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1.
The isoflavones, daidzein and genistein, have been isolated and identified as the major inducers of nod genes of Bradyrhizobium japonicum. The common nod genes of rhizobia are in turn responsible for stimulating root hair curling and cortical root cell division, the earliest steps in the host response. This study evaluated whether there was a relationship between root isoflavonoid production and the hypernodulation phenotype of selected soybean ( Glycine max [L.] Merr.) mutants. Three independently selected hypernodulating soybean mutants (NOD1-3, NOD2-4, and NOD3-7) and a nonnodulating mutant (NN5) were compared with the Williams parent for isoflavonoid concentrations. High performance liquid chromatographic analyses of soybean root extracts showed that all lines increased in daidzein, genistein, and coumestrol concentrations throughout the 12-day growth period after transplanting of both inoculated and noninoculated plants; transplanting and inoculation were done 6 days after planting. No significant differences were detected in the concentration of these compounds among the three noninoculated hypernodulating mutants and the Williams parent. In response to inoculation, the three hypernodulating mutants had higher isoflavonoid concentrations than did the Williams control at 9 to 12 days after inoculation when grown at 0 millimolar N level. However, the inoculated nonnodulating mutant also had higher isoflavonoid concentrations than did Williams. N application [urea, (NH 4) 2SO 4 and NO 3−] decreased the concentration of all three isoflavonoid compounds in all soybean lines. Application of NO 3− was most inhibitory to isoflavonoid concentrations, and inhibition by NO 3− was concentration dependent. These results are consistent with a conclusion that differential NO 3− inhibition of nodulation may be partially due to changes in isoflavonoid levels, although the similar response of the nonnodulating mutant brings this conclusion into question. Alternatively, the nodulation control in the NN5 mutant may be due to factors totally unrelated to isoflavonoids, leaving open the possibility that isoflavonoids play a role in differential nodulation of lines genetically competent to nodulate. 相似文献
2.
It was previously reported that three soybean ( Glycine max [L.] Merr.) nodulation mutants (NOD1-3, NOD2-4, and NOD3-7) were partially tolerant to nitrate when nitrate was supplied simultaneously with inoculation at the time of transplanting. The current study evaluated the effect of short-term nitrate treatment on nitrogenase activity (C 2H 2 reduction per plant and per nodule weight) and on relative abundance of ureides when nitrate application was delayed until plants were 3 weeks old and nodules were fully developed. Nitrogenase activity of the mutants was similar to that of Williams after an initial 3-week growth period, prior to nitrate treatment. Application of 5 millimolar nitrate resulted in greater inhibition of nitrogenase activity in Williams than in the three mutants. NOD1-3 was most tolerant of nitrate among the mutants tested and showed the highest relative abundance of ureides. Although C 2H 2 reduction activity per plant for NOD1-3 was higher than for Williams in the presence of nitrate, C 2H 2 reduction activity per gram of nodules was lower for NOD1-3 than for Williams in the presence and absence of nitrate. Compared to Williams, NOD1-3 had higher nodule ureide concentration and had similar glutamine synthetase activity in nodule tissue, indicating its nodules have normal nitrogen assimilation pathways. Nitrate application resulted in ureide accumulation in nodule tissue as well as in all plant parts assayed. Unexpectedly, nitrate treatment also increased the rate of ureide degradative capacity of leaves in both NOD1-3 and Williams. The data confirmed that nitrogenase activity of the selected nodulation mutants was more, but still only partially, tolerant of nitrate compared with the Williams parent. 相似文献
3.
Previously, we reported (a) a positive correlation between the nitrate concentrations in growth medium and ethylene evolved from uninoculated and inoculated alfalfa ( Medicago sativa) roots and (b) a negative correlation between ethylene evolution and nodulation. Here, we report that the inhibitory effect of NO 3− on nodulation of alfalfa can be eliminated by the ethylene inhibitor aminoethoxyvinylglycine (AVG). This effect was probably related to the strong inhibition (90%) of ethylene biosynthesis caused by AVG in these inoculated and NO 3−-treated roots. These results support our hypothesis that the inhibitory effect of NO 3− is mediated through the phytohormone ethylene. A possible role of endogenous ethylene in the autoregulation of nodulation also is discussed. AVG at 10 micromolar significantly (P < 0.05) increased total nitrogenase activity (acetylene reduction) in 2.5 and 5 millimolar NO 3−-fed plants probably as a result of the very high stimulation of nodulation. 相似文献
4.
