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1.
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 NH4NO3. In wild-type symbioses the application of NH4NO3 significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [14C]-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   

2.
The effect of nitrogen on excretion and metabolism of glycolate in Anabaena cylindrica (CCAP 1403/2a) was studied. Glycidate, an inhibitor of glutamate:glyoxylate aminotransferase (EC 2.6.1.4), reduced the L-methionine-DL-sulfoximine-induced NH4+ release by ca 40%, while net CO2 fixation and C2H2 reduction were not lowered. This indicates that at least a part of the glyoxylate synthesized in A. cylindrica is metabolized via glycine to serine. Addition of NH4Cl or glutamate to the medium reduced the excretion of glycolate. At pH 9, under air, NH4Cl reduced the excretion by 10–30% and under high pO2 (0.03 kPa CO2 in O2) by about 80–90%. At pH 7.5, under high pO2, NH4Cl and glulamate reduced the excretion by about 40 and 80%, respectively. Also, the presence of NH4Cl stimulated the animation of glyoxylate under such conditions as shown by an increased glycine pool and a decreased glutamate pool. We suggest that nitrogen regulates the capacity of A. cylindrica to retain and recycle glycolate intracellularly and that glutamate serves as an amino donor in the conversion of glyoxylate to glycine.  相似文献   

3.
Seedlings of Scots pine ( Pinus sylvestris L.) were grown on perlite for 21 days under controlled conditions. Apart from the water control, KNO3 (15 m M ), (NH4)2SO4 (7.5 m M ), and NH4NO3 (15 m M ) were offered to study the effects of a high nitrogen supply on nitrogen assimilation. In some experiments 1.3 m M potassium was added to the basic ammonium solutions. In labelling studies nitrate and ammonium were 2.3 atom%15N-enriched. It was found that over the 21-day period approximately three times more ammonium-N was taken up than nitrate-N. However, nitrate and ammonium, applied simultaneously, were taken up to the same extent as if they were applied separately (additivity). The presence of K+ in the medium did not affect N-uptake. Among the soluble N-containing compounds nitrate, ammonium and 8 amino acids were quantified. It was found that assimilation of nitrate can cope with the uptake of NO3 under all circumstances. Neither free nitrate nor ammonium or amino acids accumulated to an extent exceeding the values of water-grown seedlings. On the other hand, in case of high ammonium supply considerably more nitrogen was taken up than could be incorporated into nonsoluble N-containing substance ('protein'). The remaining nitrogen was found to accumulate in intermediary storage pools (free NH4+, glutamine, asparagine, arginine). Part of this accumulated N could be incorporated into protein when potassium was offered in the nutrient solution. It is concluded that potassium is a requirement for a high rate of protein synthesis not only in crop plants but also in conifers.  相似文献   

4.
Aims:  To identify if culture conditions affect the chemical composition of exopolysaccharide (EPS) produced by Aureobasidium pullulans .
Methods and Results:  In batch airlift and continuously stirred tank (CSTR) reactors the EPS produced with low (0·13 g l−1 N) initial NaNO3 or (NH4)2SO4 levels contained pullulan, with maltotriose as its major component, similar to that synthesized in the airlift reactor with high (0·78 g l−1 N) initial NaNO3 levels. EPS produced by CSTR grown cultures with high (NH4)2SO4 levels contained little pullulan, possibly because of a population shift from unicells to mycelium. This chemical difference may explain why total EPS yields did not fall as they did with cultures grown under identical conditions with high NaNO3 levels, where the pullulan component of the EPS disappeared. EPS synthesized in N-limiting chemostat cultures of A. pullulans changed little with growth rate or N source, being predominantly pullulan consisting of maltotriose units.
Conclusions:  While the EPS chemical composition changed little under N-limiting conditions, high initial medium N levels determined maltotriose content and/or pullulan content possibly by dictating culture morphology.
Significance and Impact of the Study:  These results emphasize the requirement of all studies to determine EPS chemical composition when examining the influence of culture conditions on EPS yields.  相似文献   

