The regulatory effect of melatonin on physiological,biochemical and molecular parameters in cold-stressed wheat seedlings

We investigated the possible mediatory role of melatonin in protecting wheat plants from cold stress. Ten-day-old wheat seedlings were pretreated with 1 mmol l^?1 melatonin for 12 h and subsequently exposed to stress conditions at 5/2 °C (day/night) for 3 days. Cold stress caused serious reductions in leaf surface area, water content, and photosynthetic pigment content, whereas melatonin application attenuated these reductions. Accumulation of reactive oxygen species (ROS), including superoxide and hydrogen peroxide, was very high in cold-stressed plants and caused lipid peroxidation in membranes. Concomitantly, ROS damaged the DNA profile and negatively influenced expression and/or activity of many enzymes, including RuBisCo. When compared to controls, cold-stressed plants had higher activities of the antioxidant enzymes superoxide dismutase, guaicol peroxidase, ascorbate peroxidase, and glutathione reductase and higher levels of the antioxidant compounds total ascorbate, reduced ascorbate, total glutathione, reduced glutathione, and phenolic substances; however, this elevation could not cope with the destructive effects of cold stress. Melatonin-pretreated plants exhibited greater increases in these parameters comparison with untreated cold-stressed plants. Isozyme bands monitored in native gel and RuBisCo expression supported these changes. Also, due to the cold-induced increase in dehydroascorbate and oxidized glutathione, the corrupted redox status in the cell was ameliorated by melatonin application. Similarly, levels of the osmoprotectants total soluble protein, carbohydrate, and proline were also increased by cold stress; however, melatonin-applied seedlings had a higher content of these solutes in comparison to untreated cold-stressed plants. We suggest that melatonin can improve plant resistance to cold stress in wheat seedlings by directly scavenging ROS and by modulating redox balance and other defence mechanisms.     

The antioxidant system in Suaeda salsa under salt stress

ABSTRACTSuaeda salsaL. is a typical euhalophyte and is widely distributed throughout the world. Suaeda plants are important halophyte resources, and the physiological and biochemical characteristics of their various organsand their response to salt stress have been intensively studied. Leaf succulence, intracellular ion localization, increased osmotic regulation and enhanced antioxidant capacities are important responses for Suaeda plants to adapt to salt stress. Among these responses, scavenging of reactive oxygen species (ROS) is an important mechanism for plants to withstand oxidative stress and improve salt tolerance. The generation and scavenging pathways of ROS, as well as the expression of scavenging enzymes change under salt stress. This article reviews the antioxidant system constitute of S. salsa, and the mechanisms by which S. salsaantioxidant capacity is improved for salt tolerance. In addition, the differences between types of antioxidant mechanisms in S. salsaare reviewed, thereby revealing the adaptation mechanisms of Suaeda to different habitats. The review provides important clues for the comprehensive understanding of the salt tolerance mechanisms of halophytes.KEYWORDS: Suaeda salsa, halophyte, salt-tolerance mechanism, oxidative stress, antioxidant system     

Antioxidative response mechanisms in halophytes: Their role in stress defence

Normal growth and development of plants is greatly dependent on the capacity to overcome environmental stresses. Environmental stress conditions like high salinity, drought, high incident light and low or high temperature cause major crop losses worldwide. A common denominator in all these adverse conditions is the production of reactive oxygen species (ROS) within different cellular compartments of the plant cell. Plants have developed robust mechanisms including enzymatic or nonenzymatic scavenging pathways to counter the deleterious effects of ROS production. There are a number of general reviews on oxidative stress in plants and few on the role of ROS scavengers during stress conditions. Here we review the regulation of antioxidant enzymes during salt stress in halophytes, especially mangroves. We conclude that (i) antioxidant enzymes protect halophytes from deleterious ROS production during salt stress, and (ii) genetic information from mangroves and other halophytes would be helpful in defining the roles of individual isoforms. This information would be critical in using the appropriate genes for oxidative stress defence for genetic engineering of enhanced stress tolerance in crop systems.     

