Sj. Sawyer et L. Muscatine, Cellular mechanisms underlying temperature-induced bleaching in the tropical sea anemone Aiptasia pulchella, J EXP BIOL, 204(20), 2001, pp. 3443-3456
Temperature-induced bleaching in symbiotic cnidarians is a result of the de
tachment and loss of host cells containing symbiotic algae. We tested the h
ypothesis that host cell detachment is evoked through a membrane thermotrop
ic event causing an increase in intracellular calcium concentration, [Ca2+]
(i), which could then cause collapse of the cytoskeleton and perturb cell a
dhesion. Electron paramagnetic resonance measurements of plasma membranes f
rom the tropical sea anemone Aiptasia pulchella and the Hawaiian coral Poci
llopora damicornis labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO
) revealed no membrane thermotropic event. In addition, intracellular imagi
ng using Fura-2AM as well as labeling anemones with Ca-45 revealed no signi
ficant change in [Ca2+](i). However, bleaching could be evoked at ambient t
emperature with 25 mmoll(-1) caffeine without affecting [Ca2+](i). [Ca2+](i
) could be altered with ionomycin in isolated host cells, but ionomycin cou
ld not induce bleaching in A. pulchella. As caffeine can affect levels of i
ntracellular protein phosphorylation, the ability of other agents that alte
r intracellular levels of protein phosphorylation to evoke bleaching was in
vestigated. The protein phosphatase inhibitor vanadate could induce bleachi
ng in A. pulchella. Two-dimensional gels of P-32-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 enidarian bleaching is linked to a temperature-induced al
teration in protein phosphorylation.