5.
Abstract Erythromycin formation decreased in Streptomyces erythreus as a function of the ammonium concentration present in the medium. Total inhibition of synthesis was obtained with 100 mM NH4Cl but medium pH and culture growth were not significantly affected. A similar effect was obtained with NH4NO3 or (NH4)2SO4 indicating that ammonium ion probably repressed formation of antibiotic.  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.
Roots and leaves of Zea mays L. cv. Ganga Safed-2 seedlings grown with nutrient solution containing either 10 m M KNO3 or NH4Cl or 5 m M NH4NO3 had considerably higher glutamate synthase (NADH, EC 1.4.1.14) activity than the corresponding organs from seedlings grown without any nitrogen. The supply of inorganic nitrogen for a short time, i.e. 3 h, to roots and leaves excised from seedlings grown without nitrogen also increased the enzyme activity in these organs. This increase was more pronounced with nitrate than with ammonium nitrogen. When excised roots and leaves from NH4NO3-grown seedlings were incubated in a minus nitrogen medium for 24 h, the enzyme activity declined considerably. This decline was inhibited to some extent by nitrogen, especially by nitrate. Inorganic nitrogen prevented similarly the decline in in vitro enzyme activity during 24 h storage at 25°C, more regularly for the root than for the leaf enzyme. The experiments demonstrate the role of inorganic nitrogen in the regulation of glutamate synthase activity.  相似文献   

8.
Four-year-old seedlings of Scots pine ( Pinus sylvestris L.) were exposed to filtered air (FA), and to FA supplemented with NH3 (60 and 240 μg m−3) in controlled-environment chambers for 14 weeks. Exposure to the higher NH3 concentration resulted in an increased activity of glutamine synthetase (GS, EC 6.3.1.2), and an increase in the concentrations of soluble proteins, total nitrogen, free amino acids and leaf pigments in the needles. The GS activity (μmol g−1 fresh weight h−1) in the needle extract increased to levels 69% higher than in FA and the soluble protein concentration to levels 22% higher. Total nitrogen concentration in the needles was 42% higher than in FA, while the free amino acid concentration was 300% higher, which was caused by an increase in arginine, glutamate, aspartate and glutamine. Chlorophyll a , chlorophyll b and carotenoid concentrations were 29, 38 and 11% higher, respectively. Neither the glutamate dehydrogenase (GDH, EC 1.4.1.2) activity nor the concentrations of free NH4+ and glucose in the needles were affected by exposure to NH3. After NH3 fumigation at 240 μg m−3 the starch concentration decreased by 39% relative to the FA. The results indicate that the metabolism of Scots pine acclimates to concentrations of NH3 which are 3 to 10 times higher than the average concentration in areas with intensive stock farming. The possible mechanisms underlying acclimation to NH3 are discussed.  相似文献   

9.
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   

10.
Abstract The effect of certain nitrogen compounds on nitrogenase activity was studied in cells of Azospirillum brasilense strain Sp6, grown under microaerophilic conditions with nitrogenase fully derepressed. 0.5 mM NH4Cl, 0.5 mM glutamine, 1.0 mM KNO3 and 0.1 mM KNO2 completely blocked nitrogenase activity. 1.0 mM asparagine, 1.0 mM aspartate, 1.0 mM histidine and 1.0 mM adenine did not caused no inhibition of nitrogenase; indeed asparagine, aspartate and histidine showed a slight stimulatory effect on N2 fixation. The addition of 10 mM dl -methionine- dl -sulphoximine prevented the inhibitory effect of NH4Cl and glutamine but did not counteract the effect of KNO2. Rifampicin and chloramphenicol did not prevent the inhibition of nitrogenase by NH4Cl.  相似文献   

