Analysis Of Physiological Characteristics And Expression Of Fatty Acid Desaturase Gene In Ornamental Chrysanthemum And Tea Chrysanthemum Species Under NaCl Stress

Chrysanthemum is a perennial perennial flower,one of the four major cut flowers in the world,with a long cultivation history.In this study,ornamental chrysanthemum’ Qiu Si’,’ Qiulousi’,tea chrysanthemum’Hangbaiju’ and’ Gongju’ were used as materials.Under 100 mmol/L Na Cl stress,chlorophyll fluorescence,antioxidant enzyme activity,soluble substance content and expression of membrane lipid fatty acid and fatty acid desaturation genes Cm SAD,Cm FAD2 and Cmfd7 were analyed at different times,and the physicochemical and molecular response mechanisms of chrysanthemum under salt stress were analyzed in depth.The results are as follows:(1)Under 100 mmol/L Na Cl treatment,the contents of chl a,chl b and chl(a+b)decreased gradually.Compared with the control group,the contents of chl(a+b)in’ QS’,’ QLS’,’ HBJ’ and’ GJ’ decreased by 28.13%,34.50%,21.84% and 29.58%,respectively.The change trend of chl a and chl b contents was consistent with chl(a+b),and the decrease trend of’QLS’ was the most obvious.Fv/Fo and Fv/Fm showed a decreasing trend,of which Fv/Fm of’ QS’ showed the largest decrease,14.87%compared with the control group,and Fv/Fo of’ QLS’ showed the largest decrease,38.36% compared with the control group.The fluorescence intensity FJ,FI and FP in the treatment group were lower than those in the control group.In the 820 nm curve,the lowest point position was significantly higher than that in the control group,and then gradually recovered to the control group state.(2)Under salt stress,the SOD activity of different varieties gradually increased.After 9 d treatment,the SOD activity of’ QLS’ increased by30.62% compared with the control group,with the most significant change trend.The activity of POD and CAT and the activity of SOD both increased gradually.MDA content increased gradually.After 9 d treatment,MDA content of’ HBJ’ changed most obviously,increasing69.46% compared with the control group.The content of soluble sugar and proline increased gradually.After 9 days of treatment,’ GJ’ proline increased the most,299.81%,compared with the control group.The content of soluble sugar in’ QLS’ increased the most,74.34%.The soluble protein content gradually decreased,and the soluble protein content of’ HBJ’ decreased most significantly,48.27% lower than that of the control group.(3)Under salt stress,the content of palmitic acid and stearic acid decreased gradually.After 9 d treatment,the content of palmitic acid in’HBJ’ decreased by 38.31%,and the content of stearic acid in’ QS’changed most obviously.Oleic acid,linoleic acid and linolenic acid all showed a gradually increasing trend,and the total unsaturated fatty acid content of’ GJ’ increased by 15.39% after 9 days of treatment.The ratio of unsaturated fatty acid to saturated fatty acid(USFA/SFA)and the fatty acid unsaturation index(IUFA)all showed a gradually increasing trend,of which the change degree of’ QLS’ was the most obvious,rising 94.20%and 15.71% respectively compared with the control group.The expressions of Cm SAD,Cm FAD2 and Cm FAD7 in’ qls’,’ hbj’ and’ gj’gradually increased.The relative expression of Cm SAD and Cm FAD7 genes of’ QS’ is consistent with the change trend of the other three varieties.the relative expression of Cm FAD2 genes in the’ QS’ treatment group shows a trend of increasing first and then decreasing.the peak value of cmfad2 gene expression is 1.34 times that of the control group at the 3rd day of treatment and 1.19 times that of the control group at the 9th day of treatment.Salt stress has less damage to the photosynthetic system of tea chrysanthemum than ornamental chrysanthemum,the change trend of fatty acid-related index of’ HBJ’ is the smallest,and the change trend of’QLS’ is the most obvious.The expression of fatty acid desaturase gene is basically consistent with the change of unsaturated fatty acid content.To sum up,tea chrysanthemum has stronger salt tolerance than ornamental chrysanthemum,but it does not rule out the influence of excessive light energy capture and active oxygen generation on the physical and chemical properties and fatty acid composition of plants after being subjected to salt stress.