DataSheet_1_Sugar and acid profile of loquat (Eriobotrya japonica Lindl.), enzymes assay and expression profiling of their metabolism-related genes as influenced by exogenously applied boron.docx

Soluble sugars and organic acids are the most abundant components in ripe fruits, and they play critical roles in the development of fruit flavor and taste. Some loquat cultivars have high acid content which seriously affect the quality of fruit and reduce the value of commodity. Consequently, studying the physiological mechanism of sugar-acid metabolism in loquat can clarify the mechanism of their formation, accumulation and degradation in the fruit. Minerals application has been reported as a promising way to improve sugar-acid balance of the fruits. In this study, loquat trees were foliar sprayed with 0.1, 0.2 and 0.3% borax, and changes in soluble sugars and organic acids were recorded. The contents of soluble sugars and organic acids were determined using HPLC-RID and UPLC-MS, respectively. The activities of enzymes responsible for the metabolism of sugars and acids were quantified and expressions of related genes were determined using quantitative real-time PCR. The results revealed that 0.2% borax was a promising treatment among other B applications for the increased levels of soluble sugars and decreased acid contents in loquats. Correlation analysis showed that the enzymes i.e., SPS, SS, FK, and HK were may be involved in the regulation of fructose and glucose metabolism in the fruit pulp of loquat. While the activity of NADP-ME showed negative and NAD-MDH showed a positive correlation with malic acid content. Meanwhile, EjSPS1, EjSPS3, EjSS3, EjHK1, EjHK3, EjFK1, EjFK2, EjFK5, and EjFK6 may play an important role in soluble sugars metabolism in fruit pulp of loquat. Similarly, EjPEPC2, EjPEPC3, EjNAD-ME1, EjNAD-MDH1, EjNAD-MDH5-8, EjNAD-MDH10, and EjNAD-MDH13 may have a vital contribution to malic acid biosynthesis in loquat fruits. This study provides new insights for future elucidation of key mechanisms regulating soluble sugars and malic acid biosynthesis in loquats.

可溶性糖与有机酸是成熟果实中含量最为丰富的组分，对果实风味与口感的形成发挥关键作用。部分枇杷（loquat）品种有机酸含量过高，会严重降低果实品质与商品价值。因此，研究枇杷的糖酸代谢生理机制，有助于阐明其在果实中的形成、积累与降解规律。矿质元素施用已被证实是改善果实糖酸平衡的极具潜力的途径。
本研究对枇杷树叶面喷施0.1%、0.2%及0.3%浓度的硼砂（borax），并记录了果实中可溶性糖与有机酸的含量变化。分别采用高效液相色谱-示差折光检测法（HPLC-RID）与超高效液相色谱-质谱联用法（UPLC-MS）测定可溶性糖与有机酸的含量；对糖酸代谢相关酶的活性进行定量，并通过实时荧光定量PCR（quantitative real-time PCR）检测相关基因的表达水平。
结果显示，在所有硼处理组中，0.2%硼砂为最优处理，可显著提升枇杷果实的可溶性糖含量并降低有机酸积累量。相关性分析表明，蔗糖磷酸合酶（SPS）、蔗糖合酶（SS）、果糖激酶（FK）与己糖激酶（HK）可能参与调控枇杷果肉中果糖与葡萄糖的代谢过程。其中，烟酰胺腺嘌呤二核苷酸磷酸-苹果酸酶（NADP-ME）的活性与苹果酸含量呈负相关，而烟酰胺腺嘌呤二核苷酸-苹果酸脱氢酶（NAD-MDH）的活性则与苹果酸含量呈正相关。
同时，EjSPS1、EjSPS3、EjSS3、EjHK1、EjHK3、EjFK1、EjFK2、EjFK5及EjFK6可能在枇杷果肉可溶性糖代谢中发挥重要作用。类似地，EjPEPC2、EjPEPC3、EjNAD-ME1、EjNAD-MDH1、EjNAD-MDH5-8、EjNAD-MDH10及EjNAD-MDH13可能对枇杷果实苹果酸的生物合成具有关键贡献。
本研究为未来阐明枇杷可溶性糖与苹果酸生物合成的关键调控机制提供了新的研究视角。