-B Exposure of Indoor-Grown Picea abies Seedlings Causes an Epigenetic Effect and Selective Emission of Terpenes

Metabolites in plants are essential for defence and communication with the environment. Terpenes constitute the major part of the resin in conifers. The composition of terpenes as well as of volatile terpenes changes with tissue, age, and in response to various types of stress, for example insect or pathogen attacks (Persson et al., 1993; Fäldt et al., 2006) and UV-B exposure (Zavala and Ravetta, 2002). Jasmonic acid (JA) is a main signal-mediating compound in plants in response to mechanical and biotic stress, e.g. insect stress (Ballaré, 2011). Accordingly, treatment of conifers with methyl jasmonate (MeJA) increases the terpene emission as well as tissue levels of terpenes (Martin et al., 2003). A change in terpene biosynthesis and emission is associated with increased defensive capacity in conifers against e.g. bark beetle (Franceschi et al., 2005) and pine weevil (Heijari et al., 2005). Interestingly, the response to UV-B exposure in plants has similarities to the response to other types of stress, such as insect stress (Stratmann, 2003). Excess UV-B radiation can cause direct damage to DNA and also increase the tissue level of reactive oxygen species (ROS), which in turn can damage DNA, proteins, and fatty acids in cellular membranes, as well as the photosynthetic apparatus. Accordingly, plants have to protect themselves from UV-B damage by production of UVabsorbing pigments, antioxidative metabolism, as well as DNA repair. The plant perception and signaling pathways in response to UV-B exposure are not completely known. Various signaling pathways including ROS, salicylic acid, JA, brassinolide, and ethylene have been suggested (A.H.-Mackerness, 2000; Brosché and Strid, 2003; Sävenstrand et al., 2004). Furthermore, we have earlier suggested that nicotinamide released from NAD during UV-B exposure, causing oxidative stress, could function as a signaling compound UV -B Exposure of Indoor-Grown Picea abies Seedlings Causes an Epigenetic Effect and Selective Emission of Terpenes Anna B. Ohlsson*, Patrik Segerfeldt, Anders Lindström, Anna-Karin Borg-Karlson, and Torkel Berglund