Changes in the Platycodin Content and Physiological Characteristics during the Fruiting Stage of Platycodon grandiflorum under Drought Stress

Medicinal plants are affected by drought stress, mainly reflected in the growth process and secondary metabolite synthesis. Platycodon grandifloru m (Jacq.) A. DC. is a traditional Chinese herbal medicine. The yield of Platycodon grandiflorum cannot meet the market demand, while its yield and quality are limited by the plant growth conditions. We assessed relevant indicators of growth during the fruiting stage of Platycodon grandiflorum under drought stress. The results showed that the fresh root weight (FW), photosynthesis, and chlorophyll fluorescence parameters were significantly reduced after withholding water (AW), but total superoxide dismutase (T-SOD), peroxidase (POD), and catalase (CAT) activities and the contents of soluble protein (SP), proline (PRO), and malondialdehyde (MDA) were significantly increased. The contents of platycodin D (PD) and platycodin D3 (PD3) did not change obviously after withholding water (AW), but in the autumn period, the values increased by 8.95% and 11.67%, respectively. The content of total platycodin increased significantly under drought stress, during the after rewatering (AR) and in the autumn period. The different physiological stress indicators exhibited strong correlations, had synergistic effects of mutual promotion and restriction, and responded to changes in the soil water content. These results suggest that during the fruiting stage, Platycodon grandiflorum encounters drought stress and may resist oxidative damage by increasing protective enzyme activity and osmoregulatory materials to ensure normal plant growth. According to the effect of drought stress on dry weight, the yield of Platycodon grandiflorum was not affected by drought stress, but the total platycodin content in Platycodon grandiflorum roots increased significantly. Therefore, in agricultural production, short-term drought stress should be conducted in the fruiting stage of Platycodon grandiflorum , which can both guarantee the yield and improve the quality of medicinal materials.