Investigations on leaf waxes. III. Pentacyclic triterpenes, seco-tritespenes and non-volatile aliphatics of four Hoya species and Ficus benjamina in relation to leaf age

In all the species investigated the leaf epicuticular wax composition was found to be largely dependent on leaf age. In very young, still expanding, leaves characteristic patterns of aliphatic alcohols and non-volatile aliphatic hydrocarbon homologues were found. The chain-length distributions of the latter differ among the species and seem to be age dependent. In fully expanded leaves of all the investigated species leaf epicuticular wax synthesis continues during subsequent leaf life: the amount of wax per unit leaf area increases several fold and compounds not found in very young leaves are synthesized. In all the species investigated leaf ageing is accompanied by accumulation of a complex mixture of relatively short-chain aliphatic hydrocarbon homologues. In fully expanded and older leaves of the four Hoya species especially triterpenes and aliphatic hydrocarbons are synthesized. At these stages of leaf life jeco-nor-triterpenols accumulate in the wax of H. australis and H. crassipes. These substances are absent in young leaves. In comparable stages of leaf life methyl esters of seco-triterpene acids were found in H. australis, H. lacunosa and H. crassipes. These substances are also absent in young leaves. In H. keysii, on the contrary, free triterpenols were found to accumulate during leaf ageing. In the leaf wax of quite a different latex plant, Ficus benjamina, in addition to the aliphatics, only small amounts of triterpenols are present. Several observations have lead to the conclusion that the .seco-triterpenoids found in the leaf waxes are probably enzymatically formed by the plants themselves, and not photochemically nor by microbial phyllosphere activity.