Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

A greenhouse experiment was conducted to assess whether exogenously applied 24-epibrassionlide (24-epiBL) could alleviate the adverse effects of salt on wheat. Two hexaploid wheat (Triticum aestivum L.) cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive), were grown under control (0 mM NaCl in full strength Hoagland’s nutrient solution) or saline conditions (150 mM of NaCl in full strength Hoagland’s nutrient solution). After 41 days growth of wheat plants under saline conditions, 24-epiBL was applied as a foliar spray. Four levels of BR were used as 0 (water spray), 0.0125, 0.025, and 0.0375 mg l⁻¹. Application of 24-epiBL increased plant biomass and leaf area per plant of both cultivars under non-saline conditions. However, under saline conditions, improvement in growth due to exogenous 24-epiBL was observed only in S-24. Photosynthetic rate was reduced due to salt stress in both cultivars, but this inhibitory effect was ameliorated significantly by the exogenous application of 24-epiBL. Exogenously applied 24-epiBL also enhanced the photosystem-II efficiency in both cultivars measured as F _v /F _m ratio. Although the activities of antioxidant enzymes, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were increased due to salt stress in both wheat cultivars, exogenously applied 24-epiBL had a varying effect on the antioxidant system. The activity of SOD remained unaffected in both cultivars due to 24-epiBL application, but that of POD and CAT was promoted in the salt stressed plants of cv. S-24 only. In conclusion, improvement in growth in both wheat cultivars due to foliar applied 24-epiBL was found to be associated with 24-epiBL-induced enhancement in photosynthetic capacity. The 24-epiBL-induced regulation of antioxidant enzymes or growth under saline conditions was cultivar specific.     

Exogenous proline alleviates the effects of H2O2-induced oxidative stress in wild almond species

The effect of proline on the antioxidant system in the leaves of eight species of wild almond (Prunus spp.) exposed to H₂O₂-mediated oxidative stress was studied. The levels of endogenous proline (Pro) and hydrogen peroxide, and the activities of total superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (POD) were measured. The degradation of chlorophyll but not carotenoids occurred in leaves in the solution of 5 mM H₂O₂. An increase in membrane lipid peroxidation was observed in H₂O₂ treatment, as assessed by MDA level and percentage of membrane electrolyte leakage (EL). Significant increases in total SOD and CAT activities, as well as decreases in APX and POD activities, were detected in H₂O₂-treated leaves. The three SOD isoforms showed different behavior, as Mn-SOD activity was enhanced by H₂O₂, whereas Fe-SOD and Cu/Zn-SOD activities were inhibited. In addition, Pro accumulation up to 0.1 ??mol/g fr wt, accompanied by significant decreases in ascorbate and glutathione levels, was observed in H₂O₂-treated leaves. After two different treatments with 10 mM Pro + 5 mM H₂O₂, total SOD and CAT activities were similar to the levels in control plants, while POD and APX activities were higher if compared to the leaves exposed only to H₂O₂. Pro + H₂O₂ treatments also caused a strong reduction in the cellular H₂O₂ and MDA contents and EL. The results showed that Pro could have a key role in protecting against oxidative stress injury of wild almond species by decreasing membrane oxidative damage.     

Comparison of antioxidant responses to cadmium and lead in Bruguiera gymnorrhiza seedlings

Seedlings of mangrove plant Bruguiera gymnorrhiza cultured in sand with Hoagland’s nutrient solution were treated with 1 to 30 mM Cd(NO₃)₂ or Pb(NO₃)₂ for 2 months. In all Cd/Pb treatments, the malondialdehyde content increased while the chlorophyll content declined. Peroxidase (POD) and superoxide dismutase (SOD) activities in roots increased at moderate Cd/Pb concentrations (1–10 mM), whereas decreased at higher concentrations (20–30 mM). Catalase (CAT) activity in roots was inhibited by 1–10 mM Cd but enhanced by 1–10 mM Pb. The activities of POD, SOD and CAT in leaves were less affected by Cd and Pb than in roots. A new SOD and three CAT isoenzymes were induced by Pb. In contrast, no additional SOD and CAT isoenzymes were induced by Cd.     

Changes in antioxidant enzymes and some key metabolites in some genetically diverse cultivars of radish (Raphanus sativus L.)

