Silicon-mediated alleviation of Mn toxicity in Cucumis sativus in relation to activities of superoxide dismutase and ascorbate peroxidase

The effects of exogenous silicon (Si) on plant growth, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase, and concentrations of ascorbate and glutathione were investigated in cucumber (Cucumis sativus L.) plants treated with excess manganese (Mn) (600 microM). Compared with the treatment of normal Mn (10 microM), excess Mn significantly increased H2O2 concentration and lipid peroxidation indicated by accumulation of thiobarbituric acid reactive substances. The leaves showed apparent symptoms of Mn toxicity and the plant growth was significantly inhibited by excess Mn. The addition of Si significantly decreased lipid peroxidation caused by excess Mn, inhibited the appearance of Mn toxicity symptoms, and improved plant growth. This alleviation of Mn toxicity by Si was related to a significant increase in the activities of SOD, APX, DHAR and GR and the concentrations of ascorbate and glutathione.     

Effects of exogenous salicylic acid on manganese toxicity, element contents and antioxidative system in cucumber

The effects of salicylic acid (SA) on manganese (Mn) toxicity in cucumber plants (Cucumis sativus L.) were studied by investigating the symptoms, plant growth, lipid peroxidation, antioxidative enzymes and antioxidants. Excess Mn caused serious chlorosis and inhibited the growth of cucumber plants, and dramatically increased accumulation of Mn in both shoots and roots, furthermore, inhibited the absorption of Ca, Mg and Zn. Addition of SA decreased the transport of Mn from roots to shoots, alleviated the inhibition of Ca, Mg and Zn absorption induced by excess Mn, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in cucumber leaves exposed to excess Mn, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances (TBARS). Addition of SA significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes showed different changes, addition of SA inhibited catalase (CAT) and ascorbate peroxidase (APX) activities, while increased activities of superoxide dismutase (SOD), peroxidase (POD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in cucumber leaves exposed to excess Mn. As important antioxidants, ascorbate and glutathione contents in cucumber leaves exposed to excess Mn were significantly increased by SA treatment.     

Up-regulation of the leaf mitochondrial and peroxisomal antioxidative systems in response to salt-induced oxidative stress in the wild salt-tolerant tomato species Lycopersicon pennellii

The response of the antioxidative systems of leaf cell mitochondria and peroxisomes of the cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species Lycopersicon pennellii (Lpa) to NaCl 100 mM stress was investigated. Salt-dependent oxidative stress was evident in Lem mitochondria as indicated by their raised levels of lipid peroxidation and H2O2 content whereas their reduced ascorbate and reduced glutathione contents decreased. Concomitantly, SOD activity decreased whereas APX and GPX activities remained at control level. In contrast, the mitochondria of salt-treated Lpa did not exhibit salt-induced oxidative stress. In their case salinity induced an increase in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione-dependent peroxidase (GPX). Lpa peroxisomes exhibited increased SOD, APX, MDHAR and catalase activity and their lipid peroxidation and H2O2 levels were not affected by the salt treatment. The activities of all these enzymes remained at control level in peroxisomes of salt-treated Lem plants. The salt-induced increase in the antioxidant enzyme activities in the Lpa plants conferred cross-tolerance towards enhanced mitochondrial and peroxisomal reactive oxygen species production imposed by salicylhydroxamic acid (SHAM) and 3-amino-1,2,4-triazole (3-AT), respectively.     

Effect of nitric oxide and putrescine on antioxidative responses under NaCl stress in chickpea plants

Chickpea plants were subjected to salt stress for 48 h with 100 mM NaCl, after 50 days of growth. Other batches of plants were simultaneously treated with 0.2 mM sodium nitroprusside (NO donor) or 0.5 mM putrescine (polyamine) to examine their antioxidant effects. Sodium chloride stress adversely affected the relative water content (RWC), electrolyte leakage and lipid peroxidation in leaves. Sodium nitroprusside and putrescine could completely ameliorate the toxic effects of salt stress on electrolyte leakage and lipid peroxidation and partially on RWC. No significant decline in chlorophyll content under salt stress as well as with other treatments was observed. Sodium chloride stress activated the antioxidant defense system by increasing the activities of peroxidase (POX), catalase (CAT) superoxide dismutase (SOD) and ascorbate peroxidase (APX). However no significant effect was observed on glutathione reductase (GR) and dehydro ascorbate reductase (DHAR) activities. Both putrescine and NO had a positive effect on antioxidant enzymes under salt stress. Putrescine was more effective in scavenging superoxide radical as it increased the SOD activity under salt stress whereas nitric oxide was effective in hydrolyzing H₂O₂ by increasing the activities of CAT, POX and APX under salt stress.     

