The protective effect of aminoguanidine on cerebral ischemic damage in the rat brain

The NADPH-diaphorase (NADPH-d) histochemical technique is commonly used to localize the nitric oxide (NO) produced by the enzyme nitric oxide synthase (NOS) in neural tissue. The expression of inducible nitric oxide synthase (iNOS) is induced in the late stage of cerebral ischemia, and NO produced by iNOS contributes to the delay in recovery from brain neuronal damage. The present study was performed to investigate whether the increase in nitric oxide production via inducible nitric oxide synthase was suppressed by the administration of aminoguanidine, a selective iNOS inhibitor, as it follows a decrease of NADPH-diaphorase activity (a marker for NOS) after four-vessel occlusion used as an ischemic model. The administration of aminoguanidine (100 mg/kg i.p., twice per day up to 3 days immediately after the ischemic insult) reduced the number of NADPH-diaphorase positive cells to control levels. Our results indicated that aminoguanidine suppressed NADPH-diaphorase activity, and also decreased the number of NADPH-diaphorase positive cells in the CA1 region of the hippocampus following ischemic brain injury.     

Exercise conditioning attenuates the hypertensive effects of nitric oxide synthase inhibitor in rat

Many individuals with cardiovascular diseases undergo periodic exercise conditioning with or with out medication. Therefore, this study investigated the interaction of exercise training and chronic nitric oxide synthase (NOS) inhibitor (Nitro-L-Arginine Methyl Ester, L-NAME) treatment on blood pressure and its correlation with aortic nitric oxide (NO), antioxidant defense system and oxidative stress parameters in rats. Fisher 344 rats were divided into four groups: (1) sedentary control, (2) exercise training (ET) for 8 weeks, (3) L-NAME (10 mg/kg, subcutaneous for 8 weeks) and (4) ET + L-NAME. Blood pressure (BP) was monitored weekly for 8 weeks with tail-cuff method. The animals were sacrificed 24 h after last treatments and thoracic aortic rings were isolated and analyzed. Exercise conditioning resulted in a significant increase in respiratory exchange ratio (RER), aortic NO production, NO synthase activity and inducible iNOS protein expression. Training significantly enhanced aortic GSH levels, GSH/GSSG ratio and up-regulation of aortic CuZn-SOD, Mn-SOD, catalase (CAT) glutathione peroxidase (GSH-Px) activity and protein expression and significantly decreased aortic lipid peroxidation. Chronic L-NAME administration resulted in a significant depletion of aortic NO, NOS activity, endothelial (eNOS) and iNOS protein expression, GSH level, GSH/GSSG ratio, down-regulation of aortic antioxidant enzyme activities and protein expressions. Aortic xanthine oxidase (XO) activity significantly increased with increased lipid peroxidation and protein oxidation after L-NAME administration. The biochemical changes were accompanied by increased in BP. Interaction of training and chronic NOS inhibitor treatment resulted in normalization of BP and aortic antioxidant enzyme activity and protein expression, up-regulation of aortic GSH/GSSG ratio, NO levels, Mn-SOD protein expression, depletion of GSSG, protein oxidation and lipid peroxidation. The data suggest that training attenuated the oxidative injury caused by chronic NOS inhibitor treatment by up-regulating the NO and antioxidant systems and lowering the BP in rats.     

Detection and characterisation of NAD(P)H-diaphorase activity in Dictyostelium discoideum cells (Protozoa)

In Dictyostelium discoideum (D. discoideum), compounds generating nitric oxide (NO) inhibit its aggregation and differentiation without altering cyclic guanosine monophosphate (cGMP) production. They do it by preventing initiation of cyclic adenosine monophosphate (cAMP) pulses. Furthermore, these compounds stimulate adenosine diphosphate (ADP)-ribosylation of a 41 kDa cytosolic protein and regulate the glyceraldehyde-3-phospate dehydrogenase activity. Yet, although D. discoideum cells produce NO at a relatively constant rate at the onset of their developmental cycle, there is still no evidence of the presence of nitric oxide synthase (NOS) enzymes. In this work, we detect the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity in D. discoideum and we characterise it by specific inhibitors and physical-chemical conditions that allegedly distinguish between NOS-related and -unrelated NADPH-d activity.Key words: NADPH-diaphorase activity, protozoa, nitric oxide synthase.     

