Growth, photosynthesis, and gene expression in <i>Chlamydomonas</i> over a range of CO<sub>2</sub> concentrations and CO<sub>2</sub>/O<sub>2</sub> ratios: CO<sub>2</sub> regulates multiple acclimation states
Bibliographic record
Abstract
Growth, photosynthesis, and induction of two low CO 2 -inducible genes of Chlamydomonas reinhardtii Dangeard strain CC125 were quantified in a range of physiologically relevant CO 2 and O 2 concentrations (5%0.005% CO 2 and 20% or 2% O 2 ) using airlift bioreactors to facilitate the simultaneous measurement of both growth and in situ photosynthetic rates. Within these CO 2 concentration ranges, O 2 concentrations (20% vs. 2%) had no discernable effect on growth, photosynthetic rate, or induction of the periplasmic carbonic anhydrase (Cah1) and glycolate dehydrogenase (Gdh) genes in wild-type C. reinhardtii. These results failed to support the hypothesis that the CO 2 /O 2 ratio plays any role in signaling for the up-regulation of limiting CO 2 -induced genes and (or) of the CO 2 -concentrating mechanism (CCM). The mRNA abundance of the Cah1 and Gdh genes appeared to be regulated in concert, suggesting co-regulation by the same signaling pathway, which, because of a lack of an O 2 effect, seems unlikely to involve photorespiration or a photorespiratory metabolite. Instead, it appeared that the CO 2 concentration alone was responsible for regulation of limiting CO 2 acclimation responses. Based on growth, photosynthesis, and gene expression characteristics, three distinct CO 2 -regulated physiological states were recognized within the studied parameters, a high CO 2 (5%0.5%) state, a low CO 2 (0.4%0.03%) state, and a very low CO 2 (0.01%0.005%) state. Induction of Cah1 expression and Gdh up-regulation occurred at a CO 2 concentration between 0.5% and 0.4% CO 2 , delineating the high from the low CO 2 states. Photosynthetic characteristics also were distinct in the three CO 2 -regulated physiological states, e.g., the estimated K 0.5 (CO 2 ) of the high CO 2 , low CO 2 , and very low CO 2 states were 72, 10, and 0.9 µmol·L 1 CO 2 , respectively. In addition to a greater photosynthetic CO 2 affinity, the very low CO 2 state could be distinguished from the low CO 2 state by an increased cell-doubling time and a smaller cell size.Key words: algae, Chlamydomonas, CO 2 , gene expression, induction, photorespiration, photosynthesis.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.002 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 teacher head, 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".