Red LED light promotes biomass, flowering and secondary metabolites accumulation in hydroponically grown Hypericum perforatum L. (cv. Topas)

To increase the crop yield and quality, the plant cultivation in equipped growing systems is an alternative to open field production. Artificial light sources are a critical component in the plant factory systems and red and blue wavelengths have a powerful impact on plant growth and photosynthetic capacity. In this study, the effect of different photon flux ratios of red (R) light to blue (B) LED light including 100 R:0B, 80 R:20B, 50 R:50B, 20 R:80B, 0 R:100B and white LEDs (as control) were evaluated on the growth, flowering and secondary metabolite contents of Hypericum perforatum L. cv. Topas at 150 µmol m−2 s−1 irradiation for a 16/8 h.d‐1 photoperiod. Results showed that the plant growth characteristics such as fresh and dry weight, leaf area and number, plant height, flower number and diameter were significantly (P < 0.05) maximum under the enhancement of R/B ratio, especially under 100% red light treatment. Despite the higher transpiration and net photosynthesis rate, photosynthetic pigment concentration, stomatal surface area and RuBisCO activity, the plants under the high fraction of blue light showed the poorest growth and flowering traits. The maximum content of hypericin (14.24 mg g‐1 DW), pseudohypericin (25.98 mg g−1 DW) and hyperforin (163.06 mg g−1 DW) was obtained in flower under 100% red LED. Antioxidant enzymes activities (CAT and POD), total phenolic and flavonoid content were also higher in plants exposed to the mixture of red and blue light. Plants grown under white LED were mediocre in terms of growth parameters and secondary metabolites. These findings showed that the 100% red LED light is suitable for H. perforatum plant growth, flowering, as well as secondary metabolites accumulation in the plant factory system.