Fragmentation of the gastrodermis and detachment of zooxanthellae in symbiotic cnidarians: a role for hydrogen peroxide and Ca2+ in coral bleaching and algal density control
Bibliographic record
Abstract
Coral bleaching involves the detachment of zooxanthellae and the simultaneous fragmentation of the gastrodermis. Results obtained with a cell permeant fluorescent probe for calcium ions (Ca2+) indicates that "thermal" bleaching is the result of a temperature related breakdown of the Ca2+ exclusion system. "Solar" bleaching, which takes place at lower temperatures and is driven by light, is the result of a build-up of photo-synthetically produced hydrogen peroxide in the tissues. Gastrodermal tissue with its symbionts, scraped from between septa of corals, was observed under controlled conditions of high light and temperature. Pieces of gastrodermis round off, zooxanthellae move to the surface, protrude from the surface and after a delay, detach, surrounded by a thin layer of host cytoplasm, inclusions and plasma membrane. The higher the temperature and light level the shorter the delay and higher the rate of algal detachment. Fragmentation by the ballooning-out and detachment of small spheres of cytoplasm (bleb formation) takes place simultaneously. This is likely to be due to oxidation, by hydrogen peroxide (H2O2), of -SH groups on the cytoskeleton and its attachment to the plasma membrane. Ground, polished and stained thin acrylic resin sections reveal similar processes taking place in artificially bleached corals. Isolated zooxanthellae and whole corals are shown to release H2O2 in the light. This process of algal detachment and fragmentation that takes place at normal sea temperatures may underlie the mechanism limiting algal populations in the gastrodermis and may be localized to areas with a concentration of algae near the membrane. At above-normal temperatures under the synergistic effect of light and temperature, the rate of production of H2O2 exceeds the rate at which can it be lost by diffusion or destroyed and H2O2 accumulates. This results in damage to the calcium exclusion system, detachment of zooxanthellae into the coelenteron and fragmentation of the gastrodermis. Rev. Biol. Trop. 54 (Suppl. 3): 79-96. Epub 2007 Jan. 15. El blanqueamiento de los corales implica el desprendimiento de zooxantelas y la simultánea fragmentación de la gastrodermis. Resultados obtenidos con una sonda florescente de iones Calcio (Ca2+) para células permeables, indican que el blanqueamiento "térmico" es el resultado de una interrupción del sistema de exclusión de Ca2+, provocada por la temperatura. El blanqueamiento "solar", que tiene lugar a temperaturas más bajas y está determinado por la luz, es el resultado de una acumulación de peróxido de hidrógeno producido fotosintéticamente en los tejidos. Para ver el proceso, se raspó tejido gastrodermal, junto con sus simbiontes, de entre los septos de los corales y se observó en condiciones controladas de luz y temperatura. Primero, los trozos de gastrodermis se dan vuelta, luego las zooxantelas se mueven hacia la superficie, sobresalen desde ella y tras un tiempo, se desprenden, rodeadas de una delgada capa de citoplasma del hospedero, inclusiones y membrana plasmática. Mientras mayor sea la temperatura y el nivel de luz, menor es el tiempo que tardan las zooxantelas en desprenderse y mayor es la tasa de desprendimiento algal. La fragmentación producida por el inflamación y el desprendimiento de pequeñas esferas de citoplasma (formación de ampollas), tiene lugar simultáneamente. Probablemente, esto es causado por oxidación en el citoesqueleto de grupos -SSH por el peróxido de hidrógeno (H2O2), y por su acoplamiento a la membrana plasmática. Secciones de resina acrílica delgada molida, pulida y teñida revelan que en corales blanqueados artificialmente se llevan a cabo procesos similares. Se ha demostrado que tanto las zooxantelas aisladas como los corales enteros, liberan H2O2 en la luz. Debajo este proceso de desprendimiento algal y fragmentación que tiene lugar a temperaturas normales en el mar, puede encontrarse el mecanismo que limita las poblaciones algales en la gastrodermis, el cual podría estar localizado en áreas con concentraciones de alga cerca de la membrana. A temperaturas más altas de lo normal, bajo el efecto sinérgico de la luz y la temperatura, la tasa de producción de H2O2 excede la tasa a la cual éste puede destruirse o perderse por difusión y, por ende,se acumula. Esto resulta en daño al sistema de exclusión de calcio, desprendimiento de zooxantelas hacia el celenterón y fragmentación de la gastrodermis.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 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".