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1.
Impact of gaseous nitrogen deposition on plant functioning 总被引:5,自引:0,他引:5
Dry deposition of NH3 and NOx (NO and NO2 ) can affect plant metabolism at the cellular and whole-plant level. Gaseous pollutants enter the plant mainly through the stomata, and once in the apoplast NH3 dissolves to form NH4 + , whereas NO2 dissolves to form NO3 − and NO2 − . The latter compound can also be formed after exposure to NO. There is evidence that NH3 -N and NOx -N can be reversibly stored in the apoplast. Temporary storage might affect processes such as absorption rate, assimilation and re-emission. Once formed, NO3 − and NO2 − can be reduced, and NH4 + can be assimilated via the normal enzymatic pathways, nitrate reductase (NR), nitrite reductase and the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle. Fumigation with low concentrations of atmospheric NH3 increases in vitro glutamine synthetase activity, but whether this involves both or only one of the GS isoforms is still an open question. There seems to be no correlation between fumigation with low concentrations of NH3 and in vitro GDH activity. The contribution of atmospheric NH3 and NO2 deposition to the N budget of the whole plant has been calculated for various atmospheric pollutant concentrations and relative growth rates ( RGRs ). It is concluded that at current ambient atmospheric N concentrations the direct impact of gaseous N uptake by foliage on plant growth is generally small. 相似文献
2.
The activity of glutamine synthetase (GS) in mustard ( Sinapis alba L.) and Scots pine ( Pinus sylvestris L.) seedlings was used as an index to evaluate the capacity to cope with excessive ammonium supply. In these 2 species GS activity was differently affected by the application of nitrogen compounds (NH4 + or NO3 − ). Mustard seedlings older than 5 days showed a considerable increase in GS activity after NH4 + or NO3 − application. This response was independent of the energy flux, but GS activity in general was positively affected by light. Endogenous NH4 + did not accumulate greatly after nitrogen supply. In contrast, seedlings of Scots pine accumulated NH4 + in cotyledons and roots and showed no stimulation of GS activity after the application of ammonium. In addition, root growth was drastically reduced. Thus, the pine seedlings seem to have insufficient capacity to assimilate exogenously supplied ammonium. NO3 − , however, did not lead to any harmful effects. 相似文献
3.
Translocation of NH4 + was studied in relation to the expression of three glutamine synthetase (GS, EC 6.3.1.2) isogenes and total GS activity in roots and leaves of hydroponically grown oilseed rape ( Brassica napus ). The concentration of NH4 + in the stem xylem sap of NO3 − -fed plants was 0.55–0.70 m M , which was ≈60% higher than that in plants deprived of external nitrogen for 2 days. In NH4 + -fed plants, xylem NH4 + concentrations increased linearly both with time of exposure to NH4 + and with increasing external NH4 + concentration. The maximum xylem NH4 + concentration was 8 m M , corresponding to 11% of the nitrogen translocated in the xylem. In the leaf apoplastic solution, the NH4 + concentration increased from 0.03 m M in N-deprived plants to 0.20 m M in N-replete plants. The corresponding values for leaf tissue water were 0.33 and 1.24 m M , respectively. The addition of either NO3 − or NH4 + to N-starved plants induced both cytosolic gs isogene expression and GS activity in the roots. In N-replete plants, gs isogene expression and GS activity were repressed, probably due to carbon limitations, thereby protecting the roots against the excessive drainage of photosynthates. Repressed gs isogene expression and GS activity under N-replete conditions caused enhanced NH4 + translocation to the shoots. 相似文献
4.
