Salicylic acid application alleviates the adverse effects of triclosan stress in tobacco plants through the improvement of plant photosynthesis and enhancing antioxidant system

Triclosan (TCS) is a chlorophenol which is highly bacteriostatic and used in a wide array of consumer products. TCS is now one of the most commonly detected organic pollutants in the sewage sludges. The sludge utilization for fertilizers on agricultural land would pose the risk of causing adverse effects on plant growth and yield by TCS. However, the toxicity of TCS toward plants is comparatively less understood. In this study, we assessed the effects of TCS on tobacco plants which were grown in MS medium or soils containing various concentrations of TCS. Our results indicated that TCS at the concentration of 2 mg/L could strongly inhibit the tobacco seed germination. TCS could suppress tobacco plant growth in soil with different concentrations (10, 20, and 50 mg/kg) of TCS through the downregulation of chlorophyll contents, restricting photosynthesis and increasing generation of reactive oxygen species (ROS). Salicylic acid (SA) plays important roles in the stress response of plants. The role of exogenous SA application in protecting tobacco plants from TCS stress was also investigated in this study. SA application could significantly increase net photosynthesis, enhance antioxidant enzyme activity, and thereby enhancing tobacco plant tolerance to TCS. Moreover, the activation of MPK3 and MPK6 induced by TCS was downregulated in plants with the treatment of SA. It was thus referred that mitogen-activated protein kinases (MAPKs) might play a key role in the signal transduction of TCS stress, and this process might be regulated by SA signaling. Overall, our results demonstrated that TCS had negative impacts on tobacco plants and SA played a protective role on tobacco plants against TCS stress.