In many brown algae, cytokinesis is accomplished through the centrifugal expansion of the membrane structure formed by the fusion of Golgi vesicles and flat cisternae. In contrast, it has been reported that cytokinesis in Sphacelaria rigidula progresses centripetally by adding Golgi vesicles and flat cisternae to cleaving furrows of the plasma membrane. The reason why this cytokinetic pattern was observed only in Sphacelaria species is unknown. In either cytokinesis pattern, a plate-like actin structure (the actin plate) coincides with the cytokinetic plane between the daughter nuclei. However, it is unclear how the actin plate is related to cytokinesis progression. In this study, we re-examined cytokinesis in the apical cells of S. rigidula using transmission electron microscopy. Double staining of the actin plate and the developing membrane was followed by fluorescence microscopy analysis to determine the relationship between these two formations. The results showed that cytokinesis in S. rigidula, as in many brown algae, was completed by centrifugal growth of the new cell partition membrane. A furrow of the plasma membrane was observed at the beginning of cytokinesis; however, further invagination did not occur. The actin plate arose at the center of the cytokinetic plane before membrane fusion and extended parallel to the expansion of the new cell partition membrane. When cytokinesis was slow due to insufficient Golgi vesicle supply to the cytokinetic plane in the cells under brefeldin A treatment, the extension of the actin plate was also suspended. In this study, the spatiotemporal relationship between the occurrence and expansion of the actin plate and the new cell partition membrane was revealed. These observations indicate that the actin plate might promote membrane fusion or lead to the growth of a new cell partition membrane.

中文翻译：

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褐藻 Sphacelaria rigidula（Sphacelariales，Phaeophyceae）胞质分裂过程中肌动蛋白板和新细胞分隔膜的同时可视化

在许多褐藻中，胞质分裂是通过高尔基体囊泡和扁平池融合形成的膜结构的离心膨胀来实现的。相比之下，据报道，Sphacelaria rigidula中的胞质分裂通过将高尔基体囊泡和扁平池添加到质膜的裂沟中而向心进行。为什么这种细胞因子模式仅在球形孢菌属物种中观察到的原因尚不清楚。在任一胞质分裂模式中，板状肌动蛋白结构（肌动蛋白板）与子核之间的细胞分裂平面重合。然而，肌动蛋白板与胞质分裂进程的关系尚不清楚。在这项研究中，我们重新检查了S. rigidula顶端细胞的胞质分裂使用透射电子显微镜。肌动蛋白板和显影膜的双重染色后进行荧光显微镜分析，以确定这两种结构之间的关系。结果表明，S. rigidula中的胞质分裂与许多褐藻一样，通过新细胞分隔膜的离心生长完成。在胞质分裂开始时观察到质膜沟；但是，没有发生进一步的内陷。肌动蛋白板在膜融合前出现在细胞分裂平面的中心，并平行于新细胞分隔膜的扩张而延伸。在布雷菲德菌素 A 处理的细胞中，当高尔基体小泡向细胞分裂平面供应不足导致胞质分裂缓慢时，肌动蛋白板的延伸也被暂停。在这项研究中，揭示了肌动蛋白板的发生和扩展与新的细胞分隔膜之间的时空关系。这些观察表明肌动蛋白板可能促进膜融合或导致新细胞分隔膜的生长。