11.
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   

12.
Cysteine is commonly employed as the medium reductant for ruminal bacteria, but many ruminal bacteria can use cysteine as a source of nitrogen as well as sulfur. The objective of the present study was to test a combination of dithiothreitol and sulfide as possible reductant substitutes for cysteine in anaerobic media containing ammonia as the nitrogen source. The type of reductant (cysteine versus dithiothreitol-sulfide) and ammonia concentration did not alter growth rates of Prevotella ruminicola strain B,4 (P>0.15). However, growth rates in dithiothreitol-sulfide reduced media varied tremendously between individual organisms ranging from 0.10 h−1 for Ruminococcus flavefaciens to 1.6 h−1 for Streptococcus bovis grown in 1 mM NH3-N. At both 1 and 11 mM NH4Cl, Str. bovis strain JB1 exhibited the greatest growth rate followed by Str. bovis strain C277. Megasphaera elsdenii strain T81 and Ruminococcus flavefaciens strain FD1 had the lowest growth rates at both NH4Cl concentrations. Increasing NH4Cl concentration from 1 to 11 mM resulted in increased growth rates for Ruminobacter amylophilus strains H18 and 70 and Str. bovis strain C277 (P<0.05), and decreased growth rates for S. ruminantium subsp. lactilytica strain HD4 and Str. bovis strain JB1 (P<0.01). These results indicate that dithiothreitol and sulfide can be combined as reductants in nitrogen-free basal media for most ruminal bacterial species.  相似文献   

13.
Uptake regions of inorganic nitrogen in roots of carob seedlings   总被引:2,自引:0,他引:2  
Three-week-old seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO3 and NH+4 ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH3 species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH+4/NH3 equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent free space.  相似文献   

14.
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   

15.
The effect of two different media on the growth, metabolism and viability of Scots pine ( Pinus sylvestris ) callus cultures was studied. Inorganic nitrogen in the culture media (modified MS) was in the form of either KNO3 or NH4NO3. The cultures were started from buds of mature Scots pine. Growth was poor on the medium with KNO3, but this compound had a noticeable effect on the metabolism of the callus, which was reflected in alterations in protein and polyphenol synthesis and the pH of the culture medium. Although the fresh mass, water content and viability of the callus decreased when KNO3 was the exclusive inorganic nitrogen nutrient, protein synthesis was more abundant. Electrophoretic analyses indicated alterations in the patterns of soluble proteins and purified glycoproteins. Phenylalanine ammonia-lyase (EC 4.3.1.5) activities were high in all the calluses, and concentrations of condensed tannins and their precursors, catechins, were higher than in intact buds. The role of inorganic nitrogen nutrition in the deterioration of tissues is discussed on the basis of the effect of ammonium on the metabolism of pine callus.  相似文献   

16.
The influence of salinity on the activity of nitrate reductase (NR, EC 1.6.6.1) and the level of the molybdenum cofactor (MoCo) as affected by the source and concentration of nitrogen was studied in annual ryegrass ( Lolium multiflorum cv. Westerwoldicum). Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS m−1, containing nitrogen (0.5 or 4.5 m M ) in the form of NH4NO3 or NaNO3 Salinity-treated (11.2 dS m−1) plants produced less biomass and more organic nitrogen while accumulating more NO3 than control plants. Increased nitrogen concentration in the irrigation solutions enhanced biomass and organic nitrogen production as well as NO3 accumulation irrespective of the electrical conductivity. Salinity inhibited shoot growth and increased shoot NR activity of plants receiving 4.5 m M NH4NO3 or NaNO3. Similar effects were observed in roots of plants grown in 4.5 m M NaNO3. Nitrate added to a complementation medium containing ryegrass MoCo and the NR apoprotein of Neurospora crassa mutant nit-1 stimulated the activity of the reconstituted NR (NADPH-nitrate reductase, EC 1.6.6.3). Increased salinity and nitrogen in the nutrient solutions caused an increase of MoCo content in roots and shoots. Similar results were observed for NR activity in the shoots. The increase of MoCo in response to salinity was more pronounced than that of NR, especially in the roots. We conclude that the pool size of MoCo in ryegrass is not constant, but varies in response to nutritional and environmental factors.  相似文献   

