Tayebeh Ahmadi - Department of Plant Science, Faculty of Science, Shahrekord University, Shahrekord, I. R. Iran
Leila Shabani - Department of Plant Science, Faculty of Science, Shahrekord University & Research Institute of Biotechnology, Shahrekord University, Shahrekord, I. R. Iran
Mohammadreza Sabzalian - Department of Agronomy and Plant Breeding, College of Agriculture, Isfahan University of Technology, Isfahan, I. R. Iran

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 (۷۰:۳۰ ratio), and white light spectrum with a light intensity of ۳۰۰ μmol m-۲s-۱ and with a light cycle of ۱۶ hours of light and ۸ hours darkness and temperature of ۲۵±۲°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.

Antioxidants enzymes, LED light, Lemon balm, Light quality, Phenolic compounds