Effects Of Exogenous Melatonin On Physiological Characteristics Of Pyrus Calleryana And Pyrus Betulifolia

In this study,Pyrus calleryana and Pyrus betulifolia were planted in pots The effects of different concentrations of melatonin(50,100,150,200μmol/L)on seedling growth,leaf pigment content,photosynthetic and fluorescence parameters,tissue water status,plasma membrane permeability,active oxygen metabolism,and selection and absorption capacity of plasmon were studied under NaCl stress.Objective to analyze the regulation of exogenous melatonin on salt tolerance of two kinds of seedlings under NaCl stress,and to compare the difference of physiological characteristics of different concentrations of exogenous melatonin.It will provide a new idea for landscape greening of saline soil.The main findings are as follows:(1)The growth of seedlings of Pyrus calleryana and Pyrus betulifolia were significantly inhibited under NaCl stress.Spraying different concentrations of melatonin could effectively improve the growth of ground diameter and plant height.Under 100μmol/L and 150μmol/L melatonin treatment,the growth of ground diameter and plant height of Pyrus pyrifolia were significantly increased.(2)Under NaCl stress,the pigment content,Pn,Gs,Tr,Fv/Fm and Fv/Fo of Pyrus calleryana and Pyrus betulifolia decreased with the prolongation of stress time,while C;decreased first and then increased.The above indexes of two kinds of seedlings treated with melatonin were still gradually decreased,but they increased in different degrees compared with the control,and their changes showed a trend of first rising and then decreasing with the increase of treatment concentration(3)Melatonin treatment could increase the relative water content and water saturation deficit of the two seedlings under NaCl stress.From the 5th to the 20th day,the leaf relative water content of Pyrus calleryana under 100μmol/L melatonin treatment was significantly increased;from the 5th to 25th day,the leaf relative water content and water saturation deficit of Pyrus betulifolia under 100μmol/L and 150μmol/L treatments were significantly increased.(4)Melatonin treatment decreased the relative conductivity and MDA content of the two seedlings under NaCl stress.From the 10th day to the 20th day,the relative electrical conductivity of the leaves of Pyrus calleryana under 100 μmol/L and 150μmol/L melatonin treatment decreased significantly,while that of Pyrus betulifolia decreased significantly under 150μmol/L melatonin treatment.From the 15th to 25th day,the MDA content in the leaves of Pyrus calleryana decreased significantly at 100μmol/L,while that of Pyrus betulifolia decreased significantly at 150μmol/L and 200μmol/L.(5)Different concentrations of melatonin could reduce the content of H2O2 and the rate of O2-production in leaves under NaCl stress.On the 25th day,the production rates of H2O2 and O2-reached the maximum.Compared with the control,the H2O2 Content and O2-production rate of Pyrus calleryana were significantly decreased under 50μmol/L,100μmol/L and 150μmol/L treatments,while Pyrus betulifolia were significantly decreased at 150μmol/L and 200μmol/L treatments.(6)Under NaCl stress,the activities of SOD,POD and CAT increased first and then decreased.The activities of SOD,POD and CAT increased in different degrees after melatonin treatment.Under the treatment of 100μmol/L,the activities of SOD,pod and cat of Pyrus calleryana increased the most,while the activities of SOD,pod and cat of Pyrus betulifolia increased the most under 150μmol/L treatment.(7)Melatonin treatment increased the contents of free proline and soluble protein of the two seedlings under NaCl stress.Under 100μmol/L and 150μmol/L treatments,the proline content in leaves of Pyrus calleryana was significantly increased;under 150μmol/L treatment,proline content in leaves of Pyrus betulifolia was extremely significantly increased;on the 25th day,the free proline content of both seedlings reached the maximum.Under 50μmol/L,100μmol/L and 150μmol/L treatments,the soluble protein of Pyrus calleryana increased significantly,while that of Pyrus betulifolia increased significantly under 150μmol/L treatment.(8)Melatonin treatment decreased Na+accumulation in roots,stems and leaves,increased K+content and increased K+/Na+,among which root K+/Na+increased most significantly.During the K+-Na+transport process,the selective absorption capacity of K+in Pyrus calleryana was greater than that of Na+,while that of Pyrus betulifolia was less than that of Na+.(9)The membership function analysis of the above physiological indexes showed that 100μmol/L and 150μmol/L exogenous melatonin was the best for Pyrus calleryana and Pyrus betulifolia respectively.