一氧化氮参与调节盐胁迫下脱落酸诱导的小麦幼苗叶片脯氨酸的累积

不同浓度(0.01～5.00mmol/L)的外源一氧化氮(NO)供体硝普钠(SNP)以浓度依赖性的性式诱导150mmol/LNaCl胁迫下小麦(Triticum aestivum L.cv.Yangmai 158)幼苗叶片脯氨酸的累积.其中0.1 mmol/L的SNP效果最明显,而结合采用NO清除剂c-PTIO和血红蛋白的处理均分别逆转了该效应.研究结果还发现:0.1 mmol/L SNP诱导的脯氨酸累积还可能有利于盐胁迫下小麦幼苗的保水性;0.1 mmol/L的SNP显著激活了内源ABA的合成,而结合血红蛋白的处理则证实,在外源ABA诱导脯氨酸累积的过程中NO可能作用于ABA信号分子的下游,但NO和ABA信号分子在此诱导反应中不存在累积效应.进一步研究脯氨酸合成和降解的酶促反应途径,发现外源NO处理前4天内可能主要是通过提高△'-吡咯啉-5-羧酸合成酶(P5CS)的活性来促进脯氨酸的合成,以后直至第8天主要是通过抑制脯氨酸脱氢酶(ProDH)的活性来抑制脯氨酸的降解;ABA对于P5CS和ProDH活性的调节能力弱于NO.此外,Ca2 在NO诱导的盐胁迫下小麦叶片脯氨酸累积的信号分子途径中起重要的介导作用.     

外源CO和NO对水稻种子萌发过程中干旱胁迫损伤的缓解效应

选用水稻品种‘Ⅱ优128’种子为材料,以1.0μmol.L-1高铁血红素(Hematin,H)和200μmol.L-1硝普钠(sodium nitroprusside,SNP)分别作为CO和NO供体,采用PEG-6000模拟干旱胁迫,研究外源CO和NO对干旱胁迫下水稻种子萌发和萌发过程中抗氧化能力的影响。结果表明:高铁血红素和硝普钠处理可以显著提高干旱胁迫下水稻种子的发芽率、芽长和根长;同时显著提高种子淀粉酶活性,显著增加其可溶性糖、可溶性蛋白和脯氨酸含量;还不同程度地诱导增强超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的活性,同时降低质膜相对透性和丙二醛(MDA)含量。研究证实,外源CO和NO可通过调节渗透调节物质含量和保护酶活性来有效缓解干旱胁迫对萌发水稻种子造成的氧化伤害,促进种子萌发生长。     

干旱胁迫下紫花苜蓿幼苗非结构性碳水化合物代谢对NO的响应

以紫花苜蓿（Medicago sativa）为材料,采用盆栽试验方法,用聚乙二醇（PEG-6000）作为渗透介质模拟干旱胁迫,外源喷施NO供体硝普钠,NO清除剂（carboxy-PTIO,cPTIO）,对紫花苜蓿幼苗叶片、根系中非结构性碳水化合物含量及相关酶活性的变化进行研究,探讨NO对紫花苜蓿耐旱机制的作用。结果表明：外源NO促进了紫花苜蓿叶片中淀粉的分解、根系中淀粉的积累,提高叶片及根系中可溶性糖（蔗糖、果糖和葡萄糖）含量,降低了渗透势,促进细胞吸水,缓解干旱造成的损伤。此外,外源NO能提高干旱胁迫下紫花苜蓿叶片中蔗糖合成酶（SS）、酸性转化酶（AI）和中性转化酶（NI）活性,降低了蔗糖磷酸合成酶（SPS）的活性,提高根系中SS、SPS和转化酶活性,使蔗糖的合成与分解处于高水平的动态平衡,增强了紫花苜蓿的抗旱性。而NO清除剂cPTIO则会不同程度的抑制紫花苜蓿幼苗中非结构性碳水化合物（NSC）及其相关酶活性。因此,NO可以通过调控NSC的代谢响应干旱胁迫,缓解干旱胁迫造成的不利影响,在紫花苜蓿的抗旱中扮演着重要的角色。     

Role of nitric oxide dependence on nitric oxide synthase-like activity in the water stress signaling of maize seedling

