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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00197332
