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1.
Nitrate provision has been found to regulate the capacity forChara corallina cells to take up nitrate. When nitrate was suppliedto N sufficient cells maximum nitrate uptake was reached after8 h. Prolonged treatment of the cells in the absence of N alsoresulted in the apparent ability of these cells to take up nitrate.Chlorate was found to substitute partially for nitrate in theinduction step. The effects on nitrate reductionwere separated from those on nitrate uptake by experiments usingtungstate. Tungstate pretreatment had no effect on NO3uptake induced by N starvation, but inhibitedNO3 uptake associated with NO3 pretreatment. Chloridepretreatment similarly had no effect on NO3 uptake inducedby N deprivation, but inhibited NO3 uptake followingNO3 pretreatment. The data suggest that there are atleast two mechanisms responsible for the inductionof nitrate uptake by Chara cells, one associated with NO3reduction and induced by CIO3 or NO3and one associated with N deprivation. Key words: Nitrate, Chlorate, Chara corallina, Induction 相似文献
2.
Uptake of 13C and 15N (ammonium, nitrate and urea) by Microcystis in Lake Kasumigaura 总被引:1,自引:0,他引:1
The uptake rate of carbon and nitrogen (ammonium, nitrate andurea) by the Microcystis predominating among phytoplankton wasinvestigated in the summer of 1984 in Takahamaira Bay of LakeKasumigaura. The Vmax values of Microcystis for nitrate (0.0250.046h1) and ammonium (0.150.17 h1) were considerablyhigher than other natural phytoplankton. The ammonium, nitrateand urea uptake by Microcystis was light dependent and was notinhibited with nigh light intensity. The K1 values were farlower than the Ik values. The carbon uptake was not influencedby nitrogen enrichment. Microcystis accelerated the uptake rateby changing Vmax/K s value when nitrogen versus carbon contentin cells declined. Nitrate was scarcely existent in TakahamairiBay during the summer, when Microcystis usually used ammoniumas the nitrogen source. However, the standing stock of ammoniumin the water was far lower than the daily ammonium uptake rates.Therefore, the ammonium in this water had to be supplied becauseof its rapid turn-over time (0.72.6 h). 相似文献
3.
Whole Plant Studies using Radioactive 13-Nitrogen: II. A COMPARTMENTAL MODEL FOR THE UPTAKE AND TRANSPORT OF NITRATE IONS BY Zea mays 总被引:1,自引:0,他引:1
Nitrate ion uptake by the roots of hydroponically grown maizeseedlings was measured using the short-lived isotope 13N. Itis shown to be described by a four compartment model, recognizablynitrogen in the root bathing solution, nitrogen which is readilyexchangeable from the root, nitrogen bound in the root, andnitrogen transported from the root. Some of the absorbed activity leaks back into the root bathingsolution with the efflux from the root, as a fraction of theinflux, increasing with concentration to be greater than 08at external nitrate ion concentrations above about 1.0 mol m3.The capacity of the exchangeable root pool increases with externalnitrate ion concentration, approaching the expected cytoplasmicnitrate ion content at the highest external nitrate ion concentrationsstudied (70 mol m3). The investigation has highlighted the problems of interpretinguptake profiles in experiments for which the 10 min half-lifeof 13N dictates experimental times that are comparable withthe times for saturation of root pools. Key words: Zea mays, 13N, Compartmental model, Nitrate uptake 相似文献
4.
Batch cultures of the nitrate-grown marine diatom, Skeletonemacostatum, were grown in various levels of nitrate supply, fromfull sufficiency of nitrate to 96 h of nitrate starvation Allthe cultures were maintained at low light intensity (50 µEm2 s1) to simulate the light regime of naturalphytoplankton populations in turbid waters or at the edge ofthe photic zone. The response of S costatum cells to perturbationswith 10 µM nitrate after variable starvation periods wasstudied At the deficiency-starvation borderline, the specieswas able to both increase its uptake rate and store intracellularnitrate pools. Surge, or initially high, uptake is characteristicof this situation. After long starvation periods the cells neededto acclimate to a nitrate environment before being able to utilizeit The time required for this was proportional to the previousstarvation period. Time courses of nitrate uptake and reductionwere strongly non-linear. Nitrate excretion was high (up to3 µM) under intermediate (24 and 36 h) starvation periods.Differences in the rates and times of uptake, reduction andassimilation produced strong uncoupling of the three processesThe results suggest that there is an adaptation to nitrate utilizationunder low light, nitrate shortage and discontinuous, suddennitrate inputs. 相似文献
5.
