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1.
Partitioning and utilization of assimilated C and N were compared in nonnodulated, NO 3-fed and nodulated, N 2-fed plants of white lupin ( Lupinus albus L.). The NO 3 regime used (5 millimolar NO 3) promoted closely similar rates of growth and N assimilation as in the symbiotic plants. Over 90% of the N absorbed by the NO 3-fed plants was judged to be reduced in roots. Empirically based models of C and N flow demonstrated that patterns of incorporation of C and N into dry matter and exchange of C and N among plant parts were essentially similar in the two forms of nutrition. NO 3-fed and N 2-fed plants transported similar types and proportions of organic solutes in xylem and phloem. Withdrawal of NO 3 supply from NO 3-fed plants led to substantial changes in assimilate partitioning, particularly in increased translocation of N from shoot to root. Nodulated plants showed a lower (57%) conversion of C or net photosynthate to dry matter than did NO 3-fed plants (69%), and their stems were only half as effective as those of NO 3-fed plants in xylem to phloem transfer of N supplied from the root. Below-ground parts of symbiotic plants consumed a larger share (58%) of the plants' net photosynthate than did NO 3-fed roots (50%), thus reflecting a higher CO 2 loss per unit of N assimilated (10.2 milligrams C/milligram N) by the nodulated root than by the root of the NO 3-fed plant (8.1 milligrams C/milligram N). Theoretical considerations indicated that the greater CO 2 output of the nodulated root involved a slightly greater expenditure for N 2 than for NO 3 assimilation, a small extra cost due to growth and maintenance of nodule tissue, and a considerably greater nonassimilatory component of respiration in root tissue of the symbiotic plant than in the root of the NO 3-fed plant. 相似文献
2.
The principal forms of amino nitrogen transported in xylem were studied in nodulated and non-nodulated peanut ( Arachis hypogaea L.). In symbiotic plants, asparagine and the nonprotein amino acid, 4-methyleneglutamine, were identified as the major components of xylem exudate collected from root systems decapitated below the lowest nodule or above the nodulated zone. Sap bleeding from detached nodules carried 80% of its nitrogen as asparagine and less than 1% as 4-methyleneglutamine. Pulse-feeding nodulated roots with 15N 2 gas showed asparagine to be the principal nitrogen product exported from N 2-fixing nodules. Maintaining root systems in an N 2-deficient (argon:oxygen, 80:20, v/v) atmosphere for 3 days greatly depleted asparagine levels in nodules. 4-Methyleneglutamine represented 73% of the total amino nitrogen in the xylem sap of non-nodulated plants grown on nitrogen-free nutrients, but relative levels of this compound decreased and asparagine increased when nitrate was supplied. The presence of 4-methyleneglutamine in xylem exudate did not appear to be associated with either N 2 fixation or nitrate assimilation, and an origin from cotyledon nitrogen was suggested from study of changes in amount of the compound in tissue amino acid pools and in root bleeding xylem sap following germination. Changes in xylem sap composition were studied in nodulated plants receiving a range of levels of 15N-nitrate, and a 15N dilution technique was used to determine the proportions of accumulated plant nitrogen derived from N 2 or fed nitrate. The abundance of asparagine in xylem sap and the ratio of asparagine:nitrate fell, while the ratio of nitrate:total amino acid rose as plants derived less of their organic nitrogen from N 2. Assays based on xylem sap composition are suggested as a means of determining the relative extents to which N 2 and nitrate are being used in peanuts. 相似文献
3.
The response of nonnodulated white lupin ( Lupinus albus L. cv. Ultra) plants to a range of NO 3 levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO 3 reductase (EC 1.6.6.1) activity, measurements of NO 3-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO 3 followed by 10 days with 1, 5, 15, or 30 millimolar NO 3. NO 3 reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO 3 reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO 3, respectively. Stem, petioles, and leaflets contained virtually all of the NO 3 reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO 3-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO 3 in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO 3, respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO 3. NO 3 failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO 3. Shoot organs were ineffective in storing NO 3. Even when NO 3 was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively. 相似文献
4.
