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1.
The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass 总被引:5,自引:0,他引:5
Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.J. exp. Bot.37: 919927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added 15N-labelled nitrate were exposed,in chambers, for 40 d to NH3 in the air at concentrations of16, 118 and 520 µg m3. At the highest concentrationof NH3, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg1 dry soil) and 35?2% with the higher rate (200mgN kg1 dry soil) At the intermediate concentration ofNH3, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH3, they were 5?1% and 32%. Most of the N derived from theNH3 remained in the leaves, but some was transported to theroots. The amount of N derived from the NH3 that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH3 per unit leaf area ranged from 1?7 µg dm2h1 at a concentration of 16 µg m3 to 29?0µg dm2 h1 at a concentration of 520 µgm3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH3 per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH3 in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum 相似文献
2.
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
3.
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
4.
The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses 总被引:2,自引:1,他引:1
Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO-3) content of root and shoot and NO-3 and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO-3 concentrations (0·120mol m3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m3 NO-3 For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO-3 concentration on the partitioning of NO-3 assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m3 At 5.020 mol m3 NO3,the data indicated that the shoot played an important if notmajor role in NO-3 assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO-3 assimilation at 0.5 mol m3NO-3 but shoot assimilation was predominant at 5.0 mol m3NO-3 Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m3 NO-3 Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap 相似文献
5.
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
6.
Carbon Dioxide and Ammonia Exchange in the Trachypogon Savannas of the Orinoco Llanos 总被引:1,自引:0,他引:1
Atmospheric carbon dioxide (CO2) and ammonia (NH2) exchangeswere determined in the Trachypogon savannas of the Orinoco Llanosusing the energy balance approach. Total dry mass and separatedry mass values of plant parts were used for a growth analysisof the community and for measurements of nitrogen content. Duringthe growth period, the net assimilation (P40) ranged from 0.102to 0.127 MJ m2 d1 (6.67.9 g dry mass m2d1). These figures were similar to mean crop growth ratemeasured using the mass balance approach (2.86.9 g drymass m2 d1). Analysis of the daily trend of theCO2 assimilated by the community showed a low total energy conversionof net photosynthesis (x = 0.7) compared with the values reportedfor tropical grasses. During the dry season, the community conserved71% of the maximum N accumulated during the previous wet season.Sixty-eight per cent of the community nitrogen content was lostas volatile NH3 from the community during the reproductive period.Results suggested that the predominant net NH3 efflux from thevegetation was determined by the low concentration of NH3 inthe atmosphere ( 1.8 µg m2) and the compensationconcentration point. However, N losses were balanced by annualnitrogen input to the community from precipitation and biologicalfixation. Thus, a redistribution rather than a loss of nitrogenseems to be occurring in the ecosystem. Carbon dioxide fluxes, ammonia fluxes, Trachypogon savannas, energy balance, growth analysis 相似文献
7.
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
8.
Imsande, J. 1986. Inhibition of nodule development in soybeanby nitrate or reduced nitrogen.J. exp. Bot. 37: 348355. Nodulation of hydroponically grown soybean plants [Glycine max(L.) Merr.] is inhibited by continuous growth in the presenceof 4· mol m3 KNO3 The presence of 4·0 molm3 starter nitrate for 3-6 d during noduledevelopment, however, subsequently stimulates nodule dry weightaccumulation and nitrogenase activity. These stimulations occureven though 4· mol m3 nitrate temporarily delaysnodule development, i.e. the late steps of nodule developmentare reversibly inhibited by a short-term exposure to 4·0mol m3 nitrate. On the other hand, treatment with 4·0mol m3 nitrate in excess of 14 d significantly reducesnodule dry weight Thus, extended growth in the presence of 4·0mol m3 KNO3 seems to block both early and late stepsof nodule development. Nodulation of hydroponically grown soybeansis also inhibited by continuous growth in the presence of 2·0mol m3 (NH4)2SO4 This inhibition is not caused by acidityof the growth medium. On the other hand, nodule development6 d after inoculation with Rhizoblum japonicum is not delayedby a 7-d exposure to 2·0 mol m3 (NH4)2SO4 butis partially inhibited by a prolonged exposure to (NH4)2SO4Because repression of nodulation by 4·0 mol m3KNO3 is more severe than that by 2·0 mol m3 (NH4)2SO4and because ammonium taken up by the soybean plant is not activelyoxidized to nitrate, it is suggested that there are at leasttwo mechanisms by which nitrate utilization represses noduleformation in soybean. Key words: Glycine max, nitrogen, nitrogen fixation, nodulation 相似文献
9.