Nitrate uptake and the subsequent induction of in vivo nitratereductase activity in wheat were studied by investigating aeuploid and certain ditelosomic stocks which exhibited in vivoactivity significantly greater than that of the euploid. Thekinetics of nitrate uptake were investigated, but the high activitiesof the ditelosomics were not caused by increased uptake of nitrate,although ditelo-7BL exhibited unusual uptake dynamics. Analysisof the induction of nitrate reductase activity revealed a biphasicgeneral pattern, with an initial rapid phase being followedby a slower but longer period of induction. The induction rateover the second period, although responsible for only a minorproportion of the total activity induced, was positively correlatedwith the final nitrate reductase level, unlike the rate overthe first induction period. Several stocks exhibited high inductionrates over one or other of the two phases, while ditelo- 1 Asshowed an abnormal monophasic induction pattern. At the endof the second period of induction, nitrate reductase activitybecame more or less steady, except for activity fluctuationsassociated with the time of application of induction stimuli. 相似文献
6.
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
7.
MATTSSON M; JOHANSSON E; LUNDBORG T.; LARSSON M.; LARSSON C.-M. 《Journal of experimental botany》1991,42(2):197-205
Growth and nitrate uptake kinetics in vegetatively growing barley(Hordeum vulgare L., cvs Laevigatum, Golf, and Mette) were investigatedin solution culture under long-term limitations of externalnitrogen availability. Nitrate was fed to the cultures at relativeaddition rates (RA) ranging from 0.02 to 0.2 d1. Therelative growth rate (RG, calculated for total plant dry weight)correlated well with RA in the range 0.02 to 0.07 d1.In the RA range from 0.07 to 0.2 d1 RG continued to increase,but an increasing fraction of nitrogen, added and absorbed,was apparently stored rather than used for structural growth.The RG of the roots was less affected by RA. Vmax, for net nitrateuptake increased with RA up to 0.11 d1, but decreasedat higher RA. The decline in Vmax coincided with a build-upof nitrate stores in both roots and shoots. Vmax, expressedper unit nitrogen in the plants (the relative Vmax, was higherthan required for maintenance of growth (up to 30-fold) at lowRA, whereas at higher RA the relative Vmax decreased. Kineticpredictions of steady-state external nitrate concentrationsduring N-limited growth ranged from 0.2 to 5.0 mmol m3over the RG range 0.02 to 0.11 d1. It is suggested thatthe nitrate uptake system is not under specific regulation atlow RA, but co-ordinated with root protein synthesis and growthin general. At RA higher than 0.11 d1, however, specificregulation of nitrate uptake, possibly via root nitrate pools,become important. The three cultivars showed very similar growthand nitrate uptake characteristics. Key words: Barley, growth, nitrogen limitation, nitrate uptake, kinetics 相似文献
8.
Uptake of 14C-urea by Thalassiosira pseudonana and Skeletonemacostatum grown in batch culture with NO2 and NO3as nitrogen sources was measured under three conditions: pre-depletion(when nitrogenous nutrient was present in the culture mediumat saturating concentrations), at-depletion (when nitrogenousnutrient could no longer be detected), and several hours post-depletion.Vmax-urea, the initial instantaneous uptake rate, remained constantunder all three conditions, and was in excess of uptake ratesrequired for cellular doubling. Variations in uptake under thethree conditions were observed, as functions of the length oftime over which uptake was observed and the growth rate of theculture. The maximum instantaneous uptake rate was not differentfor the three conditions; variations in uptake were due to theperiod of time over which the maximum uptake rate was maintained.The ability of cells to take up urea rapidly, even when adequatelynourished by NO2 and NO3, could be of significancein a low and variable urea-nutrient regime in the natural environment. 相似文献
9.
