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1.
PEOPLES M B.; HEBB D. M; GIBSON A. H.; HERRIDGE D. F. 《Journal of experimental botany》1989,40(5):535-542
Quantification of N2 fixation by pigeonpea (Cajanus cajan (L.)Millsp.) in the field has proved difficult using techniquessuch as 15N isotope dilution, acetylene reduction and N difference.We report experiments to develop the ureide assay of N2 fixationbased on extraction and analysis of xylem exudate. Plants ofpigeonpea cv. Quantum, inoculated with effective Rhizobium spp.CB756, were grown in a temperature-controlled glasshouse inlarge pots filled with a sand: vermiculite mixture, in waterculture and in a slightly acidic, red-brown earth in replicatedfield plots. Xylem exudate was collected as bleeding sap fromboth nodulated and unnodulated roots, and from detached nodules.Exudate was extracted also from detached shoots and stems ofpigeonpea using a mild vacuum (6070 kN m2). Largedifferences in the composition of N solutes exported from rootsof N2-dependent and nitrate-dependent plants suggested thatshifts in plant dependence on N2 fixation may be reflected byconcomitant changes in N solutes. Thus, nodulated plants weresupplied throughout growth with either N-free nutrients or nutrientssupplemented with 1, 2, 5, 5, 10, or 20 mol m3 15. Plants were harvested at regular intervals fordry matter and vacuum-extracted exudate. The relative abundanceof ureides ([ureide-N/ureide-N + nitrate-N + -amino-N] ? 100)in the exudate was highly correlated with the proportion ofplant N (calculated using a 15N isotope dilution technique)derived from N2 fixation. Two distinct phases of plant growthwere recognized and standard curves were prepared for each.The relationship between proportional dependence of plants onN2 and xylem relative ureides was unaffected by mineral-N source,i.e. nitrate or ammonium. This result is discussed in relationto interpretation of material from field-grown plants. The effectsof plant genotype, strain of rhizobia, section of stem extracted,removal of leaves, time delay between shoot detachment and extraction,and diurnal characteristics were examined in order to identifypotential sources of error and to optimize sampling procedures. Key words: Ureides, allantoin, allantoic acid, N2 fixation, pigeonpea, Cajanus cajan 相似文献
2.
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 13CO2 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 13CO2 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 m3 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, 13CO2 assimilation, xylem 相似文献
3.
Ureide Metabolism in Non-nodulated Phaseolus vulgaris L. 总被引:2,自引:0,他引:2
The distribution of ureide-N was studied throughout vegetativeand reproductive growth of non-nodulated Phaseolus vulgarisL. (bushbean) grown in nitrate nutrient solution. Largest increasesin ureide-N per plant were correlated with flowering and earlypod formation and with seed filling. Highest amounts of ureidesper organ were measured in stems and axillary trifoliates. Highestconcentrations (µmol ureide-N g1 fr. wt.) weremeasured in young developing organs and stems. Seeds did notaccumulate ureides until the ureide content of pods had reacheda maximum. Results obtained using the inhibitor of xanthine oxidase, allopurinol,are consistent with the origin of ureides via purine degradationbut alternative pathways cannot be discounted. Leaves and stems were shown to have the ability to degrade allantoatevia an enzymic process. 相似文献
4.
HANSEN ALEXANDER P.; PEOPLES MARK B.; GRESSHOFF PETER M.; ATKINS CRAIG A.; PATE JOHN S.; CARROLL BERNARD J. 《Journal of experimental botany》1989,40(7):715-724
Growth and symbiotic performance of soybean (Glycine max (L.)Merrill) cv. Bragg and three of its induced nodulation mutants(nod49, non-nodulating; ntsl 116, intermediate supernodulator;nts1007, extreme supernodulator) were compared throughout developmentunder different nitrogen regimes (0, 2, 5 and 10 mol nitratem3). Nitrogen fixation was assessed using 15N-isotopedilution and xylem sap analysis for ureide content. Both techniquesconfirmed a complete lack of N2 fixation activity in nod49.Plant reliance on nitrogen fixation by the other genotypes wasdependent on the nitrate regime and the developmental stage.The ntsl007 and ntsl 116 mutants fixed more nitrogen than theparent cultivar in the presence of 10 mol m3 nitratein the nutrient solution, but higher input of symbioticallyderived nitrogen was still insufficient to offset the amountof nitrogen removed in the harvested seed. However, the mutantsutilized less nitrate for growth than Bragg. Comparison of estimatesof N2 fixation derived from the 15N-dilution technique withthose based on relative ureide content of xylem sap indicatedthat the latter offered a simple and reliable procedure forevaluating the symbiotic performance of supernodulating plants. Key words: 15N-isotope dilution, supernodulation, ureides 相似文献
5.
