缓慢降温抑制采后鸭梨果实褐变的转录组分析及机理研究

Core browning often occurs during the storage of Yali pear, and this problem has been solved by combining timely harvesting with slow cooling. The most researches of its mechanism focus on restraining browning of Yali pear by slow cooling to restrained the respiration, ethylene production, active oxygen metabolism and various physiological and biochemical reactions, adjusted the hormone metabolism, inhibited the PPO activity, decreased the accumulation of CO2 and ethylene in ovary cavity . The PPO、POD and LOX, and the relationship between gene expression and browning have also been researched. What's the key enzyme gene that had caused fruit browning during storage? And how does it regulate the browning of fruit? These problems haven't been explained systemically by far.In this study, early picked, medium picked and late picked Yali pears are going to be treated with rapid and slow cooling. By the transcriptome sequencing technology, the key enzyme genes which caused browning in core, pulp and seed of Yali fruit will be found, cloned, and characterization analyzed. At the same time, track the respiration and ethylene release, tissue ultrastructure, key enzyme activity, isozyme and enzyme gene expression differences of the different position in storage time. The project will reveal the relationship between the key gene and browning, explore the physiological and molecular mechanisms of slow cooling inhibits the browning of Yali pears after harvest, lay the theoretical foundation to inhibit the browning of Yali pears and improve the storage quality.

鸭梨果实在贮藏中易发生果心褐变现象，生产上通常采用适时采收结合缓慢降温的方式防止褐变的发生。关于其机理研究，主要集中在缓降温抑制鸭梨果心、果肉和种子的呼吸、乙烯、活性氧代谢和各种生化反应，调节激素代谢，抑制果实PPO酶活性，降低子房室CO2和乙烯积累等方面。对PPO、POD和LOX酶及基因表达与褐变的关系也进行了初步探讨。在贮藏程中引起鸭梨褐变的关键酶基因到底是什么？它们又如何调控果实的褐变？至今还没有系统的阐述。本课题拟用急速和缓慢两种降温方式对早、中、晚三种成熟度鸭梨果实进行处理，利用转录组测序技术挖掘引起果实褐变的果心、果肉和种子的关键酶基因，并进行克隆和表征分析；同时对相应部位的呼吸和乙烯释放、组织超微结构、关键酶酶活、同工酶和酶基因表达差异进行跟踪检测，揭示关键酶基因与褐变的关系，探索缓慢降温抑制采后鸭梨果实褐变的生理及分子机理，为抑制鸭梨果实褐变，提高贮藏品质奠定理论基础。

鸭梨是我国特有的传统优势梨品种，在贮藏中容易发生果心褐变，生产上通常采用适时采收结合缓慢降温的方法加以解决。本课题主要研究快速降温和缓慢降温处理对早、中和晚采套袋鸭梨果实褐变的影响，利用转录组测序技术挖掘出引起果实褐变的关键基因并进行验证；探索缓降温抑制鸭梨果实褐变、不同降温方式对不同成熟度鸭梨褐变影响的机理。结论如下：. 对于2015年度样品：中采鸭梨果发育适中，不易褐变，缓降温抑制果实褐变；缓降温通过抑制ACO表达，延缓乙烯和呼吸高峰的出现，抑制LOX表达和LOX活性，维持果心较高的FAD表达量，保持稳定的USFA含量，维持正常的膜功能和硬度，减少褐变发生。晚采果糖度和风味增加，硬度下降，衰老快，褐变较中采果严重；缓降温使晚采果呼吸强度和乙烯释放增高，促进PAL、PPO基因上调表达、POD基因下调表达，清除自由基作用减弱，衰老加快，最后导致较急降温果更易褐变。. 对于2016和2017年度样品：早采鸭梨糖度低，酸度大，贮期不易褐变；中采果糖度、乙烯释放量、呼吸强度和抗冷性提高；晚采果风味和含糖量提高，硬度下降，衰老快。随着成熟度的提高鸭梨果实褐变严重，缓降温比急降温都加重了三种成熟度鸭梨的果心褐变。缓降温促进鸭梨采后果心ACS表达和提高ACO活性，刺激乙烯释放和呼吸作用；促进β-Gal基因表达和果实软化；促进POD基因下调表达，抑制APX和SOD基因表达，促进LOX31上调表达，降低POD、APX和SOD活性，提高LOX活性，使果实清除自由基能力降低；促进LAC6、LAC7和LAC14基因上调表达和LAC活性提高，导致鸭梨果心部位褐变较急速降温处理果严重，并且这种效应随着鸭梨果实成熟度的提高而加剧。. 综上，鸭梨果实褐变是一个复杂过程，与采前气候、管理、年份、成熟度、品质，采后降温速度、贮温、气体等因素有关；不同品质的鸭梨应采用不同的降温方式贮藏。本研究获得的与鸭梨褐变相关的重要基因，为后续进行深入研究和进一步揭示鸭梨褐变机理奠定良好基础。