The Apoplastic Pathway

The apoplastic pathways or non-living path provides a direct route to the vascular stale through the cells and spaces in the epidermis. A apoplastic path also provides direct access along the secondary root margins to xylem or phloem. The pericycle is a layer of cell cells located inside the endodermis. Casparian strips are found in the radial or transverse wall of the Endodermis. They allow the cell material to pass through the Symplast and enter the Vascular System.

As the secondary roots are located in the endodermis layer, herbicides can enter the vascular tissue without going through the symplast. This is only one of two pathways that plants use to transport water. In apoplastic transportation, water and mineral flow upward via the roots apoplast. [7] In order to determine the concentration of solutes carried in aboveground organs, a combination is used of xylem import, cell absorption, and phloem export. The apoplast has a higher transport velocity than the symplast. This method of transportation accounts for more water transport than symplastic in plant tissue.

Passive exclusion also involves the apoplastic path. Some ions enter the roots but do not reach the xylem. Water and solutes from soil could travel through the cell membranes of cortical symbiotic cells, until they reached the endodermis. Here, the plasma cells of these cells would allow them to cross. Aquaporins are used to transport water, and ion channel or transporters for solutes. It is possible for roots to have a primary endodermis without a suberised epidermis. In general, anions and cations will pass through cells more readily, especially if there are many carboxyls in the cell wall that are not occupied. Water flowing through roots in an apoplastic manner can carry large ion loads during high-transpiration periods.

The majority of soil water that is taken up by a plant will likely move across the cortex in the apoplast, while the solutes will be taken up by outer cortical or epidermal cells.

Suberisation of the endodermis prevents water and other solutes from entering the apoplast. They are instead taken up in adjacent cortical cell and moved into the endodermis via plasmodesmata.