Effects Of Potassium On The Synthesis And Accumulation Of Anthocyanins In Blueberry Frui

The blueberry is rich in anthocyanins.The process of anthocyanin synthesis is closely related to external environmental conditions.Potassium,as an activator of enzymes,is one of the environmental factors affecting anthocyanin biosynthesis.There have been few reports of transcription and anthocyanin metabolism in blueberries under different potassium conditions.In order to explore how potassium affects the synthesis and accumulation of anthocyanin in blueberry fruit.Therefore,in this paper,rabbiteye blueberry ’Powderblue’ was used as the research material,and three levels were set,namely 0g/plant(CK),10g/plant,and 40g/plant,respectively.Three levels of potassium fertilizer were applied at the three developmental stages of flowering stage(KH),young fruit stage(YG)and early fruit coloration stage(ZS).A total of seven treatments were set,namely(CK,KH-10,KH-40,YG-10,YG-40,ZS-10,ZS-40).The changes in anthocyanin content,related synthase activity,and physiological indices such as sugar and acid that cause changes in anthocyanin content in blueberries have been studied in different periods of treatment with potassium.Combined with transcriptome and metabolome correlation analysis,the key genes and key metabolites that promote anthocyanin synthesis in blueberry under potassium regulation were excavated.The main findings are as follows:(1)Potassium increased the single fruit weight of blueberry fruits,the activity of key enzymes in anthocyanin synthesis and the content of anthocyanin,and decreased the content of chlorophyll,carotenoid and titrable acid in ripe fruits.Moderate application of potassium is beneficial to increase the ratio of sugar to acid and improve fruit flavor.The single fruit weight of blueberry fruit was increased by potassium application,and the fruit was better at ripening,flowering and young fruit stage.The single fruit weight,longitudinal diameter and transverse diameter of blueberry fruit were increased by 22.54%-97.18%,5.47%-22.15% and 5.66%-27.10% compared with CK treatment,respectively.Potassium application significantly increased the activity of the key enzymes F3’5’H,F3’H,F3 H and PAL in the anthocyanin synthesis pathway in blueberries,and facilitated the synthesis and accumulation of anthocyanins.The anthocyanin content was increased by 2.28-5.57 times compared to CK.At the same time,the titratable acid content of the mature fruit is reduced,especially in the flowering and young fruit periods,with the titratable acid content of blueberry fruit decreasing by 33.33%-47.44% compared to CK.Moderate application of potassium is beneficial to sugar synthesis.The content of binding acid found that the ratio of sugar and acid in fruits treated with KH-10,YG-10 and ZS-10 was 200.12%,76.52%and 217.32% higher than CK,respectively.(2)Potassium application has been beneficial in the early synthesis of anthocyanins in blueberries,particularly in the young fruit stage.Potassium application promotes early color change in blueberries.Malvidin,petunidin and delphinidin were found to be higher than CK in fertility treatment,with levels ranging from 110.55 to 147.98 times,14.31 to 17.09 times and 4.96 to 13.82 times,respectively.YG-10 treatment significantly increased the synthesis and accumulation of Delphinidin-3-O-(6’’-O-p-coumaroyl)glucoside,peonidin-3-O-(6 "-O-p-coumaroyl)glucoside,petunidin-3-O-(6"-O-p-coumaroyl)glucoside,cyanidin-3-O-(6 "-O-coumaroyl)glucoside,cyanidin-3-O-(6 "-O-acetyl)glucoside and other anthocyanins,which were 2.79,2.59,2.39,2.91 and 2.18 times higher than KH-10,respectively.The synthesis and accumulation of malvidin,petunidin and delphinidin,is important in the deepening of early pigmentation during fertilization compared to CK.(3)Potassium Affects Anthocyanin Accumulation in Blueberry Fruit by Regulating the Expression Level of Related Structural Genes.Transcriptome sequencing was performed on fruit and CK treated at different periods of fertilization.From GO and KEGG enrichment analyses,102 genes related to sugar metabolism and 12 differential genes related to potassium transport were detected.It may be involved in the synthesis and accumulation of anthocyanins via potassium.In the anthocyanin synthesis pathway,13 genes from gene families related to anthocyanin synthesis were screened,including UGT75C1,F3 H,CHI,HCT,C12RT1,DFR,and F3’5’H,which are closely related to the production of flavonoids and anthocyanin metabolites under potassium regulation.The application of potassium fertilizer promoted the synthesis and accumulation of anthocyanin by promoting the expression of PAL,F3 ’ 5’H and F3H genes and the increase of enzyme activity.The application of potassium fertilizer at 10 g / plant in young fruit stage could not only greatly increase the content of anthocyanin,but also reduce the harm of superoxide anion free radical to fruit.The results preliminarily mastered the effect of potassium on pigment deposition and sugar level in blueberry fruit,revealed the mechanism of potassium on anthocyanin synthesis and accumulation,and provided a scientific basis for supplementing potassium fertilizer to improve fruit anthocyanin content.