Physiological Mechanism Of 5-aminolevulinic Acid(ALA) Regulating Cold And Drought Tolerance In Rapeseed(Brassica Napus L.)

Rapeseed(Brassica napus L.)is the oil crop with the largest planting area in China.In recent years,low temperature and drought frequently occur,which make rapeseed grow slowly before overwintering and fail to grow into strong seedlings for overwintering safely,thus affecting the yield and quality of rapeseed.Therefore,it is necessary to explore the effects of low temperature and drought stress on the growth of rapeseed at seedling stage,and to study the measures to improve cold tolerance and drought tolerance of rapeseed.The effects of low temperature/drought on seedling stage and the effects of exogenous5-aminolevulinic acid(ALA)on the damage of low temperature/drought stress in rapeseed were studied in two rape varieties with different sensitivity to low temperature and drought.The main results were as follows:1.Low temperature stress significantly reduced the growth of Zayou 15(ZY15)and Huiyou 49(HY49).Low temperature caused oxidative stress injury to two different low temperature sensitive rape varieties.’Huiyou 49’ was more sensitive to low temperature than ’Zayou 15’.The long-term low temperature stress significantly reduced the chlorophyll b content and chlorophyll a/b,significantly decreased the activities of SOD and POD,significantly decreased the contents of GA,IAA and CTK,and significantly increased the content of ABA in seedling leaves.2.Exogenous application of the appropriate concentration of ALA could enhance the low temperature tolerance of rapeseed,mainly in that the application of ALA could improve the antioxidant capacity and chlorophyll content of rapeseed,so as to improve the growth of rapeseed under low temperature stress,especially when the concentration of ALA was 20 mg·L-1.In the two application methods of ALA,spraying ALA first and then low temperature(ALA→LT)and spraying ALA first and then low temperature(ALA→LT),LT→ALA treatment significantly alleviated the membrane lipid peroxidation degree of rapeseed,and the effect was better than ALA→LT treatment.Among the three doses of ALA(A20,A20*2 and A40),the content of MDA and chlorophyll in rapeseed seedling leaves in A20 treatment group were the lowest and the highest.3.Under low temperature stress,leaf spraying of 20 mg·L-1ALA significantly increased GA content and significantly decreased ABA content,but had no significant effects on IAA,CTK content and the activities of APX,SOD,POD and CAT.4.Drought-stress significantly reduced the growth amount,increased the membrane lipid peroxidation degree of leaf cells and significantly reduced the chlorophyll content in leaves of the two cultivars.Drought-stress significantly increased the activities of SOD enzyme in leaves,and significantly decreased the activities of POD,CAT and APX enzyme in leaves.Drought-stress significantly reduced the contents of GA,IAA and CTK,and significantly increased the content of ABA in seedling leaves of both cultivars.5.Exogenous application of 10,20,40 and 80 mg·L-1ALA could increase the growth of rapeseed under long-term drought stress and reduce the damage of seedling under oxidative stress,and the effect was most significant when the concentration of ALA was 10mg·L-1.Spraying exogenous ALA could significantly increase the chlorophyll content,POD,CAT and APX activities,GA,IAA and CTK contents and reduce ABA content in leaves of the two cultivars.The results showed that the concentration of ALA at 20 mg·L-1 could significantly alleviate the damage caused by low temperature stress,the concentration of ALA at 10mg·L-1 could significantly alleviate the damage caused by drought stress,and the appropriate concentration of ALA could effectively improve the cold tolerance and drought tolerance of rapeseed.