of cadmium-induced oxidative stress in Ceratophyllum demersum by zinc involves ascorbate-glutathione cycle and glutathione metabolism.

To understand the interaction between Zn, an essential micronutrient and Cd, a non-essential element, Cd-10 microM and Zn supplemented (10, 50, 100, and 200 microM) Cd 10 microM treated Ceratophyllum demersum L. (Coontail), a free floating freshwater macrophyte was chosen for the study. Cadmium at 10 microM concentration decreased thiol content, enhanced oxidation of ascorbate (AsA) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively, a clear indication of oxidative stress. Zinc supplementation to Cd (10 microM) treated plants effectively restored thiols, inhibited oxidation of AsA and GSH maintaining the redox molecules in reduced form. Cd-10 microM slightly induced ascorbate peroxidase (APX, E.C. 1.11.1.11) but inhibited monodehydroascorbate reductase (MDHAR, E.C. 1.6.5.4), dehydroascorbate reductase (DHAR, E.C. 1.8.5.1) and glutathione reductase (GR, E.C. 1.6.4.2), enzymes of ascorbate-glutathione cycle (AGC). Zn supplementation restored and enhanced the functional activity of all the AGC enzymes (APX, MDHAR, DHAR and GR). Gamma-glutamylcysteine synthetase (gamma-GCS, E.C. 6.3.2.2) was not affected by Cd as well as Zn, but Zn supplements increased glutathione-S-transferase (GST, E.C. 2.5.1.18) activity to a greater extent than Cd and simultaneously restored glutathione peroxidase (GSH-PX, E.C. 1.11.1.9) activity impaired by Cd toxicity. Zn-alone treatments did not change above investigated parameters. These results clearly indicate the protective role of Zn in modulating the redox status of the plant system through the antioxidant pathway AGC and GSH metabolic enzymes for combating Cd induced oxidative stress.     

Effects of exogenous hydrogen sulfide on the redox states of ascorbate and glutathione in maize leaves under salt stress

This study investigated the effects of exogenous hydrogen sulfide (H₂S) on the redox states of ascorbate (AsA) and glutathione (GSH) in maize leaves under NaCl (100 mM) stress. Salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), Γ-glutamylcysteine synthetase (Γ-ECS), and L-galactono-1,4-lactone dehydrogenase (GalLDH), malondialdehyde content and electrolyte leakage, and reduced the ratios of reduced and oxidised forms of AsA (AsA/DHA) and GSH (GSH/GSSG) compared with control. Pretreatment with NaHS (H₂S donor) further enhanced the activities of the above enzymes except MDHAR and ameliorated the decrease in the ratios of AsA/DHA and GSH/GSSG compared with the salt stress alone. Pretreatment with NaHS significantly reduced the malondialdehyde content and electrolyte leakage induced by the salt stress. Pretreatment with NaHS alone did not affect any of the above mentioned parameters compared with the control. Our results suggest that exogenous H2S could maintain the redox states of ascorbate and glutathione by up-regulating the ascorbate and glutathione metabolism and thus play an important role for acquisition of salt stress tolerance in maize.     

Increased Vitamin C Content Accompanied by an Enhanced Recycling Pathway Confers Oxidative Stress Tolerance in Arabidopsis

Vitamin C (L-ascorbic acid, AsA) has important antioxidant and metabolic functions in both plants and animals. Once used, ascorbic acid can be regenerated from its oxidized form in a reaction catalyzed by dehydroascorbate reductase (DHAR, EC 1.8.5.1). To analyze the physiological role of DHAR catalyzing the reduction of DHA to ascorbate in environmental stress adaptation, we examined whether increasing the level of AsA through enhanced AsA recycling would limit the deleterious effects of oxidative stress. A chimeric construct consisting of the double CaMV35S promoter fused to the Myc-dhar gene was introduced into Arabidopsis thaliana. Transgenic plants were biochemically characterized and tested for responses to oxidative stress. Western blot indicated that the dhar-transgene was successfully expressed. In homozygous T_4 transgenic seedlings, DHAR overexpression was increased up to 1.5 to 5.4 fold, which enhanced foliar ascorbic acid levels 2- to 4.25-fold and ratio of AsA/DHA about 3- to 16-fold relative to wild type. In addition, the level of glutathione, the reductant used by DHAR, also increased as did its redox state. When whole plants were treated with high light and high temperature stress or in vitro leaf discs were subjected to 10 μM paraquat, transgenic plants showed a larger AsA pool size, lower membrane damage, and a higher level of chlorophyll compared with controls. These data suggested that increasing the plant vitamin C content through enhanced ascorbate recycling could limit the deleterious effects of environmental oxidative stress.     

