【作者】 汤谧；

【导师】 别之龙； 吴明珠；

【作者基本信息】 华中农业大学 ， 设施园艺学， 2010， 博士

【摘要】 甜瓜生产在世界园艺产业中占有重要地位,我国是甜瓜生产大国,随着生活水平的提高,人们对果实品质的要求越来越高。改善果实内在品质是提升甜瓜品质的关键,其中糖、酸组分及其含量对果实内在品质有着重要的影响,是决定果实风味的重要指标。本研究以新疆农业科学院哈密瓜研究中心培育出的风味甜瓜系列品种(‘风味2号’、‘风味3号’、‘风味4号’)、相关亲本(‘酸瓜’——高酸积累型和‘寿星’——低酸积累型)和传统品种(‘雪丽’和‘雪里红’)为主要实验材料,从生理、生化和基因表达等多个层面,深入探讨风味甜瓜果实高糖高酸性状形成的生物学基础。主要研究结果如下：1.对风味甜瓜果实特性的观察结果表明,‘风味2号’果实的最佳成熟期在30～35DAP之间,该时期内果实的鲜重、大小、果肉厚度、糖酸含量和一些营养指标等各项指标均有较高值。风味甜瓜的独特之处在于成熟时果肉含有酸味。独特酸味主要由柠檬酸引起,属于柠檬酸积累类型果实。2.对风味甜瓜和对照品种甜瓜植株的光合特性的观察结果表明,不同甜瓜品种的光合特性表现出一定差异。‘风味3号’和‘雪丽’在结果初期的净光合速率都高于幼苗期,‘雪里红’则略有下降,到结果中期,3个品种都较结果初期有所下降,但是‘风味3号’的下降幅度最小；‘风味3号’的叶色值显著高于对照,是其具有高光合速率的直观表现；而引起3个品种的光合效率降低的原因是叶片受到气孔限制,但是程度不一致；另外,在结果中期,‘风味3号’的胞间CO2浓度显著低于对照,表明此时‘风味3号’羧化效率高,更多的CO2被固定,生成的同化物供应果实的生长发育。3.采用GC和Real-time PCR等技术测定了不同发育时期风味甜瓜和对照品种甜瓜果实中主要可溶性糖的含量、蔗糖代谢途径关键酶基因的表达以及酶活性。结果表明,甜瓜果实在成熟前约15～20 d时出现大量的蔗糖积累,在果实成熟时,蔗糖是果实中主要的可溶性糖。在‘风味4号’和‘酸瓜’的果实发育中,SPS基因的表达和酶活性与蔗糖的积累一致,而‘寿星’在整个发育期间表现出很低的AI活性和高蔗糖含量。所以,很可能存在两种蔗糖积累的机制：一种是果实随着SPS活性增加而积累,另一种是果实在AI低于某一阈值时才出现蔗糖积累。4.采用GC和Real-time PCR等技术测定了不同发育时期风味甜瓜和对照品种甜瓜果实中主要有机酸的含量、代谢途径关键酶基因的表达以及酶活性。结果表明,柠檬酸是甜瓜果肉中的主要有机酸；在5-25 DAP期间,ACO和ME的活性都与柠檬酸含量的变化呈显著正相关,而‘风味3号’中2种酶的活性比‘雪里红’高,因此‘风味3号’的柠檬酸含量更高；‘风味4号’和‘酸瓜’中柠檬酸代谢酶类的活性普遍高于‘寿星’,表明前二者的卡尔文循环加速,柠檬酸作为中间产物其含量提高。然而‘寿星’的蔗糖含量最高,其次依次是‘风味4号’和‘酸瓜’,而酸含量的排序正好相反,该结果表明,在有机酸积累型果实中更多的同化物被分配到柠檬酸循环中来,故‘风味4号’中柠檬酸的积累很可能是由于柠檬酸循环加速导致中间产物柠檬酸的积累。5.采用GC-MS技术测定了成熟的风味甜瓜和对照品种甜瓜果实的挥发性物质。结果表明,‘风味2号’甜瓜果实成熟时有代表性的挥发性物质为邻苯二甲酸二乙酯、邻苯二甲酸二甲酯和(E,E)-2,4-癸二烯醛；而‘风味3号’和‘雪丽’果实的挥发性物质主要是酯类和酮类,其含量分别占各自总挥发性物质含量的70%以上,其余的为醇类、醛类和硫代化合物等其他物质；而‘风味3号’的酯类含量为43.03%,‘雪丽’为65.61%,‘风味3号’的酮类含量为30.08%,‘雪丽’为10.07%；4-羟基-2-丁酮和邻苯二甲酸异丁酯是‘风味3号’果实的主要挥发性物质。以上研究结果表明,相对传统甜瓜品种以及风味甜瓜亲本品种而言,风味甜瓜果实的品质发生了根本性的变化,形成了糖酸兼具的独特口感。这种品质形成的过程是：具有较强光合作用的植株为果实发育提供了更多同化物,在具有较高的糖分积累的基础上,果实还将相对更多的同化物分配到有机酸循环中而形成较多有机酸,从而使果实同时具有的较高的糖酸含量。更多还原

