Microsensor study of photosynthesis and calcification in the scleractinian coral, Galaxea fascicularis:: active internal carbon cycle
Microsensor study of photosynthesis and calcification in the scleractinian coral, Galaxea fascicularis:: active internal carbon cycle
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DOI：
10.1016/s0022-0981(02)00578-6
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发表时间：
2003-03-25
影响因子：
2
通讯作者：
de Beer, D
中科院分区：
文献类型：
--
作者：
Al-Horani, FA;Al-Moghrabi, SM;de Beer, D
在小群落的Galaxea fascicularis中研究了用于光合作用和钙化的无机碳（Ci）的来源及其在石珊瑚中的吸收机制。用微传感器直接测量了水螅体腔表面和内部的Ca ~（2+）、pH和O ~（2-）。在地面上测定总光合作用（Pg）和净光合作用（Pn）。光呼吸（LR）由Pg和Pn计算。光/暗和暗/光开关对表面和内部的Ca 2+和pH动态的影响。对腔肠进行了跟踪。为了评价不同来源的Ci对光合作用和钙化作用的影响，采用无Ci海水和碳酸酐酶（CA）抑制剂6-乙氧唑胺和乙酰唑胺，在正常海水中，Pg约为Pn的7倍，LR约为0.001。因此，Pg中产生的大部分O-2立即在呼吸中消耗，表明存在高度活跃的内部C循环。由于内部C循环高度活跃，因此用于钙化的大部分Ci将通过共生体的代谢。光合作用和钙化所需的Ci可以来自海水，其形式为游离Ci、光合产物的呼吸（内部C-循环）或摄入浮游生物的呼吸。这些碳源形成了一个共同的碳库（C-pool），用于不同的过程，在不含Cl的海水中，Pg下降了约12.5%，表明大部分光合固定的Cl可以暂时由内源提供。最初的脱钙作用，直接观察到切换到无CI海水，表明在珊瑚的钙池是可交换的。无CI海水中的部分Pg可能依赖于这种脱钙作用来提供CI。一个在面向海水的表面上，一个在面向腔肠的内胚层细胞上，而第三个在细胞内。CA的抑制使Pg降低了约30%，同时由于其沉淀减少而增加了Ca 2+的浓度。CA抑制导致的光合作用和钙化的减少表明这两个过程都需要酶来供应Ci。加入6-乙氧基唑胺后，腔肠表面和内部的pH值降低，表明CA在pH控制中的作用。(C)2002 Elsevier Science B. V.保留所有权利。
Sources of inorganic carbon (Ci) for photosynthesis and calcification and the mechanisms involved in their uptake in scleractinian corals were investigated in microcolonies of Galaxea fascicularis. Direct measurements of Ca2+ pH and O-2 on the surface and inside the polyp's coelenteron were made with microsensors. Gross photosynthesis (Pg) and net photosynthesis (Pn) were measured on the surface. Light respiration (LR) was calculated from Pg and Pn. The effect of light/dark and dark/light switches on Ca2+ and pH dynamics on the surface and inside the. coelenteron were followed. To evaluate the different sources of Ci for photosynthesis and calcification, Ci-free seawater and 6-Ethoxyzolamide and Acetazolamide, inhibitors for carbonic anhydrase (CA) were used.In normal seawater, Pg was about seven times higher than Pn, the LR was ca. 80-90% of the Pg. Thus, most of the O-2 produced in Pg are immediately consumed in respiration, indicating the presence of a highly active internal C-cycle. As the internal C-cycle is highly active, a large part of the Ci for calcification will have passed through the metabolism of the symbiont. The high LR provides ATP for energy requiring processes in light.Ci for photosynthesis and calcification can come from seawater in the form of free Ci, respiration of photosynthates (internal C-cycle) or respiration of the ingested plankton. These sources form a common carbon pool (C-pool) that is used for the different processes.In Ci-free seawater, Pg decreased by about 12.5%, indicating that most of the photosynthetically fixed Ci can temporarily be supplied from internal sources. The initial decalcification, observed directly upon the switch to Ci-free seawater, showed that the Ca-pools in the coral are exchangeable. Part of the Pg in Ci-free seawater may depend on this decalcification for its Ci supply.Three localities of CA were defined. One on the surface facing seawater and one on endodermal cells facing the coelenteron, while the third is intracellular. The inhibition of CA decreased Pg by about 30%, while it increased the concentration of Ca2+ as a result of a decrease in its precipitation. The reduction of photosynthesis and calcification by CA inhibition demonstrated that both processes need the enzyme for the supply of Ci. The pH on the surface and inside the coelenteron decreased upon 6-Ethoxyzolamide addition indicating a role of CA in pH control. (C) 2002 Elsevier Science B.V. All rights reserved.