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1.
As rice can use both nitrate (NO3-) and ammonium (NH4+), we have tested the hypothesis that the shift in the pattern of cultivars grown in Jiangsu Province reflects the ability of the plants to exploit NO3- as a nitrogen (N) source. Four rice cultivars were grown in solution culture for comparison of their growth on NO3- and NH4+ nitrogen sources. All four types of rice, Xian You 63 (XY63), Yang Dao 6 (YD), Nong Keng 57 (NK) and Si You 917 (SY917), grew well and produced similar amounts of shoot biomass with 1 mmol/L NH4+ as the only N source. However, the roots of NK were significantly smaller in comparison with the other cultivars. When supplied with 1 mmol/L NO3-, YD produced the greatest biomass; while NK achieved the lowest growth among the four cultivars. Electrophysiological measurements on root rhizodermal cells showed that the NO3--elicited changes in membrane potential (ΔEm) of these four rice cultivars were significantly different when exposed to low external NO3- (<1 mmol/L); while they were very similar at high external NO3- (10 mmol/L). The root cell membrane potentials of YD and XY63 were more responsive to low external NO3- than those of NK and SY917. The ΔEm values for YD and XY63 rhizodermal cells were almost the same at both 0.1 mmol/L and 1 mmol/L NO3-; while for the NK and SY917 the values became larger as the external NO3- increased. For YD cultivar, ΔEm was measured over a range of NO3- concentrations and a Michaelis-Menten fit to the data gave a Km value of 0.17 mmol/L. Net NO3- uptake depletion kinetics were also compared and for some cultivars (YD and XY63) a single-phase uptake system with first order kinetics best fitted the data; while other cultivars (ND and SY917) showed a better fit to two uptake systems. These uptake systems had two affinity ranges: one had a similar Km in all the cultivars (0.2 mmol/L); the other much higher affinity system (0.03 mmol/L) was only present in NK and SY917. The expression pattern of twelve different NO3- transporter genes was tested using specific primers, but only OsNRT1.1 and OsNRT2.1 expression could be detected showing significant differences between the four rice cultivars. The results from both the physiological and molecular experiments do provide some support for the hypothesis that the more popular rice cultivars grown in Jiangsu Province may be better at using NO3- as an N source.  相似文献   

2.
Cotyledons of faba bean (Vicia faba L. cv. Fiord) were removedto determine whether an apparent delay in nodulation of thiscultivar could be attributed to an inhibitor from these organs.Cotyledons were left intact or excised from seedling plants14 and 18 d after sowing and plants grown with or without 2·5mm NO3. Seedling growth was depressed when cotyledons were removed onday 14 but not when removed on day 18. Removal of the cotyledonsat day 14 reduced nodule number and nodule weight in the absenceof NO3, but in the presence of NO2, nodule numberwas unaffected and only nodule weight was reduced. Cotyledonremoval at day 18 increased both nodule number and nodule weightwith +NO3 but not with –NO2. Acetylene reduction(AR) was markedly depressed by NO3. Cotyledon removalat day 14 decreased AR but removal at day 18 resulted in anincrease in AR. We suggest from these results that faba beancotyledons have an inhibitory effect on nodule activity andon nodulation and this interacts with NO3. This can beexplained through a ‘feed-back’ regulation of N2fixation by soluble N in the seedling. Vicia faba, faba bean, nodule number, nodulation, nodule activity, acetylene reduction, N2 fixation, cotyledon removal, nitrate  相似文献   

3.
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   

4.
Experiments were conducted during the 1974–75 and 1975–76winter season with the barley (Hordeum vulgare L.) cultivarJyoti. From amongst the various plant parts, the flag leaf bladehad higher in vivo nitrate reductase (NR) activity than thelower two leaf blades, glumes, and grains. However, the potentialof a plant part to reduce NO3 is a function of its freshweight and the NR per unit fresh weight. On this basis, thesecond and third leaf blades could reduce more NO3 thanthe flag leaf blade. N fertilizer application resulted in enhancementof the activity of the leaf blades alone. N fertilizer appliedduring the reproductive phase was taken up and assimilated bythe various plant parts. The studies suggest that, even whenthe fertilizer is applied at optimum levels for obtaining maximumyields, the upper leaf blades have sub-optimal NR activity andthat there is a likelihood of either a preferential flow ofNO3 to the leaf blades or transnational barriers to NO3movement to the ear.  相似文献   

