Nitrate reductase activity and nitrate accumulation in in vitro produced axillary shoots,plantlets and seedlings of Pinus pinaster

The initial and induced in vivo Nitrate Reductase Activity, the nitrate accumulation by in vitro-produced axillary shoots and plantlets of Pinus pinaster were compared respectively with those of shoots collected from seedlings and whole plants.The usefulness of the nitrate of the medium used for in vitro axillary shoot formation is demonstrated by the occurrence of initial NR activity in the explants. When fed in a non in vitro situation with a 50 mM KNO₃ solution, they have the same induced capacity to reduce nitrate as do shoots from seedlings, even though the latter accumulate less nitrate. Plants regenerated in vitro exhibit an ability to reduce nitrate similar to that of seedlings. In both types of plants, the Nitrate Reductase potential is greater in roots than in shoots.Abbreviation NR Nitrate Reductase - BA 6-Benzyladenine     

A nitrate reductase-based colorimetric assay for the study of bacterial adherence

Washed intact cells of Escherichia coli and Staphylococcus aureus, grown under partial anaerobic conditions in nitrate media, reduced nitrate quantitatively when formate was used as a reducing substrate. Nitrate reductase was applied as an index for bacterial adherence to different target surfaces including uroepithelial cells, HeLa cells and fibrin clots. Nitrate reduction by adhered as well as control cells was determined by quantitative diazotization reaction for nitrite. Variations in the conditions which affect adherence gave rise to corresponding variations in the nitrate reduction index from which bacterial adherence can be conveniently determined under these conditions. This method is simple, reproducible and easy to perform in a short time.     

农田土壤硝酸盐积累与淋失研究进展

农田土壤硝酸盐淋失是导致地下水硝酸盐污染的主要原因。影响农田土壤中硝酸盐积累的淋失的因素很多。主要有施肥、降水、灌溉、土壤性质以及耕种制度等,过量施用氮肥,不论是单独施用无机肥、有机肥还是有机、无机混施都能造成硝酸盐在土体中大量积累;耕作和种植制度均能影响硝酸盐在土体中的积累和迁移;降水和灌溉带来的下渗水流是累积在土壤中的硝酸盐向下迁移直至淋失的必要条件,也是运载工具,而土壤中的大孔隙则是下渗水流的主要通道,农田土壤硝酸盐的积累与淋失是多种因素综合作用的结果,模型是研究和预测硝酸盐淋失的理想工具,近年来发展很快,并且得到了很好的应用。     

A nitrate reductase-based colorimetric assay for the study of bacterial adherence

H.A. SHOEB, A.F. TAWFIK AND A.M. SHIBL. 1991. Washed intact cells of Escherichia coli and Streptococcus aureus , grown under partial anaerobic conditions in nitrate media, reduced nitrate quantitatively when formate was used as a reducing substrate. Nitrate reductase was applied as an index for bacterial adherence to different target surfaces including uroepithelial cells, HeLa cells and fibrin clots. Nitrate reduction by adhered as well as control cells was determined by quantitative diazotization reaction for nitrite. Variations in the conditions which affect adherence gave rise to corresponding variations in the nitrate reduction index from which bacterial adherence can be conveniently determined under these conditions. This method is simple, reproducible and easy to perform in a short time.     

Nitrate Reductase Acivity in Leaves of Barley (Hordeum vulgare) and Durum Wheat (Triticum durum) during Field and Rapidly Applied Water Deficits

