共查询到20条相似文献,搜索用时 31 毫秒
1.
Pisum arvense plants were subjected to 5 days of nitrogen deprivation. Then, in the conditions that increased or decreased the root glutamine
and asparagine pools, the uptake rates of 0.5 mM NH 4
+ and 0.5 mM K + were examined. The plants supplied with 1 mM glutamine or asparagine took up ammonium and potassium at rates lower than those
for the control plants. The uptake rates of NH 4
+ and K + were not affected by 1 mM glutamate. When the plants were pre-treated with 100 μM methionine sulphoximine, an inhibitor of
glutamine synthesis, the efflux of NH 4
+ from roots to ambient solution was enhanced. On the other hand, exposure of plants to methionine sulphoximine led to an increase
in potassium uptake rate. The addition of asparagine, glutamine or glutamate into the incubation medium caused a decline in
the rate of NH 4
+ uptake by plasma membrane vesicles isolated from roots of Pisum arvense, whereas on addition of methionine sulphoximine increased ammonium uptake. The results indicate that both NH 4
+ and K + uptake appear to be similarly affected by glutamine and asparagine status in root cells.
The research was supported by grant of KBN No. 6PO4C 068 08 相似文献
2.
The initial product of fixation of [ 13N]N 2 by pure cultures of the reconstituted symbiotic association between Anthoceros punctatus L. and Nostoc sp. strain ac 7801 was ammonium; it accounted for 75% of the total radioactivity recovered in methanolic extracts after 0.5 min and 14% after 10 min of incubation. Glutamine and glutamate were the primary organic products synthesized from [ 13N]N 2 after incubation times of 0.5–10 min. The kinetics of labeling of these two amino acids were characteristic of a precursor (glutamine) and product (glutamate) relationship. Results of inhibition experiments with methionine sulfoximine (MSX) and diazo-oxonorleucine were also consistent with the assimilation of N 2-derived NH
4
+
by Anthoceros-Nostoc through the sequential activities of glutamine synthetase (EC 6.3.1.2) and glutamate synthase (EC 1.4.7.1), with little or no assimilation by glutamate dehydrogenase (EC 1.3.1.3). Isolated symbiotic Nostoc assimilated exogenous 13NH
4
+
into glutamine and glutamate and their formation was inhibited by MSX, indicating operation of the glutamine synthetase-glutamate synthase (GS-GOGAT) pathway: However, relative to free-living cultures, isolated symbiotic Nostoc assimilated 80% less exogenous ammonium into glutamine and glutamate, implying that symbiotic Nostoc could assimilate only a fraction of N 2-derived NH
4
+
. This implication was tested by using Anthoceros associations reconstituted with wild-type or MSX-resistant strains of Nostoc incubated with [ 13N]N 2 in the presence of MSX. The results of these experiments indicated that, in situ, symbiotic Nostoc assimilated about 10% of the N 2-derived NH
4
+
and that NH
4
+
was made available to Anthoceros tissue where it was apparently assimilated by the GS-GOGAT pathway. Since less than 1% of the fixed N 2 was lost to the suspension medium, it appears that transfer of NH
4
+
from symbiont to host tissue was very efficient in this extracellular symbiotic association.Abbreviations DON
6-diazo-5-oxo- l-norleucine
- GDH
glutamate dehydrogenase
- GOGAT
glutamate synthase
- GS
glutamine synthetase
- MSX
l-methionine- dl-sulfoximine 相似文献
3.
