多胺与乙烯对稻米氨基酸组分和含量的调控作用及其机理

Amino acids in rice grains are important nutrients for human. It is of great scientific significance to study the regulation effects and mechanisms of plant hormones on amino acid composition and content in rice grains in terms of illuminating the formation mechanism of nutritional quality and improvement of rice quality. Polyamines and ethylene are two important plant hormones, which have important regulation effects on the growth and development, yield formation, milling and appearance quality, and protein composition of rice. However, there is limited information available about the regulation effects and mechanisms of polyamines and ethylene and their interaction on amino acid composition and content in rice grains. Our project aims to use some rice varieties with different protein content as experimental materials to study the followings: (1) the changes in endogenous polyamines (free-putrescine, free-spermidine and free-spermine) and ethylene and their relationship with amino acid composition and content in rice grains during the grain filling period, (2) the changes in amino acid composition and content, activities of key enzymes and their related coding gene expression in rice grains in the formation of amino acids during the grain filling period, (3) whether amino acid composition and content could be improved in rice grains through changing endogenous polyamines and ethylene levels by fertilizer managements and chemical controls and what their regulatory principles are, thus to reveal the regulation effects and mechanisms of polyamines and ethylene on amino acid composition and content in rice grains, providing theoretical basis for genetic improvement and cultivation regulation.

稻米氨基酸是人们食用的重要营养成分。研究植物激素对稻米氨基酸组分和含量的调控作用与机理对于阐明稻米营养品质的形成机理与改良具有重要的科学意义。多胺与乙烯是两类重要的植物激素，对水稻生长发育、产量形成、稻米的加工与外观品质以及蛋白组分等具有重要调控作用。但有关多胺与乙烯及其相互作用对稻米氨基酸组分和含量的调控作用与机理，尚不清楚。本项目以蛋白质含量明显不同的水稻品种为材料，主要研究:（1）灌浆期籽粒内源多胺（腐胺、亚精胺和精胺）与乙烯的变化特点及其与稻米氨基酸组分和含量的关系，（2）灌浆期籽粒氨基酸组分和含量、氨基酸形成关键酶活性及其相关编码基因表达的变化特点，（3）通过改变内源多胺与乙烯水平进而改善稻米氨基酸组分与含量的化学、肥料调控途径及其机理，旨在揭示多胺与乙烯对稻米氨基酸组分和含量的调控作用及其机理，为稻米营养品质的遗传改良和栽培调控提供理论依据。

多胺（Polyamines, PAs）与乙烯（Ethylene, ETH）是两类重要的植物激素，对水稻生长发育、产量形成、稻米的加工与外观品质以及蛋白组分等具有重要调控作用。但有关PAs与ETH及其相互作用对稻米氨基酸组分和含量的调控作用与机理，尚不清楚。为阐明游离PAs与ETH对稻米氨基酸的调控作用及其机理，本研究以蛋白质含量明显不同的水稻品种（2个低蛋白品种、2个中蛋白品种和2个高蛋白品种）为材料，测定了灌浆期籽粒内源free-PAs[游离腐胺（free-Put）、亚精胺（free-Spd）、精胺（free-Spm）]和1-氨基环丙烷-1-羧酸（ACC, ETH合成前体）含量、乙烯释放速率（EER）、氨基酸合成关键酶活性以及精米中氨基酸含量，并观测了外源PAs和ETH相关物质、不同施氮量处理对2个中蛋白水稻品种灌浆籽粒内源free-PAs与ETH水平、氨基酸合成关键酶活性及相关编码基因的表达以及稻米氨基酸含量的影响。结果显示：（1）籽粒中free-Spd和free-Spm含量较高、EER和ACC含量较低的水稻品种，其稻米氨基酸含量较高；（2）籽粒中free-Spd和free-Spm含量及其与ACC含量的比值与稻米氨基酸含量及其合成关键酶 [谷氨酸合成酶(GOGAT)、天冬氨酸转氨酶(AST)和丙氨酸转氨酶(ALT)]活性或相关基因表达水平呈极显著正相关，而EER和ACC含量与稻米氨基酸含量及其合成关键酶活性或相关基因表达水平呈极显著负相关；（3）外源施用Spd或Spm和乙烯利（一种ETH释放剂）于稻穗可分别提高和降低籽粒氨基酸合成关键酶活性及稻米氨基酸含量，而施用其抑制剂的作用则相反；（4）籽粒free-Spd和free-Spm含量、free-PAs/ACC比值以及稻米氨基酸含量均随施氮量的增加而增加，而EER和ACC含量则随增施氮肥而降低。结果表明，籽粒free-Spd和free-Spm可通过提高GOGAT、AST和ALT的活性加强籽粒中氨基酸的生物合成，ETH可通过抑制籽粒中GOGAT、AST和ALT的活性进而阻碍氨基酸的生物合成，而free-PAs和ETH主要通过拮抗作用介导施氮量对水稻籽粒氨基酸合成与积累的影响。本研究可为稻米营养品质的遗传改良和栽培调控提供理论依据与技术支撑。