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1.
Effects of nitrogen dioxide and nitrate nutrition on nodulation, nitrogenase activity, growth, and nitrogen content of bean 总被引:1,自引:0,他引:1
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The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO2 (0-0.5 parts per million) on nodulation and in vivo acetylene reduction activity of the roots and on growth and nitrate and Kjeldahl N concentration in shoots was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) plants. Exposing 8-day old seedlings for 6 hours each day, for 15 days, to 0.02 to 0.5 parts per million NO2 decreased total nodule weight at 0 and 1 millimolar nitrate, and nitrogenase (acetylene reduction) activity at all concentrations of nitrate. The pollutant had little effect on root fresh or dry weights. Shoot growth was inhibited by NO2. The NO2 exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO2 markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO2 concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants. 相似文献
2.
Exogenous calcium affects nitrogen metabolism in root-zone hypoxia-stressed muskmelon roots and enhances short-term hypoxia tolerance 总被引:4,自引:0,他引:4
We investigated the effects of short-term root-zone hypoxic stress and exogenous calcium application or deficiency in an anoxic nutrient solution on nitrogen metabolism in the roots of the muskmelon cultivar Xiyu No. 1. Seedlings grown in the nutrient solution under hypoxic stress for 6 d displayed significantly reduced plant growth and soluble protein concentrations. However, NO3− uptake rate and activities of nitrate reductase and glutamate synthase were significantly increased. We also found higher amounts of nitrate, ammonium, amino acids, heat-stable proteins, polyamines, H2O2, as well as higher polyamine oxidase activity in the roots. In comparison to the reactions seen under hypoxic stress, exogenous calcium application led to a marked increase in plant weights, photosynthesis parameters, NO3− uptake rate and contents of nitrate, ammonium, amino acids (e.g., glutamic acid, proline, glycine, cystine, γ-aminobutyric acid), soluble and heat-stable proteins, free spermine, and insoluble bound polyamines. Meanwhile, exogenous calcium application resulted in significantly increased activities for nitrate reductase, glutamine synthetase, and glutamate synthase but decreased activities for diamine and polyamine oxidase, as well as lower H2O2 content in roots during exposure to hypoxia. However, calcium deficiency in the nutrient solution decreased plant weight, photosynthesis parameters, NO3− reduction, amino acids (e.g., alanine, aspartic acid, glutamic acid, γ-aminobutyric acid), protein, all polyamines except for free putrescine, and the activities of glutamate synthase and glutamine synthetase. Additionally, there was an increase in the NO3− uptake rate, polyamine oxidase activity and H2O2 contents under hypoxia-Ca. Simultaneously, exogenous calcium had little effect on nitrate absorption and transformation, photosynthetic parameters, and plant growth under normoxic conditions. These results suggest that calcium confers short-term hypoxia tolerance in muskmelon, most likely by promoting nitrate uptake and accelerating its transformation into amino acids, heat-stable proteins or polyamines, as well as by decreasing polyamine degradation in muskmelon seedlings. 相似文献
3.
X. H. Wang S. J. Wang Z. Chen B. Gong X. F. Wang M. Win Q. H. Shi Y. Li F. J. Yang 《Russian Journal of Plant Physiology》2016,63(4):549-557
Putrescine (Put), spermidine (Spd), and spermine (Spm) are the major polyamines (PAs) in plant, which are not only involved in the regulation of plant developmental and physiological processes, but also play key roles in modulating the defense response of plants to diverse environmental stresses. In this study, Cucumis sativus L. seedlings were cultivated in nutrient solution and sprayed with three kinds of PAs (Put, Spd, and Spm). The effects of PAs were investigated on excess nitrate stress tolerance of C. sativus by measuring growth and nitrogen (N) metabolism parameters. The contents of NO3-?N, NH4-+N, proline and soluble protein in leaves were increased; while plant height, leaf area, shoot fresh and dry weight, root fresh weight were decreased under 140 mM NO3? treatment for 7 d. In addition, the activities of nitrate reductase (NR), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) were significantly inhibited under 140 mM NO3? treatment for 7 d. With foliar treatment by 1 mM Spd or Spm under stress treatment, the contents of Spm, Put, and Spd in leaves increased significantly, except that Spm content decreased under Spd treatment. The activities of NR, glutamine synthetase (GS), GOGAT and GDH and plant height, leaf area, shoot fresh and dry weights were significantly increased. The contents of proline and soluble protein in leaves were significantly enhanced. In contrast, the accumulation of NO3-?N and NH4-+N were significantly decreased. However, there were minor differences in activities of N metabolism enzymes and the content of osmotic adjustment substances under 1 mM Put treatment. These findings suggest that 1 mM exogenous Spm or Spd could enhance the capacity of N metabolism, promote growth and increase resistance to high concentrations of NO3?. The ameliorating effect of Spd was the best, and that of Put the worst. 相似文献
4.