Nitric oxide (NO) has been known as an important signal in plant antioxidative defense but its production and roles in water stress are less known. The present study investigated whether NO dependence on a NO synthase-lika (NOS) activity is involved in the signaling of drought-induced protective responses in maize seedlings. NOS activity, rate of NO release and drought responses were analyzed when NO donor sodium nitroprusside (SNP), NO scavenger c-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramathylimidazoline-1-oxyl-3-oxide) and NOS inhibitor L-NAME (NG-nitro-L-arginine methyl ester) were applied to both detached maize leaves and whole plants. Both NOS activity and the rate of NO release increased substantially under dehydration stress. The high NOS activity induced by c-PTIO as NO scavenger and NO accumulation Inhibited by NOS inhibitor L-NAME In dehydration-treated maize seedlings Indicated that most NO production under water deficit stress may be generated from NOS-like activity. After dehydration stress for 3 h, detached maize leaves pretreated with NO donor SNP maintained more water content than that of control leaves pretreated with water. This result was consistent with the decrease in the transpiration rate of SNP-treated leaves subjected to drought treatment for 3 h. Membrane permeability, a cell injury index, was lower in SNP-trested maize leaves under dehydration stress for 4 h when compared with the control leaves. Also, superoxide dismutsse (SOD) activity of SNP combined drought treatment maize leaves was higher than that of drought treatment alone, indicating that exogenous NO treatment alleviated the water loss and oxidative damage of maize leaves under water deficit stress. When c-PTIO as a specific NO scavenger was applied, the effects of applied SNP were overridden. Treatment with L-NAME on leaves also led to higher membrane permeability, higher transpiration rate and lower SOD activities than those of control leaves, indicating that NOS-like activity was involved in the antioxidative defense under water stress. These results suggested that NO dependence on NOS-like activity serves as a signaling component in the induction of protective responses and is associated with drought tolerance in maize seedlings.     

Effect of exogenous nitric oxide on sulfur and nitrate assimilation pathway enzymes in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under drought stress

The present study aimed at investigating the effects of foliar applied nitric oxide (as SNP [sodium nitroprusside]) on sulfur (glutathione reductase, guaiacol peroxidase, and glutathione S-transferase) and nitrate assimilation (nitrite and nitrate reductase) pathway enzymes in maize (Zea mays L.) exposed to water deficit conditions. The seedlings of a drought tolerant (NK8711) and sensitive (P1574) maize hybrid were applied with various SNP doses (0, 50, 100, 150, and 200 µM) under normal and drought stress conditions. Foliar spray of 100 µM markedly improved water status and chlorophyll contents and alleviated drought-induced oxidative damages through increased antioxidant (catalase, ascorbate peroxidase, and superoxide dismutase) activities in both maize hybrids. Moreover, exogenous SNP supply increased nitrite and nitrate reductase activities and upregulated glutathione reductase, glutathione S-transferase, and guaiacol peroxidase compared to no SNP supply. Interestingly, the negative effects of excess NO generation at high SNP doses (150, 200 µM) were more pronounced in P1574 than NK8711 leading to lower biomass accumulation in drought-sensitive hybrid.     

Responses of sweet potato peroxidases to sodium nitroprusside-mediated nitric oxide

To ascertain the response of sweetpotato peroxidases (PODs) to nitric oxide (NO), we treated the leaves of sweet potato with the NO generator sodium nitroprusside (SNP) and the NO scavenger carboxyl-PTIO (cPTIO). Exogenous application of more than 5 mM SNP caused damage to sweetpotato leaves at 24 h after treatment. The accumulation of NO in leaves was positively correlated with the SNP dose. The specific activity of PODs in sweet potato leaves was markedly increased by treatment with greater than 1 mM SNP for 24 h, whereas POD activity and accumulated NO content decreased to low levels by treatment with cPTIO. Expression analysis of POD genes in response to treatment with SNP and cPTIO revealed that major stress-inducible acidic genes, such as swpa1, swpa2, swpa3, and swpa4, were specifically regulated. These results indicate that increased NO levels in sweet potato leaves are closely linked to an improved defense capability mediated by stress-inducible PODs.     

Cadmium decreases crown root number by decreasing endogenous nitric oxide,which is indispensable for crown root primordia initiation in rice seedlings

Cadmium (Cd) is toxic to crown roots (CR), which are essential for maintaining normal growth and development in rice seedlings. Nitric oxide (NO) is an important signaling molecule that plays a pivotal role in plant root organogenesis. Here, the effects of Cd on endogenous NO content and root growth conditions were studied in rice seedlings. Results showed that similar to the NO scavenger, cPTIO, Cd significantly decreased endogenous NO content and CR number in rice seedlings, and these decreases were recoverable with the application of sodium nitroprusside (SNP, a NO donor). Microscopic analysis of root collars revealed that treatment with Cd and cPTIO inhibited CR primordia initiation. In contrast, although SNP partially recovered Cd-caused inhibition of CR elongation, treatment with cPTIO had no effect on CR elongation. l-NMMA, a widely used nitric oxide synthase (NOS) inhibitor, decreased endogenous NO content and CR number significantly, while tungstate, a nitrate reductase (NR) inhibitor, had no effect on endogenous NO content and CR number. Moreover, enzyme activity assays indicated that treatment with SNP inhibited NOS activity significantly, but had no effect on NR activity. All these results support the conclusions that a critical endogenous NO concentration is indispensable for rice CR primordia initiation rather than elongation, NOS is the main source for endogenous NO generation, and Cd decreases CR number by inhibiting NOS activity and thus decreasing endogenous NO content in rice seedlings.     

