Among all potentially toxic elements, arsenic (As) is considered as one of the most toxic for the plants and, due to its carcinogenic nature, also for humans. This element can exist in the soil in different oxidation states (-III, 0, III or V) and forms (inorganic or organic). Prevailing in the environment and the most lethal are inorganic forms of As (arsenate (As^V) and arsenite (As^III)). Arsenic as a non-essential element damages the plants at various physiological and biochemical levels. Probably the most dangerous aspect of its acting in the plant body at the subcellular level is the production of the reactive oxygen species (ROS) like superoxide radical, hydroxyl radical and hydrogen peroxide. To protect themselves, the plants dispose of antioxidant systems including antioxidant enzymes (peroxidases, superoxide dismutase, catalase) or they accumulate a non-enzymatic protectant – proline. These biochemical barriers are a part of the plant immune system which includes also producing mechanical barriers. The main objective of the present study was to elucidate the role of peroxidases in the model plant tobacco (Nicotiana benthamiana) facing arsenate (Na₂HAsO₄^.7H₂O) toxicity in the controlled in vitro conditions. The seeds were surface sterilised and sown on the modified MS cultivation medium as a control treatment or As treatments (several concentrations were tested). Peroxidases as multifunctional enzymes are involved in a wide range of physiological processes. They are not only a part of an antioxidant defence but are also important players in the phenylpropanoid biosynthetic pathways allowing e. g. lignin to be synthetized. For that, the roles of peroxidases (POX) in different plant parts were assessed in the present study histochemically in situ, by measuring the specific activities of POX and at the molecular level using a real-time PCR. The work was supported by Slovak Research and Development Agency APVV under the contract Nr. APVV-17-0164.