Xylem sap composition was examined in nodulated and nonnodulated cowpea ( Vigna unguiculata [L.] Walp.) plants receiving a range of levels of NO 3 and in eight other ureide-forming legumes utilizing NO 3 or N 2 as sole source of nitrogen. A 15N dilution technique determined the proportions of plant nitrogen derived from N 2 in the nodulated cowpeas fed NO 3. Xylem sap composition of NO 3-fed, nodulated cowpea varied predictably with the relative extents to which N 2 and NO 3 were being utilized. The ratios of asparagine to glutamine (N/N) and of NO 3 to ureide (N/N) in xylem sap increased with increasing dependence on NO 3 whereas per cent of xylem nitrogen as ureide and the ratio of ureide plus glutamine to asparagine plus NO 3 (N/N) in xylem sap increased with increasing dependence on N 2 fixation. The amounts of NO 3 and ureides stored in leaflets, stems plus petioles, and roots of cowpea varied in a complex manner with level of NO 3 and the presence or absence of N 2 fixation. All species showed higher proportions of organic nitrogen as ureide and several-fold lower ratios of asparagine to glutamine in their xylem sap when relying on N 2 than when utilizing NO 3. In nodulated (minus nitrate) cowpea and mung bean ( Vigna radiata [L.] Wilczek) the percentage of xylem nitrogen as ureide remained constant during growth but the ratio of asparagine to glutamine varied considerably. The biochemical significance of the above differences in xylem sap composition was discussed. 相似文献
5.
During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N 2 and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N 2 fixation and endogenous N remobilization were estimated by 15N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N 2 or from NH 4NO 3 during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N 2 fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH 4NO 3 grown and in N 2 fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine. 相似文献
6.
The vasculature of the dorsal suture of cowpea ( Vigna unguiculata [L.] Walp) fruits bled a sugar-rich exudate when punctured with a fine needle previously cooled in liquid N 2. Bleeding continued for many days at rates equivalent to 10% of the estimated current sugar intake of the fruit. A phloem origin for the exudate was suggested from its high levels (0.4-0.8 millimoles per milliliter) of sugar (98% of this as sucrose) and its high K + content and high ratio of Mg 2+ to Ca 2+. Fruit cryopuncture sap became labeled with 14C following feeding of [ 14C]urea to leaves or adjacent walls of the fruit, of 14CO 2 to the pod gas space, and of [ 14C] asparagine or [ 14C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of 14C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of 14C distribution in phloem sap suggested that [ 14C]allantoin was metabolized to a greater extent in its passage to the fruit than was [ 14C] asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO 3-fed, non-nodulated plants were 20:2:78 in root bleeding xylem sap versus 90:10:0.1 for fruit phloem sap, suggesting that the shoot utilized NO 3-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of 15NO 3 to roots substantiated this conclusion. The amino acid:ureide ratio (nitrogen weight basis) of root xylem sap of symbiotic plants was 23:77 versus 89:11 for corresponding fruit phloem sap indicating intense metabolic transfer of ureide-nitrogen to amino acids by vegetative parts of the plant. 相似文献
7.
The effects of NO -3 and NH +4 nutrition on hydroponically grownwheat ( Triticum aestivum L.) and maize ( Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH +4 than with NO -3 nutrition.The shoot:root ratios of wheat plants were increased with NH +4compared to NO -3 nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO -3 and NH +4-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH +4-fedwheat plants were reduced to 85% of those 12 mM NO -3-fed wheatplants. In maize supplied with 4 and 12 mM NH +4 the photosyntheticrates were 87 and 82% respectively of those of NO -3-fed plants.Reduced photosynthetic rates of NH +4 compared to NO -3-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH +4 compared to NO -3 nutrition.Differences in the partitioning of biomass between the shootsand roots of NO -3-and NH +4-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH +4- thanin NO -3-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH +4-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios. Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem 相似文献
8.
