Effect of cytokinins on callus proliferation and physiological characteristics in <italic>Cornus officinalis</italic>

To establish an efficient proliferation system for Cornus officinalis callus, this study used MS medium supplemented with 0.5 mg·L-1 NAA as the co-inducer, and systematically compared the effects of thidiazuron (TDZ), 6-benzylaminopurine (6-BA), and kinetin (KT) at concentrations of 0.5–3.0 mg·L-1 on callus proliferation and physiological characteristics. The results showed that TDZ at 2.0 mg·L-1 achieved the optimal proliferation efficiency, with a proliferation rate of 653.66%. Histological analysis revealed that the callus exhibited a dense and highly uniform structure, and the contents of secondary metabolites morroniside and cornuside were significantly increased. Physiological analysis indicated that TDZ treatment effectively elevated superoxide dismutase (SOD) and peroxidase (POD) activities, reduced malondialdehyde (MDA) content, and maintained cellular redox homeostasis. In contrast, 6-BA at 1.0 mg·L-1 showed a moderate promoting effect, but higher concentrations inhibited proliferation. KT exhibited generally weak proliferative effects, and high concentrations led to an abnormal increase in cellular moisture content. Correlation analysis further indicated a positive relationship between POD activity and proliferation rate, while MDA content and moisture content were negatively correlated with proliferation rate. This study identifies 2.0 mg·L-1 TDZ as the optimal cytokinin type and concentration for C. officinalis callus proliferation, providing a theoretical basis and technical support for its large-scale cultivation and efficient production of secondary metabolites.