Three-month-old Carrizo citrange (hybrid of Citrus sinensisL. OsbeckxPoncirus trifoliata Blanco) seedlings were grown incontrolled environment chambers in pots of fine sand. Plantswere irrigated with either non-saline or saline solutions overa 3-week period. After these treatments, plants were transferredto vessels containing a 5 m M15NO3K (96% atom excess15N) solution,and transpiration as well as concentration of15N and Cl-in roots,stem and leaves were measured after 24 h. Transpiration and15NO3-uptakerates were inhibited after exposure to NaCl and the concentrationof salt pre-treatment determined the intensity of this inhibitoryeffect. To determine the effect of transpiration on NO3-absorption,net15NO3-uptake rate was measured in salt stressed and non-stressedplants exposed to different light intensities or relative humiditiesand also in detached roots. Reduction in NO3-uptake was moreclosely related to Cl-antagonism from salt stress than to reducedtranspiration rate. Copyright 1999 Annals of Botany Company Nitrate, absorption, inhibition transport system, salt, light and humidity. 相似文献
10.
Lin TY Liao BK Horng JL Yan JJ Hsiao CD Hwang PP 《American journal of physiology. Cell physiology》2008,294(5):C1250-C1260
H+-ATPase-rich (HR) cells in zebrafish gills/skin were found to carry out Na+ uptake and acid-base regulation through a mechanism similar to that which occurs in mammalian proximal tubular cells. However, the roles of carbonic anhydrases (CAs) in this mechanism in zebrafish HR cells are still unclear. The present study used a functional genomic approach to identify 20 CA isoforms in zebrafish. By screening with whole mount in situ hybridization, only zca2-like a and zca15a were found to be expressed in specific groups of cells in zebrafish gills/skin, and further analyses by triple in situ hybridization and immunocytochemistry demonstrated specific colocalizations of the two zca isoforms in HR cells. Knockdown of zca2-like a caused no change in and knockdown of zca15a caused an increase in H+ activity at the apical surface of HR cells at 24 h postfertilization (hpf). Later, at 96 hpf, both the zca2-like a and zca15a morphants showed decreased H+ activity and increased Na+ uptake, with concomitant upregulation of znhe3b and downregulation of zatp6v1a (H+-ATPase A-subunit) expressions. Acclimation to both acidic and low-Na+ fresh water caused upregulation of zca15a expression but did not change the zca2-like a mRNA level in zebrafish gills. These results provide molecular physiological evidence to support the roles of these two zCA isoforms in Na+ uptake and acid-base regulation mechanisms in zebrafish HR cells. ionocytes; Na+/H+ exchanger; skin; gill; embryo 相似文献
11.
The mechanism of uptake of dietary niacin (nicotinic acid) by intestinal epithelial cells is not well understood, and nothing is known about regulation of the uptake process. In this investigation, we used human-derived intestinal epithelial Caco-2 cells and purified intestinal brush-border membrane vesicles (BBMVs) isolated from human organ donors to assess niacin uptake. Our findings show niacin uptake by Caco-2 cells to be 1) temperature and energy dependent; 2) Na+ independent, but highly dependent on extracellular acidic pH; 3) saturable as a function of concentration, with an apparent Km of 0.53 ± 0.08 µM; 4) severely inhibited by the membrane-impermeable sulfhydryl group of reagents; and 5) highly specific for niacin but not affected by monocarboxylic acids. A marked trans stimulation in [3H]niacin efflux from preloaded Caco-2 cells by unlabeled niacin in the incubation buffer was also observed. These findings suggest the involvement of a specialized, pH-dependent, carrier-mediated mechanism for human intestinal niacin uptake. This suggestion was confirmed in studies with native human intestinal BBMVs. We also examined possible regulation of niacin uptake by Caco-2 cells via specific intracellular regulatory pathways. The results show that while the PKA-, PKC-, and Ca2+/calmodulin-mediated regulatory pathways play no role in regulating niacin uptake, a role for a protein tyrosine kinase (PTK)-mediated pathway is apparent. The results of these studies show for the first time the existence of a specialized, acidic pH-dependent, carrier-mediated system of niacin uptake by human intestinal epithelial cells that operates at the micromolar (physiological) range of niacin. The results also suggest the possible involvement of a PTK-mediated pathway in the regulation of niacin uptake. intestinal transport; transport mechanism; transport regulation 相似文献
12.