箭舌豌豆根系抗坏血酸及相关酶对镉胁迫的响应

以箭舌豌豆(Vicia sativa L.)品种L3(耐镉)和ZM(镉敏感)为材料,研究了不同程度镉胁迫下箭舌豌豆幼苗根系抗坏血酸(AsA)含量、脱氢抗坏血酸还原酶(DHAR)同工酶活性、抗坏血酸过氧化物酶(APX)同工酶活性以及APX基因表达的变化。结果显示:(1)2个箭舌豌豆品种根系AsA和脱氢抗坏血酸(DHA)含量在镉胁迫下显著升高;AsA/DHA比值在镉耐性品种L3中显著升高,在敏感品种ZM中显著下降;相同镉处理浓度下,L3根系AsA含量和AsA/DHA比值显著大于ZM。(2)2个品种根系DHAR的活性电泳共显示4条同工酶条带,它们的活性均随镉处理浓度的升高而升高;其中DHAR1只在L3显示,DHAR4只在ZM显示;相同镉处理浓度下,品种L3的DHAR的总活性大于品种ZM。(3)2个品种根系APX的活性电泳共显示11条同工酶条带,其中的APX1、2、4仅在敏感品种ZM中受镉胁迫诱导,APX 8在耐性品种L3中受到比敏感品种ZM更显著的诱导;克隆得到1个箭舌豌豆APX基因,荧光定量RT-PCR结果显示该基因的转录在L3和ZM根系均受镉处理诱导。研究表明,镉胁迫下2个箭舌豌豆品种根系AsA含量,AsA代谢相关酶DHAR和APX的活性以及APX的转录水平均显著升高;镉耐性品种L3较敏感品种ZM能更有效地促进AsA循环,维持更高的AsA水平,从而更有效地缓解镉胁迫诱导产生的氧化胁迫,这可能是L3较ZM具有更高镉耐性的重要机制之一。     

Enhanced tolerance to oxidative stress in transgenic tobacco plants expressing three antioxidant enzymes in chloroplasts

The effect of simultaneous expression of genes encoding three antioxidant enzymes, copper zinc superoxide dismutase (CuZnSOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), and dehydroascorbate (DHA) reductase (DHAR, EC 1.8.5.1), in the chloroplasts of tobacco plants was investigated under oxidative stress conditions. In previous studies, transgenic tobacco plants expressing both CuZnSOD and APX in chloroplast (CA plants), or DHAR in chloroplast showed enhanced tolerance to oxidative stresses, such as paraquat and salt. In this study, in order to develop transgenic plants that were more resistant to oxidative stress, we introduced the gene encoding DHAR into CA transgenic plants. Mature leaves of transgenic plants expressing all three antioxidant genes (CAD plants) had approximately 1.6–2.1 times higher DHAR activity, and higher ratios of reduced ascorbate (AsA) to DHA, and oxidized glutathione (GSSG) to reduced glutathione (GSH) compared to CA plants. CAD plants were more resistant to paraquat-induced stress, exhibiting only 18.1% reduction in membrane damage relative to CA plants. In addition, seedlings of CAD plants had enhanced tolerance to NaCI (100 mM) compared to CA plants. These results indicate that the simultaneous expression of multiple antioxidant enzymes, such as CuZnSOD, APX, and DHAR, in chloroplasts is more effective than single or double expression for developing transgenic plants with enhanced tolerance to multiple environmental stresses.     

Characterization of the antioxidant system during the vegetative development of pea plants

The antioxidative system was studied during the development of pea plants. The reduced glutathione (GSH) content was higher in shoots than in roots, but a greater redox state of glutathione existed in roots compared with shoots, at least after 7 d of growth. The 3-d-old seedlings showed the highest content of oxidised ascorbate (DHA), which correlated with the ascorbate oxidase (AAO) activity. Also, the roots exhibited higher DHA content than shoots, correlated with their higher AAO activity. The activities of antioxidant enzymes were much higher in shoots than in roots. Ascorbate peroxidase (APX) activity decreased during the progression of growth in both shoots and roots, whereas peroxidase (POX) activity strongly increased in roots, reflecting a correlation between POX activity and the enhancement of growth. Catalase activity from shoots reached values nearly 3 or 4-fold higher than in roots. The monodehydroascorbate reductase (MDHAR) activity was higher in young seedlings than in more mature tissues, and in roots a decrease in MDHAR was noticed at the 11^th day. No dehydroascorbate reductase (DHAR) was detected in roots from the pea plants and DHAR values detected in seedlings and in shoots were much lower than those of MDHAR. In shoots, GR decreased with the progression of growth, whereas in roots an increase was seen on the 9^th and 11^th days. Finally, superoxide dismutase (SOD) activity increased in shoots during the progression of growth, but specific SOD activity was higher in roots than in shoots.     

