Disappearance Of Nitrite Research Articles

Nitrate, but not nitrite, derived from nitrogen dioxide accumulates in Arabidopsis leaves following exposure to 15N-labeled nitrogen dioxide

ABSTRACTIt is known that when plant leaves are exposed to exogenously applied nitrogen dioxide (NO2), nitrogen derived from NO2 is reduced to amino acid nitrogen. However, whether this is the sole metabolic fate of exogenously applied NO2 is unclear. In this study, Arabidopsis leaves were exposed to 4 ppm 15N-labeled NO2 for 4 h in light, followed by capillary ion analysis and elemental analysis–mass spectrometry with an elemental analyzer connected directly to a mass spectrometer. We found that leaf cells exposed to 15N-labeled NO2 accumulated a large amount of 15N-labeled nitrate. Neither 15N-labeled nitrite nor endogenous nitrite was present in exposed leaves. It is likely that exogenously applied NO2 is first converted to nitrite, and that nitrite is oxidized to nitrate in Arabidopsis leaf cells. The complete disappearance of nitrite derived from exogenously applied NO2 and endogenous nitrite supports this mechanism.

Nitrite Reduction Assay for Whole Pseudomonas Cells

The second step of the dissimilatory denitrification pathway in which nitrite (NO2-) is converted to nitric oxide (NO) is catalyzed by the enzyme nitrite reductase. Two distinct enzymes are found in nature that catalyze this reaction, and they contain different metal sites, either iron (Fe), in the form of heme, or copper (Cu) (Zumft, 1997). The Pseudomonas stutzeri (P. stutzeri) RCH2 strain used in this assay contains both an Fe and a Cu form of nitrite reductase. In this assay, total nitrite reductase activity can be measured in whole cells using fumarate or some other carbon source as an electron source by measuring the disappearance of nitrite over time (Thorgersen et al., 2015).

15N Tracing Studies on In Vitro Reactions of Ferredoxin-Dependent Nitrite Reductase and Glutamate Synthase Using Reconstituted Electron Donation Systems.

It is known that plants contain ferredoxin (Fd)-dependent nitrite reductase (NiR) and glutamate synthase (GOGAT). The Fd-NiR reaction produces ammonia from nitrite, and the activity is usually measured by nitrite disappearance. The Fd-GOGAT reaction forms two glutamates of different origin, from glutamine and 2-oxoglutarate, and the activity is measured by the oxidation of reductant (NADPH) or by formation of total glutamate. Here, a quantitative probe of the products and efficiency of the process was conducted using (15)N tracing techniques on these reactions in vitro. We quantified the reduction of (15)N-labeled [Formula: see text] to [Formula: see text] and the formation of [(15)N]glutamate and [(14)N]glutamate from [5-(15)N-amide]glutamine plus 2-oxoglutarate by NiR and GOGAT, respectively, with the reductant-Fd-NADP(+) oxidoreductase (FNR)-Fd system as the sequential electron donors. The supply of dithionite or NADPH to recombinant cyanobacterial NiR led to electron donation system-dependent formation of [(15)N]ammonium from [(15)N]nitrite. Addition of 20 mM NaCl and 20 mM Na-ascorbate accelerated nitrite reduction under high concentrations of NADPH. A sufficient supply of NADPH to recombinant Zea mays Fd-GOGAT generated complete GOGAT activity (transferring the [5-(15)N]amide of glutamine to 2-oxoglutarate to form [(15)N]glutamate), whereas a shortage of NADPH resulted in glutaminase activity only, which removed the amide from glutamine and released ammonia and [(14)N]glutamate. We conclude that although the recombinant Fd-GOGAT enzyme has two forms of glutamate synthesis, the first by glutaminase (ammonia release by glutamine amidotransferase) and the second by glutamate synthase (coupling of the ammonia and exogenously applied 2-oxoglutarate), the first works without NADPH, while the second is strictly dependent on NADPH availability.

