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1.
Inward and Outward Movement of Ammonium in Root Systems: Transient Responses during Recovery from Nitrogen Deprivation in Presence of Ammonium 总被引:6,自引:1,他引:5
Morgan, M. A. and Jackson, W. A. 1988. Inward and outward movementof ammonium in root systems: transient responses during recoveryfrom nitrogen deprivation in presence of ammonium. J.exp. Bot. 39: 179-191. Net ammonium uptake by 20-d-old wheat (Triticum aestivum cv.Kleiber) and oat (Avena sativa cv. Tarok) seedlings was increased5- to 10-fold when the seedlings were deprived of nitrate duringthe 14-20 d period. The effect of nitrogen deprivation was toincrease net 15N-ammonium influx and decrease net 14N-ammoniumefflux during a 1 h assay period. The sizeable rate of net 15N-ammoniuminflux resulting from nitrogen deprivation was stimulated furtherby prior exposure of the seedlings to 14N-ammonium for 5 h.Additional exposure to 14N-ammonium caused the stimulated rateof 15N-ammonium influx to decline. During the 1 h assays in15N-ammonium, net 14N-ammonium efflux increased after 2 h exposureto 14N-ammonium, peaked at 510 h, and then declined.The consequence of the differential response of the influx andefflux processes in wheat was a marked decrease in net ammoniumuptake in the initial 25 h, followed by a recovery which,in turn, was followed by a slow decline. In oat, there was norecovery in net ammonium uptake after 25 h. Interference in ammonium assimilation by presence of methioninesulphoximine after 5 h did not inhibit expression of the ammonium-stimulatednet 15N-ammonium influx at 10 h but did substantially increasenet 14N-ammonium efflux. In nitrogen depleted seedlings, andin those exposed to 14N-ammonium for 2 h, subsequent net 14N-ammoniumefflux during 1 h in 15N-ammonium exceeded the quantity of 14N-ammoniuminitially in the roots. The increase in 15N-ammonium influx upon nitrogen deprivation,its further stimulation with 5-10 h exposure to ammonium andits subsequent decline, are discussed as possibly resultingfrom (a) the operation of two ammonium influx systems (b) theinterplay of tissue ammonium and a product of its assimilationrespectively acting as positive and negative effectors of asingle influx system and (c) variations in energy supply fromthe shoots. Key words: Net ammonium uptake, stimulated ammonium influx, ammonium efflux, tissue ammonium 相似文献
2.
Reciprocal Ammonium Transport Into and Out of Plant Roots: Modifications by Plant Nitrogen Status and Elevated Root Ammonium Concentration 总被引:3,自引:0,他引:3
Wheat and oat were grown for 20 d on a nitrate-containing solution(nitrogen-replete plants) or for the last 6 d of this periodon a nitrate-free solution (nitrogen-depleted plants). Exposureof the nitrogen-depleted plants on day 20 to nitrate-free solutionscontaining 500 mmol m3 ammonium (96 A% 15N) resultedin a cumulative net influx of 15N-ammonium over an 8 h periodthat was appreciably greater than that of the nitrogen-repleteplants. Both the initial rate and the more restricted rate afterthe first hour were enhanced by nitrogen deprivation. In thenitrogen-replete plants, cumulative net efflux of endogenous14N-ammonium was approximately equivalent to net ammonium uptakeduring the first hour, and was essentially complete after 12h. Pretreating nitrogen-depleted plants for 5 h in 500 mmolm3 15N-ammonium (99 A% 15N) resulted in root ammoniumconcentrations of 12.7?1.1 and 16.0?0.4 µmol for wheat and oat, respectively. Subsequent net efflux of 15N-ammoniumto 500 mmol m3 exogenous 14N-ammonium exceeded theseinitial amounts within 2 h. Increasing ambient 14N-ammoniumto 5000 mmol m3 increased net 15N-ammonium efflux suchthat net loss of the maximal original amount in the root tissuewas exceeded within 0.75 h. The data for both species indicatesubstantial reciprocal transfers of ammonium into and out ofroots of ammonium-treated plants and a significant degradationof recently synthesized products of ammonium assimilation concurrentwith ammonium assimilation. Key words: Accumulation, ammonium, efflux, oat, root, uptake, wheat 相似文献
3.
