The aim of this work was to study, as a function of the different availability of nitrogen in the reduced form, mineral and organic, the induction of the synthesis of some ROS-scavenging molecules and the evolution of some enzymatic activities such as ascorbate peroxidase (APX) and polyphenoloxidase (PPO).Chicory seedlings were grown in nutritive solution for 35 days in controlled conditions. On the 14 th day, one third of the plants was transferred into a nutritive solution containing (NH 4 ) 2 SO 4 60 mM, one third was transferred into a medium containing Urea 60 mM, and the remaining was let grow into the nutrition solution, as a control. Three samplings of leaves were performed, respectively after 21, 28 and 35 days of growth.The urea and ammonium sulphate-treated samples showed higher ascorbic acid and polyphenol contents than the control, together with a lower anthocyanins content. APX showed the highest