Mn-SOD Isoform Research Articles

Implication of Mn-cofactored superoxide dismutase in the tolerance of swarmer Pseudomonas aeruginosa to polymixin, ciprofloxacin and meropenem antibiotics.

The protective role of superoxide dismutase (Sod) against oxidative stress, resulting from the common antibiotic pathway of action, has been studied in the wild type and mutant strains of swarmer Pseudomonas aeruginosa, lacking Cytosolic Mn-Sod (sodM), Fe-Sod (sodB) or both Sods (sodMB).Our results showed that inactivation of sodB genes leads to significant motility defects and tolerance to meropenem. This resistance is correlated with a greater membrane unsaturation as well as an effective intervention of Mn-Sod isoform, in antibiotic tolerance.Moreover, loss of Mn-Sod in sodM mutant, leads to polymixin intolerance and is correlated with membrane unsaturation. Effectivelty, sodM mutant showed an enhanced swarming motility and a conserved rhamnolipid production. Whereas, in the double mutant sodMB, ciprofloxacin tolerance would be linked to an increase in the percentage of saturated fatty acids in the membrane, even in the absence of superoxide dismutase activity.The overall results showed that Mn-Sod has a protective role in the tolerance to antibiotics, in swarmer P.aeruginosa strain. It has been further shown that Sod intervention in antibiotic tolerance is through change in membrane fatty acid composition.

Senescence-specific change in ROS scavenging enzyme activities and regulation of various SOD isozymes to ROS levels in psf mutant rice leaves

To clarify the interaction between different antioxidant enzymes for monitoring oxidative stress and ROS burst in rice senescent leaves, we investigated the genotype-dependent alteration in temporal patterns of the O2•− production rate, H2O2 content, and ROS–scavenging enzyme activities during leaf senescence in two rice genotypes, namely, the premature senescence of flag leaf (psf) mutant and its wild type. Results showed that the psf mutant differed obviously from its wild type in leaf O2•− generation rate and H2O2 content accumulation, and the decreased activities of SOD, CAT, and APX in the psf leaves were strongly responsible for the increased ROS level and the accelerated leaf senescence. By contrast, the increase in POD activity was positively correlated with the senescence-related enhancement in O2•− generation in rice leaves. Among various SOD isoforms, Mn–SOD responded sensitively to the increasing O2•− generation rate, whereas Cu/Zn–SOD remained stable with the progression of leaf senescence. These findings suggest that the senescence-related decline in total SOD activity was mostly attributable to the downregulation of both the translation and transcription of Mn–SOD isoform. This occurrence finally resulted in the collapse of SOD defense system and accelerated leaf senescence for the psf mutant. Furthermore, we presented the possible contribution of several Cu/Zn–SOD expression patterns to the senescence-related O2•− detoxification in different cell compartments.

Variability in Superoxide Dismutase Isoforms in Tall and Dwarf Cultivars of Coconut (Cocos nucifera L.) Leaves

Superoxide dismutases (SODs) are ubiquitous metallo-enzymes that constitute the first line of defense against reactive oxygen species (ROS). They constitute one of the major enzymatic components of detoxi?cation of superoxide radicals generated in biological system by catalyzing its dismutation to H2O2 and finally to H2O and O2. Most plant species contain numerous SOD isoforms differing in their active site metal ions. In the present investigation, we have attempted to identify variability in superoxide dismutase (EC 1.15.1.1) isoform pattern of 13 coconut genotypes comprising six talls, five dwarfs along with two reciprocal hybrids of WCT (Tall) with COD (Dwarf). Among the genotypes studied, a significant variation was observed in SOD enzyme activity as well as in SOD isoforms pattern. A total of eight to fourteen SOD isoforms were detected in different coconut cultivars. The variation was observed only in Mn-SOD isoforms while Fe-SOD (two) and Cu/Zn-SOD (five) isoforms were similar in all the analyzed cultivars. Mn-SOD isoforms varied from one to five in numbers. Among the tall cultivars, WCT, FMST and WCT X COD showed highest number (five) of Mn-SOD isoforms as well as highest enzymatic activity followed by LCT while TPT, PHOT and ADOT showed only single isoform for Mn-SOD. All dwarfs studied were found to have similar SOD isozyme profile for all SODs i.e. one Mn-SOD, five Cu/Zn-SOD and two Fe-SOD isoforms. It was also observed that Mn-SOD does not follow the Mendelian pattern of inheritance i.e. reciprocal crosses showed Mn-SOD isoform pattern similar to their mother palm. SOD activity and isoform pattern can be utilized as a biochemical marker for varietal identification and for abiotic stress/drought tolerance breeding.