Effects of root and foliar applications of exogenous NO on alleviating cadmium toxicity in lettuce seedlings

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in lettuce seedlings were studied. SNP was added into hydroponic systems or sprayed directly on the leaves of plants grown with and without Cd. Excess supply of Cd (100 μM) caused growth inhibition, dramatically increased Cd accumulation in both leaves and roots, and inhibited the absorption of Ca, Mg, Fe and Cu. Excess Cd also decreased activities of superoxide dismutase peroxidase and catalase in leaves and roots, and increased the accumulation of superoxide anion (O ₂ ^·? ), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). Root or foliar applications of exogenous NO alleviated Cd-induced growth suppression, especially root application of 250 μM SNP and foliar addition of 500 μM SNP. Addition of SNP promoted the chlorophyll synthesis suggesting that the photosynthesis was up-regulated. Exogenous NO increased Cd-decreased activities of antioxidant enzymes and markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation. Moreover, the absorption of Ca, Mg, Fe and Cu was increased, indicating that exogenous NO stimulated H⁺-ATPase activity to promote sequestration or uptake of ions. In addition, exogenous NO also inhibited Cd transfer from roots to shoots, which may indicate that Cd retention in roots induced by NO plays a significant role in Cd tolerance in lettuce seedlings. These data suggest that under Cd stress, exogenous NO improves photosynthesis by increasing chlorophyll synthesis, protects lettuce seedlings against oxidative damage by scavenging ROS, helps to maintain the uptake of nutrient elements, and inhibits Cd transferred to shoots effectively.     

Physiology of rice tungro virus disease: Proline accumulation due to infection

Tungro virus infection stimulates proline accumulation in leaves of rice ( Oryza sativa L.), especially in a sensitive cultivar, Taichung Native 1. Disease-induced proline accumulation increases with the severity of the disease. Proline also accumulates in senescing, detached healthy rice leaves. The magnitude of proline accumulation in these leaves was further accentuated by ABA and retarded by kinetin. In the absence of drought stress, virus infection induces severe symptoms (stunting) in a drought tolerant cultivar (Lalnakanda 41) when compared to cultivars with intermediate (MW 10) and high sensitivity (Cauvery) to drought. Thus tungro virus mimics water stress in inducing proline accumulation in rice leaves. In both cases a common factor, ABA, may mediate proline accumulation. In drought stress, proline accumulation is associated with tolerance, while in virus stress, proline accumulation is connected with sensitivity. It is, therefore, clear that proline cannot always act to relieve physiological stress.     

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.     

外源一氧化氮对镉胁迫下玉米幼苗根生长及氧化伤害的影响

以玉米幼苗为材料,通过在镉处理的同时补充外源一氧化氮(NO)供体硝普钠(SNP)及其类似物[K3Fe(CN)6]、以及NO消除剂,分析NO对植物耐镉性的影响,探讨NO在植物逆境胁迫响应中的作用及其机理。结果显示:添加20μmol·L-1 SNP能显著降低镉引发的玉米幼苗根生长抑制及根尖内源镉的积累,减少电解质的渗漏以及超氧化物自由基(O2.-)和过氧化氢(H2O2)的上升幅度,抑制超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性的增加,进一步提高镉胁迫下谷胱甘肽还原酶(GR)的活性。SNP的上述效应可被NO消除剂2-(4-羧基-2-苯基)-4,4,5,5-四甲基咪唑-1-氧-3-氧化物(cPTIO)所逆转,而SNP类似物K3Fe(CN)6的应用对上述反应几乎无影响,说明该反应具有NO特异性。研究表明,外源NO能够显著缓解镉胁迫对玉米幼苗生长造成的伤害,该缓解作用主要是通过降低植株体内内源镉积累和减轻镉诱发的氧化伤害来实现的。     

