Genetic processes in Scots pine (Pinus sylvestris L.) in the Chernobyl exclusion zone As immobile organisms plants have to tolerate unfavorable environmental conditions and make use of different adaptive mechanisms to survive and reproduce successfully under stress. It is often difficult to detect the organism&rsquo;s or population&rsquo;s response to stress factors due to slow changes of environmental conditions or delayed reactions of plants. From this point of view the investigation of reactions under extreme environmental change offer unique opportunities to study adaptation mechanisms. Areas with a strong anthropogenic impact on the environment represent ideal places for research on adaptation or selection processes. For many decades ionizing radiation is well known as a strong damaging and stress factor. Radiation exposure causes heavy damages of the DNA. This leads to a decrease in fitness in the present generation and inheritable mutations which reveal their effects in later generations. On the other hand radiation exposure activates adaptation processes to ensure survival. The investigation of the influence of radiation at different levels of life organization from the DNA level to the population level can help to elucidate response mechanisms to changing environments. After the accident in 1986 at the Chernobyl Nuclear Power Plant the surrounding territories were contaminated with high amounts of radioactive material. The exclusion zone became a natural laboratory for the investigation of effects of radiation on the biocenosis ...