Influence of environmental factors on the generation of nitric oxide in the roots of etiolated pea seedlings

The article studies the nitric oxide (NO) levels in the roots of etiolated seedlings of sowing peas (Pisum sativum L.) using the DAF-2DA fluorescent probe and fluorescent microscopy. Cross sections of roots of 100–150 μm (the site of a root which is 10–15 mm from the apex) are analyzed. It is shown that the level of NO in the roots after 24 h increased by more than a factor of 2 in the versions with NaNO₂ and sodium nitroprusside. At feeding the seedlings with KNO₃, a peak in the accumulation of NO in the roots (twofold increase) was observed after 30 min. Fertilizing seedlings with L-arginine (2 mM) increased the intensity of the fluorescence of the root sections by more than a factor of 2. The inoculation of seedlings of rhizobia (Rhizobium leguminosarum bv. viceae) contributed to the reduction of NO on the background of the control (H2O) and sodium nitroprusside and nitrogen compounds. Scavengers of NO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), hemoglobin) and inhibitors of nitrate reductase and animal NO synthase (sodium tungstate and aminoguanidine hydrochloride) reduced the level of NO in the roots. The results are discussed in relation to the role of NO in plants under the influence of biotic and abiotic factors.     

Initiation of nitric oxide (NO) synthesis in roots of etiolated seedlings of pea (Pisum sativum L.) under the influence of nitrogen-containing compounds

The level of nitric oxide (NO) in roots of 2-day-old etiolated pea (Pisum sativum L.) seedlings was investigated by fluorescence microscopy using the fluorescent probe 4,5-diaminofluorescein diacetate. Segments representing transversal (cross) cuts of the roots having thickness of 100 to 150 μm (a segment of the root located 10 to 15 mm from the apex) were analyzed. A substantial concentration of NO in the roots was registered when the seedlings were grown in water (control). Addition of 4 mM sodium nitroprusside, 20 mM KNO₃, 2 mM NaNO₂, 2 mM L-arginine into the growth medium increased NO concentration with respect to the control by 1.7- to 2.3-fold. Inhibitors of animal NO-synthase — 1 mM Nω-nitro-L-arginine methyl ester hydrochloride and 1 mM aminoguanidine hydrochloride — reduced the intensity of fluorescence in the root segments in the presence of all the studied compounds. In medium with KNO₃, the inhibitor of nitrate reductase ?150 μM sodium tungstate -lowered the fluorescence intensity by 60%. Scavengers of nitric oxide — 100 μM 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and 4 μM hemoglobin — lowered NO concentration in all the studied variants. Potassium ferrocyanide (4 mM) as the inactive analog of sodium nitroprusside inhibited generation of NO. These results are discussed regarding possible pathways of NO synthesis in plants.     

Nitric oxide, polyamines and Cd-induced phytotoxicity in wheat roots

To further explore the biochemical basis of Cd toxicity in developing wheat seedlings, we studied the possible role of nitric oxide (NO) and polyamines as signaling molecules involved in metal-induced root growth inhibition. When used at 0.1 mM, sodium nitroprusside, a NO-releasing compound, inhibited root growth to a similar extent as Cd and enhanced the polyamine contents as Cd also did. Putrescine and spermidine treatments caused significant decreases in root growth with spermine giving the greatest level of inhibition (77% reduction). The simultaneous addition of Cd and inhibitors of putrescine biosynthesis (DFMA and DFMO) prevented increases in putrescine levels but did not restore normal root growth. NO content, as evidenced by the fluorescent probe DAF-FM diacetate, was found to be significantly increased in the roots of both Cd and polyamine treated plants, especially in those exposed to spermine. The effect was specific for NO since the NO scavenger cPTIO almost suppressed the fluorescent signal. Concerning the oxidative status of the root system, only Cd and spermine enhanced lipid peroxidation in roots. At the same time, all treatments led to a significant increase in levels of the non-enzymatic antioxidant defense glutathione. Our results strongly suggest that Cd and spermine treatments induce NO formation in wheat roots which, in turn, is involved in root growth inhibition.     

