Growth of dropwort plants and their accumulation of bioactive compounds after exposure to UV lamp or LED irradiation

High-energy ultraviolet (UV) light is an environmental stress that can be used to stimulate the biosynthesis of bioactive compounds in plants. This study aimed to comparatively determine the efects of UV-A, UV-B, and UV-C lamps or lightemitting diodes (LEDs) on the growth of dropwort (Oenanthe stolonifera) plants, and their contents of bioactive compounds. Dropwort seedlings with 2-3 ofshoots were transplanted in a plant factory equipped with white LED and deep fow technique systems, and cultivated under standard growth conditions for 36 days. Thereafter, the dropwort plants were supplementally exposed to one of fve UV treatments with energy equivalent to 10 W m−2: UV-C lamps for 2 days, UV-B lamps for 3 days, and UV-A lamps and LEDs with 370 nm or 385 nm peak wavelengths for 14 days. The variable fuorescence (Fv) to maximum fuorescence (Fm) ratio (Fv/Fm) of dropwort leaves began to signifcantly decrease 3 h after exposure to UV-C, and 6 h after UV-B exposure. Fluorescence in UV-C and UV-B-treated plants was lower than in control and UV-A-treated plants during the entire period of UV irradiation. The fresh weight of the shoots of plants treated with UV was not signifcantly diferent to those of the control plants during the entire UV irradiation period. The total phenolic content of dropwort shoots exposed to UV-A and UV-B treatments signifcantly increased compared to that of the control 1 day after treatment. The total phenolic content was highest in plants treated with the 370 nm UV-A LED, and this was signifcantly higher (33%) than the control. Plants treated with the 385 nm UV-A LED on day 3 of treatment had the highest total phenolic content compared to the other treatments. A similar trend was observed in contents of favonoids and persicarin. UV light induced higher anthocyanin content than the control. The activity of phenylalanine ammonia-lyase after UV treatments was signifcantly higher than the control, supporting the fndings of our bioactive compound assays. In conclusion, the results of this study suggest that irradiating vegetables with UV-A LEDs would be useful in plant factories with artifcial light for improving vegetable quality without inhibiting growth.