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1.
The distribution of NO3? reduction between roots and shoots was studied in hydro-ponically-grown peach-tree seedlings (Prunus persica L.) during recovery from N starvation. Uptake, translocation and reduction of NO3?, together with transport through xylem and phloem of the newly reduced N were estimated, using 15N labellings, in intact plants supplied for 90 h with 0.5 mM NH4+ and 0.5, 1.5 or 10 mM NO3?. Xylem transport of NO3? was further investigated by xylem sap analysis in a similar experiment. The roots were the main site of NO3? reduction at all 3 levels of NO3? nutrition. However, the contribution of the shoots to the whole plant NO3? reduction increased with increasing external NO3? availability. This contribution was estimated to be 20, 23 and 42% of the total assimilation at 0.5, 1.5 and 10 mM NO3?, respectively. Both 15N results and xylem sap analysis confirmed that this trend was due to an enhancement of NO3? translocation from roots to shoots. It is proposed that the lack of NO3? export to the shoots at low NO3? uptake rate resulted from a competition between NO3? reduction in the root epidermis/cortex and NO3? diffusion to the stele. On the other hand, net xylem transport of newly reduced N was very efficient since ca 70% of the amino acids synthesized in the roots were translocated to the shoots, regardless of the level of NO3? nutrition. This net xylem transport by far exceeded the net downward phloem transport of the reduced N assimilated in shoots. As a consequence, the reduced N resulting from NO3? assimilation, principally occurring in the roots, was mainly incorporated in the shoots. 相似文献
2.
D.T. CLARKSON A. GOJON L.R. SAKER P.K. WIERSEMA J.V. PURVES P. TILLARD G.M. ARNOLD A.J.M. PAANS W. VAALBURG I. STULEN 《Plant, cell & environment》1996,19(7):859-868
We compared influxes and internal transport in soybean plants (Glycine max cv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope15N and the radioactive isotope13N. The objective was to see whether mass spectrometric determinations of tissue 15N content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using 15N or 13N measurements with either NO3/? or NH4+ at 4 or 2 mol?3, respectively in the external solution. (2) Transport to the shoot of N from NO3 absorbed over a 5–15 min period could be monitored when the external NO3? concentration ranged from 0–05 to 4 mol m?3. NH4+ as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with 13N. (3) Influx of NO3? into root tissue could be measured by 15N enrichment after 5–10 min at concentrations approaching the probable KM of the high-affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3? is the N source. For many purposes, 15N tracing can be used satisfactorily to estimate influxes of both NO3? and NH4+ in soybean roots. Use of the short-lived radio nuclide 13N remains the method of choice for more refined measurements of internal distribution and assimilation. 相似文献
3.
William E. Holmes Donald R. Zak Kurt S. Pregitzer† John S. King† 《Global Change Biology》2003,9(12):1743-1750
Increases in atmospheric CO2 and tropospheric O3 may affect forest N cycling by altering plant litter production and the availability of substrates for microbial metabolism. Three years following the establishment of our free‐air CO2–O3 enrichment experiment, plant growth has been stimulated by elevated CO2 resulting in greater substrate input to soil; elevated O3 has counteracted this effect. We hypothesized that rates of soil N cycling would be enhanced by greater plant productivity under elevated CO2, and that CO2 effects would be dampened by O3. We found that elevated CO2 did not alter gross N transformation rates. Elevated O3 significantly reduced gross N mineralization and microbial biomass N, and effects were consistent among species. We also observed significant interactions between CO2 and O3: (i) gross N mineralization was greater under elevated CO2 (1.0 mg N kg?1 day?1) than in the presence of both CO2 and O3 (0.5 mg N kg?1 day?1) and (ii) gross NH4+ immobilization was also greater under elevated CO2 (0.8 mg N kg?1 day?1) than under CO2 plus O3 (0.4 mg N kg?1 day?1). We used a laboratory 15N tracer method to quantify transfer of inorganic N to organic pools. Elevated CO2 led to greater recovery of NH4+‐15N in microbial biomass and corresponding lower recovery in the extractable NO3? pool. Elevated CO2 resulted in a substantial increase in NO3?‐15N recovery in soil organic matter. We observed no O3 main effect and no CO2 by O3 interaction effect on 15N recovery in any soil pool. All of the above responses were most pronounced beneath Betula papyrifera and Populus tremuloides, which have grown more rapidly than Acer saccharum. Although elevated CO2 has increased plant productivity, the resulting increase in plant litter production has yet to overcome the influence of the pre‐existing pool of soil organic matter on soil microbial activity and rates of N cycling. Ozone reduces plant litter inputs and also appears to affect the composition of plant litter in a way that reduces microbial biomass and activity. 相似文献
4.