Rapid, Reversible Inhibition of Nitrate Influx in Barley by Ammonium 总被引:18,自引:2,他引:16
The rate of influx of nitrate into the roots of intact barleyplants was measured over a period of 35 min from externalnitrate concentrations of 1150 mmol m3, using13N-labelled nitrate as tracer. Ammonium at external concentrationsof 0.00550 mol m3 inhibited nitrate influx ina manner which did not conform to a simple kinetic model butincreased approximately as the logarithm of the ammonium concentration.At any particular ammonium concentration, inhibition of nitrateinflux reached its full extent within 3 min of the ammoniumbeing supplied and was not made more severe by up to 17 minpre-treatment with ammonium. On removing the external ammonium,nitrate influx returned to its original rate within about 3min. Potassium at 0.00550 mol m3 did not reproducethe rapid effect of ammonium on nitrate influx. Net uptake of nitrate also decreased when ammonium was supplied,over a similar timescale and to a similar extent as nitrateinflux. The decrease in nitrate influx caused by ammonium wassufficient to account for the observed reduction in net uptake,without necessitating any acceleration of nitrate efflux. Key words: Hordeum vulgare, roots, ion transport, short-lived isotopes, 13N 相似文献
4.
Inward and outward transport of ammonium in roots of maize and sorghum: contrasting effects of methionine sulphoximine 总被引:2,自引:1,他引:1
To examine the adaptive responses of ammonium efflux of nitrate-grownplants during first exposure to ammonium nutrition, isotopicflows of ammonium in and out of root tissue of maize (Zea maysL.) and sorghum (Sorghum bicolor L.) were delineated. Appreciableefflux of 14N-ammonium occurred during the first 2 min of exposure,suggesting that ammonium efflux is characteristic of plantsgrown with nitrate as the sole source of nitrogen. Treatmentwith methionine sulphoximine (MSX) enhanced the initial 14N-ammoniumefflux 5-fold in maize but less than 2-fold in sorghum. Increasingambient acidity from pH 6 to pH 4 had relatively little effecton 14N-ammonium efflux in either species. Initial influx ofexogenous 15N-ammonium was stimulated by MSX in maize (slightlyless at pH 4 than at pH 6), but either was not affected (atpH 6) or was inhibited (at pH 4) in sorghum. Assuming that therate of ammonium influx remained constant during the 2 h adaptationperiod, and that efflux of 15N-ammonium was negligible duringthe 0-2 min period, permitted estimates to be made of the unidirectionalinward and outward flow of the two isotopic ammonium species.The decline in efflux of endogenous 14N-ammonium after the 2min exposure was more than compensated for by an increase inefflux of the exo-genously-supplied 15N-ammonium. As a consequence,total ammonium efflux increased significantly during the adaptationperiod. By this analysis about 60% of the total efflux in maizewas as 1BN-ammonium within the 2-5 min period whereas in sorghumit was 20% to 40%. The data indicate that appreciable ammoniumefflux occurs in nitrate-grown seedlings in spite of low rootammonium concentrations, and that substantial futile cyclingof ammonium occurs in both maize and sorghum during net transportof ammonium into their root tissue. Key words: Ammonium, cycling, transport, maize, sorghum 相似文献
5.
The concentrations of glutamine and glutamate, and the abundanceof 15N in these compounds, were measured in roots of intact,nitrate-grown maize plants fed with 15N-nitrate or 15N-ammoniumfor periods of 380 min. On supplying 15N-ammonium therewas a rapid and almost linear accumulation of glutamine, itsconcentration in the roots rising 3-fold over 1 h. Supplying15N-nitrate instead of 15N-ammonium did not increase root glutamine,and the concentration of glutamate was not affected by eithertreatment. The time-course of amide 15N-labelling seen in glutamine extractedfrom roots which had been supplied with 15N-ammonium could bestbe explained by a model in which (a) the additionalglutamine which accumulates rapidly during 15N-ammonium feedingis heavily amide-labelled from the outset, and (b) of the glutaminealready present in the roots, only a small proportion (c. 1015%)incorporates 15N during the initial 6080 min of 15N-ammoniumfeeding, the remainder (c. 8590%) remaining essentiallyunlabelled over this period. The latter is assumed to be locatedin the vacuoles. Even though prior N-starvation stimulated ammonium net uptakemarkedly, the data were not of sufficient quality to show whetherthe relative sizes of the extra-vacuolar and vacuolar glutaminefractions were altered by this treatment. For that reason itwas not possible to determine whether cytosolic glutamine hasa role in regulating N-absorption. Key words: Subcellular compartmentation, regulation, N-absorption 相似文献
6.
