Iron-mediated effects on nitrate reductase in marine phytoplankton

The potential activity of nitrate reductase was determined in uni-algal cultures in the laboratory and in natural marine phytoplankton assemblages. In the laboratory bioassays, distinct differences in nitrate reductase activity were observed in iron replete versus depleted cultures for Emiliania huxleyi, Isochrysis galbana and Tetraselmis sp. Cells from iron-depleted cultures had 15 to 50 percent lower enzyme activity than those from iron-replete cultures. Upon addition of iron, nitrate reductase activity was enhanced in depleted cells up to levels comparable to those of the replete cells. Bioassays in the northern North Sea conducted in 1993, under low iron conditions, demonstrated similar results. Upon addition of 2.5 nM iron, a distinct enhancement, to a maximum of three times, of nitrate reductase activity was observed within 32 h after addition. Therefore, iron can stimulate nitrate reductase activity. In spite of the clean techniques used, some nitrate reductase activity was always observed. Iron deficiency was shown to impair nitrate reductase activity, but it is unlikely that nitrate reduction would cease completely.     

Regulation of growth in Laminaria digitata: use of in-vivo nitrate reductase activities as an indicator of nitrogen limitation in field populations of Laminaria spp.

The seasonal variation in growth rate of a population of Laminaria digitata (Huds.) Lamour growing at Arbroath, Scotland was studied between August 1981 and September 1982, and was found to follow the biphasic annual cycle typical of this genus. Growth rates were maximum (0.3 cm cm^-1 mo^-1) in early June and minimum (0.05 cm cm^-1 mo^-1) between September and January. An analysis of the relationship between the seasonal changes in environmental factors (inorganic nitrogen concentrations, irradiance and temperature) with those of growth rate and the accumulation or mobilisation of cellular reserves of carbohydrates and nitrate, indicated that growth was nitrogen-limited between June and October and light-limited (with a possible co-involvement of temperature) for the remainder of the year. These conclusions were supported by the seasonal changes in the ratio of actual: potential in-vivo nitrate reductase activities in L. digitata, thus confirming the suitability of this technique for monitoring the occurrence of nitrogen limitation in Laminaria spp. The seasonal changes in blade nitrate reductase activities closely followed those of growth rate, with maximum activities [0.3 mol NO ₃ ^- reduced g^-1 (wet wt) h^-1] being present in late May and minimum levels [0.01 mol NO ₃ ^- reduced g^-1 (wet wt) h^-1] occurring between November and March. The correlation observed between nitrate reductase activities and growth rate is consistent with the ability of Laminaria spp. to store excess inorganic nitrogen, available during winter and early spring, as NO ₃ ^- , and with the requirement to conserve enzyme protein during the summer period of nitrogen limitation.     

Effect of nitrogen supply on nitrogen uptake,accumulation and assimilation in Porphyra perforata (Rhodophyta)

Porphyra perforata J. Ag. was collected from a rocky land-fill site near Kitsilano Beach, Vancouver, British Columbia, Canada and was grown for 4 d in media with one of the following forms of inorganic nitrogen: NO ₃ ^- , NH ₄ ⁺ and NO ₃ ^- plus NH ₄ ⁺ and for 10 d in nitrogen-free media. Internal nitrogen accumulation (nitrate, ammonium, amino acids and soluble protein), nitrate and ammonium uptake rates, and nitrate reductase activity were measured daily. Short initial periods (10 to 20 min) of rapid ammonium uptake were common in nitrogen-deficient plants. In the case of nitrate uptake, initial uptake rates were low, increasing after 10 to 20 min. Ammonium inhibited nitrate uptake for only the first 10 to 20 min and then nitrate uptake rates were independent of ammonium concentration. Nitrogen starvation for 8 d overcame this initial suppression of nitrate uptake by ammonium. Nitrogen starvation also resulted in a decrease in soluble internal nitrate content and a transient increase in nitrate reductase activity. Little or no decrease was observed in internal ammonium, total amino acids and soluble protein. The cultures grown on nitrate only, maintained high ammonium uptake rates also. The rate of nitrate reduction may have limited the supply of nitrogen available for further assimilation. Internal nitrate concentrations were inversely correlated with nitrate uptake rates. Except for ammonium-grown cultures, internal total amino acids and soluble protein showed no correlation with uptake rates. Both internal pool concentrations and enzyme activities are required to interpret changes in uptake rate during growth.     

