苜蓿根瘤菌胞外多糖缺损突变体侵染方式的超微结构

应用透射电子显微镜观察到缺损胞外多糖根瘤菌突变体侵染莒蓿根的方式与前人描述的一般根瘤菌的侵染有明显不同。突变菌贴近根毛时,根毛外层壁被降解,突变菌陷入根毛外层壁中。突变菌由外层壁移入内层壁后,在菌体周围形成大量新的壁物质。被新沉积的壁物质形成细胞内生包被的突变菌进一步形成宽的感染线,这种感染线内不舍有细的颗粒基质,突变菌被包埋在壁物质中,以后感染线解体。说明突变菌感染线的发生与一般根瘤菌在巳降解的根毛壁侵染原位直接发生感染线是不一样的。突变菌诱导的根瘤起始于根的维管柱中的薄壁细胞不规则分裂,以及与木质部极相对的皮层细胞。随着根瘤进一步发育在皮层细胞内形成一个宽的分生组织带,根瘤细胞内不含突变菌,说明突变菌诱导的根瘤与野生苜蓿根瘤菌诱导的根瘤的发育途径是十分不同的。     

紫云英根瘤菌结瘤因子的初步研究

最近的研究结果表明,豆科植物与根瘤菌的共生识别是一种双向的信号物质交换过程.首先是豆科植物的根或种子分泌类黄酮物质,诱导根瘤菌的结瘤基因(nod genes)产生结瘤因子(nod factors),分泌到胞外,为植物所接受,从而引发植物某些基因表达,细胞分化,细胞壁形成,最终导致根毛变形等一系列变化.已经测定了几种苜蓿根瘤菌(Rhizobium meliloti)和豌豆根瘤菌(R.leguminosarum bv.viciae)结瘤因子的分子结构式,它们均属于寡糖胺类物质,在没有根瘤菌存在的条件下,结瘤因子能独立地促使根毛发生变形,这是检测结瘤因子是否存在的重要手段,即根毛变形试验(Root hairdeformation assay,简称Had试验).高浓度的结瘤因子甚至能诱导植物产生空瘤,其组织结构与典型的根瘤相同.     

传递细胞——物质短途运输中起作用的特化细胞

传递细胞广泛存在于植物界的各种群。传递细胞的分化主要与器官的发育程度以及转运物质的供应有关。当植物某个部位所需的运输速率远高于溶质正常跨膜运输速率时,在此部位就可能有传递细胞。传递细胞最基本的特征是细胞壁向内突起生长（壁内突）并与质膜共同形成壁膜器。壁内突从形态上可划分为2种类型：网状内突和肋状内突。大多数传递细胞壁内突的发育在沿着溶质流动的方向表现出极性。传递细胞的胞质一般比周围薄壁组织细胞浓,胞内富含线粒体和内膜分泌系统细胞器如内质网、高尔基体、小囊泡等。传递细胞在物质的短途运输中起作用。玉米胚乳传递细胞可能还具有防御病原微生物进入胚乳和胚的功能。本文就传递细胞的种类和特性、结构和功能、形成机制和诱导因素,以及基因表达调控等方面的研究进展做介绍。     

豆科植物根瘤的氨同化作用

根瘤菌能与豆科植物共生固定大气中的氮。根瘤菌专一地侵入豆科植物,引起根皮层细胞的分裂,形成根瘤。与此同时,根瘤菌细胞壁变薄,体积增大,形态显著改变,分化成类菌体。固氮酶由类菌体合成,根瘤中的类菌体是合成氨的场所。类菌体合成氨     

被子植物生殖器官中的传递细胞

传递细胞（ｔｒａｎｓｆｅｒｃｅｌｌ）是一类特殊的薄壁细胞,其特征是细胞壁向内突起生长,形成壁内突的结构,质膜紧贴细胞壁生长,从而使质膜的表面积大大增加,扩大了原生质体表面积与体积之比,有利于细胞吸收和分泌某些物质,在细胞物质的短途运输中起重要作用。超微结构研究表明,传递细胞的细胞核较大,细胞质浓,并富含线粒体、高尔基体等细胞器。传递细胞在被子植物生殖器官中普遍存在,对于这些器官完成其功能起到重要作用。下面简单介绍生殖器官各结构中存在的传递细胞及其功能。１　花柱的通道细胞开放型花柱具有花柱道,花柱…     

豆科植物SHR-SCR模块——根瘤“奠基细胞”的命运推手

豆科植物-根瘤菌共生固氮是可持续性农业氮肥的最重要来源。根瘤作为豆科植物共生固氮的一种特化植物侧生器官, 提供了根瘤菌生物固氮必需的微环境, 是根瘤菌的安身之本, 因此, 根瘤的正常发育是实现豆科植物-根瘤菌共生固氮的结构基础。根瘤器官的从头发生主要起始于根瘤菌诱导的根皮层细胞分裂。通常认为豆科植物的根皮层具备有别于非豆科植物根皮层的某种特异属性, 从而响应根瘤菌并与之建立固氮共生, 但长期以来该属性决定的分子机制一直不明确。近日, 中国科学院分子植物科学卓越创新中心王二涛团队以蒺藜苜蓿(Medicago truncatula)等豆科植物和拟南芥(Arabidopsis thaliana)等非豆科植物为研究对象, 发现豆科植物中保守的SHR-SCR干细胞模块决定了其皮层细胞分裂潜能从而赋予根瘤器官发生的命运。该研究揭示了豆科植物根瘤发育的全新机制, 提供了研究和理解植物-根瘤菌固氮共生进化的重要线索, 对提高豆科作物固氮效率和非豆科作物固氮工程具有重要意义。     

The Legume SHR-SCR Module Predetermines Nodule Founder Cell Identity

豆科植物-根瘤菌共生固氮是可持续性农业氮肥的最重要来源。根瘤作为豆科植物共生固氮的一种特化植物侧生器官, 提供了根瘤菌生物固氮必需的微环境, 是根瘤菌的安身之本, 因此, 根瘤的正常发育是实现豆科植物-根瘤菌共生固氮的结构基础。根瘤器官的从头发生主要起始于根瘤菌诱导的根皮层细胞分裂。通常认为豆科植物的根皮层具备有别于非豆科植物根皮层的某种特异属性, 从而响应根瘤菌并与之建立固氮共生, 但长期以来该属性决定的分子机制一直不明确。近日, 中国科学院分子植物科学卓越创新中心王二涛团队以蒺藜苜蓿(Medicago truncatula)等豆科植物和拟南芥(Arabidopsis thaliana)等非豆科植物为研究对象, 发现豆科植物中保守的SHR-SCR干细胞模块决定了其皮层细胞分裂潜能从而赋予根瘤器官发生的命运。该研究揭示了豆科植物根瘤发育的全新机制, 提供了研究和理解植物-根瘤菌固氮共生进化的重要线索, 对提高豆科作物固氮效率和非豆科作物固氮工程具有重要意义。     

Rpfan37在刺槐共生结瘤过程中的功能探究

目的:研究刺槐中与磷脂酰肌醇转运蛋白有较高同源性的基因Rpfan37的功能,为探究相关基因参与豆科植物与根瘤菌共生结瘤过程提供新的思路。方法:通过前期研究,建立豆科植物刺槐与共生根瘤菌互作的抑制差减杂交反交文库,筛选疑似与共生结瘤相关的基因。利用PCR技术快速克隆经实时荧光定量PCR技术(qRT-PCR)分析基因在不同接菌时间及不同植物组织的表达。构建RNA干扰(RNAi)重组载体,转农杆菌介导转化植物根部,接种根瘤菌后验证该基因在刺槐共生结瘤过程的功能。结果:基因表达分析显示,在接菌与未接菌的刺槐根中,处理后第15天,Rpfan37表达均显著上调,但接菌与未接菌处理对该基因表达无显著影响;在成熟的根瘤中,该基因仅为低水平表达。RNAi转化植株的鲜重、株高、根长及结瘤数较对照组显著降低。在显微镜下观察到RNAi植株根毛发育异常;与对照相比,RNAi转化植株形成的根毛卷曲、根毛侵染线及根瘤原基数目均显著降低。根瘤石蜡切片结果显示RNAi植株根瘤中的侵染细胞与对照相比明显减少,分析豆血红蛋白表达发现,RNAi植株中根瘤发育成熟过程明显受阻。结论:在豆科植物刺槐中发现的相关基因Rpfan37能够参与刺槐共生结瘤过程,为研究磷脂酰肌醇转运蛋白在共生结瘤过程中的作用提供了新的理论基础。     

