symplastiseen

Symplast refers to the interconnected cytoplasms of plant cells that are connected by plasmodesmata, small channels through cell walls that allow direct cytoplasmic communication. In plants, transport can occur via the symplast or the apoplast (the network of cell walls and intercellular spaces). The symplast enables movement of solutes and signals from cell to cell without crossing the plasma membrane, while the apoplast involves movements through extracellular spaces.

Plasmodesmata are the structural basis of the symplast. Each channel consists of a plasma membrane lining, a cytoplasmic sleeve, and a desmotubule derived from the endoplasmic reticulum. The connectivity of the symplast is not fixed; it can be dynamically regulated at individual plasmodesmata. A key regulatory mechanism is the deposition and removal of callose, a β-1,3-glucan, around the pore, which can increase or decrease the size exclusion limit and thereby control what passes between cells.

Symplastic transport supports the movement of a wide range of substances, including water, ions, sugars, amino acids, hormones, RNAs, and some proteins. Small, mobile molecules typically diffuse through plasmodesmata, while larger macromolecules may move by specific, regulated mechanisms. This pathway plays important roles in development, patterning, and responses to stimuli, such as wound signaling or environmental stress, by coordinating cellular activities across tissues.

Regulation of the symplast is integrated with overall plant physiology, balancing the need for rapid, coordinated responses with the control of intracellular environments. The symplast operates in concert with the apoplast to distribute resources and signals throughout the plant.