Oxidative stress response in Arabidopsis thaliana after exposure to uranium: the role of glutathione

Anthropogenic activities have caused pollution of various compartments of our environment with heavy metals, including uranium. Although it is a non-essential element, uranium can easily be taken up by plants where it can cause toxic effects, including oxidative stress. Plants have developed an antioxidative defence mechanism to counteract this stress. Glutathione (GSH) is an important antioxidant in this mechanism with three major function: redox homeostasis, metal homeostasis and detoxification. Although several studies have investigated the uranium-induced stress responses, the role of GSH during uranium stress is not completely known. The present study aimed to further investigate the role of GSH in Arabidopsis thaliana during uranium exposure. Therefore seed-lings were cultivated for 18 days in a hydroponic setup with Hoagland nutrient solution, followed by three days of exposure to different uranium concentrations, ranging from 0-50 μM. After RNA extraction, the complete transcriptome of the plants was sequenced using the Illumina HiSeq2000 platform. Due to limited root-to-shoot translocation and the limited timeframe, only the data of the roots were processed during this internship. Uranium exposure clearly disturbed the sulfur metabolism by causing a sulfur starvation response. No differentially ex-pressed genes related to glutathione synthesis where found, indicating no increased GSH biosynthesis. However, it seems that plants are trying to regulate the sulphur starvation response by providing cysteine for its essential functions as structural role in proteins by breaking down glucosinolates. Based on the differentially expressed genes, the results indicate that GSH probably don’t play an important role in detoxifying reactive oxygen species via the AsA-GSH cycle under uranium stress, since genes related to this cycle were not significantly affected. In addition, no indications for the synthesis or presence of phytochelatins were found. However, uranium disturbs the homeostasis of multiple metals among which Fe. Finally, there seems to be an important role for the role for glutathione-S-transferases in the detoxification of uranium and ROS during uranium exposure.