In the experiments reported here, seeds of the red-leaf lettuce 'Banchu Red Fire' were pre-germinated and sown in cellular trays.
The trays received light from white fluorescent lamps for 14 hours each day at 23 degsC. After 10 days, some seedlings stayed under the white light, while others were placed under either blue LEDs, red LEDs or red and blue LEDs. The light intensity was the same under all the lamps, which were on for 14 hours each day.
After one week, the plants grown under blue light had smaller leaves than those grown under white or red light. However, these leaves contained more phenols and antioxidants. Such changes should enable the seedlings to cope better with environmental stresses.
The seedlings grown under blue light had reddish leaves while those grown under red light were bright green. All were now transferred to a greenhouse at 25 degsC and grown under daylight supplemented with light from white fluorescent lamps for 12 hours each day. At the end of this period, the heaviest plants were actually those that had initially received blue light, but most of the other differences had faded.
Blue Light-Emitting Diode Light Irradiation of Seedlings Improves Seedling Quality and Growth After Transplanting in Red Leaf Lettuce by Johkan, Shoji, Goto, Hashida and Yoshihara (2010). HortScience 45 (12): 1809-1814. ISHS members can view HortScience from the website at www.ishs.org