2019 ASHS Annual Conference

Bioactive compounds such as polyphenolics have beneficial effects on human health. The application of temporary abiotic stresses to plants is a potential strategy to enhance the content of bioactive compounds. The objective of this study was to determine the effect of various UV-A LED lights on the biomass and content of bioactive compounds in kale (Brassica oleracea var. acephala). Two-week-old kale seedlings were cultivated in a closed type plant production system where air temperature, relative humidity, photosynthesis photon flux density (PPFD) and photoperiod were set at 20℃, 60%, 125 µmol·m^-2·s^-1 and 12 hours, respectively, for 3 weeks. After then, kale plants were irradiated by four types of UV-A LEDs (peak wavelength; 365, 375, 385, and 395 nm) with 30 W/m² for 7 days. As a result, image chlorophyll fluorescence (Fv/Fm) value of kale leaves was lower as the peak wavelength of UV-A LEDs was shorter. The image Fv/Fm value of UV-A LEDs_365nm treatment was 11% lower than that of the control. Fresh and dry weights of shoots and roots were significantly higher in the UV-A treated plants than the control at 7 days of treatment. In particular, UV-A LEDs_395nm showed significant increase in growth. The results of leaf area and specific leaf weight tended to be similar to previous growth results. At 3 days of UV-A radiation, chlorophyll content was highest in kale leaves under UV-A LEDs_395nm among the all treatment and the control. Total phenolic contents of UV-A LEDs_395nm at 5 and 6 days of treatment were 44% and 47% higher than those of the control, respectively, and the tendency was similarly shown in antioxidant capacity. It was supported by the activity of phenylalanine ammonia-lyase, which was increased approximately 11% and 8% by UV-A LEDs_395nm irradiation compared to the control at 5 and 6 days of treatment, respectively. These results suggested that the UV-A LEDs with relatively longer peak wavelengths were effective to improve both growth and the content of bioactive compounds in kale plants.