外源一氧化碳对干旱胁迫下水稻幼苗抗氧化系统的影响

以水稻(Oryza sativa L.) 品种‘D奇宝优1号'幼苗为材料,采用20%聚乙二醇(PEG-6000)模拟水分胁迫,研究外源一氧化碳(CO)对干旱胁迫下水稻幼苗抗氧化能力的影响,以探索CO提高水稻幼苗抗旱性的机制.结果显示,CO供体高铁血红素(Hematin,H)显著降低干旱胁迫下水稻幼苗叶片质膜相对透性和丙二醛(MDA)含量,提高脯氨酸和可溶性蛋白的含量,不同程度地促进叶片中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的活性,而CO清除剂血红蛋白(Hemoglobin,Hb)则逆转CO供体对干旱胁迫下水稻幼苗氧化损伤的缓解效应.由此表明,外源CO能通过调整保护酶活性和渗透调节物质含量来提高水稻幼苗的抗氧化能力,有效增强其抗旱性.     

Interactive role of nitric oxide and calcium chloride in enhancing tolerance to salt stress

Nitric oxide (NO), a small diffusible, ubiquitous bioactive molecule, acts as prooxidant as well as antioxidant, and also regulates remarkable spectrum of plant cellular mechanisms. The present work was undertaken to investigate the role of nitric oxide donor sodium nitroprusside (SNP) and/or calcium chloride (CaCl(2)) in the tolerance of excised mustard leaves to salt stress. After 24h, salt stressed leaves treated with SNP and/or CaCl(2), showed an improvement in the activities of carbonic anhydrase (CA) and nitrate reductase (NR), and leaf chlorophyll (Chl) content, leaf relative water content (LRWC) and leaf ion concentration as compared with the leaves treated with NaCl only. Salinity stress caused a significant increase in H(2)O(2) content and membrane damage which is witnessed by enhanced levels of thiobarbituric acid reactive substances (TBARS) and electrolyte leakage. By contrast, such increases were blocked by the application of 0.2mM SNP and 10mM CaCl(2) to salt stressed leaves. Application of SNP and/or CaCl(2) alleviated NaCl stress by enhancing the activities of antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) and by enhancing proline (Pro) and glycinebetaine (GB) accumulation with a concomitant decrease in H(2)O(2) content, TBARS and electrolyte leakage, which is manifested in the tolerance of plants to salinity stress. Moreover, application of SNP with CaCl(2) was more effective to reduce the detrimental effects of NaCl stress on excised mustard leaves. In addition to this, ameliorating effect of SNP was not effective in presence of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide]. To put all these in a nut shell, the results advocate that SNP in association with CaCl(2) plays a role in enhancing the tolerance of plants to salt stress by improving antioxidative defence system, osmolyte accumulation and ionic homeostasis.     

Nitric oxide alleviates manganese toxicity by preventing oxidative stress in excised rice leaves

In the present study, we have investigated the effects of nitric oxide (NO) on alleviating manganese (Mn)-induced oxidative stress in rice leaves. Exogenous MnCl₂ treatment to excised rice leaves for 24 and 48 h resulted in increased production of H₂O₂ and lipid peroxides, decline in the levels of antioxidants, glutathione and ascorbic acid, and increased activities of antioxidative enzymes, superoxide dismutase, guaiacol peroxidase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Treatment of rice leaves with 100 μM sodium nitroprusside (SNP), a NO donor, was effective in reducing Mn-induced increased levels of H₂O₂, lipid peroxides and increased activities of antioxidative enzymes. The levels of reduced ascorbate and glutathione were considerably recovered due to SNP treatment. The effect of SNP was reversed by the addition of NO scavenger, 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (c-PTIO) suggesting that ameliorating effect of SNP is due to release of NO. The results indicate that MnCl₂ induces oxidative stress in excised rice leaves, lowers the levels of reduced ascorbate and glutathione, and elevates activities of the key antioxidative enzymes. NO appears to provide a protection to the rice leaves against Mn-induced oxidative stress and that exogenous NO application could be advantageous in combating the deleterious effects of Mn-toxicity in rice plants.     

