基于呼吸代谢途径的采后桃果实抗氧化活性调控机制研究

There are accumulating researches indicating the antioxidant compounds from fruit have biological properties that can enhance health benefit. Since antioxidant capacity is becoming an important quality parameter for postharvest fruit, it is focusing on the regulation and improvement of antioxidant activity in postharvest fruit based on molecular and physiological mechanisms. Respiratory metabolism is one of the most important physiological activity of posthavest climacteric fruit, and is also closely related to the biosynthesis of different bioactive compounds. However, little information is available on respiratory metabolism, which could impact on the nutritive and functional properties of peach fruit after harvest. The project will identify antioxidant compounds, determine the effect of respiratory metabolism on the biosynthesis and metabolism of antioxidant composition (such as phenolic acid, flavonol, flavan-3-ol, anthocyanin and carotenoids) and key enzymes expressions in postharvest peach fruit of different varieties (Red-flesh, Yellow-flesh, and White-flesh) at different mature stages. Based on investigations from the respiration pathway, the proposal will reveal the specific mechanism of respiratory metabolism involved in the biosynthesis of such antioxidant compounds, understand the molecular basis of the biosynthetic pathway and regulation of key enzymes of flavonoids and carotenoids, and clearify the role and regulation of storage environmental conditions on the antioxdiant properties and antioxidant compounds of harvested fruits during storage. The combined results will also provide theoretical basis for regulation of antioxidant compounds metabolism and finally improves the nutritional quality in postharvest fruits.

果实中天然抗氧化物质对人类健康的作用正日益受到人们的重视，抗氧化活性的大小已成为衡量果实采后品质的一个重要指标，维持和提高果实采后抗氧化能力已成为果实采后贮运保鲜研究中的热点。呼吸代谢是跃变型果实采后重要的生理活动之一，与果实采后抗氧化物质的形成存在密切的联系，但机制不明。本项目以不同果肉颜色的桃果实（红肉桃、黄肉桃和白肉桃）和不同成熟度的桃果实为试验材料，以果实采后莽草酸和异戊二烯合成途径为核心内容，从桃果实采后呼吸跃变生理入手，研究果实采后主要酚酸、黄酮醇、黄烷-3-醇、花色苷和类胡萝卜素消长的规律，并进一步从桃果实采后呼吸代谢中间产物及关键酶与上述次生物质代谢关键酶的基因表达水平探讨呼吸代谢对果实采后抗氧化能力的影响作用，揭示呼吸代谢在桃果实采后抗氧化活性过程中的作用机制，为果实采后抗氧化物质代谢和抗氧化能力调控提供理论依据。

从桃果实中克隆了7个类胡萝卜素合成基因、向光素基因PpPHOT1以及隐花色素基因PpCRY2的cDNA全长序列。 “金丽”和“湖景”品种嫩芽中的β-胡萝卜素、叶黄素和玉米黄素含量较高。类胡萝卜素合成相关基因在果肉中的表达与总胡萝卜素、β-胡萝卜素和叶黄素变化一致，PpFPPS和PpGGPPS在果皮中的表达显著高于果肉。PpPDS表达水平与总类胡萝卜素、β-胡萝卜素、β-隐黄素、玉米黄素和叶黄素含量呈显著正相关。经1-MCP（10μL/L）处理的桃果实，类胡萝卜素合成相关基因的表达受到明显抑制，蓝光处理（40μmol /m2s）可有效缓解种抑制效应。蓝光处理显著增强了桃果实PpPHOT1和PpCRY2基因的表达。1-MCP和蓝光先后处理的“金丽”果实中PpPHOT1和PpCRY2的表达与PpGGPPS、PpPSY、PpbLCY和PpbHY的表达呈显著正相关，这可能是1-MCP和蓝光先后处理的“金丽”果实类胡萝卜素含量高于其他处理的原因之一，而PpPHOT1和PpCRY2可能是桃果实采后响应外源蓝光信号的重要因子。乙烯处理促进果实贮藏期间花色苷的合成与积累，主要通过提高贮藏后期果实中PpCHI、PpF3’H、PpANS和PpUFGT基因表达量，PpF3H是乙烯处理特有调控基因。乙烯处理通过增强了桃果实采后后熟过程乙烯合成与信号转导；1-MCP处理降低贮藏后期果实乙烯含量，主要与PpLOX3、PpERS1抑制表达以及PpCTR1的增强表达有关。1-MCP处理通过降低处理初期PpPK、PpTPI、PpCS1、PpICDH和PpMDH基因表达量，从而抑制桃果实的呼吸代谢；蓝光处理提高了桃果实贮藏前期的呼吸代谢途径中PpADH、PpHK、PpPGI、PpICDH、PpSDH和PpGDP基因表达水平，促进桃果实呼吸代谢。100 μmol/L外源褪黑素处理提高了贮藏第14 d抗坏血酸合成关键基因的表达量，促进抗坏血酸的积累，但却抑制了果实中GSH水平的升高。外源褪黑素通过上调抗氧化系统关键酶基因的表达，激活活性氧清除酶，减少ROS的积累，缓解低温胁迫对抗氧化系统的损伤。外源褪黑素处理也抑制了蔗糖分解酶基因的表达，提高了蔗糖合成相关酶基因的表达水平，维持果实较高的蔗糖和葡萄糖含量。上述结果表明，蓝光、1-MCP、乙烯和外源褪黑素可通过调控桃果实呼吸代谢进而影响果实抗氧化能力。