Changes in nitrogen cycling and retention processes in soils under spruce forests along a nitrogen enrichment gradient in Germany

A network of long-term monitoring sites on nitrogen (N) input and output of forests across Germany showed that a number of Germany's forests are subject to or are experiencing N saturation and that spruce (Picea abies) stands have high risk. Our study was aimed at (1) quantifying the changes in gross rates of microbial N cycling and retention processes in forest soils along an N enrichment gradient and (2) relating the changes in soil N dynamics to N losses. We selected spruce sites representing an N enrichment gradient (indicated by leaching : throughfall N ratios) ranging from 0.04–0.13 (low N),≤0.26 (intermediate N enrichment) to≥0.42 (highly N enriched). To our knowledge, our study is the first to report on mechanistic changes in gross rates of soil N cycling and abiotic NO₃⁻ retention under ambient N enrichment gradient. Gross N mineralization, NH₄⁺ immobilization, gross nitrification, and NO₃⁻ immobilization rates increased up to intermediate N enrichment level and somewhat decreased at highly N-enriched condition. The turnover rates of NH₄⁺ and microbial N pools increased while the turnover rates of the NO₃⁻ pool decreased across the N enrichment gradient. Abiotic immobilization of NH₄⁺ did not differ across sites and was lower than that of NO₃⁻. Abiotic NO₃⁻ immobilization decreased across the N enrichment gradient. Microbial assimilation and turnover appeared to contribute largely to the retention of NH₄⁺. The increasing NO₃⁻ deposition and decreasing turnover rates of the NO₃⁻ pool, combined with decreasing abiotic NO₃⁻ retention, possibly contributed to increasing NO₃⁻ leaching and gaseous emissions across the N enrichment gradient. The empirical relationships of changes in microbial N cycling across the N enrichment gradient may be integrated in models used to predict responses of forest ecosystems (e.g. spruce) to increasing N deposition.     

Identification and quantification of free radicals during myocardial ischemia and reperfusion using electron paramagnetic resonance spectroscopy

There is general agreement that free radicals are involved in reperfusion injury. Electron paramagnetic resonance (EPR) spectroscopy can be considered as the more suitable technique to directly measure and characterize free radical generation during myocardial ischemia and reperfusion. There are essentially two approaches used in the detection of unstable reactive species: freezing technique and spin traps. The detection of secondary free radicals or ascorbyl free radicals during reperfusion might provide an index of oxidative stress. Spin trapping can also characterize nitric oxide. EPR spectroscopy can provide important data regarding redox state and free radical metabolism but ideally, the spin traps must not interfere with cell or organism function.     

Seasonal periodicity of enteric nitric oxide synthesis and its regulation in the snail, Helix lucorum

Abstract. The snail Helix lucorum has been used as a model to study the adaptation of a nitric oxide (NO)‐forming enteric neural network to the long‐term resting period of summer estivation or winter hibernation. Quantification of the NO‐derived nitrite established that NO formation is confined to the nitric oxide synthase (NOS)‐containing myenteric network of the mid‐intestine. In active snails but not in resting snails, NO production could be enhanced by the NOS substrate l ‐arginine (l ‐ARG, 1 mM). We followed the enteric NO synthesis in a snail population kept at natural conditions for 1 year. Our findings indicate that NO synthesis was depressed in July during entry to the estivation, had a peak in autumn before hibernation, and finally was reduced during hibernation. Monoamines (histamine, serotonin, and adrenalin) could inhibit the NO liberation in active snails. Cofactors of NOS (β‐NADPH, β‐NAD, FAD, FMN, Ca²⁺, TH4) did not alter the low nitrite production in hibernating snails. We conclude that enteric NO synthesis in H. lucorum has a regular seasonal periodicity following the annual physiological cycles of terrestrial snails. During estivation or hibernation, NOS activity is blocked. Monoamines, the levels of which are elevated during hibernation, can trigger decreased NOS activity. The reduced activity of NOS cannot be restored by the administration of NOS cofactors; therefore, their absence cannot be the cause of the temporarily blocked L‐ARG/NO conversion ability of NOS.     

Omentin, a novel adipocytokine inhibits TNF-induced vascular inflammation in human endothelial cells

Omentin is a recently identified adipocytokine with insulin-sensitizing effect. While lack of omentin may be related to the pathogenesis of obesity-related cardiovascular diseases, its effect in vasculature is largely unknown. We examined effects of omentin on vascular endothelial inflammatory states. Western blotting was performed to analyze inflammatory signal transduction in cultured vascular endothelia cells. The cyclic guanosine monophosphate (cGMP) content was measured using enzyme immunoassay. Treatment of human umbilical vein endothelial cells with omentin (300 ng/ml, 20 min) induced phosphorylation of 5′-AMP-activated protein kinase (AMPK) (Thr 172) and endothelial nitric oxide (NO) synthase (eNOS) (Ser 1177). Consistently, omentin increased the cGMP level. Pretreatment with omentin (300 ng/ml, 30 min) significantly inhibited the phosphorylation of JNK as well as expression of cyclooxygenase (COX)-2 by TNF-α (5 ng/ml, 20 min–24 h). An inhibitor of JNK significantly inhibited the TNF-α-induced COX-2 expression. Inhibitory effect of omentin on TNF-α-induced COX-2 was reversed by a NOS inhibitor. The present results demonstrate for the first time that omentin plays an anti-inflammatory role by preventing the TNF-α-induced COX-2 expression in vascular endothelial cells. Omentin inhibits COX-2 induction via preventing the JNK activation presumably through activation of AMPK/eNOS/NO pathways.     