Vittoria Di Martino Rigano Vincenza Vona Catello Di Martino Carmelo Rigano 《Physiologia plantarum》1986,68(1):34-38
Cyanidium caldarium (Tilden) Geitler, a non-vacuolate unicellular alga, resuspended in medium flushed with air enriched with 5% CO2 , assimilated NH4 + at high rates both in the light and in the dark. The assimilation of NO3 − , by contrast, was inhibited by 63% in the dark. In cell suspensions flushed with CO2 -free air, NH4 + assimilation decreased with time both in the light and in the dark and ceased almost completely after 90 min. The addition of CO2 completely restored the capacity of the alga to assimilate NH4 + . NO3 − assimilation, by contrast, was 33% higher in the absence of CO2 and was linear with time. It is suggested that NO3 − and NH4 + metabolism in C. caldarium are differently controlled in response to the light and carbon conditions of the cell. 相似文献
5.
Changes in the activity and subunit composition of cytosolic glutamine synthetase (GS 1; EC 6.3.1.2) and chloroplastic GS (GS 2) were studied in response to an internal (organ ontogeny) and external signal (N source: NO3 − or NH4 + ). Maximum GS 1 activity of all organs examined was measured in the fibre roots, irrespective of the N source. The response of GS 1 to the N source was, however, organ specific. In the fibre roots, NH4 + nutrition resulted in a 2- to 7-fold (based on protein or freshweight, respectively) increase of GS 1 activity compared to NO3 − -grown plants. In contrast to the roots, GS 1 activity in the leaf blades was 2-fold lower with NH4 + nutrition, whereas only minor changes occurred in the petioles. GS 2 activity was highest in the mature and senescing leaf blade; activity was 2-fold higher with NH4 + than with NO3 − nutrition. Not only activity, but also subunit composition of GS 1 changed during organ ontogeny as well as in response to the N source. In contrast to GS 1, only minor changes were evident in GS 2 subunit composition, despite significant changes in GS 2 activity. Up to 5 different GS 1 subunits of ≈41–43 kDa were separated; they were identical in all organs examined. GS 2 was composed of 4 different subunits of ≈48 kDa. 相似文献
6.
The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO3 − ), ammonium (NH4 + ) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot–root biomass allocation were evaluated. The results indicated that NO3 − as an N source for plant growth is not substantially more expensive to utilize than either NH4 + or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot–root biomass allocation. 相似文献
7.
JOHN C. PRISCU 《Freshwater Biology》1987,17(2):331-339
SUMMARY. 1. Time-course measurements of NH4 + and NO3 − uptake were made on the natural phytoplankton populations in a eutrophic lake at a time when these nutrients were at their lowest annual concentration.
2. Both NH4 + and NO3 − uptake was increased at least five-fold during the first 5 min of incubation following near saturating pulses of these nutrients.
3. Elevated uptake was also observed following low level (∼2μg N 1−1 ) pulses of NH4 + and NO3 − , but substrate depletion during the first hour of incubation may have been partially responsible for this apparent enhancement.
4. Incorporation ofI5 N into TCA-insoluble material (protein) following the saturating NH4 + pulse was increased less than total cellular 15 N uptake, whereas no elevation of 15 N incorporation into protein was observed following a saturating NO3 − pulse.
5. The percentage ofI5 N incorporated into protein, with respect to total cellular uptake, was ∼32% and ∼12% for NH4 + and NO3 − , respectively, following 5 h of incubation. 相似文献
2. Both NH
3. Elevated uptake was also observed following low level (∼2μg N 1
4. Incorporation of
5. The percentage of
8.
Methane-dependent nitrate production by a microbial consortium enriched from a cultivated humisol 总被引:2,自引:0,他引:2
Abstract A consortium was enriched from a humisol incubated with 3.6 kPa CH4 and NH4 + . This consortium oxidized NH4 + to NO2 − and NO3 − (NO3 − /NO2 − ratio about 20) with smaller amounts of N2 O. This oxidation stopped in the stationary phase after depletion of CH4 . CH3 OH or CO2 did not support oxidation. Growth and resting cell experiments suggested that nitrification was associated with methanotrophic activity and that chemoautotrophic nitrifiers were absent. 相似文献
9.
