柠檬酸对脐橙缺硼胁迫的响应机制及其在中心代谢途径中的调控作用

Boron (B) deficiency is one of the prominent problems of tree malnutrition in the main producing areas of navel orange, and metabolism is the basis of plant growth and development. The concentrations of citric acid in leaves of navel orange with different degree of B deficiency were significantly decreased, while the changes in carbohydrate and nitrogen metabolism showed differences. Citric acid is key substance in the association of carbon and nitrogen metabolism, which may be a key factor in the regulation of carbon and nitrogen metabolism under B deficiency. However, the response mechanism of citric acid to boron deficiency and its regulation in central metabolism have not been reported. In this study, we are to analyze the dynamic relationship between the organic acid and the key carbon and nitrogen related metabolites under B deficiency, and to determine the activity of citrate metabolism related enzymes and the expression of key genes in citrate synthesis and degradation. On the basis of clarifying the response mechanism of citric acid to B deficiency, we are further to analyze the changes in the overall metabolic profile of the leaves of navel orange plants to reveal the role of citric acid in regulating the global metabolism, through exogenous citric acid combined with metabolomics technology. Finally, the effects of exogenous citric acid on the yield and quality of navel orange are to be studied by field experiment. This study is of great significance to understand the physiological response mechanism under B deficiency from the perspective of global metabolism, and it also provides theoretical basis for the application of corresponding cultivation measures on B deficiency soil. Therefore, this project has important theoretical and potential application value.

缺硼是脐橙主产区树体营养失调的突出问题之一，而代谢是植物生长发育的基础。申请者前期研究发现不同缺硼程度的脐橙叶片中柠檬酸含量均显著降低，而碳水化合物及氮代谢的变化则表现出差异，柠檬酸是联系碳氮代谢的关键物质，可能是缺硼条件下调控碳氮代谢的关键因子，但柠檬酸对缺硼的响应机制及其在中心代谢中的调控作用尚未见报道。本项目首先分析缺硼后硼和有机酸与关键碳氮代谢物的动态变化关系，并测定柠檬酸代谢相关酶活性及柠檬酸合成与降解关键基因的表达变化，在明确柠檬酸对缺硼的响应机制基础上，通过外源补充柠檬酸结合代谢组学技术，分析脐橙叶片整体代谢谱的变化，揭示柠檬酸在调控整体代谢中的作用；最后通过大田试验探究缺硼条件下外源施用柠檬酸对脐橙产量和品质的影响。本研究对从整体代谢角度理解缺硼后的生理响应机制具有重要意义，也为缺硼土壤上相应栽培措施的应用提供理论依据，因而具有重要的理论和潜在应用价值。

缺硼是脐橙主产区树体营养失调的突出问题之一，而代谢是植物生长发育的基础。申请者前期研究发现不同缺硼程度的脐橙叶片中柠檬酸含量均显著降低，而碳水化合物及氮代谢的变化则表现出差异，柠檬酸是联系碳氮代谢的关键物质，可能是缺硼条件下调控碳氮代谢的关键因子，但柠檬酸对缺硼的响应机制及其在中心代谢中的调控作用尚未见报道。本项目分析了缺硼后硼和有机酸的动态变化，并测定了柠檬酸代谢相关酶活性，在明确柠檬酸对缺硼的响应机制基础上，通过外源补充柠檬酸结合代谢组学技术，分析脐橙叶片整体代谢谱的变化，结果如下：1）短期缺硼脐橙叶片ACO酶活性与对照处理相比显著增加，而与柠檬酸合成相关的PEPC与CS的酶活性无显著变化，说明短期缺硼柠檬酸含量的下降主要是由于柠檬酸的降解增加引起的；2）长期缺硼脐橙叶片CS、PEPC和NADP-IDH酶活性均显著增加，ACO酶活性无明显变化，说明长期缺硼柠檬酸含量的上升主要是由于柠檬酸的合成增加引起的；3）正常和缺硼条件下外源柠檬酸均提高脐橙叶片柠檬酸含量，但PEPC酶活性的变化趋势相反，说明不同硼供应条件下外源柠檬酸可以调控PEPC活性；4）在营养液缺硼和正常供硼条件下外源喷施柠檬酸对叶片代谢产物和代谢通路的影响存在明显差异；5）缺硼胁迫的脐橙叶片代谢谱发生显著改变，喷施硼酸可以逆转由缺硼引起的叶片大部分代谢产物的改变，在代谢物水平上解释了缺硼后供硼对植物生长缓解作用的生理机制；6）缺硼条件下外源喷施柠檬酸也逆转了大部分由缺硼引起的代谢物变化，且与缺硼后喷施硼酸使代谢物恢复的效果类似。上述结果说明缺硼引起的代谢物变化有很大一部分可能是由于缺硼条件下柠檬酸含量下降而导致的，因此缺硼后喷施柠檬酸使很多代谢物恢复到正常水平。通过本项目的研究基本阐明了柠檬酸对缺硼的响应机制，明确了柠檬酸对不同硼水平代谢的调控作用。