Abstract
Plants produce and release a large array of volatile organic compounds that play many ecological functions. These volatile plant metabolites serve as pollinator attractants, herbivore and pathogen repellents and protect plants from abiotic stresses. To date, the geological evolution of these organic compounds remains unknown. The preservation potential of these metabolites in the fossil record is very poor due to their low boiling points. Here we report a series of volatile sesquiterpenoids, including δ-elemene, α-copaene, β-elemene, β-caryophyllene, α-humulene, germacrene D, δ-cadiene and spathunenol, from early Miocene (~17 million year) amber from eastern India. The survival of these unaltered bioterpenoids can be attributed to the existence of extraordinary taphonomic conditions conducive to the preservation of volatile biomolecules through deep time. Furthermore, the occurrence of these volatiles in the early Miocene amber suggests that the plants from this period had evolved metabolic pathways to synthesize these organic molecules to play an active role in forest ecology, especially in plant-animal interactions.
Highlights
Plants synthesize and release a vast array of volatiles organic compounds that are helpful in their interactions with their immediate environment[1, 2]
The volatile terpenoids are susceptible to diagenesis because of their low boiling points
We have identified β-caryophyllene in the total extract of the Miocene amber in considerable amount. β-Caryophyllene is found in floral fragrance in more than 50% of angiosperm tree families[9]
Summary
Gas chromatography-mass spectrometry analysis of the total extract of fossil resins includes both sesquiterpenoids and triterpenoids (Figs 1 and 2). It is worthwhile to mention that a few unaltered monoterpenoids was reported from Baltic amber and some Tertiary resins of Poland[20, 21] The aromatic sesquiterpenoids such as dihydro-ar-curcumene, calamenene and cadalene are diagenetic products of bioterpenoids such as germacrene D and cadinenes[14]. The presence of dammarane compounds (e.g., hydroxydammarenone and 20,24-epoxy-25-hyd roxydammaran-3-one) in the total extract of the amber clearly suggests that the fossil resins were produced by angiosperm tree family Dipterocarpaceae . The present study unequivocally demonstrates that the dipterocarps had evolved this biosynthetic mechanisms way back to early Miocene to produce these volatile plant metabolites We postulate that these terpenoids were used by this angiosperm family as protective agents. This study offers a new approach to unravel the geological evolution of chemically-mediated interactions between plants and their immediate biotic environment
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