Integrative roles of nitric oxide and hydrogen sulfide in melatonin-induced tolerance of pepper (Capsicum annuum L.) plants to iron deficiency and salt stress alone or in combination

There seems to be no report in the literature on the effect of melatonin (MT) in relieving the detrimental effects of combined application of salt stress (SS) and iron deficiency (ID). Therefore, the effect of MT on the accumulation/synthesis of endogenous nitric oxide (NO) and hydrogen sulphide (H₂S) and how far these molecules are involved in MT-improved tolerance to the combined application of ID and SS in pepper (Capsicum annuum L) were tested. Hence, two individual trials were set up. The treatments in the first experiment comprised: Control, ID (0.1 mM FeSO₄), SS (100 mM NaCl) and ID + SS. The detrimental effects of combined stresses were more prominent than those by either of the single stress, with respect to growth, oxidative stress and antioxidant defense attributes. Single stress or both in combination improved the endogenous H₂S and NO, and foliar-applied MT (100 µM) led to a further increase in NO and H₂S levels. In the second experiment, 0.1 mM scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) and that of H₂S, hypotuarine (HT) were applied along with MT to get further evidence whether NO and H₂S are involved in MT-induced tolerance to ID and SS. MT combined with cPTIO and HT under a single or combined stress showed that NO effect was reversed by the NO scavenger, cPTIO, alone but the H₂S effect was inhibited by both scavengers. These findings suggested that tolerance to ID and SS induced by MT may be involved in downstream signal crosstalk between NO and H₂S.     

Thiourea-mediated Nitric Oxide Production Enhances Tolerance to Boron Toxicity by Reducing Oxidative Stress in Bread Wheat (Triticum aestivum L.) and Durum Wheat (Triticum durum Desf.) Plants

Two independent experiments were performed to assess the role of thiourea (TU)-mediated nitric oxide (NO) in mitigating boron toxicity (BT) in bread wheat (Triticum aestivum L. cv. Pandas) and durum wheat (Triticum durum cv. Altıntoprak 98) plants. In the first experiment, plants of the two wheat species were grown under control (0.05 mM B) and BT (0.2 mM B) supplied to nutrient solution for 4 weeks after germination. These two treatments were also combined with TU spray at 200 or 400 mg L⁻¹ once a week during the period of stress. Boron toxicity reduced dry weights of shoot and root, leaf total chlorophyll, efficiency of photosystem II (F_v/F_m) and leaf relative water content, whereas it increased endogenous nitric oxide (NO), nitric oxide synthase (NOS), electrolyte leakage (EL), hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and leaf B content. Reductions in total dry matter were 33% and 61% of control in cvs. Pandas and Altintoprak, respectively. Exogenous application of TU improved the plant growth attributes and led to further increases in NO in the leaves. An additional experiment was set up to further understand whether or not TU mediated NO production played a significant role in mitigation of BT using 0.1 mM scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) combined with the TU treatments by spraying once a week for 4 weeks. TU-induced BT tolerance was totally eliminated by cPTIO by reversing endogenous NO levels. BT enhanced the activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC. 1.11.1.6), peroxidase (POD; EC. 1.11.1.7) and lipoxygenase (LOX; EC. 1.12.11.12) as well as the contents of soluble sugars (SS), soluble proteins and phenols, but decreased NR. TU treatments enhanced enzyme activities, but reduced contents of soluble sugars (SS), soluble protein and phenols. The present results clearly indicate that TU mediated endogenous NO significantly improved BT tolerance of wheat plants. This evidence was also supported by the increase in hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) as well as plant growth inhibition with the application of TU combined with cPTIO.

     

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), endogenous H₂S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.     

Sulfur stress-induced antioxidative responses in leaves of Triticum aestivum L.

Antioxidative responses were investigated in leaves of wheat (Triticum aestivum L.) grown at varying S levels ranging from deficiency to excess (1, 2, 4, 6 and 8 mM S). Optimum yield was observed in plants supplied with 4 mM S. Wheat responded to S deficiency and excess supply by decreasing growth of root and shoot. Chlorosis in young leaves was observed after 15 days of deficient S supply. The biomass and concentration of photoassimilatory pigments decreased in plants grown at 1, 2, 6 and 8 mM S supply. The concentration of thiobarbituric acid reactive substances (TBARS), cysteine, nonprotein thiol and hydrogen peroxide (H₂O₂) increased in plants grown under S stress. Accumulation of TBARS and H₂O₂ in leaves indicated oxidative damage in S-deficient and S-excess plants. Deficient and excess levels of S showed an increase in the activities of antioxidative enzymes superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2).     

