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1.
Regulation of nitrogenase is not sufficiently understood to engineer symbioses that achieve a high N2 fixation rate under high levels of soil N. In the present hydroponic growth chamber study we evaluated the hypothesis that nitrogenase activity and the extent of its inhibition by NO3 − may be related to both N and carbohydrate levels in plant tissues. A wide range of C:N ratios in various plant tissues (8.5 to 41.0, 1.9 to 3.7, and 0.8 to 1.8, respectively, in shoots, roots, and nodules) was generated through a combination of light and CO2 levels, using two soybean genotypes differing in C and N acquisition rates. For both genotypes, N concentration in shoots was negatively correlated to nitrogenase activity and positively correlated to the extent of nitrogenase inhibition by NO3 − . Furthermore, nitrogenase activity was positively correlated to total nonstructural carbohydrates (TNC) and C:N ratio in shoot and nodules for both genotypes. Nitrogenase inhibition by NO3 − was negatively correlated to TNC and C:N ratio in shoots, but not in nodules for both genotypes. At the onset of nitrogenase inhibition by NO3 − , C:N ratio declined in shoots but not in nodules. These results indicate that both C and N levels in plant tissues are involved in regulation of nitrogenase activity. We suggest that the level of nitrogenase activity may be determined by (1) N needs (as determined by shoot C:N) and (2) availability of carbohydrates in nodules. Modulation of the nitrogenase activity may occur through sensing changes in plant N, i.e. changes in shoot C:N ratio, possibly through some phloem translocatable compound(s). 相似文献
2.
Regulation of nitrogenase is not sufficiently understood to engineer symbioses that achieve a high N2 fixation rate under high levels of soil N. In the present hydroponic growth chamber study we evaluated the hypothesis that nitrogenase activity and the extent of its inhibition by NO3 − may be related to both N and carbohydrate levels in plant tissues. A wide range of C:N ratios in various plant tissues (8.5 to 41.0, 1.9 to 3.7, and 0.8 to 1.8, respectively, in shoots, roots, and nodules) was generated through a combination of light and CO2 levels, using two soybean genotypes differing in C and N acquisition rates. For both genotypes, N concentration in shoots was negatively correlated to nitrogenase activity and positively correlated to the extent of nitrogenase inhibition by NO3 − . Furthermore, nitrogenase activity was positively correlated to total nonstructural carbohydrates (TNC) and C:N ratio in shoot and nodules for both genotypes. Nitrogenase inhibition by NO3 − was negatively correlated to TNC and C:N ratio in shoots, but not in nodules for both genotypes. At the onset of nitrogenase inhibition by NO3 − , C:N ratio declined in shoots but not in nodules. These results indicate that both C and N levels in plant tissues are involved in regulation of nitrogenase activity. We suggest that the level of nitrogenase activity may be determined by (1) N needs (as determined by shoot C:N) and (2) availability of carbohydrates in nodules. Modulation of the nitrogenase activity may occur through sensing changes in plant N, i.e. changes in shoot C:N ratio, possibly through some phloem translocatable compound(s). 相似文献
3.
Nitrate inhibits symbiotic N2 fixation and a number of hypotheses concerned with NO3 − assimilation have been suggested to explain this inhibition. These hypotheses were tested using a pea ( Pisum sativum L. cv. Juneau) with normal nitrate reductase NR; (EC 1,6,6,4) activity and two mutants of cv. Juneau, A317 and A334, with impaired NR activity. The plants were inoculated with three strains of Rhizobium leguminosarum and grown for 3 weeks in N-free medium, followed by 1 week in medium supplemented with 0, 5 or 10 m M KNO3 before harvesting. NO3 was taken up at comparable rates by the parent and the mutants and accumulated in leaf and stem tissue of the latter. Acetylene reduction rates were inhibited similarly in both the parent and mutants in the presence of KNO3 but there were differences among rhizobial strains. Starch concentration of the nodules decreased by 46% in the presence of KNO3 and there were differences among rhizobial strains but not among pea genotypes. Malate and succinate accumulated in nodules in the presence of KNO3 . These data are not consistent with the photosynthate deprivation hypothesis as a primary mechanism for NO3 inhibition of N2 fixation since NO3 affected the nodule carbohydrate composition of all three pea genotypes in a similar manner. The lack of correlation between NR activity and NO3 inhibition of N2 fixation suggests that NO3 assimilation may be only indirectly involved in the inhibition phenomenon. 相似文献
4.