The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.) 总被引:3,自引:0,他引:3
The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 530 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170196 mg ml1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K+ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml1 whereasxylem sap contained much lower levels (0.28 mg ml1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with 14CO2. A concentration gradient ofsugar (2.1 bar m1) was recorded for stems. Levels ofsucrose, amino compounds and K+ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions 相似文献
6.
Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO3: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO3: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis 相似文献
7.
Nitrogen fixation activity in common bean is generally thoughtto be low and sensitive to soil drying and, consequently, droughtcan have important negative effects on N accumulation and yieldpotential. The objectives of this research were to examine theresponse of N2fixation to drought stress in common bean, andto test the hypothesis that drought sensitivity of N2fixationin common bean is linked to ureide levels in the plants. Twoglasshouse experiments were conducted to compare the responsesof leaf transpiration and acetylene reduction activity (ARA)to soil water contents. ARA decrease during soil dehydrationwas found to lag behind the decline in transpiration. This indicatesthat ARA is relatively less sensitive to soil dehydration comparedto leaf gas exchange. Further, in comparing two cultivars therewas no consistent difference in the relative response of ARAand transpiration to soil drying. The ureide concentrationsmeasured in common bean plants were low, ranging from 0.1 to1.0 mmol l-1in xylem sap exudates. Ureide concentrations inthe sap exudate varied significantly among the two genotypeseven though there was no difference in ARA response to drought.It was concluded that in common bean, the lower sensitivityof N2fixation to drought compared to leaf gas exchange couldbe related to low ureide concentrations in petioles and xylemsap.Copyright 1998 Annals of Botany Company Phaseolus vulgaris,nitrogen fixation, drought stress, nodules, ureides. 相似文献
8.
Shelp, B. J. 1987. The composition of phloem exudate and xylemsap from broccoli (Brassica oleracea var. italica) suppliedwith NH+4, NO3 or NH4NO3.J. exp. Bot. 38: 16191636. The detailed composition of xylem sap and exudate from stemincisions of attached inflorescences of broccoli (Brassica oleraceavar. italica) was compared in plants supplied with NH+4, NO3or NH4NO3. A phloem origin for the exudate was suggested fromthe high levels of sugars (71133 mg cm-3), amino acids(8·1-26·7 mg cm3) and K. (2·33·8mg cm3), the low levels of NO3 and Ca, the high C: N (w/w) ratios(8·333), and the alkaline pH (7·27·3).In contrast, the xylem sap was mildly acidic (pH 5·66·0),and possessed lower levels of all organic and inorganic solutesbut NO3 and Ca, and lower ratios of K: Ca, Mg: Ca and C: N (0·64·4). Glutamine was the predominant o-phthalaldehyde-reactive aminocompound in both transport fluids with the next most abundantamino acids dependent on sap type and N-form. Together witharginine, -aminobutyric acid, which was found only in the xylemstream, was enhanced by NH+4compared to NO3 -nutrition suggestingthat glutamate metabolism was stimulated in the roots. Underlimiting N the amino acid concentrations in the transport fluidswere greater with NH+4 than with NO3. NO3 reduction occurredin both the root and shoot with the latter site predominatingover the entire N range (0-300 mol m3). Even though the compositionof nitrogenous solutes in the xylem was dependent on cultivarand N source, the composition of the phloem streams supplyingthe developing inflorescence was relatively unaffected. The data on the element composition of organs and phloem sapare interpreted to suggest that, in spite of the restrictedmobility of some elements such as B and Mn, a significant proportionof their total supply to developing sinks is carried in thephloem stream. Key words: Transport fluid composition, plant nutrition, phloem mobility. 相似文献
9.