A comparison was made of energy metabolism of nodulated N 2 fixing plants and non-nodulated NO 3-fed plants of Lupinus albus L. Growth, N-increment, root respiration (O 2 uptake and CO 2 production) and the contribution of a SHAM-sensitive oxidative pathway (the alternative pathway) in root respiration were measured. Both growth rate and the rate of N-increment were the same in both series of plants. The rate of root respiration, both O 2 uptake and CO 2 production, and the activity of the SHAM-sensitive pathway were higher in NO 3-fed plants than in N 2 fixing plants. The rate of ATP production in oxidative phosphorylation was computed also to be higher in NO 3-fed plants. It is concluded that both carbohydrate costings and ATP costings for synthesis + maintenance of root material were lower in N 2 fixing than in NO 3-fed plants. The respiratory quotient of root respiration was 1.6 in N 2-fixing plants and 1.4 in NO 3-fed plants. These values were slightly higher than the values calculated on the basis of CO 2 output due to N-assimilation and the experimental values of O 2 uptake, but showed the same trend: highest in N 2 fixing plants. Root respiration of NO 3-fed plants showed a diurnal pattern (both O 2 uptake, CO 2 production and the activity of the SHAM-sensitive pathway), whilst no diurnal variation in root respiration was found in N 2 fixing plants. However, C 2H 2 reduction did show a diurnal rhythm, which is suggested to be related to the diurnal variation in transpiration. Addition of NO 3 to N 2 fixing plants increased the rate of root respiration and the activity of the alternative pathway. This treatment did not decrease C 2H 2 reduction and H 2 evolution within 4 days. Withdrawal of NO 3-supply from NO 3-fed plants decreased the rate of root respiration but had no effect on the relative activity of the alternative pathway. It is suggested that the higher rate of root respiration and the higher activity of the SHAM-sensitive pathway in NO 3-fed plants is due to a larger supply of carbohydrates to the roots, partly due to a better photosynthetic performance of the shoots and partly due to a higher capacity of the roots to attract carbohydrates. 相似文献
9.
Experiments were conducted to characterize the distribution of N compounds in the xylem sap of nodulated and nonnodulated soybean plants through development and to determine the effects of exogenous N on the distribution of N compounds in the xylem. Xylem sap was collected from nodulated and nonnodulated greenhouse-grown soybean plants ( Glycine max [L.] Merr. “Ransom”) from the vegetative phase to the pod-filling phase. The sum of the nitrogen in the amino acid, nitrate, ureide (allantoic acid and allantoin), and ammonium fractions of the sap from both types of plants agreed closely with total N as assayed by a Kjeldahl technique. Sap from nodulated plants supplied with N-free nutrient solution contained seasonal averages of 78 and 20% of the total N as ureide-N and amino acid-N, respectively. Sap from nonnodulated plants supplied with a 20 millimolar KNO 3 nutrient solution contained seasonal averages of 6, 36, and 58% of total N as ureide-N, amino acid-N, and nitrate-N, respectively. Allantoic acid was the predominant ureide in the xylem sap and asparagine was the predominant amino acid. When well nodulated plants were supplied with 20 millimolar KNO 3, beginning at 65 days, C 2H 2 reduction (N 2 fixation) decreased relative to nontreated plants and there was a concomitant decrease in the ureide content of the sap. A positive correlation ( r = 0.89) was found between the ureide levels in xylem sap and nodule dry weights when either exogenous nitrate-N or urea-N was supplied at 10 and 20 millimolar concentrations to inoculated plants. The results demonstrate that ureides play a dominant role in N transport in nodulated soybeans and that the synthesis of ureides is largely dependent upon nodulation and N 2 fixation. 相似文献
10.
