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：

---

钾通过增加柑橘中的碳流动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） 被称为优质元素，在改善糖分积累和果实品质方面起着关键作用，但其机制在很大程度上是未知的。本研究旨在阐明 K 如何通过调节纽霍尔脐橙从源叶到果实的碳流来改善糖积累。我们发现，1.5% 左右的最佳水果 K 浓度改善了柑橘的糖积累和果实品质。施用钾肥增加了汇和源的强度，这从果实和叶片中参与蔗糖 （Suc） 代谢的关键基因的生长速率、酶活性和表达水平增加可以看出。施用钾肥还促进了 Suc 从源叶到果实的运输，果实中 13C-Suc 水平的增强证实了这一点。此外，我们发现脐橙使用共塑途径将 Suc 从源叶运输到果实，而 K 应用增强了共塑负载，增强的 CF 信号和叶片中胞间连丝密度的增加证明了这一点。研究结果表明，在纽霍尔脐橙中，K 通过增加从源叶到果实的碳流来刺激果实糖的积累。