基于糖酸变化的柑橘果实枯水病发生机制的研究

Section drying of Citrus fruit, with high incidence during postharvest storage, is the major physiological disorder limiting the storage life and shelf-life quality of fruit. Deterioration of fruit edible quality, key aspect of which are sugars and organic acids, is the most notable feature of Citrus fruit of section drying. The mechanism underlying the excessive consumption of sugars and organic acids of fruit and further section drying has not yet been fundamentally clarified. Several dominant hypotheses, which were proposed by recent decades of research, claimed that certain metabolism pathways, e.g., sugar transportation from pulp to peel, respiration consumption of sugar and organic acid, are closely related to section drying in Citrus fruit. However, few study has focused on systematic analysis of the content changes in sugars and organic acids components, and further various metabolism of sugars and organic acids in Citrus fruit pulp during the process of section drying. In our previous research, the content of total soluble sugars and organic acids increased gradually from stem end to stylar end of pulp in normal fruits, which is similar with fruits of section drying to some extent. Therefore, two different parts (stem end and stylar end) of pulp are subjected parallelly to the subsequent analysis in the whole study. The present project is aimed to perform the following experiments: 1) systematic analysis of content changes in sugars and organic acids components of Citrus fruit pulp during the process of section drying; 2) to analyze changes in various metabolism pathways of sugars and organic acids in the Citrus fruit pulp during the process of section drying, mainly based on two levels, including expression of related genes and activity of related enzymes. Finally, the present project is expected to determine the variation characteristics of sugars and organic acids components of Citrus fruit pulp during the process of section drying, and further determine the major metabolic pathway which would be responsible for the content changes in sugars and organic acids of fruit. Taken these together, it is expected to elucidate the mechanism underlying section drying in Citrus fruits from the point of sugars and organic acids. The present project would be beneficial for further development of efficient strategies against section drying in Citrus fruit.

柑橘果实枯水病常发生于采后贮藏过程，是影响柑橘贮藏寿命和货架期品质的主要生理性病害。枯水果最为显著的特征是以糖酸为核心的食用品质发生劣变。学术界还未能从根本上阐明诱发果实糖酸急剧消耗并枯水的内在机制。此前研究提出多种假说，分别揭示糖从果肉到果皮的转运、果肉呼吸对糖酸的消耗等代谢途径与枯水紧密相关。但柑橘果实枯水过程中糖酸变化及糖酸代谢相关途径的系统分析鲜见报道。申请人在前期工作中发现，糖酸含量在正常果实中从果蒂处向果顶处逐渐升高，与枯水果有类似之处。因此，本项目以不同部位(果蒂处、果顶处)的柑橘果肉为实验材料，系统分析枯水病发生过程中糖酸组分含量的变化特征；并从基因表达和酶活性两个水平分析糖酸代谢途径的变化，明确枯水过程中导致果肉糖酸变化的主要代谢途径，阐明基于糖酸变化的柑橘果实枯水病发生机制。本项目将有助于从本质上探讨柑橘的枯水机制，对于枯水病高效防控技术的研发具有理论指导意义。

柑橘果实枯水病常发生于采后贮藏过程，是影响柑橘贮藏寿命和货架期品质的主要生理性病害。枯水果最为显著的特征是以糖酸为核心的食用品质发生劣变。学术界还未能从根本上阐明诱发果实糖酸急剧消耗并枯水的内在机制。此前研究提出多种假说，分别揭示糖从果肉到果皮的转运、果肉呼吸对糖酸的消耗等代谢途径与枯水紧密相关。但柑橘果实枯水过程中糖酸变化及糖酸代谢相关途径的系统分析鲜见报道。糖酸含量在正常果实中从果蒂处向果顶处逐渐升高，与枯水果有类似之处。因此，本项目以不同部位(果蒂处、果顶处)的柑橘果肉为实验材料，运用代谢组学系统分析枯水病发生过程中糖酸组分含量的变化特征；运用转录组学系统分析糖酸代谢途径基因及相关调控因子表达变化。结果阐明细胞壁组分合成可能是柑橘枯水时糖酸物质快速降解的主要原因。本项目将有助于从本质上探讨柑橘的枯水机制，对于枯水病高效防控技术的研发具有理论指导意义。