Apoplast and Symplast

The main difference between the Apoplast and Symplast Pathways is the water and minerals transport route. The apoplast pathway involves passive transport of water in which water rapidly flows through the apoplast of the root including the cell wall and intercellular spaces due to hydrostatic pressure. On the other hand, the symplast pathway involves active transport of water in which water initially enters the cell sap, and moves from one cell to another through protoplasm based on the osmotic gradient.

In this article, we will read about the difference between the apoplast and symplast pathway, the apoplast pathway definition and symplast pathway definition, how water is transported through the apoplast and symplast, and the similarities between the apoplast and symplast pathway.

Difference between Apoplast and Symplast Pathway

The apoplast vs symplast pathways are discussed below.

Basis of Comparison	Apoplast Pathway	Symplast Pathway
Components	Cell walls and extracellular spaces	Protoplast
Living or non-living components	Non-living components of the plant	Living components of the plant
Speed of water movement	Water moves rapidly	Water moves slowly in comparison to the apoplast pathway
Transportation path	Water and its solutes flow through the cell wall and extracellular space of plants	Water and its solutes flow through the cytosol and plasmodesmata of plants
Resistance	Lower resistance to water flow	Water movement is resisted to some extent.
Effect of metabolic state	Water movement is not affected.	The flow of water is affected.
Permeability	Not selective. Any substance can pass through.	Selective. Only certain substances can pass through.
Energy requirement	Passive transport, does not require energy to transport substances.	Active transport, requires energy to transport substances.
Efficiency	Less efficient, involves a longer route, and is not selective.	More efficient, involves a shorter route, and is selective
Process involved	Passive diffusion	Osmosis
Significance	Important for the absorption of water and nutrients from the soil and movement of water and nutrients in plants from the roots to the shoots through the xylem	Important for the distribution of water and nutrients throughout the plant and movement of signalling molecules and hormones from the leaves to the rest of the plant through the phloem.

What is Apoplast?

The apoplast can be defined as the intercellular space between cell membranes filled with gas and water. It also includes the interfibrillar and intermicellar space of the cell walls, and the xylem extending to the rhizoplane and cuticle of the outer plant surface. German scientist E. Münch first coined the term ‘apoplast’ in 1930. Apoplast performs several functions which includes nutrient and water transport, cellulose synthesis, and the synthesis of molecules involved in plant defense against both biotic and abiotic stresses. The molecules present in apoplast include reactive oxygen species (ROS), antioxidants, proteins, and hormones.

Apoplast Pathway

According to apoplast pathway definition it is an important route of water and nutrient absorption and transport in plants. The water and its solutes move through the extracellular space of plants by apoplast pathway in the following manner.

• The apoplast pathway starts in the root hairs which absorb water along with the nutrients from the soil by the diffusion process. Diffusion is a process by which substances move from a higher concentration zone to a lower concentration zone.
• After absorption of water by root hairs, the water and nutrients move through the cell walls and extracellular space of root cells and then to the extracellular space of stem cells., Afterward, they are transported to the upper parts of the plant.
• The apoplast pathway involves passive transport as it does not require energy to move water and nutrients through it.
• In addition, the apoplast pathway is not a selective pathway that can pass any substance through the cell wall and extracellular space.
• It has both advantages and disadvantages. As it allows all the substances to pass through it, any substance can pass through it easily and in a faster way. But the disadvantage is that it can also pass any unwanted substances of plants.

What is Symplast?

The symplast is considered as the inner living part of the plant bounded by the plasma membranes. It comprises a complete network of cytoplasm of plant cells connected by plasmodesmata. The symplast lacks cell walls and intercellular spaces. It plays an important role in the transport of water and other low-molecular-weight solutes, such as sugars, amino acids, and ions, between cells. The path created by the symplast is known as the symplastic pathway. Priestley in 1949 observed the active and passive transport of water in plants and first coined the term ‘symplastic pathway’.

Symplast Pathway

The water and its solutes are transported through the symplast pathway in the following ways:

• The water absorbed by the root from the soil first enters the cell sap and then moves from one cell into another cell
• The movement of water between the cytoplasm and the vacuoles and also through the plasma membranes and plasmodesmata occurs by osmosis. Osmosis is a process in which water moves from lower water potential to higher water potential cells.
• This pathway provides resistance to the water flow as it involves the selective plasma membrane which manages the intake of water and nutrients.
• Moreover, the metabolic state of the root also influences the symplast pathway.
• Thus, the water movement in the symplast pathway is slower than in the apoplast pathway.

Water Transport in Plants Through Apoplast and Symplast

The two major compartments of plant tissues involved in the transport of water and minerals are the apoplast and the symplast. The apoplast includes cell walls, extracellular spaces, xylem, phloem, and tracheids which are present outside of the plasma membrane. On the other hand, the symplast consists of the entire cytosol of all living plant cells and the plasmodesmata, the cytoplasmic channels interconnecting the cells.

Similarities between Apoplast and Symplast Pathway

The apoplast and symplast are two distinct pathways, but there are some similarities between these two pathways which are as follows:

• Route of Transport: In both pathways, the water and minerals are transported from root hair cells to the xylem.
• Occurrence: Both occur in the plant root cortex to the xylem components.
• Transport Substances: Both transport water and nutrients toward the xylem.

Conclusion – Differences between Apoplast and Symplast Pathway

Apoplast and symplast pathways are different routes for transporting water and solutes in plants. There are various differences between Apoplast and Symplast Pathway. Apoplast involves passive transport by diffusion driven by hydrostatic pressure, while symplast involves active transport via osmosis due to water gradient variations. Apoplast is crucial for absorbing water and nutrients from soil, transporting them via xylem from roots to shoots. Whereas symplast helps in distributing water, nutrients, and signaling molecules from leaves to the entire plant via phloem.

FAQs on Apoplast and Symplast Pathway

Which is Faster Symplast or the Apoplast Pathway?

The apoplast pathway is faster than the symplast pathway because the apoplast pathway is not selective and a simple diffusion method is involved. Moreover, the metabolic state of the root cortex cells does not affect the water movement.

Is the Apoplast Pathway Active or Passive?

The apoplast pathway is passive. It involves a simple diffusion process for which energy is not required.

Is the Symplastic Movement Active or Passive?

The symplastic movement is active because it involves a selective pathway through the osmosis process. It requires energy.

Is Symplast Living or Non-Living?

The symplast is the inner living part of a plant and consists of a complete network of the cytoplasm of plant cells connected by plasmodesmata.

What is the Difference Between Apoplast and Symplast Translocation of Materials in Plants?

Apoplast translocation moves substances through cell walls and intercellular spaces, while symplast translocation occurs via interconnected cell cytoplasm through plasmodesmata.

What is Passive Transport vs Active Transport?

Passive transport involves the movement of molecules across cell membranes without requiring energy, while active transport uses energy to move molecules against their concentration gradient, often facilitated by proteins in the cell membrane.

What is the Importance of the Casparian Strip?

The Casparian strip in plant roots acts as a barrier, ensuring selective nutrient uptake and preventing harmful substances from entering the vascular system.

Is Apoplast Active or Passive Absorption?

Apoplast absorption is a passive process where substances move through the cell walls and intercellular spaces without energy expenditure.