Smirnoff, N., Winslow, M. D. and Stewart, G. R. 1985. Nitratereductase activity in leaves of barley (Hordeum vulgare) anddurum wheat (Triticum durum) during field and rapidly appliedwater deficits.-J. exp. Bot 36: 1200-1208. The effect of field and rapidly applied water deficits on nitratereductase activity in the leaves of two barley varieties andone durum wheat variety was investigated. In field experimentsplants were subjected to irrigation at different rates in threeMediterranean environments by means of a line source sprinklerirrigation system. The environments differed in rainfall andnitrogen fertility. Plant water potentials decreased from –1.5MPa to between –2.5 and –3.0 MPa as the irrigationrate decreased. Nitrate reductase activity in the leaves ofthese plants during heading was either unaffected or sometimesincreased where the least water was supplied. Nitrate reductaseactivity was highest in the plants growing with an ample nitrogensupply irrespective of water regime. In contrast, seedlingssubject to rapidly applied water stress over 6 d lost 30-85%of their nitrate reductase activity when leaf water potentialfell from between –0.33 and –0.75 MPa to between–O.93 and –2.04 MPa. The decrease was less in theyoung leaves than in the old leaves. Polyethylene glycol inducedosmotic stress resulted in a drop in leaf water potential from–0.20 MPa to between –1.05 and –1.20 MPa alongwith a loss of 40-85% of leaf nitrate reductase activity after48 h. It is suggested that maintenance of nitrate reductase activityin field grown barley and durum wheat plants reflects an acclimationto water deficit Maintenance of nitrate assimilation duringwater stress may allow continued synthesis of nitrogenous compatiblesolutes using the excess photochemical energy available duringstomatal closure. Key words: Nitrate reductase, water stress, barley, durum wheat     

Interannual patterns of water table height and groundwater derived nitrate in nearshore sediments

Nitrate concentration and microbial nitrogen transformations in ground-water-affected sediments of Great South Bay, NY were examined over several annual cycles. Nitrate concentrations are typically higher at 40 cm depth than at the surface, while salinity generally decreases with depth. Denitrification occurs through the sediment core and is organic substrate limited at depth while being nitrate limited near the sediment-water interface. Denitrification accounts for about 50% of the biological NO₃ ^- decrease between 40 and 15 cm depth interval. Higher than average annual rainfall during 1983 and 1984 was reflected in an elevated water table as well as lower Bay salinities. Conversely, extremely low rainfall occurred in 1985 and 1986, and the water table reached an extreme low in Sep. 1986. Interestingly, the amounts of nitrate in the sediment column of our primary station varied directly with water table height and, presumably, the discharge rate of nitrate enriched groundwater. We suggest that this may be a result of the more efficient removal of advected nitrate by denitrification during low flow conditions.     

Seasonal differences in the effects of oscillatory and uni‐directional flow on the growth and nitrate‐uptake rates of juvenile Laminaria digitata (Phaeophyceae)

The influence of oscillatory versus unidirectional flow on the growth and nitrate‐uptake rates of juvenile kelp, Laminaria digitata, was determined seasonally in experimental treatments that simulated as closely as possible natural environmental conditions. In winter, regardless of flow condition (oscillatory and unidirectional) or water velocity, no influence of water motion was observed on the growth rate of L. digitata. In summer, when ambient nitrate concentrations were low, increased water motion enhanced macroalgal growth, which is assumed to be related to an increase in the rate of supply of nutrients to the blade surface. Nitrate‐uptake rates were significantly influenced by water motion and season. Lowest nitrate‐uptake rates were observed for velocities <5 cm · s^?1 and nitrate‐uptake rates increased by 20%–50% under oscillatory motion compared to unidirectional flow at the same average speed. These data further suggested that the diffusion boundary layer played a significant role in influencing nitrate‐uptake rates. However, while increased nitrate‐uptake in oscillatory flow was clear, this was not reflected in growth rates and further work is required to understand the disconnection of nitrate‐uptake and growth by L. digitata in oscillatory flow. The data obtained support those from related field‐based studies, which suggest that in summer, when insufficient nitrogen is available in the water to saturate metabolic demand, the growth rate of kelps will be influenced by water motion restricting mass transfer of nitrogen.     