Nitric oxide triggers a concentration-dependent differential modulation of superoxide dismutase (FeSOD and Cu/ZnSOD) activity in sunflower seedling roots and cotyledons as an early and long distance signaling response to NaCl stress

Dark-grown sunflower (Helianthus annuus L.) seedlings exhibit modulation of total superoxide dismutase (SOD;EC 1.15.1.1) activity in roots and cotyledons (10,000g supernatant) in response to salt stress (NaCl; 120 mM) through a differential, zymographically detectable, whole tissue activity of FeSOD and Cu/ZnSOD. Confocal laser scanning microscopic imaging (CLSM) has further shown that NaCl stress significantly influences differential spatial distribution of Cu/ZnSOD and MnSOD isoforms in an inverse manner. Dual action of nitric oxide (NO) is evident in its crosstalk with FeSOD and Cu/ZnSOD in seedling roots and cotyledons in control and NaCl− stress conditions. Cu/ZnSOD activity in the roots of 2 d old NaCl− stressed seedlings is enhanced in the presence of 125–1000 µM of NO donor (sodium nitroprusside; SNP) indicating salt sensitivity of the enzyme activity. Quenching of endogenous NO by cPTIO treatment (500, 1000 µM) lowers FeSOD activity in roots (-NaCl). Cotyledons from control seedlings show an upregulation of FeSOD activity with increasing availability of SNP (125–1000 µM) in the Hoagland irrigation medium. Quenching of NO by cPTIO provides evidence for an inverse correlation between NO availability and FeSOD activity in seedling cotyledons irrespective of NaCl stress. Variable response due to NO on SOD isoforms in sunflower seedlings reflects its concentration-dependent biphasic (pro- and antioxidant) nature of action. Differential induction of SOD isoforms by NO indicates separate intracellular signaling pathways (associated with their respective functional separation) operative in seedling roots as an early salt stress mechanism and in cotyledons as an early long-distance NaCl stress sensing mechanism.

Subcellular localization and responses of superoxide dismutase isoforms in local wheat varieties subjected to continuous soil drought

Water is a key factor influencing the yield and quality of crops. One of the parameters of plant biological tolerance to constantly changing environmental conditions is the change of activities and numerous molecular forms of antioxidant enzymes. Two durum (Triticum durum Desf.) wheat varieties contrasting for drought tolerance, such as Barakatli-95 (drought tolerant) and Garagylchyg-2 (drought sensitive) were grown over a wide area in the field. Experiments were carried out to study the effect of soil drought on changes in activities and subcellular localization of superoxide dismutase isoforms. The levels of malondialdehyde, glycine betaine and total proteins were also analyzed. The level of the enzyme activity appeared to depend on the wheat varieties, duration of drought and stages of leaf development. Native polyacrylamide gel electrophoresis (PAGE) revealed the presence of 9 isoenzymes of superoxide dismutase in wheat leaves during drought. Mn-SOD was found in the mitochondrial fractions, Fe-SOD in the chloroplast fraction and Cu/Zn-SOD is localized in all subcellular fractions. Wheat leaves contain three different isoforms of SOD (Mn-, Fe-, Cu/Zn-SOD). Three isoforms of Mn-SOD, one isoform of Fe-SOD and five of Cu/Zn-SOD were observed in wheat leaves using 3 mM KCN and 5 mM H2O2 as selective inhibitors. The expression of Mn-SOD was preferentially enhanced by drought stress. It seems that Mn-SOD isoforms more than SOD ones play a major role in the scavenging of superoxide radicals. The observed data showed that status of antioxidant enzymes such as SOD could provide a meaningful tool for depicting drought tolerance of wheat genotype.