Nitrite and Nitrate Concentrations and Metabolism in Breast Milk, Infant Formula, and Parenteral Nutrition

Dietary nitrate and nitrite are sources of gastric NO, which modulates blood flow, mucus production, and microbial flora. However, the intake and importance of these anions in infants is largely unknown. Nitrate and nitrite levels were measured in breast milk of mothers of preterm and term infants, infant formulas, and parenteral nutrition. Nitrite metabolism in breast milk was measured after freeze-thawing, at different temperatures, varying oxygen tensions, and after inhibition of potential nitrite-metabolizing enzymes. Nitrite concentrations averaged 0.07 ± 0.01 μM in milk of mothers of preterm infants, less than that of term infants (0.13 ± 0.02 μM) (P < .01). Nitrate concentrations averaged 13.6 ± 3.7 μM and 12.7 ± 4.9 μM, respectively. Nitrite and nitrate concentrations in infant formulas varied from undetectable to many-fold more than breast milk. Concentrations in parenteral nutrition were equivalent to or lower than those of breast milk. Freeze-thawing decreased nitrite concentration ~64%, falling with a half-life of 32 minutes at 37°C. The disappearance of nitrite was oxygen-dependent and prevented by ferricyanide and 3 inhibitors of lactoperoxidase. Nitrite concentrations in breast milk decrease with storage and freeze-thawing, a decline likely mediated by lactoperoxidase. Compared to adults, infants ingest relatively little nitrite and nitrate, which may be of importance in the modulation of blood flow and the bacterial flora of the infant GI tract, especially given the protective effects of swallowed nitrite.

Emissions of Nitrous Oxide, Ammonia, and Carbon Dioxide from a Cambisol at Two Contrasting Soil Water Regimes and Urea Granular Sizes

The superiority of mixing and deep placement of prilled urea (PU) or urea supergranules (USG) over surface‐broadcast application for reducing nitrogen (N) loss from lowland rice is well established. In upland agricultural systems, rainfall and/or the application and loss of irrigation water from soil systems may regulate urea N transformations and gaseous losses, depending on the method of fertilizer application and the particle size. To develop further insights into these processes, experiments were carried out in a silt loam soil mixed with PU or amended with point‐placed USG at a depth of 7.5 cm. Two soil water regimes were used: around field capacity (AFC) with low evaporative conditions (depletion: 77 to 69% water‐filled pore space, WFPS) and below field capacity (BFC) with high evaporative conditions following two irrigations (depletion: 70 to 55% WFPS). The nitrous oxide (N2O) emission was greater at AFC than at BFC, where nitrification was more rapid. The N2O peaks appeared mostly after the disappearance of nitrite (NO2 −), presumably dominated by nitrifier and/or chemodenitrification and the degree of emissions probably depended on the stability period and the reduction of NO2 − induced by the soil water regimes. The relative N2O losses from the added N were small (⩽0.20%) for all treatments after 21 days. The point at which 50% of its emissions (t½) occurred was delayed up to 6 days longer than found from the application of PU. The differences between PU and USG application were likely linked with the concentrations of ammonium (NH4 +), NO2 −, and pH. These high concentrations continued longer at AFC than at BFC and were limited to a distance of <5.0 cm from the application zone. Similarly, the relative losses of the added N ranged from 0.19 to 0.56% at AFC and 0.08 to 0.37% at BFC, the highest being with USG application. Based on the areas receiving equal N, the N2O and ammonia (NH3) emissions from USG differed marginally with PU. Carbon dioxide (CO2) release was higher at AFC than BFC, in which the USG application probably limited microbial respiration preferentially to methane oxidation. A correlation study showed that the N2O flux was best explained together with CO2, nitrate (NO3 −), NO2 −, and WFPS (R 2 = 0.67***). This indicates the influence of both auto‐ and heterotrophic microbial activities toward N2O emission, with soil water being an important regulatory factor.

Nitrite as undesirable substances in animal feed ‐ Scientific Opinion of the Panel on Contaminants in the Food Chain

Nitrite as undesirable substances in animal feed ‐ Scientific Opinion of the Panel on Contaminants in the Food Chain

Development of the modified activated sludge model describing nitrite inhibition of aerobic phosphate uptake