Electrogenic ATPase activity on the peribacteroid membrane from soybean ( Glycine max L. cv Bragg) root nodules is demonstrated. Membrane energization was monitored using suspensions of intact peribacteroid membrane-enclosed bacteroids (peribacteroid units; PBUs) and the fluorescent probe for membrane potential (ΔΨ), bis-(3-phenyl-5-oxoisoxazol-4yl) pentamethine oxonol. Generation of a positive ΔΨ across the peribacteroid membrane was dependent upon ATP, inhibited by N,N′-dicyclohexyl-carbodiimide and vanadate, but insensitive to N-ethylmaleimide, azide, cyanide, oligomycin, and ouabain. The results suggest the presence of a single, plasma membrane-like, electrogenic ATPase on the peribacteroid membrane. The protonophore, carbonyl-cyanide m-chlorophenyl hydrazone, completely dissipated the established membrane potential. The extent of reduction in the steady state membrane potential upon addition of ions was used to estimate the relative permeability of the peribacteroid membrane to anions. By this criterion, the relative rates of anion transport across the peribacteroid membrane were: NO 3− > NO 2− > Cl − > acetate − > malate −. The observation that 10 millimolar NO 3− completely dissipated the membrane potential was of particular interest in view of the fact that NO 3− inhibits symbiotic nitrogen fixation. The possible function of the ATPase in symbiotic nitrogen fixation is discussed. 相似文献
5.
Soybean ( Glycine max L. cv Williams) seeds were sown in pots containing a 1:1 perlite-vermiculite mixture and grown under greenhouse conditions. Nodules were initiated with a nitrate reductase expressing strain of Rhizobium japonicum, USDA 110, or with nitrate reductase nonexpressing mutants (NR − 108, NR − 303) derived from USDA 110. Nodules initiated with either type of strain were normal in appearance and demonstrated nitrogenase activity (acetylene reduction). The in vivo nitrate reductase activity of N 2-grown nodules initiated with nitrate reductase-negative mutant strains was less than 10% of the activity shown by nodules initiated with the wild-type strain. Regardless of the bacterial strain used for inoculation, the nodule cytosol and the cell-free extracts of the leaves contained both nitrate reductase and nitrite reductase activities. The wild-type bacteroids contained nitrate reductase but not nitrite reductase activity while the bacteroids of strains NR − 108 and NR − 303 contained neither nitrate reductase nor nitrite reductase activities. Addition of 20 millimolar KNO3 to bacteroids of the wild-type strain caused a decrease in nitrogenase activity by more than 50%, but the nitrate reductase-negative strains were insensitive to nitrate. The nitrogenase activity of detached nodules initiated with the nitrate reductase-negative mutant strains was less affected by the KNO3 treatment as compared to the wild-type strain; however, the results were less conclusive than those obtained with the isolated bacteroids. The addition of either KNO3 or KNO2 to detached nodules (wild type) suspended in a semisolid agar nutrient medium caused an inhibition of nitrogenase activity of 50% and 65% as compared to the minus N controls, and provided direct evidence for a localized effect of nitrate and nitrite at the nodule level. Addition of 0.1 millimolar sucrose stimulated nitrogenase activity in the presence or absence of nitrate or nitrite. The sucrose treatment also helped to decrease the level of nitrite accumulated within the nodules. 相似文献
6.
Either NO 3− (16 millimolar) or NH 4+ (1 millimolar) completely inhibited infection and nodulation of white clover seedlings ( Trifoliin repens) inoculated with Rhizobium trifolii. The binding of R. trifolii to root hairs and the immunologically detectable levels of the plant lectin, trifoliin, on the root hair surface had parallel declining slopes as the concentration of either NO 3− or NH 4+ was increased in the rooting medium. This supports the role of trifoliin in binding R. trifolii to clover root hairs. Agglutination of R. trifolii by trifoliin from seeds was not inhibited by these levels of NO 3− or NH 4+. The results suggest that these fixed N ions may play important roles in regulating an early recognition process in the Rhizobium-clover symbiosis, namely the accumulation of high numbers of infective R. trifolii cells on clover root hairs. 相似文献
7.
