Changes in Growth and Antioxidant Contents of Romaine Lettuce by Different UV Spectra

Abstract

The current study was conducted to determine the influence of irradiations of different UV spectra on plant growth and antioxidant compounds of two romaine lettuce cultivars('Caesar green' and 'Caesar red'). The UV treatments were consisted of three UV spectra; UV-A (314-400nm), FUV-B (290-400nm) and UV-B (274-400nm), using fluorescent lamps and irradiated for 2 hours at nighttime for 11 days under greenhouse. As the results, there were no differences in growth parameters and antioxidant compounds between UV-A treatments and control in two cultivars. On the other hand, FUV-B treatment increased significantly the contents of UV absorbing compounds, β-carotene, lutein, total phenolic compounds and anthocyanin in caesar green cultivar. It also increased UV absorbing compounds, total phenolic compounds and anthocyanin contents in caesar red cultivar without any growth reduction. UV-B treatment, however, decreased lutein, chlorophyll contents and caused growth reduction and physiological damage such as leaf chlorosis and wrinkle in both cultivars. Overall, the results indicate that supplemental FUV-B treatment, at least in part, may increase antioxidant compounds without any inhibitory effect on shoot growth in romaine lettuce. The results of the current study present a useful practical technique for increasing antioxidant compounds of romaine lettuce production in greenhouse horticulture.