大豆侧根形成对种子萌发过程中赤霉素调控的响应及机理

Soybean lateral roots (LRs) are very important to soybean plant and soybean high yield production. In addition to physical support, soybean root system can fix nitrogen，perform the absorption and transport of nutrients，water，and exchange signals with the above-ground. Soybean root system is made of a primary root that originates during embryogenesis and lateral roots that form throughout the life of the plant. LRs are initiated in the differentiation zone of primary roots from pericycle founder cells that are adjacent to the protoxylem poles. LRs are the most dynamic and physiologically active part of soybean root system. .Gibberellins (GAs)'s role in root development is poorly understood, and some reports about GAs' effect on LR formation are contradictory. Phytohormones play a central role during lateral root development. Recent report suggests that include ethylene, cytokinin, brassinosteroid, and abscisic acid (ABA) can also regulate the process, usually in an auxin-dependent manner. By contrast, to GAs, the phytohormones that regulate a wide range of developmental processes, including seed germination, leaf expansion, stem elongation, flowering, and fruit and seed development, very little is known about what role, if any, GA have in LR formation..In this study, we use soybean as material, to research response of soybean lateral root formation to gibberellins regulation during seed germination and mechanisms. Exogenous Uniconazole(S3307) and GA3 will be used to create different GAs level gradients by seed soaking. Then the presoaking seeds will be plant under sand culture condition to gain the experiment materials. the soybean seedlings with fine root will be harvest every 24 hour 14 times and every 48 hour 7 times after radicle breakthrough seedcoat(about 48hours after plant). Samples harvested every 24 hour will be used research on root morphology and lateral root primordia (LRP). Samples harvested every48 hour will be used research on root Microstructure and ultrastructure, activities of key enzymes,c of phytohormones and expression of key GENEs in taproot for LR formation. Root morphology, such as LR numbers root length, root volume etc.will be measured byWinRHIZO image analysis system,LRP will be stained by the Feulgen method , Microstructure and ultrastructure will be studied by means of both optical and electronic microscopes. activities of key enzymes will be studied by colorimetric method, concentration of phytohormones will be measured by high-performance liquid chromatography (HPLC) method, and expression of key GENEs will be studied by qRT-PCR Analysis system. Use all of the data the conclusion will be drawn for GAs' role in soybean LR formation. Meantime we will plant the presoaking seed in filed to determine response of soybean plant growth and development , yield and quality to to gibberellins regulation during seed germination.

根系是大豆非常重要的器官，侧根是大豆根系中最具动力和生理活性的部分。研究大豆侧根的形成机制，如何使栽培大豆具有更多更强大的侧根成为大豆优质高效生产中的一个重要科学问题。在大豆生产实践，赤霉素及其抑制剂（烯效唑和多效唑）经常用于种子处理，或为克服农药副作用保证大豆出苗，或为追求大豆壮苗。国内外对赤霉素对侧根形成，尤其是对大豆侧根形成的调控作用研究较少，这样就使研究种子萌发过程中赤霉素如何调控大豆侧根形成意义重大。.本研究通过不同浓度的外源赤霉素和烯效唑浸种来构建大豆种子萌发过程中不同的赤霉素水平梯度，分别从侧根形态、侧根原基发生、主根显微和超微结构、内源激素、关键酶和控制侧根形成关键基因表达等较为全面系统地分析大豆侧根形成对种子萌发过程中赤霉素调控的响应及其机理，同时辅以田间试验研究种子萌发过程中赤霉素调控对大豆产量和品质的影响，为大豆化控应用领域提供相关的理论基础和技术支持。

本研究通过不同浓度的外源赤霉素和烯效唑浸种构建完成了大豆种子萌发过程中不同的GAs梯度水平。研究不同GAs水平大豆侧根形态变化，发现低水平GAs促进根的生长，包括促进根的长度、直径和表面积及体积的增加，高水平GAs抑制根的生长。研究侧根原基发现，高水平GAs抑制侧根的生长主要是部分侧根原基没有突破表皮形成侧根。显微结构研究表明低水平GAs侧根直径增粗主要由远根尖端根直径的增粗引起，高水平GAs的侧根直径在近根尖端根直径和远根尖端根直径同时减小。超微结构研究发现低水平GAs线粒体数量、淀粉质体数量和质体数量较对照显著增多。内源激素研究发现构建的GAs水平在24h存在显著的梯度差异，这种差异随着时间的变化逐渐变小，在196h低GAs水平出现反跳GA3含量显著高于对照；对IAA和ABA的影响没有发现规律性的变化，没有检测到CK。关键酶研究表明在前期低水平GAs可以提高东农42的糖苷酶活性，低水平GAs和高水平GAs均能提高抗氧化酶活性。关键基因表达研究发现低水平GAs可以反馈调节GAs合成途径中的氧化酶基因家族GA20ox, GA3ox, 和 GA2ox的表达。利用高通量转录组分析了外源烯效唑浸种对大豆根基因表达的影响。转录组结果表明处理导致激素代谢、各类转录因子，细胞壁修饰和细胞分裂相关基因的表达均有较大改变，提出低水平GAs通过GAs和乙烯途径影响形成层调节根生长的模式：烯效唑通过抑制KO基因的表达造成植物体内低GAs水平，低水平GAs调控ACS 高表达，调控WOX4低表达，ACS 和WOX4 通过乙烯途径调节ERF1的高表达，促进形成层的增值，从而促进根系的增长。田间试验研究表明，低水平GAs显著提高苗期的叶绿素含量和降低大豆植株高度；高水平GAs显著降低苗期的叶绿素含量和提高大豆植株高度，对其他时期的作用不明显。因此烯效唑和GA3浸种的主要作用在苗期。本项目研究从形态、显微结构、内源激素变化、酶活性和转录组基因表达变化详细研究了植物激素GA及其合成抑制剂对大豆根发育的影响，揭示了其作用的分子机理，为大豆苗期使用烯效唑抵抗春季干旱提供了理论依据。