Salt stress responses of a halophytic grass <Emphasis Type="Italic">Aeluropus lagopoides</Emphasis> and subsequent recovery

To investigate the salt tolerance mechanisms, Aeluropus lagopoides as a halophytic plant was used. Plants were treated with 0, 150, 450, 600, and 750 mM NaCl and harvested at 0, 4, 8, and 10 days after treatment and 1 day and 1 week after recovery. Optimal growth, measured as fresh and dry weights, occurred at 150 mM NaCl, but it was suppressed by 450, 600, and 750 mM NaCl. Recovery significantly increased fresh and dry weights only in 750 mM NaCl-treated plants. Water content was decreased after NaCl treatment and increased after recovery. Na⁺ and proline contents and activity of superoxide dismutase (SOD) were increased after NaCl treatment and decreased after recovery in all treated plants. In contrast, K⁺ content and ascorbate peroxidase activity decreased after NaCl treatment and increased after recovery in all treated plants. Catalase (CAT) was activated only in 750 mM NaCl-treated plants. Total content of soluble protein was slightly changed after NaCl treatment. It was concluded that proline accumulation for osmotic adjustment, SOD activation for O₂^·− scavenging, and CAT activation at the higher level of salt stress to detoxify produced H₂O₂ were main A. lagopoides strategies under salt stress. A. lagopoides salt tolerance was not based on the restriction of Na⁺ uptake.     

Plant growth and responses of antioxidants of <Emphasis Type="Italic">Chenopodium album</Emphasis> to long-term NaCl and KCl stress

The effects of long-term NaCl and KCl treatment on plant growth and antioxidative responses were investigated in Chenopodium album, a salt-resistant species widely distributed in semi-arid and light-saline areas of Xinjiang, China. Growth parameters [plant height, branch number, leaf morphology and chlorophyll (Chl) content], the level of oxidative stress [superoxide anion radical (O₂ ⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations], activity of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX)], the contents of non-enzymatic antioxidants [carotenoids (Car) and ascorbic acid (AsA)] and expression of selected genes were investigated. Plants were grown in the presence of 0, 50, and 300 mM NaCl or KCl for 2 months. Growth was stimulated by 50 mM NaCl or KCl, maintained stable at 300 mM NaCl, but was inhibited by 300 mM KCl. Three hundred mM NaCl did not affect O₂ ⁻, H₂O₂, MDA, Car and AsA, but increased the activities of SOD, CAT and POX compared to the controls. RT-PCR analysis suggested that expression of some genes encoding antioxidant enzymes could be induced during long-term salt stress, which was consistent with the enzyme activities. Treatment with 300 mM KCl was associated with elevated oxidative stress, and significantly decreased Car and AsA contents. These results suggest that an efficient antioxidant machinery is important for overcoming oxidative stress induced by treatment with high NaCl concentrations in C. album. Other strategies of ion regulation may also contribute to the differential tolerance to Na and K at higher concentrations.     

Exogenous salicylic acid alleviates NaCl toxicity and increases antioxidative enzyme activity in <Emphasis Type="Italic">Lycopersicon esculentum</Emphasis>

Effects of exogenous salicylic acid (SA) on plant growth, contents of Na, K, Ca and Mg, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and contents of ascorbate and glutathione were investigated in tomato (Lycopersicon esculentum L.) plants treated with 100 mM NaCl. NaCl treatment significantly increased H₂O₂ content and lipid peroxidation indicated by accumulation of thiobarbituric acid reactive substances (TBARS). A foliar spray of 1 mM SA significantly decreased lipid peroxidation caused by NaCl and improved the plant growth. This alleviation of NaCl toxicity by SA was related to decreases in Na contents, increases in K and Mg contents in shoots and roots, and increases in the activities of SOD, CAT, GPX and DHAR and the contents of ascorbate and glutathione.     

