Nutrientional compound changes in fruits of 2 mulberries (Morus alba) varieties at different development stages

Abstract: 【Objective】The study aimed to understand the dynamic changes in the composition and accumulation of nutritional compounds during fruit development and maturation in mulberry (Morus alba L.).【Methods】In this study, the fresh weight of mulberry was measured, the fruit hardness was measured by osmometer, the soluble solid content was measured by portable sugar meter, and the titratable acid content was determined by NaOH titration, the content of total flavonoids was determined by NaNO2-Al (NO3)3 colorimetry, the content of total phenols was determined by Hungarian forint-phenol colorimetry, and the contents of soluble sugars and organic acids were determined by gas chromatographytandem mass spectrometry, qRT-PCR was used to analyze the expression of the genes related to sugar synthesis.【Results】The content of soluble solids in Anshen and Guihua increased with fruit develop-ment and ripening. There was no significant difference in the soluble solid content between Anshen and Guihua at the initial stage of fruit development, but the soluble solid content of Guihua was significantly higher than that of Anshen at the mature stage. The content of titratable acid decreased with the fruit development. At the mature stage, the titratable acid content of Anshen was significantly higher than that of Guihua. The total flavonoids and total phenolics content increased slowly in the early stage of fruit development, and there was no significant difference in total flavonoids and total phenolics content between Anshen and Guihua. After 20 days of development, the total flavonoids and total phenols content of Guihua gradually decreased, and the total flavonoids and total phenols content of mulberry increased significantly. During fruit development, the total flavonoids and phenols content of Guihua were lower than thaose of mulberry. In addition, the sucrose content of Guihua fruit, increased continuously with the fruit development, the sugar content of Anshen decreased in the early fruit development, showed an increasing trend after 30 DPA. The content of glucose and fructose increased gradually during the whole fruit development and ripening, and the content of glucose and fructose of Guihua was higher than those of Anshen, but the content of glucose and fructose of Guihua was higher than those of Anshen on 50 DAP, the fructose content of Anshen was higher than that in Guihua, and the difference was significant. Compared with the content of glucose and fructose, the accumulation level of sucrose was the lowest in the Anshen fruits. The malic acid content increased slowly in 2 cultivars, but the accumulation of malic acid in Guihua decreased after 30 DAP. The succinic acid content increased at first and then decreased during fruit development, and reached its peak on 30 DAP. The tartaric acid content showed a slow decline trend in 2 varieties, and it increased on 20 DAP in Anshen, and increased on 40 DAP in Guihua. With the development of fruit, the ratio of sugar to acid of the two varieties increased gradually, with a range of 7.99 to 81.06, and reached the maximum value at the mature stage (50 DAP), the ratio of Anshen was 81.06%, the ratio of Guihua was 57.17%, and Anshen sugar-acid ratio is greater than Guihua in each different development period. The expression analysis of the genes related to the sucrose metabolism showed that the expression of the neutral invertase 1 (INV1) gene increased with fruit development, while the highest level was reached on 30 DPA and then decreased on 40 DPA in Guihua. The expression level of the sucrose-phosphatase (SPP) gene in Guihua was significantly higher than that in Anshen. The sucrose synthase 1 (SUS1) gene was increased in both cultivars, while the sucrose synthase 2 (SUS2) gene was decreased on 30 and 50 DPA, the expression level of this gene in Guihua was higher at these two time points, and the expression trend of these sucrose metabolism related enzymes was consistent with the change of soluble sugar.【Conclusion】The phenotype and nutrition of mulberry changed with fruit development. Under the growing conditions in Chengde, Hebei province, the sugar, malic acid and soluble solid contents of Guihua fruits were higher than those of Anshen, the content of total flavone, total phenol and titratable acid of Anshen fruit was higher than those of Guihua, and the ripening time of Guihua fruit was about 10 days earlier than Anshen. In addition, the neutral invertase 1, sucrose phosphatase and sucrose synthase 2 could be used as candidate genes to regulate the sugar content of mulberry. The results of this study would provide information for the study of mulberry resources, and lay a foundation for the study of quality formation of mulberry fruits.