Soybean ( Glycine max [L.] Merr.) germplasm, isogenic except for loci controlling male sterility ( ms1) and nodulation ( rj1), was used to investigate the effects of reproductive tissue development and source of nitrogen nutrition on accumulation, transport, and partitioning of nitrogen in a greenhouse experiment. Nodulated plants were supplied nitrogen-free nutrient solution, and nonnodulated plants were supplied nutrient solution containing 20 millimolar KNO 3. Plants were sampled from flowering until maturity (77 to 147 days after transplanting). Accumulation rates of nitrogen in whole plants during reproductive growth were not significantly different among the four plant types. Nitrogen accumulation in the sterile, nonnodulated plants, however, ceased 2 weeks earlier than in fertile, nonnodulated or fertile and sterile, nodulated plants. This early cessation in nitrogen accumulation resulted in sterile, nonnodulated plants accumulating significantly less whole plant nitrogen by 133 days after transplanting (DAT) than fertile, nonnodulated plants. Thus, changing the site of nitrogen assimilation from nodules (N2-fixing plants) to roots and leaves (NO3-fed plants) resulted in similar whole-plant nitrogen accumulation rates in fertile and sterile plants, despite the absence of seed in the latter. Leaflet and stem plus petiole tissues of both types of sterile plants had significantly higher nitrogen concentrations after 119 DAT than both types of fertile plants. Significantly higher concentrations and exudation rates of nonureide, reduced-nitrogen in xylem sap of sterile than of fertile plants after 105 DAT were observed. These latter results indicated possible cycling of nonureide, reduced-nitrogen from the downward phloem translocation stream to the upward xylem translocation stream in roots of sterile plants. Collectively, these results suggest a lack of sinks for nitrogen utilization in the shoots of sterile plants. Hence, comparison of nitrogen accumulation rates for sterile and fertile plants does not provide a definitive test of the hypothesis that reproductive tissue development limits photosynthate availability for support of N2 fixation and nitrate assimilation in determinate soybeans. Nitrogen assimilation during reproductive growth met a larger proportion of the reproductive-tissue nitrogen requirement of nitrate-dependent plants (73%) than of N2-fixing plants (63%). Hence, vegetative-tissue nitrogen mobilization to reproductive tissue was a more prominent process in N2-fixing than in nitrate-dependent plants. N2-fixing plants partitioned nitrogen to reproductive tissue more efficiently than nitrate-dependent plants as the reproductive tissues of the former and latter contained 65 and 55%, respectively, of the whole-plant nitrogen at the time that nitrogen accumulation in reproductive parts had ceased (133 DAT). 相似文献
11.
Kouchi, H. and Higuchi, T. 1988. Carbon flow from nodulatedroots to the shoots of soybean { Glycine max L. Merr.) plants:An estimation of the contribution of current photosynthate toureides in the xylem stream.J. exp. Bot. 39: 10151023. Well-nodulated, water-cultured soybean plants were allowed toassimilate 13CO 2 at a constant specific activity for 10 h andthe 13C-labelling of total carbon and ureides in xylem sap wasinvestigated. Labelled carbon appeared very rapidly in the xylem stream. Percentageof labelled carbon (relative specific activity, RSA) in xylemsap was 18% at 2 h after the start of 13CO 2 assimilation andreached 53% at the end of the 10 h assimilation. The amountof labelled carbon exported from nodulated roots to the shootsvia the xylem during the 10 h labelling period accounted for33% of total labelled carbon imported into the nodulated roots.Ureides (allantoin and allantoic acid) in xylem sap were stronglydependent on currently assimilated carbon. The RSA of ureidesin xylem sap had reached 83% at the end of the assimilationperiod. Labelled carbon in ureides accounted for 51% of totallabelled carbon returned from nodulated roots to the shootsvia the xylem during the 10 h assimilation period. A treatmentwith 20 mol m 3 nitrate in the culture medium for 2 ddecreased the ureide concentration in the xylem sap slightly,but greatly decreased the RSA of ureides. By comparing the data with the results of analysis of the xylemsap of nodule-detached plants, it was concluded that the majorityof labelled carbon exported to the xylem stream from noduleswas in ureide form. A considerable amount of carbon was alsoreturned from roots to shoots via the xylem stream but it wasmore dependent on (non-labelled) carbon reserved in the roottissues. Key words: Soybean( Glycine max L.), root nodule, carbon partitoning, 13CO 2 assimilation, xylem 相似文献
12.
Nodulated and denodulated roots of adzuki bean ( Vigna angularis), soybean ( Glycine max), and alfalfa ( Medicago sativa) were exposed to 14CO 2 to investigate the contribution of nodule CO 2 fixation to assimilation and transport of fixed nitrogen. The distribution of radioactivity in xylem sap and partitioning of carbon fixed by nodules to the whole plant were measured. Radioactivity in the xylem sap of nodulated soybean and adzuki bean was located primarily (70 to 87%) in the acid fraction while the basic (amino acid) fraction contained 10 to 22%. In contrast, radioactivity in the xylem sap of nodulated alfalfa was primarily in amino acids with about 20% in organic acids. Total ureide concentration was 8.1, 4.7, and 0.0 micromoles per milliliter xylem sap for soybean, adzuki bean, and alfalfa, respectively. While the major nitrogen transport products in soybeans and adzuki beans are ureides, this class of metabolites contained less than 20% of the total radioactivity. When nodules of plants were removed, radioactivity in xylem sap decreased by 90% or more. Pulse-chase experiments indicated that CO 2 fixed by nodules was rapidly transported to shoots and incorporated into acid stable constituents. The data are consistent with a role for nodule CO 2 fixation providing carbon for the assimilation and transport of fixed nitrogen in amide-based legumes. In contrast, CO 2 fixation by nodules of ureide transporting legumes appears to contribute little to assimilation and transport of fixed nitrogen. 相似文献
13.
