Translocation and conservation of organic nitrogen within the coral-zooxanthella symbiotic system of Acropora pulchra, as demonstrated by dual isotope-labeling techniques
Translocation and conservation of organic nitrogen within the coral-zooxanthella symbiotic system of Acropora pulchra, as demonstrated by dual isotope-labeling techniques
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DOI：
10.1016/j.jembe.2006.04.011
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发表时间：
2006-08-22
影响因子：
2
通讯作者：
Ogawa, Hiroshi
中科院分区：
文献类型：
--
作者：
Tanaka, Yasuaki;Miyajima, Toshihiro;Ogawa, Hiroshi
使用 C 和 N 同位素示踪剂研究了造血型珊瑚 Acropora pulchra 及其共生藻类（虫黄藻）的碳 (C) 和氮 (N) 代谢。 A. pulchra 在含有 C-13 标记的碳酸氢盐和 (15) 标记的硝酸盐 (NO3-) 的海水中培养 24 小时（脉冲期），随后在不含 C-13 和 N-15 的海水中跟踪宿主珊瑚和虫黄藻的 C-13 和 N-15 同位素比率 2 周（追踪期）。在我们的NO3-（12μM）实验条件下，脉冲期间C和N被珊瑚-藻共生系统吸收，C：N比为23。考虑到由单独实验确定的 NO3- 吸收率的浓度依赖性，如果光合速率没有变化，在假定的原位 NO3- 条件（< 1.0 μM）下，C:N 吸收率将高出 > 3.0 倍。在脉冲期间，一半以上被吸收的 C-13 和 N-15 以有机形式出现在宿主部分中。脉冲周期结束时，宿主和藻类部分的 C-13:N-15 比率相似，表明藻类光合产物转移到宿主中。这也意味着易位产物的 C:N 比率的变化取决于虫黄藻的 N 可用性。在追逐期间，虫黄藻的原子过量（APE）N-15不断下降，而寄主的原子过量（APE）N-15略有上升。因此，两个部分的 APE N-15 似乎接近共同的稳态值，表明 15 N 在珊瑚-藻类共生系统内循环利用。至于C，在脉冲期结束时，虫黄藻光合固定的> 86%的C在宿主体内积累，并且周转时间约为。在接下来的追踪期间，主机 C 池有 20 天。用NO3-新合成的有机物的C:N比呈指数下降，对于宿主和虫黄藻来说分别收敛到5.7和4.5。这表明，高 C:N 比的有机化合物（如脂质和碳水化合物）比低 C:N 比的有机化合物（如蛋白质和核酸）被选择性消耗得更快。 (c) 2006 Elsevier B.V. 保留所有权利。
Carbon (C) and nitrogen (N) metabolism of the hermatypic coral Acropora pulchra and its symbiotic algae (zooxanthellae) was investigated using C and N isotope tracers. A. pulchra was incubated in seawater containing C-13-labeled bicarbonate and (15)-labeled nitrate (NO3-) for 24 h (pulse period), and subsequently C-13 and N-15 isotopic ratios of the host coral and the zooxanthellae were followed in C-13- and N-15-free seawater for 2 weeks (chase period). Under our experimental condition of NO3- (12 mu M), C and N were absorbed by the coral-algal symbiotic system with the C:N ratio of 23 during the pulse period. Taking account of concentration dependence of NO3- uptake rates determined by a separate experiment, C:N uptake ratios under supposed in situ NO3- conditions (< 1.0 mu M) would be > 3.0 times higher, if the photosynthetic rate did not change. During the pulse period, more than half of the absorbed C-13 and N-15 appeared in the host fraction in organic forms. C-13:N-15 ratio at the end of the pulse period was similar between the host and the algal fraction, suggesting that algal photosynthetic products were translocated to the host. It is also implied that C:N ratios of the translocated products change depending on N availability for the zooxanthellae. During the chase period, atom % excess (APE) N-15 of the zooxanthellae constantly declined, while that of the host slightly increased. Consequently, APE N-15 of the both fractions appeared to approach a common steady state value, suggesting that 15 N was recycled within the coral-algal symbiotic system. As for C, > 86% of C photosynthetically fixed by the zooxanthellae accumulated in the host at the end of the pulse period, and had a turnover time of ca. 20 days for the host C pool during the following chase period. C:N ratios of organic matter newly synthesized with NO3- exponentially declined and converged into 5.7 and 4.5 for the host and the zooxanthellae, respectively. This suggests that organic compounds of high C:N ratios such as lipids and carbohydrates were selectively consumed more rapidly than those of low C:N ratios such as proteins and nucleic acids. (c) 2006 Elsevier B.V. All rights reserved.