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MOYA A. 2007 - The Scleractinian coral biomineralization, organic matrix
and transport of ions study. PhD these. Nice Sophia-Antipolis University.
178 p.
ABSTRACT
Scleractinian corals are the main calcifying organisms of coral reefs. Most scleractinian corals establish a symbiotic relationship with phototrophic Dinoflagellates. This symbiosis is responsible for the stimulation of coral calcification by light, a phenomenon called “light enhanced calcification” (LEC). Despite numerous studies performed on this subject, the mechanisms linking photosynthesis of the symbionts to coral calcification remain largely unknown. The aim of the present work is to gain a better understanding of the calcification process and of the “light-enhanced calcification” phenomenon in the scleractinian coral Stylophora pistillata (Esper, 1797), using both physiological and molecular approaches.
Using the physiological approach, we characterized the LEC phenomenon in S. pistillata and we showed that it is not regulated by an endogenous circadian rhythm but is only due to light changes. We determined that 25 to 30 minutes are necessary to change the calcification rate between light and dark conditions. We also brought some information on the chronological response of the LEC parameter to a stress episode that occurred in our aquaria, and which leads to a severe bleaching event.
Using a molecular approach, we cloned a carbonic anhydrase in S. pistillata, and have found that this enzyme is secreted by the calcifying ectoderm. We therefore suggested that this enzyme is involved in bicarbonate supply for calcification needs. Differential expressions of carbonic anhydrase gene and other genes involved in ions transport were performed by real-time PCR. Results showed that the carbonic anhydrase gene was two-fold expressed in the dark compared to the light. We suggested that the carbonic anhydrase gene was up-regulated during the dark in order to optimize bicarbonate supply in a dark-induced acidic medium. The adaptation of the real-time PCR technique to corals is presently used for differential gene expression between day and night in order to isolate genes involved in the coral calcification process and whose expression vary between light and dark
Key-words: Scleractinian / Stylophora pistillata / calcification / symbiosis / light-enhanced calcification (LEC) / carbonic anhydrase / differential expression of genes / real-time PCR..
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