Effects of UV-B pre-treatments on physiological properties and accumulation of active ingredients in herbal plant, Prunella vulgaris

Aim: The effects of UV-B pretreatment on biosynthesis of active ingredients in Prunella vulgaris L. were studied from three aspects: active ingredients, physiological and biochemical parameters and key enzymes of rosmarinic acid metabolism pathway.Methodology: In greenhouse, the seedlings of P. vulgaris were subjected to UV-B treatment for 30 min from 10:30 a.m. to 11:00 a.m. every day for 10 days and then transplanted to field. After ripening, the leaves were harvested for physiological and biochemical estimations and the expression of key enzyme genes and the contents of active ingredients were measured by ear picking. Results: The results of active ingredient content showed that artificial UV-B radiation increased the contents of phenolic acids and individual flavonoids at mature fruiting stage compared with control plants. Physiological and biochemical results indicated that increase in peroxidase, ascorbate peroxidase, and superoxide dismutase activities seem to be active responses to alleviate the deleterious effects of UV-B in P. vulgaris. Under UV-B pre-treatment, genes related to rosmarinic acid/phenolic acid biosynthesis were significantly (p<0.05) over-expressed at seedling stage of P. vulgaris. Interpretation: This study indicated that UV-B pre-treatment in the seedling stage before transplantation to field is effective for inducing phenolic acid and flavonoid accumulation in P. vulgaris ears at mature fruiting stage.