Pre-treatment with H<Subscript>2</Subscript>O<Subscript>2</Subscript> induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 μM H₂O₂ for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H₂O₂ alone had no effect on the proline, malondialdehyde (MDA) and H₂O₂ contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 μM H₂O₂ treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H₂O₂ pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of ¹⁴CO₂ fixation was higher and MDA, H₂O₂ and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl⁻ content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H₂O₂ metabolism is involved as a signal in the processes of barley salt tolerance.     

Salicylic acid,hydrogen peroxide and calcium-induced saline tolerance associated with endogenous hydrogen peroxide homeostasis in naked oat seedlings

This study investigates the role of salicylic acid (SA), hydrogen peroxide (H₂O₂) and calcium chloride (CaCl₂) singly or in combination, in inducing naked oat plant tolerance to sodium chloride (NaCl). Two-week-old naked oat plants were pretreated with both single and double of 0.5 mM SA, 0.5 mM H₂O₂ and 5 mM CaCl₂ by adding them to the culture solution for 24 h. At the end of the pretreatment, the plants were subjected to 200 mM NaCl exposure for 7 days. Data were collected on plant biomass, H₂O₂ level, antioxidant enzyme activity, non-enzymatic antioxidant content and malondialdehyde (MDA) content. Results showed that exposure to salt significantly inhibited plant growth, and the shoot and root dry weights were reduced 47.5% and 63.4%, and the H₂O₂ levels elevated 5.8 and 2.4 times in comparison with those in the control, respectively. Under the saline stress, the activities of superoxide dismutase (SOD) and catalase (CAT) were induced, but the contents of ascorbic acid (AA) and glutathione (GSH) decreased, and MDA largely accumulated. The various pretreatments efficiently counteracted the salt-caused growth inhibition, especially with H₂O₂ + CaCl₂ the shoot and root dry weights reduced only 9.4% and 24.4% of the non salt-stressed plants. The determination of endogenous H₂O₂ level demonstrated that the pretreatments induced H₂O₂ accumulation, with H₂O₂ + CaCl₂ being most efficient, but the effect was transient. After 7 days of saline stress, the H₂O₂ contents in the pretreated shoots and roots accounted for 23.7–41.8% and 31.7–57.3% of the non-pretreated plants, varying according to the different pretreatments. Under saline stress, SOD and CAT further increased, AA and GSH maintained higher levels and MDA decreased in the pretreated plants compared to the untreated plants. With application of diphenylene iodonium (DPI) during the pretreatment, which inhibited the accumulation of H₂O₂, the ameliorative effect of the pretreatment on salt-caused plant growth inhibition was reduced. However, applied DPI at the immediate end of the pretreatment did not alter its favorable role, indicating a H₂O₂ peak formed at the early time of saline stress might play an important role in regulating plant tolerance to saline stress.     

Salt stress induction of some key antioxidant enzymes and metabolites in eight Iranian wild almond species

The present work describes the changes in the activities of key antioxidant enzymes and the levels of some metabolites in relation to salt tolerance in eight wild almond species. All the species were exposed to four levels of NaCl (control, 40, 80 and 120 mM). Plant fresh biomass, α-, γ- and δ-tocopherol, total soluble proteins, malondialdehyde (MDA_eq), H₂O₂, total phenolics, and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were analyzed in leaves of salt-stressed and non-stressed plants of the eight almond species. In all the species, salt stress significantly enhanced the activities of SOD and POD, levels of total phenolics and γ- and δ-tocopherols. High levels of salt stress significantly depressed the levels of total soluble proteins, MDA and CAT activity, while salt stress did not significantly affect leaf H₂O₂ contents. Regression analysis showed that the relationship between salt levels and total soluble proteins, CAT, γ-tocopherol, MDA_eq, SOD and POD were statistically significant. Principal component analysis discriminated the almond species based on their degree of tolerance/sensitivity to saline conditions: Prunus reuteri and P. glauca were ranked as salt tolerant, P. lycioides and P. scoparia as moderately tolerant, and P. communis, P. eleagnifolia, P. arabica and P. orientalis as salt sensitive. The results could be used for selecting salt tolerant genotypes to be used as rootstocks for almond cultivation.     