17.
The osmotic role of nitrate during aftermath growth of Lolium perenne L. cv. Réveille was investigated. Plants were grown from seed in a controlled environment using a liquid medium with 1.0 m M NH4NO3 as nitrogen source.
Eight-week-old plants were cut 4.0 cm above the root system and then harvested over a 14-day period of regrowth on the same initial nutrient solution, except that nitrate was 15N labelled. Throughout the experimental period, nitrate storage and reduction in roots were low. In stubble and especially in leaves, nitrate accumulated during the first 6 days of regrowth whereas nitrate reduction mainly occurred after this period. Analyses of carbohydrate, chloride and potassium contents in stubble and leaves showed that the accumulation of nitrate osmotically compensated for the decrease in soluble sugars during the first 6 days of regrowth.
The cumulative osmotic potential of sugars, chloride and nitrate in differently treated plants was studied in stubble and leaves. Compared with uncut plants, the lower carbohydrate concentrations found in cut plants regrowing on 1.0 m M NH4NO3 were compensated for by an accumulation of nitrate. During aftermath growth on low nitrogen nutrition (0.2 m M NH4NO3), chloride replaced nitrate, supporting the proposed osmotic function of nitrate.
It is concluded that nitrate is involved in the osmotic adjustment of ryegrass during regrowth after cutting.  相似文献   

18.
Abstract. Two anatomical variants of Panicum maximum Jacq. were observed to accumulate an unusually large number of starch grains in the bundle sheath chloroplasts when grown under controlled environmental conditions in a nutrient medium containing a low level of nitrate nitrogen (20 mg N dm−3 as KNO3). When these plants were placed under dark conditions the chloroplasts were destarched, but exhibited a marked distortion of the thylakoid membranes. Under a higher level of nitrate nitrogen supply (200 mg N dm−3 as KNO3) the number of starch grains was markedly reduced compared to that observed above in both plant variants. When the nitrogen was supplied as ammonium nitrogen (200 mg N dm−3 as NH4Cl) there was again a high level of starch in the bundle sheath chloroplasts, the level being only slightly lower than that observed at the low KNO3 supply. An unusually large number of starch grains accumulated in the bundle sheath chloroplasts in the absence of added phosphorus in the nutrient medium, in the presence of the higher nitrate nitrogen level. It is suggested that the increased starch accumulation results from a reduced trans-location of Calvin cycle intermediates out of the chloroplasts into the cytoplasm and that both nitrate nitrogen and phosphorus may play an important role in this process. A good correlation between high net photosynthetic activity and low bundle sheath starch content was observed. Nutrient medium requirements favouring low starch content in chloroplasts also favoured high net photosynthetic rates.  相似文献   

19.
The effect of various carbon sources, nitrogen sources, vitamins and trace elements on the ability of three strains (32H1, CB627, CB744) of a slow-growing Rhizobium sp. to develop nitrogenase activity in agar culture was studied. Strains 32H1 and CB627 developed nitrogenase but showed differences with respect to the nature and concentrations of carbon sources required for optimum activity. Strain 32H1 had less specific requirements than CB627 in this respect and could sustain high nitrogenase activity over a wider range of phosphate concentration (5 to 60 mmol/1) in the medium than CB627. There were only minor differences between these two strains with respect to the nitrogen source [glutamine, asparagine, histidine or (NH4SO4] required in the medium for nitrogenase induction, and nitrogenase activity in both strains was unaffected by changes in the concentration of vitamins or trace elements supplied. Strain CB744 did not develop nitrogenase activity under any of the conditions tested. Adenosine 3', 5'-cyclic monophosphate (1 mmol/1) was found to accelerate derepression of nitrogenase synthesis in agar cultures of strains 32H1 and CB627.  相似文献   

20.
The survival of Atlantic salmon smolts on exposure to constant concentrations of ammonia has been measured under laboratory conditions. At concentrations of dissolved oxygen close to the air-saturation value, the 24-h LC50 of un-ionised ammonia is 0.15 mg NH31−1 in fresh water (hardness 264 mg 1−1 as CaCO3) and 0.3 mg NH31−1 in 30% sea water; at concentrations of dissolved oxygen of 3.5 mg 1−1 in fresh water and 3.1 mg 1−1 in 30% sea water, the 24-h LC50 is 0.09 mg NH3 1−1 and 0.12 mg NH3 1−1 respectively; for fish acclimated for 1 day to a concentration of ammonia close to the 24-h median for un-acclimated fish, the median is increased between 38 and 79%, depending on test conditions.  相似文献   

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