The Physiological Mechanism Of The Effect Of Exogenous Melatonin On Quinoa(chenopodium Quinoa Willd.)under NaCl Stress

Soil salinization is a worldwide ecological problem,which severely limits global crop productivity.Quinoa,as a kind of multi-purpose nutrition crop,its seeds have higher nutritional value.It can resist a variety of extreme wild environments.It has great potential in the future agricultural production.Melatonin is a tryptophan derivative,which is widely distributed in bacteria,plants,invertebrates and vertebrates.Melatonin not only plays an important role in regulating plant growth and development,but also protects cells from damage and improves the ability of plants to resist adversity.At present,the research on quinoa mainly focuses on stress physiology and yield.The growth status and physiological changes of quinoa were analyzed under non-salt stress and salt stress by applying different concentrations of melatonin.The plants(four-week-old)were used as the experimental material.The seedings were treated in Hoagland solution with or without 200 mM NaCl.It was divided into 8 treatment groups.In these treatment,different concentrations(0,1?M,10?M and 100?M) of melatonin were added.The effects of exogenous melatonin on the growth,photosynthetic capacity,organic osmotic regulators,inorganic ions,and antioxidant capacity of quinoa were analyzed under non-salt stress and salt stress conditions.The results showed that RGR,RWC,and FW of quinoa in the treatment salt stress were significantly decreased by 48.57%,11.00%,and 26.82%,respectively(p<0.05%).Compared with the treatment of 200 mM NaCl,RGR,RWC,and FW of quinoa in the treatment mixed with 100?M melatonin were significantly increased by 1.16 times,11.03%,and 34.25%,respectively(p<0.05%).Overall,the growth of quinoa was significantly inhibited under salt stress alone,while mixed with exogenous melatonin alleviated this inhibition of salt stress.Further experimental analysis showed that:the SPAD index in young leaves,functional leaves and old leaves were significantly increased by 10.69%,7.40%,10.35%,respectively(p<0.05%).Compared with the treatment of salt stress alone,water use efficiency,and photosynthetic rate of quinoa in the treatment mixed with melatonin treatment were significantly increased by 36.00%,1.07 times,respectively(p<0.05%).Under the same conditions,the contents of K⁺,NO₃^-and SO₄^2-in each tissue of quinoa were higher,while the contents of Na⁺,Cl^-and Na⁺/K⁺in the roots were decreased.Overall,exogenous melatonin alleviated the adverse effects of salt stress by regulating the contents of chlorophyll,ion homeostasis and water use efficiency.In addition,salt stress had effects on the activity of antioxidant enzymes,which significantly decreased the POD activity by 53.32%and the content of MDA significantly increased by 20.47%,respectively(p<0.05%).Under the salt stress treatment mixed with 100?M melatonin,the activities of SOD,POD,CAT were significantly increased by 60.06%,74.16%,82.48%,respectively(p<0.05%).The content of MDA significantly decreased by 20.75%,respectively(p<0.05%).Because of enhancing the activity of antioxidant enzymes,the mixed exogenous melatonin might reduce the oxidative damage of quinoa caused by salt stress.In summary,exogenous melatonin induced growth promotion of quinoa was due to the coordinated effect of melatonin in enhancing plant photosynthetic capacity,regulating ion contents in plant,maintaining ion homeostasis and improving antioxidant capacity under salt stress.The application of appropriate concentration of melatonin could provide an effective way and a new idea to enhance the stress resistance of quinoa.The results of the present study should provided a reference for the research on improving the stress resistance of crops.