Study on the mechanism of exogenous serotonin improving cold tolerance of rapeseed (Brassica napus L.) seedlings

Cold stress disturbs numerous physiological and biochemical processes, restricting plant growth and productivity. In the current study, the protective role of exogenous serotonin in alleviating cold stress was investigated in rapeseed (Brassica napus L.) seedlings. The rapeseed seedlings were pretreated with different concentrations (0, 0.01, 0.02, 0.03, and 0.04 g L− 1) of serotonin solution and then were exposed to cold stress (4, 2, 0, and − 2 °C). The results indicated that the pretreatment of serotonin significantly increased the survival rate. Mainly, 0.03 g L− 1 of serotonin increased the survival rate by 75% compared to control conditions. The physiological and biochemical indexes and the expression of cold tolerance-related genes were analyzed in the seedlings pretreated with 0.03 g L− 1 of serotonin. The contents of proline (PRO), soluble sugar (SS), and soluble protein (SP); and the activities of antioxidant defense such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were significantly increased by exogenous serotonin under cold stress. Supplemented serotonin significantly increased the expression of SOD, COR6.6, COR15, and CBFs genes under cold stress.Overall, our results indicate that the optimal concentration (0.03 g L− 1) of exogenous serotonin maintained the osmotic potential balance in cells under cold stress by increasing the content of osmotic regulatory substances (SS, SP, and PRO), improving the scavenging ability of reactive oxygen species (ROS), increasing the antioxidant enzyme activities (CAT, POD, and SOD) and the transcriptional level of cold stress-related genes, helping rapeseed seedlings to cope with the cold stress. Therefore, serotonin-induced regulatory interactions between physiological and biochemical processes and the elevated expression of stress-associated genes may be a beneficial technique for cold stress tolerance in plants.