Amelioration of salt-induced oxidative stress in eggplant by application of 24-epibrassinolide

The effects of exogenous 24-epibrassinolide (EBR) on the growth, oxidative damage, antioxidant system and ion contents in eggplant (Solanum melongena L.) seedlings under salt stress were investigated. Eggplant seedlings were exposed to 90 mM NaCl with 0, 0.025, 0.05, 0.10 and 0.20 mg dm⁻³ EBR for 10 d. EBR, especially at concentration 0.05 mg dm⁻³, alleviated growth suppression caused by NaCl stress, decreased electrolyte leakage, superoxide production and content of malondialdehyde and H₂O₂ in NaCl-treated plants. EBR also increased activities of superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase and the contents of ascorbic acid and reduced glutathione. Furthermore, we also found that Na⁺, Cl⁻ contents were decreased, K⁺, Ca²⁺ contents and K⁺/Na⁺, Ca²⁺/Na⁺ ratios were increased in the presence of EBR under salt stress.     

Enhanced sensitivity to oxidative stress in transgenic tobacco plants with decreased glutathione reductase activity leads to a decrease in ascorbate pool and ascorbate redox state

To investigate the possible mechanisms of glutathione reductase (GR) in protecting against oxidative stress, we obtained transgenic tobacco (Nicotiana tabacum) plants with 30–70% decreased GR activity by using a gene encoding tobacco chloroplastic GR for the RNAi construct. We investigated the responses of wild type and transgenic plants to oxidative stress induced by application of methyl viologen in vivo. Analyses of CO₂ assimilation, maximal efficiency of photosystem II photochemistry, leaf bleaching, and oxidative damage to lipids demonstrated that transgenic plants exhibited enhanced sensitivity to oxidative stress. Under oxidative stress, there was a greater decrease in reduced to oxidized glutathione ratio but a greater increase in reduced glutathione in transgenic plants than in wild type plants. In addition, transgenic plants showed a greater decrease in reduced ascorbate and reduced to oxidized ascorbate ratio than wild type plants. However, there were neither differences in the levels of NADP and NADPH and in the total foliar activities of monodehydroascorbate reductase and dehydroascorbate reductase between wild type and transgenic plant. MV treatment induced an increase in the activities of GR, ascorbate peroxidase, superoxide dismutase, and catalase. Furthermore, accumulation of H₂O₂ in chloroplasts was observed in transgenic plants but not in wild type plants. Our results suggest that capacity for regeneration of glutathione by GR plays an important role in protecting against oxidative stress by maintaining ascorbate pool and ascorbate redox state.     

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.     

Copper accumulation, synthesis of ascorbate and activation of ascorbate peroxidase in Enteromorpha compressa (L.) Grev. (Chlorophyta) from heavy metal-enriched environments in northern Chile

Enteromorpha compressa is the dominant species in coastal areas of northern Chile receiving copper mine wastes. Copper remains as the main heavy metal in these coastal waters and it is accumulated in E. compressa growing at the impacted sites. Algae from these sites showed higher levels of lipoperoxides than from non‐impacted sites, which suggests the occurrence of cellular damage resulting from oxidative stress. The strong activation of ascorbate peroxidase detected in this study probably occurs in order to buffer this oxidative stress. Unexpectedly, the activity of glutathione reductase, normally coupled to ascorbate peroxidase activity, was not affected by the chronic exposure to the mine wastes. Moreover, catalase, dehydroascorbate reductase and glutathione peroxidase, commonly reported to buffer oxidative stress in plants and algae, were not detected in E. compressa from any of the studied sites. Levels of total glutathione and phenolic compounds decreased in algae from mine‐impacted sites. In contrast, high levels of dehydroascorbate were found in algae from impacted sites, whereas ascorbate remained unchanged. Therefore, it is suggested that E. compressa tolerates a copper‐enriched environment, and the accompanying oxidative stress, through the accumulation of copper, activation of ascorbate peroxidase, synthesis of ascorbate (accumulated as dehydroascorbate) and consumption of glutathione and water‐soluble phenolic compounds.     

