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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Understanding of the influences of root-zone CO2 concentration on nitrogen (N) metabolism is limited. The influences of root-zone CO2 concentration on growth, N uptake, N metabolism and the partitioning of root assimilated 14C were determined in tomato (Lycopersicon esculentum). Root, but not leaf, nitrate reductase activity was increased in plants supplied with increased root-zone CO2. Root phosphoenolpyruvate carboxylase activity was lower with NO3(-)- than with NH4(+)-nutrition, and in the latter, was also suppressed by increased root-zone CO2. Increased growth rate in NO3(-)-fed plants with elevated root-zone CO2 concentrations was associated with transfer of root-derived organic acids to the shoot and conversion to carbohydrates. With NH4(+)-fed plants, growth and total N were not altered by elevated root-zone CO2 concentrations, although 14C partitioning to amino acid synthesis was increased. Effects of root-zone CO2 concentration on N uptake and metabolism over longer periods (> 1 d) were probably limited by feedback inhibition. Root-derived organic acids contributed to the carbon budget of the leaves through decarboxylation of the organic acids and photosynthetic refixation of released CO2.
New Phytol 2005 Jan
PMID:The influence of root assimilated inorganic carbon on nitrogen acquisition/assimilation and carbon partitioning. 1572 Jun 30

Aluminum (Al) is toxic to plants when solubilized into Al(3+) in acidic soils, and becomes a major factor limiting plant growth. However, the primary cause for Al toxicity remains unknown. Nitric oxide (NO) is an important signaling molecule modulating numerous physiological processes in plants. Here, we investigated the role of NO in Al toxicity to Hibiscus moscheutos. Exposure of H. moscheutos to Al(3+) led to a rapid inhibition of root elongation, and the inhibitory effect was alleviated by NO donor sodium nitroprusside (SNP). NO scavenger and inhibitors of NO synthase (NOS) and nitrate reductase had a similar inhibitory effect on root elongation. The inhibition of root elongation by these treatments was ameliorated by SNP. Aluminum inhibited activity of NOS and reduced endogenous NO concentrations. The alleviation of inhibition of root elongation induced by Al, NO scavenger and NOS inhibitor was correlated with endogenous NO concentrations in root apical cells, suggesting that reduction of endogenous NO concentrations resulting from inhibition of NOS activity could underpin Al-induced arrest of root elongation in H. moscheutos.
New Phytol 2007
PMID:Inhibition of nitric oxide synthase (NOS) underlies aluminum-induced inhibition of root elongation in Hibiscus moscheutos. 1738 95

* In the mycorrhizal association, changes in the metabolic activities expressed by the plant and fungal partners could result from modulations in the quantity and nature of nutrients available at the plant-fungus interface. This hypothesis was tested for the nitrite reductase gene in the association Hebeloma cylindrosporumxPinus pinaster. * Transcripts from plant and fungal nitrite reductases and a fungal ammonium transporter were quantified in control uninoculated roots, extraradical mycelia and mycorrhizas formed by either wild-type or nitrate reductase deficient fungal strains. * The fungal genes were downregulated in mycorrhizas compared with extraradical hyphae. The plant nitrite reductase was induced only transiently by NO(3)(-) in the association with a wild-type strain, but permanently expressed at a high level in mycorrhizas formed by the deficient mutant. * These results suggest that reduced nitrogen compounds transferred from the fungus to the root cortical cells repress the plant nitrite reductase, thus highlighting a plant gene regulation by the nutrients available in the Hartig net.
New Phytol 2007
PMID:How does a symbiotic fungus modulate expression of its host-plant nitrite reductase? 1754 75

Here, influx and efflux of (13)NO(3)(-), and net fluxes of (14)NO(3)(-) and (14)NO(2)(-), were measured in Aspergillus nidulans mutants niaD171 and niiA5, devoid of nitrate reductase (NR) and nitrite reductase (NiR) activities, respectively. Transcript and protein abundances of NrtA, the A. nidulans principal high-affinity NO(3)(-) transporter, were determined using semiquantitative reverse transcription-polymerase chain reaction and western blots, respectively. (13)NO(3)(-) influx in niaD171 was negligible relative to wild-type values, whereas efflux to influx ratios increased nine-fold. Nevertheless, NrtA mRNA and NrtA protein were expressed at levels more than two-fold and three-fold higher, respectively, in niaD171 than in the wild-type strain. This is the first demonstration of diminished high-affinity NO(3)(-) influx associated with elevated transporter levels, providing evidence that, in addition to transcriptional regulation, control of NrtA expression operates at the post-translational level. This mechanism allows for rapid control of NO(3)(-) transport at the protein level, reduces the extent of futile cycling of NO(3)(-) that would otherwise represent a significant energy drain when influx exceeds the capacity for assimilation or storage, and may be responsible for the rapid switching between the on and off state that is associated with simultaneous provision of NH(4)(+) to mycelia absorbing NO(3)(-).
New Phytol 2007
PMID:Evidence for post-translational regulation of NrtA, the Aspergillus nidulans high-affinity nitrate transporter. 1768 85