Abstract A methanotrophic nitrifying consortium was previously obtained from a humisol which showed CH4 -dependent nitrification. Although the methanotroph could not be obtained in pure culture, three other members of the consortium have been isolated: An obligately methylotrophic Methylobacillus (Is-1) which grows only on CH3 OH and does not nitrify; a Pseudomonas (Is-2) which grows on Is-1 culture filtrate and produces NO2 − , NO3 − and N2 O from NH2 OH, and NO3 − from NO2 − ; and a second Pseudomonas (Is-3) which produces NO3 − from NH4 + or NO2 − , and N2 O from NH2 OH. A model is proposed for the trophic relations and nitrogen transformations in the consortium which may apply to some natural systems. 相似文献
10.
Nitrogen concentration, ammonium/nitrate ratio and NaCl interaction in vegetative and reproductive growth of peanuts 总被引:1,自引:0,他引:1
Peanuts ( Arachis hypogaea L. cv. Shulamit) grown with NO3 − and saline water in hydroponics responded positively to addition of nitrogen (N) in their vegetative growth, but not in desert dune sand. In order to clarify these conflicting results, peanut plants were grown in a greenhouse pot experiment with fine calcareous sand. The nutrient solution contained 0 or 50 m M NaCl and 2 or 6 m M N in the form of Ca(NO3 )2 , NH4 NO3 or (NH4 )2 SO4 . Three replicates were harvested after 48 days (beginning of reproductive stage) and three after 109 days (pod filling). In addition, gynophores were treated with 0, 50, 100, 150 or 200 m M NaCl outside the growth pot to check their sensitivity to salt. Shoot dry weight became greater with increasing NH4 + /NO3 − ratio. Increasing the N concentration from 2 to 6 m M did not change shoot dry weight of the NH4 NO3 or NH4 + -fed plants, but caused a reduction in shoot dry weight of NO3 − -fed plants. Shoot dry weight was not affected by increasing the NaCl concentration to 50 m M . Salt caused an increase in the number of gynophores per plant and a reduction of the mean pod weight. A NaCl concentration of 100 m M and above reduced gynophore vitality. It is concluded that the salt sensitivity of peanut plants resides mainly in the sensitivity of the reproductive organs. 相似文献
11.
Robert L. Bradley 《Ecology letters》2001,4(5):412-416
The appearance of soil NO3 – after forest disturbance is commonly ascribed to a higher availability of NH4 + to autotrophic nitrifiers, or to a reduction in available-C resulting in lower microbial assimilation of NO3 – . Alternatively, it has been proposed that increasing NH4 + pools following disturbance could increase net nitrification by reducing microbial assimilation of NO3 – . Forest floor material was collected from shelterwood harvest plots which displayed both low available-C and low NH4 + pools, and where previous experiments had suggested the prevalence of heterotrophic nitrification. Subsamples were amended with incremental rates of glucose-C or NH4 + , and gross NO3 – transformation rates were measured by isotope dilution. Glucose-C additions had little effect on the net difference between gross NO3 – production and consumption rates. On the other hand, NH4 + additions caused gross NO3 – consumption processes to decrease sharply, while gross NO3 – production processes remained constant. The results suggest that NH4 + can have an immediate positive effect on net nitrification rates by suppressing NO3 – assimilation and uptake systems. 相似文献
12.
Abstract A reaction diffusion model was used to simulate the mineralization processes in an Arctic sediment. The simulation and the actual sediment were compared in relation to profiles of O2 , NO3 and NH4 + . The site of particulate organic matter (POM) degradation was the single most important factor in fitting the simulation profiles to those of the sediment. It was deduced that most POM degradation occurred close to the sediment surface. When a reasonably good simulation had been obtained, the sensitivity of the model to changes in other parameters was investigated. Increases in POM degradation in the upper sediment resulted in increases in concentration of NH4 + and NO3 − , but further increases in POM degradation created anoxic conditions below 3 mm, resulting in decreases in NO3 − concentrations. The model was relatively intensive to changes in POM degradation in the lower sediment layers; increases led to more anoxic conditions and to less NO3 − . Increases in the C/N ratio of the POM in the lower sediment layers had little effect; increases in C/N in the upper layers led to a decrease in NH4 + and NO3 − . The model was sensitive to changes in the first order rate constant for nitrification, but not for denitrification. Decreases in the K m for O2 of the nitrifying bacteria had no effect on the profiles. 相似文献
13.