Induction of heat resistance in wheat seedlings by exogenous calcium,hydrogen peroxide,and nitric oxide donor: functional interaction of signal mediators

Functional interactions of calcium ions, hydrogen peroxide, and nitric oxide as signal mediators in root cells of wheat (Triticum aestivum L.) seedlings upon induction of their heat resistance was studied with use of inhibitor-based analysis. Treatment of the seedlings with hydrogen peroxide or a combination of calcium chloride with ionophore A23187 significantly increased their content of nitric oxide, which peaked 0.5–1 h after the start of the treatment. CaCl₂ or exogenous NO donor (sodium nitroprusside, SNP) transitorily increased the hydrogen peroxide level in the roots. Seedlings pretreatments with calcium chelator (EGTA), blocker of Ca²⁺ channels (LaCl₃), inhibitor of phospholipase C (neomycin), or antagonist of cyclic adenosine-5'-diphosphatribose formation (nicotinamide) more or less prevented the rise in the nitric oxide content in roots caused by exogenous H₂O₂; the SNP-induced rise in hydrogen peroxide was also damped down. However, the seedlings pretreatment with antioxidants ionol or dimethylthiourea did not hinder the increase in the NO level, which was caused by exogenous Ca²⁺. The inhibitors of NO synthase (N^G-nitro-L-arginine methyl ester, L-NAME) or nitrate reductase (sodium tungstate) did not interfere in the accumulation of H₂O₂ in root tissues stimulated by exogenous calcium. Calcium antagonists diminished the seedlings heat resistance increased by hydrogen peroxide or SNP. Antioxidants and inhibitors of NO synthase or nitrate reductase weakened the calcium-stimulated enhancement in the seedlings heat resistance. It was concluded that calcium may activate NO- and H₂O₂-generating enzymatic systems as well as participate in the transduction of signals of these mediators into genetic apparatus and in the formation of physiological reactions underlying the enhanced heat resistance.     

Nitric Oxide is Involved in the <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>-induced Lateral Root Formation in Tomato

Azospirillum spp. is a well known plant-growth-promoting rhizobacterium. Azospirillum-inoculated plants have shown to display enhanced lateral root and root hair development. These promoting effects have been attributed mainly to the production of hormone-like substances. Nitric oxide (NO) has recently been described to act as a signal molecule in the hormonal cascade leading to root formation. However, data on the possible role of NO in free-living diazotrophs associated to plant roots, is unavailable. In this work, NO production by Azospirillum brasilense Sp245 was detected by electron paramagnetic resonance (6.4 nmol. g^–1 of bacteria) and confirmed by the NO-specific fluorescent probe 4,5-diaminofluorescein diacetate (DAF-2 DA). The observed green fluorescence was significantly diminished by the addition of the specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). Azospirillum-inoculated and noninoculated tomato (Lycopersicon esculentum L.) roots were incubated with DAF-2 DA and examined by epifluorescence microscopy. Azospirillum-inoculated roots displayed higher fluorescence intensity which was located mainly at the vascular tissues and subepidermal cells of roots. The Azospirillum-mediated induction of lateral root formation (LRF) appears to be NO-dependent since it was completely blocked by treatment with cPTIO, whereas the addition of the NO donor sodium nitroprusside partially reverted the inhibitory effect of cPTIO. Overall, the results strongly support the participation of NO in the Azospirillum-promoted LRF in tomato seedlings.     

NO参与AM真菌与烟草共生过程

以烟草（Nicotiana tabacum,品种CF90NF）为材料,利用分光光度法和荧光显微技术结合药理学实验,探讨在AM真菌摩西球囊霉(Glomus mosseae,G.m)与烟草共生过程中一氧化氮(nitric oxide, NO)的作用。结果表明,烟草侧根中含有一定水平的内源NO,苗期接种G.m 10天后,烟草根系NO含量显著增加,侧根中的NO荧光强度也在接种后10天达到最强;一定浓度的NO供体硝普钠(sodium nitroprusside,SNP)能促进G.m对烟草的侵染,而NO的清除剂2-4,4,5,5-苯-四甲基咪唑-1-氧-3-氧化物( 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxidepotassium salt,cPTIO)可明显减弱侧根和菌丝中的NO的荧光强度,降低AM真菌的侵染率,表明NO参与G.m与烟草的共生过程;在G.m与烟草的共生过程中,烟草根系硝酸还原酶(nitrate reductase,NR)活性与Nia-1的表达量明显升高,且NR的抑制剂钨酸钠(sodium tungstate,Na2WO4)可以降低烟草侧根中的荧光强度,但对菌丝中的NO的荧光强度无明显影响。由此推测,来自根系NR途径的NO参与AM真菌与烟草的共生过程,菌丝中可能存在其他来源的NO。     

