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1.
Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots? 总被引:4,自引:1,他引:3
Saravitz Carole H.; Chaillou Sylvain; Musset Joanne; Raper C. David Jr.; Morot-Gaudry Jean-Francis 《Journal of experimental botany》1994,45(11):1575-1584
In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m3NH4+ to the whole root system, to a second set as 0.5 mol m3NH4+ plus 0.5 mol m3 NO3 to the whole root system,and to a third set as 1.0 mol m3 NH4+ to one-half ofa split-root system and 1.0 mol m3 NO3 to theother half. In a second experiment, 1.0 mol m3 of nitrogenwas resupplied for 4 d to whole root systems in NH4+ : NO3ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH4+ was resupplied in combination with NO3 to thewhole root system in Experiment I, cumulative uptake of NH4+for the 10 d of resupply was about twice as great as when NH4+was resupplied alone. Also, about twice as much NH4+ as NO3was taken up when both ions were resupplied to the whole rootsystem. When NH4+ and NO3 were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH4+ was about half that of NO3. The uptake of NH4+,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO3, and the stimulatingeffect of NO3 on uptake of NH4+ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH4+ and NO3 in a ratio of either1:1 or 9:1 enhanced the uptake of NH4+. The enhancement of NH4+uptake was 1.8-fold greater when the NH4+: NO3-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO3 was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO3 on enhancementof uptake of NH4+ apparently involves more than net uptake ofNO3 itself and perhaps entails an effect of NO3uptake on maintenance of K+ availability within the plant. Theconcentration of K+ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K+ concentration occurred when nitrogenwas resupplied as NH4+ alone. It is proposed that decreasedavailability of K+ within the NH4+-resup-plied plants inhibitedNH4+ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures 相似文献
2.
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
3.
Influx and Efflux of Nitrate and Ammonium in Italian Ryegrass and White Clover Roots: Comparisons Between Effects of Darkness and Defoliation 总被引:9,自引:2,他引:7
Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m3 NO3 or NH3+.Rates of net uptake, influx and translocation of NO3and NH4+ were then determined using 15N and 13N labelling techniques:between 35 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to 13N influx(IC); and 75 min into the photoperiod following 3739h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH4+ exceeded those of NO3 in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH4+ (62%) than NO3 (40%). For NH4+ this was associatedwith a large decrease in influx from 110 to 6.0µmol h1g1 root fr. wt; but for NO3, influx only decreasedfrom 42 to 37 µmol h1 g1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO3and NH4+ by, respectively, 86% and 95% of IL levels. For NH4+this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO3 the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO3(0320µmol h1 g1) and NH4+ (0030.4µmolh1 g1), assimilation in the roots of NO3(0226µmol h1 g1) and NH+4 (0589 µmolh1 g1), and the concentrations of NO3 (915mol m3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, 13N 相似文献
4.
Soybean [Glycine max (L.) Merrill] plants that had been subjected to 15 d of nitrogen deprivation were resupplied for 10 d with 1.0 mol m-3 nitrogen provided as NO3-, NH4+, or NH4(+) + NO3- in flowing hydroponic culture. Plants in a fourth hydroponic system received 1.0 mol m-3 NO3- during both stress and resupply periods. Concentrations of soluble carbohydrates and organic acids in roots increased 210 and 370%, respectively, during stress. For the first day of resupply, however, specific uptake rates of nitrogen, determined by ion chromatography as depletion from solution, were lower for stressed than for non-stressed plants by 43% for NO3- resupply, by 32% for NH4(+) + NO3- resupply, and 86% for NH4+ resupply. When specific uptake of nitrogen for stressed plants recovered to rates for non-stressed plants at 6 to 8 d after nitrogen resupply, carbohydrates and organic acids in their roots had declined to concentrations lower than those of non-stressed plants. Recovery of nitrogen uptake capacity of roots thus does not appear to be regulated simply by the content of soluble carbon compounds within roots. Solution concentrations of NH4+ and NO3- were monitored at 62.5 min intervals during the first 3 d of resupply. Intermittent 'hourly' intervals of net influx and net efflux occurred. Rates of uptake during influx intervals were greater for the NH4(+)-resupplied than for the NO3(-)-resupplied plants. For NH4(+)-resupplied plants, however, the hourly intervals of efflux were more numerous than for NO3(-)-resupplied plants. It thus is possible that, instead of repressing NH4+ influx, increased accumulation of amino acids and NH4+ in NH4(+)-resupplied plants inhibited net uptake by stimulation of efflux on NH4+ absorbed in excess of availability of carbon skeletons for assimilation. Entry of NH4+ into root cytoplasm appeared to be less restricted than translocation of amino acids from the cytoplasm into the xylem. 相似文献
5.