The physiological consequences for NO3– utilization by the plant of underexpression and overexpression of nitrate reductase (NR) were investigated in nine transformants of Nicotiana tabacum and Nicotiana plumbaginifolia. The in vitro NR activities (NRAs) in both roots and leaves of low- and high-NR tobacco transformants ranged from 5–10% to 150–200%, respectively, of those measured in wild-type plants. The level of NR expression markedly affected the NO3– reduction efficiency in detached leaves and intact plants. In both species, 15NO3– reduction ranged from 15–45% of 15NO3– uptake in the low-NR plants, to 40–80% in the wild-type, and up to 95% in high-NR plants. In the high-NR genotypes, however, total 15NO3– assimilation was not significantly increased when compared with that in wild-type plants, because the higher 15NO3– reduction efficiency was offset by lower 15NO3– uptake by the roots. The inhibition of NO3– uptake appeared to be the result of negative feedback regulation of NO3– influx, and is interpreted as an adjustment of NO3– uptake to prevent excessive amino acid synthesis. In genotypes underexpressing NR, the low 15NO3– reduction efficiency also was generally associated with a decrease in net 15NO3– uptake as compared with the wild type. Thus, underexpression of NR resulted in an inhibition of reduced 15N synthesis in the plant, although the effect was much less pronounced than that expected from the very low NRAs. The restricted NO3– uptake in low-NR plants emphasizes the point that the products of NO3– assimilation are not the only factors responsible for down-regulation of the NO3– uptake system. 相似文献
5.
Uptake of atmospheric 15 NO2 and its incorporation into free amino acids in wheat (Triticum aestivum)
Paul Weber Stefan Nußbaum Jürg Fuhrer Hans Gfeller Urs Peter Schlunegger Christian Brunold Heinz Rennenberg 《Physiologia plantarum》1995,94(1):71-77
Five-week-old wheat plants were exposed, under controlled environmental conditions, to 60 nl 1?115NO2 or to purified air. After 48 and 96 h of exposure, leaves, stalks and roots were analysed for 15N-enrichment in α-amino nitrogen of soluble, free amino acids. In addition, the in vitro nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NIR, EC 1.7.7.1) activities were determined in the leaves. NR activity in the leaves decreased continously during the 96-h exposure to purified air. In the leaves exposed to 15NO2, NR activity increased within the first 24 h, then decreased, and reached the level of controls after 96 h. NiR activity in leaves exposed to purified air was almost constant during the 96-h exposure. In leaves exposed to 15NO2, NiR activity increased within the first 48 h, then decreased, and reached the level of controls after 72 h, Exposure to 15NO2 enhanced the total content of soluble, free amino acids in all tissues analysed. Most of this increase was attributed to Glu in the leaves and to Asn plus Gln the α-amino group of soluble, free amino acids was observed in the leaves, the lowest enrichment in the roots. The main labelled amino compounds were Glu (with 8.0%15N enrichment compared to the control), γ-aminobutyric acid (GABA; 7.9%), Ala (7.2%). Ser (6.8%), Asp (5.5%) and Gln (4.6%). Appreciable incorporation of 15 into Asn was not found. After 96 h exposure to 15NO2 the 15N enrichment in the α-amino group of soluble, free amino acids in the leaves declined as compared to the values obtained after 48 h fumigation. The possible pathway and the time course of 15N incorporation into soluble, free amino acids from the 15NO2 absorbed are discussed. 相似文献
6.