5.
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 (0·1–20mol m–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m–3 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 m–3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m–3 At 5.0–20 mol m–3 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 m–3NO-3 but shoot assimilation was predominant at 5.0 mol m–3NO-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 m–3 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   

6.
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: 1015–1023. 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 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, 13CO2 assimilation, xylem  相似文献   

7.
The effects of a range of applied nitrate (NO3) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO3 concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO3 concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO3 concentration of 0 to 1·0 mol m–3then decreased only slightly with further increases in appliedNO3 of about 5·0 mol m–3. Root and shoot growth, NO3 accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m–3 NO3 at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO3 butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m–3 NO3 than with zero NO3.Root dry wt. was unaffected by NO3. Nitrate concentrationand NRA in root and shoot were always low without NO3.At 1·0 and 10 mol m3 NO3, NO3 accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO3 concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO3. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO3was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence  相似文献   

8.
Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 4–0 parts 10–6 NO2, and0.1, 0.2, and 0.4 parts 10–6 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 10–6 NO2 and 0.1 parts 10–6 O3.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 10–6 NO2 and 0.1 parts 10–6 O3. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O3 exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O3 with NO2 significantlydecreased the assimilation of NO2 by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 10–6NO2 and 0–2 parts 10–6 O3. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O3 exposure. Key words: NO2, O3, Phaseolus vulgaris, Growth, Sugars, Root respiration  相似文献   

9.
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   

10.
We studied the responses of Xanthium occidentale (Bertol.) (cockleburor Noogoora burr), a noxious weed, to atmospheric CO2 enrichmentand nitrate-N concentrations in the root zone ranging from 0.5to 25 mM. CO2 enrichment (1500 cm3 m–3) increased dry-matterproduction to about the same extent (18 per cent) at all levelsof supplied N: most of the increment in dry matter was distributedequally between leaves and roots so that there was little effecton shoot-to-root dry-weight ratios. Growth was stimulated greatlyby N and plateaued at 12 mM supplied N. Shoot-to-root dry-weightand total N ratios increased with increasing N supply. CO2 enrichmenthad no effect on the total amount of N accumulated by plants,but increased the N-use efficiency of leaves. Enriched plantshad lower concentrations and quantities of N in their leavesthan controls, and therefore lower shoot-to-root total N ratios.Little free NO3 accumulated in organs of control or enrichedplants. NO3 was the major form of N in xylem sap fromdetopped plants at low supplied NO3-N, but amino N was equalin importance at high supplied NO3-N in control and enrichedplants. Concentrations of NO3 were lower in the xylemsap of CO2 enriched plants. It was concluded that the betterN-use efficiency of CO2 enriched plants could result in increasedgrowth of X. occidentale in regions of marginal soil fertilityas atmospheric levels of CO2 increase. CO2 enrichment, nitrogen, Xanthium, Noogoora burr, cocklebur  相似文献   

11.
Respiratory oxygen consumption by roots was 1·4- and1·6-fold larger in NH+4-fed than in NO-3-fed wheat (Triticumaestivum L.) and maize (Zea mays L.) plants respectively. Higherroot oxygen consumption in NH+4-fed plants than in NO-3-fedplants was associated with higher total nitrogen contents inNH+4-fed plants. Root oxygen consumption was, however, not correlatedwith growth rates or shoot:root ratios. Carbon dioxide releasewas 1·4- and 1·2-fold larger in NO+3-fed thanin NH+4-fed wheat and maize plants respectively. Differencesin oxygen and carbon dioxide gas exchange rates resulted inthe gas exchange quotients of NH-4-fed plants (wheat, 0·5;maize, 0·6) being greatly reduced compared with thoseof NO-3-fed plants (wheat, 1·0; maize, 1·1). Measuredrates of HCO-3 assimilation by PEPc in roots were considerablylarger in 4 mM NH+4-fed than in 4 NO-3 plants (wheat, 2·6-fold;maize, 8·3-fold). These differences were, however, insufficientto account for the observed differences in root carbon dioxideflux and it is probable that HCO-3 uptake is also importantin determining carbon dioxide fluxes. Thus reduced root extension in NH+4-fed compared with NO-3-fedwheat plants could not be ascribed to differences in carbondioxide losses from roots.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration  相似文献   