Exogenous nitric oxide donor and arginine provide protection against short-term drought stress in wheat seedlings

Nitric oxide (NO) is an important plant signaling molecule that has a vital role in abiotic stress tolerance. In the present study, we assessed drought-induced (15 and 30% PEG, polyethylene glycol) damage in wheat (Triticum aestivum L. cv. Prodip) seedlings and mitigation by the synergistic effect of exogenous Arg (0.5 mM l-Arginine) and an NO donor (0.5 mM sodium nitroprusside, SNP). Drought stress sharply decreased the leaf relative water content (RWC) but markedly increased the proline (Pro) content in wheat seedlings. Drought stress caused overproduction of reactive oxygen species (ROS) and methylglyoxal (MG) due to the inefficiency of antioxidant enzymes, the glyoxalase system, and the ascorbate-glutathione pool. However, supplementation with the NO donor and Arg enhanced the antioxidant defense system (both non-enzymatic and enzymatic components) in drought-stressed seedlings. Application of the NO donor and Arg also enhanced the glyoxalase system and reduced the MG content by increasing the activities of the glyoxalase system enzymes (Gly I and Gly II), which restored the leaf RWC and further increased the Pro content under drought stress conditions. Exogenous NO donor and Arg application enhanced the endogenous NO content, which positively regulated the antioxidant system and reduced ROS production. Thus, the present study reveals the crucial roles of Arg and NO in enhancing drought stress tolerance in wheat seedlings by upgrading their water status and reducing oxidative stress and MG toxicity.     

Antioxidant Systems in Ripening Tomato Fruits

Two cultivars of tomato (Lycopersicon esculentum Mill.), Selection-7 (shelf life 7–8 d) and ARTH-3 (shelf life 14–15 d) were analyzed for oxidative stress and the antioxidant enzyme system at different stages of fruit ripening. The results presented here suggest that during the early stages of fruit ripening, efficient antioxidant system protects the tomato fruits against the damaging effect of progressive oxidative stress. At later stages, however, oxidative damage occurs due to decreased activities of the ROS scavenging enzymes.     

Seasonal variation in HSP70 expression and oxidative stress in skin of zebu (Tharparkar) and crossbred (Karan Fries) cattle under tropical climate

The study aimed to evaluate inducible HSP70 (HSP70.1 and HSP70.2) gene expression and oxidative stress status in skin of cattle during different seasons. Ten each of Tharparkar (zebu) and Karan Fries (crossbred) heifers were selected from NDRI herd, Karnal. Animals were maintained under standard managemental practices followed at the farm. Skin biopsies were aseptically collected from each animal during winter, spring, and summer. Real time PCR was performed to examine HSP70 expression. Reactive oxygen species (ROS) and antioxidant enzymes (SOD and CAT) were determined by ELISA. In both the breeds, significantly higher (p < 0.05) levels of HSP70 expression, ROS, caspases, and antioxidant enzymes were observed during summer followed by winter and spring. Breeds showed no significant difference during winter and spring. During summer, HSP70 expression, ROS, and antioxidant enzymes were higher (p < 0.05) in Karan Fries than Tharparkar, whereas caspases levels were higher in Tharparker than Karan Fries. The study concludes that levels of HSP70 expression, ROS, caspases, and antioxidant enzymes in skin of cattle were strongly affected by seasonal change in temperature. Differences exist in skin tissue thermotolerance of Tharparkar and Karan Fries cattle. This might be an efficient and centrally important mechanism for better adaptability of zebu cattle to heat stress.     

Analysis of reactive oxygen species and antioxidant defenses in complex I deficient patients revealed a specific increase in superoxide dismutase activity

The mechanism of free radical production by complex I deficiency is ill-defined, although it is of significant contemporary interest. This study studied the ROS production and antioxidant defenses in children with mitochondrial NADH dehydrogenase deficiency. ROS production has remained significantly elevated in patients compared to controls. The expression of all antioxidant enzymes significantly increased at mRNA level. However, the enzyme activities did not correlate with high mRNA or protein expression. Only the activity of superoxide dismutase (SOD) was found to correlate with higher mRNA expression in patient derived cell lines. The activities of the enzymes such as glutathione peroxidase (GPx), Catalase (CAT) and glutathione-S-transferase (GST) were significantly reduced in patients (p<0.05 or p<0.01). Glutathione reductase (GR) activity and intracellular glutathione (GSH) levels were not changed. Decreased enzyme activities could be due to post-translational or oxidative modification of ROS scavenging enzymes. The information on the status of ROS and marking the alteration of ROS scavenging enzymes in peripheral lymphocytes or lymphoblast cell lines will provide a better way to design antioxidant therapies for such disorders.     

