Monoterpene emissions contribute to thermotolerance in Cinnamomum camphora

Abstract

High temperature promoted monoterpene emission from Cinnamomum camphora , and monoterpenes scavenged ROS and protected photosynthesis to improve thermotolerance in plants. High temperature impacts plant growth and development with a reduction in photosynthetic rate and an increase in reactive oxygen species (ROS) levels. To reveal the effects of monoterpene emissions on improving plant thermotolerance, the emissions of monoterpenes from Cinnamomum camphora under high-temperature stress and oxygenated monoterpenes under H2O2 stress were analyzed. ROS metabolism and photosynthetic abilities under high-temperature stress after monoterpene synthesis was blocked by fosmidomycin were also investigated. High temperature promoted the emission of monoterpenes as well as two oxygenated monoterpenes, eucalyptol and α-terpineol. In addition, seven new oxygenated monoterpenes occurred at 45 °C. Similar results were also found under H2O2 stress, suggesting that ROS induced by high temperature may oxidize monoterpenes to generate oxygenated forms. Fosmidomycin treatment caused an increase in ROS and thiobarbituric acid reactive substance content, even though antioxidant enzyme activities were also higher. However, no changes occurred in antioxidant carotenoids synthesized from the same precursors as monoterpenes, indicating that monoterpenes can serve as antioxidant agents in the cells. In addition, fosmidomycin caused a decline in photosynthesis under high temperature, due to the decrease of quantum yield and electron transport rate. Therefore, monoterpenes play an important role in plant thermotolerance by scavenging ROS and protecting photosystems.