Chemical characterization of the periderm tissue of some angiosperm species: recognition of an insoluble, non-hydrolyzable, aliphatic biomacromolecule (Suberan)

In order to establish the chemical relationship between the liptinitic maceral suberinite and its recent counterpart, an inventory of the constituents of isolated outer bark tissue (periderm) of five extant angiosperm species was made. Samples were analyzed by means of chemical degradation methods in combination with Curie-point pyrolysis-gas chromatography-mass spectrometry and gas chromatrography-mass spectrometry. It was demonstrated that the periderm of the species investigated consisted of complex mixtures of lipids and biomacromolecules which include the biopolyester suberin, tannins, polysaccharides, lignin, and a hitherto unknown insoluble, non-hydrolyzable highly aliphatic biomacromolecule, named suberan. The liptinitic nature of the maceral suberinite can probably be explained by assuming selective preservation and consequent selective enrichment of suberan during the processes of diagenesis. The lignin present in the periderm of extant angiosperms is of a distinctively different monomeric composition from that of the corresponding wood with a marked guaiacyl over syringyl predominance. The presence of different physiological functions within the plant is offered as explanation for this divergence.