Potassium stimulates fruit sugar accumulation by increasing carbon flow in Citrus sinensis

Abstract

Soluble sugars contribute to the taste and flavor of citrus fruit. Potassium (K), known as a quality element, plays key roles in improving sugar accumulation and fruit quality, but the mechanism is largely unknown. This study aims to elucidate how K improves sugar accumulation by regulating carbon flow from source leaves to fruit in Newhall navel orange. We found that optimal fruit K concentrations around 1.5% improved sugar accumulation and fruit quality in citrus. K application increased the strength of both sink and source, as indicated by the increased fruit growth rate, enzyme activities and expression levels of key genes involved in sucrose (Suc) metabolism in fruit and leaf. K application also facilitated Suc transport from source leaves to fruit, as confirmed by the enhanced 13C-Suc level in fruit. Furthermore, we found that navel orange used the symplastic pathway for transporting Suc from source leaves to fruit, and K application enhanced symplastic loading, as demonstrated by the intensified carboxyfluorescein signal and increased plasmodesmata density in leaves. The findings reveal that K stimulates fruit sugar accumulation by increasing carbon flow from source leaves to fruit in Newhall navel orange.

Acknowledgements

This research was supported by the Fundamental Research Funds for the Central Universities (2662022ZHQD002), the National Natural Science Foundation of China (No. 32001986), the National Key Research and Development Program of China (2019YFD1000103), and the Modern Citrus Industry Technology System of China (CARS-26).

Author contributions

K.W.: investigation, methodology, data curation, visualization, writing original draft. C.H.: supervision, resources. P.L.: investigation. Y.H.: investigation. X.S.: writing - review and editing. Q.T.: data curation. Z.P.: writing - review and editing. S.X.: writing - review and editing. Z.D.: investigation. S.W.: funding acquisition, validation, resources, supervision, writing - review and editing.

Data availability statement

The data underlying this article are available in the article and in its online supplementary material.

Conflict of interest

The authors declare no competing interests.

Supplementary data

Supplementary data are available at Horticulture Research online.

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