NADPH-diaphorase and nitric oxide synthase in the canine superior cervical ganglion

By means of NADPH-diaphorase (NADPH-d) histochemistry and nitric oxide synthase (NOS) immunohistochemistry, we demonstrate that considerable numbers of NADPH-d-positive neurons are distributed throughout the canine superior cervical ganglion (SCG). These neurons also show NOS immunoreactivity. This finding indicates that NADPH-d histochemistry, a simple and reliable technique, can be used as a reliable marker of NOS activity in the sympathetic innervation of canine head and neck. The present findings suggest that the participation of nitric oxide in the SCG differs greatly between species.     

Activation of the mitogen-activated protein kinase cascade through nitric oxide synthesis as a mechanism of neuritogenic effect of genipin in PC12h cells

Prominent neurite outgrowth induced by genipin, a plant-derived iridoid, was substantially inhibited by addition of NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase (NOS) inhibitor, and carboxy-PTIO, an NO scavenger, in PC12h cells. Increases of the NADPH-diaphorase activity and neuronal and inducible NOS proteins in cells preceded the neurite outgrowth after addition of genipin to medium. NO donors could induce the neurite outgrowth dose-dependently in the cells. On the other hand, an inhibitor of soluble guanylate cyclase (SGC), which is known to be a stimulatory target of NO, abolished greatly the genipin-induced neurite outgrowth. Addition of extracellular signal-regulated kinase (ERK) kinase inhibitors could almost completely abolish the neurite induction. L-NAME remarkably depressed genipin-stimulated phosphorylation of ERK-1 and -2. A neuritogenic effect of nerve growth factor (NGF) in PC12h cells was also remarkably inhibited by the NOS inhibitor, NO scavenger and SGC inhibitor. These findings suggest that induced NO production followed by cyclic GMP-mediated stimulation of the mitogen-activated protein kinase (MAPK) cascade is implicated in the neuritogenesis by genipin and NGF in PC12h cells.     

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.     

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。     

Involvement of Ca2+/calmodulin-dependent protein kinase II in endothelial NO production and endothelium-dependent relaxation

Nitric oxide (NO) is synthesized from l-arginine by the Ca(2+)/calmodulin-sensitive endothelial NO synthase (NOS) isoform (eNOS). The present study assesses the role of Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) in endothelium-dependent relaxation and NO synthesis. The effects of three CaMK II inhibitors were investigated in endothelium-intact aortic rings of normotensive rats. NO synthesis was assessed by a NO sensor and chemiluminescence in culture medium of cultured porcine aortic endothelial cells stimulated with the Ca(2+) ionophore A23187 and thapsigargin. Rat aortic endothelial NOS activity was measured by the conversion of l-[(3)H]arginine to l-[(3)H]citrulline. Three CaMK II inhibitors, polypeptide 281-302, KN-93, and lavendustin C, attenuated the endothelium-dependent relaxation of endothelium-intact rat aortic rings in response to acetylcholine, A23187, and thapsigargin. None of the CaMK II inhibitors affected the relaxation induced by NO donors. In a porcine aortic endothelial cell line, KN-93 decreased NO synthesis and caused a rightward shift of the concentration-response curves to A23187 and thapsigargin. In rat aortic endothelial cells, KN-93 significantly decreased bradykinin-induced eNOS activity. These results suggest that CaMK II was involved in NO synthesis as a result of Ca(2+)-dependent activation of eNOS.     

Macrophage cytotoxicity against Entamoeba histolytica trophozoites is mediated by nitric oxide from L-arginine.