The oxidative stress caused by NaCl in Azolla caroliniana is mitigated by nitrate

In order to assess the role of the antioxidant defense system against salt treatment, the activities of some antioxidative enzymes and levels of some nonenzymatic antioxidants were estimated in Azolla caroliniana subjected to NaCl treatment (50 mM) for 10 days in absence or presence of nitrate. In A. caroliniana, salt treatment in absence of nitrate preferentially enhanced electrolyte leakage, lipid peroxidation, and H₂O₂ content. Also, the specific activitiy of guaiacol peroxidase (POX), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) increased. In addition, reduced glutathione level increased and consequently, glutathione/oxidized glutathione (GSH/GSSG) ratio increased. Accumulation of Na⁺ increased significantly by salinity stress which resulted in a significant decrease in K⁺ accumulation, accordingly, K⁺/Na⁺ ratio decreased. Replacement of potassium chloride by potassium nitrate in nutrient solution under salt stress (50 mM NaCl) exhibited a reduction in electrolyte leakage, lipid peroxidation, and H₂O₂ contents. Conversely, the specific activity of APX, POX, GR, CAT, and SOD increased. The content of total ascorbate decreased, in contrast, reduced and GSSG increased and the ratio of GSH/GSSG increased 2.3-fold compared to the control value. Sodium ion accumulation was minimized in the presence of nitrate, potassium ion accumulation increased and as a result, K⁺/Na⁺ ratio increased when compared with the corresponding salinized plants. The differential changes in the specific activity of antioxidant enzymes due to NaCl treatment and nitrate may be useful as markers for recognizing salt tolerance in A. caroliniana.     

Developmental changes of antioxidative systems in tobacco leaves as affected by limited sucrose export in transgenic plants expressing yeast-invertase in the apoplastic space

It is generally believed that a restricted export of carbohydrates from source leaves causes oxidative stress because of an enhanced utilisation of O₂ instead of NADP⁺ as electron acceptor in photosynthesis. To test this hypothesis, developmental changes of antioxidative systems were investigated in wild-type and transgenic tobacco (Nicotiana tabacum L.) suffering from disturbed sink-source relations by expression of yeast invertase in the apoplastic space. Young expanding leaves of the wild type contained higher activities of Superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1), glutathione reductase (EC 1.6.4.2) and a higher glutathione content than mature source leaves. The activity of monodehydroascorbate-radical reductase (EC 1.1.5.4) and the ascorbate content remained unaffected by the developmental stage in the wild type. In young expanding leaves of the transgenic plants the capacity of the antioxidative systems was similar to or higher than in corresponding leaves from the wild type. Source leaves of transgenic tobacco with an increased carbohydrate content showed a small chlorophyll loss, an increased malondialdehyde content, a selective loss of the activities of Cu/Zn-superoxide dismutase isoenzymes and a fourfold decrease in ascorbate compared with the wild type. There was no evidence that the protection from H₂O₂ was insufficient since source leaves of transgenic tobacco contained increased activities of catalase, ascorbate peroxidase, and monodehydroascorbate-radical reductase and an increased ascorbate-to-dehydroascorbate ratio compared with source leaves of the wild type. In severely chlorotic leaf sections of the transgenic plants, most components of the antioxidative system were lower than in green leaf sections, but the ascorbate-to-dehydroascorbate ratio was increased. These results suggest that carbohydrate-accumulating cells have an increased availability of reductant, which can increase the degree of reduction of the ascorbate system via glutathione-related systems or via the activity of monodehydroascorbate-radical reductase. At the same time, transgenic tobacco leaves seem to suffer from an increased oxidative stress, presumably as a result of a decreased consumption of O ₂ ^.- by Cu/Zn-superoxide dismutases in the chloroplasts. There was no evidence that carbohydrate-accumulating leaves acclimated to enhanced O ₂ ^.- production rates in the chloroplasts.     

