The ecophysiology of iron and vanadium accumulation by North Atlantic ascidians
Notice bibliographique
Résumé
Some ascidians (Tunicata, Ascidiacea) accumulate high levels of iron and/or vanadium in their tissues, the latter being very unusual among animals. Previous work has investigated aspects of the vanadium accumulation by Phlebobranch ascidians, including the identification of the vanadocytes, the oxidation state of the vanadium and the pH in the vacuole in which it is held, and a proposed reduction mechanism for vanadium. The iron dynamics of these animals have received comparatively little attention. There is also a lack of data on the ecophysiological aspects of ascidian metal accumulation. This thesis examines the seasonal variation in vanadium and iron concentrations of two Phlebobranch ascidians, Ciona intestinalis and Ascidia callosa, which accumulate vanadium and iron, and a Stolidobranch ascidian, Halocynthia pyriformis, which accumulates iron only. Experiments examined whether these metal concentrations are responsive to increased food availability and dissolved vanadium concentration. -- An HPLC method was developed to simultaneously measure vanadium and iron in large numbers of biological samples. Using this method, a study of the metal concentrations of some tissues of C. intestinalis from Woods Hole, USA, found that the vanadium and iron concentrations in the hemocytes and other tissues was higher in March than in the fall or summer sampling periods, corresponding with high activity of a key enzyme of a proposed reductive pathway (G6PDH). A feeding experiment investigated whether food availability/particle concentration affects the vanadium and iron concentrations of C. intestinalis. While there were few differences in metal concentrations among high and low food groups, vanadium levels were maintained and iron levels rose compared to animals sampled fresh from Woods Hole. The former may be indicative of low vanadium loss rates and the latter of the importance of dietary sources of iron. -- This pattern was confirmed by a year long study of the vanadium and iron concentrations of tissues of two ascidians from Newfoundland, Canada. A. callosa, a high level vanadium accumulator, exhibited a peak in the vanadium and iron concentrations of the hemocytes and other tissues in spring prior to the spring plankton bloom. This corresponded with an increase in both the total number of circulating hemocytes and the proportion of cells containing reduced vanadium. H pyriformis, a non vanadium accumulator, exhibited a peak in the iron concentration of some tissues at the spring bloom. A vanadium enrichment experiment indicated that A. callosa can respond to increased environmental vanadium concentration. Vanadium concentration of the hemocytes and other tissues initially increased, followed by a marked decline, although remaining elevated above that of control animals. The vanadium exposed animals also displayed an increase in the total number of circulating hemocytes and the number of vanadocytes in all sampling periods. The vanadium levels used in this experiment did not cause an increase in the vanadium concentration of H. pyriformis.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,002 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».