Salicylic acid(SA) is a plant hormone that plays an important role in plant immunity and stress response. The hormone is involved in processes such as reactive oxygen species (ROS) accumulation and hypersensitive response (a type or programmed cell death that acts to limit the spread of biotrophic pathogens by killing infected tissue). Salicylic acid is an important signaling molecule in response to plant stress. Recent evidence suggest that SA may bind to thimet oligopeptidase proteins: TOP1 and TOP2. Our goal was to determine what the role of these proteins play in stress response. We used mutant strains of the model plant Arabidopsis thaliana that have one of both of these TOP proteins knocked out and exposed them to different types of biotic and abiotic stress. We analyzed different factors such as gene expression, ROS accumulation, stress tolerances, root length and ion leakage. We have found evidence that the TOP proteins may play important role in oxidative stress related signaling.