85.1 Friday, Jan. 6 Autophagic degradation and bleaching in the symbiotic anemone, Aiptasia pallida HANES, S. D.*; KEMPF, S. C.; Auburn University, Auburn, AL; Auburn University, Auburn, AL email@example.com
Over the past few decades, coral reefs have dramatically declined as a result of mass mortality bleaching events that have been linked to elevated sea surface temperatures and global climate change. Coral bleaching involves the loss of essential, photosynthetic dinoflagellates (Symbiodinium) from host gastrodermal cells in response to temperature and/or light stress conditions. Although numerous potential cellular bleaching methods have been proposed, there remains much uncertainty regarding which mechanisms occur during early stages of host stress. In this study, multiple techniques were utilized to determine specific cellular events that occur during the early bleaching process, including 1) transmission electron microscopy (TEM), 2) biochemical induction, and 3) immuno-labeling. Bleaching was induced by exposing both symbiotic and aposymbiotic symbiotic anemones, Aiptasia pallida, to heat-light stress conditions of ~32.5oC at 120 μmols irradiance for 12 hrs followed by 12 hrs in the dark at 24 oC daily for 2 days. Ultrastructural examinations revealed numerous autophagic structures and associated cellular degradation in tentacle tissues after ~12 hrs of stress treatment or after 12 hrs of exposure to the known autophagy inducer, rapamycin. Additionally, symbionts were observed detaching from highly degraded gastrodermal cells in an apocrine-like manner. Autophagic activity was then monitored using immunofluorescence, resulting in positive labeling with the autophagy marker, MAP LC3B. This study provides the first ultrastructural evidence of host autophagic degradation during thermal stress in a cnidarian system and also supports earlier suggestions that autophagy is an active cellular mechanism during early stages of bleaching.