Photosynthetic Adjustment to Temperature
Bibliographic record
Abstract
The description of a general mechanism for photosynthetic adjustment to temperature that encompasses all autotrophic species is not possible for three principal reasons: (i) inherent genetic diversity, (ii) differential strategies in growth and development, and (iii) organisms respond to temperature changes rather than to absolute temperature. Thus, ‘high’ and ‘low’ temperature are relative terms and will differ for pyschrophilic, mesophilic and thermophilic organisms. However, given this complexity, some consensus regarding photosynthetic adjustment to temperature is emerging. At low temperature (0–10 °C), photosynthesis is constrained thermodynamically. This may be manifested by chloroplast phosphate limitation due to reduced rates of sucrose synthesis and/or source-sink limitations. In this case, rates of CO2 uptake and O2 evolution are regulated directly through metabolite accumulation (feedback inhibition) and photosynthetic control. Alternatively, feedback inhibition may be regulated indirectly through catabolite repression of photosynthetic genes. Although light may exacerbate susceptibility to photoinhibition at low temperature in many species, cold grown, chilling-tolerant plants exhibit increased capacity for carbohydrate synthesis at low temperature which alleviates phosphate limitation, supplies a cryoprotectant and results in higher photosynthetic capacity than warm-grown plants. However, photosynthetic adjustment in cold-grown higher plants and algae does not reflect adjustment to low temperature per se, but rather, changes in excitation pressure on PS II. In contrast, photosynthesis in chilling-sensitive plants is not only constrained thermodynamically by low temperature but is also severely inhibited developmentally. Through a comprehensive molecular genetic study, a direct link between photosynthetic temperature acclimation and thylakoid lipid unsaturation has been established in cyanobacteria. However, the evidence for such a link in algae and higher plants is still equivocal. PS I may be primary site for photoinhibition at low temperatures in some chilling-sensitive species. Furthermore, susceptibility to low temperature photoinhibition is reduced by altering the level of unsatruation of chloroplast lipids in chilling-sensitive transgenic tobacco plants. With respect to high temperature (35–50 °C ), the consensus is that thylakoid membrane stability limits photosynthetic performance. In contrast to low temperature, light protects against high temperature inhibition of photosynthesis.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
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".