Programmed cell death is induced by hydrogen peroxide but not by excessive ionic stress of sodium chloride in the unicellular green alga Chlamydomonas reinhardtii

Eukaryotic microalgae serve as indicators of environmental change when exposed to severe seasonal fluctuations. Several environmental stress conditions are known to produce reactive oxygen species in cellular compartments, resulting in oxidative damage and apoptosis. The study of cell death in higher plants and animals has revealed the existence of an active ‘programmed cell death’ (PCD) process and similarities between such processes suggest an evolutionary origin. A study was undertaken to examine the morphological, biochemical and molecular responses of the unicellular green alga Chlamydomonas reinhardtii after exposure to oxidative (10 mM H₂O₂) and osmotic (200 mM NaCl and 360 mM sorbitol) stress. Concentrations of H₂O₂ (2–50 mM), NaCl and sorbitol (100–800 mM) were negatively correlated with growth. Biochemical analyses showed an increase in intracellular H₂O₂ production (2.2-fold with H₂O₂ and ~1.2–1.4-fold with NaCl and sorbitol) and activities of some antioxidant enzymes [super oxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)]. Alteration of mitochondrial membrane potential (MMP) was observed upon treatment with H₂O₂ and NaCl, but not with sorbitol, indicating that the ionic stress component of NaCl altered the MMP. In addition, H₂O₂ led to the activation of a caspase-3-like protein, increase in the cleavage of a poly(ADP) ribose polymerase-1 (PARP-1)-like enzyme and formation of DNA nicks and laddering. With NaCl and sorbitol, no caspase activation, nor oligonucleosomal DNA laddering was observed, indicating non-apoptotic death. However, genomic DNA of NaCl (800 mM)-stressed cells, but not those of sorbitol-treated cells showed complete shearing. We conclude that the ionic rather than the osmotic component of NaCl leads to necrosis. These results unequivocally suggest that the vegetative cells of C. reinhardtii respond differentially to various stress agents, leading to different death types in the same organism. Moreover, unlike most other organisms, when exposed to NaCl this alga does not undergo PCD.     

Role of hydrogen peroxide in regulating glucose-6-phosphate dehydrogenase activity under salt stress

The role of hydrogen peroxide in the regulation of glucose-6-phosphate dehydrogenase (G6PDH) activity in the red kidney bean (Phaseolus vulgaris L.) roots under salt stress (100 mM NaCl) was investigated. Salt stress caused the increase of the activities of G6PDH and antioxidative enzymes including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), as well as H₂O₂ production. The application of H₂O₂ (1 mM) also enhanced the activities of G6PDH as well as antioxidative enzymes. In the presence of exogenous CAT, H₂O₂ content was decreased, and the enhanced activities of G6PDH and antioxidative enzymes induced by NaCl or by exogenous H₂O₂ were also abolished, suggesting that the enhancement of the above enzyme activities under salt stress was a result of the increased endogenous H₂O₂ levels. Further results showed that the effects of NaCl and H₂O₂ on the activities of antioxidative enzymes were diminished by Na₃PO₄ (a G6PDH inhibitor), suggesting G6PDH activity is required in enhancing the activities of antioxidative enzymes. The enhanced membrane leakage, lipid peroxidation, H₂O₂ and O₂ — contents, G6PDH and antioxidative enzyme activities under salt stress were all recovered to control level when the red kidney bean seedlings treated with 100 mM NaCl for 6 d were transferred to the control conditions for 8 d.     

