Alleviating Effects Of Exogenous Selenium On Strawberry Seedlings Under Chilling Stress And The Change Of Its Ascorbate-Glutathione Cycle Characteristics

This research used two different cultivarss of strawberry seedlings (cv. Akihime and cv. Benihope)as plant material. The seedling were sprayed with 4 different concentrations of sodium selenite(Na2SeO3)solution on the parts that above the earth, then treated under low temperature (0℃) for 6 h or 12 h. The related physiological characteristics were studied under the chilling stress. And during the recovery growth part, the related enzyme activities and component contents in the AsA-GSH cycle were measured as well. We discussed the effects of exogenous selenium on cold tolerance and recovery growth ability of strawberry seedlings. Thus the following relevant physiological index were abstracted and determined, which included the chlorophyll and malonaldehyde (MDA) content, the net photosynthesis rate (Pn), the stomatal conductance(Gs), the intercellular CO2 concentration (Ci), superoxide dismutase (SOD), peroxide enzyme (POD), catalase (CAT) activity, and the relative electric conductivity, and enzyme activities and component contents in the AsA-GSH cycle. The main results were as follows.1. The chilling stress leaded to a great accumulation of MDA and H2O2 in the leaves, and caused the biomembrane damage. Meanwhile it decreased the content of chlorophyll, the net photosynthesis rate (Pn), the stomatal conductance (Gs), the intercellular CO2 concentration (Ci)which were all closely related with photosynthesis. We found that the factor which was responsible for the reduction of photosynthesis was non-stomatal limitation. Besides, the stress activated the antioxidant defense system of strawberry seedlings. The activities of superoxide dismutase (SOD), peroxide enzyme (POD) and catalase(CAT) were significantly increased, so as the enzyme activities and component contents in the AsA-GSH cycle too.2. The exogenous selenium could alleviate the effect of chlorophyll damdge, decreased the accumulation of MDA and H2O2. The decline of the net photosynthesis rate (Pn), the stomatal conductance (Gs) and the intercellular CO2 concentration (Ci) were also alleviated effectively. The antioxidant defense system of strawberry seedlings, which included SOD, POD, CAT and the key enzyme in the AsA-GSH cycle (APX, GR, MDHAR, DHAR) were also improved. And the concentration of exogenous selenium was more effective when it’s between 2.5 mg·L-1 and 5.0 mg·L-1.3. Under the chilling stress, the cv. Benihope has stronger antioxidant ability than the cv. Akiliime.4. After the strawberry seedlings were released from the low temperature, the exogenous selenium also had certain influence on the physiological characteristics. The activity of the APX was still increased on the second days of recovery growth.And the exogenous selenium also made the content of AsA and GSH changed on opposite way. The enzyme activities and component contents in the AsA-GSH cycle were back to the normal level on the day 6.In conclusion, the exogenous selenium had obvious alleviating effects on the strawberry seedlings under the chilling stress, which could be used on the cultivation of strawberry in winter.