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1.
Induction of ammonium assimilation: leguminous roots compared with nodules using a split root system 总被引:1,自引:0,他引:1
Paul H. S. Reynolds Michael J. Boland Graeme S. McNaughton Raymond D. More William T. Jones 《Physiologia plantarum》1990,79(2):359-367
A split root system for nitrogen uptake, in which one part of the root system was exposed to nitrogen-free nutrient and the other to circulated buffered ammonium, was used to investigate the effects of ammonium per se on the enzyme pathway for its assimilation in nodules and roots of leguminous plants. Plants of Trifolium repens L. cv. Grasslands Huia grown in the system showed similar growth and similar free amino acid content in the NH+ 4 -fed roots and in nodulated plants. Studies of ammonium assimilation using [13 N]-NH+ 4 , applied to Glycine max [L.] Merr. cv. Amsoy plants, showed the label to be assimilated into amino acids in the NH+ 4 -fed roots and to be transported to the tops before subsequently appearing in the minus-N side of the split root system. Analysis of the xylem sap showed [13 N]-asparagine to be the principal labelled amino acid component. In these plants, levels of both allantoate and the nodule-specific isoenzyme aspartate aminotransferase-P2 were at least 10 times higher in the NH+ 4 -fed roots than in the minus-N side of the split root system. These studies strongly suggest that a nodule-type of ammonium assimilation was occurring in the NH+ 4 -fed side of the split root, and that this part of the root was transporting assimilatory products to the tops of the plants in a fashion analogous to that of a nitrogen-fixing nodule. These data implicate the involvement of NH+ 4 in the induction of its own assimilatory pathway. 相似文献
2.
We report a novel use of the 15 N dilution technique to detail the translocation of amino compounds in the legume Sesbania rostrata . The conventional 15 N dilution technique follows the dilution of 15 N within a labelled plant, as 14 N2 is fixed by symbiotic bacteria. In our experiments, stem-nodulated Sesbania rostrata were enriched by feeding with 15 N ammonium nitrate for 2 weeks, followed by a 1 week period where the only N available to the plants was via nitrogen fixation of atmospheric N2 . We measured the composition, concentration and 15 N enrichment of amino compounds in various plant tissues, both above and below the stem nodules, using GC-MS and isotopic abundance mass spectrometry techniques. Approximately 28% of the total N in the stem nodules was derived from internal plant sources. The ureides allantoic acid and allantoin were not abundant in xylem, leaf or nodule tissues. The amides asparagine and glutamine were the major export products from stem nodules although a wide range of other amino compounds are also synthesized. Amino acids within the nodules had a low level of enrichment, demonstrating that a small fraction (≈ 11%) was derived from outside the nodules, and significant cycling of N (28% of xylem N) through the root system was revealed by measurements of 15 N distribution and amino acid concentrations. 相似文献
3.
Abstract. The principal polyamines in Alnus glutinosa roots, nodules and root pressure sap, putrescine, spermidine and spermine, were quantified by reversed-phase, high-performance liquid chromatography with fluorescence detection following precolumn derivatization with 9-fluorenylmethyl chloroformate and 1-ada-mantanamine. Putrescine was the major component of all tissues and sap. It comprised 70% or more of the polyamine pool except in roots of KNO3 -fed plants, in which similar amounts of putrescine and spermidine were present at levels five-fold lower than plants fed (NH4 )2 SO4 . Polyamine levels in nodules were 50% greater than in roots. The polyamine content of roots and nodules was not altered significantly when the nitrogen nutrition was changed from sole reliance on nitrogen fixation to partial or complete utilization of (NH4 )2 SO4 . However, the polyamine content of root pressure sap from nodulated plants increased almost four-fold when they were fed with increasing concentrations of NH4 NO3 , although the total polyamine content remained low (5mmol m−3 sap). The polyamine content of the Alnus root system changed with plant age. In particular, the spermidine content of both roots and nodules was higher in 10- as compared to 16-week-old plants. 相似文献
4.
