基于碳氮代谢的硅诱导旱盐逆境下甘草中甘草酸积累的机制

Glycyrrhiza uralensis Fisch. the first medicinal plants, was, is and will be widely used in traditional Chinese medicine. The present market is flooded with G. uralensis of artificial cultivation. However, many studies showed that the quality of cultivated G. uralensis was far below wild G. uralensis. Thus, improving the quality of cultivated G. uralensis has become the key and ultimate potential to meet the market demand and ensure the sustainable utilization of G. uralensis resources. Previous experiments have shown that Si increased the content of glycyrrhizic acid by regulating the primary metabolism of G. uralensis. Silicon (Si), an environment friendly element, has more than important effect on plant growth and development. Therefore, the present project aims to study the silicon-induced mechanism of glycyrrhizic acid accumulation in Glycyrrhiza uralensis under salt and drought stresses based on carbon and nitrogen metabolism. In this project, sand culture experiments were conducted to study the effect of Si on carbon and nitrogen metabolism of G. uralensis under drought and salt stresses, determine the response of carbon and nitrogen metabolism on Si by focusing on carbon and nitrogen metabolites, related enzyme species and its laws，and key genes expressions. In addition, this study is conducted to determine regulation of Si on glycyrrhizic acid accumulation and biosynthesis process under drought and salt stresses by focusing on biosynthesis starting materials, intermediates, enzymes and others of glycyrrhizic acid. Given the above, the effects and mechanisms of Si on the synthesis and accumulation of glycyrrhizic acid and carbon and nitrogen metabolism is resolved by correlation, path and other analysis methods. In this way, a deep theoretical basis on achieving the high quality and yield of G. uralensis cultivation under salinized soil in arid and semi-arid region will not a question of if, but when.

提高栽培甘草质量是满足市场需求和保证甘草资源可持续利用的关键和最终潜力所在。前期研究表明旱盐逆境下外源硅通过调控甘草初生代谢进而促进甘草酸积累。本项目拟通过盆栽试验，研究旱盐逆境下甘草碳氮代谢物、相关酶活性、关键基因表达、代谢平衡对硅响应的趋同和分异，明确硅参与碳氮代谢中的哪部分关键代谢途径以及限制这些途径的关键因素，揭示旱盐逆境下碳氮代谢对硅调控的响应机制；研究旱盐逆境下甘草酸及其生物合成起始物质、中间产物、关键酶基因表达对硅响应的趋同和分异，明确甘草酸生物合成和积累对硅调控的响应规律，揭示硅对甘草酸的调控作用是直接、间接或是二者兼有；采用主成分、相关、通径等方法解析对硅反应敏感的碳氮代谢物、相关酶及关键基因对甘草酸合成与积累的直接和间接作用效应及其机制，从生理和分子层面阐明基于碳氮代谢的硅调控旱盐逆境下甘草酸合成和积累的机制，为实现干旱半干旱区盐渍化土壤甘草高产优质栽培提供理论依据。

本项目采用室内沙培盆栽试验，以甘草幼苗为材料，从生理生化、转录组层面研究Si对旱盐双重胁迫下甘草碳氮代谢、生长、主要药效成分含量及甘草酸和甘草苷合成相关酶基因表达的调控效应，进一步揭示基于碳氮代谢的Si促进旱盐逆境下甘草生长及主要活性成分积累的机制，为实现干旱半干旱区盐渍化土壤甘草高产优质栽培提供理论依据。主要研究结论如下：.1、碳氮代谢：（1）Si显著缓解了旱盐胁迫对甘草幼苗GADPH和FDA酶活性的抑制作用，加速了磷酸丙糖的合成和RUBP的再生，促进了光合作用；但减少磷酸丙糖的输出，最终通过降低总活化Rubisco影响了Rubisco酶的活性。Si抑制地上部EMP途径、促进TCA循环，诱导无氧呼吸和PPP途径；Si促进地下部EMP和PPP途径，但减缓TCA循环、并抑制GABA分流。Si通过上调 HK、Susy和 TPS 表达及 SPS、Susy和INV 活性促进蔗糖、葡萄糖和果糖的积累。（2）Si通过调控NRT/NPF家族、ASS、ASL 和OCT基因表达促进甘草幼苗对N的吸收、转化及同化过程，提高脯氨酸和可溶性蛋白含量。.2、生长和活性成分积累：Si通过提高旱盐胁迫下甘草的保苗率和促进生长，进而增加生物量；Si通过调控HMGR、SQS1、SQE、β-AS、CYP72A154和4CL等基因的表达进而促进旱盐胁迫下甘草幼苗中主要活性成分的合成和积累。.3、碳氮代谢在Si诱导旱盐逆境下甘草中甘草酸积累的作用及其机制：Si一方面通过调节叶绿素含量、光合关键酶基因和酶活性以及生物量分配，改善旱盐胁迫下甘草幼苗光合作用；通过调节呼吸作用中的关键酶、改变EMP、TCA和PPP代谢的比例，进而为后续的生理过程提供更多的底物，也为应对胁迫提供更多的能量；与此同时，Si通过调控氮的吸收、转运和同化进而促进脯氨酸和可溶性蛋白的积累；最终，通过Glu与α-KG之间的转化来维持C/N代谢网络平衡，最终促进生长与甘草酸积累。