Since metabolic pathway and enzymatic clarification of poly-phosphate accumulating organisms (PAOs) are still unclear, biological phosphorus removal (BPR) sometimes become unstable. We have focused on nitrite as one of unknown factors deteriorating BPR performance. And we obtained some findings from previous studies, namely 1) nitrite inhibits phosphate uptake and growth of PAOs, 2) nitrite inhibition persists even after nitrite disappearance, 3) PAOs with the higher relative anoxic activity are less sensitive to nitrite exposure. This study provides the modified Activated Sludge Model No.2d (ASM2d) to express nitrite inhibition properly by incorporating the assumed intracellular reaction product (reaction complex) of nitrite. The model also considers the tolerance mechanism of nitrite inhibition by the denitrifying activity of PAOs. From the results of previous experiments and relevant references, the modified model called "Nitrite-Complex model" incorporates new components, namely nitrite (S(NO(2) )) and reaction complex (X(complex)), to ASM2d. The model incorporation only nitrite inhibition was able to fit with measured phosphate concentration while nitrite exists. Whereas, this model couldn't describe the persistence of nitrite inhibition after nitrite disappeared. However, result of nitrite-complex model incorporating nitrite and reaction complex inhibition, it fits well with measured phosphate concentration not only before nitrite disappeared but also after nitrite disappeared.

In vitro and in vivo kinetic handling of nitrite in blood: effects of varying hemoglobin oxygen saturation

Growing evidence suggests that nitrite, acting via reduction to nitric oxide by deoxyhemoglobin, may play an important role in local control of blood flow during hypoxia. To investigate the effect of hypoxia (65 Torr arterial Po(2)) on the kinetic properties of nitrite, a bolus injection of sodium nitrite (10 mg/kg iv) was given to normoxic or hypoxic newborn lambs, and the time course of plasma nitrite and methemoglobin (MetHb) concentrations was measured. The in vivo kinetics of nitrite disappearance from plasma were biphasic and were not affected by hypoxia. Changes in MetHb, a product of the nitrite-hemoglobin reaction, also did not differ with the level of oxygenation. Hypoxia potentiated the hypotensive effects of nitrite on pulmonary and systemic arterial pressures. The disappearance of nitrite from plasma was equivalent to the increase in MetHb on a molar basis. In contrast, nitrite metabolism in sheep blood in vitro resulted in more than one MetHb per nitrite equivalent under mid- and high-oxygenation conditions: oxyhemoglobin (HbO(2)) saturation = 50.3 +/- 1.7% and 97.0 +/- 1.3%, respectively. Under the low-oxygenation condition (HbO(2) saturation = 5.2 +/- 0.9%), significantly less than 1 mol of MetHb was produced per nitrite equivalent, indicating that a significant portion of nitrite is metabolized through pathways that do not produce MetHb. These data support the idea that the vasodilating effects of nitrite are potentiated under hypoxic conditions due to the reduction of nitrite to nitric oxide by deoxyhemoglobin.

A Random-sequential Mechanism for Nitrite Binding and Active Site Reduction in Copper-containing Nitrite Reductase

The homotrimeric copper-containing nitrite reductase (NiR) contains one type-1 and one type-2 copper center per monomer. Electrons enter through the type-1 site and are shuttled to the type-2 site where nitrite is reduced to nitric oxide. To investigate the catalytic mechanism of NiR the effects of pH and nitrite on the turnover rate in the presence of three different electron donors at saturating concentrations were measured. The activity of NiR was also measured electrochemically by exploiting direct electron transfer to the enzyme immobilized on a graphite rotating disk electrode. In all cases, the steady-state kinetics fitted excellently to a random-sequential mechanism in which electron transfer from the type-1 to the type-2 site is rate-limiting. At low [NO(-)(2)] reduction of the type-2 site precedes nitrite binding, at high [NO(-)(2)] the reverse occurs. Below pH 6.5, the catalytic activity diminished at higher nitrite concentrations, in agreement with electron transfer being slower to the nitrite-bound type-2 site than to the water-bound type-2 site. Above pH 6.5, substrate activation is observed, in agreement with electron transfer to the nitrite-bound type-2 site being faster than electron transfer to the hydroxyl-bound type-2 site. To study the effect of slower electron transfer between the type-1 and type-2 site, NiR M150T was used. It has a type-1 site with a 125-mV higher midpoint potential and a 0.3-eV higher reorganization energy leading to an approximately 50-fold slower intramolecular electron transfer to the type-2 site. The results confirm that NiR employs a random-sequential mechanism.

