细胞分裂素与氮素互作调控分蘖芽生长的作用机制

The growth status of tiller buds determines final spike number and plays an important role in grain yield formation. Previous studies have reported that endogenous cytokinins and nitrogen nutrition control the development of tillering, and the root is the primary organ to assimilate nitrogen and synthesize cytokinin. Nitrogen application affect nitrogen uptake and the synthesis of cytokinins. However, the nitrogen application levels and its morphologies exhibit very different responses. Moreover, little is known about how nitrogen application and morphology regulate the synthesis of cytokinins and nitrogen metabolism, resulting in affecting the growth of tiller buds. Therefore, experiments are carried out in an artificial climate chamber and field conditions. Wheat cultivars are grown in the pots with different concentrations and types of nitrogen. The objectives of this study are: (i) to quantify the variation of tillers regarding nitrogen assimilate, the synthesis of endogenous cytokinins of root and tiller buds at different nitrogen morphologies and levels application; (ii) to identify regulating effects of nitrogen nutrients on root morphology formation and microstructure; and (iii) to study the relationship between nitrogen absorption and distribution and the growth of tiller buds, and the regulating mechanism for optimization of and N application levels and morphologies. The results of this study will further provide a theoretical basis for improving the development of wheat tiller, and provide a theoretical basis for improving grain yield by nitrogen fertilizer application.

分蘖由分蘖芽生长而成，其生长状况直接决定分蘖成穗与否及成穗质量，调控分蘖生长以调优群体质量是促进小麦增产提质的重要途径。分蘖芽生长受细胞分裂素（CTK）与氮素（N）营养控制，根系是两者合成与吸收的主要器官，外源N供应对根系N吸收及CTK合成积累有显著影响。但不同N浓度及形态（硝态氮和铵态氮）存在截然不同的效应，以致二者如何调节内源CTK与N代谢以影响分蘖芽生长，迄今认识尚少。本项目以分蘖力差异显著的小麦品种为材料，设置不同N浓度及形态和外源CTK试验，研究不同遗传背景下小麦内源CTK合成积累与N吸收转运差异及机制；氮素对根系内源CTK合成积累、N吸收转运及分蘖芽生长的调节效应，深入探讨分蘖芽生长与氮素吸收分配的关系，进而阐明CTK与氮素互作调控分蘖芽生长的作用机制，研究结果对认识氮素调控分蘖芽生长的内在机制具有重要的栽培学理论意义，为合理运用氮肥调控分蘖芽生长以构建高质量群体提供理论依据。

分蘖由分蘖芽生长而成，其生长状况直接决定分蘖成穗与否及成穗质量，调控分蘖生长以调优群体质量是促进小麦增产提质的重要途径。分蘖芽生长受细胞分裂素（CTK）与氮素（N）营养控制，根系是两者合成与吸收的主要器官，外源N供应对根系N吸收及CTK合成积累有显著影响。但不同N浓度及形态（硝态氮和铵态氮）存在截然不同的效应，以致二者如何调节内源CTK与N代谢以影响分蘖芽生长，迄今认识尚少。为此本项目设置氮素浓度与外源CTK喷施互作试验、氮素形态配比试验，研究氮素与外源CTK对根系生长发育、N吸收转运与分蘖芽生长的调节效应，深入探讨分蘖芽生长与根系生长、氮素吸收分配的关系，进而阐明CTK与氮素互作调控分蘖芽生长的作用机制。结果表明，低氮促进了根系初生根及次生根的生长，根系的生长与分蘖芽生长竞争蔗糖与氮素。喷施外源6-BA促进了分蘖芽伸长和分蘖发生。低氮下喷施6-BA提高了叶片光合速率和根系活力，这促进了蔗糖和氮素向分蘖芽转运。低氮下喷施6-BA显著提高了分蘖节内源Zt含量，降低了ABA含量。相关性分析表明，分蘖芽生长与内源Zt呈极显著正相关与ABA含量、IAA/Zt比值、GA3/Zt比值及ABA/Zt比值呈显著负相关。低施氮量下喷施外源6-BA提高了小麦籽粒产量和氮肥偏生产力。高NH4+/NO3-比降低了叶片叶绿素含量及叶片光化学效率，降低了根系总根长和比根长。增大NH4+/NO3-比显著促进了根系O2-的积累，转录组和蛋白质组分析表明过多的O2-的积累导致根系木质化加强和谷胱甘肽代谢增强。上调的差异基因和蛋白主要涉及GSTs酶和根系木质素合成关键酶，这导致根系木质素合成增多，抑制了根系氮素吸收转运，进而降低了叶片光合能力，最终降低了植株生物量。