Suberin is a term used to define a specific cell wall component that occurs, for example, in phellem (cork) endodermal and exodermal cells and is characterized by the deposition of both poly(phenolic) and poly(aliphatic) domains. Historically, the poly(phenolic) domain has been likened to lignin, and while there is an element of truth to this comparison, recent evidence supports an alternative view in which the poly(phenolic) domain contains a significant amount of nonlignin precursors (principally hydroxycinnamic acids and their derivatives) that are covalently linked to each other in a manner analogous to the monolignols in lignin. Similarly, the conceptual model in which the poly(aliphatic) domain of suberized tissues is represented as a random network of polyesterified, modified fatty acids and alcohols has been replaced with one comprising a three-dimensional, glycerol-bridged network. Taken together, a new model for suberin is emerging in which a hydroxycinnamic acid -monolignol poly(phenolic) domain, embedded in the primary cell wall, is covalently linked to a glycerol-based poly(aliphatic) domain located between the primary cell wall and the plasma membrane. The structural and biochemical evidence supporting this new suberin paradigm are examined in this minireview, along with the presentation of a new structural model encompassing a current view of the structure of suberin.Résumé : Le terme subérine définit une composante pariétale cellulaire spécifique qu'on retrouve, par exemple, au niveau du suber (écorce) et des cellules endodermales et exodermales; elle se caractérise par la déposition à la fois de substances des domaines poly(phénolique) et poly(aliphatique), pour un tissus donné. Historiquement, le domaine poly(phénolique) a été assimilé à la lignine et, bien qu'il y ait un élément de vérité dans cette comparaison, une preuve récente supporte une interprétation alternative selon laquelle le domaine poly(phénolique) contient une quantité significative de précurseurs sans affinité avec la lignine (principalement des acides hydrocinnamiques et leurs dérivés) qui sont liés par covalence les uns aux autres de manière analogue aux monolignols de la lignine. De même, le modèle conceptuel selon lequel le domaine poly(aliphatique) des tissus subérifiés est représenté comme un réseau aléatoire d'acides gras modifiés et d'alcools polyestérifiés, a été remplacé par un modèle comportant un réseau tridimensionnel lié par le glycérol. Pris dans son ensemble, un modèle nouveau est en émergence pour la subérine selon lequel un domaine poly(phénolique) basé sur l'acide hydrocinnamique -monolignol, enrobé dans la paroi cellulaire primaire, est lié par covalence à un domaine poly(aliphatique) basé sur le glycérol et localisé entre la parois cellulaire primaire et la plasmalemme. Dans cette minisynthèse, l'auteur examinent les preuves structurales et biochimiques supportant ce nouveau paradigme pour la subérine, et présente un nouveau modèle structural englobant une perception courante de ce que pourrait être la struc...

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Suberin is an abundant, complex, intractable, plant cell wall polymeric network that forms both protective and wound-healing layers. Its function is, therefore, critical to the survival of all vascular plants. Its chemical structure and biosynthesis are poorly defined, although it is known to consist of both aromatic and aliphatic domains. While the composition of the aliphatic component has been fairly well characterized, that of the phenolic component has not. Using a combination of specific carbon-13 labeling techniques, and in situ solid state 13C NMR spectroscopic analysis, we now provide the first direct evidence for the nature of the phenolic domain of suberin and report here that it is almost exclusively comprised of a covalently linked, hydroxycinnamic acid-derived polymeric matrix.

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Soybean (Glycine max L. Merr.) is a versatile and important agronomic crop grown worldwide. Each year millions of dollars of potential yield revenues are lost due to a root rot disease caused by the oomycete Phytophthora sojae (Kaufmann & Gerdemann). Since the root is the primary site of infection by this organism, we undertook an examination of the physicochemical barriers in soybean root, namely, the suberized walls of the epidermis and endodermis, to establish whether or not preformed suberin (i.e. naturally present in noninfected plants) could have a role in partial resistance to P. sojae. Herein we describe the anatomical distribution and chemical composition of soybean root suberin as well as its relationship to partial resistance to P. sojae. Soybean roots contain a state I endodermis (Casparian bands only) within the first 80 mm of the root tip, and a state II endodermis (Casparian bands and some cells with suberin lamellae) in more proximal regions. A state III endodermis (with thick, cellulosic, tertiary walls) was not present within the 200-mm-long roots examined. An exodermis was also absent, but some walls of the epidermal and neighboring cortical cells were suberized. Chemically, soybean root suberin resembles a typical suberin, and consists of waxes, fatty acids, ω-hydroxy acids, α,ω-diacids, primary alcohols, and guaiacyl- and syringyl-substituted phenolics. Total suberin analysis of isolated soybean epidermis/outer cortex and endodermis tissues demonstrated (1) significantly higher amounts in the endodermis compared to the epidermis/outer cortex, (2) increased amounts in the endodermis as the root matured from state I to state II, (3) increased amounts in the epidermis/outer cortex along the axis of the root, and (4) significantly higher amounts in tissues isolated from a cultivar (‘Conrad’) with a high degree of partial resistance to P. sojae compared with a susceptible line (OX760-6). This latter correlation was extended by an analysis of nine independent and 32 recombinant inbred lines (derived from a ‘Conrad’ × OX760-6 cross) ranging in partial resistance to P. sojae: Strong negative correlations (−0.89 and −0.72, respectively) were observed between the amount of the aliphatic component of root suberin and plant mortality in P. sojae-infested fields.