The radiotracer N-13 was used to undertake compartmental analyses for
NO3- in intact non-mycorrhizal roots of Picea glauca (Moench) Voss. se
edlings. Three compartments were defined, with half-lives of exchange
of 2.5 s, 20 s, and 7 min. These were identified as representing surfa
ce adsorption, apparent free space, and cytoplasm, respectively. Influ
x, effux, and net flux as well as cytoplasmic and apparent-free-space
nitrate concentrations were estimated for three different concentratio
n regimes of external nitrate. external NO3- for 3d, influx was calcul
ated to be 0.09 mu mol . g(-1). h(-1) (at 10 mu M [NO3-](o)), 0.5 mu m
ol . g(-1). h(-1) (at 100 mu M [NO3-](o)), and 1.2 mu mol . g(-1). h(-
1) (at 1.5 mM [NO3-](o)). Efffux increased with increasing [NO3-[(o))
constituting 4% of influx at 10 mu M, 6% at 100 mu M, and 21% at 1.5 m
M. Cytoplasmic [NO3-] was estimated to be 0.3 mM at 10 mu M [NO3-](o),
2mM at 100 mu M [NO3-](o), and 4mM at 1.5mM [NO3-](o), while free-spa
ce [NO3-] was 16 mu M, 173 mu M, and 2.2 mM, respectively. A series of
experiments was carried out to confirm the identity of the compartmen
ts resolved by efflux analysis. Pretreatment at high temperature or ap
plication of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen per
oxide made it possible to distinguish the metabolic (cytoplasmic) phas
e from the remaining two (physical) phases. Likewise, varying [Pi] of
the medium altered efflux and thereby [NO3-](cyt), but did not affect
[NO3-](free) (space.)