共生藻的耐熱性及其光合作用膜穩定性的差異

Abstract

珊瑚礁是具備高生物多樣性與高生產力的生態系之一，其存在是建立在珊瑚蟲與單細胞的渦鞭毛藻-共生藻的互利共生關係上。外界環境的擾動容易造成珊瑚白化-共生藻被趕出珊瑚宿主。在導致珊瑚白化的因子中，熱逆境是最為顯著且影響廣泛的因子之一。熱逆境會損害光合作用膜以及造成電子滲漏導致氧化逆境。共生藻是一類具有很高遺傳多樣性的渦鞭毛藻，這種多樣性也展現在它們的生理表現上的差異。例如提供宿主營養的多寡，抗氧化能力，熱敏感性等等生理性質的差異。在本篇研究，以葉綠素螢光儀偵測共生藻在短期熱逆境下的光合作用系統最大效率以評估共生藻的耐熱性以及光合作用膜的穩定性。研究結果顯示3株不同遺傳背景的共生藻面臨熱逆境時，共生藻C1具有較高的光合作用膜穩定性，達到40.3 ℃。而耐熱性,C56a相近的亞系群具有較高的耐熱性。本篇研究擴展了我們對於共生藻生理極限與潛力的了解。

Coral reefs are one of the most biologically diverse and productive ecosystems, and their existence depends on the mutualistic symbiosis between coral and and a single celled dinoflagellate alga; Symbiodinium. The perturbation to this symbiosis could cause coral bleaching; the expulsion or loss of of Symbiodinium from the coral host. Among the various factors of inducing coral bleaching, thermal stress is the wide spread and prominent one. Thermal stress damages the photosynthetic membranes of Symbiodinium and induce oxidative stress by leakage of reactive oxygen species. However, Symbiodinium has high genetic diversity, resulting in their differential physiological performance. For example, the ability to provide photosynthetic products to host, antioxidant capability and thermal susceptibility. In this study, we used maximum photochemical efficiency coupled with short term thermal stress to assess the melting temperature and thermal tolerance of several strains of Symbiodinium. Our results showed that among 3 Symbiodinium types studied, Symbiodinium C1 has the highest melting temperature of photosynthetic membranes at 40.30 ºC. As for the thermal tolerance, Symbiodinium C56a’ showed higher thermal tolerance than Symbiodinium clade D. This study extends our knowledge toward Symbiodinium and their physiological potential and limits under thermal stress.