| The stems and blade of sweetpotato[Ipomoea batatas(L.)Lam.] are part of its aboveground vines,and the biomass is considerable.Existing studies have shown that sweetpotato blade are rich in phenolic acids,flavonoids and other phenolic substances,which have antioxidant,hypoglycemic and anti-tumor effects,and are widely used in food,medicine,health care products and cosmetics.Therefore,it is of great theoretical significance and application value to study the content of phenolic compounds in sweetpotato blade and its variation among genotypes as well as the molecular mechanism of phenolic substance biosynthesis.However,most of the current studies on sweetpotato blades focus on the determination of phenolic content in sweetpotato varieties,and there is a lack of further research on the inherent reasons for the differences in phenolic content between genotypes.Based on this,this paper conducts the following two aspects of research:(1)The phenolic substance content and antioxidant activity of 86 genotypes in our breeding process were determined in 2020,and 32 representative genotypes were screened out,in 2021,the color values,photosynthetic pigment,total protein content,antioxidant enzyme activity,phenolic substance content,and antioxidant capacity in blade of 32 sweetpotato genotypes were measured and correlated,and the changes of above physiological and biochemical indicators of Wan1314-6 and Shangshu 19 at the growth period of 40,65,90,115 and 140 days were studied;(2)Transcriptome analysis was performed on the folaiges of Wan1314-6 and Shangshu 19 at 115 days of growth,and combined with the previous data,the relevant genes that may affect the metabolism of phenolic substances in sweetpotato leaves were screened.Through the above research,we hope to screen out the excellent germplasm resources for blade utilization and explore the mechanism of genotype differences in phenolic content in blade,so as to lay a theoretical and scientific basis for further selection and breeding of leafy sweetpotato varieties.The main findings of this paper are as follows:1.The content of phenolic substances in sweetpotato blades was significantly different between genotypes and during the growth period;the trend of change during growth period was also different among genotypes.In 2020,the total polyphenol content of sweetpotato blades and the ABTS+ clearance ability of blade extracts were significantly different among 86 genotypes,and the range,mean and coefficient of variation of the total polyphenol content were 4.69-26.84 mg GAE/g FW,12.66GAE/g FW,38.31%,respectively,and the range,mean and coefficient of variation of EC50 values of ABTS+ clearance capacity were 1.41-8.58mg/m L FW,98 mg/m L FW,40.20%,respectively.The total polyphenols and total flavonoid contents of the32 genotypes screened from preceding 86 genotypes were 2.17-28.90 mg GAE/g FW and 2.95-12.66 mg RE/g FW in 2021,respectively,and the maximum difference in content were 13.32 and 4.29 times than those of minimum,respectively,and there were significant differences between genotypes.Although the total polyphenol and total flavonoid contents of genotypes Wan1314-6 and Shangshu19 blades both showed an increase and then a decrease during the their growth period,Shangshu19 with low polyphenol content reached a stable state at 65 d after transplanting,while Wan1314-6 with high polyphenol content increased until 115 d after transplanting before reaching its peak.2.blade color population classification,phenol content population classification and correlation between phenolic content and physiological and biochemical indexes in sweetpotato blades.The 32 genotypes were clustered into four color genotype populations and six populations of phenol content according to blade color values and phenol content,respectively.The correlation analysis between phenol content and antioxidant capacity,blade color,pigment content and other physiologic indicators at different analytical scales showed that there was a significant positive correlation between the five indicators of total polyphenols,total flavonoid content,ABTS free radical scavenging ability,DPPH radical scavenging ability and iron ion reduction capacity,and the total polyphenol,total flavonoid content was significantly negatively correlated with the blade color value b* only between the lines in the green genotype population,and in the remaining cases,the phenol content was not significantly correlated with the other metrics,indicating that the increase in the blade phenol content by breeding did not affect the improvement of photosynthesis efficiency,protein content and antioxidant enzyme function indicators.3.Principal component analysis screened out three germplasm resources with excellent phenol content in blades.In this study,through the main component analysis of 11 physiological and biochemical indexes including phenol content and antioxidant capacity in the blades of 32 sweetpotato genotypes,these 11 indicators were simplified to 4 principal components with characteristic values greater than 1,according to the main component score and comprehensive score combined with the storage roots traits,three high-quality leaf species using sweet potato germplasm resources were screened,namely Wan 1314-6,18-2-57,15-12-2.Wan1314-6 blades have high content of phenols,strong antioxidant capacity,high protein content,green and tender blades,and could be used as excellent parents for the breeding leafy vegetable varieties and leaf feed varieties,its storage root starch content is 20.12%,and the anthocyanin content is 32.00mg/100 g,and the storage roots and vines can be concomitantly utilized.Although the content of phenolic substances in the blades of 18-2-57 is not too high,the comprehensive ability of the three antioxidant capacities is good,its starch content in storage roots is 24.14%,and the starch yield is high,the storage roots and vines can be concomitantly utilized,and could also be used as parents in starch variety breeding for screening new varieties with better comprehensive utilization of storage roots and vine.15-12-2 had the highest content of phenolic substances,but the antioxidant capacity was common,its content of three pigments in blades was high,and the starch content in storage roots was up to 28%,it could be crossbred with 18-2-57 to screen new varieties with better comprehensive utilization of storage roots and vines.4.Based on transcriptome sequencing,relevant genes that may affect the metabolism of phenolic substances in sweetpotato blades were obtained.In this study,transcriptome sequencing was performed on blades of two sweetpotato genotypes Wan1314-6 and Shangshu 19,and a large number of transcripts were obtained.Fifteen differentially expressed genes in the phenolic metabolism pathway of the two genotypes were screened out by analyzing the function of the differentially expressed genes.Among them,PAL,HCT,4CL involved in chlorogenic acid synthesis,CHI,CHS,F3’H involved in flavonoid synthesis,CCOAOMT,CAD,POD2,F5’H involved in lignin synthesis may be the key genes affecting the difference in phenolic content between the two genotypes,which explains the possible reasons for the difference in phenolic content between the two genotypes at the molecular level.In summary,firstly,this paper screened 32 representative genotypes in the preliminary test of the total polyphenol content of 86 genotypes of sweetpotato blades,and studied the phenol content,antioxidant capacity,blade color,photosynthetic pigment content,total protein content,antioxidant enzyme activity and the changes of these indicators during the growth period of Wan1314-6 and Shangshu 19.The results showed that sweetpotato blades were rich in phenols and had a significant positive correlation with antioxidant capacity,there is no contradiction between the breeding for improving phenol content and the breeding for high photosynthetic efficiency,high nutrient protein leafy vegetable varieties,and high protein feed varieties.Screening of three high-quality leaf-use sweetpotato germplasm resources by combining two years of experimental data.Secondly,transcriptome sequencing and preliminary analysis of two genotypes,Wan1314-6 and Shangshu19 with high and low phenolic content identified genes that may affect the phenolic metabolism in sweetpotato blades.The results of this study provide a reference for the selection and breeding of sweetpotato varieties with integrated use of storage roots and blades,and also lay a foundation for the future improvement of sweetpotato blade quality by genetic means. |
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