Effect of sodium nitroprusside on heat resistance of wheat coleoptiles: Dependence on the formation and scavenging of reactive oxygen species

The effect of nitric oxide donor sodium nitroprusside (SNP) on resistance of coleoptiles of 4-day-old etiolated seedlings of wheat (Triticum aestivum L., cv. Elegiya) to damaging heating (10 min at 43°C) and possible dependence of this effect on changes in the activities of enzymes producing and scavenging reactive oxygen species (ROS) were studied. Treatment of coleoptiles with 500 μM SNP considerably boosted generation of superoxide anion radical therein. This effect was substantially suppressed by blocker of calcium channels (lanthanum chloride), calmodulin antagonist (chlorpromazine), and inhibitor of NADPH-oxidase (imidazole) but not by peroxidase inhibitor (salicylhydroxamic acid). NO donor activated antioxidant enzymes (superoxide dismutase, catalase, and soluble peroxidase) and elevated heat resistance of wheat coleoptiles. NO scavenger methylene blue, antioxidant agent ionol, calcium antagonists, and NADPH-oxidase inhibitor imidazole substantially reduced the elevation of heat resistance of wheat coleoptiles induced by NO donor. It was concluded that SNP-induced heat resistance of coleoptiles depended on calcium and ROS, whose production is probably boosted by activation of NADPH-oxidase.     

Potassium-Induced Regulation of Cellular Antioxidant Defense and Improvement of Physiological Processes in Wheat under Water Deficit Condition

Drought is the most common form of abiotic stress that reduces plant growth and productivity. It causes plant injuries through elevated production of reactive oxygen species (ROS). Potassium (K) is a vital plant nutrient that notably ameliorates the detrimental effect of drought stress in the plant. A pot experiment was conducted at the Laboratory of Plant Stress Responses, Faculty of Agriculture, Kagawa University, Japan, under controlled environment of green house to explore the role of K in mitigating drought severity in wheat (Triticum asevitum L.) seedlings. Three days after germination, seedlings were exposed to three water regimes viz., 100, 50, and 20% field capacity (FC) for 21 days. Potassium was adjusted in Hoagland nutrient solution at 0, 6 and 12 mM concentration and applied to pot instead of normal water. Results show that, water deficit stress notably reduced plant growth, biomass accumulation, leaf relative water content (RWC) along with reduced photosynthetic pigments. Increased amount of biochemical stress markers viz., malondialdehyde (MDA), hydrogen peroxide (H₂O₂), methylglyoxal (MG), proline (Pro) as well as an impaired antioxidant defense system were observed in drought affected wheat plants. On the contrary, K supplementation resulted in improvement of biochemical and physiological parameters that worked behind in improving growth and development of the wheat plants. In addition, enzymes of ascorbateglutathione (AsA-GSH) cycle were also enhanced by supplemented K that accelerated the ROS detoxification process in plant. Although glyoxalse system did not performed well till MG was detoxified might following another short stepped pathways. Our results revealed that drought stressed plants showed better performances in terms of biochemical and physiological attributes, antioxidant defense and glyoxalase system, as well as ROS detoxification due to K supplementation with better performance at 12 mM K added in 50% FC growing condition.     