Positive influences of high concentrations of dissolved inorganic carbon (DIC) in the growth medium of salinity-stressed plants are associated with carbon assimilation through phosphoenolpyruvate carboxylase (PEPc) activity in roots; and also in salinity-stressed tomato plants, enriched CO2 in the rhizosphere increases NO?3uptake. In the present study, wild-type and nitrate reductase-deficient plants of barley (Hordeum vulgare L. cv. Steptoe) were used to determine whether the influence of enriched CO2 on NO?3 uptake and metabolism is dependent on the activity of nitrate reductase (NR) in the plant. Plants grown in NH4+and aerated with ambient air, were transferred to either NO3? or NH4+ solutions and aerated with air containing between 0 and 6 500 μmol mol?1 CO2. Nitrogen uptake and tissue concentrations of NO3? and NH4+ were measured as well as activities of NR and PEPc. The uptake of NO?3 by the wild-type was increased by increasing CO2. This was associated with increased in vitro NR activity, but increased uptake of NO3? was found also in the NR-deficient genotype when exposed to high CO2 concentrations; so that the influence of CO2 on NO3? uptake was independent of the reduction of NO3? and assimilation into amino acids. The increase in uptake of NO3? in wild-type plants with enriched CO2 was the same at pH 7 as at pH 5, indicating that the relative abundance of HCO3? or CO2 in the medium did not influence NO3? uptake. Uptake of NH4+ was decreased by enriched CO2 in a pH (5 or 7) independent fashion. Thus NO3? and NH+4 uptakes are influenced by the CO2 component of DIC independently of anaplerotic carbon provision for amino acid synthesis, and CO2 may directly affect the uptake of NO3? and NH4+ in ways unrelated to the NR activity in the tissue. 相似文献
7.
The response of the tubers to NO3– was studied in comparison to the other organs of Solanum tuberosum var. Sava, with special focus on: (a) whether tubers are capable of primary N assimilation; (b) whether N assimilation is stimulated by NO3–; and (c) whether primary N assimilation in tubers is important for tuber growth. NO3– reduction via nitrate reductase (NR; EC 1.6.6.1) and NH4+ assimilation via glutamine synthetase (GS; EC 6.3.1.2) occurred predominantly in the shoots, but up to 20% was contributed by the tubers under low‐NO3– conditions. NR activation was highest in tubers (up to 90%) and declined in all organs with increasing NO3– supply. NR and GS activity responded with a decline in tubers and roots as opposed to an increase in the shoots. This corresponded to relative organ growth: growth of tubers and roots was stimulated relative to that of shoots at a limiting NO3– supply. Absolute growth of all organs was stimulated by NO3–, whereas tuber number declined. The concentration of N compounds increased with NO3– supply in all organs: NO3– increased most dramatically in the shoots (81‐fold), free amino acids most markedly in the tubers (three‐fold). The amount of patatin and of the 22 kDa protein complex in the tuber reached a minimum when the amount of Rubisco in the shoot reached maximum as a response to NO3– supply. Tuber sucrose and starch increased by 40%, whereas glucose and fructose declined two‐fold as plant N status increased. It is concluded that tubers are potentially N autotroph organs with capacity for de novo synthesis of amino acids. Primary N assimilation in tubers, however, declines with increasing NO3– supply and is not of major importance for tuber growth. 相似文献
8.
