原生质丝（英语：Plasmodesmata）为植物细胞和部分藻类细胞壁间贯穿细胞壁的特有孔道，可以让相邻细胞的细胞质相互流通。有微小孔道，为细胞间物质运输与信息传递的重要信道，信道中有一连接两细胞内质网的连丝微管，细胞质可经由原生质丝交流及运输，此过程称为共质体运输。

目前已知拥有原生质丝的包含植物界的所有物种，以及藻类中轮藻纲、轮藻目、褐藻纲和鞘毛藻目。

植物细胞拥有动物细胞所没有的细胞壁，邻近的细胞借由薄板相互分隔。虽然细胞壁对于部分蛋白质及溶质具有穿透性，但原生质丝对于共质体内的胞内运输更可以控制原生质流的流向以及穿透的物质。

Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages, and species that have these structures include members of the Charophyceae, Charales, Coleochaetales and Phaeophyceae (which are all algae), as well as all embryophytes, better known as land plants. Unlike animal cells, almost every plant cell is surrounded by a polysaccharide cell wall. Neighbouring plant cells are therefore separated by a pair of cell walls and the intervening middle lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata enable direct, regulated, symplastic intercellular transport of substances between cells. There are two forms of plasmodesmata: primary plasmodesmata, which are formed during cell division, and secondary plasmodesmata, which can form between mature cells.