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Old 11-08-2011, 09:21 AM   #1
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Default nike heels sale 生物固氮作用

生物固氮作用简介固氮微生物种类自生固氮微生物光合固氮微生物化能自养固氮微生物异养固氮微生物共生固氮微 生物联合固氮微生物红萍和鱼腥藻联合体系固氮地衣自生固氮微生物生物固氮作用的条件生物固氮系统固氮的生物 化学与生理学共生与自生的区分概念代表生物代谢类型固氮量对植物的作用应用 生物固氮作用简介  估计全球每年生物固氮作用所固定的氮(N2)约达17500万吨,其中耕地土壤约有4 400万吨,超过了每年施入土壤4000万吨肥料氮素(工业固氮)的量(Burris,1977)。因此, 生物固氮作用有很大潜力。   生物固氮概括地说是指某些微生物和藻类通过其体内固氮酶系的作用将分子氮转变为氨的作用。 因地壳含有极少的可溶性无机氮盐,所有生物几乎都需要依赖固氮生物固定大气中的氮而生存,因此生物固氮对维 持自然界的氮循环起着极为重要的作用。对固氮生物的研究和利用能为农业开辟肥源,对维持和提高土壤肥力有很 大意义,ray ban wayfareers。   固氮生物又叫做固氮微生物。固氮微生物种类  到1982年固氮微生物达70多个属,大多数是原核微生 物(细、放、蓝细菌),也有真菌。根据固氮微生物与高等植物以及其他生物关系,分为三个类型:自生固氮微生 物、共生固氮微生物和联合固氮微生物。自生固氮微生物  在土壤中或培养基中生活时,可以自行固定空气中的 分子态氮(氨态氮)。在进行固氮作用时对植物或其它生物没有明显的依存关系。   常见的自生固氮微生物包括以圆褐固氮菌为代表的好氧性自生固氮菌、以梭菌为代表的厌氧性自生固氮菌,以 及以鱼腥藻、念珠藻和颤藻为代表的具有异形胞的固氮蓝藻(异形胞内含有固氮酶,可以进行生物固氮)。光合固 氮微生物  能进行光合作用,以二氧化碳为碳源、光合产物为能源进行固氮作用的微生物。有蓝细菌(见蓝藻门 )中的许多属种(如念珠藻属、鱼腥藻属等)和光合细菌中的红螺菌属以及绿硫菌属等。化能自养固氮微生物   有些化能自养微生物(如氧化亚铁硫杆菌等)能以二氧化碳、亚铁氧化物和分子态氮为碳、能、氮源。异养固氮微 生物  进行异养生活,以适宜的有机碳化合物为碳源和能源,满足生活和固氮的需要。这个生理、生态群包括许 多种类,如固氮菌科的所有属、芽孢杆菌属、梭菌属的一些种、固氮螺菌属、肠杆菌科的一些属种、反硫化细菌、 产甲烷细菌和其他一些异养细菌的种类。共生固氮微生物  只有和植物互利共生时,才能固定空气中的分子态氮 。也就是说,二种微生物紧密地生长在一起时,由固氮的共生菌进行分子态氮的还原作用。联合固氮微生物  有 些固氮微生物如固氮螺菌、雀稗固氮菌等,能够生活在玉米、雀稗、水稻和甘蔗等植物根内的皮层细胞之间。这些 固氮微生物和共生的植物之间具有一定的专一性,但是不形成根瘤那样的特殊结构。这些微生物还能够自行固氮, 它们的固氮特点介于自生固氮和共生固氮之间,ray ban online,这种固氮形式叫做联合固氮。联合固氮微生物常见的有以下两种类型:红萍和鱼腥藻联合体系  红萍(又称绿 萍,学名满江红)鳞片叶的叶腔内有鱼腥藻生长,行共生固氮作用。固氮地衣  有些地衣的光合伙伴是固氮蓝细 菌,能进行固氮作用。自生固氮微生物生物固氮作用的条件  1.防氧保护系统(好气性固定微生物需具备之) ;   2.能量和电子供体,以及传递电子的电子载体系统   3.固氮酶催化系统;   4.氨、氨基酸同化成蛋白质系统   共生固氮微生物生物固氮作用的条件则更复杂。生物固氮系统  具有生物固氮能力的仅限于原核生物,即细 菌和蓝绿藻。有些固氮微生物,如蓝绿藻自生于陆地或水域生态系统中,其他则群生于寄生植物的根际,其中对高 等植物最为重要的有与豆科植物或结瘤的非豆科植物共生的固氮微生物,timberland boots shop 叶柏寿。在陆地生态系统中主要有三种固氮体系,即共生固氮、联合固氮和自生固氮体系。三种固氮体系中,能源和固氮 能力都存在明显差异。共生体系由于固氮微生物直接从寄主植物获得碳水化合物作为固氮能源,其固氮能力最强。 豆科(Leguminosae)植物近2000个种中约有15%具有共生固氮系统,其中近300种豆科植物 中有90%与根瘤菌共生形成根瘤。如大豆、蚕豆、三叶草、苜蓿与根瘤菌的共生,是农业中最重要的共生体系。 在森林和林地中有8个科23个属的植物与固氮微生物形成共生体系。如赤杨属(Alnus)和蓟木属(Cea nothus)与放线菌之间形成结瘤共生体系。这些非豆科植物是缺氮土壤的先锋植物。   豆科植物根上的根瘤是由于根瘤菌侵入根部后形成的,根瘤是固氮的场所。根瘤菌侵入寄主的过程很复杂。在 根瘤菌入侵寄主根毛或表皮细胞之前,土壤中的根瘤菌是一种不能运动的小球菌(图5-19)。由于植物根分泌物(氨基酸、维生素)的影响,这些小球菌产生鞭毛,具有移动侵入寄主的能力。根瘤菌 在根表面分泌某种未知物质(分子)使根毛弯曲。这种物质的分泌受到根释放成分(如类黄酮)的促进。