G. W. KOCH E.-D. SCHULZE F. PERCIVAL H. A. MOONEY C. CHU 《Plant, cell & environment》1988,11(8):755-767
Abstract. Wild radish plants deprived of, and continuously supplied with solution NO?3 for 7 d following 3 weeks growth at high NO?3 supply were compared in terms of changes in dry weight, leaf area, photosynthesis and the partitioning of carbon and nitrogen (NH2-N and NO?3-N) among individual organs. Initial levels of NO?3-N accounted for 25% of total plant N. Following termination of NO?3 supply, whole plant dry weight growth was not significantly reduced for 3 d, during which time plant NH2-N concentration declined by about 25% relative to NO?3-supplied plants, and endogenous NO?3-N content was reduced to nearly zero. Older leaves lost NO?3 and NH2-N, and roots and young leaves gained NH2-N in response to N stress. Relative growth rate declined due both to decreased net assimilation rate and a decrease in leaf area ratio. A rapid increase in specific leaf weight was indicative of a greater sensitivity to N stress of leaf expansion compared to carbon gain. In response to N stress, photosynthesis per unit leaf area was more severely inhibited in older leaves, whereas weight-based rates were equally inhibited among all leaf ages. Net photosynthesis was strongly correlated with leaf NH2-N concentration, and the relationship was not significantly different for leaves of NO3?-supplied compared to NO?3-deprived plants. Simulations of the time course of NO?3 depletion for plants of various NH2-N and NO?3 compositions and relative growth rates indicated that environmental conditions may influence the importance of NO?3 accumulation as a buffer against fluctuations in the N supply to demand ratio. 相似文献
9.
Net rates of NO3? and K+ uptake were compared for oilseed rape (Brassica napus L. cv. Jet neuf), perennial ryegrass (Lolium perenne L. cv. S23), Italian ryegrass (Lolium multiflorum Lam. cv. Augusta) and wheat (Triticum aestivum L. cv. Fen-man) in flowing solution culture during a 4-day sequence of low-low-high-high natural irradiance. Concentrations of NO3? (10 μM) and K+ (2.5 μM) in solutions were maintained automatically and hourly variation in net uptake of these ions was measured. During the 2 days of low irradiance (<1 MJ m?2 day?1) the uptake rates of both ions by all species were low at <1 mmol NO3?, m?2 h?1 and <0.4 mmol K+ m?2 h?1. Uptake increased in each species during the first day of high irradiance (7.90 MJ m?2 day?1) to >4 mmol NO3? m?2 h?1 and >1.4 mmol K+ m?1 h?1. These higher rates were maintained throughout the following night. The lag-time between maximum irradiance and the onset of the highest acceleration in uptake was greater for NO3? (5–8 h) than for K+ (≤1 h) in rape, wheat and Italian ryegrass. Uptake of NO3?, by perennial ryegrass showed an almost constant acceleration for 18 h following maximum irradiance. In all species the measured maximum inflows (uptake rate per unit root length) of both ions were greater than theoretical maximum potential inflows to a non-competing infinite-sink root in soil, by factors of 7 and 36, respectively, for NO3? and K+, averaged over all species. 相似文献
10.
The immediate effects of tillage on protected soil C and N pools and on trace gas emissions from soils at precultivation levels of native C remain largely unknown. We measured the response to cultivation of CO2 and N2O emissions and associated environmental factors in a previously uncultivated U.S. Midwest Alfisol with C concentrations that were indistinguishable from those in adjacent late successional forests on the same soil type (3.2%). Within 2 days of initial cultivation in 2002, tillage significantly (P=0.001, n=4) increased CO2 fluxes from 91 to 196 mg CO2‐C m?2 h?1 and within the first 30 days higher fluxes because of cultivation were responsible for losses of 85 g CO2‐C m?2. Additional daily C losses were sustained during a second and third year of cultivation of the same plots at rates of 1.9 and 1.0 g C m?2 day?1, respectively. Associated with the CO2 responses were increased soil temperature, substantially reduced soil aggregate size (mean weight diameter decreased 35% within 60 days), and a reduction in the proportion of intraaggregate, physically protected light fraction organic matter. Nitrous oxide fluxes in cultivated plots increased 7.7‐fold in 2002, 3.1‐fold in 2003, and 6.7‐fold in 2004 and were associated with increased soil NO3? concentrations, which approached 15 μg N g?1. Decreased plant N uptake immediately after tillage, plus increased mineralization rates and fivefold greater nitrifier enzyme activity, likely contributed to increased NO3? concentrations. Our results demonstrate that initial cultivation of a soil at precultivation levels of native soil C immediately destabilizes physical and microbial processes related to C and N retention in soils and accelerates trace gas fluxes. Policies designed to promote long‐term C sequestration may thus need to protect soils from even occasional cultivation in order to preserve sequestered C. 相似文献
11.