Phosphinothricin (glufosinate), an irreversible inhibitor of glutamine synthetase, causes an inhibition of photosynthesis in C 3 ( Sinapis alba) and C 4 ( Zea mays) plants under atmospheric conditions (400 ppm CO 2, 21% O 2). This photosynthesis inhibition is proceeding slower in C 4 leaves. Under non-photorespiratory conditions (1000 ppm CO 2, 2% O 2) there is no inhibition of photosynthesis. The inhibition of glutamine synthetase by phosphinothricin results in an accumulation of NH 4
+. The NH 4
+-accumulation is lower in C 4 plants than in C 3 plants. The inhibition of glutamine synthetase through phosphinothricin in mustard leaves results in a decrease in glutamine, glutamate, aspartate, asparagine, serine, and glycine. In contrast to this, a considerable increase in leucine and valine following phosphinothricin treatment is measured. With the addition of either glutamine, glutamate, aspartate, glycine or serine, photosynthesis inhibition by phosphinothricin can be reduced, although the NH 4
+-accumulation is greatly increased. This indicates that NH 4
+-accumulation cannot be the primary cause for photosynthesis inhibition by phosphinothricin. The investigations demonstrate the inhibition of transmination of glyoxylate to glycine in photorespiration through the total lack of amino donors. This could result in a glyoxylate accumulation inhibiting ribulose-1,5-bisphosphate-carboxylase and consequently CO 2-fixation.Abbreviations GOGAT
glutamine-2-oxoglutarate-amidotransferase
- GS
glutamine synthetase
- PPT
phosphinothricin
- MSO
methionine sulfoximine
- RuBP
ribulose-1,5-bisphosphate 相似文献
4.
The effects of inorganic nutrient (ammonium [NH 4 + ] and nitrate [NO 3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N 2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO 3 − , or NH 4 + did not affect short-term rates of N 2 fixation. This may be an important factor that allows for continued N 2 fixation in oligotrophic areas where recycling processes are active. N 2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH 4 + , NO 3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO 3 − , proportional increases in NO 3 − uptake and decreases in N 2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH 4 + , NO 3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH 4 + , glu, or gln. Cells incubated with NH 4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N 2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N 2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N 2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH 4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N 2 and take up NH 4 + and how natural populations continue to fix N 2 once combined N concentrations increase within a bloom. 相似文献
5.
To investigate the role of ammonium-assimilating enzyme in heterocyst differentiation, pattern formation and nitrogen fixation, MSX-resistant and GS-impaired mutants of Anabaena 7120 were isolated using transposon (Tn5-1063) mutagenesis. Mutant Gs1 and Gs2 (impaired in GS activity) exhibited a similar rate of nitrogenase activity compared to that of the wild type under dinitrogen aerobic conditions in the presence and absence of MSX. Filaments of Gs1 and Gs2 produced heterocysts with an evenly spaced pattern in N 2-grown conditions, while addition of MSX altered the interheterocyst spacing pattern in wild type as well as in mutant strains. The wild type showed complete repression of heterocyst development and nitrogen fixation in the presence of NO 3
– or NH 4
+, whereas the mutants Gs1 and Gs2 formed heterocysts and fixed nitrogen in the presence of NO 3
– and NH 4
+. Addition of MSX caused complete inhibition of glutamine synthetase activity in wild type but Gs1 and Gs2 remained unaffected. These results suggest that glutamine but not ammonium is directly involved in regulation of heterocyst differentiation, interheterocyst spacing pattern and nitrogen fixation in Anabaena. 相似文献
6.
Addition of NH 4Cl at low concentrations to Azotobacter chroococcum cells caused an immediate cessation of nitrate uptake activity, which was restored when the added NH
4
+
was exhausted from the medium or by adding an NH
4
+
assimilation inhibitor, l-methionine- dl-sulfoximine (MSX) or l-methionine sulfone (MSF). In the presence of such inhibitors the newly-reduced nitrate was released into the medium as NH
4
+
. When the artificial electron donor system ascorbate/N-methylphenazinium methylsulfate (PMS), which is a respiratory substrate that was known to support nitrate uptake by A. chroococcum while inhibiting glutamine synthetase activity, was the energy source, externally added NH
4
+
had no effect on nitrate uptake. It is concluded that, in A. chroococcum cells, NH
4
+
must be assimilated to exert its short-term inhibitory effect on nitrate uptake. A similar proposal was previously made to explain the short-term ammonium inhibition of N 2 fixation in this bacterium.Abbreviations MOPS
morpholinopropanesulfonic acid
- MSX
l-methionine- dl-sulfoximine
- PMS
N-methylphenazinium methylsulfate
- MSF
l-methionine sulfone 相似文献
7.
