Enhancement of flavonoid synthesis and antioxidant activity in Scutellaria baicalensis aerial parts by UV-A radiation

Ultraviolet-A (UV-A) can affect plant secondary metabolism, but the flavonoid synthesis in Scutellaria baicalensis Georgi aerial parts in response to UV-A radiation was not clear. Therefore, the effects of UV-A radiation on flavonoid synthesis in S. baicalensis aerial parts were investigated in this study. The results showed that the total flavonoid content in aerial parts of S. baicalensis reached the maximum value (41.86 mg g−1) after 7 d of UV-A radiation. Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) analysis showed that the composition of flavonoids was not changed, but the contents of different components were changed according to High-Performance Liquid Chromatography (HPLC) analysis. Compared with the control treatment, the contents of scutellarin, baicalin and wogonoside were increased by 2.70-fold, 2.22-fold and 2.31-fold, respectively. However, scutellarein and baicalein decreased by 1.80-fold and 1.91-fold respectively. Meanwhile, UV-A radiation significantly increased the contents of nitric oxide (NO) and hydrogen peroxide (H2O2), and enhanced the activities of Phenylalanine ammonia lyase (PAL), Cinnamic acid 4-hydroxylase (C4H), and 4-coumarate CoA ligase (4CL). In addition, the antioxidant activity of S. baicalensis aerial part extracts after UV-A radiation was stronger than that of the control treatment. Further correlation analysis showed that there was a significant correlation between total flavonoid content and NO, H2O2, PAL, C4H, and 4CL. The enhancement of the antioxidant activity of S. baicalensis aerial part extracts was significantly correlated with total flavonoid, baicalin, wogonin and scutellarin content. This study shows that UV-A radiation can be used as an effective and economic way to increase the flavonoid contents in S. baicalensis aerial parts and promote the antioxidant activity of its extracts.