Leaf wax of Lactuca sativa and Plantago major

Abstract

Wax layers of plants are able to accumulate semivolatile organic compounds (SOCs) from the atmosphere. In this study, the composition of the leaf cuticular waxes of lettuce ( Lactuca sativa) and common plantain ( Plantago major) was determined for future studies on the role of cuticular waxes in the uptake and bioaccumulation of SOCs. In addition, to find a suitable extraction solvent to be used in these studies, the extraction efficiency of several solvents for the cuticular wax of the plants was studied. Leaf wax of L. sativa consists mainly of long-chain linear alcohols and minor amounts of fatty acids, while the major components of leaf wax of P. major are the free polar triterpene acids, oleanolic and ursolic acid, and the linear alkanes C 27H 56C 33H 58. The wax composition of both species only slightly changes with leaf developmental stage. This property makes them highly suitable as test plants in studies on uptake of SOCs. The waxes of both plant species are readily extractable with chloroform, toluene and dichloromethane. A mixture of chloroform and methanol 2:1 additionally extracted internal lipids and chlorophyll and, therefore, is not suitable. The apolar solvent, n-hexane, did not extract the triterpene acids of P. major. However, this solvent readily extracted the relatively apolar leaf wax of L. sativa. Since the extraction of SOCs (also from deeper embedded wax layers) can only be efficient if all the components of the cuticular wax are removed, we recommend to test the extraction efficiency of the solvent for each plant species beforehand.