Light-induced disappearance of nitrite in the presence of iron (III)

Understanding of rapid disappearance of nitrite in natural waters and its impact on nitrogen natural cycling has remained limited. We found that NO − 2 disappeared rapidly in pH 3.2 aqueous Fe(III) solutions both in sunlight and in 356 nm light. Quantum yields of the NO − 2 loss at 356 nm were 0.049–0.14 for initial levels of 10–80 μm NO − 2 and 200 μm Fe(III). The NO − 2 loss (at 356 nm) followed apparent first-order kinetics. The rate constants were 1.3 × 10 –3 (40 μm NO − 2) and 4.1 × 10 –4 s –1 (80 μm NO − 2) for 100 μm Fe(III), and 2.3 × 10 –3 (40 μm NO − 2) and 7.5 × 10 –4 s –1 (80 μm NO −1 2) for 200 μm Fe(III) ( t 1/2=8.7, 27.9, 5.1, and 15.3 min, respectively). The rate constants were directly proportional to [Fe(III)] 0 and inversely proportional to [NO − 2] 0. Agreement between the rate constants obtained experimentally and those calculated mechanistically supports the hypothesis that NO − 2 was oxidized to NO 2 by  OH radicals from photolysis of FeOH 2+ complexes, and at high [NO − 2] 0 (e.g., 80 μm) relative to [Fe(III)] 0, hydrolysis of NO 2 or N 2O 4 to form NO − 3 and NO − 2 could be significant. This study showed that light and Fe(III)-induced oxidation of NO − 2 (rate=∼10 –1–10 –2 μm s –1) was more rapid than its direct photolysis (rate= ∼10 –4 μm s –1), and the photolysis could be a significant source of  OH radicals only in cases where the Fe(III) level is much lower than the NO − 2 level ([Fe(III)]/[NO − 2] < 1/80). This study suggests that the light and Fe(III)-induced oxidation of NO − 2 would be one potential important pathway responsible for the rapid transformation of NO − 2 in acidic surface waters, especially those affected by acid-mine drainage or volcanic activities. This study also may be of interest for modeling certain acidic atmospheric water environments.

Catalytic liquid‐phase nitrite reduction: Kinetics and catalyst deactivation

AbstractLiquid‐phase reduction using a solid catalyst provides a potential technique for the removal of nitrites from waters. Activity and selectivity measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi‐batch slurry reactor, which was operated at temperatures below 298 K and atmospheric pressure. The effects of catalyst loading and initial nitrite concentration on the reaction rate were also investigated. The Pd monometallic catalysts were found to be advantageous over the Pd‐Cu bimetallic catalyst with respect to either reaction activity or selectivity. Among the catalysts tested, minimum ammonia formation was observed for the Pd(l wt. %)/γ‐Al2O3 catalyst. The proposed intrinsic rate expression for nitrite disappearance over the most selective catalyst is based on the steady‐state adsorption model of Hinshelwood, which accounts for a dissociative hydrogen adsorption step on the catalyst surface and an irreversible surface reaction step between adsorbed hydrogen species and nitrite ions in the Helmholtz layer. Both processes occur at comparable rates. An exponential decay in the activity of Pd(l wt. %)/γ‐Al2O3 catalyst has been observed during the liquid‐phase nitrite reduction. This is attributed to the catalyst surface deprotonation, which occurs due to the partial neutralization of stoichiometrically produced hydroxide ions with carbon dioxide.

Denitrification kinetics in an activated sludge system

For all water bodies especially for sea, lakes, and ground waters it is very important that nutrient pollution is the least possible (minimal). From municipal and industrial waste waters where considerable amount of nutrients is expected it is possible to remove nutrients with biological treatment. The first step is usually aerobic activated sludge treatment and the second step is combined anaerobic-anoxic-aerobic step in different combinations. A very effective process for nitrogen removal is anoxic activated sludge system. It is very important that in the first aerobic step complete nitrification is achieved. In our laboratory denitrification kinetics was studied. The objective of this study was determination of denitrification velocity and attendance of different parallel phenomena such as nitrite, disappearance of nitrate and nitrite, sulphide formation, etc. Denitrification process was studied in two systems, in closed system (such as in closed reactors for denitrification) and in open systems (such as in open denitrification tanks). We found out that denitrification rate in closed systems was from about 8 to 52 mg/l.h and was dependent on activated sludge type, sludge concentration, and temperature of the system. In open system (such as in an anoxic aeration tank) the rate of denitrification was lower than in closed system; it was from 4 to 15 mg/l.h dependent on activated sludge type, sludge concentration, and temperature of the system. Experiments were carried out in the range of temperature from 20° to 30°C.