Ion-selective microelectrodes were used to measure NH 4+, NO 3– and H + fluxes along the primary root of maize seedlings. Plants were exposed to nutrient solutions containing NH 4+, NO 3– or both ions. Nitrogen fluxes along the root varied substantially among the different treatments. Net NH 4+ and NO 3– uptake and H + extrusion were low at the very apex of the root and generally increased in the more basal regions. In the absence of nitrogen or in the presence of NO 3– alone, net H + uptake (and root surface alkalinization) occurred at the root tip (0–1 mm), whereas net H + extrusion occurred in all other regions. In the presence of NH 4+ alone, a dramatic increase in net H + extrusion was detected in all regions except for the region 6–11 mm from the apex. In contrast, when NO 3– alone was supplied, net H + extrusion was depressed at all locations except for the tip (0–1 mm). When both NH 4+ and NO 3– were supplied, NO 3– uptake was suppressed at all locations while net H + extrusion was increased relative to NO 3– alone. The capacities to absorb NH 4+ and NO 3– at the tip were similar, as indicated by flux rates when NH 4+ or NO 3– were supplied as sole sources, but when supplied together, net NO 3– uptake was half that of net NH 4+ uptake, indicating that NH 4+ may satisfy the nitrogen requirements of the poorly vascularized apical tissue in the most energy-efficient way. The high spatial resolution of the measurements enabled us to establish that acidification in the root expansion zone is maintained regardless of nitrogen source. 相似文献
8.
Growth, chemical composition, and nitrate reductase activity (NRA) of hydroponically cultured Rumex crispus, R. palustris, R. acetosa, and R. maritimus were studied in relation to form (NH 4
+, NO 3
-, or both) and level of N supply (4 m M N, and zero-N following a period of 4m M N). A distinct preference for either NH 4
+ or NO 3
- could not be established. All species were characterized by a very efficient uptake and utilization of N, irrespective of
N source, as evident from high concentrations of organic N in the tissues and concurrent excessive accumulations of free NO 3
- and free NH 4
+. Especially the accumulation of free NH 4
+ was unusually large.
Generally, relative growth rate (RGR) was highest with a combination of NH 4
+ and NO 3
-. Compared to mixed N supply, RGR of NO 3
-- and NH 4
+-grown plants declined on average 3% and 9%, respectively. Lowest RGR with NH 4
+ supply probably resulted from direct or indirect toxicity effects associated with high NH 4
+ and/or low Ca 2+ contents of tissues. NRA in NO 3
- and NH 4NO 3 plants was very similar with maxima in the leaves of ca 40 μmol NO 2
- g -1 DW h -1. ‘Basal’ NRA levels in shoot tissues of NH 4
+ plants appeared relatively high with maxima in the leaves of ca 20 μmol NO 2
- g -1 DW h -1. Carboxylate to organic N ratios, (C-A)/N org, on a whole plant basis varied from 0.2 in NH 4
+ plants to 0.9 in NO 3
- plants.
After withdrawal of N, all accumulated NO 3
- and NH 4
+ was assimilated into organic N and the organic N redistributed on a large scale. NRA rapidly declined to similar low levels,
irrespective of previous N source. Shoot/root ratios of -N plants were 50–80% lower than those from +N plants. In comparison
with +N, RGR of -N plants did not decline to a large extent, decreasing by only 15% in -NH 4
+ plants due to very high initial organic-N contents. N-deprived plants all exhibited an excess cation over anion uptake (net
proton efflux), and whole-plant (C-A)/N org ratios increased to values around unity.
Possible difficulties in interpreting the (C-A)/N org ratio and NRA of plants in their natural habitats are briefly discussed. 相似文献
9.
The effects of metabolic and protein synthesis inhibitors on NH 4
+ uptake by Pisum arvense plants at low (0.05 mM) and high (1 mM) external ammonium concentration were studied. In short-time experiments cycloheximide
decreased the ammonium uptake rate at low level of NH 4
+ and increased the absorption of NH 4
+ from uptake medium containing high ammonium concentration. Arsenate and azide supplied into uptake solutions at low ammonium
concentration strongly decreased or completely suppressed the NH 4
+ uptake rate, respectively. When the experiments were carried out at high level of ammonium only azide decreased the uptake
rate of NH 4
+ and arsenate stimulated this process. Dinitrophenol very strongly repressed the uptake rate of NH 4
+ at both ammonium concentrations. After removing dinitrophenol from both solutions, neither at low nor high external ammonium
level the recovery of NH 4
+ uptake rate was achieved within 150 min or 3 h, respectively. The recovery of NH 4
+ uptake rate after removing azide was observed within 90 min and 3 h at low and high ammonium concentrations, respectively.