Blooms of surf-zone diatoms along the coast of the Olympic Peninsula,Washington. IV. Nitrate reductase activity in natural populations and laboratory cultures of Chaetoceros armatum and Asterionella socialis

Nitrate reductase (NR) activity in the surf-zone diatom Chaetoceros armatum T. West was studied in its natural habitat at Copalis Beach, Olympic Peninsula, Washington (USA) over a period of 18 months. Variations of enzyme activity were found, depending on the season and the time of day. General seasonal trends in NR activity were correlated with nitrate concentrations in the surf-zone. The results also indicated that several factors may limit the activity of the enzyme. This is one of the reasons why NR activity could not be correlated with environmental nitrate concentration on the basis of individual measurements at a given point in time. Enzyme inhibition due to the presence of ammonium occurred on several occasions throughout the study period, and could be detected by the NR assay. This phenomenon for the most part masked any pattern of diel periodicity in NR activity that might have been expected to exist in cells in the natural environment. Cultures of C. armatum and Asterionella socialis Lewin and Norris were also studied in the laboratory. A diel fluctuation in NR activity corresponding to the pattern shown in natural phytoplankton by other authors was exhibited in C. armatum under a light-dark regime of 8 h light – 16 h dark and a light intensity of 400 lux.     

Light regulation of nitrate reductase in Ulya fenestrata (Chlorophyceae)

Observations were made on the behavior of nitrate reductase activity in the green alga Ulva fenestrata under controlled light:dark regimes. The activity of nitrate reductase (NR) was examined in response to normal seasonal photoperiods as well as in response to shortened or extended periods of darkness. NR activity exhibits a light-dependent diurnal rhythm under both normal summer and winter photoperiods, with a maximum in the early morning (2 to 2.5 h after the start of illumination). This peak of activity is followed by a lower steady-state level of activity which is sustained throughout the light period. There is a sustained minimal level of activity in darkness. The morning peak in activity is always observed as long as tissue is illuminated, irrespective of the previous light or dark treatments. As such, it appears that nitrate reductase activity in U. fenestrata is under circadian control. There is no major difference in the NR activity pattern between summer and winter plants, except that the peak activity values in winter plants are consistently much higher (5 times) than in summer plants. The study also suggests that illumination prior to the normal start of photoperiod triggers a different set of regulatory mechanisms, indicating that the physiological state of plants is important in dictating the NR activity response to illumination.Please address all correpondence and requests for reprints to G. J. Smith at his present address (Hopkins Marine Station)     

Nitrate reductase and glutamine synthetase activity,internal N pools,and growth of<Emphasis Type="Italic"> Ulva lactuca</Emphasis>: responses to long and short-term N supply

Fast-growing macroalgae, including Ulva lactuca Linnaeus, respond rapidly to changes in nutrient conditions, particularly to short-term N supply. This ability to rapidly take up and assimilate N contributes to the increasing occurrence of macroalgal blooms in heavily N loaded coastal ecosystems. To determine whether long-term nutrient histories affect short-term responses in activity of N-assimilating enzymes, including nitrate reductase (NRA) and glutamine synthetase activity (GSA), internal N storage, and macroalgal growth, we conducted an in situ nitrate fertilization experiment between 7 and 22 July 2004, with fronds of U. lactuca collected from estuaries with high and low N loads in Waquoit Bay, Cape Cod, Massachusetts, USA (N 41° and W 70°). Initial NRA, GSA, % N, δ¹⁵N, and growth of U. lactuca fronds were higher in the site where nitrate was in high supply. Differences in NRA persisted even after short-term experimental enrichment. Differences in internal N pools, δ¹⁵N, and growth, in contrast, mirrored the changes of nutrient supply. The rate of turnover of the internal N content of U. lactuca was quite short (<2 d), and turnover of enzyme activity may have been even shorter. N isotopic fractionation by U. lactuca appeared to be of small magnitude, unlike the case of phytoplankton, and similar to that of vascular plants. δ¹⁵N was a better indicator of short-term response to external and internal nutrient supplies in U. lactuca than enzyme activity or N content, and may reliably detect rapid changes in N availability, source, and uptake and assimilation processes.     

