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1.
Nitrate Uptake and Assimilation following Nitrate Deprivation 总被引:2,自引:0,他引:2
Upon first exposure to , the uptake and reduction capacities of dark-grown corn (Zea maysL.) roots are initially low, but increase markedly within 6h. The development of the accelerated uptake rate appears to be substrate induced as is reductase (NR), the first enzyme in the assimilatory pathway. However, the inductionof uptake is independent of NR induction. The effect of deprivation was studied to determine the role of endogenous on subsequent uptake and reduction. Corn roots were induced for 24 h in 05 mol m3 nutrient solution and then exposed for 0 to 32 h to -free nutrient solution. Uptake and reduction of were determined periodically by exposing sets of roots to a1 h pulse of 0.5 mol m3 . Neither uptake (4.57 µmol root1 h1)nor the percentage of absorbed reduced (27%) was changed significantly (P 0.05) by exogenous deprivation. However, the estimated induced componentof uptake decreased significantly (50% after 32 h). Concurrently, the non-induced basal componentof uptake increased. Previously accumulated decreased from 23 to 4.5 µmol root1 after 32 h of exogenous deprivation. Nearly equivalent quantities of endogenous were used for translocation and reduction during deprivation. During each 1 h pulse, the amounts of translocation and net efflux of to the uptake solution were similar. Net efflux of was strongly correlated (r = 0.991) to the amount of endogenous . The remaining endogenous and its rate of utilization were apparently sufficient to minimize a rapid declineor complete loss in both the induced uptake state and the rate of in vivo assimilation. Key words: reduction, translocation, efflux, root, Zea mays L 相似文献
2.
TOLLEY-HENRY LESLIE; RAPER C. DAVID JR.; GRANATO TOM C. 《Journal of experimental botany》1988,39(5):613-622
Net uptake of by non-nodulated soybean plants [Glycine max (L.) Merr.cv. Ransom] growing in flowing hydroponiccultures containing 05, 1.0 and 10-0 mol m3 was measured daily during a 24-d period of vegetativedevelopment to determine if amplitude of maximum and minimumrates of net uptake are responsive to external concentrations of . Removal of from the replenished solutions during each 24-h period was determinedby ion chromatography. Neither dry matter accumulation nor theperiodicity of oscillations in net uptakerate was altered bythe external concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly3-fold in response to external concentrations. The maxima and minima, respectively, changed from 4.0 and 06mmol per gram root dry weight per day at an external solution level of 05 mol m3 to 152and -27 mmol per gram root dry weight per day at an external solution level of 100mol m3 . The negative values for minimum net uptake rate from100 mol m3 solutions show that net efflux was occurring andindicate thatthe magnitude of the efflux component of net uptake was responsiveto external concentration of . Key words: Nitrate uptake rate, carbon-nitrogen partitioning, flowing solution culture 相似文献
3.
Nitrate Transport Characteristics in Hordeum vulgare L. Seedlings using Three Different Tracer Techniques 总被引:2,自引:0,他引:2
Deane-Drummond, C. E. and Thayer, J.R. 1986. Nitrate transportcharacteristics in Hordeum vulgare L. seedlings using threedifferent tracer techniques.J. exp. Bot. 37: 429439. and have been used to investigate various properties of nitrate uptake and translocation intoHordeum vulgare L seedlings. Short term / influx into seed lings grown in CaSO4 was stimulated by after a lag of 2 h. The apparent kinetics of shortterm / influx over the concentration range 0?00?7mol m fitted Michaelis-Menten equations The apparent Vmax didnot change when seedlings were used that had been pretreatedin 10 or 100 mmol m3 and Vmax=3.77 and 3?56µmol g1 fr. wt. h1respectively. The apparent Michaelis constants were also similarand Km=0?47 and 0?45 mol m3 respectively. Longer term pulse chase experiments with the heavy isotope 15Nhave shown that feeding roots with resulted in the preferential appearance of 15N labelled aminoacids in the xylem sap. Pulse chase experiments with the radioisotope13N have shown that feeding shoots with resulted in a radial pattern of distnbution of labelin the leaf veins, which can be detected using autoradiography. The limitations and advantages of all three techniques are comparedby reference to other known experimental data. Key words: 36Chlorate, 13nitrate, 15nitrate, Hordeum vulgare 相似文献
4.