12.
Tuberized tap roots of Witloof chicory (Cichorium intybus L.)were forced by placing in a dark chamber in a hydroponic systemunder high RH to produce an etiolated bud, the chicon. Plantswere fed nutrient solutions with two NO3concentrations of 1·5or 18 mol m–3 NO3, or demineralized water. The nutrientsolutions were labelled with 2% atom excess 15N. Although thechicon biomass increased with increasing NO3 concentration inthe nutrient solution, the chicon dry weight remained unchanged.The increased chicon biomass was, therefore, due to more waterin the chicon. The N in the chicon originated from either anendogenous source, the root, and/or an exogenous source, thenutrient solution. Organic N reserves remobilization and transferto the chicon were not been affected by NO3 supply. At the endof the forcing period 75% of the root N had been remobilized.Differences in the amount of N in the chicons of the three treatmentswere due to the uptake of exogenous N. The flux of exogenousnitrogen to the chicon in high NO3-plants was 2- to 6-fold higherthan in the low NO3-plants and, at the end of the forcing period,exogenous nitrogen contributed 30% of total chicon N in highNO3-plants and 10% in low NO3-plants. Net uptake of NO3 by chicory plants during the forcing processwas a function of N influx and N efflux. The increase in N influxwas accompanied by an increase in exogenous N flux to the chiconand probably a shift in root and/or chicon osmotic potentialwhich increased water flux to the chicon. Since NO3 did notaccumulate in either the chicon or the root, it is proposedthat osmotic solutes, such as organic acids and amino acidsmay be involved in osmotic potential changes in chicory duringthe forcing process. Key words: Cichorium intybus L., efflux, influx, nitrogen (15NO3) nutrition, remobilization  相似文献   

13.
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 nitratem–3). 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 m–3 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   

14.
Relationships between nitrate (NO-3) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (15–30%) with increased applied NO-3concentrationfrom 0 to 5–20 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH+4) or 5 mMNO-3but NH+4did not affect the rate of mobilization of seedreserves. Chloride (Cl-) was similar to NO-3in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO-3or Cl-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH+4did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO-3or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO-3did not affect total seedling water or residualseed water content until 10–14 DAS. The effects of seedN and NO-3on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO-3is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization  相似文献   

15.
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   

16.
The cultivation of narrow-leafed lupins (Lupinus angustifoliusL.) increase rates of subsoil acidification, and this is thoughtto be partly related to their pattern of nutrient uptake andH+/OH- excretion. The main hypothesis of this study was thatH+ and OH- excretion is not distributed evenly over the entirelength of the root system but is limited to zones where excesscation or anion uptake occur. Seedlings of nodulated lupinswere grown in solution culture using vertically split pots thatallowed the upper and lower zones of the root system to be suppliedwith varying concentrations of K+ and NO-3. Net H+/OH- excretionwas equated to the addition of NaOH/HCl required to maintaina constant pH in the nutrient solution during a 4-d treatmentperiod and nutrient uptake was measured by depletion from solutionin each zone of the split pots. The excess of cation over anion uptake was positively correlatedwith H+ excretion in each rooting zone. In zones where K+ wassupplied at 1200 µM, cation uptake was dominated by K+and up to twice as much H+ was excreted than in zones whereK+ was absent. In zones where NO-3 was supplied at 750 µM,the anion/cation uptake was balanced, however H+ excretion continuedto occur in the zone. When NO-3 was supplied at 5000 µM,anion uptake exceeded cation uptake but there was no OH- excretion.Organic acid anions may be excreted by lupins to maintain theirinternal electroneutrality when anion uptake exceeds cationuptake. Rhizosphere pH would not increase unless the pKa ofthe excreted organic anions was greater than the external pH.Copyright1993, 1999 Academic Press Lupinus angustifolius L., H+/OH- excretion, nutrient uptake, cation-anion balance, vertical split root  相似文献   