Role of phosphoenolpyruvate carboxylase in anaplerosis in the green microalga Dunaliella salina cultured under different nitrogen regimes 总被引:1,自引:0,他引:1
Anaplerosis plays a very important role in providing C for N assimilation. In green algae and higher plants, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) is the main anaplerotic carboxylase. On this basis we hypothesize that N availability affects PEPC expression. In order to test this hypothesis, the model organism Dunaliella salina was cultured under a variety of N growth regimes. Our results show that the level of PEC activity was unaffected by the N form in which N was supplied to the cells, when N concentration was low (0.5–0.01 m M ). When cells were adapted to growth at 5 m M N, however, PEPC activity on a per cell basis was substantially higher in NH4 + -adapted cells as compared to their NO3 – -adapted counterparts; however, the same difference was not observed on a protein basis. This notwithstanding, even at low N, PEPC of cells cultured in the presence of either NH4 + or NO3 – appeared to differ in their molecular masses. These results suggest that cells adapted to different N-form express distinct PEPC isoforms. In addition to this, we observed that, in algae adapted to high (5 m M ) NH4 + concentration, a PEPC isoform was induced that differed from the isoforms observed in algae adapted to lower concentrations of the same N-source. These findings lead us to conclude that the expression of PEPC isoforms in D. salina responds to the variation in the C-skeleton demand deriving from changes in the chemical form and availability of N. 相似文献
14.
Rocio J. Alcántara-Hernández César Valenzuela-Encinas Francisco J. Zavala-Díaz de la Serna Javier Rodriguez-Revilla Luc Dendooven & Rodolfo Marsch 《FEMS microbiology letters》2009,298(1):56-66
Assimilatory nitrate reduction (ANR) is a pathway wherein NO3 − is reduced to NH4 + , an N species that can be incorporated into the biomass. There is little information about the ANR genes in Archaea and most of the known information has been obtained from cultivable species. In this study, the diversity of the haloarchaeal assimilatory nitrate-reducing community was studied in an extreme saline alkaline soil of the former lake Texcoco (Mexico). Genes coding for the assimilatory nitrate reductase ( narB ) and the assimilatory nitrite reductase ( nirA ) were used as functional markers. Primers to amplify and detect partial narB and nirA were designed. The analysis of these amplicons by cloning and sequencing showed that the deduced protein fragments shared >45% identity with other NarB and NirA proteins from Euryarchaeota and <38% identity with other nitrate reductases from Bacteria and Crenarchaeota . Furthermore, these clone sequences were clustered within the class Halobacteria with strong support values in both constructed dendrograms, confirming that desired PCR products were obtained. The metabolic capacity to assimilate nitrate by these haloarchaea seems to be important given that at pH 10 and higher, NH4 + is mostly converted to toxic and volatile NH3 , and NO3 − becomes the preferable N source. 相似文献
15.
New macro and microelement solutions were formulated for stimulation of growth and embryogenesis in white and chlorophyllous megagametophyte and embryo callus lines of Picea abies (L.) Karst. Macroelement media with different NH4 + and NO3 − ratios (1:2 and 1:4), the increased level of several microelements and the effect of organic nitrogen (100 mg 1−1 casein hydrolysate, 0.25 m M arginine and 0.5 m M glutamine) were tested with 4 combinations of growth regulators (2,4-dichlorophe-noxyacefic acid or indole-3-butyric acid, kinetin). Green chlorophyll-containing, in contrast to white callus lines, grew quite well without exogeneously added organic nitrogen. The ratio between NH4 + and NO3 − was not significant. The increased levels (μ M ) of several microelements: B (200), Zn (50), I (25), Cu (1), Co (0.5) and in addition Ni (0.1) improved callus growth in some lines more than 50% (DW) compared to cultures grown on the micronutrients of Murashige and Skoog. The response of different callus lines varied with the combinations of growth regulators. Embryogenesis did not occur in chlorophyllous callus lines in any of the 24 media combinations tested, but some very good media could be found for white megagametophyte and embryo callus lines. Microelements, favourable combination of growth regulators and organic nitrogen were especially important. A megagametophyte callus subcultured for 4 years was also able to form numerous proembryos. 相似文献
16.