Root respiration associated with nitrate assimilation by cowpea 总被引:2,自引:1,他引:1
Nitrate uptake by roots of cowpea (Vigna unguiculata) was measured using 15NO3−, and the energy cost to the root was estimated by respirometry. Roots of 8-day-old cowpea seedlings respired 0.6 to 0.8 milligram CO2 per plant per hour for growth and maintenance. Adding 10 millimolar NO3− to the root medium increased respiration by 20 to 30% during the following 6 hours. This increase was not observed if the shoots were in the dark. Removal of NO3− from the root medium slowed the increase of root respiration. The ratios of additional respiration to the total nitrogen uptake and reduced nitrogen content in roots were 0.4 gram C per gram N and 2.3 grams C per gram N, respectively. The latter value is close to theoretical estimates of nitrate assimilation, and is similar to estimates of 1 to 4 grams C per gram N for the respiratory cost of symbiotic N2 fixation. 相似文献
5.
Evidence for cotransport of nitrate and protons in maize roots : I. Effects of nitrate on the membrane potential 总被引:16,自引:5,他引:11
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The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of seedlings grown in the absence of nitrate, but, within 3 hours of initial exposure to 0.1 millimolar nitrate, increased to that of nitrate-grown roots. Chloride elicited a separate electrical response with a pattern similar to that of the nitrate response. However, the results presented in this study strongly indicate that the electrical response to nitrate reflects the activity of a nitrate-inducible membrane transport system for nitrate which is distinct from that for chloride. Inhibitors of the plasmalemma H+-ATPase (vanadate, diethylstilbestrol) completely inhibited both parts of the electrical response to nitrate, as did alkaline external pH. The magnitude of the initial nitrate-dependent, membrane potential depolarization was independent of nitrate concentration, but the subsequent nitrate-dependent hyperpolarization showed saturable dependence with an apparent Km of 0.05 millimolar. These results support a model for nitrate uptake in maize roots which includes a depolarizing NO3−/H+ symport. The model proposes that the nitrate-dependent membrane potential hyperpolarization is due to the plasma membrane proton pump, which is secondarily stimulated by the operation of the NO3−/H+ symport. 相似文献
6.
Restricted nitrate influx and reduction in corn seedlings exposed to ammonium 总被引:4,自引:6,他引:4
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The effect of ambient ammonium (0.5 millimolar [14NH4]2SO4) added to a nutrient solution containing 1.0 millimolar K15NO3, 99 atom per cent 15N, upon [15N]nitrate assimilation and utilization of previously accumulated [14N]nitrate was investigated. Corn seedlings, 5-day-old dark-grown decapitated (experiment I) and 10-day-old light-grown intact (experiment II), which had previously been grown on K14NO3 nutrient solution, were used. In both experiments, the presence of ambient ammonium decreased [15N]nitrate influx (20% after 6 hours) without significantly affecting the efflux of previously accumulated [14N]nitrate. In experiment I, relative reduction of [15N]nitrate (reduction as a percentage of influx) was inhibited more than was [15N]nitrate influx. Nevertheless, in experiment I, where all reduction could be assigned to the root system, the absolute inhibition of reduction during the 12 hours (13 micromoles/root) was less than the absolute inhibition in influx (24 micromoles/root). The data suggest that the influence of ammonium on [15N]nitrate influx could not be totally accounted for by the decrease in the potential driving force which resulted from restricted reduction; an additional impact on the influx process is indicated. Reduction of [15N]nitrate in experiment II after 6 hours accounted for 30 and 18% of the tissue excess 15N in the control and ammonium treatments, respectively. Relative distribution of 15N between roots and exudate (experiment I), or between roots and shoots (experiment II) was not affected by ammonium. On the other hand, the accumulation of [15N]nitrate in roots, shoots, and xylem exudate was enhanced by ammonium treatment compared to the control, whereas the accumulation of reduced 15N was inhibited. 相似文献
7.
