Increase in chlorogenic acid concentration in lettuce by overnight supplemental lighting and CO2 enrichment
Chlorogenic acid (CGA) has been attracting attention as an antioxidant that affects human health. As we previously reported, overnight supplemental lighting (OSL) with light-emitting diodes (LEDs) can promote the growth of some leafy vegetables. However, when we investigated some functional materials in lettuce 'Greenwave' grown under OSL, a drastic increase in CGA concentration was observed. In Experiment 1, plants were exposed to low and high intensities (10 and 50 µmol m-2 s-1, respectively) of OSL using blue, green, red, and far-red LEDs in growth chambers equipped with white fluorescent lamps as the main light source. In the growth chamber, we set the photoperiod such that the day/night time was 10/14 h. OSL was used for irradiation for 14 h during the night. OSL with blue and red LEDs increased the CGA concentration compared with that obtained using no supplemental lighting; however, other light qualities of OSL could not demonstrate any change in the CGA concentration. In particular, five times higher CGA concentration (60 mg 100 g FW-1) was observed in lettuce grown under OSL using red LEDs with high intensity than those grown under no supplemental lighting. In Experiment 2, lettuce plants were grown under OSL (17:00-7:00 HR) with red LEDs in a greenhouse throughout the year. Unlike the results of experiment 1, the CGA concentration in lettuce was unstable, and OSL could not maintain a high CGA concentration, particularly during summer. However, during winter, OSL increased the CGA concentration in lettuce. Furthermore, CO2 enrichment under OSL increased the CGA concentration up to 50 mg 100 g FW-1 on day 14 of treatment in the greenhouse. Therefore, it was concluded that OSL and CO2 enrichment can promote CGA accumulation in lettuce; however, the increased CGA concentration under OSL could depend on other environmental factors.
Yoshida, H., Sekiguchi, K., Okushima, L., Sase, S. and Fukuda, N. (2016). Increase in chlorogenic acid concentration in lettuce by overnight supplemental lighting and CO2 enrichment. Acta Hortic. 1134, 293-300
antioxidant, blue light, CO2 enrichment, polyphenol, LED, red light