Karim Widiastuti, Seidi Azadeh, Hill Ross, Chow Wah S, Minagawa Jun, Hidaka Michio, Takahashi Shunichi
Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, 903-0213 Japan These authors contributed equally to this work.
Research School of Biology, The Australian National University, ACTON, Australian Capital Territory 2601, Australia These authors contributed equally to this work.
Plant Cell Physiol. 2015 Jun;56(6):1162-71. doi: 10.1093/pcp/pcv040. Epub 2015 Mar 9.
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.
来自共生藻属的甲藻与许多海洋无脊椎动物形成共生关系，包括造礁珊瑚。共生藻在基因上具有多样性，获取合适的共生藻系统型对于宿主在高光等栖息地环境中生存至关重要。不同共生藻系统型对高光的敏感性存在差异，但控制光敏感性的机制尚未完全明确。在本研究中，我们使用耐高光和高光敏感的共生藻系统型，研究了决定对高光敏感性的因素。在不同光照强度下的生长实验中，共生藻CS - 164（B1分支）和CCMP2459（B2分支）分别被鉴定为耐高光和高光敏感的系统型。高光暴露后对光系统II（PSII）最大量子产率和最大光合放氧速率的测量表明，CCMP2459比CS - 164对PSII的光抑制更敏感，并且往往更快地失去最大光合活性。对不同波长范围光下PSII光损伤的测量表明，两种共生藻系统型中的PSII在光谱较短波长区域（<470 nm）对光损伤明显更敏感。重要的是，CCMP2459中的PSII，而不是CS - 164中的PSII，在470 - 550和630 - 710 nm左右的光谱区域对光损伤也敏感，共生藻的光合天线蛋白在这些区域有光吸收峰。这一发现表明，高光敏感的CCMP2459对PSII存在额外的光损伤成分，导致其对高光更敏感。我们的结果表明，共生藻系统型中PSII对光损伤的敏感性不同，这决定了它们对高光的敏感性。