The relationship between nitrous oxide (N2O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N2O regardless of input level. We conducted a 3‐year, high‐resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N2O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0–292 kg N ha?1) to four replicate plots of continuous maize. We measured N2O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N2O fluxes were moderately low (ca. 20 g N2O‐N ha?1 day?1) at levels of N addition to 101 kg N ha?1, where grain yields were maximized, after which fluxes more than doubled (to >50 g N2O‐N ha?1 day?1). This threshold N2O response to N fertilization suggests that agricultural N2O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs. 相似文献
12.
Fu-Cang Zhang Shao-Zhong Kang Fu-Sheng Li Jian-Hua Zhang 《植物学报(英文版)》2007,49(4):455-462
In the present study, we investigated whether growth and main nutrient ion concentrations of cabbage (Brassica campestris L.) could be increased when plants were subjected to different NH4^+/NO3- ratios. Cabbage seedlings were grown in a greenhouse in nutrient solutions with five NH4^+/NO3- ratios (1:0; 0.75:0.25; 0.5:0.5; 0.25:0.75; and 0:1). The results showed that cabbage growth was reduced by 87% when the proportion of NH4^+-N in the nutrient solution was more than 75% compared with a ratio NH4^+/NO3- of 0.5:0.5 35 d after transplanting, suggesting a possible toxicity due to the accumulation of a large amount of free ammonia in the leaves. When the NH4+/NO3- ratio was 0.5:0.5, fresh seedling weight, root length, and H2PO4- (P), K^+, Ca^2+, and Mg^2+ concentrations were all higher than those in plants grown under other NH4^+/NO3- ratios. The nitrate concentration in the leaves was the lowest in plants grown at 0.5: 0.5 NH4^+/NO3-. The present results indicate that an appropriate NH4^+/NO3- ratio improves the absorption of other nutrients and maintains a suitable proportion of N assimilation and storage that should benefit plant growth and the quality of cabbage as a vegetable. 相似文献
13.
TIM J. CLOUGH JANET E. BERTRAM ROBERT R. SHERLOCK ROBERT L. LEONARD BARBARA L. NOWICKI† 《Global Change Biology》2006,12(2):352-363
There is considerable uncertainty in the estimates of indirect N2O emissions as defined by the Intergovernmental Panel on Climate Change's (IPCC) methodology. Direct measurements of N2O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N2O budget. The objectives of this research were to measure the N2O fluxes from a spring‐fed river, relate these fluxes to the dissolved N2O concentrations and NO3‐N loading of the river, and to try to define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N2O L?1. River NO3‐N and dissolved N2O concentrations ranged from 2.5 to 5.3 mg L?1 and 0.4 to 1.9 μg N2O‐N L?1, respectively, with N2O saturation reaching 404%. Floating headspace chambers were used to sample N2O fluxes. N2O‐N fluxes were significantly related to dissolved N2O‐N concentrations (r2=0.31) but not to NO3‐N concentrations. The N2O‐N fluxes ranged from 38 to 501 μg m?2 h?1, averaging 171 μg m?2 h?1 (±SD 85) overall. The measured N2O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N2O present in the groundwater that fed the river. 相似文献
14.
