Intracellular location of nitrate reductase and nitrite reductase in spinach and sunflower leaves

Inhibition of nitrite in prepared dish of Brassica chinensis L. during storage via non-extractable phenols in hawthorn pomace: A comparison of different extraction methods

The objective of this study was to investigate whether non-extractable phenols (NEP) prepared by acid, enzymatic and alkaline hydrolysis in hawthorn pomace could reduce the nitrite content in prepared vegetable dishes (PVDs), analyzed through ultraviolet spectrophotometry and high performance liquid chromatography. The results showed that on the seventh day of storage, compared with the control group, the nitrite content of the samples added with acid, enzymatic and alkaline hydrolyzed NEP decreased by 40%, 28% and 19%, respectively, depending on different contents and chemical compositions of the recovered NEP. The nitrite reduction caused by NEP was mainly attributed to the growth inhibition of microorganisms producing nitrite (e.g., Escherichia coli and Pseudomonas aeruginosa) and the direct scavenging effect on nitrite, rather than affecting the activities of nitrate reductases and nitrite reductases in plant tissues. Use of hawthorn pomace is potentially a promising option to reduce nitrite in PVDs.

Garlic essential oil microcapsules prepared using gallic acid grafted chitosan: Effect on nitrite control of prepared vegetable dishes during storage

In order to lower the nitrite content in prepared vegetable dishes (PVDs) within a week, microcapsules loaded with garlic essential oils (GEO) were prepared using modified chitosan (CS) with different mass ratios of gallic acid (GA) to CS, and their physicochemical properties were determined. The effects of GEO alone and of microcapsules made using native CS and GA-CS (GA-grafted CS) with the highest conjugation degree on the nitrite content in PVD_S were measured quantitatively. Also, the reasons for the differences were identified. The results showed that the microcapsules prepared using GA-CS (at a mass ratio of 0.5:1) presented the best physicochemical properties, including antioxidant activity, encapsulation efficiency, sustained release, etc. GA-CS microcapsules enhanced growth inhibition of bacteria producing nitrites, thus showing its excellent ability to inhibit nitrites, compared to GEO alone and microcapsules made using native CS. GA-CS encapsulation is a new option to lower the nitrite content in PVDs.

Ultrastructural demonstration of ferricyanide reductase (Diaphorase) activity in the envelopes of the plastids of etiolated barley (Hordeum vulgare L.) leaves

Electron-dense precipitate was found consistently in the plastid envelope compartment in etiolated barley (Hordeum vulgare L.) leaves, incubated prior to fixation with succinate or malate as substrates and ferricyanide as the electron acceptor. Sulfhydryl reagents p-chloromercuribenzoate and N-ethylmaleimide abolished this reaction, while KCN did not affect it. Prefixation with 0.1% glutaraldehyde followed by incubation in basic media did not change the fine structural localization of precipitate, whereas pretreatment with 1.25% glutaraldehyde resulted in aspecific precipitation. Omission of the subtrate from the medium brought about diminished or negative reaction. Our results indicate that a (possibly not yet assembled) nitrate reductase complex is present in the plastid envelope compartment, the diaphorase part of which is responsible for the observed precipitation.

Intracellular distribution of enzymes associated with nitrogen assimilation in roots

The cellular distribution of enzymes involved in nitrogen assimilation: nitrate reductase (EC 1.6.6.2), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), and glutamate dehydrogenase (EC 1.4.1.3) has been studied in the roots of five plants: maize (Zea mays L. hybrid W 64A x W 182E), rice (Oryza sativa L. cv. Delta), bean (Phaseolus vulgaris L. cv. Contender), pea (Pisum sativum L. cv. Demi-nain), and barley (Hordeum vulgare L.). Initially, cell organelles were separated from soluble proteins by differential centrifugation. Cell organelles were also subjected to sucrose density gradients. The results obtained by these two methods indicate that nitrite reductase and glutamate synthase are localized in plastids, nitrate reductase and glutamine synthetase are present in the cytosol, and glutamate dehydrogenase is a mitochondrial enzyme.

Histochemical localization of nitrate reductase

NADH-dependent nitrate reductase (E.C. 1.6.6.1) was ultrastructurally localized in norflurazon-treated and control soybean cotyledons [Glycine max (L.) Merr.] by a method based upon the increase in osmiophilia due to the formation of an azo dye. The reaction product was observed in small vesicles throughout the cytoplasm. An apparent transport of nitrite to the plastid, the site of nitrite reduction, may occur through fusion of the nitrite-containing vesicles with the chloroplast envelope. Plants grown in tungstate lacked nitrate reductase activity as measured by standard assay procedures, and showed no increase in osmiophilia, suggesting a degree of specificity of this cytochemical procedure.

The effect of nitrogen refeeding on starved cells of Platymonas striata Butcher

A rapid uptake of nitrogen was observed in nitrogen-starved cells of Platymonas striata after refeeding with ammonium or nitrate ions. This was followed by a net loss of nitrogen per cell. Cells initially grown in and then starved in a regime of continuous light showed greater increases in average cell nitrogen on refeeding with ammonium or nitrate ions than did cells initially grown in and then starved in a regime of alternating light and darkness. A particulate subcellular location was observed for nitrate reductase (EC 1.6.6.1) in broken cell suspensions prepared by sonication. Nitrite reductase (EC 1.6.6.4) was located in the soluble fraction of these cell suspensions. Broken cell preparations displayed a lowered nitrate reductase activity as compared with the particulate component of these preparations. This was shown not to be due to heat-stable inhibitors present in the soluble phase of the cell. It appeared to be an artefact produced by the high nitrite reductase activity of the broken cell preparations, which removed much of the nitrite as it was formed. Nitrogen starvation of nitrate-grown cultures produced cellular increases in nitrate reductase and nitrite reductase activities which were further increased after the addition of nitrate. The results are discussed.

