Apoplast

Apoplast and symplast are two separate pathways in plants to pass water along with ions from root hair via root cortex to xylem elements. These routes may exist either simultaneously or separately having different rates. Let’s get to know these pathways and differences among them.

What is Apoplast?

Apoplast is the space lying outside the plasma membrane consisting of intercellular spaces along with cell wall. It does not involve protoplasm in the plant tissues and therefore considered to be a non-living part of the plant. Apoplast makes a major pathway known as apoplastic pathway which supports water and ions to xylem elements from soil through the root.

The major part of water is transported apoplasty in the root cortex as cortical cells are packed loosely and offers low resistance to the flow of water. The apoplastic route is blocked by a Casparian strip of endodermal cells. Hence, the symplastic route is utilized to deliver water and ion over the cortex. Since apoplast is made up of non-living components, the apoplastic route is least affected by the metabolic state of the root.

Symplast consists of cytoplasm network of every plant cell interconnected by plasmodesmata. Symplast does not involve intercellular spaces and cell wall and therefore considered as the complete living component of the plant tissue. The pathways of ion and water created by symplast are known as the symplastic pathway. This pathway offers resistance to the flow of water since the selective plasma membrane of the root cells handles the intake of ion and water. Moreover, symplasty is affected by metabolic states of the root. The symplastic route occurs beyond the endodermis in plants with secondary growth.

Differences between Apoplast and Symplast

Criteria	Apoplast	Symplast
Parts	Consist of intercellular spaces and cell wall.	Consist of protoplasm.
Living and Nonliving parts	Consists of non-living parts.	Consists of living parts.
The rate of Pathways	Apoplastic pathway is fast.	Symplastic pathway is slower than the apoplastic pathway.
Metabolic State	No effect on water movement.	Metabolic states interfere the flow of water in the symplastic pathway.
Transportation	More ion and water are transported through the apoplastic pathway in the cortex.	Water and ion are mainly delivered through symplastic pathway beyond cortex.