Platycodon grandiflorus (PG) is a perennial herb, and its dried root is an important traditional Chinese herb. Mutation breeding induces plant variation, but may cause adverse effects. To explore the effects of 60 Co-γ irradiation on the seedlings of PG, PG seeds were treated with 60 Co-γ rays at doses of 50, 100, 200, and 400 Gy, and their germination and growth performance during the seedling stage were observed. Exposure to 60 Co-γ irradiation significantly impaired PG development in a dose-dependent manner. Compared with the control, 400 Gy group exhibited a 19.5% reduction in germination rate and complete seedling lethality (0% survival). Conversely, the 50 Gy treatment promoted vegetative growth, increasing both leaf number and leaf area. The lethal dose 50% (LD 50 ) of PG seeds was calculated as 171 Gy. With increasing irradiation dose, chlorophyll content, transpiration rate, and stomatal conductance in PG seedlings gradually decreased, while net photosynthetic rate and intercellular CO 2 concentration initially increased and then decreased. The contents of proline (Pro), malondialdehyde (MDA), and hydroxyl radicals (OH •- ) continuously increased. Activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) gradually increased under low-dose irradiation (50 Gy and 100 Gy) but progressively declined under high-dose irradiation (200 Gy and 400 Gy). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations revealed that chloroplast structure damage in PG intensified with increasing irradiation dose, accompanied by progressive deterioration of leaf surface structure. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis demonstrated that irradiation doses of 50-200 Gy significantly upregulated genes associated with photosynthesis and chlorophyll metabolism, whereas 400 Gy irradiation markedly suppressed their expression. Based on M 1 physiology, we preliminarily suggest 50-100 Gy as an optimal dose range for 60 Co-γ irradiation in seed form of PG. These findings offer a foundation for exploring mutation breeding, pending confirmation through heritable genetic analyses.
Zhu et al. (Sun,) studied this question.