此后,根 瘤菌分泌酶溶解根毛细胞壁,根瘤菌随即由此处侵入根毛,根毛形成侵染丝(infectionthread) 。根瘤菌在侵染丝中大量繁殖随侵染丝进入皮层。根瘤菌被释放到皮层细胞质中,刺激细胞的分裂和生长形成根瘤 (root nodule)(图5-19)。根瘤中大部分为含有根瘤菌的四倍体细胞,只有少部分为未被侵染的二倍体细胞。成熟根瘤中的根瘤菌失 去鞭毛而成为不能移动的类菌体(bacteriod),一个典型的根瘤细胞中通常含有数千个类菌体,这些类 菌体在细胞内聚成一个个小群体,每个小群体有数个类菌体组成(大豆根瘤中为4~6个)。每群体外面有一层膜 包着,此膜称为类菌体外周膜(peribacteroid membrane),在此膜与类菌体之间的空间称为类菌体外周空间(peribacteriodspace )。在类菌体外周膜以外的细胞质中存在着豆血红蛋白(leghemoglobin)。此蛋白含有红色的血红 素基团(hemegroup)。据认为豆血红蛋白的作用是为类菌体在严格控制的条件下供应氧。因为类菌体的 呼吸作用需要氧,但过多的氧则会抑制催化氮素固定的固氮酶的活性。   根瘤中的固氮作用只在类菌体内进行。寄主植物向类菌体供给碳水化合物,主要形式是蔗糖。类菌体利用这些 糖进行呼吸作用,产生电子和ATP,将N2还原成NH4+。固氮的生物化学与生理学  生物固氮的总反应式 如下:   N2+8e+16MgATP+16H2O→2NH3+H2+16MgADP+16Pi+8 H+   催化此反应的酶是固氮酶。固氮酶是多功能的氧化还原酶,除了还原N2以外,还能还原多种类型的底物,如 乙炔、氰化物、氧化亚氮、联氨、叠氮化物和H+等。用气相色谱仪能很容易测定乙炔还原成乙烯的产生量,这为 研究固氮酶活性提供了极为简单的方法。该法对生物固氮研究取得重大进展发挥了作用。   固氮酶由铁钼蛋白(Fe-Moprotein)和铁蛋白(Fe-protein)组成。这两个蛋白单独存在时都不呈现固氮酶活性,只有两者聚合构成复合体时才有催化氮还原 的功能。铁钼蛋白由分子量分别为51kD和60kD的2个α亚基和2个β亚基组成的四聚体(α2β2),分 子量约为220~245kD,交警追查违法车辆时为保护同事殉职(图)。每分子铁钼蛋白含有两个钼原子,28个铁原子。铁蛋白的分子量在59~73kD之间,由两个分子量同为3 0kD的亚基组成(γ2)。铁蛋白含有4个铁原子,ugg shoes kids 东方白鹳。在氮还原为NH4+的过程中,固氮酶中的Fe和Mo都发生氧化还原反应,如图5-20所示。类菌体利用碳水化合物进行呼吸作用产生NADH或NADPH和ATP。已经查明,固氮的天然电子 传递体(供体)有铁氧还蛋白、黄素氧还蛋白等。固氮生物体内存在着ATP和二价的金属离子(如Mg2+)是 固氮不可缺少的条件。只有在Mg2+的作用下,ATP才可以与Fe蛋白结合,而且必需有Fe-Mo蛋白的参与才发生ATP水解反应。Fe蛋白将电子传递给Fe-Mo蛋白的同时伴随着ATP水解产生ADP。Fe-Mo蛋白最后将电子传递给N2和质子,产生2分子NH3和1分子H2。   固氮酶对氧敏感,其催化反应需在厌氧下进行。除了专性厌氧的生物外,氧对其他固氮生物的固氮酶有损伤作 用,但这些生物通过呼吸作用产生固氮必需的ATP又需要氧,所以高效率的固氮作用一般是在微氧下进行的。不 同固氮生物避免氧对固氮酶伤害的机制各异。如具有异形胞的蓝藻的固氮功能主要在异形胞中进行,这种细胞外有 一层防氧进入的糖脂组成的外膜,缺少水光解放氧的PSⅡ,其中戊糖磷酸途径的两种酶活性较低,而超氧物歧化 酶和脱氢酶活性都比较强,使异形胞保持了一个微氧环境。豆科植物的根瘤中类菌体有一层类菌体周膜,瘤内皮层 内侧细胞排列紧密并形成间隙,两者对于保持类菌体的低氧环境十分重要。此外,根瘤细胞内的豆血红蛋白也部分 地控制着类菌体氧气的需求。在非豆科植物共生固氮体系中,在与放线菌共生的瘤中有囊泡存在,nike heels sale,这种囊泡可能与蓝藻的异形胞一样具有防氧功能。很明显,共生体系中的根瘤本身就是一个良好的 氧保护系统。   在类菌体内合成的NH3(很可能是NH4+)要从类菌体内运出来,才能参与寄主植物中的代谢。在含类菌 体细胞的细胞质中,NH4+转化成谷酰胺、谷氨酸、天冬酰胺和酰脲。这些物质由转移细胞分泌到木质部,运输 到植物的其他部分。   由于生物固氮的重要性,有关控制生物固氮的环境与遗传因素的研究受到重视。研究表明,凡是能增加植物光 合作用能力的因素,如合适的水分、温度、强光照和高CO2水平等都可以促进固氮作用。豆科植物与固氮生物的 遗传因素也影响固氮作用的速率和产量。例如其中一个遗传因素是豆科植物的结瘤能力,它依赖于根瘤菌与寄主植 物之间的由遗传控制的识别过程。为提高结瘤能力,科学工作者正在进行改造根瘤菌基因以及选择合适的寄主品种 的研究工作。另外一个遗传因素是固氮酶在还原N2的同时还原H+。由总反应式可见,固氮酶催化 的反应中有1/4的电子用于还原H+产生H2。而H2被还原后逸出进入大气,women ugg,这个过程使能量白白浪费。不过,大多数根瘤菌和自生固氮细菌均含有氢化酶,该酶将H2氧化成H2O,这一 过程推动由ADP和Pi合成ATP的反应。有研究表明,与具有较高氢化酶活性的根瘤菌共生的豆科植物(如大 豆)的产量比与无氢化酶活性的根瘤共生的稍高。