Salt-induced changes in the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and lipid peroxidation in terms of malondialdehyde (MDA), level of H₂O₂, and some key metabolites such as soluble proteins, free proline and phenolics in the leaves of six radish cultivars (Radish Red Neck, Radish Lal Pari, Radish Mino Japani, Radish 40 Days, Mannu Early and Desi) were investigated. Varying levels of NaCl (0, 80 and 160 mM) applied for 40 days adversely affected the shoot fresh weight, chlorophyll contents and soluble proteins, while increased the levels of proline, and the activities of SOD, POD and CAT. However, leaf H₂O₂ and total phenolic contents were not affected by salt stress. Cultivars Mannu Early, Radish 40 Days and Desi were relatively higher in shoot fresh weight (percent of control) while cvs. Radish Mino Japani and Mannu Early in proline, and cvs. Radish 40 Days and Desi in total soluble proteins at 160 mM of NaCl. However, levels of H₂O₂ and phenolics were higher in cvs. Desi, Radish Lal Pari and Mannu Early and SOD, POD and CAT activities only in Radish Lal Pari and Mannu Early than the other cultivars under saline conditions. Overall, the differential salt tolerance of radish cultivars observed in the present study was not found to be associated with higher antioxidant enzyme activities and other key metabolites analyzed, so these attributes cannot be considered as selection criteria for salt tolerance in radish.     

Exogenous application of salicylic acid alleviates cadmium toxicity and reduces hydrogen peroxide accumulation in root apoplasts of Phaseolus aureus and Vicia sativa

We examined ameliorative effects of salicylic acid (SA) on two cadmium (Cd)-stressed legume crops with different Cd tolerances, viz. Phaseolus aureus (Cd sensitive) and Vicia sativa (Cd tolerant). Cd at 50 μM significantly increased the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^·−) in root apoplasts of P. aureus and V. sativa. When comparing the two species, we determined that Cd-induced production of H₂O₂ and O₂^·− was more pronounced in P. aureus root apoplasts than in V. sativa root apoplasts. V. sativa had higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) than P. aureus in root symplasts and apoplasts. Seed-soaking pretreatment with 100 μM SA decreased Cd-induced production of H₂O₂ and O₂^·− in apoplasts of both species, and increased activities of symplastic and apoplastic SOD, symplastic APX, and apoplastic CAT under Cd stress. Hence, SA-induced Cd tolerances in P. aureus and V. sativa are likely associated with increases in symplastic and apoplastic antioxidant enzyme activities.     

沼泽、盐化沙丘过渡带和沙丘生境下芦苇的光合及生理生化特性

对于田地区3种不同生境(沼泽、盐化沙丘过渡带和沙丘顶)芦苇的生长环境特征、光合特性、渗透调节及抗氧化系统的特征进行研究。结果表明:芦苇叶片的Pn日变化在沼泽生境呈单峰曲线,在盐化沙丘过渡带和沙丘顶部均为双峰曲线,光合"午休"现象明显,气孔导度降低是其主要原因。脯氨酸和可溶性糖含量随根区土壤水分减少和盐分加剧增加显著,其中可溶性糖含量变化剧烈,对抵御干旱和盐渍化危害的贡献较大。芦苇叶片超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性随干旱及盐分加剧增加显著,两者对水分亏缺的响应较盐分敏感,且可有效缓解沙丘生境由于缺水所造成的氧化损伤,使丙二醛(MDA)含量维持在相对较低水平。过氧化物酶(POD)活性在沙丘和盐渍化生境内都比较高,对抵抗盐渍化和干旱起着同样重要的作用。     

Antioxidative responses to different altitudes in leaves of alpine plant Polygonum viviparum in summer

