比较代谢组学揭示琥珀古植物源指纹图谱

Comparative Metabolomic Reveals Chemotaxonomic Markers of Resin Fossils for Identification of Botanical Origins

  • 摘要: 琥珀中的甾萜化合物是高等植物分泌的次生代谢物1。因不同植物分泌出的次生代谢物不同,这些丰富的甾萜化合物可作为解译琥珀古植物来源的化学指纹2。但是,现有关于琥珀或树脂化石的化学分类难以区分出琥珀古植物来源的种属,甚至较为粗略层次的分类指标(如生物分类系统中的门、科等)都未见系统研究3-6。本研究借用了生物化学领域中常用的比较代谢组学研究思路7-8,以顶空固相微萃取与全二维气相色谱-飞行时间质谱联用为技术手段,系统分析了来自古裸子植物(始新世柏科、白垩纪南洋杉科)和古被子植物(中新世龙脑香料、中新世豆科植物)琥珀中的甾萜化合物9,鉴定的次生代谢物包括83种单萜、186种倍半萜、84种二萜和43种正构烷烃。通过保留指数校正及与国际标准NIST质谱数据库比对,明确了其中大部分次生代谢物的结构及其化学名称。在化学分类前,我们先测试了样品的镜质体反射率和最大热解峰温(Tmax),证明本文选取的四类琥珀样品具有非常相似的热成熟度;再利用多元统计法从鉴定的396种甾萜化合物中提取出了四条琥珀古植物来源分类标准:(1)根据单萜和二萜的相对含量可区分裸子植物琥珀和被子植物琥珀;(2)10种化学分类标志物可用于区分出两种裸子植物琥珀,包括柏科和南洋杉科;(3)被子植物琥珀中,豆科琥珀和龙脑香料的化学超类存在差异,豆科琥珀的主要成分是倍半萜和二萜,而龙脑香料的主要成分是单萜和倍半萜;(4)其它特殊的化学成分可将豆科琥珀的古植物源鉴定到属级别(Hymenaea mexicana and Hymenaea protera)。由于古植物次生代谢物成分是由植物的基因组控制,本文揭示的化学分类标志具备遗传基础10-12,研究结果全面建立了古树脂植物次生代谢物数据库,为古植物及古环境研究提供数据基础。

     

    Abstract: The terpene compounds in amber are secondary metabolites secreted by higher plants. Due to the different secondary metabolites secreted by various plants, these abundant terpene compounds can serve as chemical fingerprints for interpreting the ancient plant sources of amber1-2. However, the existing chemotaxonomy of fossil resins is limited in its ability to distinguish them at phylum, family, and genus levels using small amount of samples3-6. Herein an advanced head-space solid phase microextraction-comprehensive two-dimensional gas chromatography- time-of-flight mass spectrometer platform was established to analyze the complex compositions of resin fossils derived from ancient gymnosperms (e.g., Eocene Cupressaceae, Cretaceous Araucariaceae) and angiosperms (Miocene Dipterocarpaceae and Miocene Hymenaea)7-9. The secondary metabolites including 83 monoterpenes, 186 sesquiterpenes, 84 diterpenes, and 43 n-alkanes, were annotated and then chemically fingerprinted for the first time. Prior to conducting chemical composition classification, this study tested the vitrinite reflectance of resin-bearing rocks and maximum pyrolysis peak temperature (Tmax) of the ambers to demonstrate their similar thermal maturity. After that, chemotaxonomic markers were disclosed using multivariate statistical analysis to identify the botanical origins of resin fossils, and four identification rules were concluded. Gymnosperm and angiosperm resins can be distinguished by the relative content of monoterpenes and diterpenes; Eocene Cupressaceae and Cretaceous Araucariaceae resins can be identified by ten chemotaxonomic markers which were screened out by orthogonal partial least-squares regression; Miocene Hymenaea and Dipterocarpaceae resins have different combinations of chemical superclasses, with sesqui- and di-terpenes being the major compositions of Hymenaea resins, and mono- and sesqui- terpenes accounting for most of the compositions of Dipterocarpaceae resins; Specific chemotaxonomic markers can identify Hymenaea mexicana and Hymenaea protera resins. As the chemical components of fossil resins were determined by the genes present in their botanical origins, the chemotaxonomic markers revealed in this study have a genetic basis10-12. These findings provide a comprehensive database of secondary metabolites from ancient resin plants, which can be utilized for further research on their corresponding paleoenvironment and to clarify their phylogeny.

     

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