Initial rate studies of spinach (Spinacia oleracea L.) nitrate reductase showed that NADH:nitrate reductase activity was ionic strength dependent with elevated ionic concentration resulting in inhibition. In contrast, NADH:ferricyanide reductase was markedly less ionic strength dependent. At pH 7.0, NADH:nitrate reductase activity exhibited changes in the Vmax and Km for NO3− yielding Vmax values of 6.1 and 4.1 micromoles NADH per minute per nanomoles heme and Km values of 13 and 18 micromolar at ionic strengths of 50 and 200 millimolar, respectively. Control experiments in phosphate buffer (5 millimolar) yielded a single Km of 93 micromolar. Chloride ions decreased both NADH:nitrate reductase and reduced methyl viologen:nitrate reductase activities, suggesting involvement of the Mo center. Chloride was determined to act as a linear, mixed-type inhibitor with a Ki of 15 millimolar for binding to the native enzyme and 176 millimolar for binding to the enzyme-NO3− complex. Binding of Cl− to the enzyme-NO3− complex resulted in an inactive E-S-I complex. Electron paramagnetic resonance spectra showed that chloride altered the observed Mo(V) lineshape, confirming Mo as the site of interaction of chloride with nitrate reductase. 相似文献
8.
Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψπ) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized
to (Ψπ) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl2 or Na2SO4. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO3. The nutrient solutions were sampled for NO3 analysis each day immediately before renewing the solutions. The accumulative loss of NO3 from the solutions was considered to be uptake whereas NO3 reduction was the difference between uptake and seedling content. Lowering the (Ψπ) of the nutrient solutions resulted in decreased concentrations of NO3 in the plant, little or no effect (except at the lowest (Ψπ) level) on uptake, and increased nitrate reductase activity. Increased rates of NO3 reduction were in particular associated with the Cl concentration of the nutrient solution. 相似文献
9.
Michael R. Betlach James M. Tiedje Richard B. Firestone 《Archives of microbiology》1981,129(2):135-140
The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3
-, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3
- was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3
- at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar K
mvalues, 7 M. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium. 相似文献
10.
I. Prášil 《Biologia Plantarum》1975,17(3):223-225
The absorption of nitrate and the activity of nitrate reductase were much lower in Ca-deficient plants ofCururbita pepo L., cv. ‘Kveta’ than in normal plants grown in complete nutrient solution for a period of 8 days. After the addition of nitrate to the nutrient medium, nitrate reductase activity in the roots of NO3-deficient plants sharply rose during the first 6 h and then remained constant during the following 6 h; the content of endogenous NO3 ? rose slowly and continuously. These processes were depressed in (Ca, NO3)-deficient plants independently of the addition of Ca2+ to the medium in the variant with NO3 ?. Thus it seems that the whole nitrogen metabolism,i.e. both NO3 ? absorption and the synthesis of nitrate reductase, is impaired in Ca-deficient plants. 相似文献
11.