Nitrogen utilization by plant species from acid heathland soils: I. Comparison between nitrate and ammonium nutrition at constant low pH 总被引:4,自引:2,他引:2
Seven heathland species, four herbaceous plants and three dwarfshrubs, were tested for their capacity to utilize NH4+ or NO3. When cultured in solution at pH 4.0 with 2mol m3 N,all species showed similar growth responses with respect toN source. Nitrate was assimilated almost equally well as ammonium,with relative growth rate generally averaging 58% lowerfor NO3 grown plants, albeit not always significantly.However, N source was significantly and consistently correlatedwith biomass partitioning, as NH4+-fed plants allocated moredry matter to shoots and less to roots when compared to NO3-fed plants. The strong difference in biomass partitioning mayrelate to the relative surplus of carbon per unit plant N (or,alternatively, the relatively suboptimal rate of N assimilationper unit plantC) in NO3-fed plants Inherently slow-growing dwarf shrubs accumulated virtually nofree nitrate in their tissues and reduction of nitrate was strictlyroot-based. Faster-growing herbaceous plants, however, partitionedthe assimilation of nitrate over both shoots and roots, therebyaccumulating relatively high tissue NO3 levels. Ion uptakerates depended clearly on the relative shoot demand.At similar shoot demands, especially in the herbaceous species,specific uptake rates for N and total inorganic (non-N) anionswere higher in NH4+ -fed plants, whereas the uptake rate fortotal (non-N) cations was higher in NO3-fed plants. Rateof P uptake was enhanced with increasing plant demand, but wasindependent of the N source. Net H+ extrusions ranged from 1.00to 1.34 H+ per NH4+, and from 0.48 to 0.77 H+per NO3 taken up. Key words: Ammonium, biomass partitioning, heathland plants, low pH, nitrate, nitrate reductase activity, relative shoot demand, specific absorption rate 相似文献
6.
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
7.
From compartmental analysis of 15N elution measurements, concentrationsand fluxes of NH+4 and NO3 were estimated for corticalcells in excised root segments, when bathed in a complete nutrientsolution, in which 20 mol m3 NH4+ or NO3 werethe single N sources. The results were compared with those fornutrient solution containing 20 mol m3 NH4NO3. No nitratereductase activity was detected in the roots but rapid assimilationof NH4+ occurred, due to glutamine synthetase activity. Theefflux curves for NH4+, on a 'µg 15N remaining againsttime' basis, deviated from the criteria determining conformityto first order kinetics, since the slowest rate constant wasan order of magnitude lower than that exhibited by the curvefor efflux versus time. The data were transformed to conformto the appropriate criteria, revealing a large slowly exchangingpool equated with assimilated NH4+. The presence of NO3had little effect on NH4+ uptake and exchange, but NH4+ suppressedNOj uptake and reduced exchange across plasmalemma and tonoplast.It was established that NH4+ absorption was an active process.However, NH4+ entering and leaving the vacuole was overestimated,since the flux equation used did not differentiate between total15NH4 influx at the plasmalemma and that at the tonoplast, afterassimilation. The only active NO3 transfer was influxat the plasmalemma. The results were compared with those ofothers using13N and 36C1O3 analogues to measure NH4+ and NO3fluxes in cereal roots. Key words: Ammonium, nitrate, compartmental analysis, 15N, active transport 相似文献
8.
Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium 总被引:11,自引:1,他引:10
RUFTY THOMAS W. Jr; JACKSON WILLIAM A.; RAPER C. DAVID Jr. 《Journal of experimental botany》1982,33(6):1122-1137
Experiments were conducted to investigate the effect of concentrationof NH4+ in nutrient solution on root assimilation of NO3and to determine whether the NH4+NO3 interaction wasmodified in the presence of K+. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO3)2and varying concentrations of (NH4)2SO4 in the absence or presenceof 0.15 mM K2SO4. The accelerated phase of NO3 uptakeappeared most sensitive to restriction by additions of 0.15mM (NH4)2SO4. In the absence of K+, the restriction increasedonly slightly even when solution (NH4)2SO4, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH4+in the tissue from about 7.0 to 35 µmol g1 fr.wt. of root. Increasing concentrations of solution NH4+ progressivelyinhibited net K+ uptake. At the highest solution NH4+ concentrations,there was an initial net efflux of K+ and no net influx occurredduring the treatment period. The severity of the NH4)SO4 restrictionof NO3 uptake was moderated considerably in the presenceof K+ as long as a net influx of K+ occurred. However, net influxof K+ was not associated with alteration of NH4+ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO3 uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH4+ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH4+. Several mechanisms were postulatedto account for the moderating influence of K+. In all experiments,root NO3 reduction was restricted by the presence ofambient NH4+. The quantitative decreases in reduction tendedto be less than decreases in NO3 uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded. 相似文献
9.
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
10.
Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown for 71 d in flowing nutrient solutions containingN as 10 mmol m3 NH4NO3, under artificial illumination,with shoots at 20/15°C day/night temperatures and root temperaturereduced decrementally from 20 to 5°C. Root temperatureswere then changed to 3, 7, 9, 11, 13, 17 or 25°C, and theacquisition of N by N2 fixation, NH4+ and NO3 uptakewas measured over 14 d. Shoot specific growth rates (d. wt)doubled with increasing temperature between 7 and 17°C,whilst root specific growth rates showed little response; shoot:root ratios increased with root temperature, and over time at11°C. Net uptake of total N per plant (N2 fixation + NH4++ NO3) over 14 d increased three-fold between 3 and 17°C.The proportion contributed by N2 fixation decreased with increasingtemperature from 51% at 5°C to 18% at 25°C. Uptake ofNH4+ as a proportion of NH4+ + NO3 uptake over 14 d variedlittle (5562%) with root temperature between 3 and 25°C,although it increased with time at most temperatures. Mean ratesof total N uptake per unit shoot f. wt over 14 d changed littlebetween 9 and 25°C, but decreased progressively with temperaturebelow 9°C, due to the decline in the rates of NH4+ and NO3uptake, even though N2 fixation increased. The results suggestthat N2 fixation in the presence of sustained low concentrationsof NH4+ and NO4 is less sensitive to low root temperaturethan are either NH4+ or NO3 uptake systems. White clover, Trifolium repens L. cv. Huia, root temperature, nitrogen fixation, ammonium, nitrate 相似文献
11.
Promotion of Assimilation of Ammonium Ions by Simultaneous Application of Nitrate and Ammonium Ions in Radish Plants 总被引:1,自引:0,他引:1
When radish plants were grown in nutrient solutions that containedammonium ions (NH4+) as the sole source of nitrogen, they grewpoorly and accumulated high levels of NH4+ in their leaves.However, radish plants cultured in 5 mM NH4+ plus 1 mM NO3(a ratio of 5 : 1 in forms of nitrogen; referred to as 5:lmix-N)grew well and accumulated very low levels of NH4+ in their leaves.After radish plants were cultured in solutions that containedNO3, or NH4+, or 5: lmix-N for a week, they were thensupplied with the same nitrogen source labeled with 15N forone day. The uptake of 15N from labeled NH4+ into total nitrogenwas the highest in plants supplied with 5:1mix-N. These plantsconverted far fewer labeled NH4+ into free NH4+ than did NH4+-fedplants, but converted many more labeled NH4+ into the insolublefraction than did NH4+- or NO3-fed plants. The presence of a small amount of nitrate was shown to stimulatethe assimilation of ammonium ions and the synthesis of proteins. (Received October 26, 1988; Accepted January 24, 1989) 相似文献
12.
Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH4NO3.J. exp. Bot.38: 5366 The effects of root temperature on uptake and assimilation ofNH4+ and NO3 by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m3 NH4NO3 in solution.Total uptake of nitrogen over 14 d increased threefold between313?C but was constant above 13?C. Net uptake of NH4+exceeded that of NO3 at all temperatures except 17?C,and represented 4765% of the total uptake of nitrogen.Unit absorption rates of NH4+ and of 1?52?7 for NO3suggested that NO3 absorption was more sensitive thanNH4+ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 325?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO3 that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake 相似文献
13.