Increased macrophyte nitrate reductase activity as a consequence of groundwater input of nitrate through sandy beaches

While most marine macrophytes preferentially assimilate ammonium to meet growth demand for nitrogen, some also utilize nitrate and exhibit high nitrate reductase activity (NRA). Although nitrate concentrations are often low in coastal waters during the summer and sandy beaches are generally considered to be low nutrient-input habitats, we have observed elevated NRA in leaves of some eelgrass (Zostera marina L.) plants growing immediately adjacent to the shoreline. We postulated that nitrate may become available to eelgrass and macroalgae via groundwater inputs that enter the nearshore water column. To address this possibility, we investigated the availability of groundwater nitrate for the induction of NRA in the leaves of eelgrass and in the macroalgaeSargassum filipendula C. Agardh (Phaeophyceae) andEnteromorpha intestinalis L. Link (Chlorophyceae) collected adjacent to two sandy beaches in the vicinity of Woods Hole, Massachusetts, USA. Induction of NRA was determined in the laboratory for eelgrass collected from one of the beach sites and from an offshore site, Lackey's Bay, which is isolated from groundwater input. At the two beach locations, pore water nitrate concentrations were 100 to 400µM within a few meters inland from the waterline. Nitrate efflux into the nearshore water column was quite high and variable (2160±660µmol m^–2 h^–1) when associated with rapid percolation (37±11 1 m^–2 h^–1) of nitrate-enriched pore water. Turbulent wave mixing rapidly diluted the nitrate. Macroalgae and eelgrass growing adjacent to a beach with high nitrate efflux had NR activities three- to sevenfold higher than those of algae and eelgrass growing along a beach section with low nitrate efflux. NRA of eelgrass plants from Lackey's Bay and Great Harbor increased in response to low daily nitrate additions (10 to 25µM) in the laboratory, with higher nitrate additions (50 to 200µM) yielding less dramatic responses. The increase in NRA was roughly three times higher for Great Harbor than for Lackey's Bay eelgrass. It appears that groundwater input of nitrate is sufficient to induce NRA in marine macrophytes growing near some beaches, including those with turbulent wave mixing.     

Voltammetric analysis of metallothioneins and copper (II) in fish for water biomonitoring studies

An major research area in environmental chemistry is the development of methods for the analysis of biomarkers. Metallothioneins are used as biomarkers in studies of heavy metals exposure in water, because metallothioneins are synthesized and accumulated when organisms are exposed to toxic concentrations of pollutants. In this work, simple and sensitive voltammetric methods were developed for metallothionein and copper (II) determinations in fish liver Lepomis gibbosus. Both analytical methodologies were optimized and applied to samples extracted from individuals previously submitted to sub-lethal toxicological trials with copper sulphate (CuSO₄) and cadmium chloride (CdCl₂). The obtained results showed that both methods are very precise, sensitive, and involve simple sample preparation processes. Moreover, metallothioneins showed better correlation with the toxic exposure than Cu²⁺. To the best of our knowledge, this is the first time that hepatic metallothioneins and Cu²⁺ contents are voltammetrically determined in order to be compared in their function as heavy metal biological indicators.     

Inorganic nitrogen metabolism in marine bacteria: Nitrate uptake and reduction in a marine pseudomonad

Growth experiments in batch cultures indicated that the uptake of nitrate by the marine pseudomonad PL1 was inhibited in the presence of ammonia provided that the ammonia concentration was higher than 1 mM. At ammonia concentrations of less than about 1 mM, however, both nitrate and ammonia were utilised simultaneously. The saturation constants for nitrate and ammonia uptake were both 2.6x10^-4 M, and similar to the Michaelis constants of nitrate reductase for nitrate (2.9x10^-4 M) and glutamine synthetase for ammonia (2x10^-4 M). Nitrate reductase activity linked to NADH was detected in chemostat-grown cultures with nitrate as nitrogen source, and in cultures containing limiting concentrations of nitrate and ammonia, ammonia or glutamate. Enzyme synthesis appeared to be repressed in cultures containing an excess of ammonia or glutamate. Chemostat cultures utilised ammonia or glutamate in preference to nitrate, while there was no marked preference between ammonia and glutamate.     