Mitochondrial manganese-superoxide dismutase expression in ovarian cancer: role in cell proliferation and response to oxidative stress

Superoxide dismutases (SODs) are important antioxidant enzymes responsible for the elimination of superoxide radical (O(2)(-)). The manganese-containing SOD (Mn-SOD) has been suggested to have tumor suppressor function and is located in the mitochondria where the majority of O(2)(-) is generated during respiration. Although increased reactive oxygen species (ROS) in cancer cells has long been recognized, the expression of Mn-SOD in cancer and its role in cancer development remain elusive. The present study used a human tissue microarray to analyze Mn-SOD expression in primary ovarian cancer tissues, benign ovarian lesions, and normal ovary epithelium. Significantly higher levels of Mn-SOD protein expression were detected in the malignant tissues compared with normal tissues (p < 0.05). In experimental systems, suppression of Mn-SOD expression by small interfering RNA caused a 70% increase of superoxide in ovarian cancer cells, leading to stimulation of cell proliferation in vitro and more aggressive tumor growth in vivo. Furthermore, stimulation of mitochondrial O(2)(-) production induced an increase of Mn-SOD expression. Our findings suggest that the increase in Mn-SOD expression in ovarian cancer is a cellular response to intrinsic ROS stress and that scavenging of superoxide by SOD may alleviate the ROS stress and thus reduce the simulating effect of ROS on cell growth.     

Overexpression of the Wheat Expansin Gene TaEXPA2 Improved Seed Production and Drought Tolerance in Transgenic Tobacco Plants

Expansins are cell wall proteins that are grouped into two main families, α-expansins and β-expansins, and they are implicated in the control of cell extension via the disruption of hydrogen bonds between cellulose and matrix glucans. TaEXPA2 is an α-expansin gene identified in wheat. Based on putative cis-regulatory elements in the TaEXPA2 promoter sequence and the expression pattern induced when polyethylene glycol (PEG) is used to mimic water stress, we hypothesized that TaEXPA2 is involved in plant drought tolerance and plant development. Through transient expression of 35S::TaEXPA2-GFP in onion epidermal cells, TaEXPA2 was localized to the cell wall. Constitutive expression of TaEXPA2 in tobacco improved seed production by increasing capsule number, not seed size, without having any effect on plant growth patterns. The transgenic tobacco exhibited a significantly greater tolerance to water-deficiency stress than did wild-type (WT) plants. We found that under drought stress, the transgenic plants maintained a better water status. The accumulated content of osmotic adjustment substances, such as proline, in TaEXPA2 transgenic plants was greater than that in WT plants. Transgenic plants also displayed greater antioxidative competence as indicated by their lower malondialdehyde (MDA) content, relative electrical conductivity, and reactive oxygen species (ROS) accumulation than did WT plants. This result suggests that the transgenic plants suffer less damage from ROS under drought conditions. The activities of some antioxidant enzymes as well as expression levels of several genes encoding key antioxidant enzymes were higher in the transgenic plants than in the WT plants under drought stress. Collectively, our results suggest that ectopic expression of the wheat expansin gene TaEXPA2 improves seed production and drought tolerance in transgenic tobacco plants.     

WGA reduces the level of oxidative stress in wheat seedlings under salinity

Protective effect of exogenous wheat germ agglutinin (WGA) on wheat seedling (Triticum aestivum L.) during salinity stress was studied. In particular, we examined the state of pro- and antioxidant systems as well as the level of peroxide oxidation of lipids and electrolyte leakage under control conditions and when stressed with NaCl. Generation of superoxide anions and activity of both superoxide dismutase (SOD) and peroxidase increased during saline stress. Accumulation of O₂ ^·− resulted in peroxide oxidation of lipids and electrolyte leakage in response to stress. The injurious effect of salinity on root growth of seedlings was manifested by a decreased mitotic index (MI) in apical root meristem. This study show that WGA pretreatment decreased salt-induced superoxide anion generation, SOD and peroxidase activities, levels of lipid peroxidation and electrolytes leakage as well as correlating with a reduction in the inhibition of root apical meristem mitotic activity in salt-treated plants. This suggests that exogenous WGA reduced the detrimental effects of salinity-induced oxidative stress in wheat seedlings. Thus WGA effects on a balance of reactive oxygen species (ROS) and activities of antioxidant enzymes may provide an important contribution to a range of the defense reactions induced by this lectin in wheat plants.     