Antioxidant enzymatic activities and gene expression associated with heat tolerance in the stems and roots of two cucurbit species ("Cucurbita maxima" and "Cucurbita moschata") and their interspecific inbred line "Maxchata".

The elucidation of heat tolerance mechanisms is required to combat the challenges of global warming. This study aimed to determine the antioxidant enzyme responses to heat stress, at the enzymatic activity and gene expression levels, and to investigate the antioxidative alterations associated with heat tolerance in the stems and roots of squashes using three genotypes differing in heat tolerance. Plants of heat-tolerant “C. moschata”, thermolabile “C. maxima” and moderately heat-tolerant interspecific inbred line “Maxchata” genotypes were exposed to moderate (37 °C) and severe (42 °C) heat shocks. “C. moschata” exhibited comparatively little oxidative damage, with the lowest hydrogen peroxide (H2O2), superoxide (O2−) and malondialdehyde (MDA) contents in the roots compared to stems, followed by “Maxchata”. The enzyme activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD) were found to be increased with heat stress in tolerant genotypes. The significant inductions of FeSOD, MnSOD, APX2, CAT1 and CAT3 isoforms in tolerant genotypes suggested their participation in heat tolerance. The differential isoform patterns of SOD, APX and CAT between stems and roots also indicated their tissue specificity. Furthermore, despite the sequence similarity of the studied antioxidant genes among “C. maxima” and “Maxchata”, most of these genes were highly induced under heat stress in “Maxchata”, which contributed to its heat tolerance. This phenomenon also indicated the involvement of other unknown genetic and/or epigenetic factors in controlling the expression of these antioxidant genes in squashes, which demands further exploration.

Effect of macro- and micro-nutrient limitation on superoxide dismutase activities and carotenoid levels in microalga Dunaliella salina CCAP 19/18

The aim of this study was to assess the effects of sixteen stress conditions on total carotenoid production and the response of antioxidative enzyme superoxide dismutase (SOD) in microalga Dunaliella salina. Of the stress conditions tested, high-light illumination (240 μmol photons m(-2) s(-1)) in combination with nitrogen depletion were the conditions associated with maximum carotenoid production and which induced Fe-SOD and retained the specific Mn-SOD isoform. Removal of the micronutrients manganese (Mn), Zinc (Zn) and Iron (Fe) as well as nitrogen from the medium enhanced carotenoid production on day 5, while the removal of nitrogen and Mn from the growth medium drastically affected carotenoid production at all time-points. The differential response of SODs influences the levels of carotenoid biosynthesis as chronic molecular defence strategies of D. salina.

Antioxidative Responses in Calli of Two Populations of Acanthophyllum laxiusculum With and Without B-chromosomes under Salt Stress

Salinity is one of the most significant stresses that affect plant growth and agricultural production. Considerable efforts have therefore been made to investigate how plants respond to salt stress. To investigate the responses of Acanthophyllum to salinity stress, changes on lipid peroxidation, H2O2 content and the activity of antioxidant enzymes in calli of two Acanthophyllum laxiusculum variants, without (variant A) and with (variant B) B-chromosomes, were analyzed. Under salinity stress, lipid peroxidation and H2O2 content decreased in variant A compared to variant B. Moreover, variant A produced a higher amount of proline under salt stress than variant B. In calli of variant A, salinity stress preferentially enhanced the activities of the superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2), whereas it decreased their activity in variant B. Guaiacol peroxidase (GPX, EC 1.11.1.7) activity decreased with increasing NaCl concentrations in variant A but its activity increased in variant B. After native polyacrylamide gel electrophoresis (PAGE) analysis, calli of both A and B variants had only Mn-SOD and Fe-SOD isoforms. Expression of the isoforms mentioned above, showed marked increase in variant A; while in variant B salinity caused a significant reduction as compared to control. Moreover, changes in the CAT and GPX isoforms pattern of treated plants were in accordance with the activity changes in time. These results suggest that variant A was able to induce better antioxidative responses against salt stress than variant B.

