Abstract: Lamiophlomis rotata is an endangered medicinal plant found in the Qinghai-Tibet Plateau. The seedlings of L. rotata have poor cold resistance. In order to better understand the physiology of cold injury in this species and to provide scientific information that may lead to more successful domestic cultivation, the effect of exogenously applied Ca²⁺ on cold resistance regulation of wild seedling plants was investigated. Seedlings with soil (from Maqu County, Gansu Province) were transplanted into pots. Different concentrations of CaCl₂ solution (0, 5, 10, 15, 20 and 25 mmol·L^-1) were sprayed onto the seedlings,and the seedlings then immediately exposed to a range of low temperatures (4, 0 and -4 ℃) for 24 h, while pots of a control (CK) treatment were maintained at 25 ℃. After the 24 h cold exposure, various physiological traits including membrane stability, osmotic adjustment, membrane lipid peroxidation, and antioxidant enzyme activities in the leaves of the seedlings were measured. The results showed that exogenous Ca²⁺ had a significant impact on the resistance index of L. rotata after low temperature treatment, and the magnitude of the protective effect varied across the tested concentrations. The optimal CaCl₂ application rate was 15 mmol·L^-1. At this CaCl₂ concentration, the test plants had significantly increased soluble sugar content, and increased activities of antioxidant enzymes such as superoxide dismutase and peroxidase, which consequently reduced the membrane lipid peroxidation and enhanced the stability of the membrane systems. In addition, exogenous Ca²⁺ reduced relative membrane conductivity and leaf malondialdehyde content and increased root activity. In conclusion, exogenous Ca²⁺ improved the cold resistance of L. rotata seedlings, and has potential value as a tool to enhance cold tolerance in domestication and culture of L. rotata.

Key words: Lamiophlomis rotata, exogenous Ca²⁺, cold tolerance, physiological traits, effect