Most of the urea entering Chara australis cells is rapidly metabolizedto produce CO2, which diffuses out of the cells into the surroundingmedium. A simple and convenient apparatus to measure both the14C-urea retained by cells and the 14CO2 released into the mediumwas developed and used in a study of urea transport in Chara.The permeability coefficient for urea in the Chara plasmalemmawas estimated from the slope of an uptake versus concentrationfunction as 85 nm s-1. Computer modelling of urea uptake andmetabolism suggests that this could be a 20% underestimate ofthe true value.The corresponding permeability coefficients forthiourea and N-methyl-urea were estimated in the same way as34 and 35 nm s-1, respectively. These permeabilities are muchgreater than expected on the basis of either/water partitioncoefficients for the solutes and are consistent with the diffusionof urea and its similarly-sized analogues through aqueous poresin the plasmalemma.At external concentrations of urea less than20 mmol m-3, the bulk of the uptake is effected by a specifictransport mechanism with an apparent Km for urea of less than1.0 mmol m-3. This transport system operates most rapidly withexternal pH in the range 6.57.5 and is influenced bythe nitrogen status of the cell.Evidence is produced here suggestingthat the specific transport of urea may be an active process. Key words: Chara, urea uptake, metabolism, diffusion, specific transport 相似文献
13.
Mature field-grown kiwifruit vines (Actinidia deliciosa var.deliciosa cv. Hayward) were fertilized with 15N-labelled fertilizer(ammonium sulphate, 10 atom % 15N, 50 kgN ha-1) to investigatethe timing of uptake of fertilizer nitrogen (N) and its availabilityfor new season's growth. Treatments were applied on four occasions,representing 2, 6, 10 and 14 weeks prior to budbreak. Samplesof root, stem, cordon, fruiting cane, vacuum-extracted xylemsap, and new season's growth were collected at fortnightly intervalfrom early winter until 2 months after budbreak. Two weeks after application of each treatment, 15N equivalentto an average of 7% of the applied label was recovered in rootmaterial. Although label was taken up by roots, there was nomovement of 15N within the plant until about 1 month prior tobudbreak when it was measured in the stem and cordon. Fertilizernitrogen was not detected at the distal end of fruiting canes,and in new season's growth until 3-4 weeks after budbreak. Beforebudbreak, all nitrogen in the xylem sap was in amino forms.Nitrate appeared 4 weeks after budbreak, and although more enrichedwith 15N than the amino nitrogen, accounted for only 19% ofthe label. Eight weeks after budbreak, nitrate nitrogen accountedfor 57% of the label. There were no major treatment effects of 15N on vines in eitherspring or at harvest, although enrichments in fruit and leavesfrom the earliest treatment tended to be less at the end ofthe season than those from the later applications.Copyright1993, 1999 Academic Press Actinidia deliciosa, kiwifruit, nitrogen, 15N, nutrient uptake 相似文献
14.
Uptake capabilities for ammonium (NH4+) and urea by diatoms(Thalassiosira pseudonana and Skeletonema costatum) growingon oxidized forms of nitrogen were studied in short-term uptakeexperiments. Even when nutrient-saturated, an enhanced uptakecapability not coupled with the growth rate was present forNH4+ and urea. No such enhanced uptake ability was seen forNO2 or NO3 under either nutrient-saturated ornutrient-depleted conditions. The presence of NH4+ decreasedthe enhanced ability to take up urea, but the urea uptake ratein 5 min incubations remained greater than the growth rate evenwhen NH4+ was present. 相似文献
15.
Movements of K+ during Shutting and Opening of the Trap-Lobes in Aldrovanda vesiculosa 总被引:1,自引:0,他引:1
K+ movements during the shutting and subsequent opening of trap-lobesin Aldrovanda vesiculosa were measured using 86Rb as a tracerfor K+. Immediately after the shutting, a large amount of 86Rbpre-loaded in the trap-lobes was detected in the hollow spaceinside the shut trap. This may indicate that much of the K+in the active motor cells leaks out during the shutting, resultingin turgor loss in the cells. 86Rb(K+) uptake in the trap wasactive. During the opening process, enhanced 86Rb uptake wasobserved. The time course of this uptake was similar to thatof the opening of the trap-lobes, and both courses were acceleratedby IAA. Enhanced K+ uptake may restore the turgor in activemotor cells. The quantity of K+ that moved during the shuttingor opening was estimated as 20% of that in the active motorcells in the open state of the trap-lobes. The K+ efflux acrossthe membranes of the active motor cells may be caused by a largeincrease in bulk flow triggered by an action potential, andwas estimated as 6,200 pmol.cm2.