Nitrogen fixation and nodule permeability to O2 diffusion are decreased by drought stress. Since γ‐aminobutyric acid (GABA) synthesis is rapidly stimulated by a variety of stress conditions including hypoxia, it was hypothesized that decreased O2 availability in nodules stimulates glutamate decarboxylase (GAD) activity (EC 4.1.1.15), thereby resulting in GABA accumulation. First, the amino acid composition of xylem sap was determined in plants subjected to soil water deficits. While the xylem sap concentration of several amino acids increased when the plant was subjected to a water deficit, the greatest increase was in GABA. GABA accumulation was examined in response to stress induced by hypoxia or the addition of polyethylene glycol (PEG) to the nutrient solution. The exposure of soybean nodules to hypoxia for 6 h enhanced the GABA concentration by 6‐fold, but there was no change in GABA concentration in response to the PEG treatment. No major changes in the in vitro GAD activity were measured in nodule cytosol or bacteroids. The present data do not support the hypothesis that decreased nodule O2 permeability and a resulting O2 deprivation inside nodules may stimulate in vitro GAD activity and thus GABA accumulation. However, the data could indicate a possible effect of hypoxia and drought stress on the in vivo activity of GAD. 相似文献
5.
Seasonal patterns of N translocation in the xylem sap of Betula pendula were studied, to determine whether specific amino acids were recovered in spring as a consequence of N remobilization. Seedlings were grown in sand culture and provided with 15 NH4 15 NO3 (at 2·2 atom percent excess) for one growing season. The following winter dormant trees were transplanted into fresh sand and given N at natural abundance thereafter. Destructive harvests were taken during bud burst and leaf growth to determine the pattern of 15 N remobilization and N uptake, along with isolation of xylem sap for analysis of their amino acid profiles and 15 N enrichment by GC-MS. 15 N remobilization occurred immediately following bud burst, while N derived from root uptake did not appear in the leaves until 12 d after bud burst. During N remobilization there was a 10-fold increase in the concentration of N in the xylem sap, due predominantly to increases in citrulline and glutamine. The 15 N enrichment of these two amino acids demonstrated the increase in their concentration in the xylem sap following bud burst was due to N remobilization. These results are discussed in relation to measuring N remobilization and storage capacity of trees in the field. 相似文献
6.
Oxygen and the regulation of nitrogen fixation in legume nodules 总被引:3,自引:0,他引:3
In N2 -fixing legume nodules, O2 is required in large amounts for aerobic respiration, yet nitrogenase, the bacterial enzyme that fixes N2 , is O2 labile. A high rate of O2 consumptition and a cortical barrier to gas diffusion work together to maintain a low, non-inhibitory O2 concentration in the central, infected zone of the nodule. At this low O2 concentration, cytosolic leghemoglobin is required to facilitate the diffusion of O2 through the infected cell to the bacteria. The resistance of the cortical diffusion barrier is variable and is used by legume nodules to regulate the O2 concentration in the infected cells such that it limits aerobic respiration and N2 fixation at all times. The resistance of the diffusion barrier and therefore the degree of O2 limitation seems to be regulated in response to changes in the O2 concentration of the central infected zone, the supply of phloem sap to the nodule, and the rate of N assimilation into the end products of fixation. 相似文献
7.
Published data on, and hypotheses regarding the effect of NO− 3 on functioning of legume root nodules are reviewed. It is concluded that a short-term reversible effect of NO− 3 may act via an increased resistance to O2 diffusion in nodules; this is coupled to decreased bacteroid respiration. For longer exposures to NO− 3 nodule activity is irreversibly lost, but how this relates to carbohydrate deprivation or NO-2 accumulation is unclear. Complicating factors include denitrification reactions and the interaction of NO− 2 with leghaemoglobin. 相似文献
8.
Assimilation of N by heterotrophic soil microbial biomass is associated with decomposition of organic matter in the soil. The form of N assimilated can be either low molecular weight organic N released from the breakdown of organic matter (direct assimilation), or NH+ 4 and NO− 3 from the soil inorganic N pool, into which mineralized organic N is released (mineralization immobilization turnover). The kinetics of C and N turnover in soil is quantifiable by means of computer simulation models. NCSOIL was constructed to represent the two assimilation schemes. The rate of N assimilation depends on the rate of C assimilation and microbial C/N ratio, thereby rendering it independent of the assimilation scheme. However, if any of the N forms is labeled, a different amount of labeled N assimilation will be simulated by the different schemes. Experimental data on inorganic N and 15 N and on organic 15 N dynamics in soils incubated with 15 N added as NH+ 4 or organic N were compared with data simulated by different model schemes. Direct assimilation could not account for the amount of 15 N assimilated in any of the experimental treatments. The best fit of the model to experimental data was obtained for the mineralization immobilization turnover scheme when both NH+ 4 and NO− 3 were assimilated, in proportion to their concentration in the soil. 相似文献
9.
