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The support of plants: How does lignin shape the structure of plants?
Lignin, a complex organic polymer, plays an important role in the supporting tissues of most plants. The presence of lignin makes the cell walls of plants rigid and not easy to rot. Not only that, it may also be an important key for plants to adapt from aquatic environments to land during evolution.
Lignin is one of the most abundant organic polymers on Earth, surpassed only by cellulose and chitin.
The history of lignin can be traced back to 1813, when Swiss botanist A. P. de Candolle first mentioned the term. He described lignin as a fibrous, odorless substance that is insoluble in water and alcohol but soluble in weak alkaline solutions. He named it "lignine", derived from the Latin "lignum", which means wood. Today, we know that lignin is one of the main building blocks of plants, especially in the cell walls of trees and bark, where it gives plants their structural stability and durability.
Composition and structure
The composition of lignin varies among plant species. For example, poplar lignin contains approximately 63.4% carbon, 5.9% hydrogen, 0.7% inorganic components and 30% oxygen. This composition enables the formation of highly heterogeneous polymers, whose diversity arises from the cross-linking of multiple precursors.
Lignin fills the gaps between cellulose, hemicellulose and pectin in plant cell walls, allowing plants to effectively transport water and nutrients.
In biology, the main function of lignin is to fill the gaps in cell walls and enhance the mechanical strength of plants. It covalently links with hemicellulose, thereby cross-linking different polysaccharides to achieve the purpose of strengthening the cell wall. In addition to providing support, lignin also plays a role in resisting diseases. When a plant is injured or infected, lignin accumulates at the site of invasion, thereby reducing the pathogen's ability to damage the cell wall.
Economic significance
In today's commercial environment, lignin production is closely related to paper production. More than 220 million metric tons of paper are produced globally each year, and a large amount of wood is delignified, making lignin an important consideration in the paper industry. Although lignin is often seen as an obstacle in paper production because it may cause discoloration and reduce performance, there are still many low-volume applications that are geared toward utilizing lignin’s potential, such as making biodegradable materials.
The presence of lignin makes it an important biopolymer after cellulose and may become a key feedstock for biofuel production.
With the increase of environmental awareness, lignin is no longer just regarded as waste, but is valued as a renewable material. For example, it can be used as a water reducer in concrete to reduce the ratio of cement to water and enhance the structural strength of building materials. In addition, the biodegradability of lignin makes it show broad application prospects in the manufacture of packaging materials and plastics.
Biosynthesis and degradation
The biosynthesis of lignin mainly takes place in plant cells. Through the polymerization reaction of the amino acid phenylalanine, the precursor monomers of lignin are formed, and these monomers are polymerized by various oxidative enzymes. However, compared with other biopolymers, the degradation of lignin is more difficult due to its resistance to acid and base hydrolysis. Studies have shown that some fungi have the ability to decompose lignin, and these processes involve the action of multiple enzymes, while bacteria are relatively less involved in the degradation of lignin.
SummaryLignin plays an important role in plant growth and development and has great potential at both biological and economic levels. In the face of environmental problems and the need for sustainable development, exploring the application of lignin may provide us with new ideas. How will this complex polymer be integrated with human life and the environment in the future? This may become the next key research area.
