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Cellular mechanisms underlying temperature-induced bleaching in the tropical sea anemone Aiptasia pulchella

Sara J. Sawyer^* and Leonard Muscatine

Department of Organismic Biology, Ecology and Evolution, University of California – Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA
Present address: 2410 Soda Canyon Road, Napa Valley, CA 94558, USA

View larger version (15K): [in a new window]   Fig. 1. Peak height ratio (height of the lipid signal/height of the water signal) of the electron paramagnetic resonance spectrum generated from membranes from Aiptasia pulchella and Pocillopora damicornis and labeled with 0.1 µmol l-1 TEMPO over the temperature range 0–40°C. r2=0.98 for each.

View larger version (14K): [in a new window]   Fig. 2. The effect of a 2.5 h treatment with different concentrations of caffeine on release of symbiotic algae from Aiptasia pulchella. The control (C) anemones were held at 25°C, while the cold-shocked anemones (CS) were held at 12°C for 2.5 h. Cell release is expressed as a percentage of the total number of symbiotic dinoflagellates in the anemone [(released/released+retained)x100] released into the medium. Values are means + S.E.M., N=15 in each condition. *Significantly different from the control value, P0.01.

View larger version (14K): [in a new window]   Fig. 3. The effect of varying the duration of exposure to 25 mmol l-1 caffeine on release of symbiotic algae from Aiptasia pulchella. The control anemones (C) were held at 25°C, while the cold-shocked anemones (CS) were held at 12°C for 2.5 h. Cell release is expressed as a percentage of the total number of symbiotic dinoflagellates in the anemone [(released/released+retained)x100] released into the medium. Values are means + S.E.M., N=5 in each condition. *Significantly different from the control value, P0.01.

View larger version (55K): [in a new window]   Fig. 4. Photomicrographs of the product of release from Aiptasia pulchella after treatment with 25 mmol l-1 caffeine. In A, the product was stained with 0.01 % fluorescein diacetate (x4000). Host cell cytoplasm is visible at the interstices of the algae; in B, the product was stained 0.01 % Hoechst 33258 (x4000). The host cell nucleus is visible adjacent to the algal doublet.

View larger version (11K): [in a new window]   Fig. 5. The effect of a 2.5 h treatment with 25 mmol l-1 caffeine on the percentage of total protein released from aposymbiotic Aiptasia pulchella. The control anemones were held at 25°C, while the cold-shocked anemones were held at 12°C for 2.5 h. Values are means + S.E.M., N=6 in each condition.

View larger version (13K): [in a new window]   Fig. 6. The intracellular Ca2+ concentration in isolated host cells from Aiptasia pulchella treated with either 10-6 mol l-1 ionomycin or 25 mmol l-1 caffeine. Ca2+ values were obtained from computer analysis of stored images of cells labeled with Fura-2AM. Values are means + S.E.M., N=20 for ionomycin-treated cells; N=12 for caffeine-treated cells.

View larger version (16K): [in a new window]   Fig. 7. The intracellular Ca2+ concentration in isolated host cells (N=30) from Aiptasia puchella and the Ca2+ concentration of a buffer containing 150 µmol l-1 Ca2+ obtained by Ca2+ imaging using the dye Fura-2AM during temperature stress. The cells were subjected to a temperature stress from 20.4 to 36° C and back to 22°C, while the buffer was subjected to a temperature change from 21.6 to 36.5°C and back to 22°C.

View larger version (11K): [in a new window]   Fig. 8. The amount of cAMP (pmol mg-1 protein) in the sea anemone Aiptasia pulchella cold-shocked at 12°C, held at 25°C (Control), incubated in 25 mmol l-1 caffeine at 25°C for 2.5 h or heat-shocked at 30°C for 14 h. Values are means + S.E.M., N=4. *Significantly different from the control value, P0.05.

View larger version (12K): [in a new window]   Fig. 9. The effect of a 2.5 h treatment with two concentrations of vanadate on the release of symbiotic algae from Aiptasia pulchella. The control anemones (C) were held at 25°C, while the cold-shocked anemones (CS) were held at 12°C for 2.5 h. Cell release is expressed as a percentage of the total number of symbiotic dinoflagellates in the anemone [(released/released+retained)x100] released into the medium. Values are means + S.E.M., N=4 in each condition. *Significantly different from the control value, P0.0004.

View larger version (47K): [in a new window]   Fig. 10. Autoradiographs of 32P-phosphorylated proteins separated by two-dimensional gel electrophoresis from the control value anemones held at 25°C, anemones cold-shocked at 12°C and anemones treated with 25 mmol l-1 caffeine for 2.5 h. The arrows point to a group of proteins that are of equal molecular mass (MW) but are differentially phosphorylated.

View larger version (24K): [in a new window]   Fig. 11. Schematic representation of how cell adhesion is controlled in the tropical sea anemone Aiptasia pulchella, indicating that increased and decreased temperature as well as altered protein phosphorylation induce host cell detachment.

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