The regulation of NH 4
+ uptake by some inhibitors at low external ammonium level was investigated using plasma membrane vesicles isolated from roots
by two-phase partitioning. Orthovanadate completely suppressed the uptake of NH 4
+ by vesicles and quinacrine decreased the NH 4
+ uptake which 55 suggests that ammonium uptake depends on activities of plasma membrane-bound enzymes. On the other hand,
it was found that dinitrophenol completely reduced the NH 4
+ uptake by vesicles.
The various effects of inhibitors on ammonium uptake dependent on external ammonium concentration suggest the action of different
ammonium transport systems in Pisum arvense roots. The ammonium transport into root cells at low NH 4
+ level requires energy and synthesis of protein in the cytoplasm.
The research was supported by grant of KBN No. 6PO4C 068 08 相似文献
10.
Ammonium assimilation was followed in N-starved mycelia from the ectomycorrhizal Ascomycete Cenococcum graniforme. The evaluation of free amino acid pool levels after the addition of 5 millimolar NH 4+ indicated that the absorbed ammonium was assimilated rapidly. Post-feeding nitrogen content of amino acids was very different from the initial values. After 8 hours of NH 4+ feeding, glutamine accounted for the largest percentage of free amino acid nitrogen (43%). The addition of 5 millimolar methionine sulfoximine (MSX) to NH 4+-fed mycelia caused an inhibition of glutamine accumulation with a corresponding increase in glutamate and alanine levels. Using 15N as a tracer, it was found that the greatest initial labeling was into glutamine and glutamate followed by aspartate, alanine, and ornithine. On inhibiting glutamine synthetase using MSX, 15N enrichment of glutamate, alanine, aspartate, and ornithine continued although labeling of glutamine was quite low. Moreover, the incorporation of 15N label in insoluble nitrogenous compounds was lower in the presence of MSX. From the composition of free amino acid pools, the 15N labeling pattern and effects of MSX, NH4+ assimilation in C. graniforme mycelia appears to proceed via glutamate dehydrogenase pathway. This study also demonstrates that glutamine synthesis is an important reaction of ammonia utilization. 相似文献
11.
Substantial concentrations of NH 4
+ are found in the apoplast of the leaves of Brassica napus. Physiological studies on isolated mesophyll protoplasts with 15NH 4
+ revealed the presence of a high-affinity ammonium transporter that shared physiological similarity to the high-affinity NH 4
+ transporters in Arabidopsis
thaliana ( AtAMT1;3). PCR techniques were used to isolate a full-length clone of a B. napus homologue of AMT1 from shoot mRNA which showed 97% similarity to AtAMT1;3. The full-length cDNA when cloned into the yeast expression vector pFL61 was able to complement a yeast mutant unable to grow on media with NH 4
+ as the sole nitrogen source. Regulatory studies with detached leaves revealed a stimulation of both NH 4
+ uptake and expression of mRNA when the leaves were supplied with increasing concentrations of NH 4
+. Withdrawal of NH 4
+ supply for up to 96 h had little effect on mRNA expression or NH 4
+ uptake; however, plants grown continuously at high NH 4
+ levels exhibited decreased mRNA expression. BnAMT1;2mRNA expression was highest when NH 4
+ was supplied directly to the leaf and lowest when either glutamine or glutamate was supplied to the leaves, which directly paralleled chloroplastic glutamine synthetase (GS2) activity in the same leaves. These results provide tentative evidence that BnAMT1;2may be regulated by similar mechanisms to GS2 in leaves. 相似文献
12.
