A background of ionising radiation is generally present in the environment coming from cosmic sources or natural occurring radioactive materials. However, the use of different radionuclides for industry, medicine or research has led to potential local increases of radioactive material in the environment and hence to an increased risk of exposure to radiation of organisms inhabiting these areas. Although in recent years considerable progress has been made to develop a framework for risk assessment of the exposure of non-human biota to radioactive substances, major challenges still remain. In particular, the mechanisms that lead to radiation-induced effects in organisms exposed chronically to low levels of radiation are not fully understood. This knowledge can enhance the robustness and scientific reliability of screening values and environmental protection criteria.
Ionising radiation can induce genotoxic effects by interacting with DNA either directly or indirectly. In addition to DNA damage oxidative stress originating from an enhanced production of reactive oxygen species (ROS), can lead to alterations in proteins and lipids. Damage to DNA can manifest itself as DNA adducts, single and double strand breaks, oxidative changes and DNA lesions. Organisms can react upon exposure to ionising radiation by inducing different stress and/or DNA repair mechanisms, minimising adverse effects but even inducing adaptive responses. The induction of a stress response is generally preceded by an alteration in gene expression. Although this general scheme for radiation-induced effects is known, the different genes activated or silenced after exposure to low-dose radiation are not elucidated. Regulation of gene expression can be orchestrated among others by small non-protein coding RNA fragments like miRNA’s. These are important in the rapid silencing of gene expression for example in response to external stimuli or stressors. Studying the regulation of and the alterations in gene expression can give clear indications on the mechanisms underlying the response as well as the effects induced in plants.