Effects of the nitric oxide donor sodium nitroprusside on antioxidant enzymes in wheat seedling roots under nickel stress

The inhibitory effect of nickel on the growth of wheat (Triticum aestivum L.) seedlings and the alleviation of nickel toxicity by nitric oxide (NO) were investigated. Nickel (Ni) at 100 μM caused striking reduction in seedling growth and significant overproduction of MDA and H₂O₂ in the roots. Supplementation with NO donor sodium nitroprusside (SNP) could significantly reverse the inhibitory effect of nickel in a dose-dependent manner. K₃Fe(CN)₆, a SNP analogue, which does not release NO, had no ameliorative effect on Ni toxicity in wheat.. In addition, application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO scavenger, could dramatically counteract the stimulatory effects of SNP on the growth of wheat seedling roots under Ni stress, confirming that NO rather than other compounds derived from SNP was responsible for the alleviating effect of Ni toxicity. Further results showed that SNP enhanced the activities of guaiacol peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, EC 1..1..5.1..1), glutathione reductase (GR, EC 1.6.4.2), and glutathione S-transferase (GST, EC 2.5.1.18) in wheat seedling roots under nickel stress, while no significant difference in the activity of catalase (CAT, EC 1.11.1.6) in wheat roots supplemented with SNP or without it was observed. These results clearly indicate that NO has a protective role in Ni-induced oxidative damage through modulation of antioxidant enzymes.     

Glutamine synthetase and glutamate dehydrogenase in cadmium-stressed triticale seedlings

The studies were performed on young triticale seedlings grown on a mineral medium containing 5 mM NO ₃ ⁻ as the nitrogen source, with the addition of 0.5 mM CdCl₂. It was determined that cadmium ions accumulated mainly in the plant roots. Decreases in nitrate concentrations both in the roots and shoots of seedlings, as well as decreases in soluble protein contents with simultaneous increases in endopeptidase activity were also observed. Both in roots and shoots significant decreases in glutamic acid were noted. Toxic cadmium ion accumulation in seedlings significantly modified activity of primary nitrogen assimilating enzymes, i.e. glutamine synthetase (GS, EC 6.3.1.2) and glutamate dehydrogenase (GDH, EC 1.4.1.2). There was a significant decrease in GS activity both in roots and in shoots of the stressed plants, in comparison to plants grown without cadmium. In shoots of the control plants and plants subjected to stress two GS isoforms were discovered: cytoplasmatic (GS₁) and chloroplastic (GS₂). Substantial decreases in total glutamine synthetase activity in green parts of seedlings, occurring under stress conditions, result from dramatic decrease in GS₂ activity (by 60 % in relation to the control plants); despite simultaneous increases in the cytoplasmatic isoform (GS₁) activity by approx. 96 %. Cadmium ions accumulating in roots and shoots of seedlings not only increased GDH activity, but also modified its coenzymatic specificity.     

Physiological effects of exogenous nitric oxide on Brassica juncea seedlings under NaCl stress

The study was conducted to investigate the physiological effects of exogenous NO on potherb mustard (Brassica juncea Coss.) seedlings under salt stress. The plants were grown in Hogland nutrient solution for 15 d and treated with 150 mM NaCl, NO donor sodium nitropruside (SNP) and NO scavenger methylene blue (MB-1) for 4 d. The NaCl stress increased superoxide dismutase, peroxidase and ascorbate peroxidase activities and malondialdehyde (MDA) and free proline contents, and decreased soluble protein content. However, the application of exogenous NO limited the production of MDA and free proline, while markedly promoted SOD, POD and APX activity.     

Treatment of nitric oxide supplemented with nitrogen and sulfur regulates photosynthetic performance and stomatal behavior in mustard under salt stress

Nitric oxide (NO) is a hormone that connects numerous reactions in plant cells under normal and environmental stress conditions. The application of 100 µM NO as sodium nitroprusside (SNP; NO donor) applied individually or in combination with N or S in different combinations (i.e. 100 mg N or S kg⁻¹ soil applied at the time of sowing [100 N + 100S]_0d or with split, 50 mg N or S kg⁻¹ soil at the time of sowing and similar dose at 20 d after sowing [50 N + 50S]_0d + [50 N + 50S]_20d) was tested to alleviate salt stress in mustard (Brassica juncea L.). Application of 100 µM NO plus split application of N and S more significantly promoted stomatal behavior, photosynthetic and growth performance in the absence of salt stress and maximally alleviated effects of salt stress through increased N- and S-use efficiency, proline and antioxidant system. The combined application of N and S at the time of sowing was lesser effective in promoting photosynthesis and growth under salt or no salt stress conditions in presence or absence of NO. The study suggests that salt stress effects on the photosynthetic performance are mitigated more efficiently when NO was applied together with the split application of N and S given at two stages, and the photosynthetic activity was promoted under salt stress through increased N and S assimilation and antioxidant system. This strategy may be adopted in agricultural system for overcoming salt stress effects on performance of mustard.     