Drought stress induces oxidative stress and the antioxidant defense system in ascorbate-deficient vtc1 mutants of Arabidopsis thaliana

Drought stress has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). To increase our understanding of the effects of drought stress on antioxidant processes, we investigated the response of the ascorbate-deficient Arabidopsis thaliana vtc1 mutant to drought stress. After drought stress, vtc1 mutants exhibited increases in several oxidative parameters, including H₂O₂ content and the production of thiobarbituric acid reactive substances. Decreases in chlorophyll content and chlorophyll fluorescence parameters were also observed. The vtc1 mutants had higher total glutathione than did wild-type (WT) plants after 48 h of drought stress. A reduced ratio of glutathione/total glutathione and an increased ratio of dehydroascorbate/total ascorbate were observed in the vtc1 mutants compared with the WT plants. In addition, the activities of enzymes that are responsible for ROS scavenging, including superoxide dismutase, catalase, and ascorbate peroxidase, were decreased in the vtc1 mutants compared with the WT plants. Similar reductions in activity in the vtc1 mutant were observed for the enzymes that are responsible for the regeneration of ascorbate and glutathione, including monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that low intrinsic ascorbate and impaired ascorbate–glutathione cycling in the vtc1 mutant induced a decrease in the reduced form of ascorbate, which enhanced sensitivity to drought stress.     

Oxidative Stress Responses Accompanying Photoinactivation of Catalase in NaCI-treated Rye Leaves

When segments of rye leaves (Secale cereale L.) grown at 90 μmol m^?2 s^?1 PAR were incubated at a higher photon flux of 400–500 μ mol m^?2 s^?1 PAR in the presence of 0.2-0.6 M NaCl, a preferential loss of catalase activity was induced. The extent of this decline increased with the concentration of NaCl. In addition, the accumulation of alternative antioxidative components, such as ascorbate, glutathione, glutathione reductase, or peroxidase, was inhibited. The total content of H₂O₂ was, however, lower in catalase-depleted than in untreated control leaves. The occurrence of strong oxidative stress in NaCl-treated leaves was indicated by marked declines in the ratios of reduced to oxidized ascorbate and glutathione and by the degradation of chlorophyll in light. The specific elimination of catalase activity by the inhibitor aminotriazole was also accompanied by a rapid decline in the ratio of reduced to oxidized glutathione but other symptoms of oxidative stress were much less severe than in the presence of NaCl. However, all symptoms of photooxidative damage seen in NaCl-treated leaves were closely mimicked by treatment with the translation inhibitor, cycloheximlde, in light. The results suggest that NaCl-induced oxidative damage in light was predominantly mediated by the inhibition of protein synthesis. By this inhibition the resynthesis of catalase, which has a high turnover in light, was blocked and the leaves were thus depleted of catalase activity and, in addition, the intensification of alternative antioxidative systems was also prevented.     

Getting to the roots of Cicer arietinum L. (chickpea) to study the effect of salinity on morpho-physiological,biochemical and molecular traits

The effect of saline irrigation (EC_iw 6 dS m^?1 and 9 dS m^?1) on the roots of Cicer arietinum L. genotypes was examined at morpho-physiological, biochemical and molecular levels. Reduction in root growth due to salinity was observed, but less effect was seen on the roots of genotypes KWR 108, ICCV 10, CSG 8962, and S7 as compared to the other genotypes. Cell turgor was maintained in tolerant genotypes through optimum water relations and osmoprotectants (proline and total soluble sugars) than the sensitive cultivars. Salinity caused oxidative stress as increased hydrogen peroxide and malondialdehyde were noticed, where low accumulation was observed in tolerant genotypes due to the higher activity of enzymatic antioxidants (superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and peroxidase). Na⁺/K⁺ ratio increased, but more increment was reported in sensitive cultivars. Gene expression studies depicted that genes encoding pyrroline-5-carboxylate synthetase and pyrroline-5-carboxylate reductase got upregulated and that of proline dehydrogenase was downregulated and more fold change with respect to control was in the salt tolerant check CSG 8962 and the genotype KWR 108. Higher expression of the genes encoding reactive oxygen species scavenging enzymes namely, superoxide dismutase, catalase, peroxidase, and those involved in the ascorbate–glutathione cycle was noticed in KWR 108 and CSG 8962 than ICC 4463. Enhanced expression of sodium transporter HKT1 due to salinity can be correlated with ion homeostasis maintenance. Cumulative effects of osmolytes, enzymatic antioxidants and maintaining ion homeostasis in root enable chickpea plants to survive in saline environments.     

