生理成熟前玉米籽粒水分时空分布特征及其形成的生理生化机制

The excessive kernel moisture content at harvest (H-KWC) is a limiting factor seriously affecting maize production in China. H-KWC is determined by both the kernel moisture content at physiological maturity (P-KWC) and the physical dehydration process after physiological maturity. However, little is known about the physiological dehydration process before physiological maturity and the mechanisms therein, which determines the P-KWC and is closely associated with the interior physiological process of maize grain. In the previous study, we have identified the characteristics of physiological dehydration among different varieties and their relationship with the grain-filling process. On this basis, maize cultivars with different P-KWC will be selected as materials. Both field experiment and grain vitro culture experiment will be conducted in this study. Firstly, nuclear magnetic resonance imaging (MRI) will be used to monitor moisture migration and distribution in endosperm at different positions of grain. Secondly, the dynamic relationship between water moisture variation and starch content and starch granule morphology will be studied by electron microscopy. In addition, variations of endogenous hormone contents, enzymes activities and gene expression patterns involved in starch synthesis process will be investigated by UPLC-MS/MS, qRT-PCR and other techniques to ascertain their effects on kernel moisture migration and distribution. Finally, the spatial and temporal distribution characteristics of moisture in maize kernels before physiological maturity and its physiological and biochemical mechanisms will be elucidated. The results of this study will provide a theoretical basis for deepening the physiological dehydration mechanism of maize kernels and the selection of suitable varieties for mechanical grain harvest.

收获时籽粒含水率（H-KWC）过高严重制约我国玉米生产。H-KWC由籽粒生理成熟时含水率（P-KWC）和生理成熟后的物理脱水速率共同决定，而受籽粒内部生理过程调控并决定P-KWC的生理脱水过程及其机制尚不明确。我们前期研究已初步明确不同品种生理脱水规律及其与灌浆过程的关系。在此基础上，本项目拟以P-KWC差异显著的玉米品种为材料，将大田试验和籽粒离体培养相结合，首先，借助核磁共振成像系统研究籽粒水分在不同层次胚乳中的迁移及分布规律；其次，通过树脂切片电镜观察等方法研究不同层次胚乳淀粉积累、淀粉粒形成动态及其与水分的对应关系；并运用液质联用、qRT-PCR等技术，分析内源激素含量、淀粉合成关键酶活性、关键编码基因表达量的动态变化对籽粒水分分布与迁移的调控效应，进而阐明玉米籽粒水分时空分布特征形成的生理生化机制。以期为深化玉米籽粒生理脱水机制的研究以及适宜机械粒收品种的选育提供理论依据。

收获时籽粒含水率（H-KWC）过高严重制约我国玉米生产。H-KWC由籽粒生理成熟时含水率（KWC）和生理成熟后的物理脱水速率共同决定，而受籽粒内部生理过程调控并决定P-KWC的生理脱水过程及其机制尚不明确。本项目以P-KWC差异显著的玉米品种为材料，首先，明确了授粉后不同时期各品种籽粒含水率、水分含量的差异，确定了“脱水关键期”。其次，发现玉米籽粒水分空间分布差异与籽粒淀粉积累、淀粉粒排布、胚乳细胞程序化死亡密切相关。淀粉在整个胚乳中的分布、淀粉粒多面体化发生时间提前，紧密的排列方式以及顶部胚乳细胞PCD的发生均能促进籽粒中水分下移，利于生理成熟期籽粒含水率的降低。通过对玉米籽粒蛋白质组的分析，我们发现在脱水关键期籽粒的防御能力显著提高：与籽粒的耐脱水性、抗氧化能力、解毒能力和其他胁迫响应能力等相关蛋白均显著上调表达。这些蛋白的上调表达有利于籽粒建立完善、多样化且稳定的防御体系，从而让籽粒可以在复杂的环境中生存。而防御体系的建立可能促进了籽粒的净脱水的发生和进行。本项目研究结果为深化玉米籽粒生理脱水机制的研究提供了理论依据。