【作者】 王云华；

【导师】 张楚富；

【作者基本信息】 武汉大学 ， 生物化学与分子生物学， 2005， 硕士

【摘要】 在黄瓜种子萌发和幼苗发育过程中,需要进行一系列复杂的物质转化,因此这一过程中需要与许多氮素代谢相关的酶类参与。在本文中,我们研究了在硝态氮存在或缺乏下,测定了黄瓜种子萌发和子叶发育过程中子叶可溶性蛋白质含量;谷氨酰胺合成酶(GS)、谷氨酸脱氢酶(NAD(H)-GDH)、异柠檬酸脱氢酶(NADP~+-IDH)活性以及可溶性总糖含量和氨离子浓度的变化。在子叶发育初期,无论外源氮存在与否,每对子叶可溶性蛋白质含量和GS、NADH-GDH、NAD~+-GDH活性随发育上升。在外源氮存在下,第4天后,可溶性蛋白质含量虽有所下降,但基本保持恒定;第6天后,GS和NADH-GDH活性逐渐降低,NAD~+-GDH却相反增高。但在无外源氮条件下,于第4天后,可溶性蛋白质水平以及GS、NADH-GDH和NAD~+-GDH活性都逐渐降低。在子叶发育的整个过程中,外源氮对GS、NAD~+-GDH和NADP~+-IDH活性,氨离子浓度和可溶性总糖含量有促进作用,尤其是在子叶发育的后期对NAD~+-GDH活性的促进更为明显。 GS同工酶随着发育而变化,在干种子中,只观察到一种不同于GS1和GS2的同工酶形式,随着发育过程迅速消失。在种子萌发和子叶发育过程中,子叶GS1活性先于GS2出现,两者的活性在发育的前期均很快升高,子叶绿化后GS2占据着明显的优势,而且氮素的存在能显著增高GS2的活性;在子叶发育后期这两种同工酶的活性逐步下降。在真叶的发育中,也同样观察到两种GS同工酶,以GS2为主。在暗转光后,GS2明显被诱导;而当光/暗转换后,不论是在子叶中还是真叶中,GS1的活性都有明显的增多。GS同工酶活性的随发育以及环境条件的变化而改变的现象是与它们在代谢上的功能需要是一致的。更多还原

【Abstract】 Complex changes of substances occur with cucumber seed germination and cotyledon development, and many kinds of enzymes, especially enzymes in nitrogen metabolism, are involved in these processes.We investigated the activities of GS, NADH(H)-GDH, NADP~+-IDH, and the content of soluble protein, total soluble sugar and ammonium concentration were also determined in the development of cucumber(Cucumis sativus L.) cotyledon at the presence or absence of nitrate. In the early days of the development, the level of the protein and the activities of GS, NADH-GDH, and NAD~+-GDH in each pair of cotyledons increased whether exogenous nitrogen was existent or not. After the 4th days, the level of the protein was constant roughly, though it was declined little at the presence of the exogenous nitrogen. The activities of GS and NADH-GDH fell gradually, but NAD~+-GDH was raised markedly after the 6th days. At the absence of the exogenous nitrogen, the levels of the protein, GS, NADH-GDH, and NAD~+-GDH decreased gradually at the same stage. In the whole course of the development, the activities of GS, NAD~+-GDH, NADP~+-IDH, the content of total soluble sugar and ammonium concentration increased by exogenous nitrogen, and NAD~+-GDH activity was promoted remarkably in the late stage of the development particularly.GS isozymes changed with the cucumber seed germination and cotyledon development. In dry seeds, only one GS isozyme was detected, which was different from GS1 and GS2, and disappeared very soon. During cotyledon development, GS1 appeared earlier than GS2, and both GS1 and GS2 activities were enhanced in the early stage of the development. GS2 was a predominant isozyme after the cotyledon greening, and nitrate could remarkably enhance the activity of GS2. At the late stage,both GSl and GS2 activities declined with culture time. In leaf development, the GS isozymes were also determined, and GS2 was predominant. Turn cucumber seedlings from dark to light, GS2 was induced obviously. However, turning the seedlings from light to dark, GSl activity was increased markedly in cotyledon and leaf. These changes of GS isozymes and their activities as development and environmental conditions were consistent with their function in the metabolism.更多还原