title: "Super-quenching" state protects Symbiodinium from thermal stress - Implications for coral bleaching.
abstract: The global rise in sea surface temperatures causes regular exposure of corals to high temperature and high light stress, leading to worldwide disastrous coral bleaching events (loss of symbiotic dinoflagellates (Symbiodinium) from reef-building corals). Our picosecond chlorophyll fluorescence experiments on cultured Symbiodinium clade C cells exposed to coral bleaching conditions uncovered the transformations of the alga's photosynthetic apparatus (PSA) that activate an extremely efficient non-photochemical "super-quenching" mechanism. The mechanism is associated with a transition from an initially heterogeneous photosystem II (PSII) pool to a homogeneous "spillover" pool, where nearly all excitation energy is transferred to photosystem I (PSI). There, the inherently higher stability of PSI and high quenching efficiency of P(700)(+) allow dumping of PSII excess excitation energy into heat, resulting in almost complete cessation of photosynthetic electron transport (PET). This potentially reversible "super-quenching" mechanism protects the PSA against destruction at the cost of a loss of photosynthetic activity. We suggest that the inhibition of PET and the consequent inhibition of organic carbon production (e.g. sugars) in the symbiotic Symbiodinium provide a trigger for the symbiont expulsion, i.e. bleaching.
authors: Max Planck Institute for Chemical Energy Conversion, Mülheim a.d. Ruhr D-45470, Germany; Institute of Physical and Theoretical Chemistry, Goethe University, Frankfurt D-60438, Germany.
authors: Chavdar
authors: C
authors: Slavov
authors: Plant Functional Biology and Climate Change Cluster (C3), School of the Environment, University of Technology, Sydney, NSW 2007, Australia.
authors: Verena
authors: V
authors: Schrameyer
authors: Max Planck Institute for Chemical Energy Conversion, Mülheim a.d. Ruhr D-45470, Germany.
authors: Michael
authors: M
authors: Reus
authors: Plant Functional Biology and Climate Change Cluster (C3), School of the Environment, University of Technology, Sydney, NSW 2007, Australia.
authors: Peter J
authors: PJ
authors: Ralph
authors: Plant Functional Biology and Climate Change Cluster (C3), School of the Environment, University of Technology, Sydney, NSW 2007, Australia; Centre for Marine Bio-Innovation, School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
authors: Ross
authors: R
authors: Hill
authors: Institut für Molekulare Biowissenschaften, Goethe Universität, Frankfurt D-60438, Germany.
authors: Claudia
authors: C
authors: Büchel
authors: Plant Functional Biology and Climate Change Cluster (C3), School of the Environment, University of Technology, Sydney, NSW 2007, Australia; School of Biological Sciences, University of Sydney, NSW 2006, Australia. Electronic address: a.larkum@sydney.edu.au.
authors: Anthony W D
authors: AW
authors: Larkum
authors: Max Planck Institute for Chemical Energy Conversion, Mülheim a.d. Ruhr D-45470, Germany. Electronic address: alfred.holzwarth@cec.mpg.de.
authors: Alfred R
authors: AR
authors: Holzwarth
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000469:parasitology*; D002734:Chlorophyll / Q000378:metabolism; D004141:Dinoflagellida / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D004579:Electron Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D008163:Luminescent Measurements / Q000379:methods; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D010084:Oxidation-Reduction / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013312:Stress, Physiological / Q000502:physiology*; D013559:Symbiosis / Q000502:physiology*; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects; D013997:Time Factors
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C001785:chlorophyll P 700
keywords: Coral bleaching; Global climate change; Non-photochemical quenching; Photosynthesis; Symbiodinium; Symbiosis