1 This paper is dedicated to the memory of Professor Joji Ashidawho established the physiology of rapid movement in Aldrovandavesiculosa. (Received July 22, 1982; Accepted November 11, 1982) 相似文献
16.
Methods are described for studying the uptake, by hydroponicallygrown Zea mays seedlings, of ammonium and nitrate ions labelledwith radioactive nitrogen-13, which has a half-life often minutes.For nitrate only, some of the activity absorbed by the rootexchanges back out again into the root bathing solution. Theamount of this activity is about five times too large to beattributable to exchange with ions in the root cortical apoplasm.Much of it must be transferred from the root symplasm with ahalf-time of exchange of 25 min. After exposing the rootto the labelled solution, equilibrium rates of transport to,and distribution in the shoot were attained within 2 min, fornitrate, or 5 min, for ammonium. The pools within the root,and the transport pathway through which the label passes musttherefore rapidly attain the specific activity of the nutrientsolution. Distribution patterns through the plant are reasonablyconsistent with earlier work on nitrogen assimilation and transport. Key words: Zea mays, Nitrate uptake, Amonium uptake, 13N tracer 相似文献
17.
L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake 总被引:1,自引:0,他引:1
The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H+ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The Km values of thethree affinity sites were 1.4 x 103 M, 1.3 x 104M, 4.3 x 105 M; the maximum velocity values were 3.3x 108, 4.5 x 109, 1.8 x 109 mol/10 min/4x 106 cells. (Received April 18, 1981; Accepted August 25, 1981) 相似文献
18.
The use of chlorate as an analogue for NO3 during nitrateuptake into Chara corallina cells has been investigated. NO3inhibits 36C1O3 influx into Chara over the concentrationrange 01000 mmol m3. Lineweaver-Burke plots ofthe data are characteristic of competitive inhibition by NO3in the low concentration range (0300 mmol m3 ClO3)and apparent KINO3 is 140 mmol m3 which is of a similarorder of magnitude as apparent KmCIO3- 180 mmol m3. Athigher substrate concentrations the inhibition by NO3was not characteristic of competitive or uncompetitive inhibition. 36C1O3/NO3 influx was dependent on K+ and Ca2+in the external medium and inhibited by FCCP. NO3 pretreatmentor N starvation increased subsequent 36C1O3/NO3influx into Chara. A comparison between rates of net NO3uptake and 36C1O3/NO3 influx supported the previoushypothesis that NO3 efflux is an important componentin the determination of overall uptake rates. Key words: Nitrate, Chara, 36CIO3 相似文献
19.
Transport of thiamine in human intestine: mechanism and regulation in intestinal epithelial cell model Caco-2 总被引:1,自引:0,他引:1
Said Hamid M.; Ortiz Alvaro; Kumar Chandira K.; Chatterjee Nabendu; Dudeja Pradeep K.; Rubin Stanley 《American journal of physiology. Cell physiology》1999,277(4):C645
The present studyexamined the intestinal uptake of thiamine (vitaminB1) using the human-derivedintestinal epithelial cells Caco-2 as an in vitro model system.Thiamine uptake was found to be 1)temperature and energy dependent and occurred with minimal metabolicalteration; 2) pH sensitive;3)Na+ independent;4) saturable as a function ofconcentration with an apparent Michaelis-Menten constant of 3.18 ± 0.56 µM and maximal velocity of 13.37 ± 0.94 pmol · mgprotein1 · 3 min1;5) inhibited by the thiaminestructural analogs amprolium and oxythiamine, but not by unrelatedorganic cations tetraethylammonium, N-methylnicotinamide, and choline; and6) inhibited in a competitive mannerby amiloride with an inhibition constant of 0.2 mM. The role ofspecific protein kinase-mediated pathways in the regulation of thiamineuptake by Caco-2 cells was also examined using specific modulators ofthese pathways. The results showed possible involvement of aCa2+/calmodulin (CaM)-mediatedpathway in the regulation of thiamine uptake. No role for proteinkinase C- and protein tyrosine kinase-mediated pathways in theregulation of thiamine uptake was evident. These results demonstratethe involvement of a carrier-mediated system for thiamine uptake byCaco-2 intestinal epithelial cells. This system isNa+ independent and is differentfrom the transport systems of organic cations. Furthermore, aCaM-mediated pathway appears to play a role in regulating thiamineuptake in these cells. 相似文献
20.
Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO2uptake and not an increased CO2, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation 相似文献