Abscisic acid improves drought tolerance of triploid bermudagrass and involves H2O2- and NO-induced antioxidant enzyme activities

Drought is a major limiting factor for turfgrass growth. Protection of triploid bermudagrass against drought stress by abscisic acid (ABA) and its association with hydrogen peroxide (H₂O₂) and nitric oxide (NO) were investigated. ABA treatment increased relative water content, decreased ion leakage and the percentage of dead plants significantly under drought stress. Superoxide dismutase (SOD) and catalase (CAT) activities increased in both ABA-treated and control plants, but more in ABA-treated plants, under drought stress. Malondialdehyde, an indicator of plant lipid peroxidation, was lower in ABA-treated plants than in control plants, indicating that ABA alleviated drought-induced oxidative injury. ABA treatment increased H₂O₂ and NO contents. ABA-induced SOD and CAT activities could be blocked by scavengers of H₂O₂ and NO, and inhibitors of H₂O₂ and NO generation. The results indicated that H₂O₂ and NO were essential for ABA-induced SOD and CAT activities. Both H₂O₂ and NO could induce SOD and CAT activities individually. SOD and CAT induced by H₂O₂ could be blocked by scavenger of NO and inhibitors of NO generation, while SOD and CAT induced by NO could not be blocked by scavenger of H₂O₂ and inhibitor of H₂O₂. The results revealed that ABA-induced SOD and CAT activities were mediated sequentially by H₂O₂ and NO, and NO acted downstream of H₂O₂.     

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.     

Salt and paraquat stress tolerance results from co-expression of the Suaeda salsa glutathione S-transferase and catalase in transgenic rice

GST (Glutathione S-transferase, EC 2.5.1.18) and CAT (Catalase, EC 1.11.1.6) play important roles in oxidative stress resistance. In this study, we transferred both GST and CAT1 of Suaeda salsa into rice (Oryza sativa cv. Zhonghua No.11) by Agrobacterium tumefaciens-mediated transformation under the control of cauliflower mosaic virus (CaMV) 35S promoter, and investigated whether co-expressing the GST and CAT1 in transgenic rice could reduce oxidative damage. Salt and paraquat stresses were applied. The data showed that co-expression of the GST and CAT1 resulted in greater increase of CAT and SOD (Superoxide Dismutase, EC 1.15.1.1) activity in the transgenics compared to non-transgenics following both stress imposition. Whereas the significant increase of GST activity in transgenics only occurred in paraquat stressed plants. While the generation of H₂O₂, Malon dialdehyde and plasma membrane relative electrolyte leakage decreased in the transgenics than in non-transgenics under the same conditions. Moreover, the transgenic rice seedlings showed markedly enhanced tolerance to salt stress compared with non-transgenics upon 200 mM NaCl treatment in greenhouse. The enhancement of the active oxygen-scavenging system that led to increased oxidative stress protection in GST + CAT1-transgenic rice plants could result not only from increased GST and CAT activity but also from the combined increase in SOD activity.     

The effect of salt stress on lipid peroxidation and antioxidative enzymes in callus of two <Emphasis Type="Italic">Acanthophyllum</Emphasis> species

The changes in lipid peroxidation and the involvement of the antioxidant system in relation to salt stress tolerance were investigated in the callus of Acanthophyllum glandulosum and Acanthophyllum sordidum. The callus was subjected to NaCl stress (50–200 mM) for 40 d. The callus of A. glandulosum was less sensitive to NaCl stress than that of A. sordidum. Increasing concentrations of NaCl from 50 to 200 mM correlated to increased proline content in A. glandulosum. Total protein content was higher in extracts of A. glandulosum than in extracts of A. sordidum under both control and salinity treatments. Compared with A. sordidum, lipid peroxidation and H₂O₂ content were lower and the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase, and glutathione reductase were higher in A. glandulosum under salt stress. Activity staining of antioxidant enzymes separated by native polyacrylamide gel electrophoresis (PAGE) revealed that callus of A. sordidum had five Fe-SOD isoforms and one Mn-SOD isoform, all of which were reduced by salinity. In A. glandulosum, two Mn-SOD, three Fe-SOD, and one Cu/Zn-SOD isoforms were detected. Out of these six SOD isoforms, expression of the Mn-SOD and Fe-SOD isoforms was enhanced at 100 mM and higher NaCl concentrations. Two and six GPX isoforms were detected in A. sordidum and A. glandulosum, respectively. Expression of the single CAT isoform in A. sordidum was preferentially reduced by salinity. In A. glandulosum, the two CAT isoforms showed differential down regulation under NaCl stress, with the CAT2 isoform detected only under control condition. These results suggest that A. glandulosum callus is better protected against salinity-induced oxidative damage by maintaining higher activities of antioxidant enzymes than the callus of A. sordidum.     

