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

Nitric oxide in plants: an insight on redox activity and responses toward abiotic stress signaling

Plants, as sessile organisms, are subjected to diverse abiotic stresses, including salinity, desiccation, metal toxicity, thermal fluctuations, and hypoxia at different phases of plant growth. Plants can activate messenger molecules to initiate a signaling cascade of response toward environmental stresses that results in either cell death or plant acclimation. Nitric oxide (NO) is a small gaseous redox-active molecule that exhibits a plethora of physiological functions in growth, development, flowering, senescence, stomata closure and responses to environmental stresses. It can also facilitate alteration in protein function and reprogram the gene profiling by direct or indirect interaction with different target molecules. The bioactivity of NO can be manifested through different redox-based protein modifications including S-nitrosylation, protein nitration, and metal nitrosylation in plants. Although there has been considerable progress in the role of NO in regulating stress signaling, still the physiological mechanisms regarding the abiotic stress tolerance in plants remain unclear. This review summarizes recent advances in understanding the emerging knowledge regarding NO function in plant tolerance against abiotic stresses. The manuscript also highlighted the importance of NO as an abiotic stress modulator and developed a rational design for crop cultivation under a stress environment.

Overexpression of rice lectin receptor-like kinase, OsLec-RLK, confers salinity stress tolerance and increases seed yield in pigeon pea (Cajanus cajan (L.) Millsp.)

KEY MESSAGE

OsLec-RLK overexpression enhances cell signalling and salt stress tolerance in pigeon pea, enhancing seed yield and harvest index and thus, enabling marginal lands to increase food and nutritional security. Lectin Receptor-like kinases (Lec-RLKs) are highly effective cell signaling molecules that counteract various stresses, including salt stress. We engineered pigeon pea by overexpressing OsLec-RLK gene for enhancing salt tolerance. The OsLec-RLK overexpression lines demonstrated superior performance under salt stress, from vegetative to reproductive phase, compared to wild types (WT). The overexpression lines had significantly higher K+/Na+ ratio than WT exposed to 100 mM NaCl. Under salt stress, transgenic lines showed higher levels of chlorophyll, proline, total soluble sugars, relative water content, and peroxidase and catalase activity than WT plants. Membrane injury index and lipid peroxidation were significantly reduced in transgenic lines. Analysis of phenological and yield attributes confirmed that the OsLec-RLK pigeon pea lines maintain plant vigor, with 10.34-fold increase in seed yield (per plant) and 4-5-fold increase in harvest index of overexpression lines, compared to wild type. Meanwhile, the overexpression of OsLec-RLK up-regulated the expression levels of histone deacetylase1, acyl CoA, ascorbate peroxidase, peroxidase, glutathione reductase and catalase, which were involved in the K+/Na+ homeostasis pathway. This study showed the potential of OsLec-RLK gene for increasing crop productivity and yields under salt stress and enabling the crops to be grown on marginal lands for increasing food and nutritional security.

Involvement of GLR-mediated nitric oxide effects on ROS metabolism in Arabidopsis plants under salt stress

Plant glutamate receptor-like channels (GLRs) play important roles in plant development, immune response, defense signaling and Nitric oxide (NO) production. However, their involvement in abiotic stress responses, particularly in regulating Reactive Oxygen Species (ROS), is not well understood. This study aimed to investigate GLR-mediated NO production on ROS regulation in salt-stressed cells. To achieve this, Arabidopsis thaliana Columbia (Col-0) were treated with NaCl, glutamate antagonists [(DNQX (6,7-dinitroquinoxaline-2,3-dione and AP-5(D-2-amino-5-phosphono pentanoic acid)], and NO scavenger [cPTIO (2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt)]. Salt-stressed plants in combination with DNQX and AP-5 have exhibited higher increase in lipid peroxidation (TBARS), hydrogen peroxide (H2O2) and superoxide radical (O-2) contents as compared to solely NaCl-treated plants. Furthermore, NO and total glutathione contents, and S-nitrosoglutathione reductase (GSNOR) activity decreased with these treatments. AP-5 and DNQX increased the activities of NADPH oxidase (NOX), catalase (CAT), peroxidase (POX), cell wall peroxidase (CWPOX) in salt-stressed Arabidopsis leaves. However, their activities (except NOX) were significantly inhibited by cPTIO. Conversely, the combination of NaCl and GLR antagonists, NO scavenger decreased the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) resulting in elevated GSSG levels, a low GSH/GSSG ratio, impaired ROS scavenging, excessive ROS accumulation and cell membrane damage. The findings of this study provide evidence that GLR-mediated NO plays a crucial role in improvement of the tolerance of Arabidopsis plants to salt-induced oxidative stress. It helps to maintain cellular redox homeostasis by reducing ROS accumulation and increasing the activity of SOD, GSNOR, and the ASC-GSH cycle enzymes.

