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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00197331
