Using bionanoparticles plays an important role in increasing agricultural productivity. In recent years, the use of nanoparticles in plants has been considered as pesticides, protective agents and nutrients. The present study investigates the effects of different concentrations of bio-synthesized silver nanoparticles (AgNPs) on growth indices, secondary metabolites, proline, carbohydrates, and antioxidant enzymes activity of Melissa Officnalis L. The Plantlets were treated with different concentrations of AgNPs (0, 20, 60 and 100 ppm) at eight leaf stages. Seedlings performances in terms of growth, antioxidant defence and secondary metabolites content were studied under three different concentrations (20, 60, and 100 ppm) at different days of AgNPs showed growth promotory effect on M. officinalis. The maximum growth rate and photosynthesis pigments content were observed at 60 ppm AgNPs concentration on day 15. Proline and carbohydrate contents increased significantly compared to the control by all concentrations of AgNPs which exhibited time-dependent response. The AgNPs also enhanced secondary metabolites content in M. officinalis seedlings. The highest amount of rosmarinic acid (about 50 mg/g DW) was obtained for those plants treated with 60 and 100 ppm of AgNPs on day 15 which was about 3 fold higher than control. Up-regulation of antioxidant enzymes was observed with AgNPs which led to decrease in MDA content. Our findings confirmed for the first time that biologically synthesized AgNPs at specific levels has significant growth promotory effect as well as increased production of valuable secondary metabolites. تفاصيل المقالة