Lignifiointi

Lignifiointi, often translated as lignification, is a biological process that occurs in plant tissues, particularly in the secondary cell walls of xylem. It involves the deposition of lignin, a complex polymer, within the cellulose and hemicellulose matrix of the cell wall. This process significantly strengthens and hardens the plant cell, making it more rigid and resistant to mechanical stress and pathogen attack.

Lignin is a heterogeneous phenolic polymer composed of phenylpropane units. Its biosynthesis is a complex enzymatic pathway involving the oxidation of precursor alcohols derived from the shikimate pathway. Once formed, these monolignols are transported to the cell wall and polymerized by enzymes like laccases and peroxidases. The specific arrangement and type of phenylpropane units contribute to the diverse properties of lignin found in different plant species and tissues.

The primary function of lignification is to provide structural support to plants, enabling them to grow upright and withstand environmental forces. In vascular plants, lignified xylem vessels are crucial for efficient water transport due to their rigidity, which prevents collapse under tension. Lignin also plays a role in defense, acting as a physical barrier against herbivores and microbes. Furthermore, it contributes to the waterproofing of cell walls, reducing water loss. The presence and extent of lignification are key factors in determining the strength and durability of wood, a major lignified plant material.