Effects of Exogenous Thermospermine and Its Synthesis Inhibitor on Low-temperature Stress Tolerance of Wucai

INTRODUCTION: Thermospermine, as a structural isomer of spermine, is an important substrate involved in plant growth and development, as well as responses to biotic and abiotic stress. RATIONALE: At present, there are few reports on the relationships between thermospermine and the responses of low-temperature stress in plants, for which a primary analysis of their relationships in wucai was conducted. Firstly, the optimal concentration of exogenous thermospermine alleviating the damage of wucai caused by low temperature was analyzed. Then, thermospermine synthesis inhibitor combined with the optimized concentration of thermospermine was used under low temperature condition in order to further analyze whether thermospermine plays a role in the tolerance of low-temperature. RESULTS: When wucai was treated with lower concentrations (0.05 and 0.1 mmol·L–1) of thermospermine, the electrolyte leakage, hydrogen peroxide, superoxide anion and malondialdehyde contents decreased with different degrees, and the dry and fresh weight increased; while the effects weakened with the increase of thermospermine concentration. The evaluation of membership function showed that the average membership function values decreased gradually with the increase of the concentration, and the score at 0.05 mmol·L–1 thermospermine was the highest. The addition of thermospermine synthesis inhibitor under low temperature made the two inbreeding lines of wucai with different low-temperature tolerance accumulate more hydrogen peroxide and superoxide anion, and increase electrolyte leakage and malondialdehyde content. Furthermore, when thermospermine synthesis inhibitor was applied in combination with thermospermine, it can alleviate the damage of low temperature aggravated by inhibitor treatment alone. Thermospermine treatment was associated with higher activities of superoxide dismutase (SOD) and peroxidase (POD). CONCLUSION: 0.05 mmol·L–1 thermospermine could effectively alleviate the damage of low temperature on wucai seedlings, and thermospermine synthesis is closely related to the low-temperature tolerance of wucai, which may improve low-temperature tolerance through maintaining higher antioxidant enzyme activities, especially SOD and POD.