首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 78 毫秒
1.
As part of a programme of acquiring data for preparing standards to safeguard European, nonsalmonid, freshwater fish from pollution, toxicity tests were carried out in hard, well-aerated water. Asymptotic median lethal concentrations (LC50s) of undissociated ammonia, cyanide, nitrite and phenol to one or more of three species were determined. The LC50s were as follows: to common carp 16mg1-1 as NO2–N; to perch 0.1 mg1-1 as HCN; to roach 0.35 mg1-1 as NH3-N, 0-11mg1-1 as HCN, 10.1 mg1-1 asNO2-Nand 10mg-1 as phenol. In order to define these LC50s, exposure periods within the range 0.3 days (phenol) to 14 days (nitrite) were required. Comparisons are made with other data and the tentative water quality 'criteria' proposed by the European Inland Fisheries Advisory Commission.  相似文献   

2.
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   

3.
The plant fraction of alfalfa ( Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH-NR from the cytosol of nodules not treated with NO3- was about 30 nmol (mg protein)-1-h-1 and was not basically affected by NO3 addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein)-1h-1 using methyl viologen as electron donor. This activity strongly increased with NO3 concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein)-1h-1 at 50 to 200 mM NO3.
Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO2 accumulating in the cytosol upon NO3, supply, and the different response to NO3 of bacteroid and cytosolic NRs support the concept that most of this NO2 comes from the bacteroids.  相似文献   

4.
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 N2O. This oxidation stopped in the stationary phase after depletion of CH4. CH3OH 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   

5.
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   

6.
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, NH4NO3 or (NH4)2SO4. 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 NH4NO3 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   

7.
Response of nitrogen metabolism to boron toxicity in tomato plants   总被引:1,自引:0,他引:1  
Boron (B) toxicity has become important in areas close to the Mediterranean Sea where intensive agriculture has been developed. The objective of this research was to study the effects of B toxicity (0.5 m m and 2.0 m m B) on nitrogen (N) assimilation of two tomato cultivars that are often used in these areas. Leaf biomass, relative leaf growth rate (RGRL), concentration of B, nitrate (NO3), ammonium (NH4+), organic N, amino acids and soluble proteins, as well as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthase (GS), glutamate synthetase (GOGAT) and glutamate dehydrogenase (GDH) activities were analysed in leaves. Boron toxicity significantly decreased leaf biomass, RGRL, organic N, soluble proteins, and NR and NiR activities. The lowest NO3 and NH4+ concentration in leaves was recorded when plants were supplied with 2.0 m m B in the root medium. Total B, amino acids, activities of GS, GOGAT and GDH increased under B toxicity. Data from the present study prove that B toxicity causes inhibition of NO3 reduction and increases NH4+ assimilation in tomato plants.  相似文献   

8.
Growth and proteinase production by Micrococcus sp. INIA 528 in a batch-operated laboratory fermentor were investigated, with trypticase soy broth as the basal medium for studies on optimum temperature, pH and medium composition. Maximum growth was recorded at 34°C and pH 715, whereas optimum temperature and pH for proteinase production were 31°C and pH 6.25. Maximum rate of enzyme production occurred during the late log and early stationary phases of growth. Addition of 5.0 g 1-1 yeast extract, 1.0 g 1-1 glucose, 1.0 g 1-1 MgSO4 or 1.0 g 1-1 K2HPO4 to basal medium resulted in a lower enzyme yield, but supplementation of basal medium with 2.5 g 1-1 (NH4)2SO4 increased enzyme production by 45%. A high initial biomass added to fresh broth supplemented with 2.5 g 1-1 (NH4)2SO4 only increased enzyme activity by 19%, compared to the maximum enzyme activity achieved with the standard inoculum.  相似文献   

9.
SUMMARY. 1. Time-course measurements of NH4+ and NO3uptake 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 of I5N into TCA-insoluble material (protein) following the saturating NH4+ pulse was increased less than total cellular 15N uptake, whereas no elevation of 15N incorporation into protein was observed following a saturating NO3pulse.
5. The percentage of I5N 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   

10.
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   

11.
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   

12.
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, 13N 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   

