INSIGHT INTO THE CHEMICAL COMPOSITION OF THE FOLIAR STRUCTURE IN EXTINCT AND EXTANT TAXA BELONGING TO CYCADOPHYTES

LAFUENTE DIAZ, MAITEN A.; ERWIN L. ZODROW; D'ANGELO, JOSÉ A.; DEL FUEYO, GEORGINA M.

San Salvador de Jujuy

Simposio; XVIII Simposio argentino de Paleobotánica y Palinología; 2022

INSIGHT INTO THE CHEMICAL COMPOSITION OF THE FOLIAR STRUCTURE IN EXTINCT AND EXTANT TAXA BELONGING TO CYCADOPHYTESLafuente-Diaz Maiten A.1, Zodrow Erwin L.2, D'Angelo José A.3,4 y Del Fueyo Georgina M.11 Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”. Avda. Ángel Gallardo 470,C1405DJR Ciudad Autónoma de Buenos Aires, Argentina. maitenlafuentediaz@gmail.com; georgidf@yahoo.com.ar2 Palaeobotanical Laboratory, Cape Breton University. 1250 Grand Lake Rd., Sydney, Nova ScotiaB1P 6L2, Canada. zzodrovii@gmail.com3 Universidad Nacional de Cuyo, FCEN, MS5502JMA, Mendoza, Argentina.4 Cape Breton University, Department of Mathematics, Physics & Geology, 1250 Grand Lake Road,Sydney, Nova Scotia, B1P 6L2, Canada. jose_dangelo@cbu.caThemolecular characterization of Cycas rumphii (extant Cycadales) leaves using semi-quantitative Fourier TransformInfrared (FTIR) spectroscopy is performed. The resulting chemical informationis compared to that of fossil leaves of Cycadales and Bennettitales. Thus, theaim of this contribution is to study functional groups; i.e., structuralcompounds as well as primary and secondary metabolites making up Cycadophytesplants. For that, foliar FTIR data of Cycasrumphii (extant Cycadales; NY 581/2006-F) are compared with those of Pseudoctenis ornata (extinct Cycadales; BA Pb1217, 1220, 1222) and Ptilophyllum micropapillosum (Bennettitales; MPM Pb 15355) samples. The fossil taxa are foliar compressionswith well-preserved cuticles which were collected from two different geologicalunits outcropping in the Santa Cruz Province (Argentina). Particularly, Pseudoctenis ornata was recovered from theBaqueró Group (Punta Del Barco Formation, Aptian), whereas Ptilophyllum micropapillosum from theSpringhill Formation (Hauterivian–Barremian). Fossil and extant specimens werespectroscopically analyzed using two sample forms: 1) complete leaf (mesophyll+ cuticles) and 2) cuticles. Semi-quantitative IR-data were statistically analyzedusing principal component analysis. The spectroscopic pattern of C. rumphii resembles that of thecuticles of P. micropapillosum. Thecuticles of these two taxa show a high content of aromatic functional groups(C=C contribution), a relatively low contribution of aliphatic- andoxygen-containing compounds, and low cross-linking of polymeric structures (highCHal/C=O values). The relatively strong aromatic contribution recorded for C. rumphii leaves is mainly related tocutin/cutan monomers (phenylpropanoids and aromatic domains) and phenoliccompounds (e.g., lignins, tannins), which are present in cuticles (including lignifiedstomata) and in mesophyll (e.g., hypodermic fibers, transfusion tissue,conspicuous midribs). Additionally, C.rumphii spectra exhibit distinctive peaks related to cell wall components (i.e.,pectic polysaccharides, hemicelluloses, and celluloses) in the 1200-800 cm-1 region. On the other hand, P. ornata differs from the remaining taxa by having the highest aliphaticcontents. Chemical differences between fossil and extant Cycadales samples maybe more related to the original chemistry of P. ornata rather than to their systematic affinity. However, the previouslyreported natural oxidation as a consequence of the volcanic activity during theBaqueró Group sedimentation where the parent plants of P. ornata inhabited cannot be ruled out. In conclusion,the microanatomical differences that allow the distinction between Cycadalesand Bennettitales are not reflected as chemical differences. In contrast, FTIRspectroscopic data support the morphological similarities between Cycadales andBennettitales, being Cycas rumphii and Ptilophyllum micropapillosum, chemically similar interms of functional-groups contributions.Contribution funded by grants: ANPCyT-PICT 528/12, 2015-2206, and 2020-2271