Effects Of Exogenous Melatonin On Physiological Characteristics In Chrysanthemum Under NaCl Stress

Soil salinization is one of the factors that restrict the growth and development of plants.It is an important way to alleviate salt stress by exogenous substance to reduce the damage to plants and enhance salt tolerance of plants.In this study,the effects of exogenous melatonin at different concentrations on alleviating growth inhibition and injury of`Huangju'plants under salt stress(140mmol·L<sup>-1</sup>NaCl)were studied.On this basis,the physiological indexes of exogenous melatonin on antioxidant enzyme activity,photosynthetic parameters,chlorophyll content,fluorescence parameters,osmotic adjustment substance content,ascorbic Acid-glutathione system enzyme activity and reactive oxygen species scavenging system of`Huangju'plants were studied.The aim is to study the regulation function of exogenous melatonin on salt tolerance of'Chrysanthemum morifolium',so as to provide scientific basis for production practice of relieving salt stress of Chrysanthemum morifolium and in-depth discussion on salt tolerance mechanism of Chrysanthemum morifolium.The main research results are as follows:1.The appropriate concentration of exogenous melatonin treatment can alleviate the damage of salt stress to the antioxidant enzymes and osmotic regulators of`Huangju'.The activity of antioxidant enzymes and the content of osmotic regulators in`Huangju'increased under salt stress.Melatonin 50-250?mol·L^-11 could increase the activity of antioxidant enzymes and the content of osmotic regulators in'Huangju'under salt stress to varying degrees,and decrease the content of malondialdehyde?MDA?.Among them,150?mol·L^-1melatonin had the best effect on alleviating salt stress injury.2.Effects of Exogenous Melatonin on Ascorbic Acid-Glutathione Cycle of'Huangju'under Salt Stress:under salt stress,the content of reactive oxygen species?ROS?in`Huangju'plants increased significantly,and the content of H<sub>2</sub>0<sub>2</sub>,O<sub>2</sub><sup>-</sup>,APX and DHAR activity increased primitively and then decreased;GR,ASA,DHA,GSH,ASA+DHA,ASA/DHA,GSH+GSSG,GSH/GSSG activity increased first,then decreased,then increased.After spraying melatonin,the enzymatic reaction of ascorbic Acid-glutathione cycle?ASA-GSH?in the leaves of`Huangju'were significantly increased.Among them,the contents of ASA,DHA,GSH and GSSG in the leaves of`Huangju'increased;the contents of APX,GR and DHAR increased;the contents of hydrogen peroxide and superoxide anion also increased significantly.3.Effects of exogenous melatonin on antioxidant enzymes of`Huangju'under salt stress:under salt stress,the activities of superoxide dismutase?SOD?,catalase?CAT?and peroxidase?POD?of`Huangju'plants increased first and then decreased.Spraying melatonin could significantly increase SOD,POD and CAT activities in leaves of`Huangju'seedlings,and enhance the ability of removing reactive oxygen species and reduce the content of malondialdehyde under stress,thus enhancing salt tolerance of`Huangju'plants.4.Effects of exogenous melatonin on Photosynthesis of`Huangju'under salt stress:under salt stress,the content of photosynthetic pigments and stomatal conductance?Gs?,transpiration rate?Tr?,initial fluorescence?FO?values of`Huangju'were significantly increased,and the contents of maximum fluorescence?Fm?,variable fluorescence?Fv?,and actual photochemical efficiency?PSII?of`Huangju'were significantly decreased.After spraying melatonin,the contents of Gs,Tr and FO were significantly increased,the contents of Fm,Fv and PSII were decreased,photosynthesis was enhanced,the transmission efficiency of photosynthetic electrons was enhanced,and the share of light energy allocated to photochemistry reaction was increased.5.Effects of exogenous melatonin on Osmotic Adjustment Substances of`Huangju'under salt stress:under salt stress,the contents of soluble protein and proline in`Huangju'plants increased continuously,and the content of soluble sugar increased first and then decreased.Spraying melatonin significantly increased the contents of proline,soluble protein and soluble sugar in`Huangju'plants.These three osmotic regulators reduced the osmotic potential of plant cells,reduced water loss,and created conditions for maintaining normal physiological metabolism of cells.