lignifizierten

Lignified (in German: lignifiziert; the form lignifizierten is a declined adjective meaning “lignified”) describes plant tissues in which lignin has been deposited in the cell walls, producing a rigid, water-impermeable wall. Lignification is a developmental process that strengthens tissues and often accompanies secondary wall formation after cellulose deposition.

The process involves the phenylpropanoid pathway that produces monolignols such as coniferyl, sinapyl, and p-coumaryl alcohols. These monolignols are transported to the cell wall and polymerized by oxidative enzymes, including peroxidases and laccases. The resulting lignin polymer is heterogeneous, chemically cross-linked with polysaccharides, and varies in composition among species and tissues. Lignified walls become markedly more rigid and less extensible than primary walls.

Biological significance includes enhanced mechanical support for stems and branches, improved vertical strength, and reduced cell-wall porosity. Lignified tissues are often less susceptible to pathogen intrusion and provide efficient water conduction in vascular tissues. Typical lignified tissues include xylem elements such as tracheids and vessels, as well as sclerenchyma fibers and sclereids. In woody plants, extensive lignification underpins wood formation; in herbaceous plants, some tissues may undergo partial lignification during maturation.

Detection and study of lignified tissues employ histochemical staining (for example, phloroglucinol-HCl produces a red color in lignin) and quantitative assays (such as Klason lignin analysis). The degree and pattern of lignification vary by species, organ, and developmental stage, reflecting functional requirements and ecological adaptation.