Expression of Characteristics of Ammonium Nutrition as Affected by pH of the Root Medium 总被引:6,自引:1,他引:5
CHAILLOU S.; VESSEY J. K.; MOROT-GAUDRY J. F.; RAPER C. D. JR; HENRY L. T.; BOUTIN J. P 《Journal of experimental botany》1991,42(2):189-196
To study the effect of root-zone pH on characteristic responsesof -fed plants, soybeans (Glycine max {L.}Merr. cv. Ransom) were grown in flowing solution culture for21 d on four sources of N (1.0 mol m3 , 0.67 mol m3 plus 0.33 mol m3, 0.33 mol m3 plus 0.67 mol m3 , and 1.0 mol m3) with nutrient solutions maintained at pH 6.0, 5.5, 5.0, and 4.5. Amino acid concentration increased inplants grown with as the sole source of N at all pH levels. Total amino acid concentration in the rootsof -fed plants was 8 to 10 times higher than in -fed plants, with asparagine accounting for more than 70% of the total in the roots of these plants.The concentration of soluble carbohydrates in the leaves of-fed plants was greater than that of -fed plants, but was lower in roots of -fed plants, regardless of pH. Starch concentration was only slightlyaffected by N source or root-zone pH. At all levels of pH tested,organic acid concentration in leaves was much lower when was the sole N source than when all or part of theN was supplied as . Plants grown with mixed plus N sources were generally intermediate between - and -fed plants. Thus, changes in tissue compositioncharacteristic of nutrition when root-zone pH was maintained at 4.5 and growth was reduced, still occurredwhen pH was maintained at 5.0 or above, where growth was notaffected. The changes were slightly greater at pH 4.5 than athigher pH levels. Key words: Ammonium, nitrogen nutrition, root-zone pH, soybean, tissue composition 相似文献
5.
BECANA MANUEL; APARICIO-TEJO PEDRO M.; S?NCHEZ-D?AZ MANUEL 《Journal of experimental botany》1986,37(6):798-806
Three-month-old plants (vegetative stage) of alfalfa (Medicagosaliva L cv. Aragon) were supplied for one week with 1.0dm3(uniformly distributed) nutrient solutions containing 0 or 20mol m3 . One week after initiation of treatment, the plants were subjected to drought by withholding water. Bacteroidsand cytosol of nodules were obtained at different stages ofstress, and used for enzyme assays and for determination of, and . Proteins of bacteroids were more stable than cytosolic proteinswith respect to the detrimental effects of water stress and. Protein contents of bacteroids and cytosol were inversely related to proteolytic activitiesagainst azocasein in both nodule fractions. Specific nitrate reductase activity (NRA) and nitrite reductaseactivity (NiRA) of bacteroids from -treated plants were inhibited by c. 70% and 45%, respectively, as leafwater potential (w) declined from 0.5 MPa (control) to1.8 MPa. At still lower w both activities began to increase:NRA was doubled, whereas NiRA only returned to its control level.Cytosolic NRA was strongly inhibited by drought, but the correspondingNiRA remained constant. Ammonia concentration in bacteroids and nodule cytosol keptbasically constant, whereas accumulated in the cytosol at severe stress, due to the activationof bacteroid nitrate reductase. Results indicate that nitrate and nitrite reductases of thebacteroids and the nodule cytosol act in different form: assimilatory,the cytosolic enzymes; and dissimilatory, the enzymes of bacteroidsat low w The possibility that assimilation of also occurs in bacteroids at control or mild waterstress conditions is suggested. Key words: Assimilatory and dissimilatory reduction, bacteroids, Medicago saliva, nodule cytosol, water stress 相似文献
6.