玉米胚乳传递细胞的结构观察研究

以玉米品种'登海11号'为材料,分别于授粉后8、10、15和20 d采集颖果,取所需部位并采用树脂包埋的方法及半薄和超薄切片技术,对玉米胚乳传递细胞进行了显微和超微结构观察.结果显示:(1)胚乳传递细胞的壁内突从外层向内层依次递减,溶质浓度逐步降低,形成了明显的溶质浓度梯度,有利于溶质的运输;(2)中层胚乳传递细胞和内层胚乳传递细胞的邻壁上存在胞间连丝或一些孔径较大的胞壁孔道,从而使溶质更快的进入内层胚乳传递细胞;(3)在壁内突周围存在许多线粒体.研究表明,玉米胚乳传递细胞的结构适合溶质运输.     

豇豆根瘤菌NGR234和紫云英根瘤菌109感染紫云英的比较研究

利用光学和电子显微镜对紫云英根瘤菌菌株109和广宿主的快生型根瘤菌菌株NGR234感染温带型豆科植物紫云英进行了研究,结果表明根瘤菌感染紫云英是通过在根毛中形成侵染线的途径。电子显微镜研究揭示了固氮根瘤中细胞内侵染线的存在。接种二天后,首先可观察到根毛的卷曲或分枝。接种四至五天后,在每株植物卷曲的根毛中可看到侵染线。接种八至十天后的植株出现肉眼可见的根瘤。菌株NGR234能够在紫云英上诱导根毛的卷曲,侵染线和根瘤的形成,但所形成的根瘤却未能固氮,根瘤中无明显的类菌体区,但有少数包有细菌的侵染线。NGR234抗抗菌素的衍生菌均未能使紫云英结瘤。将NGR234的共生质粒转移至三叶草、苜蓿、豌豆、快生型大豆根瘤菌和农杆菌,亦未能使这些细菌获得紫云英上结瘤的能力。     

水稻无侧根突变体RM109的显微结构及其根毛形态观察

水稻原品种"大力"以NaN3诱变方法获得了稳定突变体RM109.显微结构观察表明,RM109种子根外表根毛稀少且短小,无侧根发生,而"大力"品种则有侧根发生,且密生根毛.根毛观察比较显示,距种子根根端1 cm处的RM109根毛数是"大力"品种的19%,差异极显著,根直径与"大力"品种差异不显著;距根端8 cm处的RM109根毛数和根直径分别是"大力"品种的45%和79%,二者差异极显著;距根端3 cm处,RM109最大根毛长是"大力"品种的33%,差异极显著;RM109种子根根端到根毛发生区的长度,与"大力"品种的差异不显著.     

Calcium Spiking Patterns and the Role of the Calcium/Calmodulin-Dependent Kinase CCaMK in Lateral Root Base Nodulation of Sesbania rostrata

Nodulation factor (NF) signal transduction in the legume-rhizobium symbiosis involves calcium oscillations that are instrumental in eliciting nodulation. To date, Ca²⁺ spiking has been studied exclusively in the intracellular bacterial invasion of growing root hairs in zone I. This mechanism is not the only one by which rhizobia gain entry into their hosts; the tropical legume Sesbania rostrata can be invaded intercellularly by rhizobia at cracks caused by lateral root emergence, and this process is associated with cell death for formation of infection pockets. We show that epidermal cells at lateral root bases respond to NFs with Ca²⁺ oscillations that are faster and more symmetrical than those observed during root hair invasion. Enhanced jasmonic acid or reduced ethylene levels slowed down the Ca²⁺ spiking frequency and stimulated intracellular root hair invasion by rhizobia, but prevented nodule formation. Hence, intracellular invasion in root hairs is linked with a very specific Ca²⁺ signature. In parallel experiments, we found that knockdown of the calcium/calmodulin-dependent protein kinase gene of S. rostrata abolished nodule development but not the formation of infection pockets by intercellular invasion at lateral root bases, suggesting that the colonization of the outer cortex is independent of Ca²⁺ spiking decoding.     