Electrochemical removal of nitrate in industrial wastewater

A number of recent studies have demonstrated that electrochemical technologies, including electroreduction (ER), electrocoagulation (EC), and electrodialysis (ED), are effective in nitrate elimination in wastewater due to their high reactivity. To obtain the maximal elimination efficiency and current efficiency, many researchers have conducted experiments to investigate the optimal conditions (i.e., potential, current density, pH value, plate distance, initial nitrate concentration, electrolyte, and other factors) for nitrate elimination. The mechanism of ER, EC and ED for nitrate removal has been fully elucidated. The ER mechanism of nitrate undergoes electron transfer and hydrogenation reduction. The EC pathways of nitrate removal include reduction, coagulation and flotation. The ED pathways of nitrate include redox reaction and dialysis. Although the electrochemical technology can remove nitrate from wastewater efficiently, many problems (such as relatively low selectivity toward nitrogen, sludge production and brine generation) still hinder electrochemical treatment implementation. This paper critically presents an overview of the current state-of-the-art of electrochemical denitrification to enhance the removal efficiency and overcome the shortages, and will significantly improve the understanding of the detailed processes and mechanisms of nitrate removal by electrochemical treatment and provide useful information to scientific research and actual practice.

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Composition chimique élémentaire (C,H, N) et équivalent énergie d'Acartia clausi (Crustacea: Copepoda), espèce importante dans la bioénergétique des écosystèmes côtiers de Méditerranée nord-occidentale

Fixed-point sampling of a shallow tidal estuary was performed hourly for 14 d in summer of 1982 and again in winter of 1983. This sampling regime was of statistically appropriate duration to allow characterization of the variability between periods of 2 to 96 h by spectral analysis of the time-series. The project (PULSE) took place in the Newport River Estuary, located behind the Outer Banks of North Carolina, USA. In all, twentyeight parameters were monitored, encompassing the meteorology, hydrology, water chemistry and phytoplankton-production physiology. Although the annual cycle was monitored, only the winter and summer seasons are compared here, i.e., the lowest water temperatures with the highest water temperatures. The physics, chemistry and biology of the estuary at the hourly scale were highly variable and non-random. The estuary is riverine in winter; growth-limiting nitrogen is supplied as nitrate (NO ₃ ^- ) and ammonium (NH ₄ ⁺ ) by runoff from the drainage basin. In summer, the estuary is lagoonal; nitrogen is supplied as NH ₄ ⁺ by biological regeneration. Chlorophyll a biomass varies primarily at the 4 d period in winter and at the diel period in summer. Although finely tuned to environmental variability, phytoplankton abundances were at equilibrium insofar as daily chlorophyll production was balanced by losses, i.e., grazing, export and deposition. Most important, high-frequency processes, here periods at the scale of cell-division times, can be very important in phytoplankton ecology.     

双酚A对青岛大扁藻的干扰效应

为了探讨双酚A(bisphenol A,BPA)对海洋微藻的生态毒性效应,实验选择了以青岛大扁藻(Platymonas helgolanidica)作为受试物种,设置6个实验浓度(即0、2、4、6、8、10 mg·L-1)对微藻进行了96 h暴露处理,测定了不同浓度暴露下对青岛大扁藻的生长以及抗氧化系统酶活性等指标。研究结果表明,BPA对青岛大扁藻的96h-EC50为9.32 mg·L-1,属高毒类污染物。青岛大扁藻经过BPA暴露处理后,细胞密度下降,细胞色素含量降低,并且呈现明显的剂量-效应关系;细胞抗氧化系统中超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)、谷胱甘肽还原酶(GR)活性均受到干扰。     

Homogeneous and heterogeneous photolysis of nitrate in the atmosphere: state of the science,current research needs,and future prospects

● Recent advances in the photolysis of nitrate/HNO₃ are reviewed. ● Mechanisms and key factors affecting the photolysis of nitrate/HNO₃ are summarized. ● Atmospheric implications and future research recommendations are provided. Nitrate is an important component of atmospheric particulate matter and affects air quality, climate, human health, and the ecosystem. Nitrate was previously considered a permanent sink for nitrogen oxides (NO_x). However, this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO_x (i.e., renoxification). The photolysis of nitrate/HNO₃, especially in the particulate phase or adsorbed on particles, can be a significant renoxification process in the atmosphere. The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO_x, but also provide long-distance transport of NO_x in the form of nitrate, which affects local and regional atmospheric chemistry and air quality. This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO₃ under various atmospheric conditions, with a focus on mechanisms and key factors affecting the process. The atmospheric implications are discussed and future research is recommended.     