Antioxidative responses of Calendula officinalis under salinity conditions.

To gain a better insight into long-term salt-induced oxidative stress, some physiological parameters in marigold (Calendula officinalis L.) under 0, 50 and 100 mM NaCl were investigated. Salinity affected most of the considered parameters. High salinity caused reduction in growth parameters, lipid peroxidation and hydrogen peroxide accumulation. Under high salinity stress, a decrease in total glutathione and an increase in total ascorbate (AsA + DHA), accompanied with enhanced glutathione reductase (GR, EC 1.6.4.2) and ascorbate peroxidase (APX, EC 1.11.1.11) activities, were observed in leaves. In addition, salinity induced a decrease in superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POX, EC 1.11.1.7) activities. The decrease in dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities suggests that other mechanisms play a major role in the regeneration of reduced ascorbate. The changes in catalase (CAT, EC 1.11.1.6) activities, both in roots and in leaves, may be important in H2O2 homeostasis.     

Effects of lanthanum on the ascorbate and glutathione metabolism of Vigna radiata seedlings under salt stress

In order to elucidate the role of lanthanum (La) in response of Vigna radiata to a salt stress, we investigated the effects of La on the ascorbate and glutathione metabolism. The results show that in comparison with a control, the salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), γ-glutamylcysteine synthetase (γ-ECS), and L-galactono-1,4-lactone dehydrogenase (GalLDH), and the content of ascorbic acid (AsA) and glutathione (GSH). It also increased the malondialdehyde content (MDA) and electrolyte leakage. The salt stress significantly decreased the ratios of AsA/dehydroascorbate (DHA) and GSH/glutathione disulphide (GSSG) compared with the control. The pretreatment with La not only significantly increased the activities of the above enzymes, the content of AsA, GSH, and the ratios of AsA/DHA and GSH/GSSG, but also significantly reduced the MDA content and electrolyte leakage compared with the salt stress alone. Our results suggest that La could up-regulate the ascorbate and glutathione metabolisms and could have an important role for acquisition of salt stress tolerance in Vigna radiata.     

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.     

乙烯与NO互作对镉胁迫下荷花的抗坏血酸-谷胱甘肽循环的影响

以荷花‘微山湖红莲’实生苗为试验材料,研究镉(Cd,50 μmol·L^-1)胁迫下,外源乙烯前体1-氨基环丙烷羧酸(ACC,100 μmol·L^-1)、ACC与一氧化氮合酶(NOS)抑制剂N-硝基-L-精氨酸(L-NNA,200 μmol·L^-1)、ACC与硝酸还原酶(NR)抑制剂钨酸钠(Tu,1 mmol·L^-1),ACC与一氧化氮(NO)清除剂2-苯基-4,4,5,5-四甲基咪唑啉-3-氧代-1-氧(PTIO,200 μmol·L^-1),外源NO供体硝普钠(SNP,500 μmol·L^-1)、SNP与乙烯信号转导抑制剂硫代硫酸银(STS,100 μmol·L^-1)处理下荷花幼苗叶片的受害程度及抗坏血酸(AsA)-谷胱甘肽(GSH)循环的变化情况.结果表明: Cd胁迫下,荷花叶片受害症状明显,其相对电导率、丙二醛(MDA)、AsA和GSH含量显著上升,抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)活性明显降低;ACC的添加进一步增加了Cd对荷花叶片的毒害症状,并加剧了4种抗氧化酶活性的降低,但增加了抗氧化剂的含量;SNP的添加对荷花叶片的伤害起到加重作用,并导致GR和MDHAR活性降低以及AsA和GSH含量的升高;PTIO可显著提高Cd和ACC复合处理下荷花叶片APX、GR、MDHAR和DHAR的活性并降低AsA和GSH的含量,而L-NNA和Tu效果不如PTIO明显;STS可显著缓解Cd和SNP复合处理下荷花叶片的毒害症状,并提高4种抗氧化酶的活性、降低AsA和GSH的含量.由此说明,乙烯和NO在AsA-GSH循环中存在互作,二者相互促进,共同调控AsA-GSH循环,进而参与调控荷花对Cd胁迫的响应.     

The oxidative stress caused by salinity in two barley cultivars is mitigated by elevated CO2

Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 m M NaCl) on protective enzyme activities under ambient (350 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ concentrations were investigated in two barley cultivars ( Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO₂, upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO₂ alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO₂ and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO₂ mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.