Nitric oxide modulates antioxidant defense and the methylglyoxal detoxification system and reduces salinity-induced damage of wheat seedlings

The present study investigates the possible regulatory role of exogenous nitric oxide (NO) in antioxidant defense and methylglyoxal (MG) detoxification systems of wheat seedlings exposed to salt stress (150 and 300 mM NaCl, 4 days). Seedlings were pre-treated for 24 h with 1 mM sodium nitroprusside, a NO donor, and then subjected to salt stress. The ascorbate (AsA) content decreased significantly with increased salt stress. The amount of reduced glutathione (GSH) and glutathione disulfide (GSSG) and the GSH/GSSG ratio increased with an increase in the level of salt stress. The glutathione S-transferase (GST) activity increased significantly with severe salt stress (300 mM). The ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT) and glutathione peroxidase (GPX) activities did not show significant changes in response to salt stress. The glutathione reductase (GR), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon the imposition of salt stress, especially at 300 mM NaCl, with a concomitant increase in the H₂O₂ and lipid peroxidation levels. Exogenous NO pre-treatment of the seedlings had little influence on the non-enzymatic and enzymatic components compared to the seedlings of the untreated control. Further investigation revealed that NO pre-treatment had a synergistic effect; that is, the pre-treatment increased the AsA and GSH content and the GSH/GSSG ratio, as well as the activities of MDHAR, DHAR, GR, GST, GPX, Gly I, and Gly II in most of the seedlings subjected to salt stress. These results suggest that the exogenous application of NO rendered the plants more tolerant to salinity-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.     

Selenium-Induced Up-Regulation of the Antioxidant Defense and Methylglyoxal Detoxification System Reduces Salinity-Induced Damage in Rapeseed Seedlings

The present study investigates the regulatory role of exogenous selenium (Se) in the antioxidant defense and methylglyoxal (MG) detoxification systems in rapeseed seedlings exposed to salt stress. Twelve-day-old seedlings, grown in Petri dishes, were supplemented with selenium (25 μM Na₂SeO₄) and salt (100 and 200 mM NaCl) separately and in combination, and further grown for 48 h. The ascorbate (AsA) content of the seedlings decreased significantly with increased salt stress. The amount of reduced glutathione (GSH) and glutathione disulfide (GSSG) increased with an increase in the level of salt stress, while the GSH/GSSG ratio decreased. In addition, the ascorbate peroxidase (APX) and glutathione S-transferase (GST) activity increased significantly with increased salt concentration (both at 100 and 200 mM NaCl), while glutathione peroxidase (GPX) activity increased only at moderate salt stress (100 mM NaCl). Glutathione reductase (GR) activity remained unchanged at 100 mM NaCl, while it was decreased under severe (200 mM NaCl) salt stress. Monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon the imposition of salt stress, whereas a sharp decrease of these activities was observed under severe salt stress (200 mM NaCl). Concomitant increases in the levels of H₂O₂ and lipid peroxidation (MDA) were also measured. Exogenous Se treatment alone had little effect on the non-enzymatic and enzymatic components. However, further investigation revealed that Se treatment had a synergistic effect: in salt-stressed seedlings, it increased the AsA and GSH contents; GSH/GSSG ratio; and the activities of APX, MDHAR, DHAR, GR, GST, GPX, CAT, Gly I, and Gly II. As a result, addition of Se in salt-stressed seedlings led to a reduction in the levels of H₂O₂ and MDA as compared to salt stress alone. These results suggest that the exogenous application of Se rendered the plants more tolerant to salt stress-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.     

