- Suberin
Suberin is a waxy substance found in higher
plant s. Suberin is a main constituent of cork, and is named after theCork Oak , "Quercus suber".Anatomy and physiology
Suberin is highly
hydrophobic and its main function is to preventwater from penetrating the tissue. Inroot s suberin is deposited in the radial and transversecell wall s of the endodermal cells. This structure is known as theCasparian strip or Casparian band. Its function is to prevent water and nutrients taken up by the root from entering the stele via theapoplast . Instead, water must traverse theendodermis through thesymplast . This allows the plant to select thesolute s that pass further into the plant. It thus forms an important barrier to harmful solutes.Mangrove s use suberin to minimizesalt intake from theirlittoral habitat, for example.Suberin is found in the
phellem layer of theperiderm (or cork). This is outermost layer of thebark . The cells in this layer are dead and abundant in suberin, preventing water loss from the tissues below. Suberin can also be found in various other plant structures. For example, the net structure in the rind of anetted melon is suberin.Structure and biosynthesis
Suberin consists of two domains, a polyaromatic and a polyaliphatic domain. The polyaromatics are predominantly located within the primary cell wall, and the polyaliphatics are located between the
primary cell wall and theplasmalemma . The two domains are supposed to be cross-linked. The exact qualitative and quantitative composition of suberinmonomer s varies in different species. Some commonaliphatic monomers include -hydroxyacids (mainly 18-hydroxyoctadec-9-enoic acid) and ,-diacids (mainly octadec-9-ene-1,18-dioic acid). The monomers of the polyaromatics arehydroxycinnamic acid s and derivatives, such as feruloyltyramine.In addition to the aromatics and aliphatics components,
glycerol has been reported a major suberin component in somespecies . The role of glycerol is proposed to interlink aliphatic monomers, and possibly also to link polyaliphatics to polyaromatics, during suberinpolymer assembly. Thepolymerization step of aromatic monomers has been shown to involve aperoxidase reaction.The
biosynthesis of the aliphatic monomers shares the same upstream reactions withcutin biosynthesis, and the biosynthesis of aromatics shares the same upstream reactions withlignin biosynthesis. Lignin and suberin are the only known biological polymers that are irregular.
Wikimedia Foundation. 2010.