17.
Root ammonium transport efficiency as a determinant in forest colonization patterns: an hypothesis 总被引:3,自引:0,他引:3
H. J. Kronzucker M. Y. Siddiqi A. D. M. Glass D. T. Britto 《Physiologia plantarum》2003,117(2):164-170
Ratios of ammonium (NH4 + ) to nitrate (NO3 – ) in soils are known to increase during forest succession. Using evidence from several previous studies, we hypothesize that a malfunction in NH4 + transport at the membrane level might limit the persistence of early successional tree species in later seral stages. In those studies, 13 N radiotracing was used to determine unidirectional fluxes and pool sizes of NH4 + and NO3 – in seedlings of the late-successional species white spruce ( Picea glauca ) and in the early successional species Douglas-fir ( Pseudotsuga menziesii var. glauca ) and trembling aspen ( Populus tremuloides ). At high external NH4 + , the two early successional species accumulated excessive NH4 + in the root cytosol, and exhibited high-velocity, low-efficiency (15% to 22%), membrane fluxes of NH4 + . In sharp contrast, white spruce had low cytosolic NH4 + accumulation, and lower-velocity but much higher-efficiency (65%), NH4 + fluxes. Because these divergent responses parallel known differences in tolerance and toxicity to NH4 + amongst these species, we propose that they constitute a significant driving force in forest succession, complementing the discrimination against NO3 – documented in white spruce (Kronzucker et al. 1997). 相似文献
18.
Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase-deficient mutant) plants exposed to NH4 NO3 总被引:1,自引:0,他引:1
David C. Taylor Barry J. Shelp Louise M. Nelson Bernard Grodzinski 《Physiologia plantarum》1988,74(4):593-601
Carbon and nitrogen partitioning was examined in a wild-type and a nitrate reductase-deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH4 NO3 . In wild-type symbioses the application of NH4 NO3 significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [14 C]-labelled (NO3 − , NH4 + , amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO3 − and NH4 + or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium /legume interactions are made. 相似文献
19.
Net fluxes of NH4 + and NO3 – along adventitious roots of rice ( Oryza sativa L.) and the primary seminal root of maize ( Zea mays L.) were investigated under nonperturbing conditions using ion-selective microelectrodes. The roots of rice contained a layer of sclerenchymatous fibres on the external side of the cortex, whereas this structure was absent in maize. Net uptake of NH4 + was faster than that of NO3 – at 1 mm behind the apex of both rice and maize roots when these ions were supplied together, each at 0·1 mol m–3 . In rice, NH4 + net uptake declined in the more basal regions, whereas NO3 – net uptake increased to a maximum at 21 mm behind the apex and then it also declined. Similar patterns of net uptake were observed when NH4 + or NO3 – was the sole nitrogen source, although the rates of NO3 – net uptake were faster in the absence of NH4 + . In contrast to rice, rates of NH4 + and NO3 – net uptake in the more basal regions of maize roots were similar to those near the root apex. Hence, the layer of sclerenchymatous fibres may have limited ion absorption in the older regions of rice roots. 相似文献
20.
The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3 − , no such increase could be detected in the needles. Detached seedlings placed in NO3 − solution showed increasing NR activities with increasing NO3 − concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2 − (g fresh weight)−1 h−1 to about 400 nmol NO2 − (g fresh weight)−1 h−1 . This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2 − (g fresh weight)−1 h−1 . Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx -fumigated seedlings compared to corresponding controls. 相似文献