骆驼刺根瘤菌的超微结构研究

用透射电子显微镜研究骆驼刺根瘤中的根瘤菌。结果表明。在成熟的骆驼刺根瘤中,根瘤菌的大小、数量、形态、分布位置及精细结构随寄主细胞的发育程度不同而异。早期侵染细胞中,根瘤菌小,数量少,一般呈球形或椭球形,位于细胞壁附近及靠近核区的地方,没有聚磷酸盐颗粒和聚羟基丁酸。成熟侵染细胞中,根瘤菌个体较大,数量较多．多呈棒状,少数为球形或椭球形。有很多根瘤菌还呈现明显的“T”形、“Y”形或“V”形,菌体占满了整个细胞,这时的根瘤菌大多数含有聚羟基丁酸和聚磷酸盐颗粒。而在衰老的侵染细胞中,根瘤菌细胞质收缩,电子密度增高．形状变得很不规则,有的根瘤菌解体,呈现膜泡状结构,菌体中含有数量不等的聚羟基丁酸和聚磷酸盐颗粒。球状根瘤菌从侵染初期到侵染细胞裂解的整个阶段中都仔在。并且观察到的处于分裂状态的根瘤菌都是球状菌,因此可以推测骆驼刺根瘤中是以球状根瘤菌来进行增殖的。     

结合态氮对根瘤菌生长液诱导的苜蓿根毛变形的抑制

以苜蓿根瘤菌和其宿主苜蓿为材料,由结合态氮影响苜蓿根瘤菌生长液诱导宿主根毛变形的功能发现,硝态氮和铵态氮均能有效地抑制根瘤菌生长液诱导的宿主根毛变形。而其抑制作用随结合态氮浓度的增加、作用时间的延长而增强。该抑制作用发生在结合态氮浓度和作用时间分别达到1mmol/L和12h时,或当其浓度和作用时间分别为6mmol/L和48h时,根瘤菌生长液引起根毛变形的植株百分率下降到10％。硝态氮与铵态氮抑制根瘤菌生长液诱导根毛变形的作用相类似。     

Ultrastructure of infection-thread development during the infection of soybean by Rhizobium japonicum

The location and topography of infection sites in soybean (Glycine max (L.) Merr.) root hairs spot-inoculated with Rhizobium japonicum have been studied at the ultrastructural level. Infections commonly developed at sites created when the induced deformation of an emerging root hair caused a portion of the root-hair cell wall to press against an adjacent epidermal cell, entrapping rhizobia within the pocket between the two host cells. Infections were initiated by bacteria which became embedded in the mucigel in the enclosed groove. Infection-thread formation in soybean appears to involve degradation of mucigel material and localized disruption of the outer layer of the folded hair cell wall by one or more entrapped rhizobia. Rhizobia at the site of penetration are separated from the host cytoplasm by the host plasmalemma and by a layer of wall material that appears similar or identical to the normal inner layer of the hair cell wall. Proliferation of the bacteria results in an irregular, wall-bound sac near the site of penetration. Tubular infection threads, bounded by wall material of the same appearance as that surrounding the sac, emerge from the sac to carry rhizobia roughly single-file into the hair cell. Growing regions of the infection sac or thread are surrounded by host cytoplasm with high concentrations of organelles associated with synthesis and deposition of membrane and cell-wall material. The threads follow a highly irregular path toward the base of the hair cell. Threads commonly run along the base of the hair cell for some distance, and may branch and penetrate into subjacent cortical cells at several points in a manner analagous to the initial penetration of the root hair.     