Soybeans grown with 2 millimolar NO 3−, which optimized apparent N 2 fixation by Rhizobium symbionts, showed significantly different rates of apparent photosynthesis and C 2H 2 reduction during seedling development at two irradiances. Those physiological processes were lower for several weeks in plants grown at 1,500 microeinsteins per meter 2 per second than in those exposed to 700 microeinsteins per meter 2 per second. The irradiance-induced retardation was evident in short-term rates of apparent photosynthesis and N 2 fixation, as well as in measures of dry matter and total N accumulation. In spite of their previously inhibited development, plants grown at 1,500 microeinsteins per meter 2 per second were indistinguishable by day 28 from those exposed to 700 microeinsteins per meter 2 per second in terms of whole-shoot CO 2-exchange rate; by day 35 they were identical in terms of whole-plant C 2H 2-reduction rate. On day 38 there was no significant difference in dry weight or N content between treatments. Shifting plants between irradiance treatments on day 21 showed that the higher irradiance also had a short-term inhibitory effect on C 2H 2 reduction. The fact that 16 millimolar NO 3− prevented the continuous exposure to 1,500 microeinsteins per meter 2 per second from inhibiting apparent photosynthesis suggested that seedlings grown on 2 millimolar NO 3− with Rhizobium were N-limited. Although rates of apparent photosynthesis were similar by day 28, the additional week required to produce equal rates of apparent N 2 fixation between irradiance treatments showed that physiological adaptations of shoots, as well as photosynthesis per se, can affect root nodule activity. 相似文献
8.
Growth-chamber studies were conducted to evaluate nitrogen assimilationby three hypernodulated soybean [ Glycine max (L.) Merr.] mutants(NOD13, NOD24, NOD37) and the Williamsparent. Seeds were inoculated at planting and transplanted atday 7 to nutrient solution with 1 mol m 3 urea (optimizesnodule formation) or 5 mol m 3 NO 3 (inhibits noduleformation). At 25 d after planting, separate plants were exposedto 15NO 2 or 15NO 3 for 3 to 48 h to evaluate N 2 fixationand NO 3 assimilation. Plant growth was less for hypernodulatedmutants than for Williams with both NO 3 and urea nutrition.The major portion of symbiotically fixed 15N was rapidly assimilated(30 min) into an ethanol-soluble fraction, but by 24 h aftertreatment the ethanolinsoluble fraction in each plant part wasmost strongly labelled. Distribution patterns of 15N among organswere very similar among lines for both N growth treatments aftera 24 h 15N 2 fixation period; approximate distributions were40% in nodules, 12% in roots, 14% in stems, and 34% in leaves.With urea-grown plants the totalmg 15N fixed plant 1 24h 1 was 1·18 (Williams), 1·40 (N0D1-3),107 (NOD2-4), and 0·80 (NOD3-7). The 5 mol m -3 NO 3- treatmentresulted in a 95 to 97% decrease in nodule mass and 15N 2 fixationby Williams, while the three mutants retained 30 to 40% of thenodule mass and 17 to 19% of the 15N 2 fixation of respectiveurea-grown controls. The hypernodulated mutants, which had restrictedroot growth, absorbed less 15NO 3- than Williams, irrespectiveof prior N growthcondition. The 15N from 15NO 3- was primarilyretained in the soluble fraction of all plant parts through24 h. The 15N incorporation studies confirmed that nodule developmentis less sensitive to external NO 3- in mutant lines than in theWilliams parent, and provide evidence that subsequent metabolismand distribution within the plant was not different among lines.These results further confirm that the hypernodulated mutantsof Williams are similar in many respects to the hyper- or supernodulatedmutants in the Bragg background, and suggest that a common mutationalevent affectingautoregulatory control of nodulation has beentargeted. Key words: Glycine max (L.) Merr., soybean, N 2fixation, nitrate assimilation, nodulation mutants, 15N isotope 相似文献
9.
The inducibility and kinetics of the NO 3−, NO 2−, and NH 4+ transporters in roots of wheat seedlings ( Triticum aestivum cv Yercora Rojo) were characterized using precise methods approaching constant analysis of the substrate solutions. A microcomputer-controlled automated high performance liquid chromatography system was used to determine the depletion of each N species (initially at 1 millimolar) from complete nutrient solutions. Uptake rate analyses were performed using computerized curve-fitting techniques. More precise estimates were obtained for the time required for and the extent of the induction of each transporter. Up to 10 and 6 hours, respectively, were required to achieve apparent full induction of the NO 3− and NO 2− transporters. Evidence for substrate inducibility of the NH 4+ transporters requiring 5 hours is presented. The transport of NO 3− was mediated by a dual system (or dual phasic), whereas only single systems were found for transport of NO 2− and NH 4+. The Km values for NO 3−, NO 2−, and NH 4+ were, respectively, 0.027, 0.054, and 0.05 millimolar. The Km for mechanism II of NO 3− transport could not be defined in this study as it exhibited only apparent first order kinetics up to 1 millimolar. 相似文献
10.