Monitoring of soil biochemical quality parameters under greenhouse spinach cultivation through animal waste recycling

Under the intensive agricultural system, direct application of animal slurries to soils can provide a sustainable disposal of these wastes by inducing positive changes in soil quality and fertility. However, how animal wastes quantitatively affect the key nutrients (C, N, P and S) transforming soil enzymes is not clearly known. A greenhouse spinach cultivation study demonstrated that pig slurry, either in raw (RS) or processed (aerobically aged) (PS) form, significantly (p?β-glucosidase (23–39%), urease (59–103%), nitrate reductase (73–103%) and dehydrogenase (27–72%)) and microbial growth in soil as compared to the unamended control. However, it did not significantly (p?>?.05) alter the aryl sulphatase enzyme activity. Slurry applications also significantly improved the macro (N, P and K) and micronutrients (Cu, Mn, Zn and Fe) uptake by spinach plant and hence the yield (2.9–3.38 times higher than control). Similarly, compared to chemical fertilisers the application of pig slurries improved soil biological and biochemical parameters as well as plant nutrients uptake. This study demonstrated the closing of global energy and nutrient cycles through land application of animal wastes without compromising the crop yield.     

Catalytic reduction for water treatment

Treating water contaminants via heterogeneously catalyzed reduction reaction is a subject of growing interest due to its good activity and superior selectivity compared to conventional technology, yielding products that are non-toxic or substantially less toxic. This article reviews the application of catalytic reduction as a progressive approach to treat different types of contaminants in water, which covers hydrodehalogenation for wastewater treatment and hydrogenation of nitrate/nitrite for groundwater remediation. For hydrodehalogenation, an overview of the existing treatment technologies is provided with an assessment of the advantages of catalytic reduction over the conventional methodologies. Catalyst design for feasible catalytic reactions is considered with a critical analysis of the pertinent literature. For hydrogenation, hydrogenation of nitrate/nitrite contaminants in water is mainly focused. Several important nitrate reduction catalysts are discussed relating to their preparation method and catalytic performance. In addition, novel approach of catalytic reduction using in situ synthesized H₂ evolved from water splitting reaction is illustrated. Finally, the challenges and perspective for the extensive application of catalytic reduction technology in water treatment are discussed. This review provides key information to our community to apply catalytic reduction approach for water treatment.

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Nitrate reductase activity in Zostera marina

Eelgrass (Zostera marina L.) has access to nutrient pools in both the water column and sediments. We investigated the potential for eelgrass to utilize nitrate nitrogen by measuring nitrate reductase (NR) activity with an in vivo tissue assay. Optimal incubation media contained 60 mM nitrate, 100 mM phosphate, and 0.5% 1-propanol at pH 7.0. Leaves had significantly higher NR activity than roots (350 vs 50 nmoles NO ₂ ^– produced g FW^–1 h^–1). The effects of growing depth (0.8 m MLW, 1.2 m, 3.0 m, 5.0 m) and location within the eelgrass meadow (patch edge vs middle) on NR activity were examined using plants collected from three locations in the Woods Hole area, Massachusetts, USA, in July 1987. Neither depth nor position within the meadow appear to affect NR activity. Nitrate enrichment experiments (200 M NO ₃ ^– for 6 d) were conducted in the laboratory to determine if NR activity could be induced. Certain plants from shallow depth (1.2 m) showed a significant response to enrichment, with NR activity increasing from >100 up to 950 nmoles NO ₂ ^– g FW^–1 h^–1 over 6 d. It appears that Z. marina growing in very shallow water (0.8 m) near a shoreline may be affected by ground water or surface run-off enrichments, since plants from this area exhibited rates up to 1 600 nmol NO ₂ ^– g FW^–1 h^–1. Water samples from this location consistently had slightly higher NO ₃ ^– concentrations (1.4 M) than all other collection sites (0.7 M). Thus, it is possible that chronic run-off or localized groundwater inputs can create sufficient NO ₃ ^– enrichment in the water column to induce nitrate reductase activity in Zostera leaves.     