Apparatus is described for exposing plants to low concentrationsof SO2 (50500µg m3 in air) and for measuringeffects on photosynthesis, dark respiration, and transpiration.Temperature, humidity, and irradiance in the chambers were controlledindependently, and fans ensured that leaf boundary layer resistanceswere low. Experiments with plants of Vicia faba in clean andpolluted air showed that: (i) a depression of net photosynthesisby 50 µg m3 SO2 depended on boundary layer resistanceand on irradiance; (ii) stomatal resistance was increased ordecreased by 50 µg m3 SO2 when relative humidityin the chambers was low (35% r.h., 22 °C) or high (50% r.h.,22 °C) respectively. 相似文献
10.
Rhizosolenia mats conduct extensive vertical migrations in theoligotrophic central North Pacific (cNP) gyre that permit thesediatoms to acquire nitrate at depth and return to the surfacefor photosynthesis. The ultimate fate of this N within the ecosystemis unknown, but may include remineralization by grazing, lossto depth by sinking biomass, or N excretion by Rhizosoleniamats. Direct release of N by mats into the mixed layer wouldrepresent an upward biological pump that circumvents the diffusionbarriers and nutrient sinks at the base of the oceanic euphoticzone. We examined Rhizosolenia mat N release along a transect(2831° N) in the summer of 2002 (Hawaii to California)and 2003 (Hawaii to west of Midway Island) using sensitive fluorometricand chemiluminescence methods. Nitrate, NO2 and NH4+release was determined. Nitrate and NH4+ release by the matsoccurred in both 2002 (22.84 ± 6.04 and 3.69 ±1.74 nmol N µg1 Chl a h1, respectively)and 2003 (23.74 ± 3.54 and 3.60 ± 0.74 nmol Nµg1 Chl a h1, respectively). Nitrite releaseonly occurred in the 2003 summer period but occurred in bothyears when Fe chelators were added. Fv/Fm values decreased westwardin 2003 suggesting a gradient of increasing physiological stresstowards the west. The various physiological measures are consistentwith concurrent Fe stress; however, other possibilities exist.Nitrate excretion was the dominant form of N release in bothyears and provided a substantial addition to the ambient nitratepool in the mixed layer. Rhizosolenia mat nitrate release suppliesat least 47% of the nitrate pool on daily basis, andpossibly as much as 27%. Rhizosolenia mats are part of a largephytoplankton community that appears to migrate, and rates couldbe significantly higher. Literature reports suggest little orno nitrification in the upper euphotic zone, and thus biologicaltransport and release of nitrate may be a major source to thisregion. This N release is uncoupled from upward CO2 transportand, like N2 fixation, provides a component of the N pool availablefor net carbon removal. 相似文献
11.