Antioxidant response to drought in red and white clover

Antioxidant response to drought in red (Trifolium pratense L., cv. “Start”) and white clover (Trifolium repens L, cv. “Haifa” and cv. “Debut”) grown as soil cultures was evaluated in water-deprived and recovered plants. Drought provoked oxidative stress in leaves confirmed by the considerable changes in electrolyte leakage, malondialdehyde, hydrogen peroxides and proline contents. Immunoblot of Δ-1-pyrroline-5-carboxylate synthetase (P5CS), which catalyzes the first two steps in proline biosynthesis, revealed strong induction of the enzyme in red clover plants submitted to drought. Water-deprived white clover plants exhibited distinct P5CS profiles. This was related to different drought tolerance of the studied T. repens cultivars. Isoenzyme analyses of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) demonstrated certain differences in antioxidant defence among the tested varieties. It was confirmed that MnSOD (in both T. repens and T pratense) and FeSOD (in T. repens) isoforms were the most affected by drought. The red clover cultivar “Start” exhibited the lowest FeSOD and POX activities which could contribute to its poor performance under water deprivation.

The effect of hypoxia on intermediary metabolism and oxidative status in gilthead sea bream (Sparus aurata) fed on diets supplemented with methionine and white tea

The present study evaluates the influence of previous nutritional status, fish fed on diets supplemented with tea and methionine, on acute hypoxia tolerance and subsequent recovery of Sparus aurata juveniles. Four isonitrogenous (45% of protein) and isolipidic (18% lipid) diets were formulated to contain 0.3% methionine, 2.9% white tea dry leaves or 2.9% of white tea dry leaves+0.3% methionine. An unsupplemented diet was used as control. Hepatic key enzymes of intermediary metabolism and antioxidant status, superoxide dismutase isoenzyme profile, glutathione (total, reduced and oxidized) and oxidative damage markers were determined under normoxia, hypoxia challenge and during normoxia recovery. Dietary white tea inclusion decreased plasma glucose levels under normoxia and seemed to induce an increase in anaerobic pathways as showed by enhanced liver lactate dehydrogenase activity. Hypoxia challenge reversed some of the responses induced by diet tea supplementation. Hypoxia decreased plasma glucose levels, increased glucose 6-P-dehydrogeanse activity, decreased superoxide dismutase activity (especially Mn-SOD and CuZn-SOD isoforms) and increased glutathione peroxidase activity in all dietary treatments. Catalase activity during hypoxia varied with dietary treatments and glutathione reductase was not modified. Antioxidant defenses were insufficient to avoid an oxidative stress condition under hypoxia, independently of dietary treatment. In general, pre-challenge values were recovered for almost all parameters within 6h recovery time.

Toxic Effects of Imidazolium Ionic Liquids on the Green Seaweed Ulva lactuca: Oxidative Stress and DNA Damage

The green credentials of ionic liquids (ILs) are being increasingly questioned due to the growing evidence of their toxicity to aquatic ecosystems, although the mechanisms of toxicity are unknown. This study provides insights into the mechanism of toxicity and biological effects of 1-alkyl-3-methylimidazolium bromide [C(n)mim]Br (n = 4 to 16) on the marine macroalga Ulva lactuca. The cell viability of this alga during IL exposure was found to be negatively correlated to the chain length of the alkyl group. The IL ([C(12)mim]Br) exposure triggers the generation of reactive oxygen species (ROS viz. O(2)(•-), H(2)O(2), and OH(•)), damage of the membrane and DNA, and inhibition of antioxidant systems in the alga. The enhanced production of ROS and lipid peroxidation in the alga subjected to LC(50) concentration for 4 days was largely attributed to lipoxygenase (LOX) activity coupled with the induction of two LOX isoforms (~80 kDa and ~55 kDa). Pretreatment of the algal thallus with enzyme inhibitors such as diphenylene iodonium, sodium azide, cantharidin, and oxadiazoloquinoxalin-1-one, prior to [C(12)mim]Br exposure showed the regulation of ROS by the activation of membrane bound NADPH-oxidase and cytochrome oxidase. The IL exposure resulted in the accumulation of n-3 and n-6 fatty acids at 0.5 LC(50) concentration indicating the induction of desaturase enzymes. Furthermore, antioxidant enzyme activities such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) were enhanced by 1.3-2.0-fold, while glutathione peroxidase (GSH-Px) diminished, together with a higher regeneration rate of reduced ascorbate and glutathione. The isoforms of antioxidant enzymes, namely, Mn-SOD (~85 kDa), APX (~125 and 45 kDa), and GR (~135 kDa) regulated differentially to IL exposure. The comet assay performed for the first time for seaweeds revealed the significant induction of DNA damage (>50-70% increase in % tail DNA over control) in alga exposed to ≥ LC(50) concentration.