Sodium nitroprusside improved the quality of Radix Saposhnikoviae through constructed physiological response under ecological stress

The ecological significance of secondary metabolites is to improve the adaptive ability of plants. Secondary metabolites, usually medicinal ingredients, are triggered by unsuitable environment, thus the quality of medicinal materials under adversity being better. The quality of the cultivated was heavily declined due to its good conditions. Radix Saposhnikoviae, the dried root of Saposhnikovia divaricata (Turcz.) Schischk., is one of the most common botanicals in Asian countries, now basically comes from cultivation, resulting in the market price being only 1/10 to 1/3 of its wild counterpart, so improving the quality of cultivated Radix Saposhnikoviae is of urgency. Nitric oxide (NO) plays a crucial role in generating reactive oxygen species and modifying the secondary metabolism of plants. This study aims to enhance the quality of cultivated Radix Saposhnikoviae by supplementing exogenous NO. To achieve this, sodium nitroprusside (SNP) was utilized as an NO provider and applied to fresh roots of S. divaricata at concentrations of 0.03, 0.1, 0.5, and 1.0 mmol/L. This study measured parameters including the activities of antioxidant enzymes, secondary metabolite synthesis enzymes such as phenylalanine ammonia-lyase (PAL), 1-aminocyclopropane-1-carboxylic acid (ACC), and chalcone synthase (CHS), as well as the contents of NO, superoxide radicals (O2·-), hydrogen peroxide (H2O2), malondialdehyde (MDA), and four secondary metabolites. The quality of Radix Saposhnikoviae was evaluated with antipyretic, analgesic, anti-inflammatory effects, and inflammatory factors. As a result, the NO contents in the fresh roots were significantly increased under SNP, which led to a significant increase of O2·-, H2O2, and MDA. The activities of important antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were found to increase as well, with their peak levels observed on the 2nd and 3rd days. PAL, ACC, and CHS activities were also significantly enhanced, resulting in the increased secondary metabolite contents of Radix saposhnikoviae in all groups, especially the 0.5 mmol/L SNP. The four active ingredients, prim-O-glucosylcimifugin, cimifugin, 4'-O-β-D-glucosyl-5-O-methylvisamminol, and sec-O-glucosylhamaudol, increased by 88.3%,325.0%, 55.4%, and 283.8%, respectively, on the 3rd day. The pharmaceutical effects of Radix Saposhnikoviae under 0.5 mmol/L SNP were significantly enhanced. Exogenous SNP can induce the physiological response of S. divaricata under adverse conditions and significantly improve the quality of Radix Saposhnikoviae.

Achieving abiotic stress tolerance in plants through antioxidative defense mechanisms

Climate change has increased the overall impact of abiotic stress conditions such as drought, salinity, and extreme temperatures on plants. Abiotic stress adversely affects the growth, development, crop yield, and productivity of plants. When plants are subjected to various environmental stress conditions, the balance between the production of reactive oxygen species and its detoxification through antioxidant mechanisms is disturbed. The extent of disturbance depends on the severity, intensity, and duration of abiotic stress. The equilibrium between the production and elimination of reactive oxygen species is maintained due to both enzymatic and non-enzymatic antioxidative defense mechanisms. Non-enzymatic antioxidants include both lipid-soluble (α-tocopherol and β-carotene) and water-soluble (glutathione, ascorbate, etc.) antioxidants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) are major enzymatic antioxidants that are essential for ROS homeostasis. In this review, we intend to discuss various antioxidative defense approaches used to improve abiotic stress tolerance in plants and the mechanism of action of the genes or enzymes involved.

