What is the Difference Between Plasmodesmata and Desmotubule

The main difference between plasmodesmata and desmotubule is that plasmodesmata are microscopic channels traversing the walls of plant cells whereas desmotubule is a tube of the appressed endoplasmic reticulum (ER), usually found in plasmodesmata. Furthermore, plasmodesmata allow the transport and signaling between two plant cells while desmotubule allows the transport of some molecules apart from the main route of transport produced by plasmodesmata.

Plasmodesmata and desmotubule are two structures in the plant cell wall, facilitating the transport of molecules between adjacent plant cells.

Key Areas Covered

1. What are Plasmodesmata
     – Definition, Structure, Function
2. What is a Desmotubule
     – Definition, Structure, Function
3. What are the Similarities Between Plasmodesmata and Desmotubule
     – Outline of Common features
4. What is the Difference Between Plasmodesmata and Desmotubule
     – Comparison of Key Differences

Key Terms

Cell Junctions, Cell Signalling, Desmotubule, Endoplasmic Reticulum, Plant Cell, Plasmodesmata, Transport

What are Plasmodesmata

Plasmodesmata are a type of cell junctions found in plant cells, directly connecting the adjacent cytoplasm. They are a type of living bridges between plant cells resembling the gas junctions between animal cells. Generally, plasmodesmata penetrate both primary and secondary cell wall of plant cells, allowing some molecules to pass through the two cytoplasms. These molecules include proteins, transcription factors, mRNA, siRNA, and pathogenic particles such as viral genomes and viroids. Therefore, plasmodesmata play a role in intracellular communication as well. Due to the presence of plasmodesmata, plant tissues can form a syncytium, a multinucleate mass of cytoplasmic continuity.

Figure 1: Plasmodesmata Structure

Furthermore, a primary plasmodesma is formed by trapping a portion of the endoplasmic reticulum across the middle lamella during the formation of the primary cell wall in the newly divided plant cells. Secondary plasmodesmata occur on the existing cell walls of the non-dividing cells. Approximately, 103 and 105 plasmodesmata occur between two adjacent cells. Additionally, the plasma membrane, the cytoplasmic sleeve, and the desmotubule are the three layers of plasmodesmata. Here, the plasma membrane of a plasmodesma contains similar phospholipid bilayer as the cell membrane. On the other hand, the cytoplasmic sleeve is a fluid-filled space, which is a continuous extension of the cytosol. Also, desmotubule is the tube formed from the appressed endoplasmic reticulum.

What is a Desmotubule

Desmotubule is a tube within the plasmodesma formed by the appressed endoplasmic reticulum. Majority of plasmodesmata contain a desmotubule. However, the desmotubule does not completely fill the channel made by the plasmodesmata. Therefore, a ring of shares cytoplasm occurs surrounding the desmotubule. In the general sense, the desmotubule is a compact, cylindrical segment of the endoplasmic reticulum found inside the larger tubule structure of the plasmodesmata.

Figure 2: Desmotubule Structure

Moreover, the diameter of a desmotubule can be around 15 nm. Therefore, it is one of the highly compressed biological membranes ever known. However, it can widen in order to form a lumen embedded with proteins that are responsible for connecting the desmotubule membrane to the plasma membrane. Significantly, the main function of the desmotubule is the lateral transfer of lipid molecules responsible for cell signaling. In addition, desmotubule provides structural support to the plasmodesmata.

Similarities Between Plasmodesmata and Desmotubule

• Plasmodesmata and desmotubule are two structures present in the plant cell wall.
• Their main function is to facilitate the transport of molecules between two plant cells.
• Moreover, they are a type of cell connections or cell junctions.
• They form a channel through the cell wall of plants.

Difference Between Plasmodesmata and Desmotubule

Definition

Plasmodesmata refer to a narrow thread of cytoplasm, which passes through the cell walls of adjacent plant cells and allows communication between them, while desmotubule refers to a tube of the appressed endoplasmic reticulum that runs between two adjacent plant cells. Thus, this is the main difference between plasmodesmata and desmotubule.

Structure

Furthermore, the plasmodesmata are composed of three layers: the plasma membrane, the cytoplasmic sleeve, and the desmotubule. However, desmotubule is a tube made up of the appressed endoplasmic reticulum.

Diameter

Also, the diameter of a plasmodesma is 50–60 nm while the diameter of a desmotubule is approximately 15 nm. Hence, this is another difference between plasmodesmata and desmotubule.

Connection

Another difference between plasmodesmata and desmotubule is that plasmodesmata connect adjacent cytoplasm while desmotubules connect adjacent endoplasmic reticulum.

Function

Besides, plasmodesmata are responsible for the transport of molecules and signaling between two plant cells while desmotubule is responsible for the transport of some molecules apart from the main passage of molecules formed by plasmodesmata. Thus, this is the functional difference between plasmodesmata and desmotubule.

Type of Transport

Moreover, plasmodestama transport proteins, transcription factors, short interfering RNA, messenger RNA, viroids, and viral genomes while desmotubule transports lipids responsible for the cell signaling pathway.

Conclusion

Plasmodesmata are a type of cell junctions responsible for connecting adjacent plant cells through their cell walls. The three components of a plasmodesma are the plasma membrane, the cytoplasmic sleeve, and the desmotubule. The main function of plasmodesmata is to transport molecules including proteins, RNA, and viral genomes. In comparison, desmotubule is a tube inside the plasmodesmata, involved in the transport of lipids responsible for cell signaling by connecting the adjacent endoplasmic reticulum. Therefore, the main difference between plasmodesmata and desmotubule is structure and function.

References:

1. “Plasmodesmata.” Molecular Expressions Cell Biology: Plant Cell Structure – Plasmodesmata, National High Magnetic Field Laboratory, 13 Nov. 2015, Available Here.

Image Courtesy:

1. “Plasmodesmata en” By User:Zlir’a – File:Plasmodesmata.svg (CC0) via Commons Wikimedia  
2. “Plasmodesmata structure” By Smartse – Own work by uploader based on figure 1 (CC BY-SA 3.0) via Commons Wikimedia