In Myrica gale L. plants the assimilation of ammonia released by symbiotic Frankia was observed by 15 N2 labelling and subsequent analysis of the isotopic enrichment of nodule amino acids over time by single ion monitoring gas chromatography-mass spectrometry. In detached nodules of Myrica , glutamine was the first amino acid labelled at 30 s and subsequently the amino acids glutamate, aspartate, alanine and γ-amino butyric acid (GABA) became labelled. This pattern of labelling is consistent with the incorporation of ammonium via glutamine synthetase [GS; EC 6.3.1.2]. No evidence for the ammonium assimilation via glutamate dehydrogenase [GDH; EC 1.4.1.2] was observed as glutamate became labelled only after glutamine. Using attached nodules and pulse-chase labelling, we observed synthesis of glutamine, glutamate, aspartate, alanine, GABA and asparagine, and followed the transport of fixed nitrogen in the xylem largely as glutamine and asparagine. Estimation of the cost of nitrogen fixation and asparagine synthesis in Myrica nodules suggests a minimum of one sucrose required per asparagine produced. Rapid translocation of recently fixed nitrogen was observed in Myrica gale nodules as 80% of the nitrogen fixed during a 1-h period was translocated out of the nodules within 9 h. The large pool of asparagine that is present in nodules may buffer the transport of nitrogen and thus act to regulate nitrogen fixation via a feedback mechanism. 相似文献
10.
Abstract. Presence of 2.4-diaminobutyric acid (A2 bu), a neurotoxin, in tissues of flatpea ( Lathyrus sylvestris L.) necessitates a thorough understanding of the regulation of this nonprotein amino acid before the species can be recommended to livestock producers for forage applications. To determine how different concentrations and ratios of NO3 and NH+ 4 in growth media influence the levels of A2 bu and other free amino acids in the 'Lathco'flatpea cultivar, plants were grown hydroponically in controlled environments. The concentration of A2 bu was highest in tissues when the NO3 to NH+ 4 ratio in the nutrient solution was low. Responses of amides and other nonprotein amino acids, especially in the roots, followed a similar trend. Free protein amino acids in leaves and stems were generally unaffected by changes in NO3 to NH+ 4 ratios. In roots, protein amino acids increased as the NO3 to NH+ 4 ratio in the growth medium increased. Ammonium inhibited shoot and root growth; NO3 alleviated the toxic effects of NH+ 4 . Soluble protein concentrations were higher in the shoots of NO3 -fed plants and in the roots of plants supplied with NH+ 4 . These results suggest that accumulation of A2 bu and other nonprotein amino acids, as well as asparagine and glutamine, plays a role in detoxification of NH+ 4 and storage of N. 相似文献
11.
The effect of N-source on the interaction between carbon and nitrogen metabolism was evaluated by measuring phosphoenolpyruvate carboxylase (PEPcase; EC 4.1.1.31) activity in callus tissue of maize ( Zea mays L. cv. Prisma) sub-cultured under different N-nutrition conditions: nitrate, ammonium or combinations of both. By comparison with the condition where both salts were supplied (control), nitrate as the sole N-source led to an increase in PEPcase activity. Ammonium alone gave a drastic decrease of tissue growth. Extracts from calli grown on equivalent media supplied with 15 N-nitrate or 15 N-ammonium were analysed by 15 N-NMR. The labelling of amino acids in the NMR spectra showed that when 15 NO− 3 was the unique N-source, 15 N mainly accumulated in NδGln, Glu and Ala. With 15 NH+ 4 only the NδGln and γ-aminobutyric acid were labelled. The addition of both gave rise to labelled Gln, Asn, Glu, Asp, Ala, Val and γ-aminobutyric acid independently of the origin of the label. In vivo 31 P-NMR allowed the cytoplasmic and vacuolar pH to be measured. The cytoplasmic pH showed an increase of approximately 0.3 units when nitrate was the sole source of nitrogen and a corresponding decrease when ammonium was added alone. Vacuolar pH decreased in both treatments. These results are discussed on the basis of the effect of the N-source on carbon metabolism. A hypothesis of PEPcase activation as due to the increase of cytoplasmic pH upon nitrate uptake is proposed. 相似文献
12.
