Difference between Apoplast and Symplast

The plant receives water from the soil mostly through root hairs into the piliferous layer to inner most part of cell in the root. Root hairs are long tubular shaped, and present outside the part of epidermal cells that increase the surface area available for water absorption from the soil.

The soil solution usually has a larger water potential as compared to piliferous layer cells. As a result, osmosis allows water to enter the root from the soil. The root has a water potential that ranges from higher in the piliferous layer to lower in the cells next to the xylem.

As a result, a gradient is maintained, and water flows across the root from epidermis to xylem via cortex, endodermis, pericycle, and xylem parenchyma in a down gradient of water potential.

Osmosis allows the root hair cells to absorb water from the soil. Through the root cortex, this water is transferred to the root's xylem. Osmosis is another method for transporting water. The two channels by which water absorb by root hair cells moves to the xylem part of the root are apoplast and symplast. Water passes through the cell walls and intracellular spaces of the root cortex via the apoplastic pathway. Water flows through the protoplasts of the root cortex in the symplastic route. The key difference between apoplast and symplast is that apoplast provides fully permeable route, means passive diffusion movement of water but symplast offers selectively permeable movement of water by process of osmosis.

Let's understand both pathways broadly.

Pathways of Apoplast

In plant Apoplast refers to the non-protoplasmic components of a plant. These components are in discontinuous gaps and divided into two areas. The cortex and tissues outside the endodermis make up one area. The stele tissues, such as tracheids and arteries that sit within the endodermis, make up the other region. Endodermis is responsible for the apoplast discontinuity.

Water flows through the walls of neighbouring cells from root hair to xylem without crossing any membranes or cytoplasm. The apoplastic route is the name given to this pathway. At no point, the apoplastic route breach a cytoplasmic membrane. This signifies that the water is moving due to passive diffusion. The path has the least amount of hindrance to water movement. The presence of impermeable suberin casparian strips present in the walls of endodermal cells barely interrupts this process.

Water cannot travel from outside to inside or back through the Casparian strips in the endodermal cell wall unless it goes through the cell membrane and cytoplasm of the endodermal cells. These strips contain suberin, a waterproof material that resists apoplastic water movement.

In apoplast, water and minerals movement take place through the porous cell walls that surround the plant cell instead of passing through the plasma membrane of a cell.

Symplast Pathway

Symplasts work together to build a continuous system. The protoplasmic components of a plant are referred to as symplast. Cell connections called plasmodesmata or cytoplasmic strands join the protoplasms of the cells. From cell to cell, it connects the cortical protoplast, endodermis, and vascular tissue. Water is transported to xylem by passing through the root hair cells via the symplast of the root cortex. The symplastic pathway is the name given to this path. In symplastic pathway, water penetrates the cytoplasm of the cell through the plasma membrane.

Transmembrane Pathway or Non-vacuolar Symplast Pathways:

Water flows from cell to cell through the protoplasm in this pathway. It doesn't go inside the vacuoles of the cells. Plasmodesmata unites the cytoplasm of the neighboring cells. Plasma membrane present in plant cell helps to move water from one cell to another forming a continuous channel until it reaches xylem.

Vacuolar Symplast Pathway:

Each root cell in this route acts as a miniature osmotic system. Through osmosis, the root hair cell takes water from the soil. Then, it enters the vacuoles of nearby cortical cells. The cycle continues until water reaches the cells of the xylem parenchyma.

Water in the symplast and cell vacuoles is in continual balance with apoplastic water. Water exchange occurs continuously across both the cell and vacuolar membranes. In fact, both routes are involved in the transport of water through the cortex.

Similarities Apoplast and Symplast

Both pathways help in movement of Water from root hair cells to the xylem

The root cortex contains both apoplast and symplast.

Water and nutrients are carried to the xylem via both apoplast and symplast.

What is the difference between an apoplast and a symplast?

Definition

Apoplast refers to non-protoplasmic components of a plant, such as cell walls and intracellular spaces.

Symplast refers to a plant's continuous network of protoplasts that are linked together by plasmodesmata.

Components

Nonprotoplasmic components such as cell walls and intracellular compartments make up the apoplast.

Protoplast is used to make the symplast.

Living/Non-living

Apoplast: A plant's nonliving elements make up the apoplast.

Symplast: The symplast is made up of a plant's live elements.

The Flow of Water

Apoplast: Passive diffusion is used to move the water.

Symplast: Water move because of Osmosis

Water Movement Opposition

Apoplast: The apoplast has a lower resistance to water flow.

Symplast: The symplast resists water movement to some extent.

The Water's Movement Speed

Apoplast: Water moves quickly through the apoplast.

Symplast: Water moves more slowly across the symplast.

Metabolic State

In water transport, the root cortex of the cell does not affect the metabolic rate in the apoplastic channel.

Water transport via the symplastic channel is heavily influenced by the metabolic status of the cells in the root cortex.

Significance

Apoplast: During the root's secondary growth, the apoplastic channel transports the majority of the water.

Water travels through the symplastic pathway beyond the cortex.

Conclusion

Plants uses two channels to carry water from root hair cells to the xylem of the root: apoplast and symplast. The non-living components of a plant, such as cell walls and intracellular space, are referred to as apoplast. The living components of a plant, such as protoplasms, are referred to as symplast. Water travels by passive diffusion along the apoplastic route. The symplastic pathway, on the other hand, uses osmosis to transport water across cell membranes. The mechanism of water transport differs significantly between apoplast and symplast.