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

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

Methyl jasmonate and salicylic acid elicitation induces ginsenosides accumulation, enzymatic and non-enzymatic antioxidant in suspension culture Panax ginseng roots in bioreactors

The effects of methyl jasmonate (MJ) and salicylic acid (SA) on changes of the activities of major antioxidant enzymes, superoxide anion accumulation (O₂ ⁻), ascorbate, total glutathione (TG), malondialdehyde (MDA) content and ginsenoside accumulation were investigated in ginseng roots (Panax ginseng L.) in 4 l (working volume) air lift bioreactors. Single treatment of 200 μM MJ and SA to P. ginseng roots enhanced ginsenoside accumulation compared to the control and harvested 3, 5, 7 and 9 days after treatment. MJ and SA treatment induced an oxidative stress in P. ginseng roots, as shown by an increase in lipid peroxidation due to rise in O₂ ⁻ accumulation. Activity of superoxide dismutase (SOD) was inhibited in MJ-treated roots, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), SOD, guaiacol peroxidase (G-POD), glutathione peroxidase (GPx) and glutathione reductase (GR) were induced in SA-treated roots. A strong decrease in the activity of catalase (CAT) was obtained in both MJ- and SA-treated roots. Activities of ascorbate peroxidase (APX) and glutathione S transferase (GST) were higher in MJ than SA while the contents of reduced ascorbate (ASC), redox state (ASC/(ASC+DHA)) and TG were higher in SA- than MJ-treated roots while oxidized ascorbate (DHA) decreased in both cases. The result of these analyses suggests that roots are better protected against the O₂ ⁻ stress, thus mitigating MJ and SA stress. The information obtained in this work is useful for efficient large-scale production of ginsenoside by plant-root cultures.     

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

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

Antioxidative responses of Calendula officinalis under salinity conditions.

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

Antioxidative response of <Emphasis Type="Italic">Hordeum maritimum</Emphasis> L<Emphasis Type="Italic">.</Emphasis> to potassium deficiency

The objective of the present study was to determine the influence of potassium deprivation on the halophyte species Hordeum maritimum grown in hydroponics for 2 weeks. Treatments were with potassium (+K) or without potassium (−K). Growth, water status, mineral nutrition, parameters of oxidative stress [malondialdehyde (MDA), carbonyl groups (C=O), and hydrogen peroxide concentration (H₂O₂) contents], antioxidant enzyme activities [superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate peroxidase (MDHAR, EC 1.6.5.4), dehydroascorbate peroxidase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2)], and antioxidant molecules [ascorbate (ASC), and glutathione (GSH)] were determined. Results showed that the growth of vegetative organs decreased owing to potassium deficiency with roots (−36%) more affected than shoots (−12%). Water status was only diminished in roots (reduction of 24%). Potassium deprivation decreased potassium concentration in both organs, this decrease was more pronounced in roots (−81%) than in shoots (−55%). In contrast to carbonyl groups, MDA content increased owing to potassium deprivation. Except for CAT activity that remained unaffected; SOD, GPX, APX, GR, MDHAR, and DHAR activities were significantly increased. H₂O₂ concentration was negatively correlated with the activities of enzymes and the accumulation of non-enzymatic antioxidants implicated in its detoxification. In conclusion, a cooperative process between the antioxidant systems is important for the tolerance of H. maritimum to potassium deficiency.     

Kinetics of the Anti-oxidant Response to Salinity in the Halophyte Cakile maritima

The effects of NaCl stress on the activity of anti-oxidant enzymes （superoxide dismutase, catalase （CAT）, peroxidase （POD）, ascorbate peroxidase （APX）, monodehydroascorbate reductase, dehydroascorbate reductase （DHAR）, and glutathione reductase （GR））, anti-oxidant molecules （ascorbate and glutathione）, and parameters of oxidative stress （malondialdehyde （MDA）, electrolyte leakage, and H2O2 concentrations） were investigated in Cakile maritima, a halophyte frequent along the Tunisian seashore. Seedlings were grown in the presence of salt （100, 200, and 400 mmol/L NaCl）. Plants were harvested periodically over 20 days. Growth was maximal in the presence of 0-100 mmol/L NaCl. At 400 mmol/L NaCl, growth decreased significantly. The salt tolerance of C. maritima, at moderate salinities, was associated with the lowest values of the parameters indicative of oxidative stress, namely the highest activities of POD, CAT, APX, DHAR, and GR and high tissue content of ascorbate and glutathione. However, prolonged exposure to high salinity resulted in a decrease in anti-oxidant activities and high MDA content, electrolyte leakage, and H2O2 concentrations. These results suggest that anti-oxidant systems participate in the tolerance of C. maritima to moderate salinities.     