Induction of salt tolerance in Brassica rapa by nitric oxide treatment

Salinity is one of the major plant abiotic stresses increasing over time worldwide. The most important biological role of nitric oxide (NO) in plants is related to their development and growth under abiotic conditions. The present experiment was conducted to study the effect of salt stress (0 and 100 mM) and NO (0 and 80 μM) on two different ecotypes of Brassica rapa (L.): PTWG-HL and PTWG-PK. The different growth attributes, biochemical and physiological parameters, and the mineral contents were examined. The results indicated increased hydrogen peroxide (H2O2), relative membrane permeability, malondialdehyde (MDA), and Na+ content and decreased plant biomass in both ecotypes (PTWG-PK and PTWG-HL) under salt stress. In contrast, NO treatment resulted in increased plant biomass, chlorophyll content, and total soluble proteins and decreased H2O2, relative membrane permeability, MDA, total phenolic content, catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and Na+. The combined effect of salt stress and NO application increased the chlorophyll a content, total phenolic content, and total soluble proteins, but decreased H2O2, relative membrane permeability, MDA, and Na+. The response of carotenoids, anthocyanins, and K+, Ca2+, and Cl- ions varied in both ecotypes under all treatment conditions. The PTWG-PK ecotype showed maximum overall growth response with the application of NO. Henceforth, it is proposed that the molecular mechanisms associated with NO-induced stress tolerance in plants may be exploited to attain sustainability in agriculture under changing climate scenarios.

Plant Growth Regulators Improve Grain Production and Water Use Efficiency of Foeniculum vulgare Mill. under Water Stress

The development of methods increasing plant water use efficiency (WUE) would enhance the ability to grow wild aromatic and medicinally important species. The aim of this research was to determine the effect of plant growth regulators (PGRs) applied by spraying on stress resistance and WUE of fennel subjected to water stress. Plants in the generative stage were more drought tolerant than those in the vegetative stage. Water stress at vegetative stage decreased plant biomass and grain yield by 60% and 61%, respectively. Severe water stress in vegetative stage reduced grain production by 56%, and grains had 43% lower mass than those from non-stressed plants. Application of PGRs at both stages of growth increased grain yield and biomass, but the magnitude of increase depended on the type and application time of PGRs. Plants grown in well-watered conditions and sprayed with methyl jasmonate during the vegetative stage had the highest grain production (2.7 g plant⁻¹), whereas under moderate water stress, plants yielded the best (2.1 g plant⁻¹) when sprayed with epibrassinolide. The maximum WUE for grain (0.91 g L⁻¹) and essential oil production (20 mg L⁻¹) was noted in plants exposed to moderate stress and treated with methyl jasmonate during the vegetative stage.

Effect of sodium nitroprusside on physiological and anatomical features of salt-stressed Raphanus sativus

Sodium nitroprusside (SNP), which produces nitric oxide (NO) has the well-documented potential to alleviate the adverse effects of various abiotic stressors such as salinity. The present study aimed at investigating how the application of SNP can ameliorate the adverse effects of salt stress and boost tolerance in Raphanus sativus. Salt stress induced by application of 100 or 200 mM NaCl significantly decreased photosynthetic pigments and chlorophyll fluorescence, followed by a significant reduction in carbohydrate content. SNP treatment increased salt-tolerance in plants by inhibiting the adverse effect of salinity on the photosynthetic apparatus and the accumulation of sugars. Salt stress was accompanied by a reduction in total antioxidant power (FRAP), accumulation of damaging levels of H₂O₂, lipid peroxidation, and reduction in protein, while SNP enhanced FRAP, reduced H₂O₂ and lipid peroxidation, and restored protein abundance. SNP treatment also increased hypocotyl growth of salt-stressed plants, accompanied by improvement in anatomical structure. Cross sections of the hypocotyl showed increased diameter of the central cylinder and thickness of the casparian strip in the SNP-treated plants under stress conditions. Indeed, the observed improvement in the growth of hypocotyl and leaves of salt-stressed radish plants treated with SNP, in parallel with improved physiology and anatomical features, suggested that NO can regulate diverse mechanisms to effectively increase salt tolerance.