Interannual patterns of water table height and groundwater derived nitrate in nearshore sediments

Nitrate concentration and microbial nitrogen transformations in ground-water-affected sediments of Great South Bay, NY were examined over several annual cycles. Nitrate concentrations are typically higher at 40 cm depth than at the surface, while salinity generally decreases with depth. Denitrification occurs through the sediment core and is organic substrate limited at depth while being nitrate limited near the sediment-water interface. Denitrification accounts for about 50% of the biological NO₃ ^- decrease between 40 and 15 cm depth interval. Higher than average annual rainfall during 1983 and 1984 was reflected in an elevated water table as well as lower Bay salinities. Conversely, extremely low rainfall occurred in 1985 and 1986, and the water table reached an extreme low in Sep. 1986. Interestingly, the amounts of nitrate in the sediment column of our primary station varied directly with water table height and, presumably, the discharge rate of nitrate enriched groundwater. We suggest that this may be a result of the more efficient removal of advected nitrate by denitrification during low flow conditions.     

Nitrate enhances the survival of Mycobacterium tuberculosis during inhibition of respiration

When oxygen is slowly depleted from growing cultures of Mycobacterium tuberculosis, they enter a state of nonreplicating persistence that resembles the dormant state seen with latent tuberculosis. In this hypoxic state, nitrate reductase activity is strongly induced. Nitrate in the medium had no effect on long-term persistence during gradual oxygen depletion (Wayne model) for up to 46 days, but significantly enhanced survival during sudden anaerobiosis. This enhancement required a functional nitrate reductase. Thioridazine is a member of the class of phenothiazines that act, in part, by inhibiting respiration. Thioridazine was toxic to both actively growing and nonreplicating cultures of M. tuberculosis. At a sublethal concentration of thioridazine, nitrate in the medium improved the growth. At lethal concentrations of thioridazine, nitrate increased survival during aerobic incubation as well as in microaerobic cultures that had just entered nonreplicating persistence (NRP-1). In contrast, the survival of anaerobic persistent (NRP-2) cultures exposed to thioridazine was not increased by the addition of nitrate. Nitrate reduction is proposed to play a role during the sudden interruption of aerobic respiration due to causes such as hypoxia, thioridazine, or nitric oxide.     

广州市饮用水源中硝酸盐亚硝酸盐含量与癌症死亡率联系

本文探讨了饮用水源中硝酸盐和亚硝酸盐污染对癌症死亡率的影响。收集了1991～1998年广州市饮用水源中硝酸盐、亚硝酸盐和癌症死亡率的历史数据,并分析了它们之间的相关性。结果显示,饮用水源中硝酸盐氮和亚硝酸盐氮的总浓度与癌症死亡率呈正相关关系(R²=O.76,P<0.05)。对广州市各区的数据分析表明,饮用水源中亚硝酸盐氮和癌症死亡率有较高的相关性(R²=0.56,P<0.05),且硝酸盐氮和癌症死亡率的相关性也很高(R²=0.66,P<0.01)。这说明了1991～1998年期间,广州市区居民癌症死亡率的逐年递增很可能与饮用水源中硝酸盐和业硝酸盐含量的增加有关。此次研究结果说明饮用水源中的硝酸盐及亚硝酸盐可能是重要的致癌因子。     

Phytochrome, nitrate movement, and induction of nitrate reductase in etiolated pea terminal buds

The role of phytochrome in the induction of nitrate reductase of etiolated field peas (Pisum arvense L.) was examined. Terminal bud nitrate concentration increased in darkness, and the increase correlated with induction of nitrate reductase following brief exposure of intact plants to red, blue, far red, and white lights. Brief light exposure of intact plants stimulated nitrate uptake and induction of nitrate reductase by terminal buds subsequently excised and incubated on nitrate solution in darkness; exposure of excised buds in contact with nitrate led to less uptake but more induction. Nitrate and nitrate reductase activity both declined during incubation with water, irrespective of light treatment. Nitrate enrichment of intact terminal buds and uptake into excised buds and increases in nitrate reductase activity were all red/far red reversible. Dimethyl sulfoxide (1%, v/v) and sugars (sucrose 0.5%, glucose 1, w/v), although stimulating nitrate uptake into excised tissue in darkness, failed to enhance nitrate reductase activity over dark controls. Phytochrome may regulate nitrate reductase via both nitrate movement and a general mechanism such as enhancement of protein synthesis.     