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

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

Kinetics of the Anti-oxidant Response to Salinity in the Halophyte Cakile maritima

The effects of NaCl stress on the activity of anti-oxidant enzymes (superoxide dismutase, catalase (CAT),peroxidase (POD),ascorbate peroxidase (APX), monodehydroascorbate reductase, dehydroascorbate reductase (DHAR), and glutathionereductase (GR)), anti-oxidant molecules (ascorbate and glutathione), and parameters of oxidative stress (malondialdehyde(MDA), electrolyte leakage, and H_2O_2 concentrations) were investigated in Cakile maritima, a halophyte frequent along theTunisian seashore. Seedlings were grown in the presence of salt (100, 200, and 400 mmol/L NaCI). Plants were harvestedperiodically over 20 days. Growth was maximal in the presence of 0-100 mmol/L NaCl. At 400 mmol/L NaCl, growthdecreased significantly. The salt tolerance of C. maritima, at moderate salinities, was associated with the lowest values ofthe parameters indicative of oxidative stress, namely the highest activities of POD, CAT, APX, DHAR, and GR and high tissuecontent of ascorbate and glutathione. However, prolonged exposure to high salinity resulted in a decrease in anti-oxidantactivities and high MDA content, electrolyte leakage, and H_2O_2 concentrations. These results suggest that anti-oxidantsystems participate in the tolerance of C. maritima to moderate salinities.     

The effect of salt stress on lipid peroxidation and antioxidants in the leaf of the cultivated tomato and its wild salt‐tolerant relative Lycopersicon pennellii

The possible involvement of the antioxidative system in the tolerance to salt stress was studied in the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (M82) and its wild salt‐tolerant relative L. pennellii (Corn) D'Arcy accession Atico (Lpa). All analyses, except that of monodehydroascorbate reductase (MDHAR), were performed of the youngest fully‐expanded leaf of control and salt (100 m M NaCl) stressed plants, 4, 7, 10, 14, 18 and 22 days after completing the stress treatment. In Lpa, constitutive level of lipid peroxidation and activities of catalase (CAT) and glutathione reductase (GR) were lower while the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were inherently higher than in M82. Relative to M82, lipid peroxidation was much lower and the activities of SOD, CAT and APX were higher in Lpa at 100 m M NaCl. The activity of DHAR decreased more in Lpa than in M82 under salt stress, and the activity of MDHAR, which was lower in Lpa than in M82 under control conditions, increased much more and to a higher level in salt‐treated Lpa plants. GR activity decreased similarly in the two species under salt stress. The results of these analyses suggest that the wild salt‐tolerant Lpa plants are better protected against active oxygen species (AOS), inherently and under salt stress, than the relatively sensitive plants of the cultivated species.     

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

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

Differential responses of antioxidative defense system to prolonged salinity stress in salt-tolerant and salt-sensitive Indica rice (Oryza sativa L.) seedlings

The present investigation evaluated the ability of an antioxidative defense system in terms of the tolerance against salinity-induced oxidative stress and also explored a possible relationship between the status of the components of an antioxidative defense system and the salt tolerance in Indica rice (Oryza sativa L.) genotypes. When the seedlings of a salt-sensitive cultivar was grown in sand cultures containing different NaCl concentrations (7 and 14 dS m^?1) for 5–20 days, a substantial increase was observed in the rate of superoxide anion (O ₂ ^·? ) production, elevated levels of H₂O₂ and thiobarbituric acid reactive substances (TBARS) which indicated an enhancement in lipid peroxidation. A declination in the level of thiol clearly indicated an increase in the protein oxidation as well as a decline in the reduced forms of ascorbate (AsA) and glutathione (GSH) and the ratios of their reduced to oxidized forms occurred in the salt-sensitive seedlings. Similar treatment caused a very little alteration or no change in the levels of these components in the seedlings of salt-tolerant cultivar. The activity of antioxidative enzymes superoxide dismutase (SOD), its isoform Cu/Zn-SOD and ascorbate peroxidase (APX) increased in both the cultivars against salinity. In salt-sensitive seedlings, the activity of the various enzymes, guaiacol peroxidase (GPX), catalase (CAT), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) increased at moderate salinity treatment of 7 dS m^?1 NaCl while the activities of these enzymes declined with higher salinity level of 14 dS m^?1 NaCl. However, a consistent increase was observed in the activities of these enzymes of salt-tolerant seedlings with an increase in the duration and the level of the salinity treatment. The results suggest that a higher status of antioxidants (AsA and GSH) and a coordinated higher activity of the enzymes (SOD, CAT, GPX, APX, and GR) can serve as the major determinants in the model for depicting salt tolerance in Indica rice seedlings.