Monoterpene emissions and their protection effects on adult Cinnamomum camphora against high temperature

Key message The four chemotypes of adult C. camphora released different monoterpenes which protected these plants against high temperature by lowering ROS levels and maintaining photosynthetic abilities. High temperature seriously impacts plant growth and development, and terpenes are believed to improve plant thermotolerance through indoor experiments using seedlings. To uncover the actual protection effects of monoterpenes on outdoor adult plants, we investigated the monoterpene emissions, reactive oxygen species (ROS) metabolism, and photosynthetic abilities in four chemotypes of adult Cinnamomum camphora that were blocked monoterpene synthesis by fosmidomycin (Fos) under high temperature in summer (the mean highest temperature at about 38.2 °C). Eucalyptol (EuL), linalool (Lnl), borneol (BeL), and camphor (CmR) chemotypes of C. camphora released an abundance of monoterpenes, with eucalyptol, linalool, endo-borneol, and camphor as the typical monoterpene, respectively. When the four chemotypes of C. camphora were treated with Fos, their monoterpene emission was inhibited remarkably, with disappearance of some monoterpenes. In that case, the content of O 2 − , H 2 O 2 , and thiobarbituric acid reactive substance (TBARS) in the four chemotypes of C. camphora significantly increased although antioxidant enzyme activities remarkably increased, and the photosynthetic abilities significantly decreased by declining the quantum production and electron transport in photosystem II and increasing the dissipation of absorbed light energy. Among the four chemotypes, monoterpenes might play the maximum roles in CmR lowering ROS levels and in EuL maintaining photosynthesis. It can be speculated that monoterpenes can protect adult C. camphora against high temperature by lowering ROS levels and maintaining photosynthetic abilities.