Studies of Fossil and Modern Spore Wall Biomacromolecules using13C Solid State NMR

A range of Carboniferous lycophyte megaspore exines have been investigated using 13 C magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Their composition differs considerably from sporopollenin obtained from an extant lycophyte. The differences observed result in part from varying degrees of diagenesis. Fossil fern spores, gymnosperm megaspore-membranes and pollen have also been examined. These show a similar composition to the fossil lycophyte megaspores. The constituent material of all of these exines differs considerably from the sporopollenin obtained from comparable extant samples. Despite the changes in composition observed on fossilisation, differences in composition between the major groups of plants may be preserved to some extent in the fossil material. Walls of the fossil prasinophycean algal cyst Tasmanites have been examined and these show a greater similarity to fossil cuticle and algaenans than to sporopollenins. The effect of oxidative maceration on fossil and modern sporopollenins has also been investigated. The main influence of oxidative maceration is the removal of unsaturated carbon environments such as aromatics; this causes fossil spores to be more susceptible to oxidative maceration than the modern exines. Heating of modern exine material models the alteration of exines by diagenesis. The changes that occur on heating an extant sample to 150–225°C give a chemical composition that is similar to those of the fossil sporopollenins.