Thermal responses of Symbiodinium photosynthetic carbon assimilation
Thermal responses of Symbiodinium photosynthetic carbon assimilation
复制标题
共生藻光合碳同化的热响应
作者：
Clinton A. Oakley;G. Schmidt;B. Hopkinson
造礁石珊瑚与其甲藻共生体共生藻属之间的共生关系是基于碳交换。这种共生关系被热诱导的珊瑚漂白破坏，这是一种应激反应，珊瑚宿主在生理受损时驱逐其藻类共生体。溶解无机碳（DIC）供应的中断或Rubisco的热失活已被提出作为导致漂白反应的初始热损伤的位点。共生藻具有非常不寻常的II型核酮糖二磷酸羧化酶/加氧酶（Rubisco），其表现出较低的CO2：O2特异性，并且可能比其他藻类和陆地植物的I型Rubiscos更热不稳定。CO2浓缩机制（CCM）的组成部分为光合作用提供无机碳，也可能对温度敏感。在这里，我们研究的能力，四个培养的共生藻菌株获得和固定DIC的温度梯度。令人惊讶的是，相对于DIC浓度（KP），CCM功能的指数，光合作用的半饱和常数，下降，随着温度的升高，在四个菌株中的三个，表明在高温下光合碳收购的潜力更大。在第四菌株中，温度对KP没有影响。没有发现CCM的热抑制的证据，我们得出结论，CCM组件不太可能是热损伤的主要部位。减少光合量子产率，热漂白的一个标志，观察到在低DIC浓度，留下开放的可能性，减少无机碳的可用性是参与漂白。
The symbiosis between hermatypic corals and their dinoflagellate endosymbionts, genus Symbiodinium, is based on carbon exchange. This symbiosis is disrupted by thermally induced coral bleaching, a stress response in which the coral host expels its algal symbionts as they become physiologically impaired. The disruption of the dissolved inorganic carbon (DIC) supply or the thermal inactivation of Rubisco have been proposed as sites of initial thermal damage that leads to the bleaching response. Symbiodinium possesses a highly unusual Form II ribulose bisphosphate carboxylase/oxygenase (Rubisco), which exhibits a lower CO2:O2 specificity and may be more thermally unstable than the Form I Rubiscos of other algae and land plants. Components of the CO2 concentrating mechanism (CCM), which supplies inorganic carbon for photosynthesis, may also be temperature sensitive. Here, we examine the ability of four cultured Symbiodinium strains to acquire and fix DIC across a temperature gradient. Surprisingly, the half-saturation constant of photosynthesis with respect to DIC concentration (KP), an index of CCM function, declined with increasing temperature in three of the four strains, indicating a greater potential for photosynthetic carbon acquisition at elevated temperatures. In the fourth strain, there was no effect of temperature on KP. Finding no evidence for thermal inhibition of the CCM, we conclude that CCM components are not likely to be the primary sites of thermal damage. Reduced photosynthetic quantum yields, a hallmark of thermal bleaching, were observed at low DIC concentrations, leaving open the possibility that reduced inorganic carbon availability is involved in bleaching.