Transcript responses in leaves of ozone-treated beech saplings seasons at an outdoor free air model fumigation site over two growing seasons

The still most abundant air pollutant, tropospheric ozone, leads to severe oxidative stress in plants. To investigate the ozone responsiveness of trees, we carried out a microarray analysis of beech saplings, grown around a free air lysimeter station in the years 2005 and 2006. The microarrays revealed ozone-responsive expressed sequence tags (ESTs), derived from a suppression subtractive hybridisation cDNA library. Chronic ozone exposure effects were investigated at different time points throughout the whole vegetation period in 2005 and 2006. Significantly regulated ESTs were calculated with R-packages. Different transcript patterns in both years could be related to weather conditions and consequential a different ozone uptake. Fewer transcriptome changes were found in 2005 compared to 2006. Induction of ESTs involved in cell structure, related to stress response and cell walls, signal transduction, as well as disease and defence in July and August indicated ozone-related stress responses in both years. An early response to ozone on primary metabolism, or, more precisely, on plant growth and photosynthesis, was observed in July and August particularly in the year 2006. This study demonstrated a clear transcriptional ozone response of juvenile beech, the most important deciduous tree in Central Europe, under free air conditions.