Suberin is a biomacromolecule found in the outermost phellem cells of periderm tissues in many land plants, such as the cork oak. It has a wide range of protective functions, including guarding against water loss, protecting against pathogenic attack, and healing wounds. The well-recognized shortcomings of current structural models have led to debate regarding the arrangement of its components; some evidence suggests that their deposition into the apoplastic barrier between the primary and tertiary cell wall occurs via a self-assembly guided process. Drawing on prior observations of suspended solids formed spontaneously by potato periderm extracts, we have devised a simplified suberin model system comprised of compounds that represent each of the structural domains: juniperic acid (ω-hydroxy fatty acid), ferulic or sinapic acid (aromatic component) and glycerol (possible ester linkage). A suspended threadlike precipitate was observed 21 days after mixing the three components in an equimolar ratio. The ‘bulk’ chemical structure of the new solid was analyzed using solid-state <sup>13</sup>C NMR and LC-MS, showing that all the components were incorporated within the solid and that ester bonds exist between them. The surface of the material was found to contain virtually no glycerol using ATR-FTIR, perhaps suggesting that the esters are “inside” the assembly. Low-angle XRD analysis gave D-spacings of ~1.9 to 3 nm, in agreement with inter-lamellar spacings measured from TEM images. Taken together, these findings show that three constituents can spontaneously form a lamellar network similar to suberin in native or wounded potato tissue, even without enzyme catalysts or an apoplastic cellular compartment. A physicochemical understanding of this self-assembly process involving fatty and aromatic acids could hold future promise for the development of industrial materials with versatile protective functions.

Three-component model for potato suberin biopolymer supports a self-assembly process

2019 Fall National Meeting

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