Mountain environmental stresses result in increased formation of hydrogen peroxide (H₂O₂) and accumulation of malondialdehyde (MDA) in leaves of Polygonum viviparum. The activities of several antioxidative system enzymes such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the contents of several non-enzymatic antioxidants such as reduced form of ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) were investigated in leaves of P. viviparum, which were collected from three altitudes (2,200, 3,200, and 3,900 m) of Tianshan Mountain in China. The activities of these four antioxidative enzymes were accompanied by increases of H₂O₂ levels from 2,200 to 3,200 m. However, the activities of CAT and POD were decreased, whereas the activities of SOD and GR continually increased at 3,900 m. Analyses of isoforms of SOD, CAT, POD, and GR showed that the leaves of P. viviparum exposed different altitude conditions are capable of differentially altering the intensity. Additionally, two new isoforms of SOD were detected at 3900 m. A continual increase in the ASC, ASC to DHA ratio, GSH and GSH/[GSH + GSSG] ratio, and the activity of DHAR were observed in leaves of P. viviparum with the elevation of altitude. These results suggest that the higher contents of ASC, GSH as well as an increase in reduced redox state may be essential to antioxidation processes in the leaves of P. viviparum, whereas antioxidant enzymes system is a cofactor in the processes.     

Responses to drought stress in two poplar species originating from different altitudes

Cuttings of Populus kangdingensis and Populus cathayana, originating from high and low altitudes in the eastern Himalaya, respectively, were examined during one growing season in a greenhouse to determine their responses to drought stress (soil moisture decreased from 100 to 55 or 25 % field capacity). Compared to control plants grown under 100 % field capacity, those poplars grown under 55 and 25 % field capacity possessed lower increases in height and stem diameter, and higher contents of soluble sugars, free proline, malondialdehyde (MDA) and hydrogen peroxide, and higher activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR). Compared with P. cathayana with greater leaf area, P. kangdingensis with greater root/shoot ratio exhibited lower MDA and H₂O₂ contents, higher soluble sugar and free proline contents, and higher activities of CAT, SOD, POD, APX and GR. These results suggested that P. kangdingensis was more drought tolerant than P. cathayana.     

In vitro selection of salt tolerant variants following <Superscript>60</Superscript>Co gamma irradiation of long-term callus cultures of <Emphasis Type="Italic">Zoysia matrella</Emphasis> [L.] Merr.

To study growth in the presence of NaCl, in vitro plantlets regenerated from callus of manilagrass (Zoysia matrella [L.] Merr.) were cultured on regeneration medium supplemented with or without 0.3 M NaCl. The results indicated that growth was significantly inhibited by NaCl, with the leaves becoming relatively shorter and thicker. The differences of in vitro plantlets grown under NaCl stress provided specific criteria for the selection of salt tolerant variants. The 6-year maintained calli were treated with different doses (0, 5, 10, 20, 40, 80, 100, 150, 200, 250, and 300 Gy) of ₆₀Co γ rays. Regeneration rate and regeneration capacity of the calli were highest after treatment with 20 Gy ⁶⁰Co γ rays, 27.08 and 91.67% respectively. When the irradiation dose was increased to 100 Gy, 10.42% of the calli developed shoots, but at 150 Gy, both regeneration capacity and regeneration rate declined significantly, and no shoot was observed after 6 weeks of regeneration. Therefore, 100–150 Gy is the most appropriate irradiation span for inducing somaclonal variation. The irradiated calli were selected in vitro for NaCl tolerance. Five NaCl tolerant variant lines, Ze1, Fv1, Te1, Tw1, Fr1, were selected on subculture medium supplemented with 0.35 M NaCl, then transferred to regeneration medium containing 0.25 M NaCl, and grown in a greenhouse. The dark green colour index (DGCI) was used to identify the amount of injury caused by NaCl treatment. This was significantly higher in four of the lines, Ze1, Fv1, Te1, Fr1 (30.88, 31.17, 30.45 and 37.70%, respectively) compared to the control line (CK), which was regenerated from calli subcultured monthly (27.39%), indicating that watering with NaCl caused less injury in these four lines. These lines had lower proline contents than CK under salt stress. The superoxide dismutase (SOD) activity was higher in Ze1 under control condition and its peroxidase (POD) activity increased significantly under salt stress. With Fr1 catalase (CAT) activity was higher under salt stress. The higher activity of these antioxidant enzymes may contribute to the enhanced salt tolerance of the four plant lines.     

Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

Hippophae rhamnoides L. is a broadleaf deciduous woody shrub occurring in southwest China, where it has been widely used in ecological restoration. In this study we investigated growth and physiological responses of 2-year-old healthy seedlings to elevated temperature, nitrogen (N) addition and their combination in two contrasting populations from high and low elevations. In closed-top chamber experiments, two populations were subjected to two temperature conditions (ambient temperature and temperature elevated by 2.2 ± 0.2°C) and two N levels (0 and 25 g N m⁻² a⁻¹). Compared with the control, increases in total leaf area (TLA), total chlorophyll content (TC), light-saturated photosynthetic rate (P _max), guaiacol peroxidase activity (POD), catalase activity (CAT) and carbon isotope composition (δ¹³C) were greater in the high-elevation population than in the low-elevation population under elevated temperature. On the other hand, decreases in root and shoot biomass ratio (RS), TC, P _max, light saturation point (L _SP), light compensation point (L _CP), superoxide dismutase (SOD), POD, CAT and δ¹³C were lower in the high-elevation population than in the low-elevation population under N addition. Moreover, the combination of elevated temperature and N addition decreased RS, P _max, apparent quantum efficiency (Φ), SOD, POD and δ¹³C significantly more in the low-elevation population than in the high-elevation population. These results demonstrated that there are different adaptive strategies among H. rhamnoides populations, the high-elevation population exhibiting higher adaptability to elevated temperature and N addition than the low-elevation population.     

皇竹草活性氧代谢对阿特拉津胁迫的响应特征

采用水培实验研究了4个浓度（5、10、20、40 mg·L^-1）除草剂阿特拉津胁迫下,皇竹草（Pennisetum hydridum）叶片内超氧阴离子生成速率、过氧化氢（H₂O₂）含量、超氧化物歧化酶（SOD）活性、过氧化氢酶（CAT）活性、过氧化物酶（POD）活性、丙二醛（MDA）含量、原生质膜透性的变化,探讨皇竹草对阿特拉津的抗性及其生理机制。结果显示:（1）低浓度（5、10 mg·L^-1）的阿特拉津胁迫使皇竹草叶片内超氧阴离子生成速率和CAT活性升高,却使H₂O₂含量及SOD和POD活性降低,但随着培养时间的延长,培养液中阿特拉津浓度的降低导致上述指标又有恢复到正常水平的趋势;而高浓度（40 mg·L^-1）的阿特拉津胁迫则使皇竹草叶片内H₂O₂含量、SOD、POD和CAT活性持续降低。（2）在各胁迫浓度下持续胁迫10 d后,皇竹草叶片内MDA含量开始逐渐升高,并且升高幅度随着胁迫浓度的提高而明显增加,但各胁迫浓度下叶片原生质膜相对透性未见明显的变化。研究表明,皇竹草可能通过活性氧等信号分子调控自身保护酶系统的活性来缓解阿特拉津造成的伤害,从而对低浓度（5、10 mg·L^-1）的阿特拉津胁迫表现出较强抗性。     

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.     

Responses of antioxidant gene, protein and enzymes to salinity stress in two genotypes of perennial ryegrass (Lolium perenne) differing in salt tolerance

Salinity could damage cellular membranes through overproduction of reactive oxygen species (ROS), while antioxidant capacities play a vital role in protecting plants from salinity caused oxidative damages. The objective of this study was to investigate the toxic effect of salt on the antioxidant enzyme activities, isoforms and gene expressions in perennial ryegrass (Lolium perenne L.). Salt-tolerant ‘Quickstart II’ and salt-sensitive ‘DP1′ were subjected to 0 and 250 mM NaCl for 12 d. Salt stress increased the content of lipid peroxidation (MDA), electrolyte leakage (EL) and hydrogen peroxide (H₂O₂), to a greater extent in salt-sensitive genotype. Salt-stressed plant leaves exhibited a greater activity of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11) at 4 d after treatment (DAT), but a lower level of enzyme activity at 8 and 12 d, when compared to the control. Catalase (CAT, EC 1.11.1.6) activity was greater at 4 DAT and thereafter decreased in salt tolerant genotype relative to the control, whereas lower than the control during whole experiment period for salt-sensitive genotype. There were different patterns of five isoforms of SOD, POD and two isoforms of APX between two genotypes. Antioxidant gene expression was positively related to isoenzymatic and total enzymatic activities during 12-d salt-treated leaves of two genotypes, with a relatively higher level in salt-tolerant genotype. Thus, salt tolerance could be related to the constitutive/induced antioxidant gene, leading to more efficient enzyme stimulation and protection in perennial ryegrass.     

