| Sweet corn is rich in nutrients,such as vitamin E(VE),polyphenols,flavonoids and other phytochemicals,these substances have antioxidant,anti-cancer and other physiological activities.Besides sweet corn has abundant genetic var iation.However,there are few data on variation distribution,synthesis,accumulation and antioxidant activities of VE in sweet corn,same as the research of polyphenols and flavonoids in sweet corn.Therefore,in this paper,the sweet corn germplasm resources were used as the research object to study the variation of VE components,combined with whole genome association analysis(GWAS),which was conducted to screen the VE synthetic genes.In addition,the research on the dynamic changes of VE contents and synthesis during kernel development,as well as the phytochemicals and its antioxidant activities of different sweet corn materials were explored,in order to provide data support for breeding workers to cultivate the sweet corn varieties with high nutritional quality.The main research results of this topic are as follows:(1)The results of determination of grain vitamin E content in 176 and 190 sweet corn germplasm resources in 2015 and 2016 showed that there are 7 VE isomers in the sweet corn grain,of which 64% is ?-VE,28% is ?-VE,6.5% For ?-VE,1.5% of ?-VE.The two-year results all showed that the range of vitamin E content varies widely among the sweet corn materials.The total VE content varied from 2.43 to 75.45 ?g/g,FW in 2015,and the total VE content ranged from 7.2 to 37.75 ?g/g,FW in 2016.(2)Comparing the total VE content of sweet corn materials,it was found that there were 5 sweet corn materials with high content levels in two years of VE determination.In addition,the total VE content of 30 sweet corn materials was at a moderate level,but there was no significant difference in the two-year results,and further study on their genetic stability could be conducted.(3)Genome-wide association analysis of seven vitamin E compone nts in sweet corn grain using a SNP marker covering the entire genome was performed in 176 associated groups of in 2015 and 190 associated groups in 2016.The results showed that the candidate genes associated with vitamin E were associated only in 2016.The association results of ?-T showed that one candidate gene was detected with the function of ?-tocopherol methyltransferase gene(VTE4/?-TMT),which directly participate in VE synthesis.The correlation result of ?-tocopherrol indicated that two candidate might indirectly affect the synthesis of vitamin E.In addition,several SNP loci were detected in association with ?-tocotrienol(?-T3)and ?-tocotrienol(?-T3).One Candidate gene was found that may indirectly influence the synthesis of vitamin E in the association results of ?-tocotrienol.In the correlation with ?-tocotrienol,there was one candidate gene that affected the metabolism of phtyl diphosphate,thus affecting the content of vitamin E synthesis substrate.(4)The dynamic accumulation process of vitamin E content during the development of sweet corn grain found that the gene expression levels of vitamin E synthase HPT and TC increased during grain development,and the content of vitamin E components also continued increasing.The gene expression of ?-TMT gradually decreased and reached a stable stage of development.The changes of ?-tocotrienol/?-tocotrienol and ?-VE/?-VE ratio were consistent with the changes of ?-TMT expression.In addition,the lipid antioxidant activity of the kernel increased with kernel development.The results showed that the genes expression of vitamin E key synthetase affects the vitamin E components and their contents.The antioxidant activity in grains is related to the content of vitamin E.Considering the level of vitamin E and the taste,it is suggested sweet corn be harvested at the later stage of kernel development.(5)The contents of phytochemicals and their antioxidant activities in five sweet corns with different genotypes were compared.The results showed that the phytochemicals of sweet corn existed in the form of bound state,and the antioxidant activity of the bound substances was higher.The ferulic acid was the main phenolic compound in sweet corn,followed by gallic acid and p-coumaric acid,and the three substances mainly existed in the bound extracts,while chlorogenic acid and vanillic acid only existed in free form.The orange sweet corn with genotype SC-151 had the highest content of total phenols and total flavonoids,and had the highest total chemical antioxidant activity(PSC value).It can be used as a high quality sweet corn breeding material. |
PDF Full Text Request