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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00197333
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