Epicuticular wax of juvenile Eucalyptus leaves and headspace analysis of leaf volatiles

Abstract

This study was performed to determine the variation in leaf epicuticular wax composition and yield between 17 species of Eucalyptus with horticultural potential, and to identify a possible solvent for epicuticular wax using headspace volatile analysis. Variation in the amount and composition of leaf epicuticular wax among 17 species of Eucalyptus L'Heritier (Myrtaceae) with horticultural potential, was characterized by GC, TLC and GC/MS. Across species, wax yield ranged from 0.7 to 4.5 mg/cm2. The major wax constituents in all species except E. delegatensis R. Baker, were beta-diketones (24.7-83.0%), followed by wax esters (6.4-26.5%), n-alkanes (3.5-26.5%), fatty acids (3-15.9%), n-alcohols (0.6-11.1%) and aldehydes (0-9.2%). In E. delegatensis the major wax constituents were wax esters (46.6%), beta-diketones (24.7%), n-alkanes (11.5%), fatty acids (7.5%), n-alcohols (5.2%) and aldehydes (4.3%). Volatile organic compounds emitted from developing Eucalyptus leaves of six species were studied using solid phase microextraction (SPME), and were analyzed by GC and GC/MS. Leaf oils were extracted from four of the six species and the relative amounts of volatile compounds in the extract and headspace compared. The major volatile constituents were alpha-pinene (11.4-57.8%, headspace; 15.3-32.2%, oil extract) and 1,8-cineole (3.2-88.6%, headspace; 20.8-54.7%, oil extract). Other terpenoids present in the headspace in significant quantities were allo-aromadendrene, viridiflorene, alpha-thujene, alpha-phellandrene, gamma-terpinene and limonene. In the oil extract, allo-aromadendrene, alpha-phellandrene, viridiflorene and limonene were present in significant quantities. Components of leaf oils are potential solvents involved in the transport of waxes from the epidermis to the cuticle, although this is not confined by the present study.