Regulation of defence responses in avocado roots infected with Phytophthora cinnamomi (Rands)

Phytophthora cinnamomi occurs worldwide and has a host range in excess of 1,000 plant species. Avocados (Persea americana Mill) have been described as highly susceptible to this soil-borne pathogen. Here, the regulation of defence responses in avocado root seedlings inoculated with P. cinnamomi mycelia is described. A burst of reactive oxygen species (ROS) was observed 4 days after inoculation. The higher physiological concentration of H₂O₂ induced by P. cinnamomi on avocado roots had no effect on in vitro growth of the oomycete. Total phenols and epicathecin content showed a significant decrease, but lignin and pyocianidins exhibited no changes after inoculation. Also, increased nitric oxide (NO) production was observed 72 h after treatment. We studied the effects of one NO donor [sodium nitroprusside (SNP)], and one NO scavenger [2- to 4-carboxyphenyl-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (CPTIO)] to determine the role of NO during root colonisation by P. cinnamomi mycelia. Pretreatment of the roots with CPTIO, but not with SNP, inhibited root colonisation suggesting an important role for NO production during the avocado–P. cinnamomi interaction. Our data suggest that although defence responses are activated in avocado roots in response to P. cinnamomi infection, these are not sufficient to avoid pathogen invasion.     

Nitric oxide is involved in nitrate-induced inhibition of root elongation in Zea mays

BACKGROUND AND AIMS: Root growth and development are closely dependent upon nitrate supply in the growth medium. To unravel the mechanism underlying dependence of root growth on nitrate, an examination was made of whether endogenous nitric oxide (NO) is involved in nitrate-dependent growth of primary roots in maize. METHODS: Maize seedlings grown in varying concentrations of nitrate for 7 d were used to evaluate the effects on root elongation of a nitric oxide (NO) donor (sodium nitroprusside, SNP), a NO scavenger (methylene blue, MB), a nitric oxide synthase inhibitor (N(omega)-nitro-L-arginine, L-NNA), H(2)O(2), indole-3-acetic acid (IAA) and a nitric reducatse inhibitor (tungstate). The effects of these treatments on endogenous NO levels in maize root apical cells were investigated using a NO-specific fluorescent probe, 4, 5-diaminofluorescein diacetate (DAF-2DA) in association with a confocal microscopy. KEY RESULTS: Elongation of primary roots was negatively dependent on external concentrations of nitrate, and inhibition by high external nitrate was diminished when roots were treated with SNP and IAA. MB and L-NNA inhibited root elongation of plants grown in low-nitrate solution, but they had no effect on elongation of roots grown in high-nitrate solution. Tungstate inhibited root elongation grown in both low- and high-nitrate solutions. Endogenous NO levels in root apices grown in high-nitrate solution were lower than those grown in low-nitrate solution. IAA and SNP markedly enhanced endogenous NO levels in root apices grown in high nitrate, but they had no effect on endogenous NO levels in root apical cells grown in low-nitrate solution. Tungstate induced a greater increase in the endogenous NO levels in root apical cells grown in low-nitrate solution than those grown in high-nitrate solution. CONCLUSIONS: Inhibition of root elongation in maize by high external nitrate is likely to result from a reduction of nitric oxide synthase-dependent endogenous NO levels in maize root apical cells.     

Nitric oxide stimulates seed germination and counteracts the inhibitory effect of heavy metals and salinity on root growth of Lupinus luteus

Nitric oxide (NO) is a bioactive molecule, which in plants was found to function as prooxidant as well as antioxidant. In the present study, we found that NO donor sodium nitroprusside (SNP) stimulates seed germination and root growth of lupin (Lupinus luteus L. cv. Ventus). Seed germination is promoted at concentrations between 0.1 and 800 μM SNP in a dose-dependent manner. The stimulation was most pronounced after 18 and 24 h and ceased after 48 h of imbibition. The promoting effect of NO on seed germination persisted even in the presence of heavy metals (Pb, Cd) and sodium chloride. Pretreatment of lupin seedlings for 24 h with 10 μM SNP resulted in efficient reduction of the detrimental effect of the abiotic stressors on root growth and morphology. The inhibitory effect of heavy metals on root growth was accompanied by increased activity of superoxide dismutase (SOD, EC 1.15.1.1.), which in roots preincubated with SNP was significantly higher. Some changes in the activity of other antioxidant enzymes, peroxidase (POX, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) were also detected. Using the superoxide anion (O₂^•–)-specific indicator dihydroethidium (DHE), we found intense DHE-derived fluorescence in heavy metal-stressed roots, whereas in those pretreated with SNP the fluorescence was very low, comparable to the level in unstressed roots. On the basis of the above data, we conclude that the protective effect of NO in stressed lupin roots may be at least partly due to the stimulation of SOD activity and/or direct scavenging of the superoxide anion.     

