Table_2_Transcriptome analysis of sugar and acid metabolism in young tomato fruits under high temperature and nitrogen fertilizer influence.xlsx

IntroductionEnvironmental temperature and nitrogen (N) fertilizer are two important factors affecting the sugar and organic acid content of tomato fruit. N is an essential nutrient element for plant growth and development, and plays a key role in regulating plant growth, fruit quality and stress response. However, the comparative effect of different N fertilizer levels on the accumulation of soluble sugar and organic acid in tomato young fruit under high temperature stress and its mechanism are still unknown.
MethodsThree N fertilizer levels (N1, N2, N3) combined with two temperatures (28/18°C, CK; 35/25°C, HT) were used to study the effects of N fertilizer, HT and their interaction on the soluble sugar and organic acid components, content, metabolic enzyme activity and the expression level of key genes in tomato young fruit, revealing how N fertilizer affects the sugar and organic acid metabolism of tomato young fruit under HT at physiological and molecular levels.
ResultsThe content of soluble sugar and organic acid in tomato young fruit under HT exposure was increased by appropriate N fertilizer (N1) treatment, which was due to the accumulation of glucose, fructose, citric acid and malic acid. High N (N3) and HT exposure had a negative impact on soluble sugar and reduce sugar accumulation. Further studies showed that due to the up-regulation of the expression of sucrose metabolizing enzyme genes (CWINV2, HK2, SPS, PK) and sucrose transporter (SUT1, SUT4, SWEETs) in tomato, N fertilizer increased the accumulation of soluble sugar by improving the sucrose metabolism, absorption intensity and sucrose transport of fruit under HT exposure. Due to the increase of PEPC gene expression, N fertilizer increased the accumulation of citric acid and malic acid by improving the TCA cycle of fruit under HT exposure.
DiscussionNitrogen fertilizer can improve the heat tolerance of tomato young fruits by improving sugar metabolism under HT exposure. The results can provide theoretical support for the correct application of N fertilizer to improve the quality of tomato fruit under HT exposure.

引言：环境温度与氮肥（nitrogen fertilizer）是影响番茄果实糖与有机酸含量的两大关键因素。氮是植物生长发育不可或缺的营养元素，在调控植物生长、果实品质及胁迫响应过程中发挥核心作用。然而，高温胁迫下不同氮肥水平对番茄幼果可溶性糖与有机酸积累的调控效应及其内在机制，目前仍未明晰。

方法：设置3个氮肥梯度（N1、N2、N3），并结合2个温度处理（28/18℃，对照（CK）；35/25℃，高温胁迫（HT）），以此探究氮肥、高温胁迫（HT）及其交互作用对番茄幼果可溶性糖与有机酸组分、含量、代谢酶活性及关键基因表达水平的影响，从生理与分子层面揭示高温胁迫下氮肥调控番茄幼果糖与有机酸代谢的具体机制。

结果：适宜浓度的氮肥（N1）处理可提升高温胁迫下番茄幼果的可溶性糖与有机酸总含量，该效应源于葡萄糖、果糖、柠檬酸及苹果酸的积累。高氮肥（N3）与高温胁迫处理则会抑制可溶性糖与还原糖的积累。进一步研究发现，高温胁迫下，氮肥可通过上调番茄蔗糖代谢酶基因（CWINV2、HK2、SPS、PK）与蔗糖转运蛋白（SUT1、SUT4、SWEETs）的表达水平，改善果实的蔗糖代谢能力、养分吸收强度与蔗糖转运效率，进而促进可溶性糖的积累。此外，因PEPC基因表达量上调，氮肥可通过提升高温胁迫下果实的三羧酸循环（tricarboxylic acid cycle，TCA）效率，促进柠檬酸与苹果酸的积累。

讨论：高温胁迫下，氮肥可通过调控糖代谢过程提升番茄幼果的耐热性。本研究结果可为高温胁迫下合理施用氮肥以改善番茄果实品质提供理论支撑。