The role of NO 3− and NO 2− in the induction of nitrite reductase (NiR) activity in detached leaves of 8-day-old barley ( Hordeum vulgare L.) seedlings was investigated. Barley leaves contained 6 to 8 micromoles NO 2−/gram fresh weight × hour of endogenous NiR activity when grown in N-free solutions. Supply of both NO 2− and NO 3− induced the enzyme activity above the endogenous levels (5 and 10 times, respectively at 10 millimolar NO 2− and NO 3− over a 24 hour period). In NO 3−-supplied leaves, NiR induction occurred at an ambient NO 3− concentration of as low as 0.05 millimolar; however, no NiR induction was found in leaves supplied with NO 2− until the ambient NO 2− concentration was 0.5 millimolar. Nitrate accumulated in NO 2−-fed leaves. The amount of NO 3− accumulating in NO 2−-fed leaves induced similar levels of NiR as did equivalent amounts of NO 3− accumulating in NO 3−-fed leaves. Induction of NiR in NO 2−-fed leaves was not seen until NO 3− was detectable (30 nanomoles/gram fresh weight) in the leaves. The internal concentrations of NO 3−, irrespective of N source, were highly correlated with the levels of NiR induced. When the reduction of NO 3− to NO 2− was inhibited by WO 42−, the induction of NiR was inhibited only partially. The results indicate that in barley leaves NiR is induced by NO 3− directly, i.e. without being reduced to NO 2−, and that absorbed NO 2− induces the enzyme activity indirectly after being oxidized to NO 3− within the leaf. 相似文献
11.
Nitrogen assimilation in three nitrate reductase (NR) mutants of soybean ( Glycine max L. Merr. cv Williams) was studied in the growth chamber and in the field. These mutants, LNR-2, LNR-3, and LNR-4, lack the non-NO 3−-inducible or constitutive fraction of leaf NR activity found in wild-type plants, but this had no effect on the concentration of nitrogen accumulated when grown on NO 3− in the growth chamber. Dry weight accumulation of two of the mutants (LNR-3 and LNR-4) was decreased relative to LNR-2 and wild type. In the field, LNR-2 had dry weights and nitrogen concentrations similar to the wild type at 34 and 61 days after planting, and at maturity. Acetylene reduction activities were also similar at 61 days. 相似文献
12.
Dissimilatory reduction of NO 2− to N 2O and NH 4+ by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N 2O production by this mechanism. In batch cultures with defined media, NO 2− reduction to NH 4+ was favored by high glucose and low NO 3− concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO 3− concentrations. With succinate as the energy source, little or no NO 2− was reduced to NH 4+ but N 2O was produced. Resting cell suspensions reduced NO 2− simultaneously to N 2O and free extracellular NH 4+. Chloramphenicol prevented the induction of N 2O-producing activity. The Km for NO 2− reduction to N 2O was estimated to be 0.9 mM NO 2−, yet the apparent Km for overall NO 2− reduction was considerably lower, no greater than 0.04 mM NO 2−. Activities for N 2O and NH 4+ production increased markedly after depletion of NO 3− from the media. Amendment with NO 3− inhibited N 2O and NH 4+ production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH 4+ but not of N 2O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N 2O at rates equal to the wild type. These observations suggest that N 2O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO 2− to NH 4+. 相似文献
13.
