| Barley(Hordeum vulgare L.var.nudum Hook.f.)is a special crop of the Qinghai-Tibetan plateau region,with a unique nutritional composition that meets the dietary requirements of "three highs and two lows",and is rich in B vitamins and mineral elements.The nutritional value of darker barley is generally higher than that of lighter barley.However,the hardness of barley seeds,their coarse texture and low digestibility severely restrict their application in the food industry.Research has found that sprouting can improve and enhance the structure and nutritional properties of cereals.Proper sprouting treatment not only improves the nutritional value of cereals,but also makes it easier for the human body to absorb and utilise macromolecular nutrients such as protein,starch and fat,while increasing the content of active substances beneficial to the human body.Therefore,the germination treatment of barley,the detection of the nutritional components of barley at different stages of germination,and the use of multi-omics techniques to comprehensively and thoroughly investigate the molecular mechanisms of the changes in nutritional components during germination can provide a theoretical basis for the further development and utilisation of germinated barley products.The main results of the study are as follows:Firstly,Longzi Black Barley(Longzi Black Barley,LBB)was selected for germination treatment and the nutrient composition of the germination stages was compared.The results showed that the growth rate of LBB was slow in the early stages of germination(0～12 h),followed by sustained growth in the middle(12～36 h)and late(36～60 h)stages of germination,with shoot length reaching 10.18-19.14 mm at the seedling stage(60～72 h).100 grain weight(dry weight)of LBB decreased slightly during germination,with a significant difference after 48 h of germination.Nutrient measurements showed that water content increased sharply in the early stages of germination due to swelling,and then increased at a relatively constant rate;starch and crude fat content decreased continuously with germination time;protein content decreased from 0 to 24 h and then increased continuously;soluble and reducing sugars decreased in the early stages of germination and increased continuously in the middle and late stages.Total phenols and total flavonoids in LBB were 18.60 μmol/g and 2.65 mg/g,respectively,both of which decreased sharply from0～12 h and then stabilised before accumulating again after the formation of seedlings(72 h).The overall trend of antioxidant activity of LBB decreased during the germination process.Transcriptome sequencing and gene expression quantification were performed for LBB at four different germination times based on de novo sequencing.A total of39,038 genes were sequenced and annotated,of which 14,451 were common to the four periods,while 322(0 h),288(12 h),470(36 h)and 1,297(60 h)were expressed genes unique to each period.Quantitative comparisons showed that 11 188 differentially expressed genes(DEGs,|log2FC| ≥ 1,p < 0.05)were the most abundant at mid-emergence(LBB-36/LBB-12);the DEGs were mainly involved in the ’metabolic’-related KEGG pathway and were predominantly up-regulated;representative DEGs were mainly involved in KEGG pathways related to "metabolism" and were predominantly up-regulated;representative pathways included: "carbohydrate metabolism","amino acid metabolism" and "biosynthesis of other secondary metabolites".The KEGG enrichment analysis was performed on all the DEGs screened,and the representative enrichment pathways included: "starch and sucrose metabolism","glutathione metabolism","phenyl propane biosynthesis ",and "flavonoid biosynthesis",and were predominantly up-regulated,indicating that these pathways are continuously regulated during LBB germination.The metabolic pathways that were significantly regulated during LBB germination were further validated by metabolomic analysis.A total of 1,015 metabolites were identified in LBB samples from three periods(0,12 and 60 h),of which 551 metabolites showed significant changes in abundance during germination,with "flavonoids","phenolic acids","amino acids and their derivatives" and "alkaloids" as the main metabolites,The abundance of 551 metabolites changed significantly during germination,with "flavonoids","phenolic acids","amino acids and their derivatives" and "alkaloids" as the main metabolites.Compared with the pre-emergence period(LBB-0),the total abundance of flavonoids continued to decrease,the total abundance of amino acids and their derivatives continued to increase significantly,and the total abundance of alkaloids increased significantly in the later stages of germination.Integration of transcriptomic and metabolomic data revealed that protein catabolism was stronger in the early stages of germination(0-12h),while anabolic activity was stronger in the later stages(12-60 h);lipid hydrolysis was significantly enhanced;substance and energy metabolism was strong;and the synthesis of antioxidants and the breakdown of peroxides were enhanced.In this study,the trends of nutrient components and metabolites in the germination process of LBB were systematically analyzed with the aid of high-throughput histological analysis,and the regulation and metabolism of flavonoid and phenolic acid metabolites in the germination process of LBB were preliminarily investigated.The results of the study provide key information on the molecular mechanisms of nutritional quality changes during barley germination,and also provide basic information for the development of new products of germinating barley,which is of great scientific significance and practical application. |
