title: Inhibition of photosynthetic CO₂ fixation in the coral Pocillopora damicornis and its relationship to thermal bleaching.
abstract: Two inhibitors of the Calvin-Benson cycle [glycolaldehyde (GA) and potassium cyanide (KCN)] were used in cultured Symbiodinium cells and in nubbins of the coral Pocillopora damicornis to test the hypothesis that inhibition of the Calvin-Benson cycle triggers coral bleaching. Inhibitor concentration range-finding trials aimed to determine the appropriate concentration to generate inhibition of the Calvin-Benson cycle, but avoid other metabolic impacts to the symbiont and the animal host. Both 3 mmol l(-1) GA and 20 μmol l(-1) KCN caused minimal inhibition of host respiration, but did induce photosynthetic impairment, measured by a loss of photosystem II function and oxygen production. GA did not affect the severity of bleaching, nor induce bleaching in the absence of thermal stress, suggesting inhibition of the Calvin-Benson cycle by GA does not initiate bleaching in P. damicornis. In contrast, KCN did activate a bleaching response through symbiont expulsion, which occurred in the presence and absence of thermal stress. While KCN is an inhibitor of the Calvin-Benson cycle, it also promotes reactive oxygen species formation, and it is likely that this was the principal agent in the coral bleaching process. These findings do not support the hypothesis that temperature-induced inhibition of the Calvin-Benson cycle alone induces coral bleaching.
authors.affiliation: Centre for Marine Bio-Innovation and Sydney Institute of Marine Science, School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney 2052 NSW, Australia ross.hill@unsw.edu.au.
authors.forename: Ross
authors.initials: R
authors.lastname: Hill
authors.affiliation: Plant Functional Biology and Climate Change Cluster University of Technology Sydney, PO Box 123, Broadway, New South Wales 2007, Australia.
authors.forename: Milán
authors.initials: M
authors.lastname: Szabó
authors.affiliation: Institute of Plant Biology Biological Research Center of the Hungarian Academy of Sciences, H-6701 Szeged, PO Box 521, Hungary.
authors.forename: Ateeq
authors.initials: A
authors.lastname: ur Rehman
authors.affiliation: Institute of Plant Biology Biological Research Center of the Hungarian Academy of Sciences, H-6701 Szeged, PO Box 521, Hungary.
authors.forename: Imre
authors.initials: I
authors.lastname: Vass
authors.affiliation: Plant Functional Biology and Climate Change Cluster University of Technology Sydney, PO Box 123, Broadway, New South Wales 2007, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ralph
authors.affiliation: Plant Functional Biology and Climate Change Cluster University of Technology Sydney, PO Box 123, Broadway, New South Wales 2007, Australia.
authors.forename: Anthony W D
authors.initials: AW
authors.lastname: Larkum
mesh_terms: D000079:Acetaldehyde / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D037421:Anthozoa / Q000378:metabolism* / Q000382:microbiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D004141:Dinoflagellida / Q000378:metabolism*; D006358:Hot Temperature; D010788:Photosynthesis; D011190:Potassium Cyanide / Q000378:metabolism; D013312:Stress, Physiological; D013559:Symbiosis
chemical_list: D002245:Carbon Dioxide; D000079:Acetaldehyde; D011190:Potassium Cyanide; C010972:glycolaldehyde
keywords: Calvin–Benson cycle; Coral bleaching; Dark reactions; Heat stress; Photoinhibition; Photosynthesis; Respiration; Symbiodinium