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, enzymes 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 symplastic pathway for transporting Suc from source leaves to fruits, and K application enhanced symplastic loading, as demonstrated by the intensified CF 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.

中文翻译：

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钾通过增加柑橘的碳流量来刺激果实糖的积累


可溶性糖有助于柑橘类水果的味道和风味。钾（K）被称为品质元素，在改善糖分积累和果实品质方面发挥着关键作用，但其机制尚不清楚。本研究旨在阐明钾如何通过调节纽荷尔脐橙从源叶到果实的碳流来改善糖积累。我们发现，最佳果实钾浓度约为 1.5%，可改善柑橘的糖积累和果实品质。施钾增强了库和源的强度，果实生长速率、酶活性以及果实和叶子中参与蔗糖（Suc）代谢的关键基因的表达水平的提高表明了这一点。施用钾还促进 Suc 从源叶到果实的转运，果实中 13C-Suc 水平的提高证实了这一点。此外，我们发现脐橙利用共生途径将 Suc 从源叶运输到果实，并且钾的施用增强了共生负荷，如叶子中 CF 信号增强和胞间连丝密度增加所证明的那样。研究结果表明，在纽荷尔脐橙中，钾通过增加从源叶到果实的碳流来刺激果实糖的积累。