| Jerusalem artichoke(Helianthus tuberosus L.),an annual sunflower species,belongs to the family Asteraceae.Specifically,an important characteristic of Jerusalem artichoke is its high tolerance to a saline environment.Jerusalem artichoke cultivation relies mainly on planting tubers,and the seedlings can survive even in severely saline-alkaline soil.Jerusalem artichoke tubers use inulin(a kind of fructan)rather than the usual starch as the main storage material,and inulin may play an important role in adapting to the physiological regulation of salt stress.In this study,0,50,150,and 250 mmol/L NaCl solutions were used to simulate the salt stress of different intensities.The inulin content and degree of polymerization were observed during the sprouting process(0-7 d)of potted Jerusalem artichoke.At the same time,the expression levels of genes encoding enzymes involved in fructan synthesis(1-FFT and 1-SST)and degradation(1-FEH)were analyzed.Additionally,the proteomic analysis of tubers of Jerusalem artichoke subjected to 150 mmol/L NaCl stress for 7 days was performed.The main content and results were as following:(1)Under 0-250 mmol/L NaCl treatment,tubers of Jerusalem artichoke can germinate and seedlings can survive.From the final seedling situation,the length of young roots and leaves of Jerusalem artichoke under salt stress was significantly shorter than that of the control and decreased with the increase of NaCl concentration.High salt stress significantly inhibited the growth of young roots and shoots of Jerusalem artichoke.(2)The content of inulin in tubers of Jerusalem artichoke had no significant changes from 1 to 7 days without salt stress,but the content of inulin in tubers of Jerusalem artichoke showed a significant decrease from 3-5 d after treatment with 150 mmol/L NaCl,but it increased rapidly or even exceeded the initial level at 7 d,that means the Jerusalem artichoke tubers may convert other stored sugars into more inulin to deal with salt stress.The inulin content was significantly lower at 250 mmol/L NaCl treatment than at 150 mmol/L NaCl treatment,indicating that stronger salt stress inhibited the mobilization of inulin in tubers.(3)Along with the sprouting process of Jerusalem artichoke tubers(1-7 d),the proportion of inulin at different degrees of polymerization(DP)also changed.The proportion of DP 2-5 inulin was changed in a gentle inverted V-shaped as time progresses,while the proportion of DP 6-10,DP 11-15,DP 16-20 and DP>20 inulin was changed in a positive V-shape that is low in the middle and high in both sides.The overall trend of the control and NaCI treatments was similar but the details were different.The proportion of DP 6-10 inulin under 150 mmol/L NaCl treatment was greater than the control at the late stage of the time course,while DP 11-15,DP 16-20 and DP>20 were higher on the 1st day than in the control,and on the 3rd-7th day were lower than the control.In addition,from the change in the degree of polymerization of inulin under salt concentrations at the 7th day,the higher the degree of polymerization of inulin,the greater the proportion of change in salt concentration between the treatments.(4)The gene expression of key enzymes 1-FFH,1-SST,and 1-FFT in inulin metabolism are complex and greatly affected by salt stress,which cannot explain the changes in inulin content and the degree of polymerization well.These results indicated that the expression level of genes is not completely consistent with the final enzyme activity.(5)During Jerusalem artichoke tuber sprouting,23 proteins were differentially expressed under salt stress(20 upregulations and 3 downregulations).Unfortunately,these differentially expressed proteins are not directly related to inulin metabolism,mostly involved in metabolic and genetic information processing. |
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