可能是前者减少了能量的浪费。基于这种认识,通过基因工程技 术可能会获得具有更高活性的氢化酶的根瘤菌并增加豆类产量。此外,用基因工程技术将固氮基因导入非豆科植物 根,促使这些植物固氮的工作也获得了一定的进展。   植物的不同生长阶段会影响生物固氮作用。如大豆、花生、木豆,通过生物固氮固定的氮素中90%在生殖阶 段中进行,oakley m fram 公司老总认为媒体报道失实掌掴记者(图),而10%在营养生长过程中进行。奇怪的是,几种豆类的生物固氮提供的氮素仅为其一生所需总氮 量的1/4至1/2,其余主要在营养生长阶段从土壤中吸收NO3-或NH4+。不过,多施氮肥并不能增产。原因是植物对氮肥吸收增加反而使生物固氮能力下降。硝酸盐肥料的影 响有几个方面:抑制根瘤菌与根毛的接触,jordan heels outlet,中止侵染丝的形成;根瘤生长缓慢,抑制已成熟根瘤的固氮作用;当增施NO3-和NH4+时,加速根瘤的衰老。共生与自生的区分概念  共生固氮微生物与绿色植物互利共生的 固氮微生物   自生固氮微生物能够独立进行固氮的微生物代表生物  共生固氮微生物 根瘤菌   自生固氮微生物 圆褐固氮菌代谢类型  共生固氮微生物异养需氧型(消费者)   自生固氮微生物异养需氧型(分解者) *无论共生还是自生都是异养需氧型   固氮量  共生固氮微生物多 自生固氮微生物少对植物的作用  共生固氮微生物 提供氮肥   自生固氮微生物 提供氮肥和生长素应用  共生固氮微生物1.对豆科作物进行根瘤菌拌种 2.用豆科植物做绿肥   自生固氮微生物 将圆褐固氮菌制成菌剂,施到土壤中 扩展阅读: 1
陈润政《植物生理学》中山大学出版社
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开放分类: 生物学,土壤学,水产学,土壤生物与土壤生物化学,水产饲料与肥料 “生物固氮作用”相关词条:
生物固氮作用(biological nitrogen fixation):生物固氮是指固氮微生物将大气中的氮还原成氨的过程。生物固氮只发生在少数的细菌和藻 类中。
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Old 11-08-2011, 09:22 AM   #2
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and if they print very well and thoroughly discouraged God of Cookery is expensive, where the cells are then printed, but the wood for the winter is particularly delicate, wood in a fire in winter, not only to vent itself, and both candidates adjustment purposes.
injury see government officials, havoc per side, and officials see the Goldwater injury, anti by the delicate, non-official of the fear injury, but because waiting for the urgent tone, the right is also used, with the injured officer to kill, readily available, but with the winter gold, the show times. Indian officials wear injury, readily available, but with the summer wood, the show times,mulberry handbags, water and fire are also economic.
injury of the official money, this is Quaker, and Goldwater injury of the official money, even a small rich pay more is not expensive, because cold water is not raw wood.
injury of the official money, is the delicate, but with the summer woods, your not the show, due to dry soil is also less scenery.
