Growth and Antioxidant Phenolic Compounds in Cherry Tomato Seedlings Grown under Monochromatic Light-emitting Diodes

Light-emitting diodes (LEDs) can be used in closed-type plant production systems as an artificial light source. Here, we determined the effects of monochromatic LEDs on the growth and production of phenolic antioxidants in cherry tomato seedlings (Solanum lycopersicum L. 'Cuty'). Two week-old seedlings germinated under normal growing conditions were transplanted into a growth chamber equipped with various monochromatic LEDs and fluorescent lamps (control), and cultivated for 4 weeks. Fresh weights of shoots and roots under LED treatment, especially, red or green, were higher than those under the control light at 4 weeks. The SPAD value of seedlings grown under blue LEDs was significantly lower than in seedlings grown under other LEDs. The plant height, stem length, and internode length of tomato seedlings grown under blue LEDs were the highest. Blue LEDs induced 1.5-2.2-fold higher stem length than red and white LEDs. Expansin gene expression was the highest under blue LEDs, consistent with the effect on stem length. Blue LEDs stimulated the biosynthesis of total phenolics, antioxidants, and total flavonoids in tomato seedlings. Specifically, the antioxidant capacity of seedlings grown under blue LEDs was 2.1-folds higher than that in seedlings grown under green LEDs. Thus, manipulating light quality using LEDs is a crucial factor for growth and antioxidant production in cherry tomato seedlings.