Effect of Terminalia arjuna on antioxidant defense system in cancer

Constant production of reactive oxygen species (ROS) during aerobic metabolism is balanced by antioxidant defense system of an organism. Although low level of ROS is important for various physiological functions, its accumulation has been implicated in the pathogenesis of age-related diseases such as cancer and coronary heart disease and neurodegenerative disorders such as Alzheimer’s disease. It is generally assumed that frequent consumption of phytochemicals derived from vegetables, fruits, tea and herbs may contribute to shift the balance towards an adequate antioxidant status. The present study is aimed to investigate the effect of aqueous extract of medicinal plant Terminalia arjuna on antioxidant defense system in lymphoma bearing AKR mice. Antioxidant action of T. arjuna is monitored by the activities of catalase, superoxide dismutase and glutathione S transferase which constitute major antioxidant defense system by scavenging ROS. These enzyme activities are low in lymphoma bearing mice indicating impaired antioxidant defense system. Oral administration of different doses of aqueous extract of T. arjuna causes significant elevation in the activities of catalase, superoxide dismutase and glutathione S transferase. T. arjuna is found to down regulate anaerobic metabolism by inhibiting the activity of lactate dehydrogenase in lymphoma bearing mice, which was elevated in untreated cancerous mice. The results indicate the antioxidant action of aqueous extract of T. arjuna, which may play a role in the anti carcinogenic activity by reducing the oxidative stress along with inhibition of anaerobic metabolism.     

Yeast Colony Survival Depends on Metabolic Adaptation and Cell Differentiation Rather Than on Stress Defense

Enzymes scavenging reactive oxygen species (ROS) are important for cell protection during stress and aging. A deficiency in these enzymes leads to ROS imbalance, causing various disorders in many organisms, including yeast. In contrast to liquid cultures, where fitness of the yeast population depends on its ROS scavenging capability, the present study suggests that Saccharomyces cerevisiae cells growing in colonies capable of ammonia signaling use a broader protective strategy. Instead of maintaining high levels of antioxidant enzymes for ROS detoxification, colonies activate an alternative metabolism that prevents ROS production. Colonies of the strain deficient in cytosolic superoxide dismutase Sod1p thus developed the same way as wild type colonies. They produced comparable levels of ammonia and underwent similar developmental changes (expression of genes of alternative metabolism and center margin differentiation in ROS production, cell death occurrence, and activities of stress defense enzymes) and did not accumulate stress-resistant suppressants. An absence of cytosolic catalase Ctt1p, however, brought colonies developmental problems, which were even more prominent in the absence of mitochondrial Sod2p. sod2Δ and ctt1Δ colonies failed in ammonia production and sufficient activation of the alternative metabolism and were incapable of center margin differentiation, but they did not increase ROS levels. These new data indicate that colony disorders are not accompanied by ROS burst but could be a consequence of metabolic defects, which, however, could be elicited by imbalance in ROS produced in early developmental phases. Sod2p and homeostasis of ROS may participate in regulatory events leading to ammonia signaling.     

Manipulation of oxidative stress responses as a strategy to generate stress-tolerant crops. From damage to signaling to tolerance

Plants exposed to hostile environmental conditions such as drought or extreme temperatures usually undergo oxidative stress, which has long been assumed to significantly contribute to the damage suffered by the organism. Reactive oxygen species (ROS) overproduced under stress conditions were proposed to destroy membrane lipids and to inactivate proteins and photosystems, ultimately leading to cell death. Accordingly, considerable effort has been devoted, over the years, to improve stress tolerance by strengthening antioxidant and dissipative mechanisms. Although the notion that ROS cause indiscriminate damage in vivo has been progressively replaced by the alternate concept that they act as signaling molecules directing critical plant developmental and environmental responses including cell death, the induction of genes encoding antioxidant activities is commonplace under many environmental stresses, suggesting that their manipulation still offers promise. The features and consequences of ROS effects depend on the balance between various interacting pathways including ROS synthesis and scavenging, energy dissipation, conjugative reactions, and eventually reductive repair. They represent many possibilities for genetic manipulation. We report, herein, a comprehensive survey of transgenic plants in which components of the ROS-associated pathways were overexpressed, and of the stress phenotypes displayed by the corresponding transformants. Genetic engineering of different stages of ROS metabolism such as synthesis, scavenging, and reductive repair revealed a strong correlation between down-regulation of ROS levels and increased stress tolerance in plants grown under controlled conditions. Field assays are scarce, and are eagerly required to assess the possible application of this strategy to agriculture.     