Seedlings of Ricinus communis L. cultivated in quartz sand weresupplied with a nutrient solution containing either 1 mol m3NO3 or 1 mol m3 NH+4 as the nitrogen source. Duringthe period between 41 and 51 d after sowing, the flows of N,C and inorganic ions between root and shoot were modelled andexpressed on a fresh weight basis. Plant growth was clearlyinhibited in the presence of NH+4. In the xylem sap the majornitrogenous solutes were nitrate (74%) or glutamine (78%) innitrate or ammonium-fed plants, respectively. The pattern ofamino acids was not markedly influenced by nitrogen nutrition;glutamine was the dominant compound in both cases. NH+4 wasnot transported in significant amounts in both treatments. Inthe phloem, nitrogen was transported almost exclusively in organicform, glutamine being the dominant nitrogenous solute, but theN-source affected the amino acids transported. Uptake of nitrogenand carbon per unit fresh weight was only slightly decreasedby ammonium. The partitioning of nitrogen was independent ofthe form of N-nutrition, although the flow of nitrogen and carbonin the phloem was enhanced in ammonium-fed plants. Cation uptakerates were halved in the presence of ammonium and lower quantitiesof K+, Na+ and Ca2+ but not of Mg2+ were transported to theshoot. As NH+4 was balanced by a 30-fold increase in chloride in thesolution, chloride uptake was increased 6-fold under ammoniumnutrition. We concluded that ammonium was predominantly assimilated inthe root. Nitrate reduction and assimilation occurred in bothshoot and root. The assimilation of ammonium in roots of ammonium-fedplants was associated with a higher respiration rate. Key words: Ricinus communis, nitrogen nutrition (nitrate/ammonium), phloem, xylem, transport, partitioning, nitrogen, carbon, potassium, sodium, magnesium, calcium, chloride 相似文献
14.
The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m3N, varying the N03/NH4+ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N03/NH4+ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH4+ by NO3 tended to enhance the plant's growth ratewhen compared to NH4+ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO3increasing from 0 to 100%. In the presence of NH4+, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH4+. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO3in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO3 [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO3 <0.20), D. flexuosashowed a strong preference for NO3 at low external nitrate(the relative uptake ratio for N03 reaching a value of2.0 at 10% NO3). The ecological significance of thisprominent high preference for NO3 at low NO3/NH4+ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N03/NH4+ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate 相似文献
15.
Barley plants (Hordewn vulgare L. cv. Atem) were grown fromseed for 28 d in flowing solution culture, during which timeroot temperature was lowered decrementally to 5?C. Plants werethen subjected to root temperatures of 3, 5, 7, 9, 11, 13, 17or 25 ?C, with common air temperature of 25/15 ?C (day/night).Changes in growth, plant total N, and NO3 levels, andnet uptake of NH4+ and NO3 from a maintained concentrationof 10 mmol m3 NH4NO3 were measured over 14 d. Dry matterproduction increased 6-fold with increasing root temperaturebetween 325 ?C. The growth response was biphasic followingan increase in root temperature. Phase I, lasting about 5 d,was characterized by high root specific growth rates relativeto those of the shoot, particularly on a fresh weight basis.During Phase I the shoot dry weight specific growth rates wereinversely related to root temperature between 313 ?C.Phase 2, from 514 d, was characterized by the approachtowards, and/or attainment of, balanced exponential growth betweenshoots and roots. Concentrations of total N in plant dry matterincreased with root temperature between 325 ?C, moreso in the shoots than roots and most acutely in the youngestfully expanded leaf (2?l6?9% N). When N contents wereexpressed on a tissue fresh weight basis the variation withtemperature lessened and the highest concentration in the shootwas at 11 ?C. Uptake of N increased with root temperature, andat all temperatures uptake of NH4+, exceeded that of NO3,irrespective of time. The proportions of total N uptake over14 d absorbed in the form of NH4+ were (%): 86, 91, 75, 77,76, 73, 77, and 80, respectively, at 3, 5, 7, 9, Il, 13, 17,and 25 ?C. At all temperatures the preference for NH4+ overNO3 uptake increased with time. An inverse relationshipbetween root temperature (311 ?C) and the uptake of NH4+as a proportion of total N uptake was apparent during PhaseI. The possible mechanisms by which root temperature limitsgrowth and influences N uptake are discussed. Key words: Hordeum vulgare, root temperature, ammonium, nitrate, ion uptake, growth rate 相似文献
16.