L. M. Cervilla B. Blasco J. J. Ríos M. A. Rosales M. M. Rubio-Wilhelmi E. Sánchez-Rodríguez L. Romero & J. M. Ruiz 《Plant biology (Stuttgart, Germany)》2009,11(5):671-677
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
5.
The short term effect of NO3 − (12 mM) on nitrate reductase (NR. EC 1.6.6.1) activity has been studied in the roots, nodules and leaves of different genotypes of Vicia faba L. at the end of vegetative growth. Root and leaf NR activity responded positively to NO3 − while nodule activity, where detected, proved to he strongly inhibited. The withdraw of this NO3 − from the solution consistently reduced activity in the roots and leaves but surprising, promoted a significant increase in nodule activity, which matched or surpassed that of control plants On the other hand, nodules developed in the presence of 8 mM NO3 − expressed an on average 141% higher level of NR activity than did controls. This effect was observed even in nodules with negligible control activity. In any case, a naturally occurring mutant (VF17) lacking root and nodule NR activity is described. The results indicate that in V. faba. the effects of NO3 − and plant genotype on NR activity depended on plant organ and time of NO3 − application, hut the distribution of NO3 − reduction through the plain was mainly dependent on plant genotype, and to a lesser extent on NO: supply and plant age. 相似文献
6.
Nitrification and denitrification by Thiosphaera pantotropha in aerobic chemostat cultures 总被引:4,自引:0,他引:4
Abstract: Thiosphaera pantotropha has been reported to denitrify aerobically and nitrify heterotrophically. However, recent evidence has indicated that these properties (particularly aerobic denitrification) have been lost. The occurrence and levels of aerobic denitrification and heterotrophic nitrification by T. pantotropha in chemostat cultures have therefore been re-evaluated. Only low nitrate reduction rates were observed: the apparent nitrogen loss was of the same order of magnitude as the combined error in the calculated nitrogen consumption. However, 15 N mass spectrometry revealed low aerobic denitrification rates (about 10% of the rates originally published by this group). Heterotrophic nitrification rates were about a third of previous observations. N2 and N2 O were both produced from NH4 + , NO3 − and NO2 − . Periplasmic nitrate reductase was present in aerobically grown cells. 相似文献
7.
Abstract A methanotrophic nitrifying consortium was previously obtained from a humisol which showed CH4 -dependent nitrification. Although the methanotroph could not be obtained in pure culture, three other members of the consortium have been isolated: An obligately methylotrophic Methylobacillus (Is-1) which grows only on CH3 OH and does not nitrify; a Pseudomonas (Is-2) which grows on Is-1 culture filtrate and produces NO2 − , NO3 − and N2 O from NH2 OH, and NO3 − from NO2 − ; and a second Pseudomonas (Is-3) which produces NO3 − from NH4 + or NO2 − , and N2 O from NH2 OH. A model is proposed for the trophic relations and nitrogen transformations in the consortium which may apply to some natural systems. 相似文献
8.
Oxygen control prevents denitrifiers and barley plant roots from directly competing for nitrate 总被引:1,自引:0,他引:1
Abstract Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O2 concentration on denitrification and NO3 − uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O2 concentration in the solution. Both Pseudomonads lacked N2 O reductase and so total denitrification could be directly measured as N2 O production.
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O2 saturation (0.14 μM O2 ) and was totally inhibited at 0.04% O2 saturation (0.56 μM O2 ). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO3 − uptake rate decreased gradually from a maximum in 21% O2 -saturated medium (air saturated) to zero at 1.6% O2 saturation (22.4 μM O2 ). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur. 相似文献
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O
9.
The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3 − , no such increase could be detected in the needles. Detached seedlings placed in NO3 − solution showed increasing NR activities with increasing NO3 − concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2 − (g fresh weight)−1 h−1 to about 400 nmol NO2 − (g fresh weight)−1 h−1 . This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2 − (g fresh weight)−1 h−1 . Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx -fumigated seedlings compared to corresponding controls. 相似文献
10.