Salt-Induced Changes in Physio-Biochemical and Antioxidant Defense System in Mustard Genotypes

Salinity stress is a major factor limiting plant growth and productivity of many crops including oilseed. The present study investigated the identification of salt tolerant mustard genotypes and better understanding the mechanism of salinity tolerance. Salt stresses significantly reduced relative water content (RWC), chlorophyll (Chl) content, K⁺ and K⁺ /Na⁺ ratio, photosynthetic rate (P_N), transpiration rate (Tr), stomatal conductance (gs), intercellular CO₂ concentration (Ci) and increased the levels of proline (Pro) and lipid peroxidation (MDA) contents, Na⁺ , superoxide (O₂^•− ) and hydrogen peroxide (H₂O₂) in both tolerant and sensitive mustard genotypes. The tolerant genotypes maintained higher Pro and lower MDA content than the salt sensitive genotypes under stress condition. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione peroxidase (GPX), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were increased with increasing salinity in salt tolerant genotypes, BJ-1603, BARI Sarisha-11 and BARI Sarisha-16, but the activities were unchanged in salt sensitive genotype, BARI Sarisha-14. Besides, the increment of ascorbate peroxidase (APX) activity was higher in salt sensitive genotype as compared to tolerant ones. However, the activities of glutathione reductase (GR) and glutathione S-transferase (GST) were increased sharply at stress conditions in tolerant genotypes as compared to sensitive genotype. Higher accumulation of Pro along with improved physiological and biochemical parameters as well as reduced oxidative damage by up-regulation of antioxidant defense system are the mechanisms of salt tolerance in selected mustard genotypes, BJ-1603 and BARI Sarisha-16.     

Effects of 28-homobrassinolide on growth, lipid peroxidation and antioxidative enzyme activities in seedlings of Zea mays L. under salinity stress

The effects of 28-homobrassinolide (28-homoBL) on seedling growth, lipid peroxidation and antioxidative enzyme activities in the seedlings of Zea mays L. (var. Partap-1) under salt (NaCl) stress were studied. The surface-sterilized seeds were germinated in petriplates containing different concentrations of NaCl (25, 50, 75 and 100 mM) only, 28-homoBL (10⁻⁷, 10⁻⁹ and 10⁻¹¹ M) only and NaCl supplemented with 28-homoBL for 7 days. The activities of superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APOX, EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) were analysed in 7 day-old seedlings. It was observed that 28-homoBL treatments reduced the toxicity of salt on seedling growth considerably. Lipid peroxidation level was significantly increased under saline stress, but lowered with 28-homoBL applications revealing less oxidative damage. Further 28-homoBL treatments to the seedlings showed an enhancement in activities of SOD, POD, CAT and APOX. The activities of all antioxidative enzymes were further increased in seedlings treated with solution containing 28-homoBL and salt together as compared to seedlings treated with different concentration of salt solution only.     

Effects of NaCl and Mycorrhizal Fungi on Antioxidative Enzymes in Soybean

The effects of different concentrations of NaCl on the activities of antioxidative enzymes in the shoots and roots of soybean (Glycine max [L.] Merr cv. Pershing) inoculated or not with an arbuscular mycorrhizal fungus, Glomus etunicatum Becker & Gerdemann, were studied. Furthermore, the effect of salt acclimated mycorrhizal fungi on the antioxidative enzymes in soybean plants grown under salt stress (100 mM NaCl) was investigated. Activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased in the shoots of both mycorrhizal (M) and nonmycorrhizal (NM) plants grown under NaCl salinity. Salinity increased SOD activity in the roots of M and NM plants, but had no effect on CAT and polyphenol oxidase activities in the roots. M plants had greater SOD, POD and ascorbate peroxidase activity under salinity. Under salt stress, soybean plants inoculated with salt pre-treated mycorrhizal fungi showed increased SOD and POD activity in shoots, relative to those inoculated with the non pre-treated fungi.     