The killing of Entamoeba histolytica trophozoites by phagocytes involves oxidative and nonoxidative mediators. In this study, we determine whether L-arginine-derived nitric oxide (NO) is involved in the killing of E. histolytica trophozoites by activated murine macrophages in vitro. Elicited peritoneal and bone marrow-derived macrophages activated with IFN-gamma alone or with IFN-gamma and LPS killed 62 to 73% of amebae, concomitant with increased levels of nitrate (NO2). Depletion of L-arginine by addition of arginase to culture medium abrogated macrophage amebicidal activity. NG-monomethyl L-arginine, an L-arginine analog, competitively inhibited NO2 release and amebicidal activity in a dose-dependent fashion, without affecting H2O2 production; however, the addition of excess L-arginine competitively restored macrophage amebicidal effects. In culture, sodium nitrite and sodium nitroprusside were cytotoxic to E. histolytica and this was reversed by the addition of myoglobin. Exogenously added FeSO4 prevented macrophage cytotoxicity. Addition of superoxide dismutase, a scavenger of O2-, partially inhibited amebicidal activity, without influencing NO2 production. Untreated and LPS-exposed macrophages produced high levels of H2O2 independent from NO2 production and amebicidal effects. However, the addition of catalase, a scavenger of H2O2, inhibited both amebicidal activity and NO2 production by activated macrophages. Our results demonstrate that NO is the major cytotoxic molecule released by activated macrophages for the in vitro cytotoxicity of E. histolytica and that O2- and H2O2 may be cofactors for the NO effector molecule.     

Localization and characterization of nitric oxide synthase at the frog neuromuscular junction

Summary. The frog neuromuscular junction is sensitive to nitric oxide (NO), since exogenously applied NO reduces the release of transmitter by presynaptic terminals and the size of ATP-induced Ca²⁺ responses in perisynaptic Schwann cells. This study aimed at determining whether an NO synthase (NOS) is present at the neuromuscular junction, notably in perisynaptic Schwann cells, the glial cells at this synapse. The NADPH-diaphorase (NADPH-d) histochemical technique revealed the presence of NOS in cell bodies and presumed processes of perisynaptic Schwann cells. Incubation with NOS inhibitors, N^G-nitro-L-arginine methyl ester or N^G-monomethyl-L-arginine-acetate, abolished the NADPH-d staining. Moreover, L-arginine, the precursor of NO, impeded the blockade by NOS inhibitors, establishing the NOS specificity of NADPH-d staining in frog tissue. The pattern of labelling with a polyclonal antibody against the neuronal form of NOS was similar to the NADPH-d staining, also suggesting the presence of a neuronal NOS in perisynaptic Schwann cells. Using electron microscopy, the NOS immunostaining was found at the membrane and occasionally in the cytoplasm of perisynaptic Schwann cells and was not detected in the nerve terminal or muscle. There was no enzymatic or immunocytochemical labelling of NOS 6 days after denervation. It is concluded that NOS is present in frog perisynaptic Schwann cells. The presence of this endogenous NOS suggests that NO may act as a diffusible glial messenger to modulate synaptic activity and synapse formation at the neuromuscular junction.     

Localization and correlation between NADPH-diaphorase and nitric oxide synthase isoforms in the porcine uterus during the estrous cycle

Nitric oxide (NO), a highly reactive free radical is involved in vasodilation, neurotransmission, hormone secretion, and reproduction. Since all known nitric oxide synthase (NOS) isoforms possess NADPH-diaphorase (NADPH-d) activity, NADPH-d histochemistry was used as a commonly accepted procedure for NOS identification. The aim of our study was to determine the cellular localization of NADPH-d, eNOS, and iNOS in the porcine uterus and the correlation between NADPH-d and NOS activity in the early, middle, late luteal, and follicular phase of the estrous cycle. Light-microscopic observations of the sections revealed the differential expression of the NADPH-d in the analyzed stages of the estrous cycle. The most intense staining was observed in the luminal epithelium in the late luteal phase and in some groups of the endometrial glands in all studied stages. Positive reaction was also found in the endothelial cells of blood vessels and in the myometrium itself. Immunostaining for eNOS was observed in the luminal and glandular epithelium in all studied stages, but no clear fluctuations were observed. The endothelium of both endometrial and myometrial blood vessels displayed pronounced eNOS immunostaining. Strong iNOS staining was observed in the luminal epithelium in the late luteal and follicular phase and in selected groups of endometrial glands. Thus, only NADPH-d and iNOS undergo cyclic changes in the studied stages of the estrous cycle. The differential expression of NADPH-d/NOS in the porcine uterine horn during the estrous cycle suggests a role for NO in modulating uterine function.     

