Ecotoxicology (2018) 27:919–935 https://doi.org/10.1007/s10646-018-1916-6 Pesticide-induced oxidative stress and antioxidant responses in tomato (Solanum lycopersicum) seedlings Shakirullah Khan Shakir 1 ● Shahid Irfan 1 ● Basreen Akhtar 1 ● Shafiq ur Rehman 1 ● Muhammad Khan Daud 2 ● Nadia Taimur 1 ● Azizullah Azizullah 1 Accepted: 12 February 2018 / Published online: 1 March 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Excessive use of pesticides can adversely affect the growth of non-target host plants in different ways. Pesticide-induced stress can affect non-target plants through elevated levels of reactive oxygen species (ROS) responsible for detrimental effects on cell metabolism, biochemical and other physiological activities. In response to oxidative stress, plant activates antioxidant defense system consisting of both enzymatic and non-enzymatic components. In the present investigation, three commonly used pesticides, emamectin benzoate, alpha-cypermethrin and imidacloprid, were assessed for causing oxidative stress in tomato. The oxidative damage induced by these pesticides at five different concentrations i.e. 1/4X, 1/2X, recommended application dose (X), 2X and 4X in the root and shoot tissues of tomato plant/seedlings were evaluated. Following pesticide exposure for 35 days, cell viability, cell injury, total soluble sugar (TSS) and total soluble proteins (TSP) were measured. Antioxidant activities were estimated by measuring activity levels of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) peroxidase (POD), ascorbate peroxidase (APX) and proline. Hydrogen peroxide (H 2 O 2 ) levels were analysed as ROS, lipid peroxidation was measured in term of thiobarbituric acid reactive substances (TBARS) as membrane damage caused by ROS was also assessed. Analysis of the data revealed that pesticides application at higher concentrations significantly elevated ROS levels and caused membrane damage by the formation of TBARS, increased cell injury and reduced cell viability both in root and shoot tissues compared with non-treated plants. Moreover, a gradual decrease in the levels of TSS and TSP was observed in plants subjected to increasing doses of pesticides. To cope with pesticide-induced oxidative stress, a significant increase in levels of antioxidants was observed in the plants exposed to higher doses of pesticides. Shoot tissues responded more drastically by producing higher levels of antioxidants as compared to root tissues indicating the direct exposure of shoots to foliar application of pesticides. Taken together, these results strongly suggested that the application of pesticides above the recommended dose can provoke the state of oxidative stress and can cause oxidative damages in non-target host plants. Keywords Pesticide-induced stress ● ROS ● Oxidative stress ● Anti-oxidants ● TBARS ● Proline Introduction In today’s modern world, several toxic chemicals are spilled in agricultural fields as a consequence of modern agri- cultural practices, heavy industrialization and faster urbanization. Due to increased rate of pest attack and unsuccessful trend in the production of pest resistant crop varieties, chemical pesticides are common tool to protect crops against pests (Yardim and Edwards 2003; Siddiqui and Ahmed 2006). During past few decades the use of pesticides has increased many folds. It has been estimated that 4.6 million tons of chemical pesticides are used worldwide annually, of which 85% are used in agriculture while the remaining 15% for other purposes (Idrovo 2000; Zhang et al. 2011). Among different categories of pesti- cides, global consumption of herbicides shares 47.5%, insecticides 29.5%, fungicides 17.5% and other pesticides contributes 5.5% (De et al. 2014). Like other parts of the world, large quantities of different pesticides are used in * Azizullah Azizullah azizswabi@hotmail.com 1 Department of Botany, Kohat University of Science and Technology, Kohat 26000, Pakistan 2 Department of Biotechnology and Genetic Engineering, Kohat University of Science and Technology, Kohat 26000, Pakistan 1234567890();,: