Cytosolic Concentrations and Transmembrane Fluxes of NH4 +/NH3. An Evaluation of Recent Proposals
Bibliographic record
Abstract
Ammonium (NH4 +) is an important, perhaps underestimated, nitrogen source for plant growth (Bloom, 1988; Glass, 1988; Kronzucker et al., 1997). In many agricultural soils it is present in millimolar concentrations in soil solution (Wolt, 1994), whereas in mature forest soils NH4 +:NO3 −ratios as high as 56:1 have been reported (Stark and Hart, 1997). In many such soils, NH4 + may constitute the only inorganic nitrogen source available to plants (Van Cleve et al., 1993). Physiological studies have demonstrated that NH4 + fluxes commonly exceed those of NO3 − from equimolar solutions, and when both ions are present, NO3 − influx is reduced within minutes of exposure to NH4 + (Lee and Drew, 1989; Gazzarini et al., 1999; Kronzucker et al., 1999). As a byproduct of photorespiration and the shikimic acid pathway, as well as through the turnover of various nitrogen pools, large quantities of NH4 + are also generated internally (Joy, 1988; Feng et al., 1998). Although much of this NH4 + is re-assimilated through the activity of Gln synthetase (GS), many plants show high values of NH4 + efflux, and some develop symptoms of toxicity when exposed to millimolar concentrations of NH4 + in nutrient media, particularly when NH4 + is the sole source of nitrogen. The actual mechanism of NH4 + toxicity is still unclear, despite extensive studies (Gerendas et al., 1997). For these reasons it is important to characterize subcellular compartmentation and fluxes of NH4 +.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".