Arsenic-induced oxidative stress in the common bean legume,Phaseolus vulgaris L. seedlings and its amelioration by exogenous nitric oxide

The adverse effects of arsenic (As) toxicity on seedling growth, root and shoot anatomy, chlorophyll and carotenoid contents, root oxidizability (RO), antioxidant enzyme activities, H₂O₂ content, lipid peroxidation and electrolyte leakage (EL%) in common bean (Phaseolus vulgaris L.) were investigated. The role of exogenous nitric oxide (NO) in amelioration of As-induced inhibitory effect was also evaluated using sodium nitroprusside (100 μM SNP) as NO donor and 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (200 μM PTIO) as NO scavenger in different combinations with 50 μM As. As-induced growth inhibition was associated with marked anomalies in anatomical features, reduction in pigment composition, increased RO and severe perturbations in antioxidant enzyme activities. While activity of superoxide dismutase and catalase increased, levels of ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase decreased significantly and guaiacol peroxidase remained normal. The over-accumulation of H₂O₂ content along with high level of lipid peroxidation and electrolyte leakage indicates As-induced oxidative damage in P. vulgaris seedlings with more pronounced effect on the roots than the shoots. Exogenous addition of NO significantly reversed the As-induced oxidative stress, maintaining H₂O₂ in a certain level through balanced alterations of antioxidant enzyme activities. The role of NO in the process of amelioration has ultimately been manifested by significant reduction of membrane damage and improvement of growth performance in plants grown on As + SNP media. Onset of oxidative stress was more severe after addition of PTIO, which confirms the protective role of NO against As-induced oxidative damage in P. vulgaris seedlings.     

硝普钠缓解镧引起的黑麦草幼苗生长抑制和根系氧化损伤

采用水培方法,研究了外源一氧化氮（NO）供体硝普钠（SNP）对300 μmol·L^-1 LaCl₃胁迫下黑麦草幼苗生长和根系活性氧代谢的影响。结果表明：在LaCl₃胁迫下,喷施50 μmol·L^-1 SNP能够抑制镧（La）从黑麦草根系向地上部的转运,缓解La对幼苗生长的抑制作用;提高幼苗根系超氧化物歧化酶和抗坏血酸过氧化物酶活性,降低过氧化物酶活性及谷胱甘肽、脯氨酸、H₂O₂、丙二醛含量、超氧阴离子产生速率和质膜相对透性,对过氧化氢酶活性和抗坏血酸含量无显著影响。表明NO可通过活性氧代谢的调节,缓解高浓度La胁迫对黑麦草幼苗生长的抑制作用。     

Early generation of nitric oxide contributes to copper tolerance through reducing oxidative stress and cell death in hulless barley roots

The objective of this study was to investigate the specific role of nitric oxide (NO) in the early response of hulless barley roots to copper (Cu) stress. We used the fluorescent probe diaminofluorescein-FM diacetate to establish NO localization, and hydrogen peroxide (H₂O₂)-special labeling and histochemical procedures for the detection of reactive oxygen species (ROS) in the root apex. An early production of NO was observed in Cu-treated root tips of hulless barley, but the detection of NO levels was decreased by supplementation with a NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO). Application of sodium nitroprusside (a NO donor) relieved Cu-induced root inhibition, ROS accumulation and oxidative damage, while c-PTIO treatment had a synergistic effect with Cu and further enhanced ROS levels and oxidative stress. In addition, the Cu-dependent increase in activities of superoxide dismutase, peroxidase and ascorbate peroxidase were further enhanced by exogenous NO, but application of c-PTIO decreased the activities of catalase and ascorbate peroxidase in Cu-treated roots. Subsequently, cell death was observed in root tips and was identified as a type of programed cell death (PCD) by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The addition of NO prevented the increase of cell death in root tips, whereas inhibiting NO accumulation further increased the number of cells undergoing PCD. These results revealed that NO production is an early response of hulless barley roots to Cu stress and that NO contributes to Cu tolerance in hulless barley possibly by modulating antioxidant defense, subsequently reducing oxidative stress and PCD in root tips.     