Abstract DNA probes of dissimilatory NO2 − - and N2 O-reductases have been used to screen for the distribution of denitrifying bacteria in soils. In control experiments with known organisms, denitrifiers gave positive DNA-DNA hybridization signals in the dot-blot experiments whereas non-denitrifiers did not hybridize in almost all cases. Bacteria from soil of our institute garden were isolated, grown up and assayed for denitrification activity and for DNA-hybridizations with both gene probes. A correlation of about 75% was obtained between activities and signals. The remainder of the isolates gave a weak signal in the dot blots and only half of them expressed denitrification activities in the cultures. The confidence of about 75% was good enough to assay for the distribution of denitrifying bacteria in five different soil-types of the Düsseldorf area. In all cases, the percentage of bacteria which gave no hybridization signal was high in the plant-free, bulk soil, whereas bacteria with strong or very strong signals favourably associated with the roots of plants isolated from the different soils. The result that denitrifying bacteria predominantly occur at the surface of roots was obtained when the samples were taken both in June and November. The probes for either NO2 − - or N2 O-reductase gave essentially the same results. For comparison, a gene probe for nitrogenase was included in this investigation. N2 -fixing bacteria showed a tendency to associate with the roots of plants in some but not in all soils. The overall number of bacteria was much higher at the roots of the plants than in the bulk soil in any of the samples assayed in the present investigation. 相似文献
11.
Biochemical characterization of nitrate and nitrite reduction in the wild-type and a nitrate reductase mutant of soybean 总被引:1,自引:0,他引:1
Enzyme activities involved in nitrate assimilation were analyzed from crude leaf extracts of wild-type (cv. Williams) and mutant ( nr1 ) soybean [ Glycine max (L.) Merr.] plants lacking constitutive nitrate reductase (NR) activity. The nr1 soybean mutant (formerly LNR-2), had decreased NADH-NR, FMNH2 -NR and cytochrome c reductase activities, all of which were associated with the loss of constitutive NR activity. Measurement of FMNH2 -NR activity, by nitrite determination, was accurate since nitrite reductase could not use FMNH2 as a reductant source. Nitrite reductase activity was normal in the nr1 plant type in the presence of reduced methyl viologen. Assuming that constitutive NR is similar in structure to nitrate reductases from other plants, presence of xanthine dehydrogenase activity and loss of cytochrome c reductase activity indicated that the apoprotein and not the molybdenum cofactor had been affected in the constitutive enzyme of the mutant. Constitutive NR from urea-grown wild-type plants had 1) greater ability to use FMNH2 as an electron donor, 2) a lower pH optimum, and 3) decreased ability to distinguish between NO3 − and HCO3 − , compared with inducible NR from NO3 − -grown nr1 plants. The presence in soybean leaves of a nitrate reductase with a pH optimum of 7.5 is contrary to previous reports and indicates that soybean is not an exception among higher plants for this activity. 相似文献
12.
Nitrate metabolism in the cyanobacterium Anabaena cycadeae: Regulation of nitrate uptake and reductase by ammonia 总被引:2,自引:0,他引:2
Suvendra N. Bagchi Upendra N. Rai Amar N. Rai Hriday N. Singh 《Physiologia plantarum》1985,63(3):322-326
Nitrogen regulation of nitrate uptake and nitrate reductase (EC 1.7.99.4) was studied in the cyanobacterium Anabaena cycadeae Reinke and its glutamine auxotroph. Development of the nitrate uptake system preceded, and was independent of, the development of the nitrate reductase system. The levels of both systems were several-fold higher in the glutamine auxotroph lacking glutamine synthetase (EC 6.3.1.2) than in the wild type strain having normal glutamine synthetase activity. The nitrate uptake system was found to be NH4-repressible and the nitrate reductase system NO3 − -inducible. NH4 + was the initial repressor signal for the uptake process which was involved in the control of the NO3 − inducible reductase system. 相似文献
13.
