Effects of UV-B Radiation on the Content of Bioactive Components and the Antioxidant Activity of Prunella vulgaris L. Spica during Development

The effects of UV-B radiation on the content of bioactive components and the antioxidant activity of Prunella vulgaris L. spica during development were studied. The experimental design involved two levels of UV-B radiation intensity (0 and 120 μW cm^-2 nm^-1). The results showed that the contents of total Flavonoids, rosmarinic acid, caffeic acid and hyperoside, as well as the antioxidant capacities (DPPH^● and ABTS•+ scavenging activities), in the spicas significantly decreased during spica development. The content of salviaflaside in the spicas significantly increased during development. The highest contents of total Flavonoids, rosmarinic acid, and caffeic acid and the highest antioxidant activities were found in spicas in the full-flowering stage, while the highest content of hyperoside was found in spicas in the bud stage. In addition, the highest content of salviaflaside was found in spicas in the mature-fruiting stage. UV-B radiation significantly promoted the synthesis of secondary metabolites, increased the contents of the main bioactive components in the three developmental stages of isolated dried spicas, and significantly increased the DPPH^● and ABTS•+ scavenging activities of P. vulgaris spicas in the mature-fruiting stage. Moreover, the total Flavonoids content was positively correlated with the DPPH^● and ABTS•+ scavenging activities, and the correlation with the DPPH^● scavenging activity was very strong. This result shows that the highest contents of the main bioactive components in the spicas were not all found in the same developmental stages of P. vulgaris. Our research revealed that the best stage for harvesting P. vulgaris spica was between the bud stage and the full-flowering stage since harvesting at this point provides a higher content of bioactive components and a higher antioxidant capacity, which is relevant for medicinal applications.