Seedlings (180-d-old) of Casuarina cunninghamianaM L., C. equisetifoliaMiq. and C. glauca Sieber inoculated with each of two differentsources of Frankia, were analysed for translocated nitrogenouscompounds in xylem sap. Analyses were also made on sap fromnodulated and non-nodulated plants of C. glauca grown with orwithout a range of levels of combined nitrogen. Xylem exudateswere collected from stems, roots, and individual nodules ofnodulated plants and from stems and roots of non-nodulated plants.While the proportional composition of solutes varied, the samerange of amino compounds was found in xylem sap from the threedifferent symbioses. In C. glauca asparagine was the major aminoacid in the root sap followed by proline, while in symbiotic C. cunninghamiana arginine accounted for more than 25% of theamino compounds. Citrulline was the major translocated productfound in the stem exudate of symbiotic C. equisetifolia. Increasingconcentrations of ammonium nitrate in the nutrient solutionresulted in increasing levels of free ammonia and glutaminein xylem sap from stems of nodulated and non-nodulated C. glauca,but there was relatively little change in the prominent solutes,e.g. citrulline, proline, and arginine. The composition of nitrogenoussolutes in stem or root exudates of C. glauca was similar tothat of exudate collected from individual nodules and on thisbasis it was not possible to distinguish specific products ofcurrent N 2 fixation in xylem. The main differences in N solutecomposition between the symbioses were apparently due to hostplant effects rather than nodulation or the levels of combinedN. Also, the data indicate that the use of the proportion ofN in sap as citrulline (or indeed any other organic N solute)could not be used as an index of nitrogen fixation. 相似文献
14.
Nodulated and unnodulated soybeans ( Glycine max [L.] Merr.) were grown in N-free or N-containing nutrient solutions, respectively. Starting at the initial flowering stage, and throughout reproductive growth, the NO 3- absorption capacity of roots of intact plants from both treatments was determined in short-term uptake experiments. Acetylene reduction activity was determined for nodulated plants. Nitrate absorption rate, expressed on a root dry weight basis, was greatest at early flowering for both nodulated and unnodulated plants. At 33 days after germination, the NO 3- absorption rate of unnodulated plants was twice as great as that of nodulated plants. During the remainder of the sampling period, NO 3- absorption rates of both nodulated and unnodulated plants decreased progressively and similarly. Maximum nodule specific activity occurred 30 days after germination, or initial flowering. However, maximum total C 2H 2 reduction activity, oner plant basis, was observed during the early stages of pod-filling. Compared to unnodulated plants dependent on NO 3- assimilation, nodulated plants were smaller, had less N in vegetative tissues, and produced less seed per plant. We suggest that the higher NO 3- absorption rate of unnodulated soybean roots, particularly during early reproductive growth, may have reflected a more favorable supply of photosynthate translocated to the roots from larger, more vigorous, non-N-stressed shoots. 相似文献
15.
Nodulated root systems of white lupin ( Lupinus albus L. cv Ultra: Rhizobium strain WU425) were exposed to Ar:O 2 (80:20, v/v) or Ar:N 2:O 2 (70:10:20, v/v/v) and C and N partitioning were examined over a 9- or 10-day period in comparison with control plants with nodulated roots retained in air. Accumulation of N ceased in plants exposed to Ar:O 2 or was much reduced in plants exposed to Ar:N 2:O 2, but net C assimilation rates and profiles of C utilization remained similar to those of control N 2-fixing plants. There was, however, a proportional reduction in CO 2 evolution from nodulated roots of the Ar:O 2 treatment. Xylem N levels fell rapidly after application of Ar:O 2. C:N ratios of phloem sap of petioles and of stem base rose during the first day of Ar:O 2 treatment and then fell progressively back to levels close to that of control plants as leaf reserves of N became available for loading of phloem. Stem top phloem sap increased progressively in C:N ratio throughout Ar:O 2 treatment, presumably due to increasing shortage of xylem derived N for xylem to phloem exchange. Reexposure of Ar:O 2-treated nodulated root systems to air prompted a rapid recovery of N 2 fixation and restoration of plant N status. Rates of N 2 fixation in plants whose roots were exposed to a range of N 2 concentrations indicated an apparent Km of 10% N 2 for the attached intact white lupin nodule. 相似文献
16.