The magnitude and impact of gaseous nitrogen dioxide (NO(2)) directly entering the leaves were investigated using foliar nitrogen isotopic composition (delta(15)N) values in tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum). Using a hydroponics-fumigation system, (15)NO(2) (20 and 40 ppb) was supplied to shoot systems and (50 and 500 microM) was supplied to root systems. Morphological, stable isotope and nitrate reductase activity (NRA) analyses were used to quantify foliar NO(2) uptake and to examine whether realistic concentrations of NO(2) influenced plant metabolism. Nicotiana tabacum and L. esculentum incorporated 15 and 11%, respectively, of (15)NO(2)-N into total biomass via foliar uptake under low supply. On a mass basis, N. tabacum and L. esculentum incorporated 3.3 +/- 0.9 and 3.1 +/- 0.8 mg of (15)NO(2)-N into biomass, respectively, regardless of availability. There were no strong effects on biomass accumulation or allocation, leaf delta(13)C values, or leaf or root NRA in response to NO(2) exposure. Foliar NO(2 )uptake may contribute a significant proportion of N to plant metabolism under N-limited conditions, does not strongly influence growth at 40 ppb, and may be traced using foliar delta(15)N values.
New Phytol 2008
PMID:Quantifying foliar uptake of gaseous nitrogen dioxide using enriched foliar delta15N values. 1806 53

* Here, cytokinin-induced nitric oxide (NO) biosynthesis and cytokinin responses were investigated in Arabidopsis thaliana wild type and mutants defective in NO biosynthesis or cytokinin signaling components. * NO release from seedlings was quantified by a fluorometric method and, by microscopy, observed NO biosynthesis as fluorescence increase of DAR-4M AM (diaminorhodamine 4M acetoxymethyl ester) in different tissues. * Atnoa1 seedlings were indistinguishable in NO tissue distribution pattern and morphological responses, induced by zeatin, from wild-type seedlings. Wild-type and nia1,2 seedlings, lacking nitrate reductase (NR), responded to zeatin with an increase within 3 min in NO biosynthesis so that NR does not seem relevant for rapid NO induction, which was mediated by an unknown 2-(2-aminoethyl)2-thiopseudourea (AET)-sensitive enzyme and was quenched by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-1-oxy-3-oxide (PTIO). Long-term morphological responses to zeatin were severely altered and NO biosynthesis was increased in nia1,2 seedlings. As cytokinin signaling mutants we used the single-receptor knockout cre1/ahk4, three double-receptor knockouts (ahk2,3, ahk2,4, ahk3,4) and triple-knockout ahp1,2,3 plants. All cytokinin-signaling mutants showed aberrant tissue patterns of NO accumulation in response to zeatin and altered morphological responses to zeatin. * Because aberrant NO biosynthesis correlated with aberrant morphological responses to zeatin the hypothesis was put forward that NO is an intermediate in cytokinin signaling.
New Phytol 2008
PMID:Zeatin-induced nitric oxide (NO) biosynthesis in Arabidopsis thaliana mutants of NO biosynthesis and of two-component signaling genes. 1829 31

Vascular tissue was recently shown to be capable of producing nitric oxide (NO), but the production sites and sources were not precisely determined. Here, NO synthesis was analysed in the phloem of Vicia faba in response to stress- and pathogen defence-related compounds. The chemical stimuli were added to shallow paradermal cortical cuts in the main veins of leaves attached to intact plants. NO production in the bare-lying phloem area was visualized by real-time confocal laser scanning microscopy using the NO-specific fluorochrome 4,5-diaminofluorescein diacetate (DAF-2 DA). Abundant NO generation in companion cells was induced by 500 microm salicylic acid (SA) and 10 microm hydrogen peroxide (H(2)O(2)), but the fungal elicitor chitooctaose was much less effective. Phloem NO production was found to be dependent on Ca(2+) and mitochondrial electron transport and pharmacological approaches found evidence for activity of a plant NO synthase but not a nitrate reductase. DAF fluorescence increased most strongly in companion cells and was occasionally observed in phloem parenchyma cells. Significantly, accumulation of NO in sieve elements could be demonstrated. These findings suggest that the phloem perceives and produces stress-related signals and that one mechanism of distal signalling involves the production and transport of NO in the phloem.
New Phytol 2008
PMID:Nitric oxide generation in Vicia faba phloem cells reveals them to be sensitive detectors as well as possible systemic transducers of stress signals. 1831 39

