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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mar. Sci. | doi: 10.3389/fmars.2019.00656

Alternative photosynthetic electron transfers and bleaching phenotypes upon acute heat stress in Symbiodinium and Breviolum spp. (Symbiodiniaceae) in culture.

  • 1University of Liège, Belgium

The breakdown of the symbiosis between cnidarians and Symbiodiniaceae often occurs upon periods of elevated sea surface temperature and gives rise to bleaching events that affect coral reefs worldwide. In the prevailing model explaining the cellular mechanisms of bleaching, an impairment of photosynthesis would be responsible for light-dependent generation of toxic reactive oxygen species and ultimately for death of symbionts and/or host cells. In some Symbiodiniaceae species, alternative photosynthetic electron flows (AEF) have been documented to occur upon a shift to high temperature, possibly contributing to photoprotection and to the balance of energetic ratio between photoproduced ATP and NADPH. By using a combination of in vivo spectrofluorimetric and oximetric techniques, we studied the capacity for electron rerouting towards oxygen and cyclic electron flow around photosystem I in nine Symbiodiniaceae species belonging to Symbiodinium and Breviolum genera upon a shift from 25°C to 33°C. CEF capacity was determined as the kinetic of PSI primary donor P700 re-reduction in the presence of DCMU, a PSII inhibitor. An active oxygen uptake in light was estimated by comparing net oxygen evolution and relatove electron transport rate of PSII at different light intensities. Among strains that showed elevated capacity for both AEF, some were thermotolerant while others were thermosensitive. Conversely, in some thermotolerant strains, capacities for these AEF were low upon heat stress. Our results thus indicate that a high CEF capacity and/or a high ability to reroute electrons towards O2 are not sufficient to confer thermal resistance of isolated Symbiodiniaceae.

Keywords: photoacclimation, coral reefs, Symbiodiniaceae, Alternative electron acceptor, Oxygen photoreduction, cyclic electron flow (CEF), photosynthetetic rate

Received: 19 Jun 2019; Accepted: 08 Oct 2019.

Copyright: © 2019 Dang, Pierangelini, Roberty and Cardol. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Stéphane Roberty, University of Liège, Liège, 4000, Liège, Belgium, sroberty@uliege.be
Prof. Pierre Cardol, University of Liège, Liège, 4000, Liège, Belgium, Pierre.cardol@ulg.ac.be