Nitrate and Nitrite Reduction

Beevers, Leonard; Hageman, R. H.

doi:10.1016/b978-0-12-675405-6.50009-7

Cited by 136 publications

(108 citation statements)

References 329 publications

Supporting

Mentioning

101

Contrasting

Unclassified

Order By: Relevance

“…However, when light intensity is limited, nitrate assimilation competes with CO 2 fixation for photochemical energy and reductants; thus, leaf assimilation is disadvantageous (Smirnoff and Stewart, 1985). Prevalent root assimilation has also been reported when external nitrate availability is limited (Beevers and Hageman, 1980). These observations indicate that nitrate distribution between roots and shoots is of physiological importance in response to changing environments, though the regulating mechanisms remain largely unidentified.…”

Section: Introductionmentioning

confidence: 72%

TheArabidopsisNitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

et al. 2010

View full text Add to dashboard Cite

Long-distance transport of nitrate requires xylem loading and unloading, a successive process that determines nitrate distribution and subsequent assimilation efficiency. Here, we report the functional characterization of NRT1.8, a member of the nitrate transporter (NRT1) family in Arabidopsis thaliana. NRT1.8 is upregulated by nitrate. Histochemical analysis using promoter-β-glucuronidase fusions, as well as in situ hybridization, showed that NRT1.8 is expressed predominantly in xylem parenchyma cells within the vasculature. Transient expression of the NRT1.8:enhanced green fluorescent protein fusion in onion epidermal cells and Arabidopsis protoplasts indicated that NRT1.8 is plasma membrane localized. Electrophysiological and nitrate uptake analyses using Xenopus laevis oocytes showed that NRT1.8 mediates low-affinity nitrate uptake. Functional disruption of NRT1.8 significantly increased the nitrate concentration in xylem sap. These data together suggest that NRT1.8 functions to remove nitrate from xylem vessels. Interestingly, NRT1.8 was the only nitrate assimilatory pathway gene that was strongly upregulated by cadmium (Cd2+) stress in roots, and the nrt1.8-1 mutant showed a nitrate-dependent Cd2+-sensitive phenotype. Further analyses showed that Cd2+ stress increases the proportion of nitrate allocated to wild-type roots compared with the nrt1.8-1 mutant. These data suggest that NRT1.8-regulated nitrate distribution plays an important role in Cd2+ tolerance.

show abstract

Section: Introductionmentioning

confidence: 72%

TheArabidopsisNitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

et al. 2010

View full text Add to dashboard Cite

show abstract

“…Ϫ by roots cells is a key process for higher plants because it is the first step of the assimilatory pathway providing most of organic nitrogen required for synthesis of biomolecules, including proteins and nucleic acids (Beevers and Hageman, 1980). More than 30 years of physiological investigations have led to the conclusion that at least three uptake systems are responsible for the influx of NO 3 Ϫ into the roots (for review, see Clarkson, 1986;Glass and Siddiqi, 1995;Crawford and Glass, 1998;Daniel-Vedele et al, 1998;Forde, 2000).…”

Section: The Uptake Of Nomentioning

confidence: 99%

Major Alterations of the Regulation of Root NO3 − Uptake Are Associated with the Mutation of Nrt2.1 and Nrt2.2 Genes in Arabidopsis

et al. 2001

View full text Add to dashboard Cite

The role of AtNrt2.1 and AtNrt2.2 genes, encoding putative NO 3 Ϫ transporters in Arabidopsis, in the regulation of high-affinity NO 3 Ϫ uptake has been investigated in the atnrt2 mutant, where these two genes are deleted. Our initial analysis of the atnrt2 mutant (S. Filleur, M. Ϫ uptake is affected in this mutant due to the alteration of the high-affinity transport system (HATS), but not of the low-affinity transport system. In the present work, we show that the residual HATS activity in atnrt2 plants is not inducible by NO 3 Ϫ , indicating that the mutant is more specifically impaired in the inducible component of the HATS. Thus, high-affinity NO 3 Ϫ uptake in this genotype is likely to be due to the constitutive HATS. Root 15 NO 3 Ϫ influx in the atnrt2 mutant is no more derepressed by nitrogen starvation or decrease in the external NO 3 Ϫ availability. Moreover, the mutant also lacks the usual compensatory up-regulation of NO 3 Ϫ uptake in NO 3 Ϫ -fed roots, in response to nitrogen deprivation of another portion of the root system. Finally, exogenous supply of NH 4 ϩ in the nutrient solution fails to inhibit 15 NO 3 Ϫ influx in the mutant, whereas it strongly decreases that in the wild type. This is not explained by a reduced activity of NH 4 ϩ uptake systems in the mutant. These results collectively indicate that AtNrt2.1 and/or AtNrt2.2 genes play a key role in the regulation of the high-affinity NO 3 Ϫ uptake, and in the adaptative responses of the plant to both spatial and temporal changes in nitrogen availability in the environment. The uptake of NO 3Ϫ by roots cells is a key process for higher plants because it is the first step of the assimilatory pathway providing most of organic nitrogen required for synthesis of biomolecules, including proteins and nucleic acids (Beevers and Hageman, 1980). More than 30 years of physiological investigations have led to the conclusion that at least three uptake systems are responsible for the influx of NO 3 Ϫ into the roots (for review, see Clarkson, 1986;Glass and Siddiqi, 1995;Crawford and Glass, 1998;Daniel-Vedele et al., 1998;Forde, 2000). Two highaffinity transport systems (HATS) are able to take up NO 3 Ϫ at low concentrations in the external medium, and display saturable kinetics as a function of the external NO 3 Ϫ concentration ([NO 3 Ϫ ] o ), with saturation in the range of 0.2 to 0.5 mm [NO 3 Ϫ ] o . One of these systems appears to be present even in plants never supplied with NO 3 Ϫ , and thus is considered as constitutive (cHATS). The other HATS is specifically stimulated by NO 3 Ϫ , and is consequently assumed to be inducible (iHATS). The maximum activity (V max ) recorded for the iHATS is generally much larger than that of the cHATS, suggesting that the former system plays a key role in the root uptake of NO 3 Ϫ from external media where [NO 3 Ϫ ] o does not exceed 1 mm. The iHATS and cHATS appear to be genetically distinct because a mutant defective in the cHATS, but not in the iHATS, has been isolated in Arabidopsis (Wang and Crawford, 1996)....

