Plant-derived triterpenoid biomarkers and their applications in paleoenvironmental reconstructions: chemotaxonomy, geological alteration, and vegetation reconstruction

抄録

Triterpenoids and their derivatives are ubiquitous in sediment samples. Land plants are major sources of nonhopanoid triterpenoids; these terpenoids comprise a vast number of chemotaxonomically distinct biomolecules. Hence, geologically occurring plant-derived triterpenoids (geoterpenoids) potentially record unique characteristics of paleovegetation and sedimentary environments, and serve as source-specific markers for studying paleoenvironments. This review is aimed at explaining the origin of triterpenoids and their use as biomarkers in elucidating paleoenvironments. Herein, application of plant-derived triterpenoids is discussed in terms of: (i) their biosynthetic pathways. These compounds are primarily synthesized via oxidosqualene cyclase (OSCs) and serve as precursors for a variety of membrane sterols and steroid hormones. Studies on OSCs and resulting compounds have helped elucidate the diversity and origin of the parent terpenoids. (ii) their chemotaxonomic significance. Geochemically important classes of triterpenoid skeletons are useful in gathering and substantiating information on botanical origin of these compounds, evolution and diversification of angiosperms, and organic matter preservation during different periods in geological history. (iii) current knowledge on their transformation into geoterpenoids via diagenetic alterations. This knowledge helped in paleoenvironmental reconstructions from the local depositional environments to paleoclimatic variations. This review focuses on triterpenoids as paleoenvironmental biomarkers, and consolidates relevant literature that can form the basis for developing tools and techniques for improved paleoenvironment reconstruction. Future investigations should focus on detecting as yet unknown classes of triterpenoids and their biosynthetic pathways, inclusion of this information in automated databases, and identification of geoterpenoids as potential biomarkers to further our understanding of paleoenvironments and paleoclimate.