Searching for chemotaxonomic signals by Fourier Transform Infrared Spectroscopy in cuticles and compressions of perilacustrine remains of Corystospermales (Upper Triassic of Cacheuta, Mendoza, Argentina)

D'ANGELO, J.A., VOLKHEIMER, W.

Barcelona

Congreso; 4º International Limnogeology Congress; 2007

International Association of Limnogeology (IAL)

Cuticles and compressions of Triassic plants are analyzed by Semi-quantitative Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM). Several corystosperm specimens from the southern side of the Cacheuta hill (Cacheuta Formation, lower to upper Upper Triassic), Cacheuta, Mendoza, Argentina are studied here. Leaf cuticular SEM analysis of Dicroidium odontopteroides var. odontopteroides (Morris) Gothan and Johnstonia coriacea var. coriacea (Johnston) Walkom exhibit an excellent preservation state, revealing no taxonomic differences. In addition, FT-IR semi-quantitative variables and functional groups are determined searching for chemotaxonomic signals in corystosperm cuticles and compressions. Infrared (IR) spectra obtained from cuticles and compressions of corystosperms show the presence of several functional groups: aliphatic, hydroxyl, carbonyl, aromatic as well as some other oxygen-containing groups. In the region below 1700 cm-1, cuticular specimens show distinct bands. Here, simple and pyrolytically labile ester carbonyl groups are absent. Ketone and carboxylic acid groups, yielded by hydrolysis of simple esters and subsequent oxidation of the mid-chain alcohol produced, replace them. Semi-quantitative data derived from FT-IR spectra are statistically analyzed using one-way analysis of variance test (ANOVA). One-way ANOVA reveals significant differences between cuticles and their corresponding compressions (p < 0.05) regarding the FT-IRderived variables here considered. This is supported by two distinctive features found in FT-IR spectra of compressions (non-chemically treated materials), which are absent in cuticle spectra: (a) one prominent band centered at about 1608-1620 cm-1 and (b) distinct aromatic C-H out-of-plane bands at approximately 880, 820 and 750 cm-1. These regions likely represent the contribution of non-cuticular organic matter (e.g., vitrinitic matter). No statistically significant differences (p > 0.05) between abaxial and adaxial cuticular surfaces neither in Johnstonia coriacea nor in Dicroidium odontopteroides are found. Infrared-derived ratios here considered in compression samples do not differ significantly between taxa (p > 0.05). Similarly, comparison between cuticles of the two taxa does not show statistical differences (p > 0.05) regarding the FT-IR variables here considered. Based on previously established morphological similarities (SEM microscopical studies) and the novel, independent FT-IR features here presented, it might be stated that there are no significant differences between the cuticles of the two taxa here studied. Nevertheless, the application of the FT-IR technique to the chemotaxonomic study of the Corystospermaceae foliage will require more data from these and some other taxa (including the use of some other analytical techniques, such as pyrolysis-gas chromatography/mass spectrometry), before obtaining definitive conclusions.