Alleviation of salt-induced adverse impact via mycorrhizal fungi in Ephedra aphylla Forssk

The current investigation was carried out to examine the role of arbuscular mycorrhizal fungi (AMF) in alleviating adverse effects of salt stress in Ephedra aphylla. The plants were exposed to 75 and 150 mM sodium chloride (NaCl) stress with and without application of AMF. Salt stress caused significant decrease in chlorophyll and carotenoid contents; however, the application of AMF restored the pigments content in salt-affected plants. Proline, phenols, and lipid peroxidation were increased with increasing concentration of NaCl, but lower accumulation has been reported in plants treated with AMF. NaCl stress also showed increase in different antioxidant enzymes activities (catalase, ascorbate peroxidase, peroxidase, glutathione reductase, and superoxide dismutase), and further increase was observed in plants treated with AMF. The nutrient uptake, Na⁺ and Na/K ratio increased and potassium and phosphorus were decreased with increasing concentration of NaCl in the present study. However, the colonization with AMF significantly increased K⁺ and P and reduced Na⁺ uptake. It is concluded that presown soil treatment with AMF reduced severity of salt stress in E. aphylla through alterations in physiological parameters, antioxidants and uptake of nutrients.     

Physiological Mechanisms for High Salt Tolerance in Wild Soybean (Glycine soja) from Yellow River Delta,China: Photosynthesis,Osmotic Regulation,Ion Flux and antioxidant Capacity

Glycine soja (BB52) is a wild soybean cultivar grown in coastal saline land in Yellow River Delta, China. In order to reveal the physiological mechanisms adapting to salinity, we examined photosynthesis, ion flux, antioxidant system and water status in Glycine soja under NaCl treatments, taking a cultivated soybean, ZH13, as control. Upon NaCl exposure, higher relative water content and water potential were maintained in the leaf of BB52 than ZH13, which might depend on the more accumulation of osmotic substances such as glycinebetaine and proline. Compared with ZH13, activities of antioxidant enzymes including superoxide dismutase, catalase, ascorbate peroxidase and contents of ascorbate, glutathione and phenolics were enhanced to a higher level in BB52 leaf under NaCl stress, which could mitigate the salt-induced oxidative damage in BB52. Consistently, lipid peroxidation indicated by malondialdehyde content was lower in BB52 leaf. Photosynthetic rate (Pn) was decreased by NaCl stress in BB52 and ZH13, and the decrease was greater in ZH13. The decreased Pn in BB52 was mainly due to stomatal limitation. The inhibited activation of rubisco enzyme in ZH13 due to the decrease of rubisco activase content became an important limiting factor of Pn, when NaCl concentration increased to 200 mM. Rubisco activase in BB52 was not affected by NaCl stress. Less negative impact in BB52 derived from lower contents of Na⁺ and Cl^- in the tissues, and non-invasive micro-test technique revealed that BB52 roots had higher ability to extrude Na⁺ and Cl^-. Wild soybean is a valuable genetic resource, and our study may provide a reference for molecular biologist to improve the salt tolerance of cultivated soybean in face of farmland salinity.     

Silicon nutrition alleviates physiological disorders imposed by salinity in hydroponically grown canola (Brassica napus L.) plants

The effects of Si nutrition on transpiration, leaf anatomy, accumulation of Na⁺, K⁺, Cl^?, P, Fe and B and some reactive oxygen species related parameters were investigated in canola plants under salinity. Plants were grown hydroponically in growth chamber under controlled conditions at 0 and 100?mM NaCl each supplied with or without 1.7?mM silicon (Si) as sodium silicate. Salinity imposed significant reduction in growth parameters of plants like fresh weights of roots and shoots and leaf area. It also led to accumulation of Na⁺ and Cl^? and a decrease in the concentration of K⁺, P, B and Fe. Reduction of transpiration, stomatal density and specific leaf area in leaves and an increase in leaf thickness were amongst other symptoms in salt-affected plants. Salinity led to higher concentration of hydrogen peroxide, increased lipid peroxidation and decrease of catalase and peroxidase activity, which suggests the induction of oxidative stress in plants. Silicon nutrition could prevent toxic ions (Na⁺ and Cl^?) accumulation while higher levels of essential minerals like K⁺, P and Fe were maintained in plants. Consequently, silicon nutrition decreased oxidative stress in plants, evidenced by increase in antioxidant enzyme activity, reduction in hydrogen peroxide and lipid peroxidation.     