Differential light induction of nitrate reductases in greening and photobleached soybean seedlings 总被引:2,自引:2,他引:0
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Soybean (Glycine max [L.] Merr.) seeds were imbibed and germinated with or without NO3−, tungstate, and norflurazon (San 9789). Norflurazon is a herbicide which causes photobleaching of chlorophyll by inhibiting carotenoid synthesis and which impairs normal chloroplast development. After 3 days in the dark, seedlings were placed in white light to induce extractable nitrate reductase activity. The induction of maximal nitrate reductase activity in greening cotyledons did not require NO3− and was not inhibited by tungstate. Induction of nitrate reductase activity in norflurazon-treated cotyledons had an absolute requirement for NO3− and was completely inhibited by tungstate. Nitrate was not detected in seeds or seedlings which had not been treated with NO3−. The optimum pH for cotyledon nitrate reductase activity from norflurazon-treated seedlings was at pH 7.5, and near that for root nitrate reductase activity, whereas the optimum pH for nitrate reductase activity from greening cotyledons was pH 6.5. Induction of root nitrate reductase activity was also inhibited by tungstate and was dependent on the presence of NO3−, further indicating that the isoform of nitrate reductase induced in norflurazon-treated cotyledons is the same or similar to that found in roots. Nitrate reductases with and without a NO3− requirement for light induction appear to be present in developing leaves. In vivo kinetics (light induction and dark decay rates) and in vitro kinetics (Arrhenius energies of activation and NADH:NADPH specificities) of nitrate reductases with and without a NO3− requirement for induction were quite different. Km values for NO3− were identical for both nitrate reductases. 相似文献
12.
Jingrui Li Zhen Tian Xiaolei Wu Guiyun Lv Wanli Ma Ying Zhang Hongbo Gao 《Plant Molecular Biology Reporter》2018,36(3):530-542
Pakchoi plants were grown in 32 mM NO3? nutrient solution with or without 2.5 mM γ-aminobutyric acid (GABA) to investigate metabolite changes, gene and protein expression levels, and the activities of key enzymes related to nitrate metabolism in the leaves over a period of 0–12 days. High-nitrogen treatment enhanced plant growth and the NO3?, NO2?, NH4+, Gln, and Glu contents in the leaves; promoted the gene and protein expression of nitrate reductase (NR) and glutamate decarboxylase (GAD); and increased the activities of NR, nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and GAD. The endogenous GABA concentration in the leaves was enhanced in parallel with the increase in GAD activity. The GABA-treated leaves displayed the greatest increases in the gene and protein expression levels of NR and GAD and in the activities of NR, NiR, GS, GOGAT, and GAD. In addition, accelerated rates of nitrate reduction and assimilation were detected, and these changes occurred concurrently with the observed increases in gene or protein expression and enzyme activity. As a result, the concentrations of NH4+, Gln, Glu, and endogenous GABA were significantly elevated, and the NO3? and NO2? contents were significantly decreased, in GABA-treated leaves compared with plants exposed to nitrogen-rich conditions. Our results reveal a potential positive that GABA may act as a nitrogen source to improve the plant growth and the most prominent effect of decreasing nitrate contents by accelerating NO3? reduction and assimilation. Exogenous GABA plays an important role in reducing the NO3? content of leaves, and thereby improves the ability to harvest leafy vegetables containing higher levels of endogenous GABA. 相似文献
13.
The inclusion of sub-lethal amounts ofthe herbicide atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] in the nutrient solution supplied to maize and barley increased the growth of the root and shoot and the uptake of nitrate. The activities of nitrate and nitrite reductases, glutamine synthetase and glutamate synthase were enhanced and the amino acid and nitrate contents of the xylem sap increased. All these effects of atrazine were found only in plants grown with nitrate as the nitrogen source. The uptake of 15NO3? and its incorporation into protein in the root and shoot of maize and barley seedlings was significantly greater in the atrazine treated plants. However, a stimulation in the incorporation of leucine-[14C] into TCA-precipitable protein of detached leaves from 7-day-old barley seedlings was obtained only in the absence of a supply of combined nitrogen either in the culture medium or in the in vitro incubation mixture containing the labelled amino acid. 相似文献
14.
Assimilation and Transport of Nitrogen in Nonnodulated (NO(3)-grown) Lupinus albus L 总被引:7,自引:7,他引:0
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The response of nonnodulated white lupin (Lupinus albus L. cv. Ultra) plants to a range of NO3 levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO3 reductase (EC 1.6.6.1) activity, measurements of NO3-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO3 followed by 10 days with 1, 5, 15, or 30 millimolar NO3. NO3 reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO3 reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO3, respectively. Stem, petioles, and leaflets contained virtually all of the NO3 reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO3-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO3 in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO3, respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO3. NO3 failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO3. Shoot organs were ineffective in storing NO3. Even when NO3 was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively. 相似文献
15.