Acclimation of NO3 transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO3 supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m3 NO3at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO3 at 1, 10, 100or 1000 mmol m3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO3]e. Root specific growth rates were inversely related to [NO3]eand shoot:root ratios increased with time at [NO3]e between101000 mmol m3. Net uptake of NO3 at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO3]e between 110 mmol m3with further small increases at higher [NO3]e. Mean unitabsorption rates of NO3 between 06 d and 614d were linearly related (r2 of 0.790.99) to log10[NO].Steady-state Q10 (717°C) for uptake between 06d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO3]eof 1, 10, 100, and 1000 mmol m3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 614 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO3]e. Short-term uptake rates from1 mol m3 NO3 measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r2=0.94) between uptake rate and treatment log10 [NO3]ewhilst rates in 17°C plants were independent of prior [NO3]e. Rates of NO3 influx and efflux under different steady-stateconditions of NO3 supply and root temperature were calculatedfrom dilution of 15N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO3]e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.62.9 at 17°Cand 1.31.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.531.56 at 17°C and 1.213.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO3]e.Both fluxes were higher at 17°C than 7°C in the presenceof 1001000 mmol m3 NO3 but the trend wasreversed at 110 mmol m3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO3 glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO3 transport system under conditions of limitingNO3 supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate 相似文献
10.
Translocation of Nitrogenous Compounds in Symbiotic and Nitrate-Fed Amide-Exporting Legumes 总被引:4,自引:0,他引:4
PEOPLES MARK B.; SUDIN MOHD NOOR; HERRIDGE DAVID F. 《Journal of experimental botany》1987,38(4):567-579
Peoples, M. B., Sudin, M. N. and Herridge, D. F. 1987. Translocationof nitrogenous compounds insymbiotic and nitrate-fed amide-exportinglegumes.J. exp. Bot. 38: 567579. The transport of nitrogen from the roots and nodules of chickpea(Cicer anetinum L.), lentil (Lens culinaris Medic), faba bean(Vicia faba L.) and pea (Pisum sativum L.) was examined in glasshouse-grownplants supplied either with nitrate-free nutrients or with nutrientssupplemented with 1,2,4 or 8 mol m-3153N-nitrate. A sixth treatmentcomprised uninoculated plants supplied with 80 mol m-31513N-nitrate. For each species, more than 75% of the nitrogenwas exported from the nodules as the amides, asparagine andglutamine. In fully symbiotic plants, the amides also dominatednitrogen transport to the shoot When N2 fixation activity wasdecreased by the addition of nitrate to the rooting medium,the N-composition of xylem exudate and stem solutes changedconsiderably. The relative concentrations of asparagine tendedto increase in the xylem whilst those of glutamine were reduced;the levels of nitrate increased in both xylem exudate and thesoluble nitrogen pool of the stem with a rise in nitrate supply.The changes in relative nitrate contents reflected generallythe contributions of root and shoot to overall nitrate reductaseactivity at the different levels of nitrate used. The relationshipsbetween the relative contents of xylary or stem nitrate andamino nitrogen and the plants' reliance on N2 fixation (determinedby the 15N isotope dilution procedure) were examined. Data suggestthat compositional relationships based on nitrate may be reasonableindicators of symbiotic dependence for all species under studyexcept faba bean when greater than 25% of plant nitrogen wasderived from N2 fixation. Key words: Nitrogen, translocation, legumes 相似文献
11.
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 N2 fixation(no combined nitrogen), (3) nitrogenstarvation post-anthesisof previously N2-fixing plants. The last treatment involveddaily flushing of the root systems with 100% oxygen which suppressedpost-anthesis N2-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 O2-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 NO3-fed plants was marked by elevated vegetative biomassand low harvest indices for dry matter and nitrogen, while nitrogendeficiency of the O2-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
12.