TIM J. CLOUGH JANET E. BERTRAM ROBERT R. SHERLOCK ROBERT L. LEONARD BARBARA L. NOWICKI† 《Global Change Biology》2006,12(3):477-488
There is considerable uncertainty in the estimates of indirect N2O emissions as defined by the intergovernmental panel on climate change's (IPCC) methodology. Direct measurements of N2O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N2O budget. The objectives of this research were to measure the N2O fluxes from a spring‐fed river, relate these fluxes to the dissolved N2O concentrations and NO3‐N loading of the river, and to try and define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N2O L?1. River NO3‐N and dissolved N2O concentrations ranged from 2.5 to 5.3 mg L?1 and 0.4 to 1.9 μg N2O‐N L?1, respectively, with N2O saturation reaching 404%. Floating headspace chambers were used to sample N2O fluxes. N2O‐N fluxes were significantly related to dissolved N2O‐N concentrations (r2=30.6) but not to NO3‐N concentrations. The N2O‐N fluxes ranged from 38–501 μg m?2 h?1, averaging 171 μg m?2 h?1 (±SD 85) overall. The measured N2O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N2O present in the groundwater that fed the river. 相似文献
15.
Our previous work indicated that salinity caused a shift in the predominant site of nitrate reduction and assimilation from the shoot to the root in tomato plants. In the present work we tested whether an enhanced supply of dissolved inorganic carbon (DIC, CO2+ HCO3) to the root solution could increase anaplerotic provision of carbon compounds for the increased nitrogen assimilation in the root of salinity-stressed Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were grown in hydroponic culture with 0 or 100mM NaCl and aeration of the root solution with either ambient or CO2-enriched air (5000 μmol mol?1). The salinity-treated plants accumulated more dry weight and higher total N when the roots were supplied with CO2-enriched aeration than when aerated with ambient air. Plants grown with salinity and enriched DIC also had higher rates of NO?3 uptake and translocated more NO?3 and reduced N in the xylem sap than did equivalent plants grown with ambient DIC. Incorporation of DIC was measured by supplying a 1 -h pulse of H14CO?3 to the roots followed by extraction with 80% ethanol. Enriched DIC increased root incorporation of DIC 10-fold in both salinized and non-salinized plants. In salinity-stressed plants, the products of dissolved inorganic 14C were preferentially diverted into amino acid synthesis to a greater extent than in non-salinized plants in which label was accumulated in organic acids. It was concluded that enriched DIC can increase the supply of N and anaplerotic carbon for amino acid synthesis in roots of salinized plants. Thus enriched DIC could relieve the limitation of carbon supply for ammonium assimilation and thus ameliorate the influence of salinity on NO?3 uptake and assimilation as well as on plant growth. 相似文献
16.
Abstract Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH4+, NO3? and K+ were frequently monitored and adjusted to set values. In a pre-experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C. When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature-dependent, steady value (phase 2). The fresh: freeze-dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1). In both growth phases and at all temperatures, plants absorbed more NH4+ than NO4+, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH4+. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH4+. Specific absorption rates for NH4+, NOx?, K+ and H2PO4? showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2. The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes. 相似文献
17.
