Suber

Suber, commonly used to refer to the cork tissue and the cork itself, is a hydrophobic biopolymer that forms the protective cell walls of cork in plants. The term is closely associated with cork oak (Quercus suber), whose bark yields commercial cork. The suberin-rich tissue provides a durable barrier against water loss and pathogen ingress.

Suberin is a complex polyester composed of two main domains: an aliphatic component containing very long-chain fatty acids, ω-hydroxy acids, and α,ω-dicarboxylic acids, and an aromatic polyphenolic domain derived from hydroxycinnamic acids such as ferulic acid. These components are highly cross-linked, producing a hydrophobic network that resists permeability and contributes to mechanical resilience.

Biosynthesis occurs in specialized cork-forming tissue called the phellogen or cork cambium, which generates phellem (cork) cells that become suberized. In cork, the suberized cells are typically dead at maturity, leaving thick, suberin-rich walls that form the outer protective layer. Suberin also occurs in other plant tissues, notably in endodermal and exodermal cell walls of roots, where it helps regulate water and solute movement.

Functions and applications: The suberin-rich barrier limits water loss, protects against soil-borne pathogens, and offers mechanical protection. Economically, cork is harvested from the bark of mature cork oaks in a sustainable process that preserves the tree. Cork is widely used for bottle stoppers, as well as in flooring, insulation, and soundproofing materials.

See also: Cork oak, phellogen, endodermis, periderm.