叶面喷锌促进小麦籽粒富锌的生理及分子机制

The zinc bio-fortification in wheat is a main strategy to combat zinc malnutrition. Foliar zinc application is considered to be a fast and effective way of enriching grain zinc, which always interacts with nitrogen availability. It is therefore necessary to reveal the driving force of zinc transport to grains and the zinc-nitrogen interaction from physiological and molecular perspectives, which is beneficial for improving the efficiency of zinc transport and accumulation in wheat. The hypothesis here is that grain zinc bio-fortification via foliar application is associated with the increased zinc export out of leaves and deposition in grains, and nitrogen has a positively coordinated effect on these processes. The study would be carried out under both field and greenhouse conditions with the RNA-Seq and 68Zn and 15N isotope techniques. The objectives of this project are (1) to compare the differences in subcellular distribution of zinc between leaves with foliar zinc application at different growth stages, and clarify the fundamental factors affecting zinc export from leaves; (2) to screen the differentially expressed genes involved in zinc metabolism in leaves, rachis, and grains of plants with foliar zinc application, and figure out the key limitations of zinc transport and accumulation; (3) to investigate the responses of key genes involved in zinc translocation to post-anthesis nitrogen availability, and the coordinated translocation of nitrogen and zinc to grains. Such knowledge is valuable for revealing the driving force and mechnisms of grain zinc enrichment via foliar zinc application, and also deepening the theoretical basis for optimizing the agronomic strategies of grain zinc bio-fortification and quality improvement in wheat production.

小麦锌生物强化是解决人体缺锌问题的重要途径，而叶面喷锌是提升小麦籽粒锌含量的快速有效手段，且与氮素供应互作明显。从生理与分子角度揭示锌向籽粒运输的驱动因子及锌氮协同作用，对于提高锌转运及累积效率具有重要意义。本项目从“叶面喷锌影响叶片锌输出和籽粒锌累积及与氮素通过协同转运关系来促进小麦锌生物强化”的科学假设出发，拟采用田间及盆栽试验，结合转录组测序、68Zn和15N同位素双标记等技术开展研究工作：一是通过比较不同时期喷锌后叶片中锌的细胞学分布差异，明晰影响锌转运的基础因素；二是分析喷锌后叶片、穗梗、籽粒参与锌转运和累积过程的差异表达基因，查明影响锌转运的关键限制因素；三是研究锌转运关键基因对花后氮素营养状况的响应及不同阶段内锌氮动态变化，揭示锌氮协同转运关系。研究结果在理论上有助于阐明叶面喷锌促进小麦籽粒富锌的驱动因素及影响机制，同时为优化小麦锌生物强化和提质增效的调控措施提供理论依据。

小麦生物强化是解决人体缺锌等问题的重要途径，而叶面喷施是提升小麦籽粒微量元素含量的快速有效手段，且与氮素供应互作明显。叶面喷施促进籽粒富锌的生理机制是什么？锌向籽粒运输的驱动因子及其与氮或硒互作对生物强化效果有何影响？针对上述科学问题，我们开展了三年研究。（1）研究表明施氮和喷锌能够提升小麦籽粒锌含量，不喷锌时各施氮量小麦籽粒锌含量不足30 mg/kg，叶面喷锌处理籽粒达到富锌目标（40-60 mg/kg）；无论喷锌与否，增加施氮量均能够明显提高面粉中锌的生物有效性。（2）增加小麦花后氮素转移有利于促进锌向籽粒转运，氮、锌向籽粒的转移量及成熟期籽粒中氮、锌含量均呈显著线性正相关，且叶面喷锌时氮、锌协同效应更为显著。（3）施氮对籽粒和面粉中醇溶蛋白和谷蛋白含量提升幅度高于清蛋白和球蛋白，而喷锌不影响籽粒和面粉中蛋白质及其组分，面粉中与锌结合的氨基酸及氨基酸总量主要受供氮水平调控，而不受叶面喷锌影响。因此籽粒或面粉富锌不依赖于与锌结合的氨基酸含量的增加，即面粉（或胚乳）中存在足够用于锌储存的“锌-氨基酸”库。（4）基于转录组学等手段，初步筛选了叶面喷锌措施下小麦叶片锌转运相关的差异表达基因，分析发现叶面喷锌后植株体内存在明显的锌稳态平衡调节，但部分氨基酸合成代谢上调，有利于小麦体内锌的运输。（5）小麦灌浆前期锌硒配合喷施能够同时实现小麦籽粒富锌富硒，且不影响籽粒产量；小麦锌硒配合不影响籽粒富锌效果，但喷施后锌的加入会影响籽粒富硒效果，且在不同施氮措施下响应规律不同。研究结果可为小麦生产中通过养分资源优化管理实现小麦籽粒生物强化提供重要理论支撑和借鉴意义。项目完成了预期研究目标，发表SCI文章3篇，培养硕士研究生1名。