Effect of ionophores on denitrification inFlexibacter canadensis

Denitrification by Flexibacter canadensis was investigated by measuring the production and (or) consumption of nitrite, nitric oxide (NO), and nitrous oxide (N2O) under anaerobic conditions. Carbonyl cyanide m-chlorophenylhydrazone (CCCP), carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), 2,4-dinitrophenol, and nigericin, but not valinomycin-K+inhibited the production of nitrite and N2O from nitrate by intact cells. However, CCCP, FCCP, 2,4-dinitrophenol, nigericin, and valinomycin-K+did not affect nitrite production from nitrate by cell-free extracts. These results suggest that nitrate transport was dependent on the transmembrane pH gradient but not on the membrane potential. CCCP, FCCP, and nigericin but not 2,4-dinitrophenol and valinomycin-K+caused NO accumulation during the reduction of nitrite, and also inhibited NO consumption and N2O production from nitrite by intact cells. These results preclude an explanation for NO accumulation based on the collapse of the proton motive force by ionophores, and imply that CCCP, FCCP, and nigericin perhaps dissociated a nitrite reductase–nitric oxide reductase complex, and (or) inhibited nitric oxide reductase specifically. 2,4-Dinitrophenol and CCCP did not inhibit the reduction of N2O to dinitrogen. Addition of ≤ 1.16 μM dissolved NO did not affect the production of nitrite from nitrate, or the disappearance of nitrite or N2O. The rate of NO consumption was linear with concentrations of dissolved NO up to 67 nM. Above 67 nM NO, NO consumption was inhibited, suggesting that NO is toxic to nitric oxide reductase.Key words: ionophores, denitrification, nitric oxide, Flexibacter canadensis.

Denitrification kinetics in an activated sludge system

For all water bodies especially for sea, lakes, and ground waters it is very important that nutrient pollution is the least possible (minimal). From municipal and industrial waste waters where considerable amount of nutrients is expected it is possible to remove nutrients with biological treatment. The first step is usually aerobic activated sludge treatment and the second step is combined anaerobic-anoxic-aerobic step in different combinations. A very effective process for nitrogen removal is anoxic activated sludge system. It is very important that in the first aerobic step complete nitrification is achieved.In our laboratory denitrification kinetics was studied. The objective of this study was determination of denitrification velocity and attendance of different parallel phenomena such as nitrite, disappearance of nitrate and nitrite, sulphide formation, etc.Denitrification process was studied in two systems, in closed system (such as in closed reactors for denitrification) and in open systems (such as in open denitrification tanks). We found out that denitrification rate in closed systems was from about 8 to 52 mg/l.h and was dependent on activated sludge type, sludge concentration, and temperature of the system. In open system (such as in an anoxic aeration tank) the rate of denitrification was lower than in closed system; it was from 4 to 15 mg/l.h dependent on activated sludge type, sludge concentration, and temperature of the system. Experiments were carried out in the range of temperature from 20° to 30°C.

Observations of phytoplankton and nutrients from a Lagrangian drifter off northern California

A Lagrangian drifter was deployed in a cold filament off northern California as part of the Coastal Transition Zone program. The drifter was equipped with an optical package (consisting of a spectroradiometer, a fluorometer, and a beam transmissometer) suspended at 8.5‐m depth and a water sampler suspended at 16.3‐m depth. The drifter was recovered after 8 days. Optical, chemical, and biological properties changed considerably as the drifter moved offshore in the cold filament. Concentrations of phytoplankton chlorophyll increased rapidly in the first 2 days, in parallel with the disappearance of nitrate and nitrite. After this initial period, chlorophyll decreased gradually over the next 6 days with prominent diurnal fluctuations present in the last 3 days. Water transparency also showed similar long‐term as well as diurnal fluctuations. The phytoplankton community became increasingly dominated by large centric diatoms throughout the deployment. Although total cell volume was higher towards the middle of the deployment, this increase occurred without a parallel increase in chlorophyll. In addition, total particulate concentrations were highest nearshore. Although the drifter slippage was approximately 1 cm/s, the biological, chemical, and physical characteristics of the water were affected by both in situ changes and vertical motions of the water. These results are generally consistent with results from other up welling studies.