Dynamic Interactions between Root NH4+ Influx and Long-Distance N Translocation in Rice: Insights into Feedback Processes 总被引:3,自引:0,他引:3
Kronzucker Herbert J.; Schjoerring Jan K.; Erner Yair; Kirk Guy J.D.; Yaeesh Siddiqi M.; Glass Anthony D.M. 《Plant & cell physiology》1998,39(12):1287-1293
Ammonium influx into roots and N translocation to the shootswere measured in 3-week-old hydroponically grown rice seedlings(Oryza sativa L., cv. IR72) under conditions of N deprivationand NH4+ resupply, using 13NH4+as a tracer. Root NH4+ influxwas repressed in plants continuously supplied with NH4+ (at0.1 mM), but a high proportion of absorbed N (20 to 30%) wastranslocated to the shoot in the form of N assimilates duringthe 13-min loading and desorption periods. Interruption of exogenousNH4+ supply for periods of 1 to 3 d caused NH4+ influx to bede-repressed. This same treatment caused N translocation tothe shoot to decline rapidly, until, by 24 h, less than 5% ofthe absorbed 13N was translocated to the shoot, illustratinga clear priority of root over shoot N demand under conditionsof N deprivation. Upon resupplying 1 mM NH4+, root NH4+ influxresponded in a distinct four-phase pattern, exhibiting periodsin which NH4+ influx was first enhanced and subsequently reduced.Notably, a 25 to 40% increase in root influx, peaking at {smalltilde}2 h following re-exposure was correlated with a 4- to5-fold enhancement in shoot translocation and a repression ofroot GS activity. The transient increase of NH4+ influx wasalso observed in seedlings continuously supplied with NO3and subsequently transferred to NH4+. Extended exposure to NH4+caused root NH4+ influx to decrease progressively, while shoottranslocation was restored to {small tilde}30% of incoming NH4+.The nature of the feedback control of NH4+ influx as well asthe question of its inducibility are discussed. (Received August 7, 1998; Accepted September 21, 1998) 相似文献
17.
Growth of two actinorhizal species was studied in relation tothe form of N supply in water culture. Non-nodulated bog myrtle(Myrica gale) and grey alder (Alnus incana) were grown withNH4+, NH4NO3 or NO3 (4 mol m3 N). A nodulatedseries of bog myrtle was also cultivated in N-free medium. Relative growth rate (RGR), utilization rate of N, and shoot/rootratio were highest for the two species with the N completelysupplied as NH4+. In both species, nitrate was largely reducedin the roots and the presence of NO3 in combined-N supplyalways affected the RGR and N utilization rate negatively. BothN2 fixation and complete NO3 nutrition represented conditionsof relative N-deficiency resulting in relatively low tissue-Nconcentrations and a greater allocation of dry mass to the roots.The physiological N status of nodulated M. gale plants was comparativelygood, as indicated by a normal nodule weight ratio and a relativelyhigh N2-fixing rate per unit nodule mass. However, whole-plantN2-fixing capacity remained relatively low in comparison withacquisition rates of N in combined-N plants. The anion charge from the nitrate reduction was largely directlyexcreted as an OH efflux. H + /N ratios generally agreedwith the theory. In comparison with NH4+ nutrition, carboxylateconcentrations were higher in N2-fixing M. gale plants and theH + /N ratio in nodulated plants was less than unity below thevalue for ammonium plants as previously found for other actinorhizalspecies. Therefore, NH4+ should be an energetically more attractiveN source for actinorhizal plants than N2. The results agree with commonly accepted views on energeticsof N uptake and assimilation in higher plants and support theconcept of a basically similar physiological behaviour betweennon-legumes and legumes. Key words: Actinorhizal symbioses, ammonium, H+/OH efflux, nitrate, N2 fixation, NRA 相似文献
18.
