The Effect of Far-Red Light and Nutrient Level on the Growth and Secondary Metabolites of the In Vitro Culture of Prunella vulgaris

Abstract

Prunella vulgaris, a medicinal plant with antioxidant capacity, was investigated for its response to varying intensities of far-red light and nutrient levels. Plantlets were cultured for 30 d under low far-red light (LFR) or high far-red light (HFR) conditions and different nutrient levels (full, half, and quarter). HFR reduced leaf and branch number, dry weight, and accumulation of chlorophylls (Chl) and carotenoids (Car), while increasing plant height. Lower nutrient levels increased plant height and leaf number, but decreased branch number, Chl, and Car. HFR significantly increased total phenolic content (TPC), rutin, and rosmarinic acid levels, while total flavonoid content decreased. As nutrient levels decreased, TPC and rosmarinic acid declined. HFR induced significant DPPH scavenging activity, while reducing power increased with higher far-red light and nutrient levels. The ferrous ion chelating effect under LFR reduced with lower nutrient levels. There were strong correlations among TPC, rosmarinic acid, DPPH scavenging activity, and reducing power. In conclusion, HFR inhibited plantlet growth but enhanced secondary metabolite accumulation and antioxidant capacity. Different nutrient levels stimulated diverse growth responses, while elevated nutrient levels promoted secondary metabolite production. This study demonstrated the responses of growth, secondary metabolite accumulation, and antioxidant activity in the in vitro cultured P. vulgaris to supplemental far-red light and various nutrient levels.