Physiological responses of Agriophyllum squarrosum and Setaria viridis to drought and re-watering

Drought resistance of psammophyte determines survival and growth, but their responses to drought are not well understood. We conducted a pot experiment to study how physiological characteristics respond to drought and rehydration. We found that watering to 60-65% of field capacity (the control) provided more water than was required by Agriophyllum squarrosum and its leaves became yellow and slightly wilted. The total chlorophyll content and Fm (maximum fluorescence after dark adaptation) in control were lower than in the drought treatment, and both decreased after rehydration. With increasing drought duration and intensity, the relative water content (RWC), chlorophyll content, Fm, and the quantum efficiency of photosystem II (Fv/Fm) of Setaria viridis decreased, but malondialdehyde and membrane permeability increased. During the late drought, the activities of three antioxidant enzymes in A. squarrosum increased to prevent membrane lipid peroxidation; for S. viridis, only peroxidase and superoxide dismutase activities increased. After rehydration, RWC of both species increased, but Fv/Fm of A. squarrosum and Fm of S. viridis did not recover under severe drought. Our research illustrated that A. squarrosum is better adapted to arid environment than S. viridis, but the high soil moisture content is not conducive to normal growth of A. squarrosum.

Alleviative effects of nitric oxide on Vigna radiata seedlings under acidic rain stress

Although nitric oxide (NO) is a key regulatory molecule in plants, its function in plants under conditions of simulated acid rain (SAR) has not been fully established yet. In this study, exogenous sodium nitroprusside (SNP) at three different concentrations were applied to mung bean seedlings. Malondialdehyde (MDA), NO, hydrogen peroxide (H₂O₂), antioxidant enzyme activities, and nitrate reductases (NR) were measured. Real time PCR was used to measure the NR expression. Compared to the control, the NR activity and NO content under the pH 2 SAR decreased by 79% and 85.6% respectively. Meanwhile, the SAR treatment reduced the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), while increased MDA content. Application of SNP could potentially reverse the adverse impact of SAR, depending on its concentration. For plants under the pH 2 SAR and 0.25 mM SNP condition, the activities of SOD, POD, APX increased by 123%, 291%, and 135.7% respectively, meanwhile, MDA concentration decreased by 43%, NR activities increased by 269%, and NO concentration increased by 123.6% compared with plants undergoing only pH 2 SAR. The relative expression of the NR1 gene was 2.69 times higher than that of pH 2 SAR alone. Overall, the application of 0.25 mM SNP eliminated reactive oxygen species (ROS) by stimulating antioxidant enzyme activities, reducing oxidative stress and mitigating the toxic effects of SAR on mung bean seedlings. This research provides a foundation for further research on the mechanism of NO on plants under SAR conditions.

Calcium signaling and salt tolerance are diversely entwined in plants

In plants dehydration imposed by salinity can invoke physical changes at the interface of the plasma membrane and cell wall. Changes in hydrostatic pressure activate ion channels and cause depolarization of the plasma membrane due to disturbance in ion transport. During the initial phases of salinity stress, the relatively high osmotic potential of the rhizosphere enforces the plant to use a diverse spectrum of strategies to optimize water and nutrient uptake. Signals of salt stress are recognized by specific root receptors that activate an osmosensing network. Plant response to hyperosmotic tension is closely linked to the calcium (Ca2+) channels and interacting proteins such as calmodulin. A rapid rise in cytosolic Ca2+ levels occurs within seconds of exposure to salt stress. Plants employ multiple sensors and signaling components to sense and respond to salinity stress, of which most are closely related to Ca2+ sensing and signaling. Several tolerance strategies such as osmoprotectant accumulation, antioxidant boosting, polyaminses and nitric oxide (NO) machineries are also coordinated by Ca2+ signaling. Substantial research has been done to discover the salt stress pathway and tolerance mechanism in plants, resulting in new insights into the perception of salt stress and the downstream signaling that happens in response. Nevertheless, the role of multifunctional components such as Ca2+ has not been sufficiently addressed in the context of salt stress. In this review, we elaborate that the salt tolerance signaling pathway converges with Ca2+ signaling in diverse pathways. We summarize knowledge related to different dimensions of salt stress signaling pathways in the cell by emphasizing the administrative role of Ca2+ signaling on salt perception, signaling, gene expression, ion homeostasis and adaptive responses.

