糯玉米胚乳支链淀粉精细结构的形成机制及氮素调控

Waxy maize endosperm starch is composed of nearly 100% amylopectin. Amylopectin fine structure is the important determinant for starch physicochemical properties and quality, and its formation is controlled by the activities of starch synthesis enzymes and the expression of starch synthesis genes. Nitrogen application is the key measure to regulate starch properties. In this project, different waxy maize varieties and strains are used. During endosperm development, the changes of amylopectin fine structure are studied, the activities of starch synthesis enzymes are determined by enzymatic method, the isozyme types and expression traits are identified by Native-PAGE, the expression profiles of starch synthesis genes are discussed by real-time fluorescence quantitative PCR and northern blot, so as to clarify formation mechanism of amylopectin fine structure in waxy maize endosperm. In mature endosperm, starch physicochemical properties are analyzed to identify the relationship of amylopectin fine structure and starch physicochemical properties. The effects of nitrogen application on amylopectin fine structure, starch synthesis enzyme activities, isozyme and gene expression profiles of starch synthesis are studied to clarify the effects of nitrogen regulation on amylopectin fine structure formation in waxy maize endosperm. The results will deepen the study of formation mechanism and provide a theoretical basis for optimization technology establishment of waxy maize starch quality.

糯玉米胚乳淀粉几乎全由支链淀粉组成，支链淀粉精细结构是影响淀粉理化特性进而决定应用品质的主要因素，其形成主要受淀粉合成关键酶活性及编码基因表达的调节。氮肥运筹是调控籽粒淀粉特性的主要措施。本项目选用不同的糯玉米品种（品系）为材料，采用酶学方法、Native-PAGE、实时荧光定量PCR与Northern杂交技术，研究胚乳发育期间支链淀粉精细结构的变化，测定淀粉合成关键酶的活性，鉴定其同工酶类型及表达特性，探讨淀粉合成相关基因的表达模式，明确糯玉米胚乳支链淀粉精细结构的形成机制；分析成熟期胚乳淀粉的理化特性，明确支链淀粉精细结构与淀粉理化特性的关系；研究施氮对支链淀粉精细结构、淀粉合成关键酶活性及同工酶和相关基因表达的影响，阐明氮素对支链淀粉精细结构形成的调控效应。研究结果将深化糯玉米淀粉品质形成机制研究，为糯玉米淀粉品质调优技术的确立提供理论依据。

糯玉米胚乳淀粉几乎全由支链淀粉组成，支链淀粉精细结构是影响淀粉理化特性进而决定应用品质的主要因素，其形成主要受淀粉合成关键酶活性及编码基因表达的调节。氮肥运筹是调控籽粒淀粉特性的主要措施。本项目选用苏玉糯2号和京科糯2000为材料，设4个施氮量处理（0 kg/hm2、100 kg/hm2、200 kg/hm2、300 kg/hm2）和3个施氮方式处理（50%基肥+50%大口肥、50%基肥+50%吐丝肥、30%基肥+30%大口肥+40%吐丝肥），采用盆栽方式种植，分析胚乳发育期间支链淀粉精细结构、淀粉合成关键酶活性和相关基因表达的变化及其氮肥调控，测定成熟期籽粒淀粉的理化特性。.1. AGPase活性和SSS活性与A链呈（极）显著正相关，SBE活性与B2链呈显著正相关，DBE活性与B2链、B3链、均呈极显著正相关。因此，AGPase和SSS主要用于合成支链淀粉短链，SBE、DBE主要用于合成中长链和长链。SSI和SBEIIb相对表达量与A链呈极显著正相关，说明二者协同调控合成短链。SSIIa与B1链呈极显著正相关，与A链呈极显著负相关，说明SSIIa是将SSI所合成的短链延伸聚合成中长链。SSIIIa、SBEI和PUL均与B2链、B3链呈（极）显著正相关，说明三个基因是对SSIIa所合成中链的延伸，参与中长链和长链的合成过程。SSIIc和ISA2相对表达量与链长分布无显著性关系。.2. 透光率、蓝值、碘结合力、膨胀势、峰值粘度、峰值时间、糊化温度、胶凝化温度与B3链呈（极）显著正相关；热焓值、结晶度和尖峰强度与B2链、B3链、均呈（极）显著正相关。说明，支链淀粉的中长链比例越高，淀粉的透光率、蓝值、碘结合力、膨胀势、峰值粘度、峰值时间、糊化温度、胶凝化温度、热焓值、结晶度和尖峰强度就越高，淀粉的结构稳定性就越强。.3. 随着施氮量的增加，糯玉米籽粒支链淀粉中长链比例、淀粉合成关键酶活性和淀粉合成相关基因表达量均呈先增加后降低的变化，以施纯氮200 kg/hm2最高；不同施氮方式间相比，表现为“30%基肥+30%大口肥+40%吐丝肥”>“50%基肥+50%吐丝肥”>“50%基肥+50%大口肥”。说明，氮肥适量和分次后移能有效提高糯玉米籽粒淀粉合成关键酶活性和相关基因表达量，有利于支链淀粉长链比例的增多。