Vascular reactivity and endothelial NOS activity in rat thoracic aorta during and after hyperbaric oxygen exposure

Accumulating evidence suggests that hyperbaric oxygen (HBO) stimulates neuronal nitric oxide (NO) synthase (NOS) activity, but the influence on endothelial NOS (eNOS) activity and vascular NO bioavailability remains unclear. We used a bioassay employing rat aortic rings to evaluate vascular NO bioavailability. HBO exposure to 2.8 atm absolute (ATA) in vitro decreased ACh relaxation. This effect remained unchanged, despite treatment with SOD-polyethylene glycol and catalase-polyethylene glycol, suggesting that the reduction in endothelium-derived NO bioavailability was independent of superoxide production. In vitro HBO induced contraction of resting aortic rings with and without endothelium, and these contractions were reduced by the NOS inhibitor N(omega)-nitro-l-arginine. In addition, in vitro HBO attenuated the vascular contraction produced by norepinephrine, and this effect was reversed by N(omega)-nitro-l-arginine, but not by endothelial denudation. These findings indicate stimulation of extraendothelial NO production during HBO exposure. A radiochemical assay was used to assess NOS activity in rat aortic endothelial cells. Catalytic activity of eNOS in cell homogenates was not decreased by HBO, and in vivo HBO exposure to 2.8 ATA was without effect on eNOS activity and/or vascular NO bioavailability in vitro. We conclude that HBO reduces endothelium-derived NO bioavailability independent of superoxide production, and this effect seems to be unrelated to a decrease in eNOS catalytic activity. In addition, HBO increases the resting tone of rat aortic rings and attenuates the contractile response to norepinephrine by endothelium-independent mechanisms that involve extraendothelial NO production.     

Effect of chronic lithium administration on endothelium-dependent relaxation of rat mesenteric bed: role of nitric oxide

The mechanism of action of lithium, an effective treatment for bipolar disease, is still unknown. In this study, the mesenteric vascular beds of control rats and rats that were chronically treated with lithium were prepared by the McGregor method, and the mesenteric vascular bed vasorelaxation responses were examined. NADPH-diaphorase histochemistry was used to determine the activity of NOS (nitric oxide synthase) in mesenteric vascular beds. We demonstrated that ACh-induced vasorelaxation increased in the mesenteric vascular bed of rats treated with lithium. Acute No-nitro-L-arginine methyl ester (L-NAME) administration in the medium blocked ACh-induced vasorelaxation in the control group more effectively than in lithium-treated rats, while the vasorelaxant response to sodium nitroprusside, a NO donor, was not different between lithium-treated and control groups. Acute aminoguanidine administration blocked ACh-induced vasorelaxation of lithium-treated rats, but had no effect in the control rats. Furthermore, NOS activity, determined by NADPH-diaphorase staining, was significantly greater in the mesenteric vascular beds from chronic lithium-treated rats than in those from control rats. These data suggest that the enhanced ACh-induced endothelium-derived vasorelaxation in rat mesenteric bed from chronic lithium-treated rats might be associated with increased NOS activity, likely via iNOS. Simultaneous acute L-NAME and indomethacin administration suggests the possible upregulation of EDHF (endothelium-derived hyperpolarizing factor) in lithium-treated rats.     