Intracellular pH Regulation in Ricinus communis Grown with Ammonium or Nitrate as N Source: The Role of Long Distance Transport 总被引:6,自引:0,他引:6
Allen, S. and Raven, J. A. 1987. Intracellular pH regulationin Ricinus communis grown with ammonium or nitrate as N source:the role of long distance transport.J. exp. Bot. 38:580596. Charge balance and intracellular pH regulation were studiedin Ricinus communis grown in water culture with 10 molm3 or l-0 mol m 3 as sole N source. Seedling and 70-d-old plant parts were analysed for total P, C, organic N and S, and ash alkalinity;xylem and phloem saps were analysed for mineral ion content,and amino acids, amides, and dicarboxylates. Excreted H+ andbase were also measured. It was shown that in -N plants, H + produced and excreted directly bythe roots accounted for all net COOH produced in theplant, but not for cation uptake by net H+ exchange. IntracellularpH perturbation in the shoot was regulated partly by reduction and partly by the transportof OH- -generating dicarboxylates in the xylem. Phloem sap hadthe capacity to transport organic N and carboxylates excessto shoot requirements back to the root. In -N plants, 60% of total reduction occurred in the root, and 70% of all OH- produced by root and reduction was excreted directly as base. Very little COOfrom root reduction was stored in the root: most was transported to the shoot as xylem dicarboxylateand stored in the shoot. Of the OH- produced from shoot and reduction, 40% was stored as shoot carboxylate: the phloem saphad the capacity to transport the rest back to the roots whereit was excreted as base. Key words: Intracellular pH, ammonium nutrition, nitrate nutrition, xylem dicarboxylates, phloem dicarboxylates, charge balance 相似文献
7.
The rate of exponential growth of Amphidinium carterae Hulburtwas the same (0.025 h1) with either or as sole N-source. Nevertheless, in short-term experiments, cells growing exponentially with as N-source took up added 56 times faster than . accumulated in the cells. Addition of inhibited, reversibly, disappearance of from the medium; prior N-deprivation of the cells did not affect this inhibition. N-repIetecells, grown with as N-source, took up for several hours both in light and darkness, butthe uptake by such cells soon ceased in darkness although it continued in light. When uptake ceased, the cells could still take up rapidly in darkness. Ammonium taken up was assimilated rapidly into organic-N includingglutamine, other amino acids and protein. Ammonium uptake in darkness was accompanied by the utilizationof cellular polysaccharide, mainly glucose polysaccharide. Mostof this carbon was unavailable for the dark assimilation of. Addition of the analogue, methylammonium, did not initiate polysacchande catabolism. Itis suggested that a control mechanism is in operation, througha product of assimilation, which operates on one or more of the enzymes concerned with polysaccharidebreakdown, for example, -amylase or phosphorylase. Uptake of was accompanied by a high rate of dark 14CO2 fixation and with both Amphidintum klebsii Kof.et Swezy and A. carterae N-deprivation led to a marked increasein this rate following addition of ; addition of had much less effect. The possible implications of these findings for the eco-physiology of marine dinoflagellatesare discussed. Key words: Ammonium, nitrate, CO2 fixation 相似文献
8.
The effect of level of different counterion forms of or or both, on establishment of the Rhizobium trifolii-Trifolium repens symbiosis was evaluatedin plants cultured under bacteriologically controlled conditions. Ammonium had little effect on nodule formation, and even after exhaustion there was little compensatory nodule formation. Plant growth, nodule mass and acetylene reductionactivity all declined with increasing levels of . Except for , different counterion forms had little effect on plant growth, nodule numberand mass, and acetylene reduction activity. Ammonium markedlydecreased pH, the extent being dependent upon level and counterion present. Nitrate inhibited nodulation while levels remained in excessof plant uptake. Compensatory nodulation followed exhaustionof or at lower or levels. Nodule mass and acetylene reduction activity decreased, but plant growth increased withincreasing or levels. Nitrate raised the pH of the nutrient solution by one unit orless. Different or counterion forms had little effect on the symbiosis or plant growth. Ammonium nitrate severely inhibited nodulation but on exhaustionmarked compensatory nodulation occurred. The patterns of nodulemass, acetylene reduction activity and plant growth with increasingNH4NO3 levels were similar to or alone. Plants provided with NH4NO3 or no nitrogenwere similar in only slightly decreasing pH. Key words: Ammonium, Nitrate, Ammonium nitrate, Nitrogen fixation, Rhizobium trifolii, Trifolium repens, Symbiosis establishment, Nodulation 相似文献
9.
