PEREZ, S.; WEIS, V.; Oregon State University: Production of Nitric Oxide in the symbiotic cnidarian Aiptasia pallida as a function of heat stress

Stressful environmental conditions, such as elevated temperature, cause the symbiotic association between many cnidarians and the dinoflagellate Symbiodinium to become unstable resulting in the release of the symbiotic algal cells from host tissues. This phenomenon, known as bleaching, is a severe problem affecting numerous ecologically important species of corals living in coral reefs worldwide. However, the cellular mechanism mediating this stress response is poorly described. Using laser scanning confocal microscopy, we show that elevated temperature causes the accumulation of the signaling molecule nitric oxide (NO) in the model symbiotic anemone Aiptasia pallida. In various model systems, nitric oxide has been shown to play numerous important roles in cell signaling as well as in the response to stress. The nitric oxide signal, as measured by the increase in fluorescence of the NO-specific probe DAF-FM diacetate, is present in both intact tentacles and in isolated host cells containing algae. In addition, we show that cultured algae from subtropical Bermudian A. pallida produce more NO as a function of heat shock than those from tropical Florida Keys A. pallida. We discuss the mechanism of NO production in the symbiosis as well as its role in the cellular mechanism of bleaching.