真菌异化硝酸盐还原机理的研究进展

真菌异化硝酸盐还原途径的发现打破了反硝化仅存在于原核细胞这一传统观念。真菌异化硝酸盐还原途径是在环境中氧供给受限的情况下发生的, 包括反硝化和氨的发酵。硝酸盐能诱导产生反硝化作用的酶, 其中, 硝酸盐还原酶与亚硝酸还原酶位于线粒体中, 它们所催化的酶促反应能偶联呼吸链ATP合成酶合成ATP, 同时产生NO。与参与反硝化作用前两个酶不同, 真菌NO还原酶能以NADH为直接电子供体将NO还原为N2O, 在NAD+的再生和自由基NO的脱毒中起着重要作用。氨发酵则将硝酸盐还原成NH4+, 同时偶联乙酸的生成和底物水平磷酸化。此文从参与该过程的关键酶、关键酶的表达调节、真菌与细菌异化硝酸盐还原的比较等角度综述了真菌异化硝酸盐还原的最新研究进展。     

蔬菜营养与硝酸盐的关系

蔬菜硝酸盐累积是无公害蔬菜生产的限制因子之一,与蔬菜营养的关系密切．喜硝性是蔬菜作物的营养特性,NO3^-通过高亲和吸收转运系统和低亲和吸收转运系统被蔬菜吸收,在钼、锰、铁、铜、硫、磷等多种必需营养元素参与下被还原同化．文中简述了必需营养元素在蔬菜硝酸盐吸收和还原同化中的作用,重点论述了氮肥用量、种类及形态配比、施用时期、方法和氮素供应方式、磷素营养、钾索营养、中微量元素营养和平衡营养与蔬菜硝酸盐累积的关系,提出了今后研究工作的主攻方向,为控制蔬菜硝酸盐累积、提高蔬菜品质和生产无污染、安全、优质的无公害蔬菜提供参考．     

Oil field souring control by nitrate-reducing Sulfurospirillum spp. that outcompete sulfate-reducing bacteria for organic electron donors

Nitrate injection into oil reservoirs can prevent and remediate souring, the production of hydrogen sulfide by sulfate-reducing bacteria (SRB). Nitrate stimulates nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB) and heterotrophic nitrate-reducing bacteria (hNRB) that compete with SRB for degradable oil organics. Up-flow, packed-bed bioreactors inoculated with water produced from an oil field and injected with lactate, sulfate, and nitrate served as sources for isolating several NRB, including Sulfurospirillum and Thauera spp. The former coupled reduction of nitrate to nitrite and ammonia with oxidation of either lactate (hNRB activity) or sulfide (NR-SOB activity). Souring control in a bioreactor receiving 12.5 mM lactate and 6, 2, 0.75, or 0.013 mM sulfate always required injection of 10 mM nitrate, irrespective of the sulfate concentration. Community analysis revealed that at all but the lowest sulfate concentration (0.013 mM), significant SRB were present. At 0.013 mM sulfate, direct hNRB-mediated oxidation of lactate by nitrate appeared to be the dominant mechanism. The absence of significant SRB indicated that sulfur cycling does not occur at such low sulfate concentrations. The metabolically versatile Sulfurospirillum spp. were dominant when nitrate was present in the bioreactor. Analysis of cocultures of Desulfovibrio sp. strain Lac3, Lac6, or Lac15 and Sulfurospirillum sp. strain KW indicated its hNRB activity and ability to produce inhibitory concentrations of nitrite to be key factors for it to successfully outcompete oil field SRB.     

Transformations of inorganic nitrogen by Azospirillum spp.