Vance, C. P., Reibach, P. H. and Pankhurst, C. E. 1987. Symbiotic properties of Lotus pedunculatus root nodules induced by Rhizobium loti and Bradyrhizobium sp. ( Lotus ).
Symbiotic properties of root nodules were evaluated in glasshouse-grown Lotus pedunculatus Cav. cv. Maku inoculated with either a fast-growing Rhizobium loti strain NZP2037 or a slow-growing Bradyrhizobium sp. ( Lotus ) strain CC814s. Although the nodule mass of plants inoculated with NZP2037 was twice that of plants inoculated with CC814s, the yield of NZP2037 shoots and roots was 50% that of CC814s shoots and roots. Nodules induced by Bradyrhizobium fixed substantially more N than nodules induced by R. loti. Glucose requirements [mol glucose (mol N2 fixed)-1 ] of nodules induced by CC814s and NZP2037 were 7.1 and 16.6, respectively. Nodule enzymes of carbon and nitrogen assimilation reflected the disparity of the two sym-bioses. Xylem sap of the symbiosis with the higher yield contained a higher concentration of asparagine [9.86 μmol (ml xylem sap)'] than did the lower yielding symbiosis [5.80 umol (ml xylem sap)"']. Nodule CO2 fixation was directly linked to nodule N assimilation in both symbioses. The results indicate that the difference between the two symbioses extend to nodule N and C assimilation and whole plant N transport. The data support a role for host plant modulation of bacterial efficiency and assimilation of fixed N. 相似文献
Symbiotic properties of root nodules were evaluated in glasshouse-grown Lotus pedunculatus Cav. cv. Maku inoculated with either a fast-growing Rhizobium loti strain NZP2037 or a slow-growing Bradyrhizobium sp. ( Lotus ) strain CC814s. Although the nodule mass of plants inoculated with NZP2037 was twice that of plants inoculated with CC814s, the yield of NZP2037 shoots and roots was 50% that of CC814s shoots and roots. Nodules induced by Bradyrhizobium fixed substantially more N than nodules induced by R. loti. Glucose requirements [mol glucose (mol N
13.
Salt stress induces a decrease in the oxygen uptake of soybean nodules and in their permeability to oxygen diffusion 总被引:5,自引:0,他引:5
The effects of short-term NaCl-salinity on nodules of soybean ( Glycine max L. cv. Kingsoy) were studied on hydroponically-grown plants. Both acetylene reducing activity (ARA) and nodule respiration (O2 uptake and CO2 evolution) were immediately inhibited, and the stimulation of them by rising the external partial pressure of O2 (pO2 ) was diminished by the application of 0.1 M NaCl in the nutrient solution. The permeability of the nodule to O2 diffusion, estimated by O2 consumption or CO2 evolution, was significantly lower in the stressed nodules than in the cootrol ones. The respiratory quotient of intact nodules and the ethanol production of excised nodules were increased by low pO2 and by salt stress. These data confirm that in salt-stressed soybean nodules, O2 availability is reduced and fermentative pathways are stimulated. 相似文献
14.
Addition of NO− 3 rapidly induced senescence of root nodules in alfalfa ( Medicago sativa L. cv. Aragon). Loss of nodule dry matter began at the lowest NO− 3 concentration (10 m M ) but degradation of bacteroid proteins was only detected when nodules were supplied with NO− 3 concentrations above 20 m M .
Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate-induced although substantial enzyme activities were present in the absence of NO− 3 Typical specific activities for soluble NR and NiR of bacteroids under NO− 3 free conditions were 1.2 and 1.4 μmol (mg protein)−1 h−1 , respectively. In the presence of NO− 3 , the specific activity of NR was considerably greater than that of NiR, thus causing NO− 2 accumulation in bacteroids. Nitrite levels in the bacteroids were linearly correlated with specific activities of NR and NiR, indicating that NO− 2 is formed by bacteroid NR and that this NO− 2 in turn, induces bacteroid NiR. Accumulation of NO− 2 within bacteroids also indicates that NO− 2 inhibits nodule activity after feeding plants with NO− 3 相似文献
Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate-induced although substantial enzyme activities were present in the absence of NO
15.
S. Abarzua R. Altenburger R. Callies L.-H. Grimme A. Mayer D. Leibfritz U. Schiewer 《Physiologia plantarum》1993,89(3):659-663
Over a period of several days, rhythmic changes in extracellular NH+ 4 concentration take place in cultures of the cyanobacterium Microcystis firma (Bré et Lenorm.) Schmidle, strain Gromov/St. Petersb. 398, under conditions of restricted CO2 supply and light/dark alternation. The changes are enhanced by nitrate supply. Among the various processes generating intracellular NH+ 4 (NH4 4 uptake, NO− 3 reduction, protein and amino acid degradation, photorespiration), NO− 3 reduction appears as the one most important. This can be concluded from experiments with and without nitrate and/or ammonium in the medium. In the presence of saturating CO2 , continuous light, or continuous darkness, rhythmic NH+4 4 oscillations are not induced. Studies of the incorporation of NH+ 4 nitrogen by in vivo 15 N-NMR show that if CO2 is supplied, 15 N is accumulated in several components with the following time course: in the first hour in Gln (δ), in the second hour in the α-amino groups of most nonbranched amino acids, in the third hour in γ-aminobutyric acid (GABA), Orn (δ) and Lys (ε), and in the sixth hour in Ala. Carbon limitation, however, results in accumulation of label in the amide nitrogen of glutamine only. 相似文献
16.
Nitrogen fixation by the unicellular cyanobacterium Gloeothece. Nitrogenase synthesis is only transiently repressed by oxygen 总被引:2,自引:0,他引:2
Paul S. Maryan Robert R. Eady Alan E. Chaplin John R. Gallon 《FEMS microbiology letters》1986,34(3):251-255
Abstract The extent of recovery of nitrogenase activity of Gloeothece transferred from an atmosphere of O2 to air depended on the duration of exposure to O2 . Activity recovered at increasing rates after up to 24 h exposure to O2 and a lag before detection of activity, present after short (1 h) exposure times, disappeared with longer exposures. Synthesis of nitrogenase de novo was implicated, since chloramphenicol, tetracycline, or repressive levels of NH+ 4 , prevented recovery of activity. Specific radioimmunoassay of the rate of synthesis of the MoFe protein of nitrogenase under O2 correlated well with the activity measurements, and indicate that a shift from air to O2 only transiently represses nitrogenase synthesis. 相似文献
17.
Nitrogenase (N2 ase; EC 1.18.6.1) activity (H2 evolution) and root respiration (CO2 evolution) were measured under either N2 :O2 or Ar:O2 gas mixtures in intact nodulated roots from white clover ( Trifolium repens L.) plants grown either as spaced or as dense stands. The short-term nitrate (5 m M ) inhibition of N2 -fixation was promoted by competition for light between clover shoots, which reduced CO2 net assimilation rate. Oxygen-diffusion permeability of the nodule declined during nitrate treatment but after nitrate removal from the liquid medium its recovery parallelled that of nitrogenase activity. Rhizosphere pO2 was increased from 20 to 80 kPa under N2 :O2 . A simple mono-exponential model, fitted to the nodule permeability response to pO2 , indicated NO− 3 induced changes in minimum and maximum nodule O2 -diffusion permeability. Peak H2 production rates at 80 kPa O2 and in Ar:O2 were close to the pre-decline rates at 20 kPa O2 . At the end of the nitrate treatment, this O2 -induced recovery in nitrogenase activity reached 71 and 82%; for clover plants from spaced and dense stands, respectively. The respective roles of oxygen diffusion and phloem supply for the short-term inhibition of nitrogenase activity in nitrate-treated clovers are discussed. 相似文献
18.
