Seasonal emission of monoterpenes from four chemotypes of Cinnamomum camphora
Plant terpenes are the main functional agents in forest bathing and have great value in several industries. To uncover the seasonal variation of Cinnamomum camphora monoterpene emission and the difference among the chemotypes for promoting the development of forest bathing and exploitation of monoterpenes using the species, the emission of monoterpenes and related gene expression in the camphor chemotype, eucalyptol chemotype, linalool chemotype and borneol chemotype of C. camphora were analyzed in May (spring), July (summer) and November (autumn), and the stored monoterpenes and storage structure were investigated. Eleocytes were the storage structure of monoterpenes in C. camphora , which widely existed in the leaf palisade tissue and spongy tissue, as well as around the glands and vascular bundles. The 4 chemotypes of C. camphora released different monoterpene components which mainly derived from the immediate emission after synthesis. Camphor, eucalyptol, linalool and endo-borneol showed the uppermost emission rate and were the typical monoterpenes in the corresponding chemotype, respectively, due to the high expression of the genes encoding bornyl diphosphate synthase ( E5.5.1.8 ), linalool synthase ( TSP14 ) and (+)-neomenthol dehydrogenase ( E1.1.1.208 ) for the biosynthesis of camphor, linalool and endo-borneol, respectively, and only expression of the gene encoding 1,8-cineole synthase ( TSP-cin ) for eucalyptol biosynthesis. Among the 4 chemotypes, the linalool chemotype showed the highest emission rate of monoterpenes in the same month (without significant difference with the eucalyptol chemotype in November), due to the high expression of the genes ( dxs , dxr , ispF , gcpE , and GGPS ) in methylerythritol-4-phosphate (MEP) pathway, α-terpineol synthase gene ( E4.2.3.111 ) and TSP14 . Among the 3 months, temperature was the remarkably varied meteorological condition. The highest monoterpene emission rate from the 4 chemotypes of C. camphora was detected in July, which should result from the up-regulated expression of related genes in monoterpene biosynthesis and improved vaporization and diffusion of stored monoterpenes under high temperature, with the former providing a major contribution.
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