Simultaneous Measurement of Nitrite and Nitrate Levels as Indices of Nitric Oxide Release in the Cerebellum of Conscious Rats 总被引:2,自引:0,他引:2
Abstract: We examined the modulation of nitric oxide production in vivo by measuring levels of nitrite (NO2 − ) and nitrate (NO3 − ) in the dialysate of the cerebellum in conscious rats, by using an in vivo brain microdialysis technique. The levels of both NO2 − and NO3 − were decreased by the intraperitoneal injection of N G -nitro- l -arginine methyl ester, an inhibitor of nitric oxide synthase, whereas N G -nitro- d -arginine methyl ester had no effect. l -Arginine by itself increased NO2 − and NO3 − levels and diminished the reduction of their levels caused by N G -nitro- l -arginine methyl ester. Direct infusion of l -glutamate, N -methyl- d -aspartate, or KCl into the cerebellum through a dialysis probe resulted in an increase in NO2 − and/or NO3 − levels. The effects of N -methyl- d -aspartate and KCl were dependent on extracellular calcium. Furthermore, the stimulatory effects of l -glutamate and N -methyl- d -aspartate were inhibited by N G -nitro- l -arginine methyl ester and (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), an N -methyl- d -aspartate receptor antagonist. These results suggest that NO2 − and NO3 − levels may be related to nitric oxide production in vivo. 相似文献
14.
Abstract: The putative role of glutamine, exported from leaves to roots, as a negative feedback signal for nitrate uptake was investigated in Zea mays L. seedlings. Glutamine (Gln) was supplied by immersion of the tip-cut leaves in a concentrated solution. Nitrate (NO3 − ) uptake was measured by its depletion in amino acid-free medium. The treatment with Gln resulted in a strong inhibition of nitrate uptake rate, accompanied by a significant enrichment of amino compounds in root tissue. The effect of N-availability on NO3 − uptake was determined in split-root cultures. The plants were subjected to complete or localized N supply. Inducible NO3 − uptake systems were also induced in N-deprived roots when the opposite side of the root system was supplied with KNO3 . The inhibitory effect of Gln was unaffected by localized N supply on one side of the split-root. The potential role of Gln in the shoot-to-root control of NO3 − uptake is discussed. 相似文献
15.
Methane-dependent nitrate production by a microbial consortium enriched from a cultivated humisol 总被引:2,自引:0,他引:2
Abstract A consortium was enriched from a humisol incubated with 3.6 kPa CH4 and NH4 + . This consortium oxidized NH4 + to NO2 − and NO3 − (NO3 − /NO2 − ratio about 20) with smaller amounts of N2 O. This oxidation stopped in the stationary phase after depletion of CH4 . CH3 OH or CO2 did not support oxidation. Growth and resting cell experiments suggested that nitrification was associated with methanotrophic activity and that chemoautotrophic nitrifiers were absent. 相似文献
16.
In Nostoc muscorum (Anabaena ATCC 27893) glutamate was not metabolised as a fixed nitrogen source, rather it functioned as an inhibitor of growth. The latter effect was nitrogen source specific and occurred in N2 -fixing cultures but not in cultures assimilating nitrate or ammonium. NO3 - -grown cultures lacked heterocysts and nitrogenase activity and showed a nearly 50% reduction in glutamate uptake rates, as well as in the final extent of glutamate taken up, compared to N2 -fixing or nitrogen-limited control cultures. NH4 + -grown cultures showed a similar response, except that the reduction in glutamate uptake rates and the final exten of glutamate taken up was over 80%. The present results suggest a relation between nitrate/ammounium nitrogen-dependent inhibition of glutamate uptake, probably via repression of the glutamate transport system, and glutamate toxicity. 相似文献
17.
Impact of gaseous nitrogen deposition on plant functioning 总被引:5,自引:0,他引:5
Dry deposition of NH3 and NOx (NO and NO2 ) can affect plant metabolism at the cellular and whole-plant level. Gaseous pollutants enter the plant mainly through the stomata, and once in the apoplast NH3 dissolves to form NH4 + , whereas NO2 dissolves to form NO3 − and NO2 − . The latter compound can also be formed after exposure to NO. There is evidence that NH3 -N and NOx -N can be reversibly stored in the apoplast. Temporary storage might affect processes such as absorption rate, assimilation and re-emission. Once formed, NO3 − and NO2 − can be reduced, and NH4 + can be assimilated via the normal enzymatic pathways, nitrate reductase (NR), nitrite reductase and the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle. Fumigation with low concentrations of atmospheric NH3 increases in vitro glutamine synthetase activity, but whether this involves both or only one of the GS isoforms is still an open question. There seems to be no correlation between fumigation with low concentrations of NH3 and in vitro GDH activity. The contribution of atmospheric NH3 and NO2 deposition to the N budget of the whole plant has been calculated for various atmospheric pollutant concentrations and relative growth rates ( RGRs ). It is concluded that at current ambient atmospheric N concentrations the direct impact of gaseous N uptake by foliage on plant growth is generally small. 相似文献
18.
