活性氧导致的能荷状态和呼吸代谢途径改变在采后龙眼果实果肉自溶发生中的作用

Longan (Dimocarpus longan Lour.) is one of importmant subtropical fruit in southern China. Aril breakdown is the major quality deterioration in harvested longan fruit, which is the most important factors degrading the eating quality and commodity value of harvested longans. Our previous studies show that the senescence-induced browning development in pericarp of harvested longan fruit is associated with energy status and respiratory pathway metabolism. Reactive oxygen species (ROS) cuold promote the development of aril breakdown in harvested longan fruit. However, the changes in energy status and respiratory pathway metabolism during the development of aril breakdown in harvested longan fruit, and its relationship with the development of aril breakdown in harvested longan fruit still not clear. No literature has been published on ROS induced-changes in energy status and respiratory pathway metabolism in relation to the development of aril breakdown in harvested longan fruit. The objectives of this study are to clarify the possible mechanism of the development of aril breakdown in harvested longan fruit by investigating the changes in active oxygen metabolism, energy metabolism, respiratory metabolism, and cell wall metabolism during the development of aril breakdown in harvested longan fruit. Meanwhile, in order to further confirm the alterations in energy status and respiratory pathway metabolism caused by ROS in association with the development of aril breakdown in harvested longan fruit, the effects of ROS (H2O2 or . OH ) or ROS scavengers (propyl gallate or AsA) on the development of aril breakdown, active oxygen metabolism, energy metabolism, respiratory metabolism, and cell wall metabolism are investigated. The results hope to obtain new theory basis in clarifying possible mechanism of the development of aril breakdown in harvested longan fruit caused by ROS.

果肉自溶是采后龙眼果实主要的品质劣变现象，严重影响其食用品质和商品价值。我们前期研究发现，采后龙眼果实果皮衰老褐变与能荷状态及呼吸代谢途径有关，活性氧会促进龙眼果实采后果肉自溶的发生。但龙眼果实采后果肉自溶发生过程中能荷状态和呼吸代谢途径的改变及其与果肉自溶的关系尚不清楚，有关活性氧导致的能荷状态和呼吸代谢途径改变在龙眼果实采后果肉自溶发生中的作用机制未见报道。本研究拟从龙眼果实采后果肉自溶发生过程中的活性氧代谢、能量代谢、呼吸代谢、细胞壁物质代谢等方面，阐明龙眼果实采后果肉自溶发生机制；同时研究外源活性氧和活性氧清除剂对采后龙眼果实果肉自溶发生、活性氧代谢、能量代谢、呼吸代谢、细胞壁物质代谢的影响，来进一步证实活性氧导致的能荷状态和呼吸代谢途径改变在龙眼果实采后果肉自溶发生中的作用。研究成果可望阐明活性氧所致龙眼果实采后果肉自溶发生的可能机制方面获得新的理论依据。

本项目研究外源活性氧（过氧化氢）和活性氧清除剂（棓酸丙酯）对‘福眼’龙眼果实采后果肉自溶发生的影响及其与呼吸代谢、能量代谢、活性氧代谢和细胞壁物质代谢的关系。主要结果：1）与对照相比，过氧化氢处理龙眼果实保持较高的果实呼吸速率、果肉自溶指数、PGI、SDH、CCO、AAO、PPO和AOX活性以及NAD（H）含量，保持较低的NADK活性、G-6-PDH和6-PGDH总活性和NADP（H）含量。说明过氧化氢处理会降低PPP而提高EMP、TCA和CCP在呼吸代谢途径中所占比例，提高龙眼果实呼吸作用而促进果肉自溶。然而，棓酸丙酯处理可减轻龙眼果实果肉自溶的发生与PPP途径在呼吸代谢途径比例增加有关。2）过氧化氢处理的龙眼果实保持较高的果肉AMP含量，较低的果肉ATP、ADP含量、能荷值和ATPase活性。说明过氧化氢处理会加快能量消耗而导致能量供应不足，最后促进龙眼果肉自溶发生。棓酸丙酯处理可减轻龙眼果实果肉自溶的发生与较高保持的能荷值有关。3）过氧化氢处理龙眼果实保持较高的果肉O2-.产生速率、MDA含量，以及较低的果肉活性氧清除酶活性及其对应基因相对表达量，AsA、GSH、类黄酮和总酚含量，DPPH自由基清除能力和总还原力。表明过氧化氢处理会降低活性氧清除能力，促进果肉细胞内活性氧的产生和积累，进而促进果肉自溶发生。棓酸丙酯处理可减轻龙眼果实果肉自溶的发生与较高的活性氧清除能力有关。4）过氧化氢处理的龙眼果实保持较低果肉硬度、果肉CWM、CSP、ISP、纤维素和半纤维素含量；较高果肉的WSP含量、XET、PE、PG、β-Gal和Cx活性及基因相对表达量。结果表明过氧化氢处理会促进果肉细胞壁降解酶基因相对表达量上调而导致果肉细胞壁降解酶活性升高和加快果肉细胞壁物质降解，进而促进果肉自溶。棓酸丙酯处理可减轻龙眼果实果肉自溶的发生与细胞壁结构完整性的保持有关。