Wallace W 《Plant physiology》1973,52(3):197-201
The nitrate reductase in the mature root extract of 3-day maize (Zea mays) seedlings was relatively labile in vitro. Insoluble polyvinylpyrrolidone used in the extraction medium produced only a slight increase in the stability of the enzyme. Mixing the mature root extract with that of the root tip promoted the inactivation of nitrate reductase in the latter. The inactivating factor in the mature root was separated from nitrate reductase by (NH4)2SO4 precipitation. Nitrate reductase was found in the 40% (NH4)2SO4 precipitate, while the inactivating factor was largely precipitated by 40 to 55% (NH4)2SO4. The latter fraction of the mature root inactivated the nitrate reductase isolated from the root tip, mature root, and scutellum. The inactivating factor, which has a Q10 15 to 25 C of 2.2, was heat labile, and hence has been designated as a nitrate reductase inactivating enzyme. The reduced flavin mononucleotide nitrate reductase was also inactivated, while an NADH cytochrome c reductase in nitrate-grown seedlings was inactivated but at a slower rate. The inactivating enzyme had no influence on the activity of nitrite reductase, glutamate dehydrogenase, xanthine oxidase, and isocitrate lyase. The activity of the nitrate reductase inactivating enzyme was not influenced by nitrate and was also found in the mature root of minus nitrate-grown seedlings. 相似文献
16.
Nitrate Reductase Activity in Shoots and Roots of Maize Seedlings as Affected by the Form of Nitrogen Nutrition and the pH of the Nutrient Solution 总被引:5,自引:1,他引:4
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The effect of nitrogen form (NH4-N, NH4-N + NO3−, NO3−) on nitrate reductase activity in roots and shoots of maize (Zea mays L. cv INRA 508) seedlings was studied. Nitrate reductase activity in leaves was consistent with the well known fact that NO3− increases, and NH4+ and amide-N decrease, nitrate reductase activity. Nitrate reductase activity in the roots, however, could not be explained by the root content of NO3−, NH4-N, and amide-N. In roots, nitrate reductase activity in vitro was correlated with the rate of nitrate reduction in vivo. Inasmuch as nitrate reduction results in the production of OH− and stimulates the synthesis of organic anions, it was postulated that nitrate reductase activity of roots is stimulated by the released OH− or by the synthesized organic anions rather than by nitrate itself. Addition of HCO3− to nutrient solution of maize seedlings resulted in a significant increase of the nitrate reductase activity in the roots. As HCO3−, like OH−, increases pH and promotes the synthesis of organic anions, this provides circumstantial evidence that alkaline conditions and/or organic anions have a more direct impact on nitrate reductase activity than do NO3−, NH4-N, and amide-N. 相似文献
17.
Initial organic products of assimilation of [N]ammonium and [N]nitrate by tobacco cells cultured on different sources of nitrogen
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Glutamine is the first major organic product of assimilation of 13NH4+ by tobacco (Nicotiana tabacum L. cv. Xanthi) cells cultured on nitrate, urea, or ammonium succinate as the sole source of nitrogen, and of 13NO3− by tobacco cells cultured on nitrate. The percentage of organic 13N in glutamate, and subsequently, alanine, increases with increasing periods of assimilation. 13NO3−, used for the first time in a study of assimilation of nitrogen, was purified by new preparative techniques. During pulse-chase experiments, there is a decrease in the percentage of 13N in glutamine, and a concomitant increase in the percentage of 13N in glutamate and alanine. Methionine sulfoximine inhibits the incorporation of 13N from 13NH4+ into glutamine more extensively than it inhibits the incorporation of 13N into glutamate, with cells grown on any of the three sources of nitrogen. Azaserine inhibits glutamate synthesis extensively when 13NH4+ is fed to cells cultured on nitrate. These results indicate that the major route for assimilation of 13NH4+ is the glutamine synthetase-glutamate synthase pathway, and that glutamate dehydrogenase also plays a role, but a minor one. Methionine sulfoximine inhibits the incorporation of 13N from 13NO3− into glutamate more strongly than it inhibits the incorporation of 13N into glutamine, suggesting that the assimilation of 13NH4+ derived from 13NO3− may be mediated solely by the glutamine synthetase-glutamate synthase pathway. 相似文献
18.
