Effect of UV light on phytochemical accumulation and expression of anthocyanin biosynthesis genes in red leaf lettuce

Light manipulation is a key environmental control method to increase functional phytochemical concentrations and antioxidant capacity in leaves of leafy vegetables. Here, we evaluated the effect of UV light on the accumulation of functional phytochemicals in the leaves of red leaf lettuce. We developed a novel lighting system, consisting of UV LEDs as a UV light source and red LEDs as a photosynthetic light source. Red leaf lettuce grown under white light was used as the plant material. Three peak wavelengths (310, 325, and 340 nm) of UV lights at 0.5 W m^-2 for 16 h were added to the white light for 3 d prior to harvest. Anthocyanin concentration and ORAC value of the leaves were measured every 8 h. mRNA gene expression of chalcone synthase (CHS) and the flavonoid 3-O-glucosyltransferase (UFGT) were also analyzed every 8 h. Anthocyanin concentration was significantly higher at 310 nm compared with 325 and 340 nm. Total ORAC values of the UV treatments were higher than in the control. CHS was highest at 310 nm, followed by 325 nm. UFGT increased with time, similarly to the anthocyanin concentration. These results indicated that UV-B light stimulated the biosynthesis of anthocyanin and other antioxidant polyphenols. From this research, we concluded that addition of UV light 1 to 3 d prior to harvest is effective for the production of functional phytochemical rich lettuce.