【Abstract】 The melon production plays an important role in the horticultural industry of the world, and China is one of the great melon-producing countries. The fruit quality became more and more cruial to consumers with the improvement of living standards of people. To improve the fruit inner quality is the key to raise melon quality, and the compositions and contents of sugars and acids impact the melon inner quality significantly because they reflect an important indicator of fruit flavor. Cucumis melo L. Flavor Melon series were a kind of novel melon and bred out by Xinjiang Academy of Agricultural Science. These melon fruits cause both high sugar and high acid accumulation. In this reserach, the leaves and fruit flesh of Flavor Melon series (’Flavor No.2’,’Flavor No.3’, and’Flavor No.4’), some parents of Flavor Melon [’Suangua’(high organic acid accumulation-type) and’Shouxing’(low organic acid accumulation-type)] and some traditional melon cultivars (’Xueli’and’Xuelihong’) as the experiment materials, in order to conduct a combined physiology, biochemical and gene expression study to understand the differential accumulation of sugar and acid in melon fruits and to explore the biological basis of the formation of high sugar and high acid contents. The main results were as follows:1. The observation of fruit characteristics of Flavor Melon revealed that the fruit of ’Flavor No.2’obtained the best quality during 30-35 DAP, involving fresh weight, size, pulp thickness, contents of sugar and acid, and some other index. The sour tasted fruit was the novelty of’Flavor No.2’, and this was resulted from the accumulation of citric acid.2. The observation of photosynthetic characteristics of Flavor Melon and control cultivars revealed that there were some differences in different melon cultivars. The net photosynthetic rate of’Flavor No.3’and’Xueli’in the initial stage of fruit development were higher than those in vegetative growth stage, instead’Xuelihong’was lower. In the middle stage of fruit development, the net photosynthetic rate of three cultivars were all lower than those in the initial stage, additionally the decline in’Flavor No.3’was the least. The SPAD value of ’Flavor No.3’was higher than those of control melons, and this was an obvious appearance suggesting its higher photosynthetic rate. The declines of photosynthetic rate in three cultivars were because of the stomatal limitation in different degree. In the middle stage of fruit development, the intercellular CO2 concentration of ’Flavor No.3’was significant lower than the control melon, this indicated that the carboxylation efficiency of Flavor No.3’was higher, and more CO2 was fixed, so more photosynthate were supplied for the fruit development.3. GC and real-time PCR techniques were used to determine the main soluble sugar content, sugar metabolic pathway key enzyme genes expression and activity in Flavor Melon and control cultivars at different developmental stages. The results showed that there was a large number of sucrose accumulation when 15-20 d before melon fruit got mature. And sucrose is the major soluble sugar in mature fruit. In’Flavor No.4’and ’Suangua’, SPS gene expression and enzyme activity consistent with the accumulation of sucrose, while the’Shouxing’ performed a very low activity and high sucrose content of AI during the entire development. Therefore, it is likely that there are two mechanisms for the accumulation of sucrose, one is the accumulation of sucrose is along with the increasing SPS activity, the other is the accumulation of sucrose occurs when AI activity was below a certain threshold.4. GC and real-time PCR techniques were used to determine the dominant orgaic acids content, acid metabolic pathway key enzyme genes expression and activity in Flavor Melon and control cultivars at different developmental stages. The results revealed that citric acid is the major organic acid in mature fruit. During 5-25 DAP, the ACO and ME activities were correlated to the citric acid content, and the activities in ’Flavor No.3’ were hgher than those in ’Xuelihong’, so the citric acid content was higher in the former. The activities of citric acid metabolic pathway key enzymes in’Flavor No.4’and ’Suangua’ were mostly higher than those in’Shouxing’, as a result, citric acid increased. However, the sucrose content in’Shouxing’was the highest, and followed by’Flavor No.4’and’Suangua’, and the acid content was inverse。So it suggested that the Krebs cycle was accelerated and more photosynthate were subjected to the partitioning in the citric acid metabolism in acid-accumulation melons. 5. The volatile substances in mature Flavor Melon and control cultivars fruits was measured by GC-MS. The results showed that, the representative volatile substances in mature’Flavor No.2’fruit were diethyl phthalate, dimethyl phthalate, and (E, E)-2,4-decadienal; and the volatile substance in’Flavor No.3’ and ’Xueli’fruit were mainly esters and ketones, which accounted for more than 70% of the total content of volatile substances, and the rest were alcohols, aldehydes, sulfur-containing compounds and so on. The ester content was 43.03% in ’Flavor No.3’, and 65.61% in ’Xueli’, while the ketone content was 30.08% in ’Flavor No.3’, and 10.07% in ’Xueli’.4-Hydroxy-2-butanone and 1,2-benzenedicarboxylic acid butyl 2-methylpropyl ester were the main volatile substances is’Flavor No.3’.Taken together, the quality of Flavor Melon fruits are dramatically different from the traditional cultivars and its parents, and the formation mechanism is speculated in two aspects as follow:on the one hand, the photosynthesis of leaves are stronger, so they could supply more photosynthate for fruit development; on the other hand, as there are more photosynthate in fruit, some are metabolized to be sugars and accumulation, at the same time, some assimilates are subjected to the partitioning in the citric acid metabolism, and as a result citric acid increased in amount as an intermediate product in the cycle.更多还原