Effects of Drought and Rehydration on the Physiological Responses of Artemisia halodendron

Artemisia halodendron is a widely distributed native plant in China’s Horqin sandy land, but few studies have examined its physiological responses to drought and rehydration. To provide more information, we investigated the effects of drought and rehydration on the chlorophyll fluorescence parameters and physiological responses of A. halodendron to reveal the mechanisms responsible for A. halodendron’s tolerance of drought stress and the resulting ability to tolerate drought. We found that A. halodendron had strong drought resistance. Its chlorophyll content first increased and then decreased with prolonged drought. Variable chlorophyll fluorescence (Fv) and quantum efficiency of photosystem II (Fv/Fm) decreased, and the membrane permeability and malondialdehyde increased. When plants were subjected to drought stress, superoxide dismutase (SOD) activity degraded under severe drought, but the activities of peroxidase (POD) and catalase (CAT) and the contents of soluble proteins, soluble sugars, and free proline increased. Severe drought caused wilting of A. halodendron leaves and the leaves failed to recover even after rehydration. After rehydration, the chlorophyll content, membrane permeability, SOD and CAT activities, and the contents of the three osmoregulatory substances under moderate drought began to recover. However, Fv, Fv/Fm, malondialdehyde, and POD activity did not recover under severe drought. These results illustrated that drought tolerance of A. halodendron resulted from increased enzyme (POD and CAT) activities and accumulation of osmoregulatory substances.

Grain Legumes and Fear of Salt Stress: Focus on Mechanisms and Management Strategies

Salinity is an ever-present major constraint and a major threat to legume crops, particularly in areas with irrigated agriculture. Legumes demonstrate high sensitivity, especially during vegetative and reproductive phases. This review gives an overview of legumes sensitivity to salt stress (SS) and mechanisms to cope with salinity stress under unfavorable conditions. It also focuses on the promising management approaches, i.e., agronomic practices, breeding approaches, and genome editing techniques to improve performance of legumes under SS. Now, the onus is on researchers to comprehend the plants physiological and molecular mechanisms, in addition to various responses as part of their stress tolerance strategy. Due to their ability to fix biological nitrogen, high protein contents, dietary fiber, and essential mineral contents, legumes have become a fascinating group of plants. There is an immense need to develop SS tolerant legume varieties to meet growing demand of protein worldwide. This review covering crucial areas ranging from effects, mechanisms, and management strategies, may elucidate further the ways to develop SS-tolerant varieties and to produce legume crops in unfavorable environments.

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.

Molecular insights into the functional role of nitric oxide (NO) as a signal for plant responses in chickpea

The molecular mechanisms and targets of nitric oxide (NO) are not fully known in plants. Our study reports the first large-scale quantitative proteomic analysis of NO donor responsive proteins in chickpea. Dose response studies carried out using NO donors, sodium nitroprusside (SNP), diethylamine NONOate (DETA) and S-nitrosoglutathione (GSNO) in chickpea genotype ICCV1882, revealed a dose dependent positive impact on seed germination and seedling growth. SNP at 0.1mM concentration proved to be most appropriate following confirmation using four different chickpea genotypes. while SNP treatment enhanced the percentage of germination, chlorophyll and nitrogen contents in chickpea, addition of NO scavenger, cPTIO reverted its impact under abiotic stresses. Proteome profiling revealed 172 downregulated and 76 upregulated proteins, of which majority were involved in metabolic processes (118) by virtue of their catalytic (145) and binding (106) activity. A few crucial proteins such as S-adenosylmethionine synthase, dehydroascorbate reductase, pyruvate kinase fragment, 1-aminocyclopropane-1-carboxylic acid oxidase, 1-pyrroline-5-carboxylate synthetase were less abundant whereas Bowman-Birk type protease inhibitor, non-specific lipid transfer protein, chalcone synthase, ribulose-1-5-bisphosphate carboxylase oxygenase large subunit, PSII D2 protein were highly abundant in SNP treated samples. This study highlights the protein networks for a better understanding of possible NO induced regulatory mechanisms in plants.

