symplasten

Symplasten, in botany, refers to the symplast—the continuous network of cytoplasm within plant tissues that is linked from cell to cell by plasmodesmata. This cytoplasmic pathway contrasts with the apoplast, the extracellular spaces including cell walls and intercellular channels.

The symplast comprises the cytoplasm of many plant cells, along with their organelles, connected through plasmodesmata that traverse cell walls. This creates a coordinated intracellular network through which water, ions, nutrients, and signaling molecules can move without crossing the plasma membrane of every cell. Plasmodesmatal connectivity is not uniform and can be regulated by development, environmental conditions, and callose deposition at plasmodesmatal orifices, which can restrict or permit transport.

Functionally, the symplast enables symplastic transport, an important route for distributing nutrients and signals throughout tissues. It plays a central role in processes such as phloem loading and unloading, lateral transport in leaves, and root uptake under endodermal control. The Casparian strip in roots limits apoplastic flow, thereby increasing the relative importance of the symplastic pathway for controlling solute entry into the vascular system.

Regulation of symplastic connectivity is dynamic and context-dependent. Factors such as developmental stage, hormonal signals, stress conditions, and enzymatic activity affecting plasmodesmata permeability influence how substances move through the symplast.

See also: apoplast, plasmodesmata, symplastic transport, Casparian strip.