title: Ultrastructural study of plasmodesmata in the brown alga Dictyota dichotoma (Dictyotales, Phaeophyceae).
abstract: Plasmodesmata are intercellular bridges that directly connect the cytoplasm of neighboring cells and play a crucial role in cell-to-cell communication and cell development in multicellular plants. Although brown algae (Phaeophyceae, Heterokontophyta) are phylogenetically distant to land plants, they nevertheless possess a complex multicellular organization that includes plasmodesmata. In this study, the ultrastructure and formation of plasmodesmata in the brown alga Dictyota dichotoma were studied using transmission electron microscopy and electron tomography with rapid freezing and freeze substitution. D. dichotoma possesses plasma membrane-lined, simple plasmodesmata without internal endoplasmic reticulum (desmotubule). This structure differs from those in land plants. Plasmodesmata were clustered in regions with thin cell walls and formed pit fields. Fine proteinaceous "internal bridges" were observed in the cavity. Ultrastructural observations of cytokinesis in D. dichotoma showed that plasmodesmata formation began at an early stage of cell division with the formation of tubular pre-plasmodesmata within membranous sacs of the cytokinetic diaphragm. Clusters of pre-plasmodesmata formed the future pit field. As cytokinesis proceeded, electron-dense material extended from the outer surface of the mid region of the pre-plasmodesmata and finally formed the nascent cell wall. From these results, we suggest that pre-plasmodesmata are associated with cell wall development during cytokinesis in D. dichotoma.
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan. yellowplanterauchi@fsc.hokudai.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Terauchi
authors.forename: Chikako
authors.initials: C
authors.lastname: Nagasato
authors.forename: Naoko
authors.initials: N
authors.lastname: Kajimura
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Mineyuki
authors.forename: Kazuo
authors.initials: K
authors.lastname: Okuda
authors.forename: Christos
authors.initials: C
authors.lastname: Katsaros
authors.forename: Taizo
authors.initials: T
authors.lastname: Motomura
mesh_terms: D000464:Alginates / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure*; D002482:Cellulose / Q000378:metabolism; D015925:Cryopreservation; D048749:Cytokinesis / Q000502:physiology*; D055032:Electron Microscope Tomography / Q000379:methods*; D017110:Freeze Substitution; D020723:Glucuronic Acid / Q000378:metabolism; D006603:Hexuronic Acids / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D016253:Microscopy, Immunoelectron; D000459:Phaeophyceae / Q000502:physiology / Q000648:ultrastructure*; D031425:Plasmodesmata / Q000648:ultrastructure*
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D002482:Cellulose