Antioxidant response of a novel Streptomyces sp. M3004 isolated from legume rhizosphere to H2O2 and paraquat

This paper aims to investigate the effect of H₂O₂ and paraquat on the activities of superoxide dismutase (SOD) and catalase (CAT), and membrane lipid peroxidation (LPO) levels in newly isolated Streptomyces sp. M3004. SOD activities of Streptomyces sp. M3004, grown in 10 mM and 30 mM H₂O₂, were significantly lower than the control cultures. On the other hand, as an antioxidant enzyme, CAT activity in both H₂O₂ treatment conditions increased significantly compared with the control. These activity values in 10 mM and 30 mM H₂O₂ treatment on the 48th hour of incubation were 3.8- and 6.6-fold higher than the control, respectively. SOD activity decreased significantly with respect to paraquat concentration, which was added at the start of the incubation. CAT activities increased significantly in 1.0 mM and 3.0 mM paraquat treatments compared to control. As an indicative marker of membrane damage, LPO levels of the novel isolate Streptomyces sp. M3004 treated with H₂O₂, and paraquat stress conditions were significantly higher than the control. Nevertheless, compared with the 30 mM H₂O₂ in both treatment conditions, LPO levels in 10 mM H₂O₂ were significantly higher. The decreases in SOD activities in paraquat and H₂O₂ treatment conditions resulted in the increases in the LPO levels although it increases in CAT activities.     

Exogenous application of mannitol and thiourea regulates plant growth and oxidative stress responses in salt-stressed maize (Zea mays L.)

Abstract

The mechanism of growth amelioration in salt-stressed maize (Zea mays L. cv., DK 647 F1) by exogenously applied mannitol (M) and thiourea (T) was investigated. Maize seedlings were planted in pots containing perlite and subjected to 0 or 100 mM NaCl in full strength Hoagland's nutrient solution. Two levels of M (15 and 30 mM) or T (3.5 and 7.0 mM) were sprayed to the leaves of maize seedlings 10 days after germination. Salinity stress caused considerable reduction in plant dry biomass, chlorophyll content, and relative water content in the maize plants. However, it increased the activities of catalase (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1), and polyphenol oxidase (PPO; EC 1.10.3.1), and levels of hydrogen peroxide (H₂O₂) and electrolyte leakage, but it did not change peroxidase (POD; EC 1.11.1.7) activity. Foliar application of M or T was found to be effective in checking salt-induced shoot growth inhibition. Exogenously applied M or T reduced the activities of CAT, SOD, POD, and PPO in the salt-treated maize plants compared to those in the plants not fed with these organic compounds. Salinity increased Na⁺ contents but decreased those of K⁺, Ca^{2 +}, and P in the leaves and roots of the maize plants. Foliar-applied M or T increased the contents of K⁺, Ca^{2 +}, and P, but decreased that of Na⁺ in the salt-stressed maize plants with respect to those of the salt-stressed plants not supplied with mannitol or thiourea. Mannitol was found to be more effective than thiourea in improving salinity tolerance of maize plants in terms of growth and physiological attributes measured in the present study.     

Influence of exogenous application of glycinebetaine on antioxidative system and growth of salt-stressed soybean seedlings (Glycine max L.)