Cell death induced by sodium nitroprusside and hydrogen peroxide in tobacco BY-2 cell suspension

The interplay between nitric oxide (NO) and reactive oxygen species can lead to an induction of cell death in plants. The aim of our work was to find out if cyanide released from sodium nitroprusside (SNP; a donor of NO) could be involved in the cell death induction, which is triggered by SNP and H₂O₂. Cell suspension of Nicotiana tabacum L. (line BY-2) was treated with 0.5 mM SNP, 0.5 mM potassium ferricyanide (PFC; analogue of sodium nitroprusside which can not release NO) and/or by 0.5 mM glucose with 0.5 U cm⁻³ glucose oxidase (GGO; a donor system of H₂O₂). The cell death was induced only by combination of SNP and GGO. Thus cyanide released was not involved in the induction of cell death. However, SNP showed toxic effect because of decrease in activities of intracellular oxidoreductases and esterases. The cell death caused by SNP and GGO occurred within 12 h. During cell death either length or width of the cell increased. Central vacuole was formed in 20 to 40 % of cells. Most of the dead cells showed a condensed cytoplasm. Two hallmarks of programmed cell death (PCD), chromatin condensation and blebbing of nuclear periphery, were observed. However, oligonucleosomal fragmentation of DNA, another hallmark of PCD, was not detected.     

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

Abstract

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

Protective role of nitric oxide against arsenic-induced damages in germinating mung bean seeds

Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and mediating a variety of physiological processes and responses to biotic and abiotic stresses including heavy metals. The present study investigated whether NO applied exogenously as sodium nitroprusside (SNP) has a protective role against arsenic (As) toxicity (applied as sodium arsenate) in Vigna radiata (mung bean) germinating seeds. Treatment with 75???M SNP significantly improved mung bean seed germination, growth, and decreased the As-accumulation. Furthermore, As-induced oxidative stress measured in terms of malondialdehyde and H₂O₂ contents was lesser upon supplementation of SNP indicating a reactive oxygen species scavenging activity of NO. In addition, supplementation of SNP markedly decreased the activity of superoxide dismutase and stimulated catalase, ??-amylase, protease and slightly changed the H⁺-ATPase activity.     

Effect of sodium nitroprusside on responses of <Emphasis Type="Italic">Melissa officinalis</Emphasis> to bicarbonate exposure and direct Fe deficiency stress

In our study, one-month-old Melissa officinalis plants were subjected to Fe-deficiency treatments, such as 10 µM Fe (as direct iron deficiency, DD), and 30 µM Fe + 10 mM NaHCO₃ + 0.5 g l^?1 CaCO₃ (as indirect iron deficiency, ID), and 30 µM Fe (as control) for 14 d. Both Fe-deficiency types reduced plant growth, photosynthetic pigment contents, an active Fe content in roots and leaves, root Fe(III)-reducing capacity, Fe-use efficiency, maximal quantum yield of PSII photochemistry, a ratio of variable to basic fluorescence, and activities of antioxidant enzymes, while they increased lipid peroxidation and a H₂O₂ content in leaves. These effects were more pronounced in plants exposed to ID with bicarbonate than those of DD plants. We showed that sodium nitroprusside (SNP), as NO donor, could ameliorate the adverse effects of bicarbonate on above traits. The methylene blue, as NO blocker, reversed the protective effects conferred by SNP in the ID-treated plants as well as DD plants. These findings suggests that NO protects photosynthesis and growth of IDtreated plants as well as DD plants by contribution in availability and/or delivery of metabolically active iron or by changing activities of reactive oxygen species-scavenging enzymes.     