ZmMKK4 regulates osmotic stress through reactive oxygen species scavenging in transgenic tobacco

Mitogen-activated protein kinase kinase (MAPKKs) are important components of MAPK cascades, which are universal signal transduction modules and play important role in regulating both plant development and biotic or abiotic stress responses. In this study, we identified the group C MAPKK gene, ZmMKK4, in maize (Zea mays L.). Overexpression of ZmMKK4 in tobacco enhanced tolerance to osmotic stress by increased proline content and antioxidant enzyme (POD) activities compared with wild-type plants. RT-PCR revealed that one peroxidase (POX) gene, NtPOX1, was higher in ZmMKK4-overexpressing plants than in the wild-type plants. In addition, the accumulation of reactive oxygen species (ROS) in ZmMKK4-overexpressing plants is much less than that of wild-type plants. These results suggest that ZmMKK4 may be involved in ROS signaling. Taken together, these results indicate that ZmMKK4 is a positive regulator of osmotic stress by regulating scavenging of ROS in plants.     

Effects of ALA on Photosynthesis,Antioxidant Enzyme Activity,and Gene Expression,and Regulation of Proline Accumulation in Tomato Seedlings Under NaCl Stress

This study examined the effects of 5-aminolevulinic acid (ALA) application on photosynthesis, activity and gene expression of key antioxidant enzymes, and on proline accumulation in tomato (Lycopersicon esculentum Mill. ‘Hezuo 903’) seedlings under NaCl stress. NaCl stress significantly decreased the net photosynthetic rates and inhibited the activity of photosystem II, whereas exogenous ALA application significantly restored the net photosynthetic rates, quantum yield of electron transport, and energy conversion efficiency of photosystem II of tomato under NaCl stress. Production of superoxide, hydrogen peroxide, and malondialdehyde strongly increased in response to NaCl stress, and these increases were significantly counteracted by ALA. ALA increased the activity of reactive oxygen species (ROS) scavenging antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase, and upregulated the expression of SOD, APX, and POD, genes that encode these enzymes in NaCl-treated plants. ALA simultaneously increased proline accumulation in tomato seedlings under NaCl stress by regulating the expression of genes that encode ALA biosynthetic enzymes and that control proline biosynthesis and metabolism, for example, expression of GluRS and GluTR was downregulated, accompanied by a significant increase in the expression of P5CS and decline in the expression of ProDH. ALA provided protection against NaCl stress by increasing photosynthetic capacity, regulating antioxidant enzyme gene expression and proline accumulation, and decreasing ROS accumulation and lipid peroxidation in tomato.     

TaCYP81D5, one member in a wheat cytochrome P450 gene cluster,confers salinity tolerance via reactive oxygen species scavenging

As one of the largest gene families in plants, the cytochrome P450 monooxygenase genes (CYPs) are involved in diverse biological processes including biotic and abiotic stress response. Moreover, P450 genes are prone to expanding due to gene tandem duplication during evolution, resulting in generations of novel alleles with the neo‐function or enhanced function. Here, the bread wheat (Triticum aestivum) gene TaCYP81D5 was found to lie within a cluster of five tandemly arranged CYP81D genes, although only a single such gene (BdCYP81D1) was present in the equivalent genomic region of the wheat relative Brachypodium distachyon. The imposition of salinity stress could up‐regulate TaCYP81D5, but the effect was abolished in plants treated with an inhibitor of reactive oxygen species synthesis. In SR3, a wheat cultivar with an elevated ROS content, the higher expression and the rapider response to salinity of TaCYP81D5 were related to the chromatin modification. Constitutively expressing TaCYP81D5 enhanced the salinity tolerance both at seedling and reproductive stages of wheat via accelerating ROS scavenging. Moreover, an important component of ROS signal transduction, Zat12, was proven crucial in this process. Though knockout of solely TaCYP81D5 showed no effect on salinity tolerance, knockdown of BdCYP81D1 or all TaCYP81D members in the cluster caused the sensitivity to salt stress. Our results provide the direct evidence that TaCYP81D5 confers salinity tolerance in bread wheat and this gene is prospective for crop improvement.