Glycerol Is a Suberin Monomer. New Experimental Evidence for an Old Hypothesis1

Abstract

The monomer composition of the esterified part of suberin can be determined using gas chromatography-mass spectroscopy technology and is accordingly believed to be well known. However, evidence was presented recently indicating that the suberin of green cotton (Gossypium hirsutum cv Green Lint) fibers contains substantial amounts of esterified glycerol. This observation is confirmed in the present report by a sodium dodecyl sulfate extraction of membrane lipids and by a developmental study, demonstrating the correlated accumulation of glycerol and established suberin monomers. Corresponding amounts of glycerol also occur in the suberin of the periderm of cotton stems and potato (Solanum tuberosum) tubers. A periderm preparation of wound-healing potato tuber storage parenchyma was further purified by different treatments. As the purification proceeded, the concentration of glycerol increased at about the same rate as that of ␣, -alkanedioic acids, the most diagnostic suberin monomers. Therefore, it is proposed that glycerol is a monomer of suberins in general and can cross-link aliphatic and aromatic suberin domains, corresponding to the electrontranslucent and electron-opaque suberin lamellae, respectively. This proposal is consistent with the reported dimensions of the electron-translucent suberin lamellae.Suberin and cutin are insoluble, lipophilic biopolymers. Together with complex mixtures of soluble lipids, they form the protective layers of higher plants: the cuticle of the epidermis and the suberin layers of the periderm and the exodermis. These cell layers are diffusion barriers for water and other

The Biopolymers Cutin and Suberin

“…The first tentative model of suberin proposed that the aliphatic constituents of suberin form a polyester to which the phenolic compounds that are cross-linked in a lignin-like manner are bound (Kolattukudy, 1981). Recently the analysis of water soluble compounds of the depolymerization reaction confirmed earlier reports of glycerol being a principal monomer (20%) of suberin in oak, cotton, and potato (Moire et al, 1999;Graça and Pereira, 2000a, b). Partial methanolysis with calcium oxide as catalyst has identified that glycerol may be present as monoacylglycerol esters of alkanoic acids, α, ω-diacids, and ferulic acid (Graça and Pereira, 2000b), as well as diglycerol ester being linked to a α, ω-diacid at both ends (Graça and Pereira, 2000c).…”

“…Thus, the hypothesis has been proposed that glycerol and α, ω-diacids may form the backbone of the suberin polymer and that thus suberin is a poly-(acylglycerol)-polyester (Graça and Pereira, 2000c). Glycerol may also cross-link the aromatic and aliphatic suberin components, corresponding to the electronopaque and electron-translucent suberin lamellae to a three-dimensional network, while aliphatic and aromatic suberin monomers may only form a linear polymer on their own (Moire et al, 1999). Glycerol and glycerol-fatty acid esters are not only components of the suberin polymer but also of suberin-associated waxes in suberized cotton fibers (Schmutz et al, 1993;.…”

“…Some plants show, however, an unusual suberin deposition. For example, cotton producing green fibers may show ectopic suberization causing their green color; this might indicate that cotton with white fibers is a mutant deficient in fiber suberization (Ryser, 1999).…”

CYP86A33-Targeted Gene Silencing in Potato Tuber Alters Suberin Composition, Distorts Suberin Lamellae, and Impairs the Periderm's Water Barrier Function

“…The glycerol content in suberin was enzymatically quantified based on the method reported in the past (Schmutz et al, 1996;Moire et al, 1999). Prior to analysis, periderm membranes were treated with a chloroform-methanol mixture as described above.…”

Monoacylglycerols Are Components of Root Waxes and Can Be Produced in the Aerial Cuticle by Ectopic Expression of a Suberin-Associated Acyltransferase

“…A substantial portion of the hydroxycinnamic acids of suberin are believed to be cross-linked (Bernards et al, 1995;Bernards, 2002). Besides aliphatic and aromatic components, suberins contain a substantial proportion of glycerol (Holloway, 1982;Grac xa and Pereira, 1997;Grac xa et al, 2002), the content of which is positively correlated to the suberization process (Moire et al, 1999). Partial chemical depolymerizations of bark and potato (Solanum tuberosum) periderm suberins have yielded fragments that include monoacylglycerols (MAGs) of a,v-dicarboxylic acids, v-hydroxy fatty acids and fatty acids, diglycerol esters of a,vdicarboxylic acids, and an v-ferulyloxy-acyl glycerol (Grac xa and Pereira, 1997Pereira, , 1999Pereira, , 2000Grac xa and Santos, 2006;Santos and Grac xa, 2006).…”