In vivo inhibition of inducible nitric oxide and evaluation of the brain tissue damage induced by Toxocara canis larvae in experimentally infected mice

Nitric oxide (NO) is known to be produced by macrophages, endothelial cells and neurons and synthesized by an enzyme called nitric oxide synthase (NOS). Various effector mechanisms and infections can affect the NO production. Excessive amount of NO will lead to biochemical reactions, which cause toxic effects. In this study the role of NO has been evaluated in larval toxocarosis, which is a systemic parasite infection caused by T. canis larvae. Infection was established in the Balb/c mice with or without inducible NOS (iNOS) inhibition and the effects of infection and NOS inhibition were observed according to the results of SOD and LPx measurements in brain tissue and NADPH-diaphorase (NADP-d) histochemistry. Results of NADPH-d histochemistry indicate that iNOS inhibition has protective effect on the brains of infected mice and that larval T. canis infection could be related to oxidative stress, and NO production and iNOS inhibition can protect the tissue from damage in this infection.     

Distribution of NADPH-diaphorase and nitric oxide synthase (NOS) in different regions of porcine oviduct during the estrous cycle.

Nitric oxide synthase (NOS) is responsible for the biological production of nitric oxide (NO) in several organs, including those of the reproductive tract. We investigated potential changes in NADPH-diaphorase (NADPH-d) activity (marker for NOS activity) and the presence and distribution of NOS in the porcine oviduct. Tissues were obtained from gilts (n=16) on different days of the estrous cycle. One fallopian tube was used for histo- and immunohistochemistry and the other for Western blotting analysis. NADPH-d activity was much higher in the epithelium of the mucosa than in the myosalpinx. The highest activity of NADPH-d was always found in the epithelium of the isthmus. The intensity of the reaction (arbitrary units +/- SEM) in isthmus epithelium increased from the postovulatory period until early proestrus (96.2 +/- 11.2) and then gradually decreased. The lowest intensity of NADPH-d reaction in the epithelium of the isthmus was seen at estrus (58.4 +/- 7.7). The most intense NADPH-d activity in myosalpinx of all parts of the oviduct was observed at the postovulatory stage of the estrous cycle (isthmus 38.3 +/- 2.5; ampulla 35.6 +/- 4.2; infundibulum 24.7 +/- 0.8) and then decreased during the remaining stages of the estrous cycle (p< 0.001). The presence of endothelial NOS (eNOS) was detected in epithelial cells of mucosa and in endothelium of vascular tissues and myosalpinx during all studied days of the estrous cycle. The positive reaction for inducible NOS (iNOS) was restricted only to the endothelium of lymph vessels and some blood vessels. Because our Western blotting analysis revealed that porcine oviduct contains eNOS but not iNOS, we suggest that eNOS is the main isoform of NOS expressed in the porcine oviduct. We concluded that the different activity of NADPH-d in the various regions of the oviduct, accompanied by changes in its activity during the course of the estrous cycle, could indicate an important role of NO in regulation of tubal function.     

NADPH-diaphorase activity in the nociceptive pathways of land snail Megalobulimus abbreviatus: the involvement of pedal ganglia

NADPH-diaphorase (NADPH-d) is a histochemical marker for nitric oxide synthase (NOS), widely used to identify nitric oxide (NO) producing cells in the nervous system of both vertebrates and invertebrates. Using NADPH-d histochemistry and semi-quantitative optical densitometry, we characterized the NO-producing neurons in the pedal ganglia of young and adult Megalobulimus abbreviatus, subjected to aversive thermal stimulus. The animals were killed at different times (3, 6, 12 and 24 h) following stimulus. The enzymatic activity was detected in different cellular subsets and neuronal processes. In all the studied pedal ganglia subregions, the optical density of positive neurons (P < 0.05) and neuropilar area 1 (P < 0.01) was significantly different in treated animals when compared to controls. The increase in nitrergic activity induced by nociceptive stimulus suggests the involvement of NO in the nociceptive circuit of M. abbreviatus, which is well maintained throughout evolution, and could be helpful in drawing cellular homologies with other gastropods.     