Nitrogen metabolism and transport were studied during reproductivedevelopment of cowpea ( Vigna unguiculata (L.) Walp. cv. Vita3) under three contrasting nitrogen regimes: (1) nitrate suppliedcontinuously (plants non-nodulated), (2) symbiotic N 2 fixation(no combined nitrogen), (3) nitrogenstarvation post-anthesisof previously N 2-fixing plants. The last treatment involveddaily flushing of the root systems with 100% oxygen which suppressedpost-anthesis N 2-fixation by 7679%, thereby making fruitgrowth almost entirely reliant upon mobilization of previouslyaccumulated nitrogen. The bulk of the xylem nitrogen (root bleedingsap or peduncle tracheal sap) of nitrate-fed plants was nitrateand amide, that of symbiotic and O 2-treated plants largely ureide.The composition of fruit cryopuncture phloem sap, however, wasclosely similar in all treatments, with most nitrogen as amidesand amino acids. The evidence suggested intense metabolic transferof root derived nitrate-N or ureide-N to amino acids by vegetativeplant parts prior to translocation to fruits. All tissues offruits showed patterns of development of enzymic activitiesconsistent with release of nitrogen from both ureides and amidesand re-assimilation of ammonia to form amino acids. Althoughthe levels of enzyme activities varied between treatments thedifferences could not be readily associated with individualpatterns of nitrogen transport in the treatments. Nitrogen sufficiencyin the NO 3-fed plants was marked by elevated vegetative biomassand low harvest indices for dry matter and nitrogen, while nitrogendeficiency of the O 2-treated plants was associated with seedabortion, small seed size and low seed nitrogen concentration,and efficient mobilization of nitrogen from vegetative partsto fruits. Key words: Nitrogen, Translocation, Cowpea 相似文献
17.
The use of the relative ureide content of xylem sap [(ureide-N/total N) × 100] as an indicator of N 2 fixation in soybeans (Merr.) was examined under greenhouse conditions. Acetylene treatments to inhibit N 2 fixation were imposed upon the root systems of plants totally dependent upon N 2 fixation as their source of N and of plants dependent upon both N 2 fixation and uptake of exogenous nitrate. Significant decreases in the total N concentration of xylem sap from plants of the former type were observed, but no significant decrease was observed in the total N concentration of sap from the latter type of plants. In both types of plants, acetylene treatment caused significant decreases in the relative ureide content of xylem sap. The results provided further support for a link between the presence of ureides in the xylem and the occurrence of N 2 fixation in soybeans. The relative ureide content of xylem sap from plants totally dependent upon N 2 fixation was shown to be insensitive to changes in the exudation rate and total N concentration of xylem sap brought about by diurnal changes in environmental factors. There was little evidence of soybean cultivars or nodulating strains affecting the relative ureide content of xylem sap. `Ransom' soybeans nodulated with Rhizobium japonicum strain USDA 110 were grown under conditions to obtain plants exhibiting a wide range of dependency upon N 2 fixation. The relative ureide content of xylem sap was shown to indicate reliably the N 2 fixation of these plants during vegetative growth using a 15N method to measure N 2 fixation activity. The use of the relative ureide content of xylem sap for quantification of N 2 fixation in soybeans should be evaluated further. 相似文献
18.