17.
The effect of exposure of kidney bean primary leaves to NO2and O3, alone or in combination, on the fate of 13CO2 assimilatedby photosynthesis was examined by 13C-NMR. There were more than70 peaks appearing in the 13C-NMR spectra for substances extractedfrom leaves with 80% ethanol. The 16 relatively well resolvedpeaks corresponded to signals from three sugars, two organicacids and four amino acids. These signals were used to estimatepool sizes and l3C incorporation. Exposures to NO2 and O3 increased the amounts of sucrose andfructose, but not the incorporation of the 13C label during10 min photosynthesis from 13CO2. This suggests the presenceof photo-synthetically inactive pools of sucrose and fructose.Amounts of glycine and serine, and 13C incorporation into them,were increased by the exposure to the pollutants. The incorporationof 13C into alanine was stimulated by exposure to NO2, but notby exposure to O3 alone. The present study shows that with only simple procedures ofsample preparations 13C-NMR provides information on the productsof photosynthesis in leaves stressed by the two air pollutants. Key words: NO2, O3, Phaseolus vulgaris, CO2 assimilation, 13C-NMR  相似文献   

18.
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 (60–70 kN m–2). 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 m–3 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   

19.
Lamaze, T., Sentenac, H. and Grignon, C. 1987. Orthophosphaterelations of root: NO3effects on orthophosphate influx,accumulation and secretion into the xylem.—J. exp. Bot.38: 923–934. Orthophosphate (Pi) accumulation by barley (Hordeum vulgareL.) roots was specifically inhibited by NO3 as comparedto Cl and SO42 –, and Pi secretion into the xylemwas stimulated. The inhibition of Pi accumulation by NO3was also observed in roots of intact photosynthesizing horsebean(Vicia faba L.), rice (Oryza sativa L.) and soybean (Glycinemax L.) plants. NO3 effects on Pi transport by rootswere more thoroughly investigated with corn (Zea mays L.). Theywere due to intracellular NO3. Pi secretion was stillstimulated by NO3 after Pi withdrawal from the absorptionsolution. 32Pi influx decreased during Pi accumulation, supportingthe hypothesis that this ion allosterically regulated its owntransport system by feedback control. This control was modulatedby other anions: the decrease was more pronounced in the presenceof nitrate. Chronologically, the depressive effect of NO3on 32Pi influx appeared after the inhibition of Pi accumulation.Furthermore, under conditions where Pi accumulation was notaffected by NO3, 32Pi influx and Pi secretion into thexylem became insensitive to the presence of nitrate. Our hypothesisis that the stimulative effect of NO3 on Pi secretionand the depressive one on 32Pi influx are the repercussionsof an increase in the Pi cytosolic concentration due to an NO3-induced decrease in Pi uptake by the vacuoles. Key words: Root, orthophosphate fluxes, orthophosphate accumulation, nitrate, ionic interaction  相似文献   

20.
Nodulation, nitrogen (N2) fixation and xylem sap composition were examined in sand cultured plants of Bambara groundnut (Vigna subterranea L.) and Kersting's bean (Macrotyloma geocarpum L.) inoculated with Bradyrhizobium strain CB756 and supplied via the roots for a 4 week period from the third week onwards with different levels of (15N)-nitrate (0–15 mM). The separate contributions of nitrate and N2 to plant nitrogen were measured by isotope dilution. Increasing levels of nitrate inhibited nodule growth (measured as dry matter or nodule N) of both species parallel with decreased dependence on symbiotically-fixed N. Specific nodule activity (N2 fixed g nodule dry−1 d−1 of nodules) was reduced progressively with time in V. subterranea at higher (5 or 15 mM) levels of NO3, but this was not so for M. geocarpum. Root xylem bleeding sap of both species showed ureides (allantoin and allantoic acid) as predominant (>90%) solutes of nitrogen when plants were relying solely on atmospheric N. Levels of ureide and glutamine decreased and those of asparagine and nitrate in xylem increased with increasing level of applied nitrate. Relative levels of xylem ureide-N were positively correlated (R2=0.842 for M. geocarpum and 0.556 for V. subterranea), and the ratio of asparagine to glutamine in xylem exudate negatively correlated (R2=0.955 for M. geocarpum and 0.736 for V. subterranea) with plant reliance on nitrogen fixation. The data indicate that xylem sap analyses might be useful for indirect field assays of nitrogen fixation by the species and that Kersting's bean might offer some potential as a symbiosis in which N2 fixation is relatively tolerant of soil N.  相似文献   

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