The effect of ozone in Scots pine (Pinus sylvestris L.): gene expression, biochemical changes and interactions with UV-B radiation

Increased levels of both ozone and ultraviolet-B radiation (W-B) are typical for high-altitude sites. Here we report on interactive effects of both stresses on Scots pine (Pinus sylvestris L,). Scots pine seedlings were exposed in a phytotron to a simulated outdoor climate. To assess effects of ozone and of W-B radiation on the plants, ozone was added at ambient or at twice-ambient levels, and W-B was eliminated or added at a low ambient level, Visible needle damage became apparent at enhanced ozone concentrations after 10 d of exposure and increased continuously. The accumulated exposure over a threshold value of 40 nL L-1 ozone (AOT40) revealed that an ozone exposure dose of 10 muL L-1 h was necessary for the development of needle injury, regardless of the UV-B conditions. Cinnamyl alcohol dehydrogenase (CAD) and stilbene synthase (STS) have been reported to be induced by ozone. The mRNAs of these stress-related enzymes were induced only under twice-ambient ozone concentrations. Ozone-induced transient STS transcript levels reached their maximal values between day 1 and day 5, and were more pronounced in the presence of W-B. Similarly, pinosylvin, as well as pinosylvin methyl ether contents, showed moderate transient increases under these conditions, In contrast, CAD mRNA content and CAD enzyme activity increased continuously under enhanced ozone concentrations, Additional UV-B resulted in suppressed transcript level and enzymatic activity of CAD. The data indicate that in conifer needles, at the level of gene expression, there is an interaction between responses to UV-B and ozone.