The effect of salt stress on lipid peroxidation and antioxidative enzymes in callus of two Acanthophyllum 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.

Exogenous proline modifies differential expression of superoxide dismutase genes in UV-B-irradiated Salvia officinalis plants

Grown in water culture 6-week-old Salvia officinalis plants with 4–5 true leaves were exposed to irradiation with UV-B (10 min, 12.3 kJ/m2), subjected to 5 mM exogenous proline in the nutrient solution, and treated with a combination of both factors. The plants responded to short UV-B irradiation by the appearance of oxidative stress, which was manifested in elevated content of malondialdehyde in leaves. Exogenous proline added 24 h before the irradiation inhibited lipid peroxidation. The total activity of superoxide dismutase (SOD) was analyzed in plant leaves, and three SOD isoforms—Mn-SOD, Fe-SOD, and Cu/Zn-SOD—were identified. Activities of these isoforms were measured over time, and the expression of their respective genes was analyzed by reverse transcription polymerase chain reaction (RT-PCR). It is shown that the addition of proline, UV-B irradiation, or combination of both treatments regulated in a differential manner the activities of SOD isoforms localized in various cell compartments. The activity of the cytosolic Cu/Zn-SOD isoform was limited by the presence of its mRNA, the content of which was regulated by mRNA synthesis or decay rate. By contrast, the activity of plastidic Fe-SOD isoform was regulated on the substrate (allosteric) level, not on the level of FSD gene expression. The activity of mitochondrial Mn-SOD isoform was insensitive to UV-B irradiation, addition of proline, or combination of both treatments, even though the level of MSD gene transcripts increased significantly after UV-B irradiation. The results indicate that MSD gene transcripts induced by UV-B were not completely processed to produce mature mRNA or mature mRNA was not capable of translation. It cannot be excluded that the synthesized macromolecule, the Mn-SOD precursor did not undergo posttranslational maturation to produce biologically active enzyme molecules. It appears that proline is involved in the differentially regulated complex expression of various SOD isoforms. This regulation is largely based on various extents of oxidative stress in different cell compartments.

The combined effect of anthracene and cadmium on photosynthetic activity of three Desmodesmus (Chlorophyta) species

Individual toxicity of heavy metals (HM) and polycyclic aromatic hydrocarbons (PAH) to plants living in water bodies is well-documented. In view of frequent joint occurrence of these compounds in the environment, plants are subjected to damage from their combined action. Cadmium and anthracene can generate production of reactive oxygen species (ROS). We have recently detected elevated activity of Fe- and Mn-SOD isoforms, indicating chloroplast and mitochondrion as the main sites of combined toxicity of HM and PAH. In the present paper, short-term (1–24h) experiments on the mechanism of combined toxicity of anthracene and cadmium to the photosynthesis of three Desmodesmus species are reported. Inhibition, stimulation or no effect on the oxygen evolution was observed following the treatment with the contaminants when applied either separately or jointly. The response pattern was both strongly species- and time-dependent. In contrast, the photosynthetic activity of cells, expressed by chlorophyll fluorescence parameters, was substantially unaffected, since no effect or, in several cases, a slight stimulation of PS II quantum efficiency (Φ PS II) were noted. A characteristic relationship between the SOD activity and the qN values was observed. The treatment of Desmodesmus cells with anthracene or cadmium had either no effect or slightly enhanced either the SOD activity or the qN value, whereas the mixture of the contaminants resulted in a multifold increase in both the SOD activity and the qN values. The results suggest that chloroplasts of algae are well protected against the combined action of the two contaminants the toxicity of which should be attributed to nucleocytoplasmic compartments and reproductive processes of the cell cycle.

Antioxidant enzymes changes in response to drought stress in ten cultivars of oilseed rape (Brassica napus L.)