Differential plant growth and osmotic effects of two maize (<Emphasis Type="Italic">Zea mays</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) cultivars to exogenous glycinebetaine application under drought stress

We investigated the effects of exogenous glycinebetaine (GB) and drought stress (DS) on grain yield (GY) and production of dry matter (DM) and osmolytes in two maize (Zea mays L.) cultivars i.e. Shaandan 9 (S₉) and Shaandan 911 (S₉₁₁) during the entire growing period. Drought stress substantially reduced DM and GY but increased free proline, endogenous GB, soluble sugar and K⁺ concentrations in leaves of both cultivars. The DM production, GY, drought index (DI) and concentrations of these osmolytes were greater for S₉ than those for S₉₁₁ under DS. The significant differences in these parameters suggested that S₉ was more drought-tolerant as compared to S₉₁₁. Additionally, foliar application of GB increased the concentrations of all osmolytes measured, DM and GY of both cultivars under DS. These positive responses of exogenous GB spray were more pronounced in S₉₁₁ as compared to those in S₉. Further correlation analysis involving a number of parameters indicated that maize production was tighterly correlated with accumulation of the osmolytes measured during DS rather than well-watered controls. Accordingly, this study demonstrated the notion of an anti-drought role of exogenous GB by osmoregulation under DS, particularly in this drought sensitive cultivar. Thus, exogenous GB application might be firstly used with drought sensitive species/cultivars when exposed to DS.     

Adaptive responses of <Emphasis Type="Italic">Populus przewalskii</Emphasis> to drought stress and SNP application

In this study we used the cuttings of Populus przewalskii Maximowicz as experimental material and sodium nitroprusside (SNP) as nitric oxide (NO) donor to determine the physiological and biochemical responses to drought stress and the effect of NO on drought tolerance in woody plants. The results indicated that drought stress not only significantly decreased biomass production, but also significantly increased hydrogen peroxide content and caused oxidative stress to lipids and proteins assessed by the increase in malondialdehyde and total carbonyl contents, respectively. The cuttings of P. przewalskii accumulated many amino acids for osmotic adjustment to lower water potential, and activated the antioxidant enzymes such as superoxide dismutase, guaiacol peroxidase and ascorbate peroxidase to maintain the balance of generation and quenching of reactive oxygen species. Moreover, exogenous SNP application significantly heightened the growth performance of P. przewalskii cuttings under drought treatment by promotion of proline accumulation and activation of antioxidant enzyme activities, while under well-watered treatment the effect of SNP application was very little.     

Overexpression of Rat Neurons Nitric Oxide Synthase in Rice Enhances Drought and Salt Tolerance

Nitric oxide (NO) has been shown to play an important role in the plant response to biotic and abiotic stresses in Arabidopsis mutants with lower or higher levels of endogenous NO. The exogenous application of NO donors or scavengers has also suggested an important role for NO in plant defense against environmental stress. In this study, rice plants under drought and high salinity conditions showed increased nitric oxide synthase (NOS) activity and NO levels. Overexpression of rat neuronal NO synthase (nNOS) in rice increased both NOS activity and NO accumulation, resulting in improved tolerance of the transgenic plants to both drought and salt stresses. nNOS-overexpressing plants exhibited stronger water-holding capability, higher proline accumulation, less lipid peroxidation and reduced electrolyte leakage under drought and salt conditions than wild rice. Moreover, nNOS-overexpressing plants accumulated less H₂O₂, due to the observed up-regulation of OsCATA, OsCATB and OsPOX1. In agreement, the activities of CAT and POX were higher in transgenic rice than wild type. Additionally, the expression of six tested stress-responsive genes including OsDREB2A, OsDREB2B, OsSNAC1, OsSNAC2, OsLEA3 and OsRD29A, in nNOS-overexpressing plants was higher than that in the wild type under drought and high salinity conditions. Taken together, our results suggest that nNOS overexpression suppresses the stress-enhanced electrolyte leakage, lipid peroxidation and H₂O₂ accumulation, and promotes proline accumulation and the expression of stress-responsive genes under stress conditions, thereby promoting increased tolerance to drought and salt stresses.     

Glycine betaine application modifies biochemical attributes of osmotic adjustment in drought stressed wheat

Nineteen wheat genotypes were used to examine the effects of foliar applied glycine betaine (GB, 100 mM) on concentration of various osmolytes (such as proline, choline, GB and sucrose) under drought stress conditions. Drought stress caused a significant increase in proline content and GB content of wheat genotypes, both at maximum tillering and anthesis stages. Choline and sucrose were accumulated significantly at higher levels under stress conditions at both the stages. GB application increased the proline content and endogenous levels of GB in comparison to their stressed counterparts both at maximum tillering and anthesis stages but this increase was observed to be genotype specific. Furthermore, significant decrease in choline levels and sucrose contents of GB treated plants at anthesis stage and enhanced levels of proline questioned about involvement of GB in production of other osmolytes as well as stage specific response of wheat genotypes to GB spray. But these changes in osmolyte accumulation (OA) were not correlated with relative water content and stress tolerance index observed, under both GB sprayed and non-sprayed drought stressed conditions. So OA could not be considered as a selection criteria for drought tolerance in wheat.