Yanjuan Yang Xiaomin Lu Bei Yan Bin Li Jin Sun Shirong Guo Takafumi Tezuka 《Journal of plant physiology》2013
The plant growth, nitrogen absorption, and assimilation in watermelon (Citrullus lanatus [Thunb.] Mansf.) were investigated in self-grafted and grafted seedlings using the salt-tolerant bottle gourd rootstock Chaofeng Kangshengwang (Lagenaria siceraria Standl.) exposed to 100 mM NaCl for 3 d. The biomass and NO3− uptake rate were significantly increased by rootstock while these values were remarkably decreased by salt stress. However, compared with self-grafted plants, rootstock-grafted plants showed higher salt tolerance with higher biomass and NO3− uptake rate under salt stress. Salinity induced strong accumulation of nitrate, ammonium and protein contents and a significant decrease of nitrogen content and the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) in leaves of self-grafted seedlings. In contrast, salt stress caused a remarkable decrease in nitrate content and the activities of GS and GOGAT, and a significant increase of ammonium, protein, and nitrogen contents and NR activity, in leaves of rootstock-grafted seedlings. Compared with that of self-grafted seedlings, the ammonium content in leaves of rootstock-grafted seedlings was much lower under salt stress. Glutamate dehydrogenase (GDH) activity was notably enhanced in leaves of rootstock-grafted seedlings, whereas it was significantly inhibited in leaves of self-grafted seedlings, under salinity stress. Three GDH isozymes were isolated by native gel electrophoresis and their expressions were greatly enhanced in leaves of rootstock-grafted seedlings than those of self-grafted seedlings under both normal and salt-stress conditions. These results indicated that the salt tolerance of rootstock-grafted seedlings might (be enhanced) owing to the higher nitrogen absorption and the higher activities of enzymes for nitrogen assimilation induced by the rootstock. Furthermore, the detoxification of ammonium by GDH when the GS/GOGAT pathway was inhibited under salt stress might play an important role in the release of salt stress in rootstock-grafted seedlings. 相似文献
19.
Effect of carbon dioxide on nitrate accumulation and nitrate reductase induction in corn seedlings 总被引:4,自引:2,他引:2
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Exposure of the leaf canopy of corn seedlings (Zea mays L.) to atmospheric CO2 levels ranging from 100 to 800 μl/l decreased nitrate accumulation and nitrate reductase activity. Plants pretreated with CO2 in the dark and maintained in an atmosphere containing 100 μl/l CO2 accumulated 7-fold more nitrate and had 2-fold more nitrate reductase activity than plants exposed to 600 μl/l CO2, after 5 hours of illumination. Induction of nitrate reductase activity in leaves of intact corn seedlings was related to nitrate content. Changes in soluble protein were related to in vitro nitrate reductase activity suggesting that in vitro nitrate reductase activity was a measure of in situ nitrate reduction. In longer experiments, levels of nitrate reductase and accumulation of reduced N supported the concept that less nitrate was being absorbed, translocated, and assimilated when CO2 was high. Plants exposed to increasing CO2 levels for 3 to 4 hours in the light had increased concentrations of malate and decreased concentrations of nitrate in the leaf tissue. Malate and nitrate concentrations in the leaf tissue of seven of eight corn genotypes grown under comparable and normal (300 μl/l CO2) environments, were negatively correlated. Exposure of roots to increasing concentrations of potassium carbonate with or without potassium sulfate caused a progressive increase in malate concentrations in the roots. When these roots were subsequently transferred to a nitrate medium, the accumulation of nitrate was inversely related to the initial malate concentrations. These data suggest that the concentration of malate in the tissue seem to be related to the accumulation of nitrate. 相似文献
20.
Summary Incorporation of15NO3- into amino acids was studied in 3-day-old aerobic rice seedlings (with coleoptile and root) subjected for 24h to anaerobic conditions. The incorporation of15N into glutamate, glutamine and alanine accounted for 89% and 84% of total incorporation in coleoptile and root, respectively. These findings indicate that, after the primary incorporation of15N into glutamate and glutamine, the main fate of nitrate nitrogen in rice seedlings subjected to anoxia is alanine. 相似文献