豆科植物根瘤中非共生的内生菌遗传多样性研究进展

在豆科植物与根瘤菌之间结合形成的固氮共生体中,其典型的特征是由特定的微共生体诱导形成的根瘤或茎瘤,除了根瘤菌外,在根瘤中同样也分离出多种与根瘤菌共生固氮无关的内生菌类群,而且根瘤菌与内生菌通常可以共存于同一个根瘤内是普遍存在的客观现象,这些非共生的内生菌生活史的一部分存在于根瘤内且不会引起植物发病,但有关它们的生态学作用还知之甚少,由于其生态上的重要性,近年来对该现象的研究不断深入.就近年来根瘤中隶属于变形菌门,放线菌门、后壁菌门的非共生的内生菌遗传多样性所取得的最新研究结果进行了总结,并介绍了根瘤中相关内生菌多样性研究的新进展.同时,指出了该研究领域存在的问题,并对未来相关研究方向做了展望.     

Lectin-enhanced accumulation of manganese-limited Rhizobium leguminosarum cells on pea root hair tips.

The ability of Rhizobium leguminosarum 248 to attach to developing Pisum sativum root hairs was investigated during various phases of bacterial growth in yeast extract-mannitol medium. Direct cell counting revealed that growth of the rhizobia transiently stopped three successive times during batch culture in yeast extract-mannitol medium. These interruptions of growth, as well as the simultaneous autoagglutination of the bacteria, appeared to be caused by manganese limitation. Rhizobia harvested during the transient phases of growth inhibition appeared to have a better attachment ability than did exponentially growing rhizobia. The attachment characteristics of these manganese-limited rhizobia were compared with those of carbon-limited rhizobia (G. Smit, J. W. Kijne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986, and J. Bacteriol. 169:4294-4301, 1987). In contrast to the attachment of carbon-limited cells, accumulation of manganese-limited rhizobia (cap formation) was already in full progress after 10 min of incubation; significantly delayed by 3-O-methyl-D-glucose, a pea lectin haptenic monosaccharide; partially resistant to sodium chloride; and partially resistant to pretreatment of the bacteria with cellulase. Binding of single bacteria to the root hair tips was not inhibited by 3-O-methyl-D-glucose. Whereas attachment of single R. leguminosarum cells to the surface of pea root hair tips seemed to be similar for both carbon- and manganese-limited cells, the subsequent accumulation of manganese-limited rhizobia at the root hair tips is apparently accelerated by pea lectin molecules. Moreover, spot inoculation tests with rhizobia grown under various culture conditions indicated that differences in attachment between manganese- and carbon-limited R. leguminosarum cells are correlated with a significant difference in infectivity in that manganese-limited rhizobia, in contrast to carbon-limited rhizobia, are infective. This growth-medium-dependent behavior offers and explanation for the seemingly conflicting data on the involvement of host plant lectins in attachment of rhizobia to root hairs of leguminous plants. Sym plasmid-borne genes do not play a role in manganese-limitation-induced attachment of R. leguminosarum.     

Phosphorylation of MtRopGEF2 by LYK3 mediates MtROP activity to regulate rhizobial infection in Medicago truncatula

The formation of nitrogen-fixing no dules on legume roots requires the coordination of infection by rhizobia at the root epidermis with the initiation of cell divisions in the root cortex. During infection, rhizobia attach to the tip of elongating root hairs which then curl to entrap the rhizobia. However, the mechanism of root hair deformation and curling in response to symbiotic signals is still elusive. Here, we found that small GTPases (MtRac1/MtROP9 and its homologs) are required for root hair development and rhizobial infection in Medicago truncatula. Our results show that the Nod factor receptor LYK3 phosphorylates the guanine nucleotide exchange factor MtRopGEF2 at S73 which is critical for the polar growth of root hairs. In turn, phosphorylated MtRopGEF2 can activate MtRac1. Activated MtRac1 was found to localize at the tips of root hairs and to strongly interact with LYK3 and NFP. Taken together, our results support the hypothesis that MtRac1, LYK3, and NFP form a polarly localized receptor complex that regulates root hair deformation during rhizobial infection.     

Root hair formation and elongation of primary maize roots

In maize ( Zea mays L. cv. LG 11) roots cultured in humid air, the presence of hairs was not related to root growth. However, maximum hair length and length