| Lycium L.is a perennial deciduous shrub of the genus Lycium in the Solanaceae family.It is usually an indefinite inflorescence plant with cross-pollination and can continuously blossom and bear fruit during the annual growth period.Due to the long flowering and fruiting periods of wolfberry,the fruits can ripen successively and be harvested commercially within a few weeks.Therefore,the phytochemical composition of L.barbarum fruits may change during the process of harvesting at different periods.In this study,ripe fruits of 10-year-old Ningxia L.barbarum ’Ningqi 1’ harvested at four different periods were used as experimental materials.The appearance quality and nutritional quality of L.barbarum fruits at four different harvesting periods were determined and analyzed,and transcriptome sequencing and untargeted metabolomics analysis were performed.To explore the quality differences of wolfberry fruits at four different harvesting periods from the physiological,biochemical,transcriptional and metabolic levels.The main findings are as follows:(1)The wolfberry fruits harvested on June 22 at the beginning of harvesting season had better appearance quality.The maximum longitudinal diameter and single fruit surface area of wolfberry fruit harvested on June 22 were 18.04 mm and 17.31 cm2,respectively,which were significantly higher than those harvested in the other three periods.The wolfberry fruits harvested on June 22 had the highest 100-grain fresh weight and 100-grain dry weight of 72.93 g and 17.31 g,respectively,which were higher than those harvested in the other three periods.The minimum dry fruit particle size of wolfberry fruits harvested on June 22 was 298 grains/50g,which was significantly lower than the fruits harvested in the other three periods.The transverse diameter of wolfberry fruits harvested on June 22 was 9.15 mm,second only to the wolfberries harvested on September 20.The comprehensive research results indicate that the appearance quality of wolfberries harvested on June 22 was generally good.(2)The wolfberry fruits harvested at the end of harvesting season on September 20 had relatively good nutritional quality.The wolfberry fruits harvested on September 20 had the highest contents of polysaccharides,total phenols,total amino acids and soluble protein with 48.79 mg/g,14.42 mg/g,8.38 mg/g and 13.51 g/100g,respectively,which were significantly higher than those harvested in the other three periods.The highest content of total soluble solid in the wolfberry fruits harvested on September 20 was 24.56%,which was higher than the fruits harvested in the other three periods.On the contrary,the lowest total acid content was 0.67%,which was significantly lower than the fruit harvested in the other three periods.The total sugar content of wolfberry fruits harvested on September 20 was 168.78 mg/g,second only to the berries harvested on June 22(174.25 mg/g).The highest contents of total flavonoids and carotenoids in wolfberry fruits harvested on June 22 were 14.46 mg/g and 18.45 mg/100g,with significant differences in total flavonoids content compared to the other three periods.The wolfberry fruits harvested on July 5 had the highest vitamin C content of 24.94 mg/100g,followed by the fruits harvested on July 18(23.66 mg/100g).The fruit harvested on September 20 exhibited abundant amino acids and proteins,high sugar and low acidity,and relatively sweet taste.(3)Differentially expressed genes in ripe wolfberry fruits at four different time periods were mainly involved in lipid,carbohydrate and amino acid metabolism.SAD,MFP,ACSL and FAD2 genes were differentially expressed in fruits at four different harvesting periods and played an important role in regulating the accumulation of fatty acids and unsaturated fatty acids in fruits at different harvesting periods.FRK and SUS showed high transcript levels in fruits harvested on September 20 and promoted the metabolism and accumulation of sugars in fruits harvested on September 20.The BAM1 gene was significantly up-regulated in the fruit harvested on June 22,which contributed to the accumulation of higher sugar content in the fruit.The differential expression of NAS,GOGAT and PAL in fruits at different harvesting periods played an important role in regulating the accumulation of nicotinamide,glutamate and phenylpropanoids in fruits.(4)The accumulation levels of metabolites in mature wolfberry fruits harvested at four different periods were significantly different.The KEGG enrichment analysis showed that the differential metabolites in the fruit of the four harvest periods were significantly enriched in Dglutamine and D-glutamate metabolism as well as ascorbic acid and aldose metabolism pathways.The clustering heat map results showed that the abundance and accumulation of metabolites in the fruit harvested on July 5,July 18 and September 20 were significantly better than those harvested on June 22,with ascorbic acid and glutamic acid accumulating in the mature L.barbarum fruit of the four different harvesting periods,with ascorbic acid accumulating at higher levels in the fruit harvested on July 5 and July 18,and glutamic acid accumulating at higher levels in the fruit harvested on July 5,July 18 and September 20,The accumulation of ascorbic acid was higher in fruits harvested on July 5 and July 18,while glutamic acid was higher in fruits harvested on July 5,July 18 and September 20 than in fruits harvested on June 22.The differential accumulation of ascorbic acid and glutamic acid in ripe wolfberry fruits at different harvesting dates played an important role in the formation of fruit quality.(5)The combined metabolomics and transcriptomics analysis showed a high proportion of differential genes involved in the phenylpropane metabolism,ascorbic acid and succinic acid metabolism pathways.PAL,C4H,4CL,HCT and COMT genes in the phenol propane metabolic pathway were differentially expressed in four different harvesting stages of wolfberry fruits,directly or indirectly regulating the accumulation of p-coumaric acid,chlorogenic acid,ferulic acid and erucic acid in fruits.The expression patterns of PMI,APX1-like,APX1,APX6 and MHDAR in the ascorbic acid metabolic pathway were consistent with the accumulation trends of ascorbic acid in mature wolfberry fruits at four different harvesting stages.The differential expression of SCS,GOGAT and GS genes in the succinate metabolic pathway in four different harvest stages of wolfberry fruits played an important role in regulating the differential accumulation of succinate,glutamate and glutamine in the fruits. |
