Photoregulation of Bioprotectant Content of Red Leaf Lettuce with Light-emitting Diodes

Lactuca sativa cv. Outredgeous was grown under either fluorescent lamps or light-emitting diodes (LEDs) to test the hypothesis that antioxidant potential could be regulated by light quality. Red leaf lettuce was grown at 300 μmol·m −2 ·s −1 of photosynthetically active radiation, 1200 μmol·mol −1 CO 2 , 23 °C, and an 18 h-light /6-h dark photoperiod in controlled-environment chambers. The LED treatments were selected to provide different amounts of red (640 nm), blue (440 nm), green (530 nm), and far-red (730 nm) light in the spectra. Total anthocyanin content and the oxygen radical absorbance capacity of the tissue were measured at harvest. The source of light had a dramatic effect on both plant growth and production of radioprotective compounds. LEDs resulted in 50% greater bioprotectant content per plant at the same light level over triphosphor fluorescent lamps. Blue LEDs (440 nm) appeared to regulate the metabolic pathways leading to increased concentration of bioprotective compounds in leaf tissue. LED lighting induced a number of effects on morphology that increased both accumulation of bioprotective compounds and total yield.