Plants of two genotypes of Lolium perenne L. cv. S23 and a L.perenne ? L. multiflorum Lam. hybrid cv. Augusta were grownin flowing solution culture. N was suppled in one treatmentat 10 mmol m3 NO3 throughout (HN), and in another(LN) the N supply was terminated after 10 d for 11 d. When was re-supplied both LN and HN plants were leftentire or defoliated. The two genotypes showed similar responsesto all treatments. The concentration of N in shoot dry matterdeclined from 4.4% to 2.0% and in the root from 2.8% to 1.0%over the 11 d of N deprivation, with 95% of the initially present being assimilated during this period. LN plantsassimilated 10% more of their total uptake than did HN plants. The in vitro nitrate reductase activity(NRA) was 10- to 50-fold higher in the youngest fully-expandedleaves than in roots and declined in the leaves during N deprivation.Between 26 d after defoliation, there was a large increasein NRA in leaves of HN (but not LN) plants. After defoliationof HN plants, net uptake from 10 mmol m3 declined to negligible levels within 15 h, but in defoliatedLN plants it increased to levels similar to those of entireHN plants (1520 µmol h1 g1 fr. wt.root) within 8 h. When was re-supplied to entire LN plants, uptake of increased to levels similar to those of entire HN plants within 2.3 h, butdid not markedly exceed that of HN plants for at least 10 h.Net uptake of by LN plants during depletion of stirred static nutrient solutions containing 1.0 mol m3 lagged behind that by HN plants by 70100 min, but the maximum unit absorption rate was similar for LNand HN plants (57 µmol h1 g1 fr.wt. root). The nature of the short-term demand for uptake following recovery from the stresses of defoliation andN starvation is discussed. Key words: Lolium perenne, Lolium multiflorum, N-deficiency, defoliation, nitrate uptake, nitrate reductase, N-assimilation 相似文献
10.
Allen, S., Thomas, G. E. and Raven, J. A. 1986. Relative uptakerates of inorganic nutrients by and grown Ricinus communis and by two Plantago species.J. exp. Bot. 37: 419428. The relative rates of uptake and assimilation of C, N, P, S,Cl, K+ , Na+ Ca2+ and Mg2+ by and grown Ricinus conimunisand by NH4NO3- grown Plantago lanceolata and P. major were calculatedfrom data presented elsewhere. Results showed that for grown Ricinus the short term relativeuptake rates, for each nutrient X did not change significantly over the steady-state periodof exponential growth. The average gave , the mean relative uptake rate during exponential growth, for each nutrient. The amountof each nutrient taken up from a nutrient solution over a periodof time could, therefore, be calculated. For and -grown R. communis,the relative uptake rate of each nutrient was a constant fractionof the relative rate of carbon assimilation. It is suggestedthat this is typical of plants of cauline habit. For both Plantago spp., the relative rates of nitrogen uptakeand assimilation fell significantly during the exponential growthphase It is suggested that this could be a characteristic ofthe growth habit of the rosette plant. Key words: Relative uptake rates, Ricinus, Plantago, ammonium, nitrate, cauline, rosette 相似文献
11.