NO和NADPH-黄递酶在绿豆下胚轴不定根发生和发育过程中的变化(英文)

研究了一氧化氮(NO)供体硝普钠(SNP)、一氧化氮清除剂c-PTIO和一氧化氮合酶(NOS)抑制剂L-NAME对绿豆(Vigna radiata L.)下胚轴插条生根的影响,并对不定根发生期间插条基部NO和NADPH-黄递酶的时空变化进行了检测。所试浓度SNP均明显促进下胚轴不定根发生。分别在插条切取后24 h和36 h于其基部维管束之间检测到NADPH-黄递酶(NOS标记酶)阳性反应和NO荧光,根原基也于48 h在相同位置出现,并于60 h进一步伸长。48-60h期间,NADPH-黄递酶的阳性反应及NO荧光有增强趋势,并主要分布在不定根分生组织中。L-NAME既减弱NADPH-黄递酶的阳性反应和NO荧光,也延缓不定根发生;而c-PTIO对NO荧光及不定根发生均有抑制作用。上述结果证明:NO在不定根发生及发育过程中有重要作用,而且此过程中的NO很可能由类似的NOS催化产生。     

NO和NADPH-黄递酶在绿豆下胚轴不定根发生和发育过程中的变化

研究了一氧化氮(NO)供体普钠(SNP)、一氧化氮清除剂C-PTIO和一氧化氮合酶(NOS)抑制L-NAME对绿豆(Vigna radiataL.)下胚轴插条生根的影响.并对不定根生期间手条基部NO 和NADPH-黄递酶的时空变化进行了检测.所试浓度SNP均明显促进下胚轴不根发生.分别插条切取后24h和36h于其基部维管束之间检测到NADPH-黄递酶(NOS标记酶)阳性反应和NO荧光,根原基也于48h在相同位置出现,并于60h进一步伸长.48~60h期间,NADPH、黄递的阳性反应及NO荧光有增强趋势,并主要分布在不定根分生组织中.L-NAME既减弱NADPH-黄递酶的阳性反应和NO荧光,也延缓不不定根发生;而c-PTIO对NO荧光及不定根生均有抑制作用.上述结果证明:NO在不定根发生及发育过程中有重要作用,而且此过程中的NO很可能由类似的NOS催化产生.     

Genotype-Dependent Effect of Exogenous Nitric Oxide on Cd-induced Changes in Antioxidative Metabolism, Ultrastructure, and Photosynthetic Performance in Barley Seedlings (Hordeum vulgare)

A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O₂^•−, H₂O₂, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P _n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD) and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover, Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced damage to leaf/root ultrastructure, and increased chlorophyll content and P _n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments. Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular structure.     

Nitric oxide as a critical factor for perception of UV-B irradiation by microtubules in Arabidopsis

Influence of ultraviolet-B (UV-B) as an abiotic stress factor on plant microtubules (MTs) and involvement of nitric oxide (NO) as a secondary messenger mediating plant cell response to environmental stimuli were investigated in this study. Taking into account that endogenous NO content in plant cells has been shown to be increased under a broad range of abiotic stress factors, the effects of UV-B irradiation and also the combined action of UV-B and NO donor sodium nitroprusside (SNP) or NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) on the MTs organization in different root cells of Arabidopsis thaliana were tested. Subsequently, realization of the MT-mediated processes such as root growth and development was studied under these conditions. Arabidopsis thaliana seedlings expressing the chimeric gene gfp-map4 were exposed to the enhanced UV-B with or without SNP or c-PTIO pretreatment. The UV-B irradiation alone led to a dose-dependent root growth inhibition and to morphological alterations of the primary root manifested in their swelling and excessive root hair formation. Moreover, dose-dependent randomization and depolymerization of MTs in both epidermal and cortical cells under the enhanced UV-B were found. However, SNP pretreatment of the UV-B irradiated A. thaliana seedlings recovered the UV-B inhibited root growth as compared to c-PTIO pretreatment. It has been shown that in 24 h after UV-B irradiation the organization of MTs in root epidermal cells of SNP-pretreated A. thaliana seedlings was partially recovered, whereas in c-PTIO-pretreated ones the organization of MTs has not been distinctly improved. Therefore, we suppose that the enhanced NO levels in plant cells can protect MTs organization as well as MT-related processes of root growth and development against disrupting effects of UV-B.     

