强筋小麦籽粒谷蛋白聚合机理及水分响应

Bread wheat (Triticum aestivum L) possesses unique dough viscoelastic properties that are primarily conferred by two groups of seed storage proteins: glutenins and gliadins. Glutenins, the major determinants of dough elasticity and bread-making properties, are classified as monomer and polymer proteins on the basis of their degree of polymerization and the biochemical characteristics of their polypeptide chains. According to their mobility on SDS-gel electrophoresis (SDS-PAGE), glutenin is a macropolymer composed of high molecular weight glutenin subunits (HMW-GS) and low molecular weight glutenin subunits (LMW-GS) joined together by intermolecular disulfide bonds. The molecular mechanism of glutenlin polymerization is not clear so far, preliminary studies indicate that irrigation scheme may influence polymerization degree of glutenin and the polymer particle size distribution, which is critical to breadmaking quality. In this proposal, we intend to explore the regulation of glutenin polymerization in response to irrigation scheme, from an integrated perspective of physiology, molecular biology and cultivation. The storage proteins including glutenlins and gliadins are investigated as a whole, with emphasis on variations of sulfhydryl group (SH) and disulfide bonds (SS), protein structure characteristics and physical properties of glutenlins in response to irrigation scheme. The relationship between expression and polymerization of glutenin is also studied in an attempt to elucidate the regularity of storage protein polymerization in response to irrigation and its effects on wheat quality. Our data may lead to further understanding of glutenin formation and provide a theoretical basis for improvement of grain processing quality.

麦谷蛋白是由高分子量谷蛋白亚基（HMW-GS）和低分子量谷蛋白亚基（LMW-GS）通过分子间二硫键（SS）交联形成的聚合体蛋白，对面团的强度和弹性起主要贡献作用。水分运筹能够改变谷蛋白聚合程度以及聚合体的粒度分布，进而影响面包烘烤品质。但水分运筹影响谷蛋白聚合程度的分子机理，尚不清楚。本研究拟采用生理学、分子生物学和栽培学相结合的方法，以贮藏蛋白及其组分谷蛋白和醇溶蛋白作为研究整体，通过研究籽粒发育不同阶段谷蛋白的功能基团巯基（SH）和二硫键（SS）变化规律、蛋白结构特征（分子量及亚基分布、二级结构）变化和谷蛋白微观结构性能变化等，探讨谷蛋白的蛋白表达特性与谷蛋白聚合的关系，从组分学角度阐明贮藏蛋白聚合规律及其对水分的响应机制，从蛋白质结构水平探明谷蛋白聚合程度对小麦品质影响的机理。本项目的完成，可为进一步丰富小麦籽粒谷蛋白形成规律，改善籽粒加工品质提供理论依据。

贮藏蛋白由单体醇溶蛋白和聚体麦谷蛋白组成，是面团的主要组成部分，并且是决定小麦加工品质的重要因素。高分子谷蛋白亚基（HMW-GS）和低分子谷蛋白亚基（LMW-GS）通过分之间二硫键（SS）交联形成了聚合体麦谷蛋白，并影响面筋的强度和弹性。二硫键在维持大分子麦谷蛋白聚合中起决定性作用。本项目以贮藏蛋白及其组分为研究对象，以谷蛋白聚合的二硫键和蛋白二级结构为切入点，围绕强筋小麦谷蛋白聚合的机理及对水分的响应开展研究。研究发现：（1）明确了谷蛋白快速积累时间向后推迟是水分供应过多导致小麦品质变差的主要原因，通过对籽粒发育不同阶段贮藏蛋白组分和结构特征的动态变化以及对水分响应的研究表明，灌水增加推迟了谷蛋白（尤其是不溶性谷蛋白）快速积累的时间，谷蛋白形成和快速积累的时间相对缩短，使成熟期籽粒中的谷蛋白（尤其是不溶性谷蛋白）积累量减少。（2）明确了强筋小麦谷蛋白聚合规律的生理生态机制及对水分的响应。适宜的水分，能够延长谷蛋白的快速积累期，增加谷蛋白亚基（尤其是HMW-GS）的积累量，提高谷蛋白聚合指数和聚合程度，增加大粒径的谷蛋白大聚合体（GMP）的比例，从而提高小麦的面团和面包品质，实现籽粒产量和品质的协同提高。（3）从蛋白质结构水平探明了谷蛋白聚合程度对强筋小麦品质影响的机理。通过对贮藏蛋白巯基、二硫键、二级结构等蛋白结构表型，GMP粒度分布和品质指标变化规律以及对水分的响应研究表明，适宜的水分供应，增加了小麦贮藏蛋白的二硫键和β-折叠含量，有利于增大谷蛋白的聚合程度和形成更多大粒径GMP颗粒，从而改善强筋小麦的加工品质。研究结果可为进一步丰富强筋小麦籽粒谷蛋白聚合规律、改善籽粒加工品质提供理论依据和支撑。