Very-long-chain 3-hydroxy fatty acids, 3-hydroxy fatty acid methyl esters and 2-alkanols from cuticular waxes of Aloe arborescens leaves

The present work aimed at a comprehensive chemical characterization of the cuticular wax mixtures covering leaves of the monocot species Aloe arborescens. The wax mixtures were found to contain typical aliphatic compound classes in characteristic chain length distributions, including alkanes (predominantly C-31), primary alcohols (predominantly C-28), aldehydes (predominantly C-32), fatty acid methyl esters (predominantly C-28) and fatty acids (bimodal distribution around C-32 and C-28). Alkyl esters ranging from C-42 to C-52 were identified, and found to mainly contain C-28 alcohol linked to C-16-C-20 acids. Three other homologous series were identified as 3-hydroxy fatty acids (predominantly C-28), their methyl esters (predominantly C-28), and 2-alkanols (predominantly C-31). Based on structural similarities and homolog distributions, the biosynthetic pathways leading to these novel wax constituents can be hypothesized. Further detailed analyses showed that the A. arborescens leaf was covered with 15 mu g/cm(2) wax on its adaxial side and 36 mu g/cm(2) on the abaxial side, with 3:2 and 1:1 ratios between epicuticular and intracuticular wax layers on each side, respectively. Terpenoids were found mainly in the intracuticular waxes, whereas very-long-chain alkanes and fatty acids accumulated to relatively high concentrations in the epicuticular wax, hence near the true surface of the leaf. (C) 2014 Elsevier Ltd. All rights reserved.