Introduction
Secondary metabolites have a complex structure which is produced by chemical bio-synthesis. Therefor, they are mostly extracted from wild or cultivated plants. The essences are natural, complex and volatile secondary metabolites which are mostly produced in medicinal and aromatic plants. Peppermint (Mentha piperita L.), a hybrid from M. aquatica and M. spicata, is an herbaceous and perennial plant belonging to Lamiaceae family.  It is widely cultivated in temperate regions of Europe, Asia, America, India and Mediterranean countries due to its commercial value and unique odor.
 Materials and Methods
In order to investigate the influence of putrescine treatment at three levels including 0, 0.1 and 1 mM, and salicylic acid treatment at three levels including 0, 0.1 and 1 mM, on the yield performance and essence components of peppermint, a field factorial experiment was performed based on complete blocks design with three replications at Research Station of Tabriz University during 2019. Peppermint seedling were prepared from Agricultural Jihad Organization of Bostan Abad and cultivated at a distance of 30×30 cm. Foliar application of salicylic acid and putrescine was carried out twice during vegetative stage of plants (with one week interval). Harvesting and bio-chemical assessments were done at stage of 25 % flowering. The essential oil of peppermint was assessed to identify its main components.   
 Results and Discussion
The results of the current study showed that the average yield of essential oil in plants treated with 1 mM salicylic acid was significantly increased compared to the control. A total of 24 compounds were identified in the essential oil of peppermint aerial parts. The main components of the essential oil were included menthone, menthol, L-menthol and 1,8-cineole. Menthone and menthol constituted 26.14 and 23.21 % of essential oil, respectively. Different concentrations of salicylic acid and putrescine increased the production rate of menthone, menthol, l-menthol and methyl acetate compounds in the essential oil compared to the control. The concentration of 1 mM salicylic acid had the greatest effect on the production of essential oil compounds. The correlation results between essential oil compounds showed that menthone has a positive and significant correlation with methyl acetate. Similarly, foliar application of salicylic acid (10 mM) and indole-3-acetic acid (1.5 mg L^-1) increased the content of main component of peppermint and lemon balm. In the other study, foliar application of lemon balm plants with salicylic acid and putrescine caused a considerable increase in monoterpenes and sesquiterpenes content which was in line with obtained results of the present study.      
 Conclusion
The plant growth regulators used in this research increased the yield and composition of the essential oil of aerial parts of peppermint, which shows that both salicylic acid and putrescine have a high potential in increasing the potency and chemical composition of the essential oil in the peppermint plant and probably in other aromatic crops. Therefore, foliar application of salicylic acid and putrescine during vegetative growth of peppermint could be introduced as influential technique to improve qualitative and quantitative characteristics of this aromatic and medicinal plant.