Molecular Structure and Biomechanics of Plant Cuticular Membranes

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The cuticle of higher plants serves as a versatile regulator of the flow of water and chemicals from the outside environment and a robust defense against bacterial and fungal attack. Waxes are deposited on a cutin polyester whereas suberin and poly(phenolics) are found in secondary growth tissues or formed as a stress response. Fruit cuticles are smart surfaces - capable of spatially selective self cleaning and regulation of their superlative mechanical performance during ripening. To establish the molecular and mesoscopic architectures underlying the protective functions of these remarkable biomaterials without destroying their unique properties, solid-state nuclear magnetic resonance, biomechanical analysis, and atomic force microscopy of the intact biopolymers will be coordinated to examine covalent structure and dynamics, stress-strain profiles, viscoelasticity, and surface topology. Three tomato fruit cuticle systems will be used to test hypotheses involving the influence of cutin molecular structure and its organization with waxes and cell walls on the mechanical integrity of fruit cuticles: a commercial cultivar from which epicuticular waxes have been removed to model environmental stress and two types of genetically characterized cuticle-deficient fruit mutants. The thematically related goals of this project include optimization of methods for structural and functional characterization of intact fruit cuticles, testing of mechanistic models for maintenance of fruit cuticle integrity under wax abrasion stress, evaluation of how cutin/wax ratios, amounts, and branched structures preclude formation of a homogeneous barrier in cuticle deficient mutant fruits, and testing of proposed architectural causes and consequences of microfissuring in precocious dehydration mutants.A multiscale approach to fruit cuticle integrity has broad potential for intellectual synergy among plant molecular biologists and geneticists, physical chemists, and bioengineers. The results of this research will guide the design strategies to enhance the hardiness and yield of agriculturally important food crops. Findings on the mechanical performance of these remarkable natural plant interfaces should also inspire the biomimetic design of self-cleaning paints and fiber-reinforced waterproofing. New NMR methodology developed for this research will be disseminated through an NSF-sponsored Research Coordination Network. Finally, the educational impact of this project will include interdisciplinary training in the biophysics of macromolecular assemblies, conducted on a campus that enrolls more than 60% Hispanic and Black students and at a university that awards almost 10% of U.S. African-American Ph.D.'s in Chemistry and Chemical Engineering. The project will form the basis for two new outreach initiatives based at CCNY and targeting nearby Upper Manhattan and Bronx high schools with substantial minority populations: (1) a semester-long lab-based Plant Biopolymers course designed for 20-student classes in CUNY's College Now partnership with the NYC Department of Education; and (2) a 40-student Gateway Lab research training workshop coordinated with CCNY's Pathways Bioinformatics and Biomolecular Center.