This work aimed to study the impacts of acquisition and assimilationof various nitrogen sources, i.e. NO3, NH4+ or NH4NO3,in combination with gaseous NH3 on plant growth and acid-basebalance in higher plants. Plants of C3 Triticum aestivum L.and C4 Zea mays L. grown with shoots in ambient air in hydroponicculture solutions with 2 mol m3 of nitrogen source asNO3, NH4+ or NH4NO3 for 21 d and 18 d, respectively,had their shoots exposed either to 320 µg m3 NH3or to ambient air for 7 d. Variations in plant growth (leaves,stubble and roots), and OH and H+ extrusions as wellas the relative increases in nitrogen, carbon and carboxylatewere determined. These data were computed as H+/N, H+/C, (C-A)/N,and (C-A)/C to analyse influences of different nitrogen sourceson acid-base balance in C3 Triticum aestivum and C4 Zea maysplants. Root growth in dry weight gain was significantly reduced bytreatment with 320 µg m3 NH3 in Triticum aestivumand Zea mays growing with different N-forms, whereas leaf growthwas not significantly affected by NH3. In comparison with C3Triticum aestivum, non-fumigated C4 Zea mays had low ratiosof OH/N in NO33-grown plants and of H+/N in NH4+- and NH 4NO3-grown plants. Utilization of NH3 from the atmospherereduced both the OHN ratios in NO3 -grown plantsand the H+/N ratio in NH4+ - and NH4NO3 -grown plants of bothspecies. Furthermore, Zea mays had higher ratios of (C-A)/Nin NH4+ - and NH4NO3-grown plants than Triticum aestivum. Thismeans that C4 Zea mays had synthesized more organic anion perunit increase in organic N than C3 Triticum aestivum plants.Within both species, different nitrogen sources altered theratios of (C-A)/N in the order: NH4NO3>NH4+>NO3.Fumigation with NH3 increased organic acid synthesis in NO3- and NH4+ - grown plants of Triticum aestivum, whereas it decreasedorganic acid synthesis in Zea mays plants under the same conditions.Furthermore, these differences in acid-base regulation betweenC3 Triticum aestivum and C4 Zea mays plants growing with differentnitrogen sources are discussed. Key words: Acid-base balance, ammonia, ammonium, nitrate, ammonium nitrate, C3 Triticum aestivum L., C4 Zea mays L. 相似文献
12.
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
13.
The layer of daytime concentration of Calanus ponticus (VC andVI C) performing daily vertical migrations and the layer ofwinter stock aggregation are confined to the depthof maximal gradient of the main pycnocline under an unusuallysharp oxycline. The concentration layer thickness ranges from2 to 2030 m and the Calanus concentration in it is >250ind. m3, sometimes being 3500 ind. m3 and evenmore. The population in the concentration layer is divided intotwo ecological groups: I, feeding and migrating specimens ofcopepodite stages V and VI, their body lipid contents being2560 µg min.1; and II, non-feeding and non-migratingspecimens of copepodite stage V, their body lipid contents being100150 µg ind.1. The relationship with oxygenconcentration was studied in both ecogroups. The experimentsshow that specimens of ecogroup II can exit at an oxygen concentrationof 0.06 ml 11, but at such concentration falling intoanabiosis. They die at 0.04 ml O2 11. Estimates of respirationof the group II specimens (winter stock) showthat lipids they store are sufficient for 7 months' survival.Depth of Calanus concentration is determined by water densityrather than concentration of oxygen. 相似文献
14.
Ammonium Nutrition in Ricinus communis: Its Effect on Plant Growth and the Chemical Composition of the Whole Plant, Xylem and Phloem Saps 总被引:2,自引:0,他引:2
