What is the Difference Between Lignin and Suberin

The main difference between lignin and suberin is that lignin is a complex organic polymer that provides structural support to the plant whereas suberin is a complex organic polymer that forms a protective barrier to the movement of water and solutes.

Lignin and suberin are two complex biopolymers in plants. They occur in the epidermis and periderm cell wall macromolecules. Typically, both lignin and suberin occur in the cell walls of dead cell layers.

Key Areas Covered

1. What is Lignin
   • Definition, Characteristics, Importance
2. What is Suberin
   • Definition, Characteristics, Importance
3. Similarities Between Lignin and Suberin
   • Lignin Outline of Common Features
4. Difference Between Lignin and Suberin
   • Comparison of Key Differences

Key Terms

Lignin, Suberin

What is Lignin

Generally, lignin is a complex organic compound that occurs in the cell walls of higher plants. It is vital in the development of bark and wood. More importantly, lignin provides structural support to the plant, preventing rotting. Usually, it is a cross-linked polymer that fills the gap between cellulose, pectin, and hemicellulose in the cell walls. In addition, lignin occurs in the vascular system, providing structural support. However, lignin is the second most abundant organic biopolymer following cellulose in plants.

Figure 1: Lignin in Developing Xylem Vessels

Furthermore, lignin is a collection of highly heterogenous polymers derived from the precursor, lignols.  Heterogeneity arises with the diverse degree of cross-linking between lignols. Further, the three main types of lignin crosslinks are coniferyl alcohol, sinapyl alcohol, and paracoumaryl alcohol. The relative amount of precursor of the biopolymer or lignol depends on the variety of plants.

What is Suberin

Suberin is another biopolymer that occurs in the dead cell walls of higher plants. However, the main feature of suberin is that it is lipophilic, containing long chain fatty acids called suberin acids and glycerol. Therefore, it is highly hydrophobic. Moreover, in the endodermal cells, suberin deposits on the radial and transverse cell walls. This structure, known as the Casparian strip or Casparian band, helps to prevent water and nutrients taken up by the root from entering the stele through the apoplast.  

Figure 2: Casparian Strip

Moreover, suberin occurs in the cork, which is the outermost layer of the bark of the plants. Suberin prevents water loss from the below tissues. Structure-wise, suberin contains two domains: a polyaromatic and a polyaliphatic domain. Predominantly, polyaromatics occur in the primary cell wall and polyliphatic occurs in between the primary cell wall and cell membrane. In addition to the aromatic and aliphatic components, glycerol is a major component of suberin in some varieties of plants.

Similarities Between Lignin and Suberin

• Lignin and suberin are complex biopolymers that occur in the cell walls of dead cells of higher plants.
• Moreover, they occur covalently linked to the lipids and carbohydrates in the cell wall.
• Both are hydrophobic.
• They also play a vital role in the secondary cell walls of plants.

Difference Between Lignin and Suberin

Definition

Lignin refers to a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody while suberin refers to an inert impermeable waxy substance present in the cell walls of corky tissues.

Significance

Usually, lignin is the second most abundant organic polymer following cellulose while suberin is lipophilic and therefore highly hydrophobic.

Occurrence

Lignin occurs in the bark and wood while suberin occurs in the Casparian strip and the cork.

Function

Lignin provides structural support to the plants while suberin forms a protective barrier to the movement of water and solutes.

Conclusion

In brief, lignin is a cross-linked polymer of the secondary cell wall of plants, mainly occurring in the bark and wood. The main function of lignin is to provide structural support to the plant. Suberin, on the other hand, is a very hydrophobic substance that occurs in the secondary cell walls. Moreover, the main function of suberin is to form a protective barrier to the movement of water and solutes. Therefore, the main difference between lignin and suberin is their structure and function.  

References:

1. Encyclopædia Britannica, inc. (n.d.). Lignin. Encyclopædia Britannica. Retrieved September 7, 2022.
2. Wikimedia Foundation. (2021, October 5). Suberin. Wikipedia. Retrieved September 7, 2022.

Image Courtesy:

1. “Xylem vessels in developing Coleus shoot (35105390750)” By Berkshire Community College Bioscience Image Library – Own Work (CC0) via Commons Wikimedia
2. “Symplastic and apoplastic water flow through root” By Dylan W. Schwilk – Own Work (CC BY-SA 4.0) via Commons Wikimedia