Mechanism of exogenous methyl jasmonate mediated AsA-GSH cycle in Summer Black grape against low temperature stress

【Objective】The aim of this study was to explore the response mechanism of the exogenous Methyl jasmonate (MeJA) regulating the ascorbic acid-glutathione (AsA-GSH) cycle of Vitis vinifera Summer Black grape to low-temperature stress.【Methods】One-year-old Summer Black grape plants were used as materials, and different concentrations of MeJA treatment groups and low-temperature stress treatment groups were set up. (1) MeJA treatment: the selected 1-year-old Summer Blackgrape plants were randomly divided into 5 groups, with 10 plants in each group. 0 (CK), 50, 100, 150, 200 μmol·L-1 MeJA solution were sprayed on the leaves, and the spraying amount was suitable for the uniform wetting of the leaf surface without water dripping. The spraying time was selected in the evening of a sunny day to reduce the evaporation and photolysis of the solution. After treatment, the grape plants were cultured in normal growth environment (temperature 25±2 ℃, relative humidity 60%-70%, light intensity 2000-3000 lx, light time 16 h·d-1 ) for 24 h, so that MeJA could be fully absorbed and utilized by the plants; (2) low temperature stress treatment: 24 h after MeJA treatment, each group of grape plants were randomly divided into two subgroups, one subgroup were continously placed in normal growth environment as normal temperature control, and the other subgroup was transferred to low temperature stress environment (temperature 0 ℃, relative humidity 60%-70%, light intensity 2000- 3000 lx, light time 16 h · d- 1 ). The low temperature stress treatment time was set to 0 (sampling before treatment as initial control), 1, 3 and 5 days. At each treatment time point, three grape plants were randomly selected from the normal temperature control group and the low temperature stress treatment group, and their functional leaves (the third to fifth fully expanded leaves from the top of the plant) were collected for the determination of various indicators. The collected leaf samples were quickly frozen with liquid nitrogen and stored in a refrigerator at -80 ℃ for standby. The growth indexes and AsA GSH cycle related indexes were measured.【Results】(1) at room temperature, the growth indexes and photosynthetic characteristics of the Summer Black grape under different concentrations of MeJA treatment had no significant difference fromthose of the control group at each time point after treatment, indicating that under normal growth environment, exogenous MeJA treatment had no significant effect on the growth indexes and photosynthetic characteristics of the Summer Black grape; Under low temperature stress, the plant height, stem diameter and leaf number of the control group increased slowly with the extension of stress time. The growth indexes of the experimental groups treated with MeJA under low temperature stress were better than those of the control group. Among them, the plant height, stem diameter and leaf number of 100 μmol·L-1 MeJA treatment group increased significantly. 100 μmol·L-1 MeJA treatment could increase the chlorophyll a content, chlorophyll b content and total chlorophyll content, increase the utilization rate of light energy, and alleviate the damage of low temperature stress to grapes. The net photosynthetic rate, stomatal conductance and intercellular carbon dioxide concentration of the experimental groups treated with MeJA under low temperature stress were higher than those of the control group, and the 100 μmol·L-1 MeJA treatment had significant effect. MeJA could alleviate the inhibition of grape photosynthesis under low temperature stress. The chlorophyll a and chlorophyll b were positively correlated with net photosynthetic rate and stomatal conductance, and negatively correlated with carbon dioxide concentration and transpiration rate. (2) The exogenous MeJA treatment could significantly improve the content of AsA and GSH and the activities of DHAR, MDHAR and GR enzymes in the Summer Black grape under low temperature stress, and enhance the efficiency of AsAGSH cycle. Under low temperature stress, the content of AsA in the control group increased slightly at the initial stage, then gradually decreased, and the content of GSH increased at the initial stage, and then gradually decreased, while the content of AsA and GSH in the experimental groups treated with MeJA were higher than those in the control group under low temperature stress, and the content of AsA and GSH in the 100 μmol·L-1 MeJA treatment group remained at a high level after 5 days of low temperature stress; At the same time, the activities of DHAR, MDHAR and GR in 100 μmol·L-1 MeJA treatment group were significantly higher than those in the control group after 5 days of low temperature stress (P＜0.05). The exogenous MeJA treatment could maintain high AsA and GSH contents, enhancethe antioxidant capacity of plants, and improve the tolerance of grapes to low temperature stress. The AsA content and GSH content in AsA-GSH cycle were positively correlated with the DHAR enzyme activity, MDHAR enzyme activity and GR enzyme activity.【Conclusion】This study clarified the regulation effect of MeJA on AsA-GSH cycle of the Summer Black grape under low temperature stress, and screened out the optimal treatment concentration, which would provide theoretical basis and technical support for cold resistant cultivation of grape.