The effect of LED light on growth, essential oil content and activity of antioxidant enzymes in pepper mint (Mentha piperita L.)

The invention of Light Emitting Diodes (LEDs) has recently provided a new opportunity for the production of medicinal, horticultural and ornamental plants in controlled environments. It is also possible to study the physiological effects of specific light wavelengths on plants. In this study, three genotypes of pepper mint (Mentha piperita) collected from Isfahan, Tabas and Ghazvin were grown in pots inside 5 incubators each containing 100% red LEDs, 100% blue LEDs, 70% red+30% blue LEDs,100% white LEDs or fluorescent, illuminating at 300 μmol m s-1 light intensity. Plants grown in the field were used as control. After two months, the growth of plants as fresh weight per pot, essential oil content and antioxidant activity of catalase, glutathione reductase, ascorbate peroxidase and superoxide dismutase were evaluated. The highest fresh weight was achieved in Isfahan genotype under the combination of red and blue lights compared to the other lights. However, there was no significant difference with plants grown in the field condition. Essential oil content was more than 4-fold higher in Isfahan genotype under red light compared to that grown in the field. The activity of antioxidant enzymes, catalase (CAT), glutathione reductase (GR) and ascorbate peroxidase (APX) were highest in plants under blue light, while the activity of superoxide dismutase (SOD) was maximum under fluorescent light. It is concluded that LEDs through stimulation of growth and accumulation of secondary metabolites could simultaneously increase plant production and quality under environmental controlled conditions compared to natural illuminated environments.