Mitochondrial morphology varies according to development and the physiological conditions of the cell. Here, we performed electron tomography using serial sections to analyze the number, individual volume, and morphological complexity of mitochondria in the cells across two generations in the life cycle of the brown alga Mutimo cylindricus. This species shows a heteromorphic alternation of generations between the macroscopic gametophyte and the crustose sporophyte during its life cycle and displays anisogamous sexual reproduction. We observed the mitochondria in the vegetative cells of gametophytes and sporophytes to mainly show tubular or discoidal shapes with high morphological complexity. The morphology of the mitochondria in the male and female gametes changed to a nearly spherical or oval shape from a tubular or discoidal shape before release. In this species, degradation of the paternal mitochondria was observed in the zygote 2 h after fertilization. Morphological changes in the mitochondria were not observed until 6 h after fertilization. Twenty-four-hour-old zygotes before and after cytokinesis showed a similar number of mitochondria as 6-h-old zygotes; however, the volume and morphological complexity increased. The results indicated that the maternal mitochondria did not undergo fission or fusion until this stage. Based on the analysis results of the number and total volume of mitochondria before and after the release of the gametes, it is possible that the mitochondria in the female gametes fuse immediately before release.

线粒体形态根据细胞的发育和生理条件而变化。在这里，我们使用连续切片进行电子断层扫描，分析褐藻Mutimo cylindricus生命周期中两代细胞中线粒体的数量、个体体积和形态复杂性。该物种在其生命周期中表现出宏观配子体和壳孢子体之间的异形世代交替，并表现出异配性生殖。我们观察到配子体和孢子体营养细胞中的线粒体主要呈管状或盘状，形态复杂性较高。雄配子和雌配子中线粒体的形态从释放前的管状或盘状变为近球形或椭圆形。在该物种中，受精后 2 小时在受精卵中观察到父本线粒体降解。直到受精后6小时才观察到线粒体的形态变化。 24小时龄的受精卵在胞质分裂前后显示出与6小时龄的受精卵相似的线粒体数量；然而，体积和形态复杂性增加了。结果表明，母体线粒体直到这个阶段才发生裂变或融合。根据配子释放前后线粒体数量和总体积的分析结果，雌配子中的线粒体有可能在释放前不久发生融合。