Modulation of nitric oxide (NO) biosynthesis in lactobacilli

We characterized effects of nitric oxide synthase (NOS) substrate L-arginine and classical inhibitors of mammalian NOS on nitric oxide (NO) biosynthesis in probiotic bacteria Lactobacillus plantarum 8P-A3. NO-synthase origin of nitric oxide detected by fluorescent NO indicator 1,2-diaminoanthraquinone (DAA) was confirmed by induction of NO production by exogenous L-arginine. None of the used inhibitors of three isoforms of mammalian NOSs (L-NAME, L-NIL, nNOS inhibitor I) showed significant inhibitory effect of lactobacillar NO-synthase activity.     

Vasorelaxant effect of the flavonoid galangin on isolated rat thoracic aorta

Here we investigated the effect of the flavonoid galangin in isolated rat thoracic aortic rings. Galangin (0.1-100 microM) induced relaxation in rings pre-contracted with phenylephrine (PE 1 microM) or with KCl (100 mM) or pre-treated with the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 100 microM), the cyclooxygenase inhibitor indomethacin (10 microM) and the adenylate cyclase inhibitor, SQ 22,536 (100 microM). In another set of experiments, rat aortic rings were incubated with galangin (1-100 microM) and the contractile responses to PE (0.001-3 microM) or to KCl (60 mM) were evaluated. We also evaluated the effect of galangin (100 microM) on PE (10 microM)-induced contraction in a Ca2+-free medium. Galangin relaxed aortic rings with or without endothelium. Galangin effect was significantly inhibited by L-NAME. Galangin inhibited the contractile response to PE, either in presence or in absence of external calcium, and to KCl. In the end, we also found that galangin caused nitric oxide (NO) release from aortic rings and abolished the increase in [Ca2+]i triggered by PE or KCl in aortic smooth muscle cells, either in presence and in absence of external Ca2+. Our results suggest that galangin reduces the contractility of rat aortic rings through an endothelium-dependent mechanism, involving NO, and also through an endothelium-independent mechanism, inhibiting calcium movements through cell membranes.     

No news on the flatworm front! Nitric oxide synthase in parasitic and free-living flatworms

The free radical nitric oxide (NO) has emerged as a simple and unique signalling molecule that can serve as neurotransmitter, paracrine substance or hormone. NO is a gas, formed by various neuronal cells, both centrally and peripherally. NO regulates cyclic GMP synthesis. The production of NO can be detected using the NADPH diaphorase (NADPH-d) histochemical stain for nitric oxide synthase (NOS). NOS was detected in two parasitic flatworms, Diphyllobothrium dendriticum and Hymenolepis diminuta, and two free-living flatworms, Planaria torva and Girardia tigrina. The staining for NOS was very strong in the nervous system of both parasitic worms. The main nerve cords, the transverse ring commmissures, nerves in association with the musculature, especially the cirrus musculature and sensory nerve endings showed NADPH-d staining. The NADPH-d staining in the free-living flatworms was much weaker. Still NOS activity was found in the neuropile of the brain and in association with the pharynx musculature. The demonstration of NOS in flatworms, indicates that NO is an old signal molecule in evolutionary terms. This revised version was published online in July 2006 with corrections to the Cover Date.     

NO参与玉米幼苗对盐胁迫的应答

以玉米幼苗为材料,研究盐胁迫下其內源NO含量、NR和NOS活性的变化;NOS专一性抑制剂L-NAME和NR非专一性抑制剂NaN3对玉米幼苗內源NO含量的影响;利用激光共聚焦显微技术观测盐胁迫下玉米幼苗根部NO含量的变化及其分布特点。结果表明,盐胁迫下玉米幼苗根尖和叶片中NO含量有猝发现象,NOS活性也随之显著提高,NR活性则显著降低;L-NAME或NaN3均可降低盐胁迫所引起的玉米幼苗NO水平的增加,L-NAME对NO含量的影响比NaN3更显著。推测,NO参与玉米幼苗对盐胁迫的应答,NOS途径是盐胁迫下玉米幼苗內源NO合成的主要途径。