title: Novel Characteristics of Photodamage to PSII in a High-Light-Sensitive Symbiodinium Phylotype.
abstract: Dinoflagellates from the genus Symbiodinium form symbiotic relationships with many marine invertebrates, including reef-building corals. Symbiodinium is genetically diverse, and acquiring suitable Symbiodinium phylotypes is crucial for the host to survive in habitat environments, such as high-light conditions. The sensitivity of Symbiodinium to high light differs among Symbiodinium phylotypes, but the mechanism that controls light sensitivity has not yet been fully resolved. In the present study using high-light-tolerant and -sensitive Symbiodinium phylotypes, we examined what determines sensitivity to high light. In growth experiments under different light intensities, Symbiodinium CS-164 (clade B1) and CCMP2459 (clade B2) were identified as high-light-tolerant and -sensitive phylotypes, respectively. Measurements of the maximum quantum yield of photosystem II (PSII) and the maximum photosynthetic oxygen production rate after high-light exposure demonstrated that CCMP2459 is more sensitive to photoinhibition of PSII than CS-164, and tends to lose maximum photosynthetic activity faster. Measurement of photodamage to PSII under light of different wavelength ranges demonstrated that PSII in both Symbiodinium phylotypes was significantly more sensitive to photodamage under shorter wavelength regions of light spectra (<470 nm). Importantly, PSII in CCMP2459, but not CS-164, was also sensitive to photodamage under the regions of light spectra around 470-550 and 630-710 nm, where photosynthetic antenna proteins of Symbiodinium have light absorption peaks. This finding indicates that the high-light-sensitive CCMP2459 has an extra component of photodamage to PSII, resulting in higher sensitivity to high light. Our results demonstrate that sensitivity of PSII to photodamage differs among Symbiodinium phylotypes and this determines their sensitivity to high light.
authors.affiliation: Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, 903-0213 Japan These authors contributed equally to this work.
authors.forename: Widiastuti
authors.initials: W
authors.lastname: Karim
authors.affiliation: Research School of Biology, The Australian National University, ACTON, Australian Capital Territory 2601, Australia These authors contributed equally to this work.
authors.forename: Azadeh
authors.initials: A
authors.lastname: Seidi
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, NSW 2052, Australia.
authors.forename: Ross
authors.initials: R
authors.lastname: Hill
authors.affiliation: Research School of Biology, The Australian National University, ACTON, Australian Capital Territory 2601, Australia.
authors.forename: Wah S
authors.initials: WS
authors.lastname: Chow
authors.affiliation: Division of Environmental Photobiology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki, 444-8585 Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Minagawa
authors.affiliation: Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, 903-0213 Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Hidaka
authors.affiliation: Research School of Biology, The Australian National University, ACTON, Australian Capital Territory 2601, Australia Division of Environmental Photobiology, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki, 444-8585 Japan shun@nibb.ac.jp.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D065638:Absorption, Radiation; D004141:Dinoflagellida / Q000254:growth & development / Q000528:radiation effects*; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010802:Phylogeny
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen
keywords: Coral bleaching; Light stress; Photoinhibition; Symbiosis; Symbiotic algae