不同氮水平下构树幼苗氮代谢调控机制研究

Nitrogen metabolism play an important role in plant normal physiological activities and protein accumulation. The paper mulberry (Broussonetia papyrifera) is perennial deciduous shrubs or trees which belongs to the family of Moraceae. In recent years, the paper mulberry has been paid high attention as woody high-protein feed resources, which provid broad prospects for the agricultural development and utilization. But so far, the paper mulberry basic research is weak, nitrogen metabolism is more rarely, whic seriously affecting the efficient use of the resource. Based on what have been achieved in our previous studies, the clonal tissue culture seedling as materials, and treated by hydroponics with nitrogen deficiency and surplus. (1) Observe the effects of nitrogen additions on the seedling growth phenotype and biomass alloction. (2). Research the changes of photosynthetic capacity in response to nitrogen supply, analysis the protein component from stems and leaves and the source of the nitrogen in each component.(3) Analysis the activity of 3 kind of key metabolic enzyme (NR, GS and GOGAT) and the dynamic changing characteristic of 4 genes expression related to nitrogen metabolism in roots, stems and leaves. Finally to clarify the mechanism of high value of nutrient accumulation and high efficiency of nitrogen metabolism. This to-be executed project will be great significance to enrich the basic theory on plant mechanism of nitrogen metabolism. And also will found important application value for cultivating new high nitrogen efficiency varieties, development of high protein feed and large-scale promotion and application on the paper mulberry.

氮代谢对植物生理活动和蛋白质积累起重要作用。构树是桑科构树属多年生落叶灌木或乔木，近年来，其作为木本高蛋白饲料资源已被高度关注，为构树农业化开发和利用提供广阔前景。但至今，对构树氮代谢及蛋白质合成的基础研究较为薄弱，严重影响了构树资源的潜力挖掘和规模推广。基于前期的工作累积，本项目以构树无性系组培苗为材料，通过15N标记的营养液进行氮缺乏和氮盈余水培处理，（1）观测氮素对幼苗生长表型和生物量分配的影响；（2）研究构树叶片光合能力，以及氮素水平对茎、叶中蛋白质及其各组分合成的影响；（3）分析根、茎、叶各器官中硝酸还原酶（NR）、谷氨酰胺合成酶（GS）和谷氨酸合成酶（GOGAT）等3种关键代谢酶活性及4类氮代谢相关基因表达的动态特征，最终阐明构树在不同氮水平下的氮代谢调控机制。这对丰富植物氮代谢机理具有重要的理论意义，对培育构树高效氮代谢品种、开发高蛋白饲料和规模化推广具有重要的应用价值。

氮代谢对植物生理活动和蛋白质合成和积累起重要作用。构树是桑科构树属多年生落叶灌木或乔木，是生态修复和经济开发的重要潜在树种。近年来，其作为木本高蛋白饲料资源已被高度关注，且在多个地区开展了广泛的种植，具有广阔的开发和利用前景。但至今对构树氮代谢机制的基础研究相对薄弱，影响了构树资源的潜力挖掘和规模推广。本项目以构树无性系组培苗为材料，通过供给不同水平的氮素对其生长形态、生理生化特性和转录基因调控等多方面多层次进行了系统研究，探索了构树在幼苗期的氮代谢调控机制。结果表明，适当水平的氮能促进植物生长、增强光合、增加含氮物浓度和强化一些重要酶的活性，然而过量的氮供给却使之受到轻微或严重的抑制。亚硝酸还原酶（NiR）和谷氨酸合成酶（GOGAT）比硝酸还原酶（NR）和谷氨酰胺合成酶（GS）表现的更敏感，在高氮水平下更易被抑制。在叶片的转录组中鉴定出161961个基因，其中与氮、丙氨酸、天冬氨酸、谷氨酸和甘油磷脂等代谢相关的差异基因在施氮后表达上调，与甘油磷脂、甘油脂、氨基糖和核苷酸糖等代谢相关的差异基因表达下调。利用WGCNA分析获得16个基因网络共表达模块，其中分别筛选出与氮代谢和磷代谢相关调节天冬酰胺合成酶和无机焦磷酸酶的两个关键基因，基因的表达特征和形态、生理以及相关代谢酶的响应表现一致，这从多层次揭示了构树氮代谢机制，为进一步研究和利用构树奠定了基础，这对丰富植物氮代谢机理具有重要的理论意义，对培育构树高效氮代谢品种、开发高蛋白饲料和规模化推广具有重要的应用价值。