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
7.
Nitrogen-13 Studies of Nitrate Fluxes in Barley Roots: II. EFFECT OF PLANT N-STATUS ON THE KINETIC PARAMETERS OF NITRATE INFLUX 总被引:5,自引:0,他引:5
Influx of nitrate into the roots of intact barley plants wasfollowed over periods of 115 min using nitrogen-13 asa tracer. Based on measurements taken over 15 min from a rangeof external nitrate concentrations (0·2250 mmolm3), the kinetic parameters of influx, Imax and Km, werecalculated. Compared with plants grown in the presence of nitrate throughout,plants that had been starved of N for 3 d showed a significantlygreater value ofImax for 13N-nitrate influx (by a factor of1·41·8), but a similar value of Km (1214mmol m3). Pre-treating N-starved plants with nitratefor about 5 h further increased the subsequent rate of 13N-nitrateinflux, but had little effect in the unstarved controls. Allowingfor this induction of additional nitrate transport, the differencein rates of nitrate influx in control and N-starved plants wassufficient to account for the previously-observed differencein net uptake by the two groups of plants. In barley plants grown without any exposure to nitrate, butwith ammonium as N-source, both Imax and Km for subsequent 13N-nitrateinflux were significantly decreased (by about one-half) comparedwith the corresponding nitrate-grown controls. The importance of changes in the rate of influx in the regulationof net uptake of nitrate is discussed. Key words: Ion transport, nitrate, influx, kinetic parameters, N-deficiency 相似文献
8.
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
9.
Rees A.P.; Owens N.J.P.; Heath M.R.; Plummer D.H.; Bellerby R.S. 《Journal of plankton research》1995,17(6):1307-1324
Carbon (C) fixation and nitrogen (N) assimilation rates havebeen estimated from 14C and 15N techniques for a 12 month periodin a Scottish sea loch. The maximum rate of nitrogen assimilated(29.92 mmol N m2 day1) was in April at the mostseaward station; similar high rates were experienced duringMay at the other stations. Carbon fixation rates were maximal(4884047 mg C m2day1) at the time of highphytoplankton biomass (maximum 8.3 mg m3 chlorophylla) during May, whilst nitrate concentrations remained >0.7µ.mol l1. C:N assimilation ratios suggest nitrogenlimitation only during the peak of the spring bloom, althoughat times nitrogen (nitrate and ammonium) concentration fellto 0.2 µmol l1 in the following months. The verticalstability of the water column, influenced by tidal and riverineflushing, varied along the axis of the loch, resulting in markeddifferences between sampling stations. Although ammonium waspreferentially assimilated by phytoplankton, >50% of productionwas supported by nitrate uptake and only during the summer monthswas the assimilation of ammonium quantitatively important. 相似文献
10.
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
11.
