Distribution of Apple Fruit Epidermal Non-polar Metabolites

Apple peel epidermis provides a resilient protective barrier against external stimuli while, also, comprising much of what is considered as fruit appearance and related phenotypic components. This dynamic structure is subject to many changes throughout the production and supply chain that can impact fruit appearance and epidermal function. Apple epidermis is comprised of live cells coated with an intractable cutin layer that is both embedded in and coated with wax. Wax and cutin are constructed of secondary metabolites principally supplied by specialized epidermal cells. In this study, we examined wax and epidermal peel cells separately to determine the origination of non-polar metabolites that comprise our whole peel analysis. ‘Granny Smith’ peel metabolites were fractionated by submerging whole fruit in hexanes and, subsequently, in chloroform, then peel was collected. Components of wax fractions and peel were identified using an LC-MS global analysis of non-polar metabolites. A wide variety of metabolites including isoprenoids, lipids, and triglycericides were identified and localized as non-wax cell metabolites if present in the peel extract following wax extraction, or extracellular wax components if present in hexanes or chloroform. Carotenyl pigments, chlorophylls and photosystem components resided within the active cell region as were phytosteryl, phytosteryl conjugates and many lipids that comprise lipid bilayers. Sesquiterpenes and triterpenes and their conjugates or oxidation products were located in the waxes. Location of these metabolically and structurally important peel components is diverse and may influence any consideration of their genesis, interactions, and products in these systems and roles they may have in phenotype and disorder related physiology.