能量亏损介导的荔枝果实采后果肉质地劣变的生理生化机制

The mechanism of texture deterioration of harvested fruit in relation to its control is a basic scientific problem in postharvest research area. It is also a difficult problem to maintain well the texture quality of fruit after harvest in practice. Polysaccharides are the major material basis for fruit texture. Based on our previous research results and knowledge of the postharvest research development, this project will use the specialty fruit (lychee) in southern China as the research material, focus on the texture quality based on arabinogalactan as one of the major polysaccharide of fresh lychee flesh, elucidate the accurate chemical structures of various polysaccharides and their changes, understand the coupling relationship of energy deficiency and oxygen free radical generation in relation to the energy deficiency threshold, determine the synergistic effect of oxygen free radicals and cell wall hydrolases on the degradation of polysaccharides, and clarify the catalytic function and mechanism of these cell wall hydrolases. The project will emphasize the degradation mechanism of arabinogalactan present in fresh lychee flesh in terms of the "energy - reactive oxygen species" trigger and the energy deficiency as an internal key factor. The results of the study will obtain a comprehensive and clear understanding of the physiological and biochemical mechanism of deterioration of flesh texture of harvested lychee fruit mediated by energy deficiency and then elucidate the change rule in the texture quality of postharvest fruit to help to improve the commercial quality.

水果采后质地品质劣变机制及其调控途径是当前研究者所关注的一个基本科学问题，也是当前水果采后研究的技术难点问题。多糖是构成果实质地的主要物质基础。本项目是在我们前期研究和对学科发展认识的基础上，以我国华南地区荔枝特色水果为研究对象，围绕果肉质地品质的核心问题，针对阿拉伯半乳聚糖作为荔枝果肉质地品质的主要多糖之一，明确多糖精确化学结构，揭示其变化信息；阐明组织能量亏损与氧自由基产生的偶联关系，并确定果肉组织能量亏损阈值；解析能量亏损与氧自由基产生因果关系以及氧自由基与细胞壁水解酶参与多糖降解的协同作用，并阐明酶催化功能与催化机制；以“能量-活性氧”作用方式为切入点和能量亏损作为内部关键因素，重点揭示阿拉伯半乳聚糖降解机制。研究成果将对能量亏损介导的荔枝果实采后果肉质地劣变的生理生化机制有一个较全面和清晰的认识，进而揭示水果采后质地品质劣变的变化规律及其机制与调控途径，提高果实商业品质。

荔枝是我国南方特色水果之一，但易发生品质劣变，严重限制物流销售。果肉自溶是影响荔枝果实质地品质的关键因素。其中，多糖结构降解是荔枝发生果肉自溶的物质基础，也是果实采后衰老的早期表现形式和基本特征；而这些变化又进一步引起细胞代谢异常,特别是分解代谢进程加快,加速果实品质劣变发生。本项目针对多糖结构与代谢，以“能量”作用方式为切入点和能量亏损作为内部关键因素，探讨了荔枝果实采后果肉多糖降解特性和能量亏损介导的多糖降解的生理生化作用机制。随着荔枝果实贮藏时期的延长，并伴随着细胞壁的解体，果肉水溶性多糖含量明显下降，并发生逐步降解作用；在荔枝果肉多糖降解过程中，明确了果肉多糖主要为阿拉伯半乳聚糖；而单糖组成以阿拉伯糖和半乳糖为主，甘露糖、葡萄糖和鼠李糖次之；多糖结构整体保持相对稳定，多糖降解主要由半乳糖醛酸主链上多种支链断裂所引起。在荔枝果实贮藏过程中，细胞壁水解酶的基因表达增强和活性增加，活性氧自由基在果肉中积累增加，并促进细胞壁多糖的降解；而果肉中的ATP、ADP含量下降，并发生能量亏损，整体细胞代谢以水解为主；LcAtpB转录水平下降，与组织能荷水平呈负相关；LcAOX1转录水平显著上调，ATP产生效率降低。ATP处理延缓了荔枝果肉中的ATP和ADP含量下降，维持了果实贮藏后期较高的能荷水平，下调了LcATP、LcAOX1和LcAAC1转录水平以及LcSnRK2转录的变化幅度，从而减轻了果肉自溶的发生。研究结果提出了基于能量调控细胞壁多糖引起的荔枝果肉自溶发生和基于多糖代谢调控荔枝果肉自溶的作用机制，促进了对能量亏损介导的荔枝果实采后果肉质地劣变的生理生化机制的认识，丰富了现有水果采后衰老生物学基础理论，研发出能量相关处理技术，为保障果实采后品质提供了重要的理论依据和实践指导。.项目获神农中华农业科技奖优秀创新团队奖和中国产学研合作创新奖，发表论文13篇(SCI收录11篇)，获国家授权发明专利2件，申请国家发明专利1件，培养硕士2名、博士1名和博士后1名。