Glycinebetaine is one of the most competitive compounds which play an important role in salt stress in plants. In this study, the enhanced salt tolerance in soybean (Glycine max L.) by exogenous application of glycinebetaine was evaluated. To improve salt tolerance at the seedling stage, GB was applied in four different concentrations (0, 5, 25 and 50 mM) as a pre-sowing seed treatment. Salinity stress in the form of a final concentration of 150 mM sodium chloride (NaCl) over a 15 day period drastically affected the plants as indicated by increased proline, MDA and Na⁺ content of soybean plants. In contrast, supplementation with 50 mM GB improved growth of soybean plants under NaCl as evidenced by a decrease in proline, MDA and Na⁺ content of soybean plants. Further analysis showed that treatments with GB, resulted in increasing of CAT and SOD activity of soybean seedlings in salt stress. We propose that the role of GB in increasing tolerance to salinity stress in soybean may result from either its antioxidant capacity by direct scavenging of H₂O₂ or its role in activating CAT activity which is mandatory in scavenging H₂O₂.     

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.     

Arbuscular mycorrhizal symbiosis modulates antioxidant response in salt-stressed Trigonella foenum-graecum plants

An experiment was conducted to evaluate the influence of Glomus intraradices colonization on the activity of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (PX), ascorbate peroxidase (APX), and glutathione reductase (GR)] and the accumulation of nonenzymatic antioxidants (ascorbic acid, α-tocopherol, glutathione, and carotenoids) in roots and leaves of fenugreek plants subjected to varying degrees of salinity (0, 50, 100, and 200 mM NaCl) at two time intervals (1 and 14 days after saline treatment, DAT). The antioxidative capacity was correlated with oxidative damage in the same tissue. Under salt stress, lipid peroxidation and H₂O₂ concentration increased with increasing severity and duration of salt stress (DoS). However, the extent of oxidative damage in mycorrhizal plants was less compared to nonmycorrhizal plants. The study reveals that mycorrhiza-mediated attenuation of oxidative stress in fenugreek plants is due to enhanced activity of antioxidant enzymes and higher concentrations of antioxidant molecules. However, the significant effect of G. intraradices colonization on individual antioxidant molecules and enzymes varied with plant tissue, salinity level, and DoS. The significant effect of G. intraradices colonization on antioxidative enzymes was more evident at 1DAT in both leaves and roots, while the concentrations of antioxidant molecules were significantly influenced at 14DAT. It is proposed that AM symbiosis can improve antioxidative defense systems of plants through higher SOD activity in M plants, facilitating rapid dismutation of O₂ ^- to H₂O₂, and subsequent prevention of H₂O₂ build-up by higher activities of CAT, APX, and PX. The potential of G. intraradices to ameliorate oxidative stress generated in fenugreek plants by salinity was more evident at higher intensities of salt stress.     

Effects of salt stress on ion content,antioxidant enzymes and protein profile in different tissues of Broussonetia papyrifera

Although some plant responses to salinity have been characterized, the precise mechanisms by which salt stress damages plants are still poorly understood especially in woody plants. In the present study, the physiological and biochemical responses of Broussonetia papyrifera, a tree species of the family, Moraceae, to salinity were studied. In vitro-produced plantlets of B. papyrifera were treated with varying levels of NaCl (0, 50, 100 and 150 mM) in hydroponic culture. Changes in ion contents, accumulation of H₂O₂, as well as the activities and isoform profiles of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the leaves, stems and roots were investigated. Under salt stress, there was higher Na⁺ accumulation in roots than in stems and leaves, and Ca^2 +, Mg^2 + and P^3 + content, as well as K⁺/Na⁺ ratio were affected. NaCl treatment induced an increase in H₂O₂ contents in the tissues of B. papyrifera. The work demonstrated that activities of antioxidant defense enzymes changed in parallel with the increased H₂O₂ and salinity appeared to be associated with differential regulation of distinct SOD and POD isoenzymes. Moreover, SDS-PAGE analysis of total proteins extracted from leaves and roots of control and NaCl-treated plantlets revealed that in the leaves salt stress was associated with decrease or disappearance of some protein bands, and induction of a new protein band after exposure to 100 and 150 mM NaCl. In contrast, NaCl stress had little effect on the protein pattern in the roots. In summary, these findings may provide insight into the mechanisms of the response of woody plants to salt stress.     

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.