Effects Of Exogenous Melatonin Pretreatment On Growth And Physiological Characteristics Of Cabbage Seedlings Under High Temperature Stress

High temperature is the most common stress factor in vegetable production,which seriously affects the yield and quality of vegetables.Since the autumn cabbages were generally planted in June and July,the high temperature led to poor seedling growth,weak stress resistance,which seriously affect the yield and quality.In recent years,the cultivated area of cabbage in China has been increasing year by year,but the high temperature in summer and the greenhouse effect have seriously affected the yield and quality of cabbage.Therefore,it is very significant to study the heat resistance under high temperature stress.In this study,the cabbage “Qin Gan58” varieties were sprayed with different concentrations of exogenous melatonin(MT)to study the temperature stress on the growth of cabbage seedlings,leaf chlorophyll content,relative conductivity,soluble protein content,malondialdehyde(MDA)content,superoxide dismutase(SOD)effect activity and other physiological indicators,in order to explore the physiological role of MT in plant resistance to adversity,which also provides a theoretical basis for the further application of MT in plant.Results were as follows:1.Pretreatment of exogenous melatonin can significantly increase the height,stem diameter,leaf length,fresh weight,root shoot ratio,seedling index,and G value of cabbage seedlings,promote the root growth of cabbage seedlings,and increase the dry weight of cabbage seedling,which makes the cabbage seedlings grow healthy and strong.2.Pretreatment of exogenous melatonin could increase the chlorophyll content in the leaves of cabbage seedlings under high temperature conditions,ensure the normal photosynthesis,significantly decrease the relative conductivity and malondialdehyde(MDA)content of cabbage seedling leaves under high temperature stress,increase the content of soluble protein and enhance the activity of superoxide dismutase(SOD).These results suggest that pretreatment of melatonin can reduce the membranous peroxide level of cabbage seedlings leaves under high temperature stress,protect the integrity of membrane,reduce electrolyte leakage,increase the activity of relative antioxidant enzyme(SOD),reduce the damage caused by high temperature of cabbage seedlings,and improve the resistance of seedling to high temperature stress.In conclusion,exogenous melatonin can effectively promote the growth of cabbage seedling under high temperature stress,increase the chlorophyll content in the leaves of cabbage seedling;reduce cell penetration,and protect cell membrane integrity;can increase the content of soluble protein,enhance the ability of the plants to coordinate metabolism;improve the activity of superoxide dismutase(SOD),can alleviate the adverse effect of high temperature on enzyme activity;promote growth of seedling,and improve the resistance of seedling to high temperature stress.