Nitric oxide affecting root growth,lignification and related enzymes in soybean seedlings

This study analyzed the involvement of nitric oxide (NO) in the root lignification of soybean seedlings. To this end, changes in root cell viability; phenylalanine ammonia-lyase (PAL) and soluble and cell wall bound peroxidase (POD) activities and lignin and hydrogen peroxide (H₂O₂) contents of soybean roots treated with the NO-donor sodium nitroprusside (SNP) and its relationships with root growth were evaluated. Seedlings were cultivated in a nutrient solution supplemented with 5 to 1,000 μM SNP for 24 h. At an extremely low concentration (5 μM), SNP induced root growth and increased lignification and activities of related enzymes (PAL and cell wall-bound POD). At a high concentration (1,000 μM), SNP reduced root growth and lignification (PAL activity and H₂O₂ and lignin contents) and caused a loss of cell viability. Application of potassium ferrocyanide (an analog of SNP that cannot release NO) and PTIO (2-phenyl-4,4,5,5,-tetramethylimidazoleline-1-oxyl-3-oxide, a scavenger of NO) revealed that the inhibitory/stimulatory effects on root lignification may be due to NO itself. These results indicate that NO, depending on its concentration, may act as a stress factor, due to its toxic action, or as a signal molecule, inducing soybean root growth and lignification.     

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.     

Nitric oxide enhances aluminum tolerance by affecting cell wall polysaccharides in rice roots

Nitric oxide (NO) is a key signal molecule involved in many physiological processes in plants. To study the mechanisms of exogenous NO contribution to alleviate the aluminum (Al) toxicity, roots of rice (Oryza sativa) seedlings pre-treated with sodium nitroprusside (SNP, a NO donor) were used to investigate the effect of Al in this study. Results indicated that NO alleviated the lipid peroxidation induced by Al and promoted the root elongation, whereas butylated hydroxyanisole (BHA), an efficient lipophilic antioxidant, alleviated the lipid peroxidation only. Rice seedling roots pre-treated with SNP followed by Al treatment had lower contents of pectin and hemicellulose, lower Al accumulation in root tips and cell walls, higher degree of methylation of pectin and lower wall Al-binding capacity than the roots with Al treatment only. Therefore, the decreased Al accumulation in the cell walls of rice roots is likely to be the reason for the NO-induced increase of Al tolerance in rice, and it seems that exogenous NO enhanced Al tolerance in rice roots by decreasing the contents of pectin and hemicellulose, increasing the degree of methylation of pectin, and decreasing Al accumulation in root cell walls.     

一氧化氮调节盐胁迫下小麦幼苗根部质膜H^＋-ATPase和焦磷酸酶活性提高耐盐性

采用外源一氧化氮(NO)供体硝普钠(SNP)研究了NO对盐胁迫下小麦(Triticum aestivum L.)幼苗耐盐性的影响。结果表明,0.1 mmol/L SNP处理显著缓解了150 mmol/L NaCl 胁迫对小麦幼苗生长的抑制效应,包括水分丧失以及叶绿素降解,从而提高了小麦幼苗的耐盐性。进一步结合1 mg/mL血红蛋白处理则显著逆转了SNP诱导的上述效应;利用亚硝酸钠和铁氰化钾作为对照也证实了NO对小麦幼苗耐盐性的专一性调节作用,并可能与NO对小麦幼苗根部质膜 H -ATPase和焦磷酸酶活性诱导有关。此外,尽管NO显著提高了盐胁迫下小麦幼苗根部细胞质膜H -ATPase和焦磷酸酶的ATP水解活性,但是对跨膜H 转运则没有明显影响。应用外源CaSO4 和 EGTA 处理也证实,Ca2 可能在NO诱导的质膜 H -ATPase和焦磷酸酶活性的提高过程中起信号作用。另外,分析盐胁迫下小麦幼苗根部 Na 和K 含量的变化也发现,NO对Na 含量没有明显影响,但是却显著提高了K 水平和K /Na 比,这可能也是NO提高小麦幼苗耐盐性的原因之一。