抗坏血酸缺失影响水稻籽粒灌浆的机理研究

Seed setting rate and grain plumpness are the main factors that affect the yield of rice, while endogenous hormones play an important role in regulating grain-filling and grain weight, and the grain physiological activities and the conversion efficiency from sucrose to starch are also important factors affecting the grain filling. As a cell senescent process occurs during endosperm development, and our previous research showed that ascorbic acid deficiency in transgenic rice suppressed for GLDH, which is a key enzyme in ascorbic acid biosynthesis in higher plants, resulted in a significantly decrease of seed setting rate and grain plumpness, this project is designed to study the relationships between ascorbic acid, endogenous hormones and the conversion efficiency from sucrose to starch using GLDH RNA interference and overexpression mutants of rice as plant materials. The changes of ascorbic acid content, expression of the GLDH gene, ROS and antioxidant system in rice leaf and grain, hormone contents and expressions of related genes, activities and gene expressions of key enzymes involved in sucrose-to-starch conversion in grain will be analyzed during grain-filling process in different mutants and wild- types. The broader purpose of this project is to elucidate the effects of ascorbic acid plays on rice grain-filling from the points of gene expression and plant physiology, which might provide some theoretical guidance to rice breeding for high yield.

结实率和籽粒充实度已成为影响水稻产量的主要因子，内源激素对籽粒灌浆进程及粒重具有重要调控作用，籽粒库的生理活性和蔗糖转化为淀粉的生化效率是籽粒灌浆的重要影响因素。胚乳的后期发育是一个典型的衰老过程，我们的前期工作表明，植物抗坏血酸合成关键酶GLDH基因的干涉型转基因水稻由于抗坏血酸缺失导致结实率与充实度显著下降。本项目利用GLDH基因干涉与超表达水稻纯合体为材料，通过分析不同突变体及野生型灌浆过程中叶片与籽粒的抗坏血酸含量、GLDH基因表达变化、活性氧和抗氧化系统变化、籽粒内源激素含量及相关基因表达变化、籽粒蔗糖-淀粉代谢关键酶活性变化及基因表达的差异，探讨抗坏血酸与籽粒内源激素、籽粒库的生理活性以及蔗糖转化为淀粉的关系，从基因表达水平与植物生理学角度系统阐明抗坏血酸对水稻籽粒灌浆影响，为水稻的高产育种提供理论指导。

结实率和籽粒充实度是影响水稻产量的主要因子，内源激素对籽粒灌浆进程及粒重具有重要调控作用，籽粒库的生理活性和蔗糖转化为淀粉的生化效率是籽粒灌浆的重要影响因素。胚乳的后期发育是一个典型的衰老过程，本项目以GalLDH基因干涉与超表达水稻纯合体为材料，通过分析不同突变体及野生型灌浆过程中叶片与籽粒的抗坏血酸（ascorbic acid，Asc）含量、GalLDH基因表达变化、活性氧和抗氧化系统变化、籽粒内源激素含量及相关基因表达变化、籽粒蔗糖-淀粉代谢关键酶活性变化及基因表达的差异，深入探讨Asc与籽粒内源激素、籽粒库的生理活性以及蔗糖转化为淀粉的关系。.本项目获得的重要结果有：1）水稻内源Asc含量的上调有利于籽粒灌浆，籽粒淀粉的排列结构以及垩白度得到改善。GalLDH超表达系水稻籽粒垩白度明显降低，胚乳淀粉粒结构紧密，Asc可能通过调控源叶的光合能力和衰老进程，影响籽粒的灌浆过程，最终影响籽粒灌浆与垩白的形成。2）Asc缺失与籽粒灌浆速率以及籽粒垩白的形成密切相关，GalLDH干涉系水稻籽粒的灌浆速度明显下降、垩白度明显增加，胚乳淀粉粒结构松散。Asc缺失导致H2O2的积累、羟自由基清除能力、总抗氧化能力以及光合能力的下降，进而影响籽粒灌浆过程中淀粉合成途径关键酶的活性和相关基因的表达，最终导致籽粒灌浆速率、淀粉特性以及垩白度的改变。3）喷施外源Asc和MeJA引起GalLDH基因干涉系水稻叶片的Asc含量、光合能力以及衰老相关基因表达的改变，进而对水稻产量性状产生不同影响。4）遮阴处理能有效改善GalLDH基因干涉系水稻的光合能力以及衰老相关基因的表达，对产量性状的改善起促进作用。.总之，本研究从基因表达水平与植物生理学调控角度系统阐明了Asc对水稻籽粒灌浆影响，为水稻的高产育种提供了新的理论指导