MACDUFF J. H.; HOPPER M. J.; WILD A.; TRIM F. E. 《Journal of experimental botany》1987,38(7):1104-1120
Oilseed rape plants (Brassica napus L. cv. Bien venu) were grownin flowing nutrient solution and acclimatized over 49 d to lowroot temperature (5 ?C) prior to treatment at root temperaturesof 3, 7, 11 or 17?C for 14 d, with common air temperature of20/15?C day/night and solution pH 6.0. The effects of root temperatureon growth, uptake and assimilation of N were compared with Nsupplied either as or at 10 mmol m3. Plant fresh weight, dry weight and leafarea increased with root temperature. Q10 values for specificgrowth rates between 7?C and 17?C were 1.10 and 1.33, respectively,under and nutrition. Fresh weight and leaf area were favoured by nutrition, particularly at 11 ?C and 17 ?C. At each temperaturethe net uptake of over 14 d was similar to that of , increasing 4-fold between 3?C and 17 ?C. Unit absorption rates of increased over the first 3 or 4 d, to an extent that increased with roottemperature. Thereafter, near constant values were maintainedat 3, 7 and 11 ?C. Unit absorption rates of at 3 ?C and 7 ?C did not increase over the first 3 or 4 d. Plantsat 17?C responded differently from those at other temperatures,with steep increases in unit absorption rates of and after day 8. The tendency for plants to adjust unit absorption rates of N over 14 d to become independentof root temperature was limited to the range 711 ?C.Q10 values between 7 ?C and 17 ?C for unit absorption rateswere 1.71.8 and 1.41.5, respectively, for and . Plants at 7, 11 and 17?C absorbed more than was subsequently assimilated, but at 3 ?C the absorption of was insufficient to meet the assimilatory demand. The results are discussed comparativelyfor and and in terms of the factors that determine unit absorption rates of N inresponse to a change in root temperature. Key words: Brassica napus, oilseed rape, root temperature, nitrate, ammonium, ion uptake rate 相似文献
12.
The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution: I. EFFECT OF CONCENTRATION 总被引:1,自引:0,他引:1
Experiments with simulated swards of perennial ryegrass (Loliumperenne L.) show the relationship between concentration in flowing nutrient solution, nitrate uptake,plant growth, and the chemical composition of roots and shoots.Rates of uptake exceeding 1 g N m2 d1 were maintainedat concentrations in solution down to 002 mg N l1. Short-term studies confirmed that at such lowconcentrations the plants were able to maintain rates of uptakeof about 85% of maximum. Between 02 and 200 mg N l1the concentration of in solution had little effect on rate of uptake or plant growth. With at 1000 and 2000 mg N l1 there was a marked reductionin weight of the shoots and, more particularly, in the lengthand tensile strength of the roots. There were several significanttrends in mineral composition of the plants (notably in S, Ca,Mg) which were apparently correlated with increasing concentrationof in solution. 相似文献
13.
The presence of exogenous stimulates O2evolution in illuminated H. africanum cells at the CO2 compensationpoint, and it is likely that reduction in the light uses reductant produced in non-cyclic electron flow.When sources of ATP other than fermentation are absent, thepresence of , light, and a functional non-cyclic electron transport pathway stimulates active, ATP-dependentH2 influx. This is consistent with non-cyclic electron flow associated with reduction being coupled to ATP synthesis. This -dependent ATP synthesis may be quantitatively important as a source ofATP during photolithotrophic growth with as N source in H. africanum and other algal unicells. 相似文献
14.
