Molecular Mechanism Of Sodium Selenite Affecting Nutritional Quality And Organic Selenium Content In Mustard

Mustard（Brassica juncea L.）originated in Asia and belongs to an annual herb of cruciferous family.It is planted in most parts of China and is an important oil crop and food crop.It is rich in a variety of proteins,vitamins,minerals and flavonoids,and has high nutritional value.At the same time,mustard also has a certain medicinal value,can clear heat and stop phlegm,cough and asthma.Selenium（Selenium）plays a vital role in plant growth.It can not only improve the germination rate and promote the growth and development,but also enhance the tolerance of plants to harsh environment and improve the fruit set rate of plants.In addition,selenium is also one of the important trace elements to maintain human life activities.It usually exists in the form of selenoprotein in the human body,which participates in various metabolism of the human body and plays a vital role in the growth and development of the human body.Cross plants have strong selenium-rich ability.By adding appropriate amount of selenium in the development of mustard,a new selenium-rich mustard has been cultivated,which can be used as a means of selenium supplement and effectively alleviate the selenium deficiency.In this experiment,we used Shandong Shouhe mustard seeds as experimental materials,added 0-40 mg/L（0,5,10,20,40 mg/L 5 concentration gradient）to the culture medium,harvested after 30 d,including physiological index,nutritional quality,antioxidant enzyme activity,total selenium content and selenium morphology.Transcriptome sequencing（RNA-Seq）was carried out for each treatment group,and these indicators were combined with weighted gene co-expression network analysis（WGCNA）with the data obtained by RNA-Seq,so as to study the growth status,nutritional quality,antioxidant enzyme activity and selenium transformation of mustard by Na₂SeO₃treatment,and explain the mechanism of mustard.The results of the study are as follows:1.The growth status of mustard at different Na₂SeO₃treatment concentrations showed relatively large differences,and the relevant physiological indicators were measured by harvesting 30 d after colonization.By comparing the germination rate,plant height,root length,biomass and photosynthetic pigment content of chlorophyll and carotenoids at 0-40 mg/L 5 treatment concentrations,it is found that the overall trend shows a trend of the first increase and then decrease,which reflects that the effect of selenium on plant growth is promoted at low concentration and suppressed at high concentration.Among them,mustard treated with 10 mg/L Na₂SeO₃had the best overall performance,with the optimal selenium concentration of 10 mg/L.In the leaves and roots of the control group,only two forms of selenium,Se（IV）and Se（VI）,were detected,while five forms of selenium were detected in the leaves and roots of the Na₂SeO₃treatment group.At the three concentrations,the selenium content in the leaves of mung bean sprouts was higher than that in the roots,indicating that the mung bean sprouts cultivated by soaking and hydroponics were mainly enriched in selenium in the leaves.Practicable.2.After examining the total selenium and selenium morphology in each treatment,the total selenium content increased with the concentration of Na₂SeO₃treatment,reaching the highest level at 40 mg/L treatment.In the control group,only two forms of Se（IV）and Se Met were detected,while the Na₂SeO₃treatment group detected Se Cys₂,Me Se Cys,Se（IV）,Se Met and Se（VI）,indicating the effectiveness of adding Na₂SeO₃to the mustard medium to bioenhance selenium-rich mustard.3.Respectively from vitamin C（Vc）,anthocyanins content,flavonoids,total phenol content,soluble sugar and soluble protein content of six aspects of mustard nutritional quality comprehensive assessment,the treatment group compared with the control group Vc and anthocyanins content have different degrees of improvement,and flavonoids content,total phenol content,soluble sugar content and soluble protein content is increased,but the overall trend is lower after the first rise.The change of these indicators indicates that the moderate amount of Na₂SeO₃can improve the nutritional quality of mustard vegetables.4.Through the detection of peroxidase,the activity of the peroxidase（POD）,superoxide dismutase（SOD）,and catalase（CAT）were all higher than the control group,while the content of malondialdehyde（MDA）was significantly lower than the control group,glutathione peroxidase（GSH）except the 40 mg/L Na₂SeO₃concentration was significantly higher than the control group,indicating that the low concentration of selenium can significantly improve the antioxidant enzyme activity of mustard.5.Differential gene analysis of 5 concentrations of 15 samples by RNA-Seq.WGCNA analysis of the transcriptomic data was combined with the analyzed morphological data,and the similar clusters were divided into 28 modules.Two modules,highly related to selenium metabolism,were selected,and GO and KEGG enrichment analysis was performed.A total of 60 key genes for the expression of selenium metabolism were selected from the two highly correlated modules for network visualization analysis.In general,this experiment explored the molecular mechanism of selenium enrichment in mustard,including the germination rate,plant height,root length,biomass,chlorophyll a,carotenoid,chlorophyll b,total chlorophyll,total selenium,vitamin C,Vc),anthocyanins,flavonoids,total phenol content,soluble sugars,MDA,GSH,SOD,POD,POD,CAT,and combined with RNA-Seq data by WGCNA analysis.