共查询到20条相似文献,搜索用时 31 毫秒
1.
Photosynthetic CO2 -fixation, chlorophyll content, growth rate and nitrate reductase activity were used to examine the influence of NH+ 4 -N and NO− 3 -N on Sphagnum magellanicum cultivated under defined conditions in phytotrons. NO− 3 -concentrations up to 322 μ M were found to be favourable. Increased NH+ 4 concentrations, however, resulted in growth inhibition and decreased chlorophyll content at concentrations ≧ 255 μ M ; e.g. 600 μ M NH+ 4 caused a 20% reduction of nitrate reductase activity and net photosynthesis. For raised bog Sphagna an improved standard nutrient solution is proposed with the following ion concentrations (μ M ): 55 Na+ ; 17 K+ ; 95 NH+ 4 ; 22 Ca2+ ; 22 Mg2+ ; 2 Fe3+ ; 20 Cl− ; 100 NO− 3 ; 57 SO2- 4 ; 7.4 H2 PO− 4 ; trace elements: A-Z solution (Hoagland) 50 μl 1000 ml−1 ; pH 5.8. 相似文献
2.
The uptake of the auxin type herbicide 2,4-D into rice seedlings ( Oryza sativa L. cv. Dunghan Shali) and its effects on the K+ , NH+ 4 and NO3 ion uptake and the K+ content were investigated at different pH values. A short incubation of the roots in 0.01 m M 2,4-D caused a marked ion uptake inhibition only at low pH. The non-auxin type herbicide benthiocarb did not produce such an inhibitory effect. Lowering of the pH in the external medium led to an increased 2,4-D uptake by the roots. These results can be explained by the increased H+ permeability of the membranes, allowing a more rapid entrance of 2,4-D into the root cells, thereby inhibiting the active ion uptake. Rice roots not subjected to 2,4-D treatment responded to H+ stress with an increased anomalous K+ uptake and a decreased K+ content. With reference to the effects of pH changes on the ion and 2,4-D uptake, possible transport mechanism of NH+ 4 and 2,4-D are briefly discussed. 相似文献
3.
Nitrite in the root zone and its effects on ion uptake and growth of wheat seedlings 总被引:1,自引:0,他引:1
The immediate and posteffects of various concentrations of NaNO2 on ion uptake of wheat ( Triticum aestivum L. cv. GK Öthalom) seedlings were studied at different pH values. Without pretreatment, the higher the concentration of NaNO2 the greater was the decrease in uptake of K+ into the roots, both at pH 4 and pH 6. At pH 6 but not at pH 4 the reverse was true when the seedlings were pretreated with NaNO2 . Due to the high Na+ content of the roots, an effect of Na+ in this process cannot be excluded. Nitrite was taken up by the roots more rapidly than nitrate. Nitrite at 0.1 m M in the medium induced the development of an uptake system for both NO− 2 and NO− 3 in wheat roots. At higher concentrations pretreatment with NO− 2 decreased NO− 3 uptake by the roots, but NO3 did not inhibit the uptake of NO2 . The toxic effect of NO− 2 was strongly pH dependent. Lower pH of the external solution led to an increased inhibition by NO− 2 of both ion uptake and growth of seedlings. The inhibitory effect of NO− 2 differed considerably for roots and shoots. The roots and especially the root hairs were particularly sensitive to NO− 2 treatment. 相似文献
4.
The two microspecies were Taraxacum sellandii Dahlst., which usually occurs in heavily fertilized grasslands, and Taraxacum nordstedtii Dahlst., which on the whole is restricted to undisturbed and mineral-poor habitats. Growth response curves were established, depicting the relative yield of (whole) plant tissue water and the internal K+ concentration (on a whole plant basis). The critical K+ concentration, i.e. the lowest [K+ ]i associated with maximal growth, was derived from the response curve. T. nordstedtii , the microspecies with the low maximal growth, showed a distinctly lower critical K+ concentration than T. sellandii. A relationship between growth potential and critical K+ concentration is proposed. Responses to a declining [K+ ]i differed between the two microspecies. The roots of T. nordstedtii stopped functioning as a sink for inulin, and mobilized additional carbohydrates for maintaining osmotic potential and growth. The productive strategy of the fast-growing T. sellantlii is lacking such a mechanism to buffer effects of a declining [K+ ]i .