Effect of added water, sodium erythorbate and storage time on the functional properties of prerigor beef preblends in a model system

Singular and combined effects of added water, sodium erythorbate and storage time on salt soluble protein extractability, bacteriological and chemical characteristics of preblended hot-boned beef were evaluated. Waterholding and gel forming capacities of preblended hot-boned beef containing either 0, 10 or 20% added water were determined. Significant interactions between added water level and storage time on microbial counts and between sodium erythorbate level and storage time on thiobarbituric acid values and residual nitrite levels were noted. The presence of sodium erythorbate resulted in a more ( P < 0·05) rapid rate of nitrite disappearance, but it did not affect ( P > 0·05) microbial counts. Salt-soluble protein extractability was not affected ( P > 0·05) by added water, but more protein could be extracted with increasing storage time. A trend existed to suggest that the presence of added water in the meat preblends slightly improved the gel formation and waterholding capacities.

Antimicrobial Effect and Disappearance of Sodium Nitrite in Staphylococcus aureus Cultures

ABSTRACT Staphylococcus aureus was sensitive to as little as 100 μg sodium nitrite (NaNO2)/mL under strictly anaerobic conditions at pH 7.3 and was more sensitive at pH 6.0. S. aureus was less sensitive to NaNO2 in the presence of 1.0‐1.5 μg O2/mL. NaNO2 disappeared during growth of S. aureus. Disappearance was greater in the system containing 1‐1.5 μg‐O2 than in strictly anaerobic cultures at an initial pH of 7.3 or 6.0. Nitrite reductase activity was not detected in either soluble or membrane fractions of S. aureus. Interaction of NaNO2 with secreted metabolic products, dismutation of NaNO2 by reduced pH and adsorption of NaNO2 to S. aureus cells were not involved in the disappearance of NaNO2. Nitrite, nitric oxide, nitrous oxide and ammonia were not end products of NaNO2 disappearance.

Nitrite utilization by excised Zea mays L. roots under anaerobic conditions

Under both aerobic and anaerobic conditions exogenously supplied nitrite was utilized by sterile excised Zea mays L. root. A slightly greater quantity of nitrite was used under aerobic conditions than under anaerobiosis. The uncoupler of oxidative phosphorylation, pentachlorophenol (PCP), diminished the utilization of nitrite under aerobic and anaerobic conditions resulting in a net accumulation of nitrite rather than a net disappearance of nitrite. Nitrite supplied together with nitrite resulted in a slight reduction in the level of nitrite utilized. Supply of exogenous nitrite had no effect on nitrate reduction under aerobic or anaerobic conditions. A net accumulation of nitrite occurs only when roots are supplied with nitrate in the absence of added nitrite. However, the level of nitrite accumulated under anaerobiosis, when roots were supplied with nitrate only, was found to be a fraction of the quantity of nitrite utilized when roots were supplied with nitrite under anaerobiosis. Nitrate utilization far exceeded the level of nitrite accumulated under anaerobiosis when roots were supplied with nitrate only.

Mixed-transfer kinetics of nitrite uptake in barley ( Hordeum vulgare L. CV. Miranda) seedlings

The characteristics of nitrite uptake kinetics were analysed in 5-day-old barley ( Hordeum vulgare L. vc. Miranda) seedlings by following nitrite disappearance from the external medium. Nitrite uptake was linear with time during the first hour and no initial lag phase was detected. The nitrite uptake pattern, as a function of increasing external nitrite concentrations (0.5–6 mM), showed a mixed transfer kinetics which could be resolved into saturation (carrier-mediated) and linear diffusion (non-carrier-mediated) components. The kinetic parameters for the isolated diffusion component as well as for the total system are reported. Both ammonium ions and p-hydroxy-mercuribenzoate ( p-HMB) dimished or abolished the carrier-mediated transport without affecting the diffusion component. Preincubation for 24 h with nitrate or nitrite led to further increases in the initial uptake rates whereas cycloheximide (CHM) prevent this stimulating effect. These results were consistent with the inducible nature of the nitrite uptake system, mediated through protein synthesis.

A laboratory silo permitting repeated sampling.

A new type of laboratory silo for studying silage fermentation is described. Samples are taken manually from the silo using a glove mounted on the apparatus. Introduction of air during sampling is prevented by a sample lock. In a preliminary experiment, the accumulation and disappearance of nitrite in wilted perennial ryegrass ensiled in the laboratory silo was monitored and there was less variation in nitrite content than when the same grass was ensiled in 2-l flasks. (Abstract retrieved from CAB Abstracts by CABI’s permission)