Physiological Characteristics Of Medicago Sativa In Response To Salt Stress And Analysis Of Root Metabolites

Salt stress,as one of the main abiotic stresses affecting crop growth,affects the nutrient absorption,photosynthesis and metabolic regulation of Medicago sativa to some extent.Medicago sativa,as an important source of plant protein and fat,its development and yield are affected by saline-alkali stress.Saline-alkali plants’ salt-tolerance involves the regulation of multiple signaling pathways.At present,little is known about the reduction of nutrient utilization rate and photosynthetic rate under saline-alkali stress.It is confirmed that the effective regulator of salt-tolerance is beneficial to the quality improvement and production of alfalfa.In order to study the effects of salt stress on Medicago sativa growth as well as the mechanism of salt tolerance of Medicago sativa,improve the breeding efficiency and crop yield of alfalfa,Medicago sativa WL525 as test materials,this study respectively to study the tendency for Medicago sativa under 150 mmol·L-1 NaCl stress of K+,Ca2+,Na+,Mg2+absorption,distribution and transportation and alfalfa chlorophyll fluorescence under salt stress curve and the change of the parameters,and through the comparison of metabonomics analysis tendency for 1,6,24 h after 150 mmol·L-1 NaCl stress of Medicago sativa root metabolic product of change,32,29 and 153 different metabolites were screened out respectively,and the metabolomic mechanism of the salt tolerance of alfalfa root system was revealed.The test results are as follows:(1)150 mmol·L-1 NaCl stress significantly increased the Na+ content in each organ of alfalfa seedlings,at the same time,K+,Ca2+,Mg2+,Fe2+,Mn2+,Cu2+and Zn2+contents in roots,stems and leaves of Medicago sativa were decreased,which resulted in a significant decrease of K+/Na+,Ca2+/Na+,Mg2+/Na+,Fe2+/Na+,Mn2+/Na+,Cu2+/Na+and Zn2+/Na+in roots,stems and leaves of Medicago sativa.The accumulation of excessive Na+in stems and leaves is a response mechanism of Medicago sativa to salt stress.(2)Under the pressure of 150 mmol L-1 NaCl,the photosynthesis activity of Medicago sativa PSI and PSII decreased overall.With the extension of salt stress time,the rapid chlorophyll fluorescence level(OJIP)of Medicago sativa decreased significantly(P<0.05),the lowest point of the MR/MRo dynamics curve was gradually extended and the lowest value swelled,VPSⅠ,VPSⅡ-PSⅠ and VPSⅡ were significantly reduced(P<0.05),and the amplitude of the DF curve decreased.PI,Fv/Fo,and Fv/Fm in Medicago sativa chlorophyll fluorescence parameters were significantly reduced with the extension of salt stress time(P<0.05),while ABS/RC,DIo/RC,TRo/RC,ETo/RC increased significantly with the extension of salt stress time(P<0.05).The changes in Medicago sativa chlorophyll fluorescence curve and parameters under salt stress show that salt stress damages the oxygen-releasing complex in the Medicago sativa leaf meat cells,reduces the activity and quantity of the photosystem reaction center,blocks the electron transmission on the photosynthesis chain and weakens the reverse transfer ability of the electrons,and destroys the energy flow between the photosynthesis transfer body Increasing the absorption of light energy,improving the oxidation activity of the optical system and promoting the electron transmission are a kind of self-protection mechanism under salt stress of Medicago sativa.(3)150 mmol·L-1 NaCl stress significantly changed the types and metabolic modes of alfalfa root metabolites,and the types and metabolic modes of Medicago sativa root metabolites were also different at different salt stress treatment times.After salt stress 1,6,24 h,the metabolites of the alfalfa root system were significantly different,and 32,29 and 153 different metabolites were screened,respectively.Under salt stress,Medicago sativa root of ABC transhipment,corneous layer synthesis,the amino acid and fatty acid metabolism,synthetic antibiotic biosynthesis and osmotic regulator,such as significant changes in metabolic pathways,salt stress,the main regulation of alfalfa root way to promote the synthesis of cuticle,improve the accumulation of soluble substances is given priority to,late salt stress,in addition to remain in the regulating mode,has formed in the early years of amino acids and fatty acid metabolism,antibiotic biosynthesis and synthesis of osmotic regulators and other metabolic pathways become major adjustment way.Changes in metabolic pathways,such as ABC transporter,cuticle synthesis,amino acid and fatty acid metabolism,antibiotic biosynthesis and osmotic regulator synthesis,are a response of alfalfa root system to salt stress.