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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 385 (1997), S. 59-61 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Inorganic nitrogen is available to plants in soil solution either as NO or as NH. Physiological competition at the root level for this resource may have profound effects on relative species performance in the field7. Most agricultural species and species confined to poor-quality ruderal or pioneer ...
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Rates of proton extrusion and potassium (86Rb) influx by intact roots of barley (Hordeum vulgare cvs. Fergus, Conquest and Betzes) plants were simultaneously measured in short-term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K+ concentrations (0.01 to 1 mol m−3), H+ efflux and K+ influx were strongly correlated in both low- and high-K+ roots, although K+: H+ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m−3), H+ efflux was either reduced or remained unchanged while K+ influxes increased. In the presence of Na2SO4, rates of H+ extrusion demonstrated similar cation dependence, although below 10 mol m−3 Na2SO4, H+ fluxes were generally 50% lower than in equivalent concentrations of K2SO4. These observations are considered in the context of current hypotheses regarding the mechanisms of k+/H+ exchange.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 54 (1982), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Barley plants were grown in nutrient solutions, which were maintained at either 0 (-P) or 15 μM orthophosphate (+P). After 11 days phosphate influx into the intact roots of the -P plants began to increase by comparison with +P plants. During this period differences became apparent between the treatments in absolute growth rates, as well as in the root:shoot ratios. Phosphate influx in the -P plants continued to increase as a function of time, to a maximum value of 2.4 μmol (g fresh wt)-1h-1 at 16 days after germination. This rate was 6 times higher than influx values for +P plants of the same age. During the period of enhanced uptake phosphate was strongly correlated (r2= 0.77) with root organic phosphate concentration. – The enhancement of inorganic phosphate influx into intact roots of -P plants was rapidly reduced by the provision of 15 μM orthophosphate. Typically, within 4 h of exposure to this concentration of phosphate, influx values fell from 1.80 ± 0.20 to 0.75 ± 0.03 μmol (g fresh wt)-1 h-1, while inorganic phosphate concentrations of the roots increased from 0.12 to 1.15 μmol (g fresh wt)-1 during the same period. Hill plots of the influx data obtained during this period, treating root inorganic phosphate as an inhibitor of influx, gave Hill coefficients close to 2. The rapidity of the reduction of influx associated with increased root inorganic phosphate together with the Hill plot data provide evidence for an allosteric inhibition of influx by internal inorganic phosphate.
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Root NO3− and NH4+ influx systems of two early-successional species of temperate (trembling aspen: Populus tremuloides Michx.) and boreal (lodgepole pine: Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forest ecosystems were characterized. NO3− and NH4+ influxes were biphasic, consisting of saturable high-affinity (HATS) and constitutive non-saturable low-affinity transport systems (LATS) that were evident at low and relatively high N concentrations, respectively. NO3− influx via HATS was inducible (IHATS); nitrate pre-treatment resulted in 8–10-fold increases in the Vmax for influx in both species. By contrast, HATS for NH4+ were entirely constitutive. In both species, Vmax values for NH4+ influx were higher than those for NO3− uptake; the differences were larger in pine (6-fold) than aspen (1·8-fold). In aspen, the Km for NH4+ influx by HATS was approximately 3-fold higher than for IHATS NO3− influx, while in pine the Km for IHATS NO3− influx was approximately 3-fold higher than for NH4+ influx. The aspen IHATS for NO3− influx appeared to be more efficient than that of pine (Vmax values for aspen being approximately 10-fold higher and Km values being approximately 13-fold lower than for pine). By contrast, only small differences in values for the NH4+ HATS were evident between the two species. The kinetic parameters observed here probably result from adaptations to the N availabilities in their respective natural habitats; these may contribute to the distribution and niche separation of these species.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. A microcomputer-based system for the measurement of changes of ion activity (H+, NO3−, K+) in the uptake solutions during ion absorption by roots of intact plants is described. Ion activities are measured by means of ion-specific electrodes in a multichannel programmable voltmeter (data acquisition/control unit) which is activated by means of a microcomputer. Incoming data are stored digitally on tape cassettes or floppy discs via the microcomputer. The speed of sampling and large numbers of samples which can be simultaneously measured and recorded make this an extremely versatile system which might be employed for measuring and recording any number of analogue voltage signals.