13.
The preference of paddy rice for NH4+ rather than NO3- is associated with its tolerance to low pH since a rhizosphere acidification occurs during NH4+ absorption. However, the adaptation of rice root to low pH has not been fully elucidated. This study investigated the acclimation of plasma membrane H+-ATPase of rice root to low pH. Rice seedlings were grown either with NH4+ or NO3-. For both nitrogen forms, the pH value of nutrient solutions was gradually adjusted to pH 6.5 or 3.0. After 4 d cultivation, hydrolytic H+-ATPase activity, V max, K m, H+-pumping activity, H+ permeability and pH gradient across the plasma membrane were significantly higher in rice roots grown at pH 3.0 than at 6.5, irrespective of the nitrogen forms supplied. The higher activity of plasma membrane H+-ATPase of adapted rice roots was attributed to the increase in expression of OSA1, OSA3, OSA7, OSA8 and OSA9 genes, which resulted in an increase of H+-ATPase protein concentration. In conclusion, a high regulation of various plasma membrane H+-ATPase genes is responsible for the adaptation of rice roots to low pH. This mechanism may be partly responsible for the preference of rice plants to NH4+ nutrition.  相似文献   

14.
The postprandial excretion pattern of ammonia in dependence of feeding regime (fasting, 1 ×/day, 2 ×/day, 4 ×/day and continuous feeding), was determined in rainbow trout ( Oncorhynchus mykiss ), using continuous flow analysis. In fed fish ammonia peaked c. 7 h after the first meal with no differences in pattern between treatments. Fasting fish did not show a pattern. Overall production rates (NH4 and NO2+ NO3) ranged from 0.29–0.31 g kg−1 BW/d in fed fish and were around 0.07 g kg−1 BW/d in fasting fish. Additionally determined total N (Kjeldahl) showed much higher values in fed fish (0.78–1.05 g kg−1 BW/d) but only slightly higher values in fasting fish (0.11 g kg−1 BW/d). Budgets of nitrogen (N) and energy (E) showed low recoveries ( c. 50% and between 50% and 70%, respectively). When correcting ammonia excretion (NH4 and NO2+ NO3) using literature data on urea excretion of O. mykiss and assuming that total N partly stemmed from uneaten but undetected feed, both N and E budgets reached a recovery of around 100% in all four fed groups. Implications of this approach are discussed in the light of incomplete budgets as determined in earlier studies.  相似文献   

15.
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   

16.
Abstract. Suspension cultured cells of Chenopodium rubrum were grown photoautotrophically under a diurnal light-dark cycle of 16-8h. The following phases of the batch culture were differentiated: a short lag, a cell division phase terminated by a pronounced transition to stationary maintenance which finally gradually passed into senescence. Nitrogen fluxes typical of these stages were followed by measuring uptake of NO3 and NH4+ from the medium and their incorporation into the cellular fractions of nitrogenous compounds. Activities of seven N-metabolizing enzymes were determined. Compartmentation of enzymes and nitrogenous compounds was analysed after isolation of intact chloroplasts and vacuoles from protoplasts. Eighty-two per cent of the N originally present in the medium was taken up and incorporated to an extent of 80% into protein until the end of the division phase. Net protein synthesis ceased upon transition to the stationary phase. During the division phase a vacuolar pool of NO3 was established and then maintained throughout the resting phase. Free cellular NH4+ was not localized within the vacuole and responded to the ammonium content of the medium. Amino acids accumulated in the cells especially during the stationary phase, during which they were present in the vacuole. Typical nitrogen relations are portrayed as flux diagrams for one day of each of the essential developmental phases. The enzyme activities were easily sufficient to account for the observed flow rates of the corresponding nitrogenous compounds. Hence, uptake of NO3 and NH4+ must be considered as steps limiting N metabolism in Chenopodium rubrum cell suspensions.  相似文献   

17.
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   

18.
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 CH3OH and does not nitrify; a Pseudomonas (Is-2) which grows on Is-1 culture filtrate and produces NO2, NO3 and N2O from NH2OH, and NO3 from NO2; and a second Pseudomonas (Is-3) which produces NO3 from NH4+ or NO2, and N2O from NH2OH. 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   

19.
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   

20.
The dose- and time-response effects of 3 days of 6 h day-time sequential exposures to NO2, SO2 and SO2+NO2 of 0.45–1.81 μl l−1 (ppm) SO2 and 1.50–7.65 μl l−1 NO2 on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian half-sib families and a population from the GFR ('Westerhof') of Norway spruce [ Piecea abies (L.) Karst.], all in their 5th growing season.
SO2+NO2 inhibited photosynthesis and transpiration and stimulated dark respiration more than SO2 alone. SO2 and SO2+NO2 at the lowest concentrations inhibited night transpiration, but increased it at the highest concentration, the strongest effects being obtained with combined exposures. Photosynthesis of the different half-sib families was affected significantly differently by SO2+NO2 exposures. NO2 alone had no effects.
Sensitivity to transpiration decline correlated negatively with branch density. Height of trees correlated postitively with decline sensitivity in the seed orchard. The distribution of photosynthesis and transpiration sensitivities over all tested half-sib families correlated negatively with the distribution of decline sensitivity of their parents in a rural Danish seed orchard. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters for selecting against novel spruce decline.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号