A non-living
continuum of the
cell wall in plants (especially in
roots) used for transport puropses. This tissue is formed by the walls of adjacent
plant cells.
Water and minerals collected by the roots need to be carried to the xylem of the plant, which can be done via the apoplast, the symplast or both.
In apoplastic transport the water does not cross the cell wall (a plasma membrane) until it reaches the casparian strip. It then enters the xylem.
Everything contained in the water passes through the apoplast as it enters the root of the plant, and may interact with it. Thus the apoplast is a very important site for research on effects of chemicals on plant growth.
Already the effects of boric acid and aluminum on the roots are being studied, and the apoplast is suggested as the site of interaction.