Allen, S. and Smith, J A. C. 1986. Ammonium nutrition in Ricinuscommunis: its effect on plantgrowth and the chemical compositionof the whole plant, xylem and phloem saps.J. exp. Bot.37: 15991610. The growth and chemical composition of Ricinus communis cultivatedhydroponically on 12 mol m 3 NO3-N were comparedwith plants raised on a range of NH4+-N concentrations. At NH4+-Nconcentrations between 0·5 and 4·0 mol m3,fresh- and dry-weight yields of 62-d-old plants were not significantlydifferent from those of the NO3-N controls. Growth wasreduced at 0·2 mol m3 NH4+-N and was associatedwith increased root. shoot and C: organic N ratios, suggestingthat the plants were N-limited. At 8·0 mol m3NH4+-N, growth was greatly restricted and the plants exhibitedsymptoms of severe NH4+ toxicity. Plants growingon NH4+-N showed marked acidification of the rooting medium,this effect being greatest on media supporting the highest growthrates. Shoot carboxylate content per unit dry weight was lower at mostNH4+-N concentrations than in the NO3-N controls, althoughit increased at the lowest NH4+-N levels. Root carboxylate contentwas comparable on the two N sources, but also increased substantiallyat the lowest NH4+-N levels. N source had little effect on inorganic-cationcontent at the whole-plant level, while NO3 and carboxylatewere replaced by Cl as the dominant anion in the NH4+-N plants.This was reflected in the ionic composition of the xylem andleaf-cell saps, the latter containing about 100 mol m3Cl in plants on 8·0 mol m3 NH4+. Xylem-saporganic-N concentration increased more than threefold with NH4+-N(with glutamine being the dominant compound irrespective ofN source) while in leaf-cell sap it increased more than 12-foldon NH4+-N media (with arginine becoming the dominant species).In the phloem, N source had little or no effect on inorganic-cation,sucrose or organic-N concentrations or sap pH, but sap fromNH4+-N plants contained high levels of Cl and serine. Collectively, the results suggested that the toxic effects ofhigh NH4+ concentrations were not the result of medium acidification,reduced inorganic-cation or carboxylate levels, or restrictedcarbohydrate availability, as is commonly supposed. Rather,NH4+ toxicity in R. communis is probably the result of changesin protein N turnover and impairment of the photorespiratoryN cycle. Key words: Ricinus, ammonium nutrition, nitrate, whole-plant composition, xylem, Phloem, amino acids, carboxylate 相似文献
15.
LARSSON MARIE; LARSSON CARL-MAGNUS; GUERRERO MIGUEL G. 《Journal of experimental botany》1985,36(9):1373-1386
Larsson, M., Larsson, C.-M. and Guerrero, M. G. 1985. Photosyntheticnitrogen metabolism in high and low CO2-adapted Scenedesmus.I. Inorganic carbon-dependent O2 evolution, nitrate utilizationand nitrogen recycling.J. exp Bot. 36: 13731386 Scenedesmus obtusiusculus Chod. was grown on an inorganic mediumflushed with either air or air supplemented with 3% CO2. Inair-grown cells, O2 evolution dependent on low, but not high,HCO3 concentrations was strongly inhibited by the carbonicanhydrase inhibitor acetazolamide. Cells grown with 3% CO2 exhibitedlow rates of O2 evolution at low external inorganic C; however,after 30 min in air O2 evolution rates at low inorganic C approachedthose of air-grown cells. These results are compatible withthe view that Scenedesmus develops a CO2 concentratingmechanism in air, with carbonic anhydrase as an importantconstituent When 3% CO2-grown cells were subjected to air-level of CO2,just a transient decline in NO3 utilization was observed,but in the presence of acetazolamide the rate of the processdecreased drastically in response to the decrease in the CO2level. In CO2-free air NO3 was taken up at high ratesbut in a deregulated manner, leading to release of NH4+. A portionof the NO3 taken up in the absence of CO2 was apparentlyassimilated Cellular nitrate reductase (NR) activity initially decreasedbut subsequently recovered after a transition from 3% CO2 toair. In the presence of acetazolamide, a persistent decreasein NR activity was observed. Cellular glutamine synthetase (GS)activity increased after transition from 3% CO2 to air, theactivity increase being unaffected by acetazolamide. NH4+ releaseto the medium in the presence of L-methionine-D, L-sulphoximine(MSO) transiently increased in 3% CO2-grown cells in responseto a transfer to air. MSO-induced NH4+ release was in fact higherin air-grown cells than in 3% CO2-grown cells. Glycollate wasinitially released after transition from 3% CO2 to air, butthere was no difference in glycollate release between MSO-treatedand untreated cells. In air-adapted Scenedesmus, N recyclingseems to be of minor importance in comparison to primary N assimilation Key words: CO2-fixation, N recycling, nitrate uptake, Scenedesmus 相似文献
16.
