Supplemental radiation of ultraviolet-A light-emitting diode improves growth, antioxidant phenolics, and sugar alcohols of ice plant

This study aimed to investigate the effects of UV-A light-emitting diodes (LEDs) and lamps on the growth and bioactive compounds of ice plant (Mesembryanthemum crystallinum). Three-week-old seedlings were germinated and grown at 23 °C air temperature, 60% relative humidity, 1000 μmol mol−1 CO2, 200 μmol m−2 s−1 (white LEDs), and a photo-period of 12 h for 3 weeks in a plant factory with artificial lighting. Plants were supplementally irradiated with different peak wavelengths of UV-A LEDs (395, 385, 375, and 365 nm) of 30 W m−2 and UV-A lamps of 15.5 W m−2 continuously for 7 days. Treatment with 395, 385, and 375 nm increased shoot fresh and dry weights than the control at 5 and 7 days of treatment. Fv/Fm value was significantly decreased at 12 h of all UV-A treatments and consistently showed lower levels compared to the control during the entire period. The photosynthetic rates of the 395 and 385 nm treatments were significantly higher than those of the other treatments. UV-A treatment enhanced total phenolic content and antioxidant capacity compared to those of the control after 3 days of treatment. Phenylalanine ammonia-lyase activity was also increased by UV-A light exposure. The content of pinitol, myo-inositol, and sucrose was increased by UV-A radiation, and the highest values were observed in the 395 nm treatment at 5 and 7 days of treatment. Our findings suggest that supplemental radiation of UV-A with a peak wavelength near 400 nm could increase the shoot biomass and antioxidant phenolics and sugar alcohols in ice plants.