毛花猕猴桃果实采后维生素C积累的调控机制研究

Vitamin C plays an important role for human health. It is well known that fresh fruits are the best source for people to absorb vitamin C. However, much of vitamin C in fruits is lost druing storage, so that maintainance of vitamin C level needs to be addressed for quality control of harvested fruits. Kiwifruits (Actinidia eriantha Benth) are promised material for study on accumulation of vitamin C in fruits during storage, since the harvested fruits can constantly maintain higher vitamin C level as compared to other commodities. In order to elucidate this special mechanism, genes including GalLDH, GalUR and DHAR associated with biosynthesis and recycle of vitamin C in kiwifruits will be cloned, and then their related bio-information will also be analyzed. Moreover, the change in metabolism of vitamin C in harvested kiwifruits, especially in activites of GalLDH, GalUR and DHAR and these genes expression in relation to regulation of vitamin C accumulation, and the effects of some inner or external factors, such as maturity, temperature and oxalic acid treatment, on accumulation of vitamin C in kiwifruits will also be investigated during storage. Therefore, the project has an important theoretic and practical meaning, not only for maintaining vitamin C in harvested fruits, but also for utilizing biotechnology to control the metabolism of vitamin C, and in turn enhancing accumulation of vitamin C in harvested fruits.

维生素C对于人体健康具有重要作用。水果是人类摄取维生素C的重要食物来源，但果实在采后贮藏中维生素C容易被降解而流失，保持维生素C含量是采后果实质量控制的重要目标。毛花猕猴桃采后果实具有保持维生素C高含量的特性，是研究采后果实维生素C积累模式的理想材料。本项目通过研究毛花猕猴桃果实维生素C合成与再生途径关键酶GalLDH、GalUR和DHAR编码基因的克隆及其生物信息学分析，毛花猕猴桃采后果实维生素C的合成与再生代谢、特别是GalLDH、GalUR和DHAR活性及其编码基因表达对果实维生素C积累的调控作用，以及成熟度、贮藏温度、草酸处理等内外因子对采后果实维生素C积累的作用效应，解析毛花猕猴桃采后果实维生素C积累的特异性机制，为有效保持采后果实的维生素C含量，特别是为通过基因工程技术调控果实的维生素C代谢、进而提高采后果实的维生素C含量等提供理论基础，因而具有较重要的理论和应用价值。

维生素C又称抗坏血酸（AsA），对于人体健康具有重要作用。水果是人类摄取AsA的重要食物来源，但采后果实的AsA容易被降解而流失，保持AsA含量是采后果实品质控制的重要目标。本项目主要研究了毛花猕猴桃‘华特’（ActiniDia eriantha ‘White’）果实AsA合成与再生关键基因的克隆及生物信息学分析，采后果实AsA积累模式及其合成、分解与再生代谢的变化，采后果实不同部位（果肉及中轴）、不同采收成熟度果实AsA积累及其合成与再生代谢的差异，以及不同贮藏温度、草酸处理对采后果实AsA积累及其合成与再生代谢的影响。主要结果如下：.1、毛花猕猴桃‘华特’采后果实富含AsA及其流失量低的特性，主要缘由采后果实具有高AsA合成与再生代谢活性。其中，L-半乳糖途径是果实AsA合成的主要途径，D-半乳糖醛酸途径是辅助途径；GalDH是L-半乳糖合成途径的限速酶，DHAR是果实AsA再生的关键酶。同时，GMP、GPP、GGP和GalDH在转录水平上调控采后果实AsA的L-半乳糖合成途径；GalUR在转录水平上调控采后果实AsA的D-半乳糖醛酸途径；AO基因是调控AsA氧化的关键基因；DHAR基因是调控AsA再生的关键基因。.2、毛花猕猴桃果实果肉和中轴的AsA水平存在差异，但果肉和中轴具有相似的AsA代谢协同调控机制。.3、采前喷施草酸提高猕猴桃果实采后AsA再生相关酶活性（APX、DHAR、GR和MDHAR的活性），从而有效提高了猕猴桃果实AsA含量，并降低果实采后AsA损失量。.4、与常温相比，毛花猕猴桃果实在低温贮藏下果肉和中轴AsA含量和AsA/DHA比值下降较缓，与果肉和中轴保持GalLDH、APX、DHAR、MDHAR和GR较高活性相关；特别是在低温贮藏下，果实的AsA再生活性比AsA合成活性更强。.5、不同采收成熟度毛花猕猴桃果实采后的AsA含量存在差异，主要缘由果实AsA合成和再生代谢的差异。.上述研究成果为调控猕猴桃等果实采后AsA的含量，降低果实采后AsA损失量，为提高采后果实的营养品质提供了理论依据。同时，为通过基因工程技术等改良选育果实采后具有高AsA合成、再生代谢活性的新品种，特别是猕猴桃新品种提供了理论基础和参考指标。