apoplasts

The apoplast is the continuous system of non-living porous cell walls and intercellular spaces within a plant. It is a crucial pathway for water and dissolved solutes to move throughout the plant's tissues. Water can move freely through the apoplast until it encounters the Casparian strip, a band of hydrophobic material within the endodermis of roots. This strip forces water and solutes to enter the symplast, the interconnected cytoplasm of living cells, for selective absorption into the vascular tissues. The apoplast's large surface area facilitates rapid movement of substances, especially in areas with high transpiration rates. It also plays a role in defense mechanisms, as some signaling molecules can travel through it to alert the plant to pathogens. The apoplast is essentially the "outside" route for transport, in contrast to the symplast's "inside" route.