Major nitrogen compounds transported in xylem vessels from roots to top in Citrus trees 总被引:1,自引:0,他引:1
Tadashi Kato 《Physiologia plantarum》1981,52(2):275-279
Four-year-old citrus trees ( Citrus unshiu Marcovitch) were fed via the roots with (15 NH4 )2sO4 or K15 NO3 as a nitrogen source. Nitrogenous compounds and their isotopic abundances in fine roots and xylem sap from trunks were assayed in order to obtain information on the species of nitrogen released by the root system into the ascending xyiem stream.
Arginine, asparagine, nitrate and proline in xylem sap accounted for 48, 21, 13 and 10%, respectively, of the total nitrogenous constituents tested in the sap. However, in the trees fed with labelled ammonium the main nitrogenous compound labelled with15 N in the xylem sap was asparagine and glutamine, which accounted for 79% and 18%, respectively, of total labelled nitrogen. In the xylem sap of trees fed with labelled nitrate, nitrate accounted for 94% of total labelled nitrogen. Nitrate and asparagine followed by glutamine showed the highest ratios of isotopic abundance in xylem sap as compared to fine roots. Proline and arginine had much lower ratios. These results indicate that nitrate, asparagine and glutamine are the main nitrogenous compounds released by the roots to the xylem stream, whereas arginine and proline are released into the xylern vessels by the trunk tissues. Furthermore, nitrate and asparagine are probably in steady movement upward in the trunk xylem, whereas glutamine is more easily taken up by the trunk tissues than nitrate and asparagine. 相似文献
Arginine, asparagine, nitrate and proline in xylem sap accounted for 48, 21, 13 and 10%, respectively, of the total nitrogenous constituents tested in the sap. However, in the trees fed with labelled ammonium the main nitrogenous compound labelled with
19.
Jesús A. G. Ochoa de Alda María I. Tapia Fabrice Franck María J. Llama Juan L. Serra 《Physiologia plantarum》1996,97(1):69-78
In an attempt to clarify the interactions between the available nitrogen source and the photosystems in cyanobacteria, O2 exchange and fluorescence emission were monitored in spheroplasts and intact cells of the non N2 -fixing cyanobacterium Phormidium laminosum (strain OH-1-p.Cl1 ) growing on different nitrogen sources or in the absence of nitrogen. Short-term (time scale of seconds to minutes), NH+ 4 addition to NO− 3 -growing or N-starved cells and, to a minor extent, NO− 3 addition to N-starved cells, induced state 2 transitions both in light and dark. Long term (time scale of days), the fluorescence yield of PSII relative to that of PSII at 77 K was higher in NO− 3 - than in NH+ 4 growing cells, and even higher in N-starved cells. In the dark, the plastoquinone pool was more reduced in NH+ 4 - than in NO− 3 -growing cells. Both PSII and PSI activities and the degree of linking between both photosystems were affected in the long term, so that non-cyclic electron transport decreased in parallel to the ferredoxin requirement to assimilate each nitrogen source. Results indicate that nitrogen metabolism exerts short- and long-term control over the photosynthetic apparatus, which acclimates to the energy requirement of the available nitrogen source. 相似文献
20.
Andrés P. Sanz Conrado Moreno-Vivián José M. Maldonado Agustín González-Fontes 《Physiologia plantarum》1995,95(1):39-44
The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied in Anabaena variabilis ATCC 29413 cells grown under a constant supply of either N, NO− 3 or NH+ 4 at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO− 3 or NH+ 4 concentrations in the medium. In cultures containing 0.1 m M NO− 3 or 0.1 m M NH+ 4 nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2 -grown cells. This activity was still present with 1 m M NO− 3 or 1 m M NH+ 4 in the medium and even with 10 m M NO− 3 , but it was completely inhibited by 5 m M NH+ 4 . Ferredoxin-nitrate reductase (EC 1.7.7.2) activity was detected only in NO− 3 grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+ 4 , promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+ -isocitrate dehydrogenase (EC 1.1.1.42), and NAD+ -malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon-nitrogen metabolism in cyanobacteria. 相似文献