Takahashi Toshiyuki, Nishida Tomoki, Saito Chieko, Yasuda Hidehiro, Nozaki Hisayoshi
Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
Sci Rep. 2015 Oct 6;5:14735. doi: 10.1038/srep14735.
A heterotrophic organism 1-2 billion years ago enslaved a cyanobacterium to become the first photosynthetic eukaryote, and has diverged globally. The primary phototrophs, glaucophytes, are thought to retain ancestral features of the first photosynthetic eukaryote, but examining the protoplast ultrastructure has previously been problematic in the coccoid glaucophyte Glaucocystis due to its thick cell wall. Here, we examined the three-dimensional (3D) ultrastructure in two divergent species of Glaucocystis using ultra-high voltage electron microscopy. Three-dimensional modelling of Glaucocystis cells using electron tomography clearly showed that numerous, leaflet-like flattened vesicles are distributed throughout the protoplast periphery just underneath a single-layered plasma membrane. This 3D feature is essentially identical to that of another glaucophyte genus Cyanophora, as well as the secondary phototrophs in Alveolata. Thus, the common ancestor of glaucophytes and/or the first photosynthetic eukaryote may have shown similar 3D structures.
20亿年前，一种异养生物捕获了一种蓝细菌，从而成为首个光合真核生物，并在全球范围内分化开来。主要的光合生物——灰胞藻，被认为保留了首个光合真核生物的祖先特征，但由于其细胞壁较厚，之前在球形灰胞藻中研究原生质体超微结构存在困难。在此，我们使用超高压电子显微镜研究了两种不同的灰胞藻物种的三维（3D）超微结构。利用电子断层扫描对灰胞藻细胞进行三维建模，清晰地显示出大量小叶状扁平囊泡分布在原生质体周边，就在单层质膜下方。这一3D特征与另一个灰胞藻属蓝载藻属以及囊泡虫类中的次生光合生物基本相同。因此，灰胞藻的共同祖先和/或首个光合真核生物可能具有类似的3D结构。
