Are hemicelluloses from Podocarpus lambertii typical of gymnosperms?

Abstract

Podocarpus lambertii, a Podocarpaceae, is a member of the most diverse family of conifers and Araucaria angustifolia, which belongs to the Araucariaceae family, is a typical gymnosperm from Southern Brazil. A structural characterisation of their hemicelluloses was carried out. The hemicelluloses were obtained by sequential and selective extraction with aqueous alkaline solvents, which resulted in the preparation of arabinoxylans (AGX) with different Xyl:Ara ratios, indicating the existence of distinct polysaccharides. Some are more exposed in the extraction process (higher arabinose content) and others which interact strongly with cellulose, had molecular mass differences, confirmed by HPSEC analysis. Isolated arabinoxylans and galactoglucomannans (GGM) had, by chemical and spectroscopic analysis, structural features similar to those found in other coniferous species. The hemicelluloses of P. lambertii and A. angustifolia had GGM:AGX ratios of 1.0:1 and 2.3:1, respectively. This proportion found in A. angustifolia is common to other gymnosperms. However, the content of AGX in P. lambertii is higher than expected, since that coniferous plants contain mainly GGM with a lower proportion of acidic arabinoglucuronoxylans. This discrepancy, added to the peculiar morphologic characteristics from the Podocarpus genus should probably be significant in the evolutionary process.