Polyamines Confer Salt Tolerance in Mung Bean (Vigna radiata L.) by Reducing Sodium Uptake, Improving Nutrient Homeostasis, Antioxidant Defense, and Methylglyoxal Detoxification Systems

The physiological roles of PAs (putrescine, spermidine, and spermine) were investigated for their ability to confer salt tolerance (200 mM NaCl, 48 h) in mung bean seedlings (Vigna radiata L. cv. BARI Mung-2). Salt stress resulted in Na toxicity, decreased K, Ca, Mg, and Zn contents in roots and shoots, and disrupted antioxidant defense system which caused oxidative damage as indicated by increased lipid peroxidation, H2O2 content, [Formula: see text] generation rate, and lipoxygenase activity. Salinity-induced methylglyoxal (MG) toxicity was also clearly evident. Salinity decreased leaf chlorophyll (chl) and relative water content (RWC). Supplementation of salt affected seedlings with exogenous PAs enhanced the contents of glutathione and ascorbate, increased activities of antioxidant enzymes (dehydroascorbate reductase, glutathione reductase, catalase, and glutathione peroxidase) and glyoxalase enzyme (glyoxalase II), which reduced salt-induced oxidative stress and MG toxicity, respectively. Exogenous PAs reduced cellular Na content and maintained nutrient homeostasis and modulated endogenous PAs levels in salt affected mung bean seedlings. The overall salt tolerance was reflected through improved tissue water and chl content, and better seedling growth.

Polyamine and nitric oxide crosstalk: Antagonistic effects on cadmium toxicity in mung bean plants through upregulating the metal detoxification, antioxidant defense and methylglyoxal detoxification systems

Cadmium (Cd) contamination is a serious agricultural and environmental hazard. The study investigates cross-protection roles of putrescine (Put, 0.2 mM) and nitric oxide (sodium nitroprusside; SNP, 1 mM) in conferring Cd (CdCl2, 1.5 mM) tolerance in mung bean (Vigna radiata L. cv. BARI Mung-2) seedlings. Cadmium stress increased root and shoot Cd content, reduced growth, destroyed chlorophyll (chl), modulated proline (Pro) and reduced leaf relative water content (RWC), increased oxidative damage [lipid peroxidation, H2O2 content, O2(∙-) generation rate, lipoxygenase (LOX) activity], methylglyoxal (MG) toxicity. Put and/or SNP reduced Cd uptake, increasd phytochelatin (PC) content, reduced oxidative damage enhancing non-enzymatic antioxidants (AsA and GSH) and activities of enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and glutathione peroxidase (GPX)]. Exogenous Put and/or SNP modulated endogenous polyamines, PAs (putrescine, Put; spermidine, Spd; spermine, Spm), and NO; improved glyoxalase system in detoxifying MG and improved physiology and growth where combined application showed better effects which designates possible crosstalk between NO and PAs to confer Cd-toxicity tolerance.

The role of antioxidant enzymes in adaptive responses to sheath blight infestation under different fertilization rates and hill densities

Sheath blight of rice, caused by Rhizoctonia solani, is one of the most devastating rice diseases worldwide. No rice cultivar has been found to be completely resistant to this fungus. Identifying antioxidant enzymes activities (activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)) and malondialdehyde content (MDA) responding to sheath blight infestation is imperative to understand the defensive mechanism systems of rice. In the present study, two inoculation methods (toothpick and agar block method) were tested in double-season rice. Toothpick method had greater lesion length than agar block method in late season. A higher MDA content was found under toothpick method compared with agar block method, which led to greater POD and SOD activities. Dense planting caused higher lesion length resulting in a higher MDA content, which also subsequently stimulated higher POD and SOD activity. Sheath blight severity was significantly related to the activity of antioxidant enzyme during both seasons. The present study implies that rice plants possess a system of antioxidant protective enzymes which helps them in adaptation to sheath blight infection stresses. Several agronomic practices, such as rational use of fertilizers and optimum planting density, involved in regulating antioxidant protective enzyme systems can be regarded as promising strategy to suppress the sheath blight development.