Rideout James W.; Chaillou Sylvain; Raper C. David Jr; Morot-Gaudry Jean-Francois Jr 《Journal of experimental botany》1994,45(1):23-33
Soybean [Glycine max (L.) Merrill] plants that had been subjectedto 15 d of nitrogen deprivation were resupplied for 10 d with1.0 mol m3 nitrogen provided as NO3, NH4+, orNH4++NO3 in flowing hydroponic culture. Plants in a fourthhydroponic system received 1.0 mol m3 NO3 duringboth stress and resupply periods. Concentrations of solublecarbohydrates 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 ionchromatography as depletion from solution, were lower for stressedthan for non-stressed plants by 43% for NO3- resupply, by 32%for NH4+ + NO3 resupply, and 86% for NH4+ resupply. Whenspecific uptake of nitrogen for stressed plants recovered torates for non-stressed plants at 6 to 8 d after nitrogen resupply,carbohydrates and organic acids in their roots had declinedto concentrations lower than those of non-stressed plants. Recoveryof nitrogen uptake capacity of roots thus does not appear tobe regulated simply by the content of soluble carbon compoundswithin roots. Solution concentrations of NH4+ and NO3 were monitoredat 62.5 min intervals during the first 3 d of resupply. Intermittenthourly intervals of net influx and net effluxoccurred. Rates of uptake during influx intervals were greaterfor the NH4+ -resupplied than for the NO3 -resuppliedplants. For NH4+ -resupplied plants, however, the hourly intervalsof efflux were more numerous than for NO3 -resuppliedplants. It thus is possible that, instead of repressing NH4+influx, increased accumulation of amino acids and NH4+ in NH4+-resupplled plants inhibited net uptake by stimulation of effluxof NH4+ absorbed in excess of availability of carbon skeletonsfor assimilation. Entry of NH4+ into root cytoplasm appearedto be less restricted than translocation of amino acids fromthe cytoplasm into the xylem. Key words: Ammonium, nitrate, nitrogen-nutrition, nitrogen-stress, soybean 相似文献
12.
CLARKSON DAVID T; SAKER LESLIE R.; PURVES JUDITH V. 《Journal of experimental botany》1989,40(9):953-963
When barley plants were grown in a solution with nitrate asthe sole N-source but deprived of sulphate (Splants)for 1 to 5 d, the capacity for sulphate transport by the rootsincreased very markedly; subsequent measurement of influx using35S-labelled showed increases of > 10-fold compared to plants continuously supplied with sulphate (+S plants).There were only small effects on plant growth over a 5 d periodand yet the influx of , labelled with the short-lived tracer 13N, was diminished by approximately 30%.By contrast, the influx of phosphate was little affected bysulphate-deprivation. When a sulphate supply was restored to S plants, the sulphate influx was quickly repressedover the subsequent 24 h and the nitrate influx was restoredto >90% of the value in +S plants. When plants were grown in a solution with a mixed nitrate andammonium supply and deprived of sulphate for 1 d or 5 d thedepression of nitrate influx was more strongly marked (up to55% depression). The influx of ammonium was also depressed after5 d of sulphate-deprivation, but not at 1 d, nor where the concentrationof ammonium in the uptake solution was lowered to 20 mmol m3or less. Additional measurements with 15N-labelled nitrate and ammoniumover longer periods were used to determine net uptake. Net uptakeof nitrate was depressed to a similar extent to efflux, butnet ammonium uptake was depressed only in unbuffered uptakesolution where the pH decreased to pH 4.9 during the uptakeperiod. The 15N-tracer experiments showed that the translocationof label to the shoot, from both nitrate and ammonium, was depressedto a greater extent than net uptake in S plants. Thedepression of nitrate influx, caused by 5 d of sulphate deprivation,could be relieved almost completely by providing plants with1.0 mol m3 L-methionine during the day prior to influxmeasurement. This treatment substantially decreased sulphateand potassium (86Rb-labelled) influx in both +S and Splants, but greatly increased total S-status of the plants.This methionine treatment had no effect on ammonium influx ornet uptake in S plants but increased influx significantlyin +S ones. When plants were grown with sulphate but deprived of nitratefor 4 d there was a marked depression of the sulphate influx(by 4865%) but a smaller effect on phosphate influx (2137%of +N). The results are discussed in relation to the effects of sulphate-deprivationon growth rate and the root: shoot weight ratio. It is concludedthat the effects on influx and net uptake of nitrogen are moresevere than could be accounted for by these factors. The decreasedtranslocation of either nitrate, or the products of nitrateand ammonium assimilation from the roots, is suggested as areason for the depression of influx. The restoration of nitrateinflux and net uptake by methionine suggests that, for thision at least, a shortage of S-amino acids within the plant maylead to the accumulation of inhibitory concentrations of non-Samino acids in the transport pool. Key words: 13N, sulphate, nitrate, ammonium, ion-uptake, barley 相似文献
13.
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
14.