Effects of foliar applications of nitric oxide and salicylic acid on salt-induced changes in photosynthesis and antioxidative metabolism of cotton seedlings

Nitric oxide (NO) is a plant signaling compound known to mitigate key physiological processes and salicylic acid (SA) is considered to be a signaling molecule that plays a key role in growth, development, and defense responses in plants under stress conditions. This work investigated the effects of sodium nitroprusside (SNP, a donor of NO) and SA on salt-tolerance of cotton (Gossypium hirsutum L.) seedlings by examining growth, photosynthetic performance, total osmoregulation substance content, antioxidative enzymes and H⁺-ATPase enzyme subjected to 100 mM NaCl. Addition of 100 mM NaCl inhibited the growth and photosynthetic parameters of cotton seedlings, and dramatically increased the electrolyte leakage, the plant contents of proline, lipid peroxidation (malondialdehyde), hydrogen peroxide (H₂O₂) and Na. Furthermore, antioxidant enzyme activities were restrained. Foliar applications of 0.1 mM SNP or/and 0.1 mM SA led to increase in the growth rate and photosynthesis, including photosystem II, net photosynthetic rate and transpiration rate, improvement of reactive oxygen species-scavenging enzymes activities and reduction of H₂O₂ accumulation in cotton seedlings induced by NaCl. In addition, membrane transport and function were facilitated by decreasing leaf electrolyte leakage, improving ion absorption and activating the osmotic-regulated substances metabolic. Further investigation also showed that SNP and SA alleviated the inhibition of H⁺-ATPase in plasma membrane induced by NaCl. The present study showed that foliar application of SNP and SA alone mitigated the adverse effect of salinity, while the combined application proved to be even more effective in alleviating the adverse effects of NaCl stress.     

Nitrogen supply as a factor influencing photoinhibition and photosynthetic acclimation after transfer of shade-grown Solanum dulcamara to bright light

We have compared the ability of shadegrown clones of Solamum dulcamara L. from shade and sun habitats to acclimate to bright light, as a function of nitrogen nutrition before and after transfer to bright light. Leaves of S. dulcamara grown in the shade with 0.6 mM NO ₃ ^- have similar photosynthetic properties as leaves of plants grown with 12.0 mM NO ₃ ^- . When transferred to bright light for 1–2 d the leaves of these plants show substantial photoinhibition which is characterized by about 50% decrease in apparent quantum yield and a reduction in the rate of photosynthesis in air at light saturation. Photoinhibition of leaf photosynthesis is associated with reduction in the variable component of low-temperature fluorescence emission, and with loss of in-vitro electron transport, especially of photosystem II-dependent processes.We find no evidence for ecotypic differentiation in the potential for photosynthetic acclimation among shade and sun clones of S. dulcamara, or of differentiation with respect to nitrogen requirements for acclimation. Recovery from photoinhibition and subsequent acclimation of photosynthesis to bright light only occurs in leaves of plants provided with 12.0 mM NO ₃ ^- . In these, apparent quantum yield is fully restored after 14 d, and photosynthetic acclimation is shown by an increase in light-saturated photosynthesis in air, of light-and CO₂-saturated photosynthesis, and of the initial slope of the CO₂-response curve. The latter changes are highly correlated with changes in ribulose-bisphosphate-carboxylase activity in vitro. Plants supplied with 0.6 mM NO ₃ ^- show incomplete recovery of apparent quantum yield after 14 d, but CO₂-dependent leaf photosynthetic parameters return to control levels.Symbols and abbreviations F_o initial level of fluorescence at 77 K - F_m maximum level of fluorescence at 77 K - F_v variable components of fluorescence at 77 K (F_v=F_m-F_o) - PSI, PSII photosystem I and II, respectively - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39)     

Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro‐Tom) plants to cadmium‐induced stress