Lucas, W. J. and Ogata, K. 1985. Hydroxyl and bicarbonateassociatedtransport processes in Chara corallintr. Studies on the lightdarkregulation mechanism.J. exp. Bot. 36: 19471958.Experiments were undertaken on the fresh water alga Chara corallinato investigate the nature of the coupling between the chloroplastsand the lightdependent OH and -associated plasmalemma transport systems. Electrophysiologicalexperiments, in which DCMU was employed, revealed that thischemical could elicit a hyperpolarization of the membrane potentialthat was identical to that normally obtained by turning offthe light. This DCMUinduced hyperpolarization was obtainedunder control () and phosphatedecoupled conditions (). Measurements of the extracellular electric potentialswhich are associated with the acidic () and alkaline (OH) regions, indicated that, in the presenceof control ()or phosphatedecoupled conditions, normal profiles were established under air, oxygenor nitrogen environments. These results indicate that the generationof the control signal(s) is related to events associated withchloroplast electron transport, rather than to changes in theflow or levels of carbon intermediates within the reductivepentose phosphate or photorespiratory cycles. Although the levelof oxygen was found to have no effect on the lightinducedactivation of the OH regions, we found that in pure oxygen thedarkinduced inactivation of the OH efflux systemwas delayed, and that partial transport function could be maintainedin the dark. The possible involvement of changes in either theratio of oxidized to reduced ferridoxin or NADP? to NADPH, aspart of this lightmediated control signal, is discussed. Key words: Chara corallina, Plasma membrance transport, OH and , regulation 相似文献
15.
The translocation of various anions, cations, and acids acrossthe membrane system of turnip mitchondria has been investigatedby light scattering techniques. The results imply that the membranesof turnip mitochondria are not permeable to choline, K+, Na+,, , , and . It has been established that Cl,, and SCN passively permeate the mitochondrial membrane. It is probable that permeates as NH3 and that and cross the membrane either as the corresponding acid or on ananion/ hydroxide antiporter. The alkali metals Na+ and K+ equilibrateacross the membrane via specific H+/Na+ and H+/K+ antiporters,having similar activity at neutral pH. 相似文献
16.
Charge balance and intracellular pH regulation were studiedin Phaseolus vulgaris grown in water culture on or as N source, or nodulated and in N-free medium. Seedlings and 36-d-old plants were analysed for total P, C, organic N and S and ash alkalinity;xylem sap was analysed for mineral ion content and amino acids,amides and dicarboxylates. Both water uptake and H+ or baseexcreted during water culture were measured. It was shown that in -grown plants, H+ excretedwas related directly to the uptake and assimilation of ; there was no cation uptake associated with netH+ exchange. All shoot N was supplied as organic N, mainly glutamine,so that shoot pH perturbation would be limited to uronate productionin situ. This could be regulated by both shoot reduction and the transport of OH-generating carboxylatesin the xylem. In plants on , the great majority of reduction occurred in the root and most of the OHproduced was converted to -COO, transported up the xylemand stored, so that the leaves in particular had a high ashalkalinity (20-fold that in the roots). Some OH, however,was excreted. Nodulated plants had a low N content, compared with the others,indicating a low rate of N2-fixation for the earlier periodof water culture. At harvest, however, the xylem sap organicN content was comparable to that of plants. H+ excretion was in excess of that required for N assimilation.It was concluded that in these plants some net H+/cation exchangehad occurred which may have been a response to low nutrient(i.e. nitrogen) status. Key words: Phaseolus vulgaris, pH regulation, nitrate nutrition, ammonium nutrition, dinitrogen fixation, xylem sap composition. 相似文献
17.
The effect of growth temperature on the short term influx of86Rb+/K+, 36Cl/Cl, , 45Ca2+/Ca2+and into barley plants (Hordeum vulgareL. cv. Betzes) has been examined. When barley plants were grownwith a differential root: shoot temperature (15 ?C/25 ?C) therewas a marked stimulation of influx of all ions except Ca2+.Q10 measurements were close to 2.0 for all ions except Ca2+,where Q10 1.0 was found. Kinetics of ion influx showed thatthere had been almost complete compensation for the lower growingtemperature over a range of concentrations. The regulation of uptake was affected by growth temperature. On exposure to 15?C efflux/influx fell initially but was restored after 5 d. Sensitivity of net uptake to was increased by growth at a lower temperature. The importance of these observations in relationto application to field experiments and the proposed mechanismfor uptake is discussed. Key words: Growth temperature, Nitrate, Ammonium 相似文献
18.
