Main content area

Epicuticular Leaf Waxes of the Hop (Humulus lupulus). Chemical Composition and Surface Structures

Gülz, P.-G., Müller, E., Herrmann, T., Lösel, P.
Zeitschrift für Naturforschung 2014 v.48 no.9-10 pp. 689-696
Humulus lupulus, alcohols, aldehydes, chemical composition, epicuticular wax, esterification, leaves, long chain fatty acids, trichomes, triterpenoids, wax esters
The epicuticular wax layer of Humulus lupulus contains homologous series of hydrocarbons, wax esters, benzylacyl esters, aldehydes, primary alcohols, fatty acids and the triterpenoids β-amyrin, α-amyrin both free and esterified with long chain fatty acids and also friedelanone. At 54%, primary alcohols form the largest component. No single class of lipids forms a pre­dominant component (i.e. more than 80%) of the wax layer. Under scanning microscopical examination, both upper and lower surfaces of H. lupulus leaves appear covered by a continuous way layer which is devoid of any sculpturing or crystalloids. Epidermal cells are arranged in dense lamellate or undulate cuticular folds. Four different types of trichomes were identified on the surfaces of hop leaves and tendrils. The adaxial leaf surface bears numerous single, uni­ cellular, silicified, pointed hairs as well as many glands. On the abaxial leaf surface there are very long pointed hairs arising only from the veins. Hairs on the hop tendrils arise from the veins but are completely different in shape having two sharp points extending at right angles to the hair-base.