The influence of NH 4+, in the external medium, on fluxes of NO 3− and K + were investigated using barley ( Hordeum vulgare cv Betzes) plants. NH 4+ was without effect on NO 3− ( 36ClO 3−) influx whereas inhibition of net uptake appeared to be a function of previous NO 3− provision. Plants grown at 10 micromolar NO 3− were sensitive to external NH 4+ when uptake was measured in 100 micromolar NO 3−. By contrast, NO 3− uptake (from 100 micromolar NO 3−) by plants previously grown at this concentration was not reduced by NH 4+ treatment. Plants pretreated for 2 days with 5 millimolar NO 3− showed net efflux of NO 3− when roots were transferred to 100 micromolar NO 3−. This efflux was stimulated in the presence of NH 4+. NH 4+ also stimulated NO 3− efflux from plants pretreated with relatively low nitrate concentrations. It is proposed that short term effects on net uptake of NO 3− occur via effects upon efflux. By contrast to the situation for NO 3−, net K + uptake and influx of 36Rb +-labeled K + was inhibited by NH 4+ regardless of the nutrient history of the plants. Inhibition of net K + uptake reached its maximum value within 2 minutes of NH 4+ addition. It is concluded that the latter ion exerts a direct effect upon K + influx. 相似文献
13.
It is commonly known that calcium promotes NO 3
- uptake in many crop species. However, calcium enhancement of NH 4
+ uptake by plants has received little attention. This study aimed to evaluate the effect of Ca supplements on NH 4
+ uptake and plant growth in solution cultured rice. Supplemental Ca applied at vegetative and reproductive phases of plant
ontogeny tended to stimulate NH 4
+ absorption, and accordingly resulted in a better straw and grain yield. However, excessively supplied Ca (400 ppm) was detrimental
to plant growth. Increases in straw and grain yield observed at Ca levels up to 300 ppm were linked to the Ca-enhanced activities
of glutamine synthetase (GS), glutamate synthase (GOGAT), and ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco). 相似文献
14.
Alfalfa ( Medicago sativa L.) N-sufficient plants were fed 1·5 mM N in the form of NO 3−, NH 4+ or NO 3− in conjunction with NH 4+, or were N-deprived for 2 weeks. The specific activity of phosphoenolpyruvate carboxylase (PEPC) from the non-nodulated roots of N-sufficient plants was increased in comparison with that of N-deprived plants. The PEPC value was highest with NO 3− nutrition, lowest with NH 4+ and intermediate in plants that were fed mixed salts. The protein was more abundant in NO 3−-fed plants than in either NH 4+- or N mixed-fed plants. Nitrogen starvation decreased the level of PEPC mRNA, and nitrate was the N form that most stimulated PEPC gene expression. The malate content was significantly lower in NO 3−-deprived than in NO 3−-sufficient plants. Root malate accumulation was high in NO 3−-fed plants, but decreased significantly in plants that were fed with NH 4+. The effect of malate on the desalted enzyme was also investigated. Root PEPC was not very sensitive to malate and PEPC activity was inhibited only by very high concentrations of malate. Asparagine and glutamine enhanced PEPC activity markedly in NO 3−-fed plants, but failed to affect plants that were either treated with other N types or N starved. Glutamate and citrate inhibited PEPC activity only at optimal pH. N-nutrition also influenced root nitrate and ammonium accumulation. Nitrate accumulated in the roots of NO 3−- and (NO 3− + NH 4+)-fed plants, but was undetectable in those administered NH 4+. Both the nitrate and the ammonium contents were significantly reduced in NO 3−- and (NO 3− + NH 4+)-starved plants. Root accumulation of free amino acids was strongly influenced by the type of N administered. It was highest in NH 4+-fed plants and the most abundant amides were asparagine and glutamine. It was concluded that root PEPC from alfalfa plants is N regulated and that nitrate exerts a strong influence on the PEPC enzyme by enhancing both PEPC gene expression and activity. 相似文献
15.
A release of ammonium by non-nitrogen-fixing Anabaena cylindrica (grown on NH 4Cl) in the presence of MSX (methionine sulfoximine) and absence of any external nitrogen source was found. In the light the release was maximal at 0.2 mM MSX, a concentration which did not affect net CO 2 fixation nor the glycollate excretion, but inhibited the glutamine synthetase activity and the reassimilation of ammonium. It is suggested that the major source of the ammonium released is the photorespiratory conversion of glycine to serine as (1) the release was stimulated by increase in light intensity, (2) high CO 2 (3%) lowered the release, if not given as a longer pretreatment (as CO 2 or HCO
3
-
) when a stimulation was observed, (3) glyoxylate and glutamate stimulated the release, the latter compound particularly under nitrogen-deficient conditions and (4) isonicotinic acid hydrazide caused a reduced release of ammonium. Furthermore, a substantial part of the ammonium released by N 2-fixing A. cylindrica in presence of MSX may thus originate from the glycollate pathway. The data show that in the light the glycine to serine conversion is active in cyanobacteria with a concomitant production of ammonium which is assimilated by glutamine synthetase.Abbreviations MSX
L-methionine- Dl-sulfoximine
- INH
isonicotinic acid hydrazide
- RuDP
ribulose 1,5-diphosphate
- Hepes
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- GS
glutamine synthetase
- GOGAT
glutamate synthase
- DTT
Dl-dithiothreitol 相似文献
16.
