Symplast

Introduction

Symplast is the protoplasts in plants interconnected by the plasmodesmata. The term “plasmodesmata” was introduced by Eduard Tangl, a professor of Botany and Pharmacognosy, when he discovered the cytoplasmic vascular strands connecting the plant cells. Plasmodesmata play a crucial role in the free movement of water and other low-molecular-weight solutes such as sugars, amino acids, and other ions in between cells, and hence, it is known as the symplastic pathway. This symplast study material focuses on water transportation in plants and similarities and differences in symplastic and apoplastic pathways.

Symplastic Pathway

The symplast is the inner part of the plant membrane bounded by the plasma membranes. It contains the complete network of the cytoplasm of plant cells connected by plasmodesmata. 

In this pathway, 

• The water absorbed from the soil first enters the cell sap and then passes from one cell into another cell

• The movement of water is between the cytoplasm and the vacuoles. It occurs beyond the cortex of plant cells through the plasma membranes and plasmodesmata

• The movement of water is also slower when compared to the apoplastic pathway

• Water moves from one cell to another by osmosis 

• Water enters one cell with a higher water potential than the adjacent cell

Water Transportation through Different Pathways

Plants require water to survive and complete their day-to-day biological processes. Water plays a vital role in germination, photosynthesis, transpiration, and transportation of nutrients. The root hair absorbs the water supplied to xylem vessels of the plant with the help of these three pathways-

• The Apoplastic Pathway: The apoplast, also called a cell wall, is present on the outer side of the cell. The apoplastic pathway enables water movement through the cell wall and other spaces between the cells

• The Symplastic Pathway: This route enables water movement from one cell to another by plasmodesmata as the symplast is the inner side of the plasma membrane

• The Transmembrane Pathway: This pathway is a combination of both the apoplast and symplast pathways. It refers to the movement of water across cells and cell walls

Transportation in Plants

Transportation in plants is carried out by two transporting tissues- xylem and phloem.

• Xylem: It transports water and other low-molecular-weight solutes from the roots to the upper surface of the plants

• Phloem: It transports prepared food from the leaves to other parts of the plants

The mechanism involved in the water movement in plants begins with water from the soil entering the plant from the root hairs and flowing from other root cells into the xylem.

Role of Symplast in Plant Roots

• A symplast is necessary to transport water from root hair to the xylem. The path through which water enters the cell is called a symplastic pathway. It is also known as the transmembrane pathway, as the water can cross cell membranes this way

• The movement of water into the cell takes place through the plasma membrane

Similarities between Apoplast and Symplast

Here are the similarities between apoplast and symplast.

• Both are routes or pathways where the water from the root hair gets transported to the xylem 
• Both these processes occur in the outer layer of the root known as the root cortex
• Apoplast and symplast take the responsibility of carrying water and the needed nutrients to the xylem

Difference between Apoplast and Symplast

Conclusion

Among the two pathways (apoplastic and symplastic), the symplastic pathways consist of living parts of the plant. These parts are the protoplasts interconnected by plasmodesmata. In symplastic pathways, the water movement is faster. However, there might be some resistance to water transportation. Overall, symplastic pathways play a major role and are crucial for the successful transfer of water and necessary nutrients to the xylem.