The photosynthetic response to CO2 concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO2 or at10000 µmol(CO2) mol1 and in winter at 6000 µmol(CO2)mol1 Plants grown and measured at ambient CO2 had highphotosynthetic rate (35 µmo1(CO2) m2 s1),high saturating photon flux density (15002000) µmolm2 s1 and low sensitivity to temperature in therange 2040 °C. Maximum photosynthetic rate (63 µmol(CO2)m2 s1) was reached at an internal CO2 concentrationof 800 µmol mol1. Plants grown at high CO2 in summerhad photosynthetic capacities at ambient CO2 which were 15%less than for plants grown at ambient CO2, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO2and high light intensity had typical response curves to internalCO2 concentration with saturation at high CO2, but for plantsgrown under high CO2 and low light and plants grown under lowCO2 and high light intensity photosynthetic rates decreasedsharply at internal CO2 concentrations above 1000 µmol1. Key words: Photosynthesis, CO2, enrichment, Eichhornia crassipes 相似文献
17.
In a coastal area of southern Chile (41° S), the major ammoniumassimilating enzyme glutamine synthetase (GS) was detected ina green dinoflagellate bloom during April 2003. High chlorophylla concentrations (1000 µg L1) attributable to Gymnodiniumcf. chlorophorum in surface waters were associated with highand very low nitrate reductase activities. Coincident with thebloom, dissolved inorganic nitrogen concentrations were nearthe detection limit (NO3 + NH4+ <0.5 µM). SinceGS correlates with the use of ammonium as an external nitrogensource, we suggest that GS activity seems to be a good indicatorof ammonium utilization in a period dominated by a single dinoflagellatespecies. 相似文献
18.
Potassium-Ammonium Uptake Interactions in Tobacco Seedlings 总被引:6,自引:0,他引:6
SCHERER HEINRICH W.; MACKOWN CHARLES T.; LEGGETT J. EVERETT 《Journal of experimental botany》1984,35(7):1060-1070
Short-term (< 12 h) uptake experiments were conducted with67-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K+ andNH4+. At equal solution concentrations (0.5 mol m3) netK+ uptake was inhibited 3035% by NH4+ and NH4+ uptakewas decreased 924%. Removal of NH4+ resulted in completerecovery in K+ uptake rate, but NH4+ uptake rate did not recoverwhen K+ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m3. The relative effectof K+-NH4+ interactions was not altered when Cl- was replacedwith SO42, but the magnitudes of the uptake rates wereless in the absence of Cl-. The Vmax for NH4+ uptake was reducedfrom 128 to 105 µmol g1 dry wt. h1 in thepresence of 0.5 mol m3 K+ and the Km for NH4+ doubledfrom 12 to 27 mmol m3 in the presence of K+. The resultsof these K+-NH4+ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K+ coupled to NH4+influx via an antiporter cannot be ruled out as contributingto the decrease in net K+ uptake. Key words: Nicotiana tabacum, K+, NH4+, Uptake interactions 相似文献
19.
Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m2 s1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O2 and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 103 µmol O2 (µgChl a)1 h1 (µEinst m2 s1)1.Differences in maximum growth rate varied as the 0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m2s1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µIrelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµI curves and explained 97% of the observed interspecificvariability.
1Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA 相似文献
20.
Plants of Lolium perenne L. cv. S23 were grown in sand culturesupplied with either ammonium (NH4+) or nitrate (NO3)in an otherwise complete nutrient solution at 12°C or 20°C.Three weeks after germination, plants were clipped weekly tosimulate grazing. After 10 weeks growth all nitrogen (N) wassupplied enriched with 15N to quantify the effects of form ofN supply and temperature on the relative ability of currentroot uptake and remobilization to supply N for laminae regrowth. The form of N supply had no effect on the dry matter partitioning,while at 20°C more dry weight was allocated to laminae regrowthand less to the remaining plant material. The current root uptakeof N, which subsequently appeared in the laminae regrowth, wassimilar for plants supplied with NH4+ or NO3, and bothwere equally reduced at the lower temperature of growth. Remobilizationof N to laminae regrowth was greater for plants receiving NH4+than NO3; remobilization with either form of N supplywas reduced at the lower temperature of growth. Remobilizationwas reduced to a lesser extent at 12°C than current rootuptake. It was concluded that remobilization became relativelymore important in supplying N for regrowth of laminae at lowertemperatures. Key words: Lolium perenne, ammonium, nitrate, temperature, remobilization 相似文献