The study was undertaken to identify the responses of antioxidant enzyme activities and their isozyme patterns in seedlings of 10 oilseed rape (Brassica napus L.) cultivars under drought stress conditions. Plants were grown under three irrigation regimes (FC; field capacity, 60% FC and 30% FC) in a greenhouse. Drought stress preferentially enhanced the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD) whereas it decreased catalase (CAT) activity. Licord with the highest level of enzyme activity under both optimum and limited irrigation regimes is reported as the most tolerant cultivar. Whereas Hyola 308 and Okapy, having the lowest enzymes activities, are mentioned as cultivars sensitive to drought stress. The native polyacrylamide gel electrophoresis (PAGE) analysis detected eight SOD isozymes. Oilseed rape leaves contained three isoforms of Mn-SOD and five isoforms of Cu/Zn-SOD. The expression of Mn-SOD was preferentially enhanced by drought stress. Five POD isoforms were detected in oilseed rape leaves. The intensities of POD-4 and -5 were enhanced under drought stress. According to the results, the appearance of new isozyme bands under drought stress conditions may be used as a biochemical marker to differentiate drought tolerant cultivars under drought stress.

Protection of insulin-producing cells against toxicity of dexamethasone by catalase overexpression

Pancreatic β cells are very sensitive to reactive oxygen species (ROS) and this might play an important role in β cell death in diabetes. Dexamethasone is a synthetic diabetogenic glucocorticoid, which impairs pancreatic β cell function. Therefore we investigated the toxicity of dexamethasone in RINm5F insulin-producing cells and its dependence on the expression level of the antioxidant enzyme catalase, which inactivates hydrogen peroxide. This was correlated with oxidative stress and cell death. An increased generation of ROS was observed in dexamethasone-treated cells together with an increase in caspase-3 activity and apoptosis rate. Interestingly, exposure to dexamethasone increased the cytosolic superoxide dismutase Cu/ZnSOD protein expression and activity, whereas the mitochondrial MnSOD isoform was not affected by the glucocorticoid. Catalase overexpression in insulin-producing cells prevented all the cytotoxic effects of dexamethasone. In conclusion, dexamethasone-induced cell death in insulin-producing cells is ROS mediated. Increased levels of expression and activity of the Cu/ZnSOD might favor the generation of hydrogen peroxide in dexamethasone-treated cells. Increased ROS scavenging capacity in insulin-producing cells, through overexpression of catalase, prevents a deleterious increase in hydrogen peroxide generation and thus prevents dexamethasone-induced apoptosis.

Antioxidative protection and proteolytic activity in tolerant and sensitive wheat (Triticum aestivum L.) varieties subjected to long-term field drought

Field drought studies were performed in order to assess oxidative stress, proteolytic activity and yield loss under natural stress conditions. Flag leaves of two drought-tolerant (Yantar and Zlatitsa) and two drought-sensitive (Miziya and Dobrudjanka) winter wheat varieties were analyzed. Stress intensity was assessed by relative electrolyte leakage and proline accumulation. Senescence progression was followed by loss of chlorophyll and protein. Lipid peroxidation, H2O2 content, activities of superoxide dismutase (SOD), catalase (CAT), and non-specific peroxidase (GPX) isoforms, as well as proteolytic activities were analyzed from heading throughout grain filling. Weakening of membrane integrity and oxidative damage to lipids were more pronounced in the sensitive varieties under field drought. The activities of Fe- and Cu/Zn SOD isoforms decreased in the controls, but remained high in drought-treated plants. The activities of MnSOD isoforms and CAT were enhanced towards grain filling, especially in the sensitive varieties under drought. GPX activities were rised under drought but progressively diminished. Accelerated senescence under field drought was linked to higher proteolytic activity with variety specific differences in the protease response, but without a clear correlation to drought resistance or sensitivity. Field drought led to higher oxidative stress more pronounced for drought sensitive varieties, especially during the grain filling period.