Various changes were noted as regards the internal concentrations of other inorganic ions, measured as a function of [K+ ]i , With declining [K+ ]i , internal NO- 3 decreased considerably in shoot and roots, especially in T. nordstedtii , while Mg2+ accumulated, especially in the roots of T. sellandii. The interactions between growth potential and the accumulation of inorganic ions are discussed. 相似文献
Various changes were noted as regards the internal concentrations of other inorganic ions, measured as a function of [K
5.
Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO− 3 , H2 PO− 4 , K+ , Mg2+ and Ca2+ were investigated.
The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum . These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.
T. nordstedtii , a microspecies of infertile sites, was most efficient in absorbing NO− 3 , H2 PO− 4 and K+ . T. sellandii and T. eudontum , both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum , internal N concentration appeared to limit growth. Efficiencies in N use, at sub-optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii , from infertile sites, and T. sellandii , from fertile sites, were established as high and low extremes, respectively. 相似文献
The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum . These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.
T. nordstedtii , a microspecies of infertile sites, was most efficient in absorbing NO
6.
Differences in osmoacclimation between sporophytes and gametophytes of the brown alga Ectocarpus siliculosus 总被引:1,自引:0,他引:1
The osmoacclimation of Ectocarpus siliculosus isolates known to have different salt tolerances was investigated. Included were isolates originating from 5 different locations in the northern hemisphere, and sporophyte and gametophyte phases of different ploidy from two of the locations were compared. The effect of salinity treatment (8–64%0 ) on inorganic ions (K+ , Na+ , Mg2+ , Cl− , SO2− 4 , phosphate) and the low molecular weight carbohydrate mannitol was measured, together with complimentary measurements of cell viability. Very different responses between isolates were obtained, both between isolates of different geographic origin and between sporophytes and gametophytes from the same parent material. A similarity in response between haploid and diploid gametophytes, and diploid and triploid sporophytes indicates that physiological differences between gametophyte and sporophyte generations are not necessarily based on ploidy changes alone. There were no identifiable differences in the responses of male and female gametophytes. K+ is the major osmolyte within the species, and differences in the regulation of K+ largely account for the observed variation in osmoacclimation, both between life history phases and between isolates from different localities. Isolates with broader salt tolerances had the higher concentrations of mannitol. There were differences between isolates in the amounts and regulation of Cl− and phosphate, the latter being present in unusually high concentrations. There were also isolate differences in the concentrations of Mg2+ and SO2− 4 , although these divalent ions were present only in low concentrations. 相似文献
7.
Abstract The kinetic parameters of NH+ 4 -uptake in yeast cells were determined by a method that is based on the following changes in the external NH+ 4 concentration in cell suspensions by using NADH-dependent glutamate formation from NH+ 4 and 2-oxoglutarate. The kinetics of the observed NADH oxidation were analyzed by computer and enabled an estimation of V max and K m of the NH+ 4 -uptake system of the cells. 相似文献
8.
Non-steady state xylem transport of fifteen elements into the tomato leaf as measured by gamma-ray spectroscopy: A model 总被引:1,自引:0,他引:1
A model describing the transport of elements through the xylem vessels into the leaf of a red cherry tomato ( Lycopersicon esculentum Mill cv. Tiny Tim) in a non-steady state situation is presented. The model describes the upward movement of ions as a mass-flow of the xylem fluid with dissolved elements, with lateral ion escape represented by a first-order process. The model is fitted to data obtained in an experiment in which 15 elements were applied in a solution to a cut stem part with attached leaf and were measured simultaneously by gamma-ray spectroscopy. The model is in good agreement with the transport into the leaf of K+ Na+ , Rb+ , Cs+ , Yb3+ , Sm3+ Zn2+ , Co2+ , Cu2+ , Sb(SO4 )2 AsO3+ 4 , WO2+ 4 ; and Mo7 O6+ 24 .
Only indirect data could be obtained for Cd2+ and La3+ because of their apparently high affinity for charged sites in the cell walls and high escape constant, respectively. The escape constants were relatively low for all anions, probably due to the presence of a large number of negative charges in the cell walls. 相似文献
Only indirect data could be obtained for Cd
9.
Developmental changes in tomato fruit composition in response to water deficit and salinity 总被引:6,自引:0,他引:6
Processing tomato ( Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na2 SO4 /CaCl2 ) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (Ψ ) and soluble solids content were determined throughout development. Fruit Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in Ψ of stressed fruits. Mineral ions (Na+ , K+ , Ca2+ , Mg2+ , Cl− and SO2- 4 ) contributed –0.31 MPa to Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K+ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit Ψ , but were independent of fruit K+ . Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits. 相似文献
10.
