Ligno-Suberized Fruit Periderm as a Mechanically Reinforced Biomacromolecular Composite.

Plant surfaces are biomacromolecular composites whose organization determines barrier performance. We examined the transition from a cutin-dominated cuticle in common cucumber to a ligno-suberized periderm in Sikkim cucumber. Multiscale microscopy and histochemistry resolved a developmental shift from a smooth epidermis to a multilayered phellem characterized by distinct suberin lamellae and lignin deposition. GC-MS-based profiling revealed that periderm formation involves a shift from C16/C18 cutin monomers to an enrichment in >C20 very-long-chain aliphatics (fatty acids, alcohols, hydroxy acids) and phenolics like ferulic acid, hydroxybenzoic acids, and p-hydroxyphenyl, guaiacyl, and syringyl lignin moieties. ssNMR confirmed the increase in oxygenated and phenolic-rich polymer assemblies, consistent with higher cross-link density. Accordingly, peridermal surfaces exhibited significantly enhanced stiffness, adhesion, and elastic resistance. DSC revealed significant elevations in glass transition temperatures (Tg) from 11 °C to 60 °C. These findings establish the fruit periderm as a mechanically robust, thermally stable composite model for sustainable biopolymer design.