Nitrate, nitrite and ammonia assimilation by leaves: Effect of light, carbon dioxide and oxygen

The assimilation of nitrate, nitrite and ammonia in barley, wheat, corn and bean leaves was studied using (15)N-labelled molecules and either leaf chamber experiments with the uptake of the nitrogen species in the transpiration stream, or vacuum-infiltration experiments. The assimilation of (15)NO3 (-) into amino nitrogen was strictly dependent on light and ceased abruptly when the light was extinguished. If the leaves were exposed to air, CO2-free air or N2 there was no effect on the rate of NO3 (-) assimilation over 0.5 h. After 1.25 h of CO2-free air, NO3 (-) assimilation into amino acids was sharply reduced. Resupply of air at this time stimulated NO3 (-) assimilation and restored it to the rate observed in leaves exposed to air only. There was no recovery by tissue pretreated for 1.25 h in N2 and subsequently resupplied with air. Incorporation of (15)NO2 (-) was also markedly dependent on light with little reduction occurring in the dark. Incorporation of (15)NH4 (+) into amino acids was stimulated 5 fold by light but considerable incorporation occurred in the dark. The presence of 100 mM NO3 (-) had no effect on the rate of incorporation of (15)NO2 (-) or (15)NH4 (+). Nitrite at 1 mM had no effect on (15)NO3 (-) incorporation but at 10 mM inhibited it completely after 0.5 h. Ammonia at 1 mM had no effect on (15)NO3 (-) or (15)NO2 (-) incorporation and while 10 mM inhibited incorporation for 0.5 h this inhibition did not persist.

Nitrite reduction in leaves; Studies on isolated chloroplasts

Chloroplast preparations from spinach leaves containing a high percentage of intact chloroplasts were capable of light dependent nitrite reduction at rates around 9 μmol/mg chlorophyll/h for at least 50 min. This reduction was inhibited by DCMU but unaffected by uncouplers of photosynthetic phosphorylation. Nitrite reduction was not accompanied by a stoichiometric evolution of oxygen evolution. The disappearance of nitrite was accompanied by an approximately stoichiometric formation of reduced nitrogen.

Some properties of two forms of nitrite reductase from corn (Zea mays L.) scutellum

Nitrite reductase from corn scutellum-a non-chlorophyllous tissue-can use methyl viologen, benzyl viologen or ferredoxin as electron donor. Little or no reduction occurs with nicotinamide or flavin nucleotides. Activity is inhibited by p-chloromercuribenzoate and by cyanide. Organic chelates, with the exception of bathocuproine disulphonate and bathophenanthroline disulphonate, are not inhibitory. Ammonia is the reaction product. Ion exchange chromatography resolves the nitrite reductase activity into two peaks with apparently represent two forms of the enzyme. Both have a molecular weight of 61-63000 as determined by molecular exclusion chromatography, and a pH optimum of 6.7-6.8. Although their properties are generally similar, they show a marked difference in thermal stability, ionic charge and behaviour during isoelectric focusing. Nitrite reductase is found largely in the soluble fraction although some particulate activity is also obtained. Both forms of the enzyme are present in the soluble and particulate fractions.

The action of nitrite on NADP reduction by intact spinach chloroplasts

Isolated, intact spinach chloroplasts incubated in light in the presence of HCO 3 (-) and NO 2 (-) have the greater proportion of their NADP present in the reduced form. The steady state concentration of NADPH in light in these chloroplasts is significantly higher in the presence of NO2 than in its absence. These results invalidate earlier conclusions (Grant and Canvin, 1970) that NO 2 (-) inhibits photosynthesis by preventing NADP reduction.

The effect of nitrate and nitrite on oxygen evolution and carbon-dioxide assimilation and the reduction of nitrate and nitrite by intact chloroplasts

Intact chloroplasts isolated from spinach reduced NO3 (-) and NO2 (-) in the light without the addition of either co-factors or added enzymes. The maximum rate observed, however, for the reduction of NO3 (-) was approximately 3μMoles hr(-1) mg(-1) (chlorophyll) and for NO2 (-) 6 μMoles hr(-1) mg(-1) (chlorophyll). These rates were consistent with the enzyme content of whole chloroplasts, but much lower than those found in whole leaf extracts.The addition of both NO3 (-) and NO2 (-) in low concentrations resulted in transient increases in both O2 evolution and CO2 fixation. The increases in oxygen evolution were not consistent in amount and bore no relation to the amount of substrate reduced. Similar transients were observed in a number of experiments when NaCl or NH4Cl were added.The addition of NO2 (-) at concentrations of 10(-4) M and above resulted in marked inhibition of both O2 evolution and CO2 fixation. NO2 (-) appears to inhibit by blocking the reduction of NADP. NO3 (-) at similar concentrations had no such effect.An increase in the soluble amino nitrogen content of the chloroplasts was observed when NO3 (-) or NO2 (-) was reduced. There was, however, no increase in the incorporation of (14)C from (14)CO2 into amino acids under these conditions. Even with the addition of ammonia the amount of (14)C incorporated into the amino acids was not changed from less than 5% of the total (14)C fixed. We conclude that while intact chloroplasts do have the ability to reduce both NO3 (-) and NO2 (-) at low rates, they do not synthesize appreciable amounts of amino acid directly, and this fact must be considered when formulating any pathways for nitrogen metabolism during photosynthesis.