Formation of Primary Intercellular Connections in Multicellular Algae

Abstract

Brown algae including Saccharina and Undaria show the largest photosynthetic organisms in coastal area. All species possess multicellularity, and there are several varieties of body plan; i.e. uniseriate and multiseriate filamentous thalli, and the complex multicellularity. Brown algal cells have tiny cytoplasmic connections, plasmodesmata, with 10-20 nm diameter. Also in land plants, plasmodesmata are observed within the septum cell wall and they are formed during the cell plate formation. When plasmodesmata are created on the cytokinesis, they are called primary plasmodesmata. Cytokinesis and existence of primary plasmodesmata in brown algae had been unclear. We examined the process of cytokinesis using electron tomography and revealed the appearance of plasmodesmata during cytokinesis. Cytokinesis of brown algae proceeds as follows; cytokinetic plane is determined by crossing region of microtubules from centrosomes, Golgi derived vesicles and flat cisternae fuse each other to form new cell partition membrane, and then centrifugally growing new cell partition membrane reaches to the mother cell wall.