The effects of varying concentrations of cadmium (Cd) on the development of Lycopersicon esculentum cv. Micro‐Tom (MT) plants were investigated after 40 days (vegetative growth) and 95 days (fruit production), corresponding to 20 days and 75 days of exposure to CdCl₂, respectively. Inhibition of growth was clearly observed in the leaves after 20 days and was greater after 75 days of growth in 1 mM CdCl₂, whereas the fruits exhibited reduced growth following the exposure to a concentration as low as 0.1 mM CdCl₂. Cd was shown to accumulate in the roots after 75 days of growth but was mainly translocated to the upper parts of the plants accumulating to high concentrations in the fruits. Lipid peroxidation was more pronounced in the roots even at 0.05 mM CdCl₂ after 75 days, whereas in leaves, there was a major increase after 20 days of exposure to 1 mM CdCl₂, but the fruit only exhibited a slight significant increase in lipid peroxidation in plants subjected to 1 mM CdCl₂ when compared with the control. Oxidative stress was also investigated by the analysis of four key antioxidant enzymes, which exhibited changes in response to the increasing concentrations of Cd tested. Catalase (EC 1.11.1.6) activity was shown to increase after 75 days of Cd treatment, but the major increases were observed at 0.1 and 0.2 mM CdCl₂, whereas guaiacol peroxidase (EC 1.11.1.7) did not vary significantly from the control in leaves and roots apart from specific changes at 0.5 and 1 mM CdCl₂. The other two enzymes tested, glutathione reductase (EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1), did not exhibit any significant changes in activity, apart from a slight decrease in SOD activity at concentrations above 0.2 mM CdCl₂. However, the most striking results were obtained when an extra treatment was used in which a set of plants was subjected to a stepwise increase in CdCl₂ from 0.05 to 1 mM, leading to tolerance of the Cd applied even at the final highest concentration of 1 mM. This apparent adaptation to the toxic effect of Cd was confirmed by biomass values being similar to the control, indicating a tolerance to Cd acquired by the MT plants.     

Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

A greenhouse experiment was conducted to assess whether exogenously applied 24-epibrassionlide (24-epiBL) could alleviate the adverse effects of salt on wheat. Two hexaploid wheat (Triticum aestivum L.) cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive), were grown under control (0 mM NaCl in full strength Hoagland’s nutrient solution) or saline conditions (150 mM of NaCl in full strength Hoagland’s nutrient solution). After 41 days growth of wheat plants under saline conditions, 24-epiBL was applied as a foliar spray. Four levels of BR were used as 0 (water spray), 0.0125, 0.025, and 0.0375 mg l⁻¹. Application of 24-epiBL increased plant biomass and leaf area per plant of both cultivars under non-saline conditions. However, under saline conditions, improvement in growth due to exogenous 24-epiBL was observed only in S-24. Photosynthetic rate was reduced due to salt stress in both cultivars, but this inhibitory effect was ameliorated significantly by the exogenous application of 24-epiBL. Exogenously applied 24-epiBL also enhanced the photosystem-II efficiency in both cultivars measured as F _v /F _m ratio. Although the activities of antioxidant enzymes, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were increased due to salt stress in both wheat cultivars, exogenously applied 24-epiBL had a varying effect on the antioxidant system. The activity of SOD remained unaffected in both cultivars due to 24-epiBL application, but that of POD and CAT was promoted in the salt stressed plants of cv. S-24 only. In conclusion, improvement in growth in both wheat cultivars due to foliar applied 24-epiBL was found to be associated with 24-epiBL-induced enhancement in photosynthetic capacity. The 24-epiBL-induced regulation of antioxidant enzymes or growth under saline conditions was cultivar specific.     

Effects of Exogenous Salicylic Acid and Nitric Oxide on Physiological Characteristics of Perennial Ryegrass Under Cadmium Stress

The effects of Cd, in combination with salicylic acid (SA) and sodium nitroprusside (SNP), on ryegrass seedlings were studied. Exposure of plants to 0.1 mM CdCl₂ for 2 weeks resulted in toxicity symptoms such as chlorosis and necrotic spots on leaves. The addition of 0.2 mM SA or 0.1 mM SNP slightly alleviated the toxic effects of Cd. After application of both SA and SNP, these symptoms significantly decreased. Treatment with Cd resulted in a decrease of dry weight of roots and shoots, chlorophyll content, net photosynthetic rate (P _n), transpiration rate (T _r), and the uptake and translocation of mineral elements. In Cd-treated plants, levels of lipoxygenase activity and malondialdehyde, hydrogen peroxide (H₂O₂), and proline contents significantly increased, whereas the activities of antioxidant enzymes, such as superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, decreased in both roots and shoots. The results indicated that Cd caused physiological stresses in ryegrass plants. The Cd-stressed plants exposed to SA or SNP, especially to SA + SNP, exhibited improved growth compared with Cd-stressed plants. Application of SA or SNP, especially the combination SA + SNP, considerably reduced root-to-shoot translocation of Cd and increased the activities of antioxidant enzymes in both roots and shoots of Cd-stressed plants. The interaction of SA and SNP increased chlorophyll content, P _n and T _r in leaves, and the uptake and translocation of mineral elements, and decreased lipid peroxidation and H₂O₂ and proline accumulation in roots and shoots. These results suggest that SA or SNP, and, in particular, their combination counteracted the negative effects of Cd on ryegrass plants.     

