Investigation of the cause of reduced sugar content in Kiyomi tangor fruit of Ziyang xiangcheng (Citrus junos Sieb. ex Tanaka) rootstock

Tiantian Dong,Xiaojia Wang,Shengjia Huang,Xia Qiu,Guochao Sun,Changwen Duan,Jin Zhu,Zhihui Wang,Yunzhenzi He,Xu Zhang,Ling Liao,Bo Xiong,Sichen Li

doi:10.1038/s41598-019-55957-3

Abstract

Ziyang xiangcheng (Citrus junos Sieb. ex Tanaka) (Cj) rootstock is effective in Citrus production; however, when Cj rootstock was used, sugar content in Kiyomi tangor fruit was significantly lower than that in the fruit produced using Poncirus trifoliata (L.) Raf. rootstock (Pt). Therefore, using K. tangor, we explored the cause of this difference, determining sugar accumulation, sucrose-metabolism enzyme activities, and gene expression. Before ripening, sugar content in fruits with Cj rootstock was significantly lower than that in fruits with Pt rootstock, due to low fructose and sucrose content. Sucrose phosphate synthase (SPS) activity of Pt was higher than that of Cj in the early growth stage (at 90–210 days after anthesis), however it was opposite at 240–300 days after anthesis. Additionally, neutral invertase (NI) activity of Pt was higher than that of Cj. Gene expression in Pt was higher than that in Cj, but is was essentially the same at maturity. SPS and NI activities and CitSPS1 expression were positively correlated with sucrose, fructose, and glucose content, but CSCW1 expression was negatively correlated with the sugars. Overall, the weak flavour of K. tangor fruit with Cj rootstock was regulated by the sucrose metabolism-related enzymes and gene expression.

Highlights

Citrus is a commercially important genus of the Rutaceae family and comprises fruit species that are cultivated globally[1,2]
The results showed that the sugars in K. tangor fruit mainly consist of the accumulated sucrose type and that the sucrose content was more than two times higher than the fructose and glucose content in the later stage of fruit development
We optimised the high-performance liquid chromatography (HPLC) method for the determination of sugar components in Citrus, and the Innoval NH2 column used in this analysis has higher application value

Summary

Introduction

Citrus is a commercially important genus of the Rutaceae family and comprises fruit species that are cultivated globally[1,2]. Sugar, which is mainly in the form of sucrose, fructose, and glucose, plays an key role in the quality and flavour, and the differences in sugar content determine the sweetness and colour of fruit[14,15]. INVs is important for carbohydrate supply to sink tissues; they play a key role in regulating, amplifying, and integrating different signals, which leads to the transportation of the end product of photosynthesis from source to sink[22,24]. Several studies have reported the correlation between sugar content and metabolism enzyme activity in mature fruit and that sucrose-metabolism enzymes play an important role in sugar metabolism[28,29]

Methods

Results

Conclusion