Adaptations of Gracilaria pacifica (Rhodophyta) to nitrogen procurement at different intertidal locations

Nitrogen uptake, assimilation and accumulation were studied in three populations of Gracilaria pacifica Abbott in Bamfield Inlet, British Columbia, Canada, over three summers, 1979–1981. Two of these populations were in the intertidal one high and one low, and the third was a subtidal cultured population. Nitrate uptake rates, internal nitrate content and nitrate reductase activities were highest in the low intertidal population. Time-courses of uptake and uptake kinetics were studied. Both nitrate and ammonium were taken up simultaneously. Thalli from the high-intertidal population showed enhanced nitrate and ammonium uptake following mild desiccation, and greater tolerance to desiccation in terms of maintaining nitrogen uptake after severe desiccation. Transplants were made to determine the effect of intertidal height and geographic location on responses to desiccation, nitrogen uptake, assimilation and accumulation. Nitrate and ammonium uptake rates were dependent on intertidal height and geographic location. Transplanting up the intertidal increased nitrate uptake and nitrate reductase activity, but decreased the nitrate content of the thalli. There were few significant differences in ammonium uptake rates, and ammonium, amino acid, and soluble-protein content of the various populations. All high-intertidal populations, transplanted or natural, showed enhanced nitrate uptake rates following desiccation. Enhanced ammonium uptake rates following desiccation were restricted to the high-intertidal thalli in only one geographic location. Tolerance to higher levels of desiccation also appeared to be intertidal height-dependent, but required more than five weeks to fully develop or disappear.     

In situ experiment of ontogenetic variability in the otolith chemistry of Stegastes partitus

Otolith chemistry can be used to assess pelagic larval fish connectivity by comparing spatially variable otolith edge chemistry (corresponding to the site of collection) to otolith core chemistry (corresponding to the site of hatching). However, because the otolith’s edge and core represent different life stages, the deposition of elements may differ, thus complicating direct comparisons of edge and core chemistry to investigate connectivity. Here we present data from a field experiment in which otoliths from embryos (3 days post-fertilization) and juveniles of Stegastes partitus were collected at the same site and time, and chemically analyzed to assess whether elemental concentrations of otoliths vary ontogenetically. Separate multivariate analyses, each investigating the spatial/temporal variability in the chemistry of either embryo otoliths or the edges of juvenile otoliths, revealed significant differences, suggesting an environmental influence to the chemical signals of otoliths. A nested multivariate analysis assessing whether otolith chemistry varied with life history stage (i.e., ontogenetic variability) indicated that elemental concentrations of embryo otoliths were significantly greater than that of juvenile otolith edges. Specifically, embryo elemental concentrations of Mn, Zn, Sn, Ba, Ce, and Pb were between 2 and 163 times greater than those of the corresponding juvenile otoliths, and thus the environment was not the primary determinant of embryo otolith chemistry. Consequently, caution is warranted when interpreting environmental patterns of otolith cores, particularly when using them as a proxy for natal signatures.     

复合垂直流人工湿地基质氧化还原酶活性研究

对复合垂直流人工湿地系统(IVCW)基质中5种常见的氧化还原酶活性进行了研究.结果表明,氧化还原酶活性存在显著性季节差异,过氧化物酶在春、夏、秋三季的酶活性显著高于冬季的酶活性(P＜0.05);多酚氧化酶和过氧化氢酶的活性最高在秋季;脱氢酶在夏、冬两季时酶活性显著高于秋季和春季的酶活性(P＜0.05);硝酸盐还原酶在春、冬季时显著高于夏、秋季(P＜0.01).空间分布上,除过氧化物酶外,湿地下行流池的酶活性显著高于上行流池,并且随着基质深度的增加递减;但基质硝酸盐还原酶各层之间差异不显著.图6表3参17