柿果实乙烯合成的启动与氧化还原电位及相关酶活性的关系

As a featuring characteristic fruit of China, persimmon (Diospyros kaki) has a wide international market, while the postharvest problems retard its industry development. Regulation of ethylene is meaningful to prolonging the fruit storage period, but the mechanism of induction of ethylene synthesis in fruit is still unknown. Our previous study suggest that on-tree transport of photosynthates to fruit inhibits the induction of ethylene synthesis in persimmon, and it is hypothesized that the sugar supply would keep the oxidation-reduction potential (ORP) at a high level so ACC could be not oxidized to ethylene. The present project will apply different pre-/post-harvest treatments to investigate their effect on fruit ethylene production, in order to the find relationship among ethylene induction, fruit ORP and related enzymes activity, also to characterize the key enzymes and their coding gene expression. The mechanism of ethylene induction in pre-/post-harvested fruit will be clarified and a unified biological model will be established. New evidence for study on ethylene regulation and guidance for improving fruit storability will be provided.

柿是我国的特色水果，具有广阔的国际市场，但采后储藏问题严重阻碍柿产业的发展。控制乙烯代谢对于延长果实储藏期具有重要意义，但乙烯生物合成的启动机制尚不清楚。申请人前期研究发现柿树体内动态的“光合产物流”对果实乙烯合成启动起到抑制作用。据此提出假设：树体“光合产物流”影响果实乙烯合成启动的实质是通过维持“高氧化还原电位”阻碍ACC氧化为乙烯。本项目拟采用采前/采后不同处理，研究对果实乙烯释放的影响，明确果实乙烯合成的启动与氧化还原电位及相关酶活性的关系，确定参与柿果实乙烯启动的关键酶并研究其编码基因的表达，阐述采前/采后柿果实乙烯合成的启动机制，建立统一的生物模型，为乙烯生物调控机理研究积累基础性资料，也为果实保鲜期的调控提供理论依据。

柿采后季节相对集中，并且对乙烯极为敏感，果实采后快速后熟，导致鲜果软化、褐变速度快，经常面临成批腐坏变质的情况，直接影响其流通、商品价值及国内外市场占有率。控制乙烯代谢对于延长果实货架期具有重要意义，本研究分别从生理生化和分子水平阐述采前/采后柿果实乙烯合成的启动机制，建立统一的生物模型，为果实保鲜调控提供理论依据。研究结果表明：（1）柿果实采前/采后通过摘叶/乙烯利等处理，打破ORP稳定状态，ORP值急剧升高，氧化还原平衡向氧化反应方向反应，引发乙烯合成的启动。同时，果实内源抗氧化剂黄酮、总酚、花青素、谷胱甘肽、抗坏血酸等大量消耗，抗氧化酶SOD、POD、GR、APX、CAT活性增强。外源AsA处理则通过促进内源AsA增加，减缓ORP的升高，抑制乙烯生物合成启动；（2）通过对转录组测序得到的DEGs进行Pathway显著富集分析发现，乙烯生物合成中的半胱氨酸和蛋氨酸代谢、乙烯信号转导、以及类胡萝卜素、谷胱甘肽、烟酸和烟酰胺等抗氧化剂合成代谢相关通路中大量基因参与柿果实乙烯合成的启动；（3）经qRT-PCR基因表达验证，以上合成代谢和信号转导通路上的关键酶基因MetE、EBF1、RBOH、CYP72A219等基因的表达量均明显升高。