The evolution of phenolic content, polyphenoloxidase (PPO) and peroxidase (POD) activity in cotton leaves treated with ethephon and MeJA was studied. Pyrocatechol and guaiacol were used as a substrate for the determination of PPO and POD activity, respectively. The total phenol content was compared under the action of both oxidation enzymes in cotton leaves. The results showed that phenolic content and PPO activity increases with of elicitor’s application on the cotton leaves. Thus, compared to the control, it is higher in ethephon-treated plants followed by MeJA-treated plants. Co-treatment of leaves with these both elicitors stimulates more phenolic compounds production as well as PPO activity thus showing a synergistic or cooperative effect. However, with respect to POD activity, elicitors have an inverse effect compared to PPOs. This indicates that catecholase activity overlapping cresolase activity under the action of MeJA or ethephon in cotton. POD is mobilized to induce the biosynthesis of lignin that constitutes a physical barrier against the pathogens. Furthermore, a part of PPO evolves in a similar way as the total phenol content would indicate an abundance of substrate of this enzyme in treated-plants with elicitors. The phenols synthesized under the action of MeJA and of ethylene could be polyphenolic nature. Concomitant treatment of plant with MeJA and ethylene in the form of ethephon is better than that of MeJA followed by ethephon