The cyanobacterium Anabaena variabilis showed a pH dependent uptake of ethylenediamine. No uptake of ethylenediamine was detected at pH 7.0. At higher pH values (e.g. pH 8.0 and pH 9.0) accumulation did occur and was attributed to diffusion of uncharged ethylenediamine in response to a pH gradient. A biphasic pattern of uptake was observed at these higher pH values. Treatment with l-methionine- d,l-sulphoximine (MSX) to inactivate glutamine synthetase (GS) inhibited the second slower phase of uptake without any significant alteration of the initial uptake. Therefore for sustained uptake, metabolism of ethylenediamine via GS was required. NH
4
+
did not alter the uptake of ethylenediamine. Ethylenediamine was converted in the second phase of uptake to an analogue of glutamine which could not be detected in uptake experiments at pH 7.0 or in uptake experiments at pH 9.0 following pretreatment of cells with MSX. Ethylenediamine treatment inhibited nitrogenase activity and this inhibition was greatest at high pH values.Abbreviations EDA
1,2-diaminoethane (ethylenediamine)
- GS
glutamine synthetase
- HEPES
4-(2-hydroxyethyl)-1 piperazine ethanesulphonic acid
- MSX
l-methionine- dl-sulphoximine
-
membrane potential
- Tricine
N-tris(hydroxymethyl) methylglycine 相似文献
17.
Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO 3
-, NH 4
+ or NH 4NO 3 with a total nitrogen concentration of 2.8 M m -3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO 3
-, NH 4
+ or NH 4NO 3. However, when NO 3
- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with 15NH 4NO 3 or NH 4
15NO 3 for 30 h, NH 4
+ uptake was generally twice as fast as NO 3
- uptake, even for plants grown in the presence of NO 3
-. Low rates of NO 3
- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO 3
-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH 4
+ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH 4
+ was the sole nitrogen source. 相似文献
19.
Glutamine auxotrophic ( Gln
-) and l-methionine d,l-sulfoximine (MSX) resistant ( MSX
r) mutants of N. muscorum were isolated and characterized for nitrogen nutrition, nitrogenase activity, glutamine synthetase (GS) activity and glutamine amide, -keto-glutarate amido transferase (GOGAT) activity. The glutamine auxotroph was found to the GOGAT-containing GS-defective, incapable of growth with N 2 or NH
4
+
but capable of growth with glutamine as nitrogen source, thus, suggesting GS to be the primary enzyme of both ammonia assimilation and glutamine formation in the cyanobacterium. The results of transformation and reversion studies suggests that glutamine auxotrophy is the result of a mutation in the gln A gene and that gln A gene can be transferred from one strain to another by transformation. 相似文献
20.
Summary Ethylenediamine (EDA) is toxic to the cyanobacterium Anabaena variabilis and inhibits nitrogenase activity. The inhibition of nitrogenase was prevented by pretreatment of cells with l-methionine- d,l-sulphoximine (MSX). Mutant strains of Anabaena variabilis (ED81, ED92), resistant to EDA, had low levels of glutamine synthetase (GS) biosynthetic activity compared with the wild type strain. ED92 had a low level of GS protein whereas ED81 had a similar level to that of the parent strain as estimated using antibodies against GS. Both strains fixed N 2 and liberated NH 4
+ into the media. Following immobilization of the mutant strains, sustained photoproduction of NH 4
+ was obtained in air-lift reactors at rates of up to 50 mol NH 4
+ mg chl a –1 h –1, which were comparable to the rates obtained when immobilized cyanobacteria were treated with MSX.Abbreviations EDA
1,2-diaminoethane (ethylenediamine)
- GS
glutamine synthetase
- MSX
l-methionine- d,l-sulphoximine 相似文献
|