Z. Zhu J. Gerendás R. Bendixen K. Schinner H. Tabrizi B. Sattelmacher U-P. Hansen 《Plant biology (Stuttgart, Germany)》2000,2(5):558-570
Abstract: NH4+‐grown plants are more sensitive to light stress than NO3?‐grown plants, as indicated by reduced growth and intervenal chlorosis of French bean (Phaseolus vulgaris L.). Measuring the time course of Fv/Fm ratios under photoinhibitory light regimes did not reveal any difference in PS II damage between NO3?‐ and NH4+‐grown plants, in spite of some indications of higher energy quenching in NO3?‐grown plants. Also, a direct action of NH4+ as an uncoupler at the thylakoid membrane could be excluded. Instead, biochemical analysis revealed enhanced lipid peroxidation and higher activity of scavenging enzymes in NH4+‐grown plants indicating that these plants make use of metabolic pathways with stronger radical formation. Evidence for higher rates of photorespiration in NH4+‐grown plants came from experiments showing that electron flux and O2 evolution were decreased by SHAM in NH4+‐grown plants, and by antimycin A in NO3?‐grown plants. Further, the comparison of electron flux and of photoacoustic measurements of O2 evolution suggested that in NH4+‐grown plants the Mehler reaction was also increased, at least in the induction phase. However, the major cause of N form‐dependent stress sensitivity is assumed to be in the coupling between photosynthesis and respiration, i.e., NO3?‐grown plants can utilize the TCA cycle for the generation of C skeletons for amino acid synthesis, thus improving the ATP: reductant balance, whereas NH4+‐grown plants have enhanced rates of photorespiration. 相似文献
18.
Andrew J. Burton Kurt S. Pregitzer Jeffrey N. Crawford Gregory P. Zogg† Donald R. Zak‡ 《Global Change Biology》2004,10(7):1080-1091
Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO2 efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO3? deposition (3 g N m?2 yr?1) to four sugar maple‐dominated northern hardwood forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO3?‐amended plots. In all subsequent measurement years, soil respiration rates from NO3?‐amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO2 efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO3? additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO2 efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO3?‐amended plots are consistent with this explanation. 相似文献
19.
NO3?-dependent O2 in synchronous Scenedesmus obtusiusculus Chod. in the absence of CO2 is stoichiometric with NH4+ excretion, indicating a close coupling of NO3? reduction to non-cyclic electron flow. Also in the presence of CO2, NO3? stimulates O2 evolution as manifested by an increase in the O2/CO2 ratio from 0.96 to 1.11. This quotient was increased to 1.36 by addition of NO2?, without competitive interaction with CO2 fixation, indicating that the capacity for non-cyclic electron transport at saturating light is non-limiting for simultaneous reduction of NO3? and CO2 at high rates. During incubation with NO3?+ CO2, no NH4+ is released to the outer medium, whereas during incubation with NO2?+ CO2, excess NH4+ is formed and excreted. NO3? uptake is stimulated by CO2, and this stimulation is also significant when the cellular energy metabolism is restricted by moderate concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, whereas NO3? uptake in the absence of CO2 is severely inhibited by the uncoupler. Also under energy-restricted conditions NO3? uptake is not competitive with CO2 fixation. Antimycin A is inhibitory for NO3? uptake in the absence of CO2, and there is no enhancement of NO3? uptake by CO2 in the presence of antimycin A. It is assumed that the energy demand for NO3? uptake is met by energy fixed as triosephosphates in the Calvin cycle. Antimycin A possibly affects the transfer of reduced triose phosphates from the chloroplast to the cytoplasm. Active carbon metabolism also seems to exert a control effect on NO3? assimilation, inducing complete incorporation of all NO3? taken up into amino acids. This control effect is not functional when NO2? is the nitrogen source. Active carbon metabolism thus seems to be essential both for provision of energy for NO3? uptake and for regulation of the process. 相似文献
20.
Abstract A 16-channel fully automated microcomputer-based system was designed to measure the disappearance of NO?3 NO?2 and NH+4 simultaneously from uptake solutions. The analyses were done using high-performance liquid chromatography. Statistical procedures were used to generate transport kinetics and interactions amongst NO?3, NO?2 and NH+4 by intact wheat seedlings. The simultaneous analysis of NO?3, NO?2 and NH+4 at real-time; the accommodation of varying sampling intervals; the capability to study up to 16 experimental units in synchrony; and the analysis of the data with a microcomputer, make this a powerful system for studying transport kinetics and interactions. 相似文献