Antioxidative Defense Potential to Salinity in the Euhalophyte Salicornia brachiata

The antioxidative defense mechanism to salinity was assessed by monitoring the activities of some antioxidative enzymes and levels of antioxidants in an obligate halophyte, Salicornia brachiata, subjected to varying levels of NaCl (0, 200, 400, and 600 mM) under hydroponic culture. In the shoots of S. brachiata, salt treatment preferentially enhanced the activities of ascorbate peroxidase (APX), guaiacol peroxidase (POX), glutathione reductase (GR), and superoxide dismutase (SOD), whereas it induced the decrease of catalase (CAT) activity. Similarly, salinity caused an increase in total glutathione content (GSH + GSSG) and a decrease in total ascorbate content. Growth of S. brachiata was optimum at 200 mM NaCl and decreased with further increase in salinity. Salinity caused an increase in Na⁺ content and a decrease in K⁺ content of shoots. Proline levels did not change at low (0-200 mM NaCl) or moderate (400 mM NaCl) salinities, whereas a significant increase in proline level was observed at high salinity (600 mM NaCl). Accumulation of Na⁺ may have a certain role in osmotic homeostasis under low and moderate salinities in S. brachiata. Parameters of oxidative stress such as malondialdehyde (MDA), a product of lipid peroxidation, and H₂O₂ concentrations decreased at low salinity (200 mM NaCl) and increased at moderate (400 mM NaCl) and high salinities (600 mM NaCl). As a whole, our results suggest that the capacity to limit ionic and oxidative damage by the elevated levels of certain antioxidative enzymes and antioxidant molecules is important for salt tolerance of S. brachiata.     

Pre treatment with Bacillus subtilis mitigates drought induced photo-oxidative damages in okra by modulating antioxidant system and photochemical activity

Growth promoting potential of Bacillus subtilis (BS) in drought stressed Abelmoschus esculentus (L.) Moench (okra) was assessed by measuring the chlorophyll stability index (CSI), chlorophyll a (Chl-a) fluorescence, leaf osmotic potential and lipid peroxidation by malondialdehyde content, emission of reactive oxygen species (ROS), osmolyte content and the activity of non-enzyme and enzyme antioxidants. BS treatment significantly increased the leaf osmotic potential, osmolyte production and the activity of non-enzyme and enzyme antioxidants under drought stress. BS treatment mitigated the drought-induced reduction in Chl a fluorescence and CSI. Concomitant increase in total sugar, proline, non-enzyme antioxidants [glutathione and ascorbate] and enzyme antioxidants like superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase modulate the intracellular ROS concentration in okra to resist the stress induced oxidative damage in BS treated plants led to fast recovery and less photodamage.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-00982-8.     

Antioxidant defense mechanism under salt stress in wheat seedlings

The present study was carried out to study the effect of salt stress on cell membrane damage, ion content and antioxidant enzymes in wheat (Triticum aestivum) seedlings of two cultivars salt-tolerant KRL-19 and salt-sensitive WH-542. Seedlings (4-d-old) were irrigated with 0, 50 and 100 mM NaCl. Observations were recorded on the 3^rd and 6^th day after salt treatment and 2^nd day after salt removal. The relative water content declined with induction of salt stress, more in WH-542 than in cv. KRL-19. K⁺/Na⁺ ratio in KRL-19 was higher than in WH-542. WH-542 suffered greater damage to cellular membranes due to lipid peroxidation as indicated by higher accumulation of H₂O₂, MDA and greater leakage of electrolytes than KRL-19. The activities of catalase, peroxidase and ascorbate peroxidase and glutathione reductase increased with increase in salt stress in both the cultivars, however, superoxide dismutase activity declined. Upon desalanization, partial recovery in the activities of these enzymes was observed in KRL-19 and very slow recovery in WH-542.     