EFFECTS OF ELEVATED [K+]0 ON THE RELEASE OF NEUROTRANSMITTERS FROM CORTICAL SYNAPTOSOMES: EFFLUX OR SECRETION? 总被引:5,自引:0,他引:5
John W. Haycock William B. Levy Larry A. Denner Carl W. Cotman 《Journal of neurochemistry》1978,30(5):1113-1125
Abstract— Elevated K+ 0 elicited a substantial Ca-independent efflux of accumulated GABA from cortical synaptosomal fractions. Efflux from tissue labelled with either NE or choline was affected considerably less by elevated K+ pulses in the absence of calcium. K-facilitated Ca-dependent efflux was large for all three of the accumulated substances. K-dependent (Ca-independent) efflux of accumulated GABA was associated with all subcellular fractions exhibiting GABA accumulation whereas K-facilitated Ca-dependent efflux was restricted to fractions containing synaptosomes. Eighty per cent of both GABA accumulation and K-dependent efflux was, however, recovered in a purified synaptosomal fraction. Alanine slightly decreased GABA accumulation, but % K-dependent efflux was not affected.
Elevated K+ , in the absence of calcium, released GABA from accumulated pools in preference to endogenous pools, whereas the Ca-dependent efflux, facilitated by K+ , was similar for both accumulated and endogenous GABA.
The Ca-independent efflux of accumulated GABA increased linearly with log [K+ ]0 between 10 and 70 mM-K+ in sodium-containing media. Prior treatment with veratridine or Na-free medium substantially decreased the Ca-independent but not the Ca-dependent GABA efflux produced by elevated K+ pulses.
The Ca-dependent and Ca-independent efflux of accumulated GABA in response to elevated K+ pulses is suggested to arise not only via different flux mechanisms but also from different GABA pools. The Ca-dependent efflux is interpreted to reflect stimulus-secretion coupling processes whereas the Ca-independent efflux may reflect membrane transport processes. 相似文献
Elevated K
The Ca-independent efflux of accumulated GABA increased linearly with log [K
The Ca-dependent and Ca-independent efflux of accumulated GABA in response to elevated K
11.
Andrés P. Sanz Conrado Moreno-Vivián José M. Maldonado Agustín González-Fontes 《Physiologia plantarum》1995,95(1):39-44
The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied in Anabaena variabilis ATCC 29413 cells grown under a constant supply of either N, NO− 3 or NH+ 4 at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO− 3 or NH+ 4 concentrations in the medium. In cultures containing 0.1 m M NO− 3 or 0.1 m M NH+ 4 nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2 -grown cells. This activity was still present with 1 m M NO− 3 or 1 m M NH+ 4 in the medium and even with 10 m M NO− 3 , but it was completely inhibited by 5 m M NH+ 4 . Ferredoxin-nitrate reductase (EC 1.7.7.2) activity was detected only in NO− 3 grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+ 4 , promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+ -isocitrate dehydrogenase (EC 1.1.1.42), and NAD+ -malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon-nitrogen metabolism in cyanobacteria. 相似文献
12.
Embryogenic cultures of cultivated carrot ( Daucus crota cv. Scarlet Nantes) were initiated from seedling hypocotyls on hormone-containing nutrient medium and from wounded zygotic embryos on hormone-free medium. Both of these cultures were maintained with continuous multiplication as unorganized, embryogenic cell masses on hormone-free medium at pH 4.0, containing NH+ 4 as the sole nitrogen source. When grown on hormone-free medium at pH 4.0, neither culture contained any elongated cells. Virtually all cells were densely cytoplasmic and nearly spherical. Some cells were enlarged, not densely cytoplasmic, but always spherical. When either culture was transferred to an auxin-containing medium at pH 5.8, numerous elongated cells were produced. Elongated cells were observed when either naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid was used, and whether the nitrogen source was NH+ 4 alone or a combination of NH+ 4 and NO− 3 . Elongated cells were more abundant when a combined nitrogen source was used. When cultures containing elongated cells were transferred to and multiplied on hormone-free or hormone-containing medium buffered at pH 4.0, all elongated cells disappeared after 2 weeks. No elongated cells were observed in any of the lines tested at pH 4.0. These results clearly show that it was the pH of the culture medium and not the presence or absence of an auxin or the nitrogen source(s) that permitted or prevented cell elongation in the embryogenic cultures tested. 相似文献
13.