Effects of light flux density (LFD) during growth and uptakeassay on induction of transport system and kinetics of transport were studied using the Azolla pinnata-Anabaena azollae association (Azolla). Theinduction and uptake kinetics of the transport system were determined using an automated system that measuredthe NO3 concentration in the growth medium as a function oftime, using an on-line high performance liquid chromatograph(HPLC) with a UV-VIS detector. Full induction of the transport system required about 1.5 to 2.0 h and occurred without any apparent lag phase,regardless of the LFD provided. The level of induction of transport of Azolla grown at 600 µmol m2s1 LFD was higher than for that grown at 100 µmolm2 s1. Similarly, 600 µmol m1 s1LFD during the assay resulted in a higher level of inductionthan did 100 umol m2 s1. An increase in the LFDeither during the growth or the assay period increased the uptake rate; however, an increase in LFD duringthe latter period had greater effect. Azolla grown and assayedat 600 umol m2 s1 had the highest uptake rate. The uptake rate at 50 cm3 m3ambient CO2 concentration was initially higher than at 305 cm3m3, but the uptake rate decreased rapidly with time andeventually dropped below that at 305 cm3 m3 CO2. Thesedata suggest that the energy required for transport in Azolla may bypass the photosynthetic CO2 fixationand carbon-cycling. Key words: carbon dioxide, concentration dependence, light flux density, uptake 相似文献
19.
Uptake of Methylammonium Ions by Hydrodictyon africanum 总被引:3,自引:0,他引:3
Methylamine influx into Hydrodictyon has been measured with[l4C]methylamine. The influx increases with rising externalpH up to about pH 8. Between pH 8 and 9 influx remains quiteconstant, with a further increase above pH 9. Influx is light-dependent,temperature-sensitive, and is decreased by . During short-term influx (less than 4 h) metabolism of methylamineappears negligible. Prolonged influx results in CH3 accumulation, and efflux of K+, Na+, and H+. There is no effecton Cl influx. Methylamine decreases the membrane electricp.d. by 60120 mV at external concentrations of 0?21?0mM. The results indicate that, below pH 9, methylamine enters thecell almost entirely as CH3. It is suggested that a passive electrogenic uniporter is involved, and thatby analogy uniport of may also be expected in Hydrodictyon. The results are discussed in relation to theevidence for uptake of CH3 and by other plant cells. 相似文献
20.
Proliferation of Maize (Zea mays L.) Roots in Response to Localized Supply of Nitrate 总被引:15,自引:0,他引:15
Maize (Zea mays L.) plants with two primary nodal root axeswere grown for 8 d in flowing nutrient culture with each axisindependently supplied with . Dry matter accumulation by roots was similar whether 1.0 mol m3 was supplied to on( or both axes. When was supplied to only one axis, however, accumulationof dry matter within the root system was significantly greaterin the axis supplied with . The increased dry matter accumulation by the +N-treated axis was attributableentirely to increased density and growth of lateral branchesand not to a difference in growth of the primary axis. Proliferation of lateral branches for the + N axis was associatedwith the capacity for in situ reduction and utilization of aportion of the absorbed , especially in the apical region where lateral primordia are initiated. Althoughreduced nitrogen was translocated to the N axis, concentrationsin the N axis remained significantly lower than in the+N axis. The concentratio of reduced nitrogen, as well as invitro reductase activity, was greater in apical than in more basal regions of the +N axis. The enhancedproliferation of lateral branches in the + N axis was accompaniedby an increase in total respiration rate of the axis. Part ofthe increased respiration was attributable to increased massof roots. The specific respiration rate (umol CO2 exolved perhour per gram root dry weight) was also greater for the +N thanfor the N axis. If respiration rate is taken as representativeof sink demand, stimulation of initiation and growth of lateralsby in situ utilization of a localized exogenous supply of establishes an increased sink demand through enhancedmetabolic activity and the increased partitioning of assimilatesto the + N axis responds to the difference in sink demand between+N and N axes. Key words: NO3- reduction, NO3- uptake nitrogen partitioning, root respiration, sink demand 相似文献