Three dicarbonyl reagents were used to demonstrate the presence of an essential arginine residue in the NO 3− uptake system from corn seedling roots ( Zea mays L., Golden Cross Bantam). Incubation of corn seedlings with 2,3-butanedione (0.125-1.0 millimolar) and 1,2-cyclohexanedione (0.5-4.0 millimolar) in the presence of borate or with phenylglyoxal (0.25-2.0 millimolar) at pH 7.0 and 30°C resulted in a time-dependent loss of NO 3− uptake following pseudo-first-order kinetics. Second-order rate constants obtained from slopes of linear plots of pseudo-first-order rate constants versus reagent concentrations were 1.67 × 10 −2, 0.68 × 10 −2, and 1.00 × 10 −2 millimolar per minute for 2,3-butanedione, 1,2-cyclohexanedione, and phenylglyoxal, respectively, indicating the faster rate of inactivation with 2,3-butanedione at equimolar concentration. Double log plots of pseudo-first-order rate constants versus reagent concentrations yielded slope values of 1.031 (2,3-butanedione), 1.004 (1,2-cyclohexanedione), and 1.067 (phenylglyoxal), respectively, suggesting the modification of a single arginine residue. The effectiveness of the dicarbonyl reagents appeared to increase with increasing medium pH from 5.5 to 8.0. Unaltered Km and decreased Vmax in the presence of reagents indicate the inactivation of the modified carriers with unaltered properties. The results thus obtained indicate that the NO 3− transport system possesses at least one essential arginine residue. 相似文献
14.
Experiments were conducted with segments of corn roots to investigate whether nitrate reductase (NR) is compartmentalized in particular groups of cells that collectively form the root symplastic pathway. A microsurgical technique was used to separate cells of the epidermis, of the cortex, and of the stele. The presence of NR was determined using in vitro and enzyme-linked immunosorbent assays. In roots exposed to 0.2 millimolar NO 3− for 20 hours, NR was detected almost exclusively in epidermal cells, even though substantial amounts of NO 3− likely were being transported through cortical and steler cells during transit to the vascular system. Although NR was present in all cell groups of roots exposed to 20.0 millimolar NO 3−, the majority of the NR still was contained in epidermal cells. The results are consistent with previous observations indicating that limited reduction of endogenous NO 3− occurs during uptake and reduction of exogenous NO 3−. Several mechanisms are advanced to account for the restricted capacity of cortical and stelar cells to induce NR and reduce NO 3−. It is postulated that (a) the biochemical system involved in the induction of NR in the cortex and stele is relatively insensitive to the presence of NO 3−, (b) the receptor for the NR induction response and the NR protein are associated with cell plasmalemmae and little NO 3− is taken up by cells of the cortex and stele, and/or (c) NO 3− is compartmentalized during transport through the symplasm, which limits exposure for induction of NR and NO 3− reduction. 相似文献
15.
Effects of Na application on the capacity of NO 3− assimilation were studied in Na-deficient Amaranthus tricolor L. cv Tricolor plants. On day 30 after germination, Na-deficient A. tricolor plants received either 0.5 millimolar NaCl or KCl. The level of nitrate reductase activity doubled within 24 hours by the addition of Na and the enhanced level was maintained thereafter. When the plants were exposed to 2 millimolar 15NO 3−, total 15N taken up by the plants was greater in the Na-treated plants than in the K-treated plants within 24 hours of the Na treatment. Incorporation of 15N into the 80% ethanol-insoluble nitrogen fraction of the Na-treated plants in the light period was about 260% of those of the K-treated plants indicating greater capacity of NO 3− assimilation in the Na-treated plants. From these results, it was demonstrated that Na application to the Na-deficient A. tricolor plants promoted NO 3− reduction and its subsequent assimilation into protein, resulting in growth enhancement. 相似文献
16.
Six genotypes of winter wheat ( Triticum aestivum L.) differing in grain protein concentration were grown on a nutrient solution containing low concentrations of NO 3− (2 millimolar). Total NO 3− uptake varied between genotypes but was not related to grain protein content. An in vivo nitrate reductase assay was used to determine the affinity of the enzyme for NO 3−, and large phenotypic variations were observed. In vivo estimations of the concentration and size of the metabolic pool were variable. However, the three genotypes with the higher ratios of metabolic pool size to leaf total NO 3− concentration were the high protein varieties. It is proposed that a high affinity of nitrate reductase for nitrate might be a biochemical marker for the capacity of the plant to continue assimilating NO 3− for a longer period during the last stage of growth. 相似文献
17.
