呼吸作用对水果采后功能性品质的调控作用

The formation and regulation of the functionally nutritional quality of harvested fruits during storage is an important scientific issue in postharvest research area. Typical climacteric fruits such as papaya, mango and banana require a respiration climacteric to reach an edible phase while the respiration climacteric is a highly coordinated activity of life through a series of complex metabolic reactions and the conversion of nutrients with the changes in color, texture, flavor and aroma components, concerning the gene expression, and physiological and biochemical metabolism of the formation and regulation of the functionally nutritional quality. The proposal will choose the climacteric fruits such as mango and papaya which are rich in antioxidant compounds such as flavonoids and carotenoids, and then investigate the formation and regulation of functionally nutritional quality of harvested fruits during storage. The project will determine antioxdiant properties, identify antioxidant compounds, elucidate the basis of respiration as a centre of the formation and regulation of the antioxidant compounds, clarify the role of sugar as a signal substance in regulating the antioxidant compounds, understand the molecular basis of the biosynthetic pathway and regulation of key enzymes (PAL, CHS, CHI and PSY) 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. Based on these investigations from the respiratory pathway, the signal substances, gene, protein, enzyme activity, metabolism system and storage conditions, the expected achievements will exhibit a more comprehensive and clear understanding of the formation and regulation of the functionally nutritional quality of postharvest climacteric fruits, which thus reveals the variation in the functionally nutritional substances, then understand the regulatory pathways of the functionally nutritional compounds and finally improves the functionally nutritional quality in postharvest fruits.

水果采后功能性营养品质的形成、变化规律及其调控途径是当前深受研究者所关注的一个重要科学问题。本项目以富含黄酮类、类胡萝卜素等抗氧化物质的芒果、木瓜呼吸跃变型果实为研究对象，重点研究果实在采后贮藏过程中抗氧化营养品质的形成与调控机制。研究内容包括明确采后芒果、木瓜果实中的抗氧化物质与抗氧化特性，探讨以呼吸作用为中心的抗氧化物质形成与调控的物质基础，阐明糖信号物质对抗氧化物质形成与调控的作用方式，并了解类黄酮、类胡萝卜素生物合成途径的关键酶（PAL、CHS、CHI、PSY等）调控的分子基础，探讨贮藏环境条件对果实采后抗氧化物质形成与调控的作用。项目从呼吸途径、信号物质、基因、蛋白、酶活性、物质代谢体系、贮藏环境因素等方面开展研究。研究成果将对呼吸跃变型果实采后营养品质的形成与调控有一个较全面和清晰的认识，进而揭示水果采后营养品质形成的变化规律及其调控途径，提高果实营养品质。

本项目在前期阶段性研究基础上，开展了包括明确富含黄酮类、类胡萝卜素等水果采后抗氧化物质与抗氧化特性，探讨抗氧化物质形成与调控的物质基础，阐明信号物质对抗氧化物质形成与调控的作用方式，并解析类黄酮、类胡萝卜素生物合成途径的关键酶调控的分子基础，以及荔枝果实采后在贮藏过程中营养品质与能量特性和能量亏缺机制和CPPU（N-2-氯-4-吡啶基）-N’-苯基脲和草酸处理对香蕉采后品质形成与后熟衰老的影响的初步机制等工作。在项目执行期间，通过HPLC-MS首先鉴定了番木瓜果肉中含有的7种类胡萝卜素，初步阐明了‘穗黄’和‘穗红’番木瓜果肉类胡萝卜素代谢相关基因表达的变化规律，并结合CPPU处理研究了延缓番木瓜成熟过程中类胡萝卜素代谢相关基因的调控机理，认为番木瓜果肉中的活性氧可能与类胡萝卜素代谢相关；并初步推测H2O2可能作为信号分子在番木瓜类胡萝卜素代谢中起着重要作用。对荔枝果实在贮藏过程中营养品质与能量特性和能量亏缺机制研究表明，LcAtpB转录水平在采后2 d迅速上调，LcAOX1转录水平显著上调，ATP产生效率降低；外源ATP处理下调LcATP、LcAOX1和LcAAC1的转录水平，并且下调了LcSnRK2的变化幅度，从而维持了果实组织能荷水平、延缓果实组织衰老劣变，认为能量耗散和转运失调可能是造成果实采后ATP合成不足从而导致采后荔枝褐变的关键因素。另外，本项目还提出了CPPU处理可保持果皮组织中内源细胞分裂素较高水平，抑制细胞分裂素氧化酶活性，进而延缓香蕉果实采后后熟衰老进程；而外源草酸处理能降低果实的乙烯释放速率和呼吸速率，延缓果皮色泽转化，提高果实组织的超氧化物歧化酶活性和抗氧化能力，抑制内源活性氧的产生。本项目研究结果有助于对水果采后营养品质的形成及其调控途径的认识，为提高果实营养品质提供了理论和技术支撑。