Manganese-induced salt stress tolerance in rice seedlings: regulation of ion homeostasis,antioxidant defense and glyoxalase systems

Hydroponically grown 12-day-old rice (Oryza sativa L. cv. BRRI dhan47) seedlings were exposed to 150 mM NaCl alone and combined with 0.5 mM MnSO₄. Salt stress resulted in disruption of ion homeostasis by Na⁺ influx and K⁺ efflux. Higher accumulation of Na⁺ and water imbalance under salinity caused osmotic stress, chlorosis, and growth inhibition. Salt-induced ionic toxicity and osmotic stress consequently resulted in oxidative stress by disrupting the antioxidant defense and glyoxalase systems through overproduction of reactive oxygen species (ROS) and methylglyoxal (MG), respectively. The salt-induced damage increased with the increasing duration of stress. However, exogenous application of manganese (Mn) helped the plants to partially recover from the inhibited growth and chlorosis by improving ionic and osmotic homeostasis through decreasing Na⁺ influx and increasing water status, respectively. Exogenous application of Mn increased ROS detoxification by increasing the content of the phenolic compounds, flavonoids, and ascorbate (AsA), and increasing the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD), and catalase (CAT) in the salt-treated seedlings. Supplemental Mn also reinforced MG detoxification by increasing the activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) in the salt-affected seedlings. Thus, exogenous application of Mn conferred salt-stress tolerance through the coordinated action of ion homeostasis and the antioxidant defense and glyoxalase systems in the salt-affected seedlings.     

Low pH altered salt stress in antioxidant metabolism and nitrogen assimilation in ginger (Zingiber officinale) seedlings

The effects of low pH on antioxidant metabolism and nitrogen (N) assimilation in ginger seedlings under salt stress were investigated. A two-way randomized block design was used: the main treatment consisted of two pH levels, normal and low pH (6.0 and 4.0, respectively), and the other treatment consisted of two salinity levels, 0 and 100 mmol l⁻¹ Na⁺ (NaCl and Na₂SO₄). The results showed that low pH decreased the malondialdehyde (MDA) and hydrogen peroxide contents of ginger seedling leaves under salt stress. Moreover, low pH and salt stress significantly decreased the contents of non-enzymatic antioxidants, including ascorbate (AsA) and glutathione (GSH), and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR). In addition, salt stress inhibited the N assimilation process in ginger seedling leaves, but low pH improved N assimilation under salt stress. Our finding was that low pH alleviated oxidative damage and promoted N assimilation under salt stress.     

Acetylsalicylic acid ameliorates negative effects of NaCl or osmotic stress in Solanum stoloniferum in vitro

The role of acetylsalicylic acid (0, 1 and 10 μM) pre-treatment in amelioration of salt and osmotic stress in a wild species of potato (Solanum stoloniferum) was investigated. We compared the effects of iso-osmotic concentrations of polyethylene glycol 6000 (15 %) and NaCl (80 mM) on the physiological responses of this species in explants grown in the liquid Murashige and Skoog medium. Both salt and drought reduced shoot growth parameters, photosynthetic pigment contents and increased lipid peroxidation, electrolyte leakage, H₂O₂ content and lipoxygenase activity. The effect of NaCl was more severe than that of polyethylene glycol. Salinity also increased Na⁺ content and decreased K⁺ content and K⁺/Na⁺ ratio. Under both stresses, the activities of superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, catalase and glutathione reductase enzymes were increased. Acetylsalicylic acid pre-treatment alleviated the adverse effects of both stresses on all parameters measured.     

Response of antioxidant systems to NaCl stress in the halophyte Cakile maritima

The effects of salt stress on antioxidative activities were investigated in a coastal halophyte, Cakile maritima . Two Tunisian accessions, Jerba and Tabarka, were compared. Plants were subjected to 100, 200, or 400 m M NaCl for 20 days. Parameters of oxidative stress [malondialdehyde (MDA), electrolyte leakage (EL), and hydrogen peroxide (H₂O₂) concentration], activities of several enzymes [superoxide dismutase (SOD), catalase (CAT), peroxydase (POD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR)], and antioxidant molecules (ascorbate, ASC, and glutathione, GSH) were determined. Growth of Jerba plants was improved at 100 m M NaCl as compared to that of control. Tabarka growth was inhibited by salt at all NaCl concentrations. The relative salt tolerance of Jerba was associated with high antioxidant enzyme activities and glutathione content, together with low MDA content, EL, and H₂O₂ concentration. Lower antioxidant activities and higher MDA content, EL, and H₂O₂ concentration were found in Tabarka. As a whole, these data suggest that the capacity to limit oxidative damage is important for salt tolerance of C. maritima .     

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.