Investigation of Selenium Effects on Arabidopsis thaliana' s Photosynthesis and Antioxidant Defence System

Plants exhibit various adaptation mechanisms in morphological, physiological, biochemical and molecular levels to cope with abiotic stress conditions such as cold, drought, excessive light, water, salt and heavy metals. In several studies it was indicated that Se plays roles in the reactive oksigen species (ROS) and antioxidants regulation, uptake and translocation of heavy metals, changing the heavy metal species which result in reconstruction of cell membrane and chloroplast structure and maintenance of photosynthetic system. However it is important to determine the optimum Se dosage because it can affect plants both positively and negatively in a dosage dependent manner. Whilst Se promotes the plant growth at low concentrations, at high concentrations it acts as a pro-oxidant and can cause oxidative damage to the plant. In light of this knowledge, effects of selenium on antioxidant defense system and photosynthesis was investigated in Arabidopsis thaliana. Wild type Arabidopsis thaliana Col. seeds were surface sterilized and were grown under hydroponic conditions. 15-day-old seedlings are treated with selenate and selenite for seven days and they were harvested. The amount of ROS (H2O2 ve O2•−) was assayed from harvested plants. Further, antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbat peroxidase (APX) ve glutathione reductase (GR)) activity and CO2 asimilation, PSI- PSII efficiency assays were carried out. Selenate and selenite treated Arabidopsis thaliana Col. plants exhibited different SOD, CAT, POX and APX antioxidant activity in the different dosages. Similar effects also observed on the cell membrane lipid peroxidation in all groups. To sum up, in this thesis the effects of selenium on photosynthesis mechanism and antioxidant defense system was performed.