Rise of activity of antioxidant enzymes and secondary metabolites under treatment with LED lights in two genotypes of Melissa officinalis

The innovation of light-emitting diodes (LEDs) has provided a new opportunity to grow plants in controlled environments. In this study, the plantlets of two genotypes of lemon balm were put for seven weeks in an incubator containing LED lamps with red, blue, red + blue (70:30 ratio), and white light spectrum with a light intensity of 300 μmol m-2s-1 and with a light cycle of 16 hours of light and 8 hours darkness and temperature of 25±2°C, and to compare with these conditions; some plantlets were also put in the greenhouse. The plantlets grown in incubators with red + blue LED lamps had higher activity of some antioxidant enzymes including catalase, guaiacol peroxidase, and ascorbate peroxidase, higher amounts of phenolic compounds and the valuable active substance of rosmarinic acid (the latter only in Ilam genotype), and phenylalanine ammonia lyase (PAL) enzyme activity than the plantlets grown in the greenhouse. However, in the Isfahan genotype significant difference in the content of rosmarinic acid was observed only between white LED light with other LED and greenhouse lights. Overall, according to the results of the current study, it can hope to use LED light sources to improve the growth and qualitative and quantitative properties of the medicinal plant, lemon balm, and also to create high-quality plants.