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The Journal of Experimental Biology 204, 3443-3456 (2001)
© 2001 The Company of Biologists Limited

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

Sara J. Sawyer* and Leonard Muscatine{ddagger}

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

*Present address: Department of Biological Sciences, Southern Illinois University, Edwardsville, Box 1651, Edwardsville, IL 62026, USA (e-mail: sasawye{at}siue.edu)

Accepted July 13, 2001

Temperature-induced bleaching in symbiotic cnidarians is a result of the detachment and loss of host cells containing symbiotic algae. We tested the hypothesis that host cell detachment is evoked through a membrane thermotropic event causing an increase in intracellular calcium concentration, [Ca2+]i, which could then cause collapse of the cytoskeleton and perturb cell adhesion. Electron paramagnetic resonance measurements of plasma membranes from the tropical sea anemone Aiptasia pulchella and the Hawaiian coral Pocillopora damicornis labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) revealed no membrane thermotropic event. In addition, intracellular imaging using Fura-2AM as well as labeling anemones with 45Ca revealed no significant change in [Ca2+]i. However, bleaching could be evoked at ambient temperature with 25 mmol l–1 caffeine without affecting [Ca2+]i. [Ca2+]i could be altered with ionomycin in isolated host cells, but ionomycin could not induce bleaching in A. pulchella. As caffeine can affect levels of intracellular protein phosphorylation, the ability of other agents that alter intracellular levels of protein phosphorylation to evoke bleaching was investigated. The protein phosphatase inhibitor vanadate could induce bleaching in A. pulchella. Two-dimensional gels of 32P-labeled proteins from cold-shocked, caffeine-treated and control anemones show that both temperature shock and caffeine alter the array of phosphorylated host soluble proteins. We conclude that cnidarian bleaching is linked to a temperature-induced alteration in protein phosphorylation.

Key words: coral, bleaching, cellular dysfunction, protein phosphorylation, sea anemone, Aiptasia pulchella, coral, Pocillopora damicornis.


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© The Company of Biologists Ltd 2001