Abstract The utilization of NO− 3 , NO− 2 and NH+ 4 was studied in whole filaments and isolated heterocysts of Anabaena 7120 (ATCC27893). NO− 3 - and NO− 2 -uptake were detectable in whole filaments but not in heterocysts, whereas NH+ 4 -uptake was detectable in both. Activity of NO− 3 -reductase was present in cell-free extracts of whole filaments but not of heterocysts, whereas activities of NO− 2 -reductase and glutamine synthetase were present in both. NO− 3 -uptake and reductase activities could not be induced in heterocysts even after prolonged incubation in NO− 3 medium. It is suggested that NO− 3 -metabolism in heterocysts is impaired due to a selective and irreversible loss of NO− 3 -uptake and reductase systems resulting in the abolition of competition for molybdenum cofactor (Mo-Co) and reductant between nitrogenase and NO− 3 -reductase, and an increase in glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase levels. 相似文献
14.
Net Glutamate Release from Astrocytes Is Not Induced by Extracellular Potassium Concentrations Attainable in Brain 总被引:2,自引:0,他引:2
Abstract: Elevated extracellular potassium concentration ([K+ ]e ) has been shown to induce reversal of glial Na+ -dependent glutamate uptake in whole-cell patch clamp preparations. It is uncertain, however, whether elevated [K+ ]e similarly induces a net glutamate efflux from intact cells with a physiological intracellular milieu. To answer this question, astrocyte cultures prepared from rat and mouse cortices were incubated in medium with elevated [K+ ]e (by equimolar substitution of K+ for Na+ ), and glutamate accumulation was measured by HPLC. With [K+ ]e elevations to 60 m M , medium glutamate concentrations did not increase during incubation periods of 5–120 min. By contrast, 45 min of combined inhibition of glycolytic and oxidative ATP production increased medium glutamate concentrations 50–100-fold. Similar results were obtained in both rat and mouse cultures. Studies were also performed using astrocytes loaded with the nonmetabolized glutamate tracer d -aspartate, and parallel results were obtained; no increase in medium d -aspartate content resulted from [K+ ]e elevation up to 90 m M , whereas a large increase occurred during inhibition of energy metabolism. These results suggest that a net efflux of glutamate from intact astrocytes is not induced by any [K+ ]e attainable in brain. 相似文献
15.
Seedlings of spring wheat ( Triticum aestivum L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K+ during different periods of time to produce plants with various K+ status. In one cultivation light-grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 m M K+ radiolabelled with 86 Rb. The uptake time was varied (5, 60 or 120 min).
The K+ concentration in the roots, [K+ ]root , increased during the course of the uptake experiments, especially in light and at initially low [K+ ]root , At the same time K+ (86 Rb) influx in the roots decreased. The simoidal relationship obtained between K+ (86 Rb) influx and [K+ ]root was affected by these changes, and Hill plots gave various Hill coefficients, nH , depending on the duration of the uptake experiments. nH from three apparently straight line segments of the same plot, in different [K+ ]root - intervals, indicated a falling degree of interaction between the binding sites as [K+ ]root increased. For the dark-grown plants negative cooperativity could not be demonstrated. 相似文献
The K
16.
Ammonium is known to inhibit nitrogenase activity, but at low concentrations it may support nitrogenase activity. This work describes the effect of different concentrations of NH+ 4 as the N-source for growth and particularly for nitrogenase-based production of hydrogen from malate, butyrate and lactate. Two different Rho-dopseudomonas strains (ATCC 23782 and ST 407) were tested. Best growth was observed in the lactate-NH+ 4 media. Photoproduction of H2 for cells grown with low levels (3.8 mmol/1) of NH+ 4 equalled that of cells grown with glutamate as N-source. 相似文献
17.
