Assimilation, translocation, and utilization of carbon between photosynthetic symbiotic dinoflagellates and their planktic foraminifera host
Assimilation, translocation, and utilization of carbon between photosynthetic symbiotic dinoflagellates and their planktic foraminifera host
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DOI：
10.1007/s00227-018-3362-7
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发表时间：
2018-06-01
期刊：
影响因子：
2.4
通讯作者：
Meibom, Anders
中科院分区：
文献类型：
--
作者：
LeKieffre, Charlotte;Spero, Howard J.;Meibom, Anders
生活在贫营养地表水环境中的一些浮游有孔虫物种与甲藻微藻处于专性共生关系，微藻可以通过光合作用吸收碳（C）。然而，C 光合产物转移到有孔虫宿主的机制和动力学，以及这种共生关系中甲藻的相关益处，却很少受到限制。因此，浮游有孔虫作为自养生物在海洋表面生态系统中的作用尚不清楚。在这里，我们用富含 C-13 的溶解无机碳进行了脉冲追踪实验，然后进行了 TEM 和定量 NanoSIMS 同位素成像，以可视化单个共生甲藻的光合 C 同化以及随后易位到其 Orbulina universa 宿主的情况。尽管大多数甲藻种群在白天从宿主内质迁移到外部刺上，但我们的观察表明，一小部分在白天保留在宿主细胞内。所有共生体，无论是在有孔虫细胞外部还是内部，都能在白天光合作用期间有效地将碳同化到淀粉节中。入夜时，所有来自外部棘外质区域的甲藻都会迁移回有孔虫细胞中。在夜间，甲藻的呼吸作用和碳易位至宿主（可能以脂质的形式），大大减少了甲藻中淀粉的丰度。甲藻有丝分裂仅在夜间观察到，前一天固定的碳有很大贡献，有助于新生物量的产生。
Some species of planktic foraminifera inhabiting oligotrophic surface water environments are in an obligate symbiotic relationship with dinoflagellate microalgae, which can assimilate carbon (C) through photosynthesis. However, the mechanism and dynamics of C photosynthate translocation to the foraminiferal host, and related benefits for the dinoflagellates in this symbiotic association, are poorly constrained. As a consequence, the role of planktic foraminifera as autotroph organisms in ocean surface ecosystems is not well understood. Here, we performed pulse-chase experiments with C-13-enriched dissolved inorganic carbon, followed by TEM and quantitative NanoSIMS isotopic imaging to visualize photosynthetic C assimilation by individual symbiotic dinoflagellates and subsequent translocation to their Orbulina universa host. Although most of the dinoflagellate population migrates out of the host endoplasm onto external spines during the day, our observations show that a small fraction remains inside the host cell during daytime. All symbionts, whether outside or inside the foraminifera cell, effectively assimilate C into starch nodules during daytime photosynthesis. At the onset of night, all dinoflagellates from the exterior spine-ectoplasm region migrate back into the foraminiferal cell. During the night, respiration by dinoflagellates and carbon translocation to the host, likely in the form of lipids, greatly reduces the abundance of starch in dinoflagellates. Dinoflagellate mitosis is only observed at night, with a substantial contribution of carbon fixed during the previous day contributing to the production of new biomass.