Effect of ozone exposure on polyamines in Scots pine trees

Effects of ozone exposure on polyamines in Pinus sylvestris L. were studied in a long-term experiment. Ten- to 15-year-old Scots pines were exposed to target ozone levels which began at ambient + 40 ppb in May, decreasing to ambient air only by September for 3 growing seasons. The amount of ozone applied followed the natural pattern of variation in ozone concentrations in Northern Finland. The free, soluble conjugated and insoluble conjugated polyamines were analyzed during the experiment and shortly after termination of exposure as well as at the beginning of the following growing season. A carry-over effect was observed as ozone-induced reduction of free spermidine in the oldest needle year class, which developed during the first exposure season of the experiment. This reduction was observed both after the second and the third ozone exposure season. Conversely, after termination of the experiment, levels of free polyamines increased in the following growing season, and soluble conjugated polyamines decreased in the developing needles. The post-treatment changes in polyamine concentrations are hypothesized to be caused by stress-induced injuries or delayed recovery of metabolic processes rather than protective responses. It is noteworthy that some responses in polyamines were found in the developing needles nine months after terminating the ozone exposure. This suggests that stress-induced injuries to older needles affected metabolism of new developing needles.