EPICUTICULAR LEAF WAXES IN THE EVOLUTION OF THE PLANT KINGDOM

Needle waxes of conifer trees consist of homologues of fatty acids, nonacosan-10-ol and predominantly bifunctional lipids with chain lengths C-12 to C-16, the alpha-omega-diols and above all the omega-OH-fatty acids, free or in form of their inner esters, the estolides. On young needles crystalloids in the shape of small round tubules formed by nonacosan-10-ol always can be observed. Leaf waxes of deciduous trees have a quite different composition. They consist mostly of homologous series of hydrocarbons, wax esters, aldehydes, alcohols and fatty acids. Further lipids are found on occasion, for example benzyl acyl esters or acetates and often triterpenoids as well. The surface wax ultrastructures of deciduous trees differ from species to species according to wax composition. Liriodendron leaves have surface crystalloids in the shape of transversally ridged rodlets formed by hentriacontan-16-one, Tilia leaves show quandrangular rodlets formed by beta-amyrenyl acetate, Quercus has fringed edged platelets formed by tetracosanol. Fagus and Castanea trees have no wax crystalloids, but only a sculptured surface structure on the upper leaf side. Gingko leaf waxes have an intermediate composition. Dominant are the homologue lipid components similar to those of deciduous trees, but nonacosan-10-ol is also present and thus the surface ultrastructure shows small round tubules like those of conifer needles. There are fundamental differences between epicuticular leaf waxes of gymnosperms and angiosperms, and fundamental evolutionary influences are found to affect the wax compositions and surface ultrastructures of these different plant classes.