Formation of a polyalkyl macromolecule from the hydrolysable component within sporopollenin during heating/pyrolysis experiments with Lycopodium spores

The most resistant component of Lycopodium spores is the macromolecule sporopollenin. The recent and fossil representatives of this material are structurally distinct and the transformations that bring about this chemical discord are poorly understood. To investigate the diagenesis of spores and their biopolymer, solvent extracted and saponified examples of Lycopodium clavatum underwent simulated diagenesis by heating (100–400 °C) under vacuum for 48 h. Following simulated maturation, spores were analysed by pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) and thermochemolysis-GC–MS. Py-GC–MS data clearly demonstrate that there is an increase in the polyalkyl hydrocarbon material in the pyrolysable component with increasing anhydrous maturation temperature. Hydrous pyrolysis of spores leads to similar changes but with an increased response from aliphatic relative to aromatic material. If the spores are hydrolysed prior to heating the generation of the polyalkyl portion of the macromolecule is markedly reduced. It appears, therefore, that the polyalkyl portion of fossil sporopollenin may be formed by maturation-induced polymerisation of the ‘labile’ hydrolysable component to form a recalcitrant polyalkyl network.

► Lycopodium spores were artificially matured to simulated diagentic changes in sporopollenin chemistry. ► Following simulated maturation, spores were analysed by pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) and thermochemolysis-GC–MS. ► Laboratory anhydrous and hydrous maturation in solvent extracted spores produces a polyalkyl macromolecule similar to that found in fossil spores. ► It appears that the polyalkyl portion of fossil sporopollenin may be formed by maturation-induced polymerisation of the ‘labile’ hydrolysable component to form a recalcitrant polyalkyl network.