Potassium stimulates fruit sugar accumulation by increasing carbon flow in Citrus

Abstract

Soluble sugar is a key factor of flavor quality in citrus. Potassium (K) is known as a quality element, which plays key roles in improving sugar accumulation and fruit quality, but the mechanisms are largely unknown. This study aims to elucidate how K improves sugar accumulation by regulating carbon flow between source and sink in Newhall navel orange (Citrus sinensis). The results demonstrated that appropriate K concentration improved fruit quality and sugar accumulations in citrus, and 1.5% of K concentration in pulp was the optimal concentration for fruit quality. K increased strength of sink and source, as supported by the increased fruit growth rate, gene expressions related to sugar metabolism and sugar transport in fruit, and photosynthesis, gene expressions of sugar metabolism in leaf, respectively, which contributed to increasing sugars accumulation. Further study indicated that K improved carbon flow from source to sink by boosting symplastic and apoplastic loading of phloem, as supported by the increased CF signal intensities, plasmodesmata densities, and the expressions ofCsSUT1andCsSUT2in leaf at early and mid stages of fruit development, finally increasing sugar accumulation in fruit. Conclusively, K stimulates fruit sugar accumulation by increasing carbon flow in Newhall navel orange.HighlightK application stimulated carbon flow between source and sink through symplastic and apoplastic loading, which were supported by the structural characteristics of phloem and the expression ofCsSUTsandCsSWEETs, ultimately promoting sugar accumulation inCitrus sinensis.

The Fertility Assessment of some Citrus Orchards in the District of Baquba

“…Through Table (9), the statistical analysis results indicate significant differences between the mean values of available potassium among the orchards in Al-Hawidr and Khan al-Walawa, with these orchards outperforming the one in Bahriz. As for the statistical analysis results between the depths' means, it showed the superiority of the first depth over the other depths.…”

“…Although Iraqi soil contains a large reservoir of potassium, it is not effectively utilized due to its slow decomposition and the limited yield that does not meet the plant's needs, especially in dense agriculture [ 8 ] . [ 9 ] found that potassium participates in many physiological processes, including regulating photosynthetic processes, improving nutrient transportation, activating carbohydrate production processes, maintaining cytoplasmic pH balance, and increasing soluble sugar accumulation in citrus fruits by facilitating nutrient transportation and carbohydrate distribution. Potassium is considered a major and essential nutrient for completing the growth process in plants.…”