Modulation of longevity and diapause by redox regulation mechanisms under the insulin-like signaling control in Caenorhabditis elegans

In Caenorhabditis elegans, the downregulation of insulin-like signaling induces lifespan extension (Age) and the constitutive formation of dauer larvae (Daf-c). This also causes resistance to oxidative stress (Oxr) and other stress stimuli and enhances the expression of many stress-defense-related enzymes such as Mn superoxide dismutase (SOD) that functions to remove reactive oxygen species in mitochondria. To elucidate the roles of the two isoforms of MnSOD, SOD-2 and SOD-3, in the Age, Daf-c and Oxr phenotypes, we investigated the effects of a gene knockout of MnSODs on them in the daf-2 (insulin-like receptor) mutants that lower insulin-like signaling. In our current report, we demonstrate that double deletions of two MnSOD genes induce oxidative-stress sensitivity and thus ablate Oxr, but do not abolish Age in the daf-2 mutant background. This indicates that Oxr is not the underlying cause of Age and that oxidative stress is not necessarily a limiting factor for longevity. Interestingly, deletions in the sod-2 and sod-3 genes suppressed and stimulated, respectively, both Age and Daf-c. In addition, the sod-2/ sod-3 double deletions stimulated these phenotypes in a similar manner to the sod-3 deletion, suggesting that the regulatory pathway consists of two MnSOD isoforms. Furthermore, hyperoxic and hypoxic conditions affected Daf-c in the MnSOD-deleted daf-2 mutants. We thus conclude that the MnSOD systems in C. elegans fine-tune the insulin-like-signaling based regulation of both longevity and dauer formation by acting not as antioxidants but as physiological-redox-signaling modulators.

Differential response of antioxidative enzymes in embryonic axes and cotyledons of germinating lupine seeds

Germination of lupine (Lupinus luteus L.) seeds was accompanied by an increase in concentration of free radicals with g1 and g2 values of 2.0056 ± 0.0003 and 2.0033 ± 0.0005, respectively. The highest intensity of free radical signal was observed in embryo axes immediately after radicle protruded through the seed coat. Hydrogen peroxide accumulated in embryonic axes and cotyledons during imbibition before the onset of germination in the seed population. The activities of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) rose progressively in embryo axes. In cotyledons SOD activity did not change significantly, while that of CAT increased during germination. The enhancement of Cu, Zn-SODs and Mn-SOD isoforms in embryonic axes was observed. A new isoform of catalase was synthesized, suggesting that it plays a relevant role during germination. SOD and CAT activities were detected in dry seeds. Free radical generation and response of antioxidative enzymes differed between embryo axes and cotyledons during the germination timecourse.

Photochemical damage and comparative performance of superoxide dismutase and ascorbate peroxidase in sugarcane leaves exposed to paraquat-induced oxidative stress

The physiological responses of sugarcane ( Saccharum officinarum L.) to oxidative stress induced by methyl viologen (paraquat) were examined with respect to photochemical activity, chlorophyll content, lipid peroxidation and superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. Thirty-day-old sugarcane plants were sprayed with 0, 2, 4, 6 and 8 mM methyl viologen (MV). Chlorophyll fluorescence was measured after 18 h and biochemical analyses were performed after 24 and 48 h. Concentrations of MV above 2 mM caused significant damage to photosystem II (PSII) activity. Potential and effective quantum efficiency of PSII and apparent electron transport rate were greatly reduced or practically abolished. Both chlorophyll and soluble protein contents steadily decreased with MV concentrations above 2 mM after 24 h of exposure, which became more pronounced after 48 h, achieving a 3-fold decrease. Insoluble protein contents were little affected by MV. Oxidative stress induced by MV was evidenced by increases in lipid peroxidation. Specific activity of SOD increased, even after 48 h of exposure to the highest concentrations of MV, but total activity on a fresh weight basis did not change significantly. Nondenaturing PAGE assayed with H 2O 2 and KCN showed that treatment with MV did not change Cu/Zn-SOD and Mn-SOD isoform activities. In contrast, APX specific activity increased at 2 mM MV but then dropped at higher doses. Oxidative damage induced by MV was inversely related to APX activity. It is suggested that the major MV-induced oxidative damages in sugarcane leaves were related to excess H 2O 2, probably in chloroplasts, caused by an imbalance between SOD and APX activities, in which APX was a limiting step. Reduced photochemical activity allowed the early detection of the ensuing oxidative stress.