Evidence of ammonium assimilation via the glutamine synthetase-glutamate synthase system in rice seedling roots 总被引:1,自引:0,他引:1
When rice seedling roots were fed 15N-ammonium for 1 hr, theamide nitrogen of glutamine showed the highest 15N abundance.Moreover, glutamine amino, glutamic acid, aspartic acid andalanine showed higher 15N abundance than ammonium did. In roots whose GS activity was inhibited with MS, both the amountof ammonium and its 15N abundance were increased. In contrast,both the amount of all examined amino acids containing glutamicacid and their 15N abundance decreased in roots whose GS activitywas inhibited. From these results, it could be concluded thatthe first step of ammonium assimilation in rice seedling rootswas mainly glutamine synthesis by GS and the second was glutamicacid formation by the GOGAT system. The results of an experiment using 15N glutamine also supportedthis conclusion. (Received February 23, 1977; ) 相似文献
15.
Nitrate Uptake and Reduction of Aseptically Cultivated Spruce Seedlings, Picea abies (L.) Karst 总被引:2,自引:0,他引:2
Spruce (Picea abies (L.) Karst.) seedlings were asepticallycultivated and the effects of different N-nutrition on net uptakeand reduction of nitrate were investigated. The characteristicsof nitrate uptake were calculated, Ks as 0?2 mol m3 andVmax as 18 µmol g1 d1. Low pH, and Al3+ in the medium caused adecrease in nitrate uptake rate. An in vivo assay was set upwhich allowed the measurement of NRA in both roots and needlesof spruce seedlings. The in vivo nitrate reductase activitywas repressed by ammonium and stimulated by nitrate. Nitratereduction was similar to nitrate uptake, negatively affectedby low pH and ammonium. Therefore, a limited N-supply to spruceseemed to occur when pH was low in the rhizosphere combinedwith the presence of Al3+ and . Key words: Spruce, nitrate uptake, nitrate reduction 相似文献
16.
Delhon Patricia; Gojon Alain; Tillard Pascal; Passama Lucien 《Journal of experimental botany》1995,46(10):1585-1594
The effect of light on NO3 utilization was investigatedin non-nodulated soybean (Clycine max L. Merr., cv. Kingsoy)plants during a 14/10 h light/dark period at a constant temperatureof 26C. A 3050% decrease of net NO3 uptake ratewas observed 26 h after the lights were turned off. Thiswas specifically due to an inhibition of NO3 influx asmeasured by 15N incorporation during 5 min. The absolute valuesof NO3 efflux depended on whether the labelling protocolinvolved manipulation of the plants or not, but were not affectedby illumination of the shoots. Darkness had an even more markedeffect in lowering the reduction of 15NO3 in both rootsand shoots, as well as xylem transport of 15NO3 and reduced15N. Concurrently with this slowing down of transport and metabolicprocesses, accumulations of NO3 and Asn were significantlystimulated in roots during the dark period. These data are discussedin view of the hypothesis that darkness adversely affects NO3uptake through specific feedback control, in response to alterationsin the later steps of N utilization which are more directlydependent on light. Key words: Glycine max, light/dark cycles, nitrate uptake, nitrate reduction 相似文献
17.
An existing system of flowing solution culture, in which pHand the concentration of several nutrient ions are automaticallymonitored and controlled, has been extended to include at 10 mmol N m3. A brief account is givenof the use of the equipment with a simulated sward of perennialryegrass (Lolium perenne L.). Uptake of measured over three successive days in June, varied with dailysolar radiation and exceeded 1000 mg N m2 d1.The uptake of showed a pattern of diurnal variation similar to the variation in solar radiation, but witha lag period for uptake of 5 h. Hourly uptake rates ranged from32 to 67 mg N m2h1 and solar radiation from 0to 2.8 MJ m2 h1. During a 24 h period, additionalmeasurements were made of K+ uptake and net H+ efflux, bothof which showed patterns of diurnal variation with lag periodsof 6 h hand 7 h, respectively. The stoichiometric ratio of thesum of and K+ to the net efflux of H+ was1.02: 1. Key words: Ion uptake, diurnal variation, Lolium perenne L. 相似文献
18.
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
19.
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
20.
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