Summer nutrient dynamics of the Middle Atlantic Bight: nitrogen uptake and regeneration 总被引:4,自引:0,他引:4
Harrison W.G.; Douglas D.; Falkowski P.; Rowe G.; Vidal J. 《Journal of plankton research》1983,5(4):539-556
Nitrate and ammonium uptake and ammonium regeneration rates(by zooplankton, microplankton and benthos) were measured onthe Atlantic continental shelf (Middle Atlantic Bight) duringsummer, 1980. Euphotic zone profiles of NO3 and NH4+uptake rates were similar in magnitude and vertical structureover a large geographical area. Microplankton NH4+ regenerationrates, although measured less frequently, also showed a relativelyconsistent vertical structure; rates were positively correlatedwith uptake rates. Nitrate assimilation (new production)was used to estimate vertical eddy diffusivity and paniculatesinking rates. Eddy diffusion estimates ranged from <0.1to >2.0 cm2 s1 and were positively related to arealprimary production. Estimated particulate sinking rates averaged5 mg at Nm2d1 and compared favorably with sedimentationrates measured from free-floating and moored sediment traps.Benthic nitrogen regeneration rates represented <10% of thispaniculate nitrogen flux. Within the mixed layer, NH4+ assimilation(regenerated production) represented 5080%of the total (NO3 + NH4+ ) nitrogen productivity and33% for the euphotic zone. Of this, 30% was attributed to zooplankton,63% to microplankton (<100 µm) and 7% to benthos. Onthe average, 74% of the microplankton NH4+ regeneration wasassociated with organisms passing 1 µm filters. 相似文献
19.
Priscu John C.; Vincent Warwick F.; Howard-Williams Clive 《Journal of plankton research》1989,11(2):335-351
The isotope 15N was used to examine nitrogen dynamics in LakesFryxell and Vanda, two permanently ice-covered Antarctic lakes.Half-saturation constants for NH4+. uptake in the shallow watersof both lakes were <10 µg N l1; uptake kineticexperiments on populations forming the deep-chlorophyll layersof these lakes showed zero-order kinetics and could not be fittedwith the Michaelis-Menten equation. Elevated uptake within thefirst few minutes following pulses of NH4+. and NO3 occurredin both lakes. NH4+ regeneration, determined from isotope dilutionexperiments, exceeded uptake at 4.6 m in Lake Fryxell, was lessthan uptake at 9 m in Lake Fryxell and was equal to uptake at10 m in Lake Vanda under the experimental conditions. NO3uptake was suppressed by NH4+ levels as low as 2 µg NH4+-N l1 in Lake Fryxell; the suppression was strongestin the near-surface populations. Substrate-saturated C:N uptakeratios (g:g) in Lake Fryxell decreased from 8.4 near the surfaceto 1.8 at the bottom of the trophogenic zone. Overall, the nitrogendynamics in these lakes are similar to other lakes and the openocean in that biological productivity during the austral summeris supported by regenerated nutrients. 相似文献
20.
36C1O3/NO3 influx into Chara cells was found to be sensitiveto pHo and a maximum was found at pHo = 4.5. By contrast 14Cmethylamine influx into Chara showed a maximum at pHo = 8.5,and at this pHo influx rates were about 150 times higher thanrates of 36C1O3/NO3 influx. However, at pHo = 4.5, 36C1O3/NO3influx rates were, in some cases, comparable with rates of 14Cmethylamine influx. 36C1O3/NO3 influx into Chara cells was stimulatedby Rb +, K+, Na +, and NH4+, but not by Cs+ or Li +. NO3 andCl reduced 14C methylamine influx into Chara by 30%. NH4+ causedvery considerable inhibition of 14C methylamine influx intoChara, but had no effect on 36C1O3/NO3 influx in the presenceof K +. Net NO3 uptake into Chara was completely prevented byNH4+ even at relatively low NH4+ concentrations (25 mmol m 3).This latter effect was reversed by diethylstilbestrol (DES).Evidence is presented for the stimulation of NO3 efflux by NH4+as the mechanism responsible for the immediate effects of NH4+on net NO3 uptake into Chara cells. Key words: Chara, 14C methylamine, 36ClO3, pH 相似文献