Nitric oxide, antioxidants and prooxidants in plant defence responses

In plant cells the free radical nitric oxide (NO) interacts both with anti- as well as prooxidants. This review provides a short survey of the central roles of ascorbate and glutathione-the latter alone or in conjunction with S-nitrosoglutathione reductase-in controlling NO bioavailability. Other major topics include the regulation of antioxidant enzymes by NO and the interplay between NO and reactive oxygen species (ROS). Under stress conditions NO regulates antioxidant enzymes at the level of activity and gene expression, which can cause either enhancement or reduction of the cellular redox status. For instance chronic NO production during salt stress induced the antioxidant system thereby increasing salt tolerance in various plants. In contrast, rapid NO accumulation in response to strong stress stimuli was occasionally linked to inhibition of antioxidant enzymes and a subsequent rise in hydrogen peroxide levels. Moreover, during incompatible Arabidopsis thaliana-Pseudomonas syringae interactions ROS burst and cell death progression were shown to be terminated by S-nitrosylation-triggered inhibition of NADPH oxidases, further highlighting the multiple roles of NO during redox-signaling. In chemical reactions between NO and ROS reactive nitrogen species (RNS) arise with characteristics different from their precursors. Recently, peroxynitrite formed by the reaction of NO with superoxide has attracted much attention. We will describe putative functions of this molecule and other NO derivatives in plant cells. Non-symbiotic hemoglobins (nsHb) were proposed to act in NO degradation. Additionally, like other oxidases nsHb is also capable of catalyzing protein nitration through a nitrite- and hydrogen peroxide-dependent process. The physiological significance of the described findings under abiotic and biotic stress conditions will be discussed with a special emphasis on pathogen-induced programmed cell death (PCD).

Nitric oxide affects salt-induced changes in free amino acid levels in maize

It was assumed that salt-induced redox changes affect amino acid metabolism in maize (Zea mays L.), and this influence may be modified by NO. The applied NaCl treatment reduced the fresh weight of shoots and roots. This decrease was smaller after the combined application of NaCl and an NO-donor ((Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, DETA/NO) in the shoots, while it was greater after simultaneous treatment with NaCl and nitro-L-arginine (L-NNA, inhibitor of NO synthesis) in the roots. The quantum yield efficiency of photosystem II was not influenced by the treatments. NaCl had a significant effect on the redox environment in the leaves as it was shown by the increase in the amount of glutathione disulphide and in the redox potential of the glutathione/glutathione disulphide redox pair. This influence of NaCl was modified by DETA/NO and L-NNA. Pharmacological modification of NO levels affected salt-induced changes in both the total free amino acid content and in the free amino acid composition. NaCl alone increased the concentration of almost all amino acids which effect was strengthened by DETA/NO in the case of Pro. L-NNA treatment resulted in a significant increase in the Ala, Val, Gly and Tyr contents. The Ile, Lys and Val concentrations rose considerably after the combined application of NaCl and DETA/NO compared to NaCl treatment alone in the recovery phase. NaCl also increased the expression of several genes related to the amino acid and antioxidant metabolism, and this effect was modified by DETA/NO. In conclusion, modification of NO levels affected salt-induced, glutathione-dependent redox changes and simultaneously the free amino acid composition and the level of several free amino acids. The observed much higher Pro content in plants treated with both NaCl and DETA/NO during recovery may contribute to the protective effect of NO against salt stress.

NOS-like-mediated nitric oxide is involved in Pinus thunbergii response to the invasion of Bursaphelenchus xylophilus

The content of NO and H(2)O(2) as well as the activities of nitric oxide synthase (NOS)-like and nitrate reductase (NR) were monitored in the needles of Pinus thunbergii infected by Bursaphelenchus xylophilus. The results showed that the content of NO increased significantly only 8 h after the invasion of B. xylophilus, while H(2)O(2) increased 12 h after invasion. NO donor SNP could promote and NO scavenger cPTIO could prevent the production of NO and H(2)O(2). The content of NO changed earlier than that of H(2)O(2). In addition, the symptoms appeared 9, 5 and 12 days, respectively, after the inoculation with B. xylophilus, SNP pre-treatment and cPTIO pre-treatment followed by B. xylophilus infection. After B. xylophilus infection, the content of NO in P. thunbergii changed fiercely more earlier than the appearance of external symptoms, which indicated that the content of NO was related with the appearance and the development of the symptoms. The treatment with L-NNA (NOS inhibitor) inhibited the content of NO significantly, whereas, Na(2)WO(4) (NR inhibitor) had no effect. The further analysis of NOS revealed that NO changed in consistent with cNOS activity. To sum up, NO, as the upstream signal molecule of H(2)O(2), was involved in the pine early response to the invasion of B. xylophilus and influenced the accumulation of the content of H(2)O(2). Moreover, NOS-like rather than NR was responsible for the endogenous NO generation, which was modulated by cNOS during the interaction between P. thunbergii and B. xylophilus. Key message NO is involved in early response of P. thunbergii to the invasion of B. xylophilus and NOS is the key enzyme responsible for NO generation in P. thunbergii.

