The surface of most aerial plant organs is covered with a cuticle that provides protection against multiple stress factors including dehydration. Interest on the nature of this external layer dates back to the beginning of the 19th century and since then, several studies facilitated a better understanding of cuticular chemical composition and structure. The prevailing undertanding of the cuticle as a lipidic, hydrophobic layer which is independent from the epidermal cell wall underneath stems from the concept developed by Brongniart and von Mohl during the first half of the 19th century. Such early investigations on plant cuticles attempted to link chemical composition and structure with the existing technologies, and have not been directly challenged for decades. Beginning with a historical overview about the development of cuticular studies, this review is aimed at critically assessing the information available on cuticle chemical composition and structure, considering studies performed with cuticles and isolated cuticular chemical components. The concept of the cuticle as a lipid layer independent from the cell wall is subsequently challenged, based on the existing literature, and on new findings pointing toward the cell wall nature of this layer, also providing examples of different leaf cuticle structures. Finally, the need for a re-assessment of the chemical and structural nature of the plant cuticle is highlighted, considering its cell wall nature and variability among organs, species, developmental stages, and biotic and abiotic factors during plant growth.

Suberin is a biopolymer that acts as a barrier between plants and the environment. It is known to be a complex polyester based on glycerol and long-chain alpha,omega-diacids and omega-hydroxyacids. How these monomeric units are assembled at a macromolecular level remains mostly unknown. The knowledge gathered in the last 10 years has opened new insights into suberin structure. Suberin oligomeric blocks have been obtained after the partial depolymerization of the biopolymer, and in-situ studies by solid-state (13)C NMR spectroscopy have shown different molecular domains and how they are spatially related. Based on these latter developments, a model is proposed for the suberin macromolecular structure. The uniqueness of the suberin polyester opens perspectives for its use as a source of bio-based materials.

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