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  • 6
    ISSN: 1432-2048
    Keywords: Cytochalasin B ; Cytoplasmic streaming ; Potassium translocation ; Koots (K+ translocation) ; Translocation (K+)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of cytochalasin B (CB), a potent inhibitor of cytoplasmic streaming, on 86Rb-labelled K+ translocation by detopped Lycopersicon esculentum Mill., Cucumis sativus L. and Zea mays L. plants was examined by measuring the radioactivity in xylem exudate before and after the addition of CB to the medium bathing the roots. CB caused complete cessation of cytoplasmic streaming in root segments within 15 min but was without effect on either total 86Rb uptake or exudation. Thus factors other than cytoplasmic streaming limit the movement of K+ across the symplast of the root of higher plants.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Planta 145 (1979), S. 395-397 
    ISSN: 1432-2048
    Keywords: Electrochemical potentials ; Hordeum ; Ion influx (root) ; Potassium influx ; Potential (electrochemical) ; Root (ion influx)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The electrochemical potential differences $$\left( {\Delta \overline \mu _{{\rm K}^ + } } \right)$$ for potassium, between excised barley (Hordeum vulgare L.) roots and external media containing 0.05 mM KCl+0.5 mM CaSO4, were determined over a 4-h period during which initially low-K+ roots accumulated K+ by pretreatment in 50 mM KCl plus 0.5 mM CaCl2. This pretreatment resulted in increased internal [K+], decreased K+ influx (as measured from 0.05 mM KCl+0.5 mM CaSO4) and decreased values of $$\Delta \overline \mu _{{\rm K}^ + }$$ . These observations indicate that the decline of K+ influx associated with increased internal K+ concentration cannot be accounted for by passive adjustment to the electrochemical gradient for this ion.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 196 (1995), S. 691-698 
    ISSN: 1432-2048
    Keywords: Ammonium ; Compartmental analysis ; Nitrogen-13 ; Picea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using 13NH 4 + as a tracer, compartmental analyses for NH 4 + were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH 4 + ([NH 4 + ]o), i.e. 0, 10, 100, and 1500 μM. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s, and 14 min, assumed to represent surface adsorption, Donnan free space, and cytoplasm, respectively. No significant differences were found in half-lives of exchange with changes in [NH 4 + ]o. Influx was calculated to be 0.96 μmol·g−1·h−1 in N-deprived plants (measured at 10 μM [NH 4 + ]o), while under steady-state conditions it was 0.21 μmol·g−1h−1 at 10 μM [NH 4 + ]o, 1.96 μmol·g−1h·−1 at 100 μM [NH 4 + ]o, and 6.45 μmol·g−1·h−1 at 1.5 mM [NH 4 + ]o. Efflux measured over the same range constituted approximately 9% of influx in N-deprived plants, 10% at 10 μM, 28% at 100 μM, and 35% at 1.5 mM [NH 4 + ]o. Cytoplasmic [NH 4 + ] was estimated at 6 m M in N-deprived plants, 2 mM at 10 μM [NH 4 + ]o, 14 mM at 100 μM, and 33 mM at 1.5 mM. Free-space [NH 4 + ] was 84 μM, 50 μM, 700 μM, and 8 mM, respectively. In comparison with previously published data on fluxes and compartmentation of NO 3 − in white-spruce seedlings, results of this study identify a pronounced physiological preference of this species for NH 4 + over NO 3 − as an inorganic N source in terms of uptake and intracellular accumulation. The significant ecological importance of this N-source preference is discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Planta 196 (1995), S. 674-682 
    ISSN: 1432-2048
    Keywords: Compartmental analysis ; Nitrate (compartmentation, flux) ; Nitrogen-13 ; Picea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The radiotracer 13N was used to undertake compartmental analyses for NO 3 − in intact non-mycorrhizal roots of Picea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO 3 − for 3 d, influx was calculated to be 0.09 μmol·g−1·h−1 (at 10 μM [NO 3 − ]o), 0.5μmol·g−1·h−1 (at 100 μM [NO inf3 sup− ]o), and 1.2 μmol · g−1· h−1 (at 1.5 mM [NO 3 − ]o). Efflux increased with increasing [NO 3 − ]o, constituting 4% of influx at 10 μM, 6% at 100 μM, and 21% at 1.5 mM. Cytoplasmic [NO 3 − ] was estimated to be 0.3 mM at 10 uM [NO 3 − ]o, 2mM at 100 μM [NO 3 − ]o, and 4mM at 1.5 mM [NO 3 − ]o, while free-space [NO 3 − ] was 16 μM, 173 μM, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO 3 − ]cyt, but did not affect [NO 3 − ]free space.
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  • 10
    ISSN: 1432-2048
    Keywords: Compartmental analysis ; Nitrate (induction of uptake) ; Nitrate reductase ; Nitrogen-13 ; Picea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using 13NO 3 − -efflux analysis, the induction of nitrate uptake by externally supplied nitrate was monitored in roots of intact Picea glauca (Moench) Voss. seedlings over a 5-d period. In agreement with our earlier studies, efflux analysis revealed three compartments, which have been identified as surface adsorption, apparent free space, and cytoplasm. While induction of nitrate uptake was pronounced, NO 3 − fluxes in induced plants were decidedly lower and the induction response was slower than in other species. Influx rose from 0.1 μmol·g−1·h−1 (measured at 100 μM [NO 3 − o) in uninduced plants to a maximum of 0.5 μmol·g−1h−1 after 3 d of exposure to 100 μM [NO 3 − o and declined to 0.3–0.4 μmol·g−1h−1 at the end of the 5-d period. Efflux remained relatively constant around 0.02-0.04 μmol·g−1h−1, but its percentage with respect to influx declined from initially high values (around 30%) to steady-state values of 4–7%. Cytoplasmic [NO 3 − ] ranged from the low micromolar in uninduced plants to a maximum of 2 mM in plants fully induced at 100 μM [NO 3 − ]o. In-vivo root nitrate reductase activity (NRA) was measured over the same time period, and was found to follow a similar pattern of induction as influx. The maximum response in NRA slightly preceded that of influx. It increased from 25 nmol·g−1·h−1 without prior exposure to NO 3 − to peak values around 150 nmol· g−1h−1 after 2 d of exposure to 100 μM [NO 3 − ]o. Subsequently, NRA declined by about 50%. The dynamics of flux partitioning to reduction, to the vacuole, the xylem, and to efflux during the induction process are discussed.
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