Alleviation of exogenous oligochitosan on wheat seedlings growth under salt stress

Hydroponic experiments were carried out to study the role of oligochitosan in enhancing wheat (Triticum aestivum L.) resistance to salt stress. Data were collected on plant biomass, chlorophyll content, photosynthetic rate (P (n)), stomatal conductance (g (s)), proline content, antioxidant enzyme activities, and malondialdehyde (MDA) content. Under 150 mM salt stress, plant growth was significantly inhibited. Shoot length, root length, and dry weight were sharply reduced by 26%, 31%, and 20%, respectively, of the control. Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were increased by 28%, 13%, and 26%, respectively, of the control and MDA content largely accumulated, which was 1.5-fold of the control. However, 0.0625% oligochitosan pretreatment alleviated the adverse effects of salt stress, which was reflected by increasing root length, shoot length, dry weight, chlorophyll content, P (n,) and g (s). Furthermore, it also showed that oligochitosan pretreatment significantly increased antioxidant enzyme (SOD, CAT and POD) activities, and reduced MDA content in leaves. Meanwhile, the accumulation of proline was markedly accelerated. The results indicated that oligochitosan pretreatment ameliorated the adverse effects and partially protected the seedlings from salt stress during the following growth period.

Role of nitric oxide in tolerance of plants to abiotic stress

Nitric oxide (NO) has now gained significant place in plant science, mainly due to its properties (free radical, small size, no charge, short-lived, and highly diffusible across biological membranes) and multifunctional roles in plant growth, development, and regulation of remarkable spectrum of plant cellular mechanisms. In the last few years, the role of NO in tolerance of plants to abiotic stress has established much consideration. As it is evident from the present review, recent progress on NO potentiality in tolerance of plants to environmental stresses has been impressive. These investigations suggest that NO, itself, possesses antioxidant properties and might act as a signal in activating ROS-scavenging enzyme activities under abiotic stress. NO plays an important role in resistance to salt, drought, temperature (high and low), UV-B, and heavy metal stress. Rapidly increasing evidences indicate that NO is essentially involve in several physiological processes; however, there has been much disagreement regarding the mechanism(s) by which NO reduces abiotic stress.

Evidence for a role of exogenous glycinebetaine and proline in antioxidant defense and methylglyoxal detoxification systems in mung bean seedlings under salt stress

In mung bean seedlings, salt stress (300 mM NaCl) caused a significant increase in reduced glutathione (GSH) content within 24 h of treatment as compared to control whereas a slight increase was observed after 48 h of treatment. Highest oxidized glutathione (GSSG) content was observed after 48 h to treatment with a concomitant decrease in glutathione redox state. Glutathione peroxidase, glutathione S-transferase, and glyoxalase II enzyme activities were significantly elevated up to 48 h, whereas glutathione reductase and glyoxalase I activities were increased only up to 24 h and then gradually decreased. Application of 15 mM proline or 15 mM glycinebetaine resulted in an increase in GSH content, maintenance of a high glutathione redox state and higher activities of glutathione peroxidase, glutathione S-transferase, glutathione reductase, glyoxalase I and glyoxalase II enzymes involved in the ROS and methylglyoxal (MG) detoxification system for up to 48 h, compared to those of the control and mostly also salt stressed plants, with a simultaneous decrease in GSSG content, H2O2 and lipid peroxidation level. The present study suggests that both proline and glycinebetaine provide a protective action against saltinduced oxidative damage by reducing H2O2 and lipid peroxidation level and by enhancing antioxidant defense and MG detoxification systems.