【作者】 蒋亚华；

【导师】 曹碚生； 缪旻珉；

【作者基本信息】 扬州大学 ， 蔬菜学， 2005， 硕士

【摘要】 与大多数高等植物不同,黄瓜以水苏糖作为体内光合产物的主要运转形式。黄瓜体内的同化物在从源到库的运输过程中,需要经历蔗糖、葡萄糖、果糖与水苏糖之间的数次转化,但上述转化反应发生的具体部位一直不明。与蔗糖运输型植物相比,水苏糖运转型植物的光合产物在输出之前尚需经历由蔗糖合成水苏糖的额外步骤,可以预料,水苏糖运转型植物在一个昼夜周期中的源库变化规律将较蔗糖运输型植物更为复杂,但目前水苏糖运转型植物这方面的资料相当少。为此,本实验选择黄瓜成熟叶片、韧皮部汁液、果实、种子、叶柄、果柄、根系、生长点等部位,在一天中同化物的运输旺盛期研究各部位碳水化合物的含量及相关酶的活性,同时以叶片、韧皮部汁液、果肉、种子四个部位为对象,研究一个昼夜周期中各种碳水化合物含量及相关酶活性的变化,以期在器官水平阐明上述转化反应发生的部位,探明一个昼夜周期中黄瓜碳水化合物运转代谢的曰变化规律。所得结论如下: Ⅰ 黄瓜经光合作用合成蔗糖后,在叶片中即开始合成水苏糖。当水苏糖被运输到果柄部位时,被迅速分解成蔗糖,以蔗糖的形式继续向果实中运输。种子中的水苏糖是以由果肉运输而来的葡萄糖、果糖或蔗糖为原料在种子内部原位合成,而不是从果肉中直接运输而来。 Ⅱ 黄瓜成熟叶片中各种可溶性糖所占的比例在一个昼夜周期中富有变化,夜间直至上午10:00,葡萄糖和果糖是叶片中的主要可溶性糖,但下午13:00至16:00,水苏糖成为成熟叶片中含量最高的可溶性糖。这种变化主要由叶片中水苏糖含量的剧烈昼夜变化所引起。 Ⅲ 当黄瓜同化物从源叶向外运输时,韧皮部汁液中的可溶性糖以水苏糖为主,运输完毕后则以蔗糖为主,黄瓜夜间韧皮部的装载可能存在质处体途径。 Ⅳ 黄瓜成熟叶片在夜间可以以淀粉、葡萄糖、果糖、水苏糖、蔗糖等各种形式贮藏尚未运出的同化物,而此时韧皮部汁液中葡萄糖、果糖、水苏糖的含量极低。更多还原

【Abstract】 Cucumber (Cucumis Sativus. L.) is different from other high plants in translocating photoassimilate primarily in the form of stachyose rather than sucrose. From source to sink in cucumber, photoassimilate changes several times between sucrose, glucose, fructose and stachyose, but where these conversional reactions take place is poorly understand in detail. Comparing with sucrose-transporting plants, stachyose-transporting plants need an additional metabolic step, i.e. synthesizing stachyose from sucrose before photoassimilate loading. It is supposed that the diurnal pattern of photoassimilate translocation from source to sink is more complicated in stachyose-transporting plants, however, up to date little research has focus on this field. Therefore, carbohydrates content and related enzymes activity were investigated in mature leaf, phloem sap, mesocarp, seed, petiole, peduncle, root and central spike at 16:00 p.m. to clarify the position of sucrose-stachyose conversion in cucumber. In addition, the diurnal pattern of these carbohydrates and enzymes in mature leave, phloem sap, mesocarp and seed were also studied. The results showed that:I After forming sucrose by photosynthesis, stachyose is synthesized in leaf in cucumber leaf. Stachyose is catabolized rapidly to sucrose in peduncle after long-distance transportation, and the sucrose formed is continually transported into the fruit. Stachyose in seed is not transported from fruit directly but synthesized in situ by glucose 、 fructose or sucrose coming from fruit.II The ratio concentration of different soluble sugars in cucumber mature leaf of cucumber changes during a photoperiod. Glucose and fructose are the primary soluble sugars from night to 10:00 a.m., but at 13:00-16:00 p.m., stachyose becomes the most abundant oligosaccharides. This diurnal change is mostly due to the tempestuousfluctuation of stachyose concentration in mature leaf.III During photoassimilate transportation, the primary soluble sugar in phloem sap is stachyose. When transportation is finished, sucrose becomes the main sugar in phloem sap. An apoplastic phloem loading pathway may exist in cucumber during night.IV Cucumber leaf may store photoassimilate in the forms of starch, glucose, fructose, stachyose and sucrose at night. The concentrations of glucose, fructose and stachyose in phloem sap are much lower than in leaf. The mechanism maintaining concentration difference of these sugars between leaf and phloem is unknown. There may be some unique mechanisms modulating source-sink translocation by which some sugars (such as stachyose) in leaf were prevented from loading into the phloem further in night.V The proportion of different soluble sugars in cucumber mesocarp changes regularly in a diurnal cycle. Concentration of fructose and glucose remain low level during 10:00-13:00, increase to maximal values at 16 p.m., then decline slowly, but still maintain relatively high level during nocturnal time. Stachyose can not be detected in mesocarp, but a -galactosidase, a key enzyme catabolize stachyose maintain high activity in a photoperiod. The results indicate that at least a little stachyose has been transported into cucumber mesocarp ,but was catabolized by a -galactosidase rapidly.VI Stachyose level is lower than glucose, fructose and sucrose levels in cucumber seeds from 14-days-after-anthesis fruit. Stachyose showed very little accumulation during night, coupled with significant a -galactosidase activity at this time in seeds, indicating stachyose may be catabolized into other sugars to be substrates for respiration or embryogenesis at night in young cucumber seeds.更多还原