Reexamination of cell contents in Pennsylvanian spores and pollen grains using Raman spectroscopy

Permineralization offers exceptional structural preservation to the level of cellular components, many of which are found within fossilized plant specimens. In some cases, structures within plant cells, particularly those found within spores and pollen grains, have been interpreted as nuclei. Although these structures have been studied morphologically and ultrastructurally, little is known about their composition and origin. This study uses petrographic thin sections and ultraviolet (UV) Raman spectroscopy to reexamine cellular inclusions within three types of Pennsylvanian spores and pollen grains with the intent to interpret the molecular composition and therefore, the identity of these structures. Thin sections are examined using Raman spectroscopy, which indicates the presence of disordered carbonaceous material and calcite. There is no significant difference in the chemical composition between the intracellular inclusions and surrounding areas within each specimen. This study represents one of the first applications of Raman spectroscopy in which the internal cell contents of fossil plant taxa are analyzed. Results do not support the presence of nuclei, although further examination is recommended to elucidate the origin and identity of the intracellular inclusions.