The cellular mechanisms involved in temperature-induced cnidarian bleaching

Temperature stress causes loss of algae (dinoflagellates) from the normally stable cnidarian-algal symbiosis and results in a condition known as bleaching. Bleaching is manifested as the detachment and loss of entire host cells containing their endosymbiotic algae and often leads to host mortality. The cellular mechanisms involved in the temperature-induced loss of host cells is the subject of this thesis.; We first tested whether temperature induced cnidarian bleaching is accompanied by altered plasma membrane fluidity. EPR measurements on animal plasma membranes from the tropical sea anemone, Aiptasia pulchella, and the coral, Pocillopora damicornis, labeled with two different spin probes revealed no thermotropic event in the plasma membranes from either animal over the temperature range 0-40{dollar}spcirc{dollar}C.; We then tested the hypothesis that host cell detachment is evoked through a temperature-induced change in the intracellular calcium ( (Ca{dollar}sp{lcub}2+{rcub}rbrackrmsb{lcub}i{rcub}{dollar}) which could then cause collapse of the cytoskeleton and perturb cell adhesion. Intracellular imaging of calcium-specific fluorochromes or measurement of {dollar}sp{lcub}45{rcub}{dollar}Ca flux revealed no significant change in (Ca{dollar}sp{lcub}2+{rcub}rbrackrmsb{lcub}i{rcub}{dollar} with temperature in A. pulchella. Additionally, using immunocytochemical techniques, we observed the microfilament and microtubule cytoskeleton in sections of both symbiotic and aposymbiotic Aiptasia pulchella at its growth temperature (25{dollar}spcirc{dollar}C) and after cold shock (2.5h at 12{dollar}spcirc{dollar}C) or heat shock (14h at 30{dollar}spcirc{dollar}C). There was no detectable affect of temperature shock on the gross organization of the microfilament or the microtubule network. Bleaching could be evoked in A. pulchella at 25{dollar}spcirc{dollar}C with 2.5 {dollar}times{dollar} 10{dollar}sp{lcub}-2{rcub}{dollar}M caffeine without changing (Ca{dollar}sp{lcub}2+{rcub}rbrackrmsb{lcub}i{rcub}{dollar} and without altering cytoskeletal architecture.; Caffeine affects phosphodiesterase activity; thus caffeine, and by inference temperature, may cause bleaching by affecting pathways of protein phosphorylation. Unlike temperature stress, caffeine induces an increase in intracellular cAMP. Both caffeine and temperature stress alter the phosphorylation of proteins as detected by 2-D gels of {dollar}sp{lcub}32{rcub}{dollar}P labeled proteins from cold shocked, caffeine treated, and control anemones.; The mechanism of temperature-induced cnidarian host cell detachment may ultimately reside in phenomena which alter protein phosphorylation.