every spring wood fire was blazing, but not for this summer woods of autumn gold water, for the Jinshui synthesis, and winter gold is not for this theory, a decline Wang Qi, also have different access to the spring wood fire every ,handbags online cheap, Muhuo brightly lit, see the official negative, while the autumn gold water, Jinshui synthesis, see the official without problems, if students apply for G months, while the branch or sub-or e, will become the water bureau, dry days, the small, that the official Star as long as Jen-kuei, not through dry first, then for your grid, and the Iron Chef of injuries, said officials see the same on the official also stressed the road waiting too. Although the Sun is printed
God of Cookery, also won the food, while the summer Mu Huo-sheng, light show and you have used, and Muhuo pleased to see the watermark the same injury on the official also stressed the meaning of waiting too. The cases of many of these can not be described one by one and stretch it, extend the time in school, try to figure out work from, since the will of God and Ming.
above together with the climate of the pros and cons with God.
label healthy food handouts with the character of God injured officer
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Old 11-08-2011, 09:23 AM   #3
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45325 2009年03月24日22:38 Reading (loading. ..) Comments ( 11) Category: Yuanyuan 's now like a person ,alexa mulberry, maybe just a look,handbags online, a touch , but even a simple pass .
perhaps he did not know you exist , and even will ignore you , but your eyes have been unable to leave him.
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mind when you hear from other people talk about him , it is urgent to know things about him , but can not put this kind of desire on his face , and only hold back the urge to ask clear , careful Listen ,paul smith wallet, do not miss the slightest .
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Third Sister ah. . . . Finally finished
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Old 11-08-2011, 09:23 AM   #4
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138332 2007 年 07 月 09 日 19:19 Reading (loading. ..) Comments (0) Category: Personal Diary
Yesterday In the taxi on the chance to hear a long time ago that Eric Moo first

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