Effects of nitrate on influx, efflux and translocation of potassium in young sunflower plants 总被引:3,自引:0,他引:3
Sune Pettersson 《Physiologia plantarum》1984,61(4):663-669
Influx, efflux and translocation of K+ (86 Rb) were studied in the roots of sunflower seedlings ( Helianthus annuus L. cv. Uniflorus) treated with 0–4.0 m M NO3 − during a 9 day growth period or a 24 h pretreatment period. Roots treated with high levels of NO3 − absorbed and translocated more K+ (86 Rb) than seedlings treated with low levels of NO3 − . The content of K+ in the shoots was, however, higher in seedlings treated with low levels of NO3 − , indicating a low rate of retranslocation of K+ in those plants. K+ (86 Rb) efflux was highest into the low-NO3 − solutions. All effects on K+ (86 Rb)-fluxes were more obvious in high-K plants than in low-K plants. The results are discussed in relation to the Dijkshoorn-Ben Zioni hypothesis for K+ + NO3 − -uptake and translocation in plants. 相似文献
19.
Effects of exogenous application and stem infusion of ascorbate on soybean (Glycine max) root nodules 总被引:1,自引:0,他引:1
Numerous biochemical and physiological studies have demonstrated the importance of ascorbate (ASC) as a reducing agent and antioxidant in higher plant metabolism. Of special note is the capacity of ASC to eliminate damaging activated oxygen species (AOS) including O2 −· and H2 O2 . N2 -fixing legume nodules are especially vulnerable to oxidative damage because they contain large amounts of leghaemoglobin which produces AOS through spontaneous autoxidation; thus, ASC and other components of the ascorbate–reduced glutathione (ASC–GSH) pathway are critical antioxidants in nodules. In order to establish a meaningful correlation between concentrations of ASC and capacity for N2 fixation in legume root nodules, soybean ( Glycine max ) plants were treated with excess ASC via exogenous irrigation or continuous intravascular infusion through needles inserted directly into plant stems. Treatment with ASC led to striking increases in nitrogenase activity (acetylene reduction), nodule leghaemoglobin content, and activity of ASC peroxidase, a key antioxidant enzyme. The concentration of lipid peroxides, which are indicators of oxidative damage and onset of senescence, was decreased in ASC-treated nodules. These results support the conclusion that ASC is critical for N2 fixation and that elevated ASC allows nodules to maintain a greater capacity to fix N2 over longer periods. 相似文献
20.
Growth and the efficiency of root respiration of Pisum sativum as dependent on the source of nitrogen 总被引:1,自引:0,他引:1
Growth and efficiency of root respiration were investigated in Pisum sativum L. cv. Alaska and cv. Rondo. Plants were grown in culture solutions, either in symbiosis with Rhizobium leguminosanm , or with an abundant supply of nitrate or ammonium and completely lacking nodules. In comparison with plants utilizing nitrate or ammonium, Ni-fixing plants showed lower rates of dry matter and nitrogen accumulation, as well as lower rates of total and cytochrome-mediated root respiration. Rates of shoot dry matter accumulation and root respiration in plants utilizing ammonium were lower than in plants utilizing nitrate. The efficiency of root respiration was high in N2 -fixing plants, as indicated by a low activity of the SHAM-sensitive, alternative, non-phosphorylating pathway. In nitrate and ammonium grown plants of cv. Alaska, the efficiency of root respiration was about the same, and in both cases lower than in N2 -fixing plants. The efficiency of root respiration in non-symbiotically grown pea plants was generally higher than in many non-legumes. Comparison of the ATP costs of synthesis of root dry matter for different N-sources was complicated by large differences in relative growth rate of the root and in shoot to root ratio between N-treatments. A quantitative correction of the ATP production during synthesis of root dry matter for differences in shoot to root ratio and root maintenance respiration has been made. It is concluded that ATP costs of root dry matter production are highest in the case of N2 -fixing plants. In plants utilizing ammonium, ATP costs of synthesis of root dry matter were slightly lower than in plants utilizing nitrate. The physiological significance of the alternative pathway in root metabolism is discussed in relation to the assimilation of different sources of nitrogen. 相似文献