Mechanism of the Down Regulation of Photosynthesis by Blue Light in the Cyanobacterium <i>Synechocystis</i> sp. PCC 6803
Bibliographic record
Abstract
Exposure to blue light has previously been shown to induce the reversible quenching of fluorescence in cyanobacteria, indicative of a photoprotective mechanism responsible for the down regulation of photosynthesis. We have investigated the molecular mechanism behind fluorescence quenching by characterizing changes in excitation energy transfer through the phycobilin pigments of the phycobilisome to chlorophyll with steady-state and time-resolved fluorescence excitation and emission spectroscopy. Quenching was investigated in both a photosystem II-less mutant, and DCMU-poisoned wild-type Synechocystis sp. PCC 6803. The action spectra for blue-light-induced quenching was identical in both cell types and was dominated by a band in the blue region, peaking at 480 nm. Fluorescence quenching and its dark recovery was inhibited by the protein cross-linking agent glutaraldehyde, which could maintain cells in either the quenched or the unquenched state. We found that high phosphate concentrations that inhibit phycobilisome mobility and the regulation of energy transfer by the light-state transition did not affect blue-light-induced fluorescence quenching. Both room temperature and 77 K fluorescence emission spectra revealed that fluorescence quenching was associated with phycobilin emission. Quenching was characterized by a decrease in the emission of allophycocyanin and long wavelength phycobilisome terminal emitters relative to that of phycocyanin. A global analysis of the room-temperature fluorescence decay kinetics revealed that phycocyanin and photosystem I decay components were unaffected by quenching, whereas the decay components originating from allophycocyanin and phycobilisome terminal emitters were altered. Our data support a regulatory mechanism involving a protein conformational change and/or change in protein-protein interaction which quenches excitation energy at the core of the phycobilisome.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 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".