Effect of osmotic stress and sodium nitroprusside pretreatment on proline metabolism of wheat seedlings

Effect of osmotic stress and sodium nitroprusside (SNP, NO donor) pretreatment on growth and proline metabolism of wheat seedlings was investigated. Polyethylene glycol 6000 treatment for 2, 4 and 6 d could be termed as mild, moderate and severe stress, respectively, according to decrease in the relative water content. Severe osmotic stress significantly decreased the growth and photochemical efficiency, and increased proline content due to activation of its synthesis. 0.2 mM SNP pretreatment enhanced growth of wheat seedlings, increased variable to maximum fluorescence ratio (F_v/F_m) and fluorescence yield, while decreased proline content. However, 2 mM SNP retarded the seedlings growth and chlorophyll a fluorescence, and increased proline accumulation. Our results showed that NO might be involved in the regulation of osmotic stress in a concentration-dependent manner.     

Silicon and Nitric Oxide-Mediated Regulation of Growth Attributes,Metabolites and Antioxidant Defense System of Radish (<i>Raphanus sativus</i> L.) under Arsenic Stress

Arsenic (As) contaminated food chains have emerged as a serious public concern for humans and animals and are known to affect the cultivation of edible crops throughout the world. Therefore, the present study was designed to investigate the individual as well as the combined effects of exogenous silicon (Si) and sodium nitroprusside (SNP), a nitric oxide (NO) donor, on plant growth, metabolites, and antioxidant defense systems of radish (Raphanus sativus L.) plants under three different concentrations of As stress, i.e., 0.3, 0.5, and 0.7 mM in a pot experiment. The results showed that As stress reduced the growth parameters of radish plants by increasing the level of oxidative stress markers, i.e., malondialdehyde and hydrogen peroxide. However, foliar application of Si (2 mM) and pretreatment with SNP (100 µM) alone as well as in combination with Si improved the plant growth parameters, i.e., root length, fresh and dry weight of plants under As stress. Furthermore, As stress also reduced protein, and metabolites contents (flavonoids, phenolic and anthocyanin). Activities of antioxidative enzymes such as catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD), and polyphenol oxidase (PPO), as well as the content of non-enzymatic antioxidants (glutathione and ascorbic acid) decreased under As stress. In most of the parameters in radish, As III concentration showed maximum reduction, as compared to As I and II concentrations. However, the individual and combined application of Si and NO significantly alleviated the As-mediated oxidative stress in radish plants by increasing the protein, and metabolites content. Enhancement in the activities of CAT, APX, POD and PPO enzymes were recorded. Contents of glutathione and ascorbic acid were also enhanced in response to co-application of Si and NO under As stress. Results obtained were more pronounced when Si and NO were applied in combination under As stress, as compared to their individual application. In short, the current study highlights that Si and NO synergistically regulate plant growth through lowering the As-mediated oxidative stress by upregulating the metabolites content, activity of antioxidative enzymes and non-enzymatic antioxidants in radish plants.

     

Differential responses of hydrogen peroxide, lipid peroxidation and antioxidant enzymes in Azolla microphylla exposed to paraquat and nitric oxide

The present investigation was carried out to decipher the interplay between paraquat (PQ) and exogenously applied nitric oxide (NO) in Azolla microphylla. The addition of PQ (8 ??M) increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) by 1.7, 2.7, 3.9 and 1.9 folds respectively than that control in the fronds of Azolla. The amount of H₂O₂ was also enhanced by 2.7 times in the PQ treated plants than that of control. The supplementation of sodium nitroprusside (SNP) from 8?C100 ??M along with PQ, suppressed the activities of antioxidative enzymes and the amount of H₂O₂ compared to PQ alone. The drop in the activity of antioxidative enzymes ?? SOD, GPX, CAT and APX was highest (39.9%, 48.4%, 41.6% and 41.3% respectively) on the supplementation of 100 ??M SNP with PQ treated fronds compared to PQ alone. The addition of NO scavengers along with NO donor in PQ treated fronds neutralized the effect of exogenously supplied NO. This indicates that NO can effectively protect Azolla against PQ toxicity by quenching reactive oxygen species. However, 200 ??M of SNP reversed the protective effect of lower concentration of NO donor against herbicide toxicity. Our study clearly suggests that (i) SNP released NO can work both as cytoprotective and cytotoxic in concentration dependent manner and (ii) involvement of NO in protecting Azolla against PQ toxicity.