Ectomycorrhizal (ECM) fungi are often considered to be most prevalent under conditions where organic sources of N predominate. However, ECM fungi are increasingly exposed to nitrate from anthropogenic sources. Currently, the ability of ECM fungi to metabolize this nitrate is poorly understood. Here, growth was examined among 106 isolates, representing 68 species, of ECM fungi on nitrate as the sole N source. In addition, the occurrence of genes coding for the nitrate reductase enzyme (nar gene) in a broad range of ectomycorrhizal fungi was investigated. All isolates grew on nitrate, but there was a strong taxonomic signature in the biomass production, with the Russulaceae and Amanita showing the lowest growth. Thirty-five partial nar sequences were obtained from 43 tested strains comprising 31 species and 10 genera. These taxa represent three out of the four clades of the Agaricales within which ECM fungi occur. No nar sequences were recovered from the Russulaceae and Amanita, but Southern hybridization showed that the genes were present. The results demonstrate that the ability to utilize nitrate as an N source is widespread in ECM fungi, even in those fungi from boreal forests where the supply of nitrate may be very low.
New Phytol 2008
PMID:Growth on nitrate and occurrence of nitrate reductase-encoding genes in a phylogenetically diverse range of ectomycorrhizal fungi. 1878 55

Atmospheric nitrogen deposition can cause major declines in bryophyte abundance yet the physiological basis for such declines is not fully understood. Bryophyte physiological responses may also be sensitive bioindicators of both the impacts of, and recovery from, N deposition. Here, responses of tissue nutrients (nitrogen (N), phosphorus (P) and potassium (K): NPK), N and P metabolism enzymes (nitrate reductase and phosphomonoesterase), photosynthetic pigments, chlorophyll fluorescence, sclerophylly and percentage cover of two common bryophytes (Pseudoscleropodium purum and Rhytidiadelphus squarrosus) to long-term (11 yr) enhanced N deposition (+3.5 and +14 g N m(-2) yr(-1)) are reported in factorial combination with P addition. Recovery of responses 22 months after treatment cessation were also assessed. Enhanced N deposition caused up to 90% loss of bryophyte cover but no recovery was observed. Phosphomonoesterase activity and tissue N:P ratios increased up to threefold in response to N loading and showed clear recovery, particularly in P. purum. Smaller responses and recovery were also seen in all chlorophyll fluorescence measurements and altered photosynthetic pigment composition. The P limitation of growth appears to be a key mechanism driving bryophyte loss along with damage to photosystem II. Physiological measurements are more sensitive than measurements of abundance as bioindicators of N deposition impact and of recovery in particular.
New Phytol 2008
PMID:Bryophyte physiological responses to, and recovery from, long-term nitrogen deposition and phosphorus fertilisation in acidic grassland. 1880 Oct 5

The aim of this study was to investigate the physiological significance of increased proline loading to phloem caused by water-deficit stress in relation to nitrogen (N) uptake and assimilation. N uptake and N assimilation were quantified by 15N tracing in well-watered (control) and water deficit-stressed white clover (Trifolium repens). De novo proline synthesis and proline loading to the phloem were also compared between treatments. The relationships among proline concentrations in phloem exudates, N uptake, and assimilation of newly absorbed N were assessed. The newly synthesized proline in the phloem exudates increased rapidly after 3 d of water deficit. The water-deficit treatment significantly reduced the maximum nitrate reductase activity (NRA), and also attenuated de novo synthesis of amino acids and proteins in the roots. The increase in proline concentrations in phloem exudates was closely related to reductions in NRA in the roots, N uptake, and the assimilation of newly absorbed N. The accumulation of proline induced in roots by exogenous proline and NH4Cl treatments was closely associated with the decrease in NRA. These results indicate that increased proline transport to roots via phloem caused by water deficit has a significant influence on the down-regulation of N uptake and the assimilation of newly absorbed N.
New Phytol 2009
PMID:Increased proline loading to phloem and its effects on nitrogen uptake and assimilation in water-stressed white clover (Trifolium repens). 1928 78


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