Exposures to elevated CO2, elevated temperature and enhanced UV-B radiation modify activities of polyphenol oxidase and guaiacol peroxidase and concentrations of chlorophylls, polyamines and soluble proteins in the leaves of Betula pendula seedlings

The activity of polyphenol oxidase (PPO) and guaiacol peroxidase (POD) and the concentrations of chlorophylls, free polyamines and soluble proteins were determined from the leaves of six genotypes of silver birch (Betula pendula Roth) seedlings exposed to short-term elevated carbon dioxide (CO2), temperature (T), ultraviolet-B irradiation (UV-B, 280-315 nm) and their combinations. Results showed that the activity of PPO in the leaves was low but increased by elevated CO2 and elevated T. The POD activity varied between the genotypes due to an interactive effect of CO2 × UV-B. The soluble proteins were clearly decreased by elevated CO2, but the level of response varied among the genotypes. The concentrations of chl a and total chlorophylls were lower in the leaves treated with elevated CO2 than in leaves grown at ambient CO2. An interactive effect of CO2 × UV-B on the chl a/b ratio was found. Elevated T increased chl b concentration and decreased chl a/b ratio. Temperature treatments also caused variation in the concentrations of chl a, chl b and total chlorophylls among the genotypes. Polyamine analyses showed that the concentrations of putrescine were increased and spermine decreased in leaves treated with elevated T. However, the change in putrescine by elevated T was clearer at ambient CO2 than in eCO2 environment (significant effect of T × CO2). In conclusion, the defensive enzymes, photosynthetic pigments, soluble proteins and growth-regulating polyamines in silver birch leaves were not susceptible to enhanced UV-B radiation. In contrast, all the variables responded to elevated T and/or elevated CO2, reflecting the enhancive effects of climate change conditions not only on leaf productivity, but also on leaf turn-over rate. Most of these climate-driven changes were not regulated by UV-B radiation.