COMPARTMENTATION AND FLUX CHARACTERISTICS OF NITRATE IN SPRUCE

The radiotracer N-13 was used to undertake compartmental analyses for NO3- 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, effux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. external NO3- for 3d, influx was calculated to be 0.09 mu mol . g(-1). h(-1) (at 10 mu M [NO3-](o)), 0.5 mu mol . 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 mM. 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-space [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 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 [NO3-](cyt), but did not affect [NO3-](free) (space.)