show abstract

“…In leaves, the reductant and ATP for nitrate reduction and for the subsequent ammonium assimilation are generated directly or indirectly by light reactions of photosynthesis (Beevers and Hageman, 1980). When nitrate assimilation occurs in the roots, high amounts of photosynthates must be translocated to the roots and oxidized to provide the required reductants, energy and carbon skeletons.…”

Section: Introductionmentioning

confidence: 99%

“…Nitrate is the predominant form of available nitrogen to most cultivated plants grown under normal field conditions (Beevers and Hageman, 1980). Nitrate absorbed by plants is reduced to nitrite by nitrate reductase (NR, EC 1.6.6.1) in the cytosol of cells.…”

Section: Introductionmentioning

confidence: 99%

“…Nitrite is subsequently reduced to ammonium by nitrite reductase in the plastids, and ammonium is then incorporated into amino acids. Probably, NR represents the rate-limiting step in nitrate assimilation, and can be used as a marker for the capacity of roots and shoots of immature and mature plants to assimilate external nitrogen (Beevers and Hageman, 1980;Oaks, 1994). Nitrate is easily transported in the plant and can be reduced both in leaves and roots.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Partitioning of nitrate reductase activity in Coffea arabica L. and its relation to carbon assimilation under different irradiance regimes

Carelli

Fahl

2006

Braz. J. Plant Physiol.

View full text Add to dashboard Cite

The distribution of in vivo nitrate reductase (EC 1.6.6.1) activity (NRA) between leaves and roots was studied in young coffee plants (Coffea arabica L.) grown in pots with watered sand in a glasshouse and irrigated with nutrient solution. The influence of irradiance regimes on the partitioning of NRA, and its relation with CO 2 assimilation, was also evaluated in plants grown under approximately 20, 50 and 100% of full sunlight. Time-course of nitrate accumulation in nitrogenstarved plants showed a similar pattern in leaves and roots after supplying 15 mmol L -1 nitrate, indicating efficient ability of the roots to export nitrate to the shoot. At the same time, NRA was rapidly induced in both tissues. In shoots, NRA partitioning was synchronized among the various leaf pairs. The initial increase in NRA, as each leaf pair emerged, coincided with the optimum NRA values of the next older leaf pair. However, the average shoot NRA remained relatively constant for each sampling date. During the first 23 weeks of vegetative growth, the mean NRA was 32% higher in leaves than in roots. The irradiance regimes influenced the partitioning of NRA between leaves and roots. The NRA leaf /root ratio was 0.72, 1.21 and 1.05, respectively, for plants grown under 20%, 50% and 100% of full sunlight. Leaf NRA was positively correlated with CO 2 assimilation, in response to irradiance regimes. Under favorable CO 2 assimilation conditions, higher NRA was observed in leaves than in roots, and the contrary trend occurred under limiting CO 2 assimilation conditions. Under moderate irradiance regime the leaves were the main site of nitrate reduction, contributing with 70% of the whole plant nitrate assimilation. Key words: coffee, growth, leaf/root ratio, nitrate assimilation, photosynthesis, shading Partição da atividade da redutase de nitrato em Coffea arabica L. e sua relação com a assimilação do carbono em diferentes níveis de irradiância: Estudou-se a distribuição da atividade da redutase de nitrato (ARN) in vivo entre folhas e raízes de plantas jovens de café (Coffea arabica L.) cultivadas em vasos contendo areia lavada, em casa de vegetação, e irrigadas com solução nutritiva. Também foi avaliada a influência de regimes de irradiância na partição da ARN e na assimilação do CO 2 , em plantas cultivadas aproximadamente sob 20, 50 e 100% da luz solar. Após o fornecimento de 15 mmol L -1 nitrato, para plantas deficientes em nitrogênio, o acúmulo de nitrato nas folhas e raízes apresentou padrão semelhante, indicando capacidade eficiente das raízes em exportar nitrato para a parte aérea. Ao mesmo tempo, ARN foi rapidamente induzida nos dois tecidos. Na parte aérea, houve um sincronismo na partição da ARN entre os diversos pares de folhas. O aumento da ARN, quando cada par de folhas emerge, coincidiu com as maiores ARN no par de folhas imediatamente mais velho. Contudo, a média da ARN na parte aérea permaneceu relativamente constante, para cada data de amostragem. Durante as primeiras 25 semanas de crescimento vegetativo, a ARN média foi ...

show abstract

Nitrate and Nitrite Reduction

Cited by 136 publications

References 329 publications

TheArabidopsisNitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

TheArabidopsisNitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

Major Alterations of the Regulation of Root NO3 − Uptake Are Associated with the Mutation of Nrt2.1 and Nrt2.2 Genes in Arabidopsis

Partitioning of nitrate reductase activity in Coffea arabica L. and its relation to carbon assimilation under different irradiance regimes

Contact Info

Product

Resources

About