密植群体玉米气生根的衰老机理及其分子调控途径研究

It is still one of the key measures to increase the population density in order to enhance maize yield in China and the world. Under the background of higher planting density, problems of lodging and premature aging need to solve at present. While aerial root has significant impact on grain yield formation and lodging after maize flowering. The project intends to study aerial root physiological and biochemical basis of aging and differences of its transcriptome and metabolomic in higher density population. Ultimately, it provides theoretical basis for breeding of high-density-tolerance maize varieties and the cultivation of lodging resistance and anti-aging. . Zhengdan 958 which is the main variety in production is chosen to test material, and the planting density includes 22500 plants per hectare、60000 plants per hectare and 90000 plants per hectare. The key points of research are aerial root aging mechanism and the density of stress response. The research content is as follows: aerial root growth characteristics and its aging process; aerial root senescence mechanism of enzymes and hormones metabolism; differences of aerial root metabolomic and transcriptome between the free growth and density stress condition. . The applicant has done some research on yield formation and lodging resistance of maize aerial root in high population, so as to lay the good foundation for the project. The project is a blend of traditional agriculture experiment，physiological and biochemical laboratory analysis, as well as the modern transcriptome, metabolomic and bioinformatics. Physiological, biochemical and molecular regulation mechanism of maize aerial root aging will be parsed gradually from macroscopic to microcosmic, and then deepen the understanding of close planting cultivation from the molecular level.

增加群体密度仍然是我国玉米提高单产的关键措施。当前高密度种植背景下，玉米植株早衰和倒伏问题亟需解决，而气生根对玉米籽粒产量形成和倒伏有重大影响。项目拟研究密植群体玉米气生根衰老的生理生化基础及其转录组、代谢组差异，最终为耐密玉米品种的选育和抗倒防衰栽培提供理论依据。项目以我国主推玉米品种郑单958为材料，在22500株/公顷、60000株/公顷、90000/公顷株密度下，重点研究气生根衰老机理及其对密度胁迫的响应。具体研究内容如下：玉米气生根的生长特性及其衰老进程；玉米气生根衰老的酶学机制和激素代谢过程；自由生长与密度胁迫条件下，玉米气生根的代谢组学和转录组学差异。申请人前期已经进行了密植群体玉米气生根的产量形成及其抗倒性能的研究，为项目实施奠定良好基础。项目融合了传统农学田间试验与室内生理生化分析以及现代转录组学、代谢组学和和生物信息学，可从分子水平上加深对密植栽培的认识。

当前高密度种植背景下，玉米植株早衰和倒伏问题亟需解决，而气生根对玉米籽粒产量形成和倒伏有重大影响。项目以我国主推玉米品种郑单958为材料，在22500株/公顷、60000株/公顷、90000株/公顷密度下，重点研究气生根衰老机理及其对密度胁迫的响应。具体研究内容如下：玉米气生根的生长特性及其衰老进程；玉米气生根衰老的酶学机制和激素代谢过程；自由生长与密度胁迫条件下，玉米气生根的代谢组学和转录组学差异。1500株/亩自由生长条件下，郑单958气生根层数可达3层，根条数60.7。气生根对密度反应极为敏感，呈极显著负相关关系。不同层次气生根自下而上长度和须根条数增加。开花期，气生根N、P、K、Fe、Mn含量高于次生根，可见其对玉米花后矿质离子转运的重要性。而全生育气生根Cu、Mn含量低于次生根，这可能与独特根系类型有关。开花期，气生根Zn含量高于次生根,而成熟期低于次生根。由上可见，与次生根相比，气生根在玉米花后矿质营养吸收、转运方面有其独特方式，有待于进一步研究。植物激素在玉米生长发育过程中发挥重要作用。在玉米气生根初始延伸的大喇叭口期，玉米气生根IAA含量高于次生根，而ABA含量低于次生根，说明此时气生根处于旺盛发育时期。随着密度增加，IAA含量逐步降低，ABA含量逐步升高，气生根生长受到抑制；玉米气生根SOD活性高于次生根，活性氧清除能力加强。而气生根ABA含量高于次生根，这可能与其暴露在空气中，所处环境复杂多变有关。当密度由1500株/亩增加到6000株/亩时，玉米气生根有196个基因发生变化，其中下调表达105个，上调表达91个。下调表达基因主要与膜转运有关，上调表达基因主要与生物合成和抗逆性应激有关；同时玉米气生根代谢组发生明显变化，共有2902个阴阳离子表达量显著变化，其中1493个上调表达，而1409个下调表达。差异代谢物生物学功能主要与代谢途径、次生代谢物合成、氨基酸生物合成等有关。