Possible effects of chemical heterogeneity in higher land plant cuticles on the preservation of its ultrastructure upon fossilization

Abstract

Morphologically well preserved fossilized cuticles of Symplocos hallensis of Eocene age from Geiseltal (Germany) and isolated cuticles from its “extant relative” Symplocos paniculata have been studied in order to determine the possible impact of diagenetic processes on the structure and chemical composition of higher plant cuticles. Both samples were studied by means of transmission electron microscopy, ultrahistochemical staining reactions, and extraction, and chemical degradation methods in combination with gas chromatography-mass spectrometry and Curie-point pyrolysis-gas chromatography/mass spectrometry. Diagenesis apparently induced several significant changes in the cuticle of S. hallensis. There were considerable differences in leaf anatomy and fine structure between the two species. A cuticle proper could not be detected in S. hallensis but ultrastructural observations permit the inference that it could have disintegrated as first part of the cuticular membrane during diagenesis. Furthermore, the fossil species S. hallensis contained, apart from the resistant biopolymer cutan, “cutin-derived” material with non-saponifiable intermolecular linkages instead of the saponifiable biopolyester cutin present in S. paniculata. The “cutin-derived” material could either have been biosynthesized by the plant itself or be the result of diagenetically induced reactions of reactive groups, such as epoxide, originally present in the cutin. It is speculated that the absence the cuticle proper in S. hallensis is related to its very specific chemical composition which is different from that of the cuticular layer.