Study On The Mechanism Of Exogenous Melatonin Relieving Physiology Of Chrysanthemum Under High Temperature Stress

In this study,the cut flower Chrysanthemum morifolium’Jinba’was used as the material.After exogenous spraying of melatonin,the chrysanthemum was subjected to two high-temperature stress treatments at 33/28℃and 40/35℃for 96h.Changes in growth conditions,photosynthesis,chloroplast ultramicrostructure,chlorophyll content;osmotic adjustment,cell membrane peroxidation defense system,etc.,explored the mitigation effect and physiological mechanism of exogenous MT on chrysanthemum under high temperature stress,with a view to solving It provides scientific basis for the harm caused by high temperature stress to chrysanthemum in production practice and in-depth discussion of the high temperature resistance mechanism of chrysanthemum.The main findings are as follows:1.Exogenous MT can significantly increase the height of chrysanthemum seedlings under normal temperature and high temperature stress,and increase the dry weight of the shoot and root system of chrysanthemum seedlings.Among them,33/28℃high temperature stress has no obvious effect on the growth of chrysanthemum,40/35℃high temperature shows curly and black new leaves at the stem end,and most of the lower leaves are yellow.The symptoms of chrysanthemum seedlings pre sprayed with MT are light,only The leaves were slightly withered and yellow,and the alleviating effect was obvious.2.With the prolongation of high temperature stress time,the chloroplast and thylakoid structure of chrysanthemum leaves were damaged,Pn,Gs,Tr,CE,AQY of leaves were decreased,Ci was increased,and the degree of high temperature injury was large（P<0.05）.D,Fo and q N of leaves increased significantly,Fv/Fm,ΦPSII,Fv’/Fm’,ERT and q P decreased continuously,which indicated that high temperature reduced the photochemical activity of PSII reaction center,resulting in excess light energy and decreased light reaction,and chlorophyll content decreased,resulting in the overall reduction of photosynthesis.Chrysanthemum plants pre-sprayed with exogenous MT can maintain the polarity of chloroplasts under high temperature stress,showing vague thylakoid lamina lamellae and fewer osmium corpuscles.The levels of photosynthesis parameters and chlorophyll fluorescence parameters are basically normal The relative water content and chlorophyll content of the leaves remain stable,thereby alleviating the adverse effects of high temperature on the photosynthesis of chrysanthemum.3.The active oxygen content increased with temperature stress and time extension.Pre-spraying exogenous（MT）could significantly reduce the H₂O₂ content,O₂ˉ˙,MDA content and relative conductivity in the leaves of chrysanthemum seedlings under high temperature stress,and the SOD in the leaves of chrysanthemum seedlings,CAT,POD activity increased.It shows that MT pretreatment can increase the activity of antioxidant enzymes in chrysanthemum,balance the content of active oxygen,reduce the level of membrane peroxidation,the integrity of lipid membrane,reduce the extravasation of electrolyte,normalize the physiological metabolism of chrysanthemum plants and relieve heat stress The damage caused to the chrysanthemum seedlings will increase the plant’s resistance to high temperature stress.4.Pre-spraying exogenous MT can enhance the osmotic adjustment ability of chrysanthemum under high temperature stress.Under high temperature stress,the soluble protein content and soluble sugar content of chrysanthemum plants increased significantly,and proline showed a tendency to increase first and then decrease.The content of osmotic adjustment substance at 40/35℃is higher than 33/28℃high.Pre-spraying exogenous MT can significantly increase the content of proline,soluble sugar and soluble protein in chrysanthemum plants.MT can maintain the balance of the osmotic pressure of the chrysanthemum leaves through the effect of organic osmotic adjustment substances on the chrysanthemum seedlings,thereby enhancing the heat resistance of the chrysanthemum plants.5.High temperature stress continuously reduced the GSH and As A content of chrysanthemum,while DHA and GSSG content showed an upward trend,leading to the decrease of As A/DHA,GSH/GSSG ratio and As A+DHA,and the greater the degree of high temperature stress and the longer the duration of the stress,the lower The degree of increase and increase increased,but did not show significant effects on GSH+GSSG;APX,MDHAR,DHAR,and GR activities increased first and then decreased under high temperature stress.Exogenous MT can effectively increase APX,GR,DHAR,and MDHAR activity and As A and GSH content increase the level of As A-GSH cycle,make the cell membrane stable,relieve the damage to chrysanthemum plants under high temperature,and make chrysanthemum seedlings grow normally under high temperature stress.