Azospirillum spp. participate in all steps of the nitrogen cycle except nitrification. They can fix molecular nitrogen and perform assimilatory nitrate reduction and nitrate respiration. Culture conditions have been defined under which nitrate is used both as terminal respiratory electron acceptor and as nitrogen source for growth. Nitrate and, possibly to a very limited extent, nitrite, but not sulfate, iron or fumarate support anaerobic respiration. Under anaerobic conditions, nitrate can also supply energy for nitrogen fixation but without supporting growth. Nitrate-dependent nitrogenase activity lasts only for 3–4 h until the enzymes of assimilatory nitrate reduction are synthesized. Nitrite accumulates during this period and inhibits nitrogenase activity at concentrations of about 1 mM.     

The EU Nitrates Directive: a European approach to combat water pollution from agriculture

From 1991 onward, the European Union (EU) member states have had to comply with the Nitrates Directive. The aim of this directive is to sustainably protect ground and surface waters from pollution with nitrogen (nitrate) originating from agriculture. Agriculture is, on an EU level, the largest single source of nitrate (runoff, leaching) pollution, although households and industries also contribute to some extent. An important element in the directive is the reporting every 4 years on the monitoring of ground- and surface-water quality. Furthermore, all 15 member states are compelled to designate so-called Nitrate Vulnerable Zones (NVZs). These are regions where the nitrate concentrations in the groundwater amount to 50 mg/l or more. In addition to Codes of Good Agricultural Practice, valid on a countrywide basis and often consisting of voluntary-based measures, specific Action Programmes with mandatory measures have to be developed for the NVZs. The first reporting period ended in 1995. This paper describes the progress in member states" compliance with the Nitrates Directive during the second period (1996-1999), with a focus on the agricultural practices and action programmes. An evaluation of the member states' reports shows that good progress is being made on the farmers" awareness of the need to comply with EU regulations on the protection of the aquatic environment. Action programmes are valuable tools to enforce measures that lead to a reduction of the water pollution by agricultural activities. Regional projects show that significant improvements can be achieved (e.g., reduced fertiliser inputs) while maintaining crop yields and thus maintaining the economic potential of agriculture.     

Factors influencing nitrate depletion in a rural stream

A mass balance procedure was used to analyze rates of nitrate depletion in three adjacent reaches of West Duffin Creek, Ontario, Canada. Daily nitrate losses in individual reaches were highly variable (0.5–24 kg N) during low and moderate stream flows in May–October, 1982–1985. Nitrate removal efficiency (nitrate loss as a % of nitrate input) showed a rapid exponential decline with increased nitrate inputs to each reach. Nitrate losses and nitrate removal efficiency also had a significant negative correlation with stream discharge. The association of large nitrate loads with high stream discharge reduced the nitrate removal capacity of the stream because of shorter residence times and a higher ratio of water volume to stream bed area. Water temperature exhibited a significant positive correlation with nitrate loss which may reflect increased denitrification at higher temperatures.Variations in nitrate losses and nitrate removal efficiency between the three reaches were highly influenced by differences in water residence time. Standarized nitrate losses with respect to water residence time revealed a longitudinal decline in nitrate depletion between the reaches which was associated with a downstream decrease in stream nitrate concentration and in the organic carbon content of fine textured sediments from pool habitats.     

Studies on nitrate uptake by solution grown corn (Zea mays) L. genotypes

Nitrate depletion from the media by intact corn seedlings grown under solution culture was measured over a period of time. Two methods were assessed to differentiate corn genotypes for nitrate uptake ability: (1) Nitrate uptake per day per plant basis. (2) Nitrate uptake per day per gram root dry matter basis. The former method was found to be superior as it gave significant and positive correlations with dry matter, nitrate, and reduced nitrogen accumulation in stem, leaf and roots. Nitrate uptake was found to vary with plant age. Root mass and efficiency of roots appear to contribute to the total nitrate uptake ability of the genotype. Corn genotypes studied exhibited marked differences in nitrate uptake ability.