Formation of unidentified nitrogen in plants: an implication for a novel nitrogen metabolism

Plants take up inorganic nitrogen and store it unchanged or convert it to organic forms. The nitrogen in such organic compounds is stoichiometrically recoverable by the Kjeldahl method. The sum of inorganic nitrogen and Kjeldahl nitrogen has long been known to equal the total nitrogen in plants. However, in our attempt to study the mechanism of nitrogen dioxide (NO₂) metabolism, we unexpectedly discovered that about one-third of the total nitrogen derived from ¹⁵N-labeled NO₂ taken up by Arabidopsis thaliana (L.) Heynh. plants was converted to neither inorganic nor Kjeldahl nitrogen, but instead to an as yet unknown nitrogen compound(s). We here refer to this nitrogen as unidentified nitrogen (UN). The generality of the formation of UN across species, nitrogen sources and cultivation environments for plants has been shown as follows. Firstly, all of the other 11 plant species studied were found to form the UN in response to fumigation with ¹⁵NO₂. Secondly, tobacco (Nicotiana tabacum L.) plants fed with ¹⁵N-nitrate appeared to form the UN. And lastly, the leaves of naturally fed vegetables, grass and roadside trees were found to possess the UN. In addition, the UN appeared to comprise a substantial proportion of total nitrogen in these plant species. Collectively, all of our present findings imply that there is a novel nitrogen mechanism for the formation of UN in plants. Based on the analyses of the exhaust gas and residue fractions of the Kjeldahl digestion of a plant sample containing the UN, probable candidates for compounds that bear the UN were deduced to be those containing the heat-labile nitrogen–oxygen functions and those recalcitrant to Kjeldahl digestion, including organic nitro and nitroso compounds. We propose UN-bearing compounds may provide a chemical basis for the mechanism of the reactive nitrogen species (RNS), and thus that cross-talk may occur between UN and RNS metabolisms in plants. A mechanism for the formation of UN-bearing compounds, in which RNS are involved as intermediates, is proposed. The important broad impact of this novel nitrogen metabolism, not only on the general physiology of plants, but also on plant substances as human and animal food, and on plants as an integral part of the global environment, is discussed.Abbreviations NO Nitric oxide - NO₂ Nitrogen dioxide - RNS Reactive nitrogen species - UN Unidentified nitrogen - TNNAT, RNNAT, INNAT and UNNAT Total, Kjeldahl, inorganic and unidentified nitrogen in naturally fed plants, respectively - TNNIT, RNNIT, INNIT and UNNIT Total, Kjeldahl, inorganic and unidentified nitrogen derived from nitrate, respectively - TNNO2, RNNO2, INNO2 and UNNO2 Total, Kjeldahl, inorganic and unidentified nitrogen derived from NO₂, respectively     

Involvement of nitric oxide in cerebroside-induced defense responses and taxol production in <Emphasis Type="Italic">Taxus yunnanensis</Emphasis> suspension cells

This work was to characterize the generation of nitric oxide (NO) in Taxus yunnanensis cells induced by a fungal-derived cerebroside and the signal role of NO in the elicitation of plant defense responses and taxol production. (2S,2′R,3R,3′E,4E,8E)-1-O-β-d-glucopyranosyl-2-N-(2′-hydroxy-3′-octadecenoyl)-3-hydroxy-9-methyl-4,8-sphingadienine at 10 μg/ml induced a rapid and dose-dependent NO production in the Taxus cell culture, reaching a maximum within 5 h of the treatment. The NO donor sodium nitroprusside (SNP) potentiated cerebroside-induced H₂O₂ production and cell death. Inhibition of nitric oxide synthase activity by phenylene-1,3-bis(ethane-2-isothiourea) dihydrobromide or scavenging NO by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide partially blocked the cerebroside-induced H₂O₂ production and cell death. Moreover, NO enhanced cerebroside-induced activation of phenylalanine ammonium-lyase and accumulation of taxol in cell cultures. These results are suggestive of a role for NO as a new signal component for activating the cerebroside-induced defense responses and secondary metabolism activities of plant cells. Taxol is a trademark of Bristol-Myers Squibb, Madison, NJ.     

An Inhibitory Role of Nitric Oxide in the Dynamic Regulation of the Blood-Brain Barrier Function

1. The present study aimed at elucidating the effect of nitric oxide (NO) on blood-brain barrier (BBB) function with mouse brain capillary endothelial (MBEC4) cells. 2. Histamine (20–100 μM) evoked NO production (1.6–7 μM) in MBEC4 cells in a dose-dependent manner. 3. The permeability coefficient of sodium fluorescein for MBEC4 cells and the cellular accumulation of rhodamine 123 in MBEC4 cells were increased dose-dependently by the addition of NO solutions (14 and 28 μM) every 10 min during a 30-min period. 4. The present study demonstrated that NO increased the permeability and inhibited the P-glycoprotein efflux pump of brain capillary endothelial cells, suggesting that NO plays an inhibitory role in the dynamic regulation of the BBB function.