Soybean ( Glycine max [L.] Merr. cv Davis) was grown in a split-root growth system designed to maintain control of the root atmosphere. Two experiments were conducted to examine how 80% Ar:20% O 2 (Ar:O 2) and air (Air) atmospheres affected N assimilation (NH 4NO 3 and N 2 fixation) and the partitioning of photosynthate to roots and nodules. Application of NH 4NO 3 to nonnodulated half-root systems enhanced root growth and root respiration at the site of application. A second experiment applied Ar:O 2 or air to the two sides of nodulated soybean half-root systems for 11 days in the following combinations: (a) Air to both sides (Air/Air); (b) Air to one side, Ar:O 2 to the other (Air/Ar:O 2), and (c) Ar:O 2 to both sides (Ar:O 2/Ar:O 2). Results indicated that dry matter and current photosynthate ( 14C) were selectively partitioned to nodules and roots where N 2 was available. Both root and nodule growth on the Air side of Air/Ar:O 2 plants was significantly greater than the Ar:O 2 side. The relative partitioning of carbon and current photosynthate between roots and nodules on a half-root system was also affected by N 2 availability. The Ar:O 2 sides partitioned relatively more current photosynthate to roots (57%) than nodules (43%), while N 2-fixing root systems partitioned 36 and 64% of the carbon to roots and nodules, respectively. The Ar:O 2 atmosphere decreased root and nodule respiration by 80% and nitrogenase activity by 85% compared to half-root systems in Air while specific nitrogenase activity of nodules in Ar:O 2 was 50% of nodules supplied Air. Results indicated that nitrogen assimilation, whether from N 2 fixation or inorganic sources, had a localized effect on root development. Nodule development accounted for the major decrease in total photosynthate partitioning to non-N 2-fixing nodules. Soybean compensates for ineffective nodulation by controlling the flux of carbon to ineffective nodules and their associated roots. 相似文献
19.
Increased concentrations of nitrate in a nutrient solution (2, 5, and 10 millimolar KNO 3) were correlated with increased shoot:root ratios of non-nodulated soybeans ( Glycine max [L.] Merr.) grown in sand culture. While altering the pattern of C and N partitioning, the N treatments did not affect whole plant photosynthesis over the study period. To determine the mechanism responsible for the observed changes in assimilate partitioning, detailed C and N budgets were worked out with plants from each N treatment over three consecutive 4-day periods of midvegetative growth. The information for the C and N budgets from the 2 and 10 millimolar NO 3− treatments was combined with data on the composition of xylem and phloem exudates to construct a series of models of C and N transport and partitioning. These models were used to outine a `chain-reaction' of cause-and-effect relationships that may account for the observed changes in assimilate partitioning in these plants. The proposed mechanism identifies two features which may be important in regulating the partitioning of N and other nutrients within the whole plant. (a) The concentration of N in the phloem is highly correlated with the N concentration in the xylem. (b) The amount of N which cycles through the root—from phloem imported from the shoot to xylem exported by the root—is regulated by the root's requirement for N: only that N in excess of the root's N requirements is returned to the shoot in the xylem. Therefore, roots seem to have the highest priority for N in times of N stress. 相似文献
20.
Background and aims Nickel (Ni) has become a major heavy metal contaminant. The form of nitrogen nutrition remarkably affects IRT1 expression in roots. IRT1 has an activity of transporting Ni 2+ into root cells. Therefore, nitrogen-form may affect Ni accumulation and toxicity in plants. The assumption was investigated in this study. Methods The Arabidopsis plants were treated in Ni-contained growth solutions with either nitrate (NO 3 ?) or ammonium (NH 4 +) as the sole N source. After 7-day treatments, Ni concentration, IRT1 expression, Ni-induced toxic symptoms and oxidative stress in plants were analyzed. Results The NO 3 ?-fed plants contained a higher Ni concentration, had a greater IRT1 expression in roots, and developed more severe toxic symptoms in the youngest fully expanded leaves, compared with the NH 4 +-fed plants. The Ni-induced growth inhibition was also more significant in NO 3 ?-fed plants. Interestingly, Ni exposure resulted in greater hydrogen peroxide (H 2O 2) and superoxide radical (O 2 . ?) accumulations, more severe lipid peroxidation and more cell death in NO 3 ?-fed plants, whereas the opposite was true for NH 4 +-fed plants. Furthermore, the Ni-enhanced peroxidase (POD) and superoxide dismutase (SOD) activities were greater in NO 3 ?-fed plants Conclusion NO 3 ? nutrition promotes Ni uptake, and enhances Ni-induced growth inhibition and oxidative stress in plants compared with NH 4 + nutrition. 相似文献
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