C.E. DEANE-DRUMMOND 《Plant, cell & environment》1985,8(2):105-110
Abstract. Net NO3 uptake by NO− 3 deficient Chara cells was used to calculate [NO− 3 ]c assuming that the cytoplasm occupies 10% total volume and that nitrate reduction and storage are negligible (i.e. maximum [NO− 3 ]c was calculated). A linear relationship was found between NO− 3 efflux and [NO− 3 ]c . There was an initial burst of NO− 3 efflux when NH+ 4 was added, followed by a slower efflux rate which matched influx rate such that net NO− 3 uptake was zero. Over 50% of NO− 3 that had been taken up in 2 h was lost within the first 5 min of NH+ 4 addition. The Nernst equation was used to predict the direction of the electrochemical driving force for NO− 3 entry. Under the experimental conditions used NO− 3 efflux is actively transported. The differential involvement of both NO− 3 influx and NO− 3 efflux in the regulation of NO− 3 uptake is discussed and a model is proposed to account for these results which envisages discrete NO− 3 influx and NO− 3 efflux carriers. 相似文献
18.
The use of compound continuous flow diffusion chemostats to study the interaction between nitrifying and nitrate-reducing bacteria 总被引:1,自引:0,他引:1
Abstract The interactions occuring between populations of a nitrate-respiring Vibrio sp. and autotrophic nitrifying bacteria belonging to the genera Nitrosomonas and Nitrobacter have been investigated in a compound bi-directional flow diffusion chemostat at a dilution rate of 0.025 h−1 and a temperature of 25°C. When grown under NO− 3 limitation, the Vibrio sp. produced NH+ 4 as the principal end-product of nitrate respiration, and there was a corresponding significant increase in cell numbers of the Nitrosomonas sp. population, which derived energy by the oxidation of NH+ 4 to NO− 2 . Nitrite in turn was used by the Nitrobacter sp. population as an energy source with the concomitant regeneration of NO− 3 . Under NO− 3 excess growth conditions the Vibrio sp. produced NO− 2 rather than NH+ 4 as the major product of NO− 3 dissimilation, and growth of the Nitrobacter population was stimulated as increased quantities of NO− 2 became available. In contrast, the Nitrosomonas sp. population declined sharply as the energy source NH+ 4 became limiting. These data demonstrate that defined mixed populations of obligately aerobic nitrifying bacteria and facultatively anaerobic nitrate respiring bacteria can co-exist for extended time periods and operate an internal nitrogen cycle which is energetically beneficial to both populations. 相似文献
19.
The effects of K+ concentration, light intensity and CO2 levels on the volume of Commelina communis L. guard cell protoplasts were studied. Two degrees of swelling response were observed, both dependent on an external supply of K+ , but not necessarily on the supply of a permeant anion. The presence of K+ itself, independent of light or CO2 level, stimulated swelling at a relatively slow rate. When K+ , light and low CO2 conditions were supplied together, the swelling was relatively rapid and of high magnitude. The rapid swelling was specific for K+ and Rb+ giving a half maximal effect after 2 h at a KCl concentration of about 18 mmol m−3 . The addition of CaCl2 at 1 mol m−3 inhibited K+ -dependent swelling under all conditions tested. The response to light and low CO2 levels by Commelina guard cell protoplasts is thought to reflect a high degree of physiological integrity. 相似文献
20.
Potassium ion channels in the plasmalemma 总被引:2,自引:0,他引:2
Friedrich-Wilhelm Bentrup 《Physiologia plantarum》1990,79(4):705-711
The potassium ion is an indispensible cytosolic component of living cells and a key osmolyte of plant cells, crossing the plasmalemma to drive physiological processes like cell growth and motor cell activity. K+ transport across the plasmalemma may be passive through channels, driven by the electrochemical gradient, K+ equilibrium potential (EK ) – membrane potential (Vm ), or secondary active by coupling through a carrier to the inward driving force of H+ or Na+ . Known K+ channels are permeable to monovalent cations, a permeability order being K+ > Rb+ > NH4 + > Na+ ≥ Li+ > Cs+ . The macroscopic K+ currents across a cell or protoplast surface commonly show rectification, i.e. a Vm -dependent conductance which in turn, may be controlled by the cytosolic activity of Ca2+ , of K+ , of H+ , or by the K+ driving force. Analysis by the patch clamp technique reveals that plant K+ channels are similar to animal channels in their single channel conductance (4 to 100 pS), but different in that a given channel population slowly activates and may not inactivate at all. Single-channel kinetics reveal a broad range of open times (ms to s) and closed times (up to 100 s). Further progress in elucidating plant K+ channels will critically depend on molecular cloning, and the availability of channel-specific (phyto)toxins. 相似文献