MACDUFF J. H.; JARVIS S. C.; LARSSON C-M.; OSCARSON P. 《Journal of experimental botany》1993,44(9):1475-1484
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·030.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3] between 10100 mmol m3(RGR=0·15 0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·030·06d1 , but decreased thereafter to a theoretical minimumvalue at RGR 相似文献
13.
Nodulated 1-1.5-year-old plants of Acacia littorea grown inminus nitrogen culture were each partnered with a single seedlingof the root hemiparasite Olax phyllanthi. Partitioning of fixedN between plant organs of the host and parasite was studiedfor the period 48 months after introducing the parasite.N fluxes through nodules of Acacia and xylem-tapping haustoriaof Olax were compared using measured xylem flows of fixed Nand anatomical information for the two organs. N2 fixation duringthe study interval (635 µg N g FW nodules1 d1)corresponded to a xylem loading flux of 0.20 µg N mm2d1 across the secretory membranes of the pencycle parenchymaof the nodule vascular strands. A much higher flux of N (4891µg mm2 d1) exited through xylem at the junctionof nodule and root. The corresponding flux of N from host xylemacross absorptive membranes of the endophyte parenchyma of Olaxhaustorium was 1.15 µg N mm1 d1, six timesthe loading flux in nodules. The exit flux from haustorium toparasite rootlet was 20.0 pg N mm1 d1, 200-foldless than that passing through xylem elements of the nodule.Fluxes of individual amino compounds in xylem of nodule andhaustorium were assessed on a molar and N basis. N flux valuesare related to data for transpiration and partitioning of Cand N of the association recorded in a companion paper. Key words: Olax phyllanthi, host-parasite relationships, N flux, Acacia, N2 fixation 相似文献
14.
Removal of the blade from the leaf subtending the first flowerbud on Cyclamen persicum Swan Lake plants causedthe petiole of that leaf to senesce, but had no effect on thegrowth of the flower peduncle in the debladed petiole's axil.A 10 mg NAA l1 application generally had no effect onpetiole senescence, peduncle elongation or flowering date whenapplied to the cut end of the petiole after blade removal. A25 mg GA3 l1 application or a combination of 25 mg GA3l1 application or a combination of 25 mg GA3 l1plus 10 mg NAA l1 delayed petiole senescence and enhancedpeduncle elongation and subsequent flowering. No treatment significantlyaltered peduncle length at the time of flowering. Cyclamen persicum Mill, Swan Lake, tissue receptivity, flowering, GA3, NAA 相似文献
15.
The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses 总被引:2,自引:1,他引:1
Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO-3) content of root and shoot and NO-3 and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO-3 concentrations (0·120mol m3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m3 NO-3 For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO-3 concentration on the partitioning of NO-3 assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m3 At 5.020 mol m3 NO3,the data indicated that the shoot played an important if notmajor role in NO-3 assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO-3 assimilation at 0.5 mol m3NO-3 but shoot assimilation was predominant at 5.0 mol m3NO-3 Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m3 NO-3 Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap 相似文献
16.
Kreuzwieser Jrgen; Herschbach Cornelia; Stulen Ineke; Wiersema Peter; Vaalburg Willem; Rennenberg Heinz 《Journal of experimental botany》1997,48(7):1431-1438
The processes of NO3 uptake and transport and the effectsof NH4+ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO3 net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentKm of 9.2 µM and a Vmax of 366 nmol g1 FW h1.NH4+, when present in excess to NO3, or 10 mM L-glutamateinhibited the net uptake of NO3 Apparently, part of NO3taken up was loaded into the xylem. Relative xylem loading ofNO3 ranged from 3.21.6 to 6.45.1% of NO3 netuptake. It was not affected by treatment with NH4+ or L-glutamate.16N/13N double labelling experiments showed that NO3efflux from roots increased with increasing influx of NO3and, therefore, declined if influx was reduced by NH4+ or L-glutamateexposure. From these results it is concluded that NO3net uptake by non-mycorrhizal beech roots is reduced by NH4+or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae 相似文献
17.
Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO3-nutrition for 51 d under control (0.05 mol m3Na+ and 10 mol m3 Cl) and saline (40 mol m3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K+, Na+, Mg2+, and Ca2+ and the anions Cl, NOJ,malate, phosphate, and SO42. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO2 from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K+, Na+, and Cl over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO3 uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO3reduction in the roots was specificallyinhibited. Uptake and xylem transport of K+ was more severelyinhibited than photosynthetic carbon gain or NO3 uptakeby the root. K+ transport in the phloem was even more severelyrestricted under saline conditions. Na+ and Cl flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K+ supply and astrongly increased phloem translocation of Na+ contribute tothe adverse effects of salt in this species. Restriction ofK+ supply occurs by diminished K+ uptake and even more by reducedK+ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K+, Na+, CI 相似文献
18.
Negative linear relations were detected (P < 0·005)between the rate of progress from sowing to panicle initiationand CO2 concentration (210-720 µmol CO2 mol-1 air) fortwo genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relationsbetween CO2 concentration and the rate of progress from sowingto first flowering were also negative in soyabean [Glycine max(L.) Merrill] (P < 0·025), but positive in cowpea[Vigna unguiculata (L.) Walp.] (P < 0·025), albeitthat in both grain legumes sensitivity was much less than insorghum. Thus CO2 elevation does not delay flowering in allshort-day species. The considerable effect of CO2 concentrationon times to panicle initiation resulted in large differencesamong the sorghum plants at this developmental stage; with increasein CO2 concentration, plants were taller with slightly moreleaves and more pronounced apical extension. At the same timeafter sowing however, sorghum plants were heavier (P < 0·05)at 210 than at 360 µmol CO2 mol-1 air. In contrast, relationsbetween the dry masses of the soyabean and cowpea plants andCO2 concentration were positive and curvilinear (P < 0·05).It is suggested that the impact of global environmental changecould be severe for sorghum production in the semi-arid tropics.Copyright1995, 1999 Academic Press Sorghum bicolor (L.) Moench., sorghum, Glycine max (L.) Merrill, soyabean, Vigna unguiculata (L.) Walp., cowpea, development, flowering, CO2, dry matter accumulation, environmental change 相似文献
19.
Influence of the Form of Nitrogen Supply on Root Uptake and Translocation of Cations in the Xylem Exudate of Maize (Zea mays L) 总被引:1,自引:0,他引:1
Concentrations of inorganic cations are often lower in plantssupplied with NH4+ as compared with NO3. To examine whetherthis is attributable to impaired root uptake of cations or lowerinternal demand, the rates of uptake and translocation of K,Mg, and Ca were compared in maize plants (Zea mays L.) withdifferent growth-related nutrient demands. Plants were grownin nutrient solution with either 1·0 mol m3 NO3or NH4+ and the shoot growth rate per unit weight of roots wasmodified by varying the temperature of the shoot base (SBT)including the apical shoot meristem. The shoot growth rate per unit weight of roots, which was takenas the parameter for the nutrient demand imposed on the rootsystem, was markedly lower at 12°C than at 24°C SBT.As a consequence of the lower nutrient demand at 12°C SBT,uptake rates of NO3 and NH4+ declined by more than 50%Compared with NO3 supply, NH4+ nutrition depressed theconcentrations of K and particularly of Ca in the shoot, bothin plants with high and with low nutrient demand. This indicatesa control of cation concentration by internal demand ratherthan by uptake capacity of the roots. Translocation rates of K, Mg and Ca in the xylem exudate werelower in NH4+- than in NO3-fed plants. Net accumulationrates of Ca in the shoot were also decreased, whereas net accumulationrates of K in the shoot were even higher in NH4+-fed plants.It is concluded that reduced cation concentrations in the xylemsap of plants supplied with NH4+ are due to the lower demandof cations for charge balance. The lower K translocation tothe shoot is compensated by reduced retranslocation to the roots.For Ca, in contrast, decreased translocation rates in NH4+-fedplants result in lower shoot concentration. Key words: Nitrogen form, cation nutrition, charge balance, xylem exudate, recirculation 相似文献
20.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献