Membrane associated nitrate reductase (NR) was detected in plasma membrane (PM) fractions isolated by aqueous two-phase partitioning from barley ( Hordeum vulgare L. var CM 72) roots. The PM associated NR was not removed by washing vesicles with 500 millimolar NaCl and 1 millimolar EDTA and represented up to 4% of the total root NR activity. PM associated NR was stimulated up to 20-fold by Triton X-100 whereas soluble NR was only increased 1.7-fold. The latency was a function of the solubilization of NR from the membrane. NR, solubilized from the PM fraction by Triton X-100 was inactivated by antiserum to Chlorella sorokiniana NR. Anti-NR immunoglobulin G fragments purified from the anti-NR serum inhibited NO 3− uptake by more than 90% but had no effect on NO 2− uptake. The inhibitory effect was only partially reversible; uptake recovered to 50% of the control after thorough rinsing of roots. Preimmune serum immunoglobulin G fragments inhibited NO 3− uptake 36% but the effect was completely reversible by rinsing. Intact NR antiserum had no effect on NO 3− uptake. The results present the possibility that NO 3− uptake and NO 3− reduction in the PM of barley roots may be related. 相似文献
18.
The effect of exogenous NH 4+ on NO 3− uptake and in vivo NO 3− reductase activity (NRA) in roots of Phaseolus vulgaris L. cv Witte Krombek was studied before, during, and after the apparent induction of root NRA and NO 3− uptake. Pretreatment with NH 4Cl (0.15-50 millimolar) affected neither the time pattern nor the steady state rate of NO 3− uptake. When NH4+ was given at the start of NO3− nutrition, the time pattern of NO3− uptake was the same as in plants receiving no NH4+. After 6 hours, however, the NO3− uptake rate (NUR) and root NRA were inhibited by NH4+ to a maximum of 45% and 60%, respectively. The response of the NUR of NO3−-induced plants depended on the NH4Cl concentration. Below 1 millimolar NH4+, the NUR declined immediately and some restoration occurred in the second hour. In the third hour, the NUR became constant. In contrast, NH4+ at 2 millimolar and above caused a rapid and transient stimulation of NO3− uptake, followed again by a decrease in the first, a recovery in the second, and a steady state in the third hour. Maximal inhibition of steady state NUR was 50%. With NO3−-induced plants, root NRA responded less and more slowly to NH4+ than did NUR. Methionine sulfoximine and azaserine, inhibitors of glutamine synthetase and glutamate synthase, respectively, relieved the NH4+ inhibition of the NUR of NO3−-induced plants. We conclude that repression of the NUR by NH4+ depends on NH4+ assimilation. The repression by NH4+ was least at the lowest and highest NH4+ levels tested (0.04 and 25 millimolar). 相似文献
19.
The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO 3− + NO 2− concentrations (≤26 μM) were below the apparent Km (50 μM) for nitrate. During the rainy season, when ambient NO 3− + NO 2− concentrations were higher (37 to 89 μM), an accurate estimate of the Km could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N 2O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N 2O in the presence of C 2H 2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N 2O loss was caused by incomplete blockage of N 2O reductase by C 2H 2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N 2 m −2 h −1 (for undisturbed sediments) to 17 to 280 μmol of N 2 m −2 h −1 (for shaken sediment slurries). 相似文献
20.
Leaf area, chlorophyll content, net CO 2 photoassimilation, and the partitioning of fixed carbon between leaf sucrose and starch and soluble protein were examined in Glycine max (L) Merr. cv Williams grown under three different nitrogen regimes. One group (Nod+/+) was inoculated with Bradyrhizobium and watered daily with a nutrient solution containing 6 millimolar NH 4NO 3. A second set (Nod+/−) was inoculated and had N 2 fixation as its sole source of nitrogen. A third group (Nod −) was not inoculated and was watered daily with a nutrient solution containing 6 millimolar NH 4NO 3. The mean net micromole CO 2 uptake per square decimeter per hour of the most recently matured source leaves was similar among the three groups of plants, being about 310. Mean leaf area of the source leaves, monitored for net photosynthesis was also similar. However, the mean milligram of chlorophyll per square decimeter of Nod+/− test leaves was about 50% lower than the other groups' leaves and indicated nitrogen deficiency. Thus, Nod+/− utilized their chlorophyll more efficiently for photosynthetic CO 2 uptake than the plants of the other treatments. The ratio of foliar carbohydrate:protein content was high in Nod+/− but low in the plants from the other two treatments. This inverse relationship between foliar protein and carbohydrate content suggests that more fixed carbon is diverted to the synthesis of protein when nitrogen availability is high. It was also found that Nod+/− sequestered more storage protein in their paraveinal mesophyll than plants of the other treatments. This study indicates that when inorganic nitrogen regimes are used to control photosynthate partitioning, then both leaf carbohydrate and leaf protein must be considered as end products of carbon assimilate allocation. 相似文献
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