Antioxidant responses of the pest natural enemy Hylyphantes graminicola (Araneae: Linyphiidae) exposed to short-term heat stress

Temperature is a critical abiotic factor that causes physiological changes in arthropods. However, little is known about the effect of heat stress on the antioxidant responses of Araneae species. Hylyphantes graminicola is a dominant predator in many cropping systems in China. In the present study, the effect of short-term heat stress (36, 38, 40 or 42 °C) on the reactive oxygen species (ROS) levels, the activities of antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], peroxidases [POD] and glutathione-S-transferases GST]), total antioxidant capacity (TAC), malondialdehyde (MDA) concentrations and survival of H. graminicola spiderlings and adults were investigated. The results showed that H. graminicola adults had a significantly higher survival rate compared to spiderlings at 40 °C. The heat stress increased ROS contents in H. graminicola. The SOD, CAT, POD and GST activities increased in spiderlings and adults under heat stress. These data suggest a defensive function for these enzymes in alleviating oxidative damage. Specifically, SOD plays a key role in reducing the high level of superoxide radicals in spiderlings and adults. Moreover, the POD and CAT capabilities for scavenging H₂O₂ in spiderlings were similar, and CAT may play a more important role than POD in scavenging H₂O₂ in adults at 42 °C. The spiderling TAC increased significantly at 40 and 42 °C, and the adult TAC was stable at 36–40 °C but decreased at 42 °C. These data suggest that TAC was insufficient in H. graminicola adults under more severe stress conditions. These results further our understanding of the physiological response of Araneae species exposed to heat stress.     

Water availability effects on antioxidant enzyme activities, lipid peroxidation, and reducing sugar contents of alfalfa (Medicago sativa L.)

To understand alfalfa (Medicago sativa L.) reactions to osmotic stress, solutions with −0.5, −1 and −1.5 MPa osmotic potentials using PEG (Poly ethyleneglycol) and distilled water as control were prepared. In a germination test, eleven alfalfa cultivar seeds were allowed to germinate in these solutions. M. sativa cv. Yazdi and M. sativa cv. Gharayonje, selected as tolerant and sensitive cultivars, respectively, and were used for further studies. In all PEG solutions, root and shoot dry weights decreased in both cultivars. Under different levels of osmotic stress, root to shoot ratio increased significantly in Yazdi, whereas this parameter showed no significant differences in Gharayonje. Yazdi cultivar also showed higher activities of SOD (Superoxide dismutase), APX (Ascorbate peroxidase), CAT (Catalase), POD (Peroxidase), and higher reducing sugar contents of leaves in comparison with Gharayonje. These higher antioxidant activities help the tolerant cultivar to decrease oxidative damages of osmotic stress to membrane lipids as compared with its sensitive counterpart. As a result, electrolyte leakage and the amounts of MDA (Malondialdehyde), were higher in Gharayonje. This study highlights the importance of enzymatic and non-enzymatic antioxidant systems in scavenging reactive oxygen species which is caused by osmotic stress. It is seems that antioxidant systems are more active in tolerant cultivars than those of sensitive ones.     

Growth stage-based modulation in antioxidant defense system and proline accumulation in two hexaploid wheat (Triticum aestivum L.) cultivars differing in salinity tolerance

Changes in the antioxidant defense system and proline accumulation were examined at different growth stages (vegetative, boot and reproductive) in plants of two hexaploid spring wheat cultivars (S-24, salt tolerant; MH-97, salt sensitive), grown in hydroponics and salinity-affected with 0, 50, 100 and 150 mM of NaCl. Salt stress provoked a marked decline in plant dry mass and ascorbic acid contents, and increased proline, total soluble proteins and H₂O₂ contents in both wheat cultivars at all growth stages. However, higher accumulation of proline and H₂O₂ contents was recorded at the vegetative and boot stages, respectively, in both wheat cultivars. Salt stress caused a consistent rise in the activities of some key antioxidant enzymes (CAT, SOD, POD, and APX) at all growth stages only in the salt tolerant cultivar S-24, whereas such pattern of enhanced activities of enzymatic antioxidants in cv. MH-97 was found only at the vegetative stage under saline regimes. Maximum activities of various enzymatic antioxidants were observed at the vegetative stage in both wheat cultivars under varying external salt treatments. The results showed that high salinity tolerance of cv. S-24, as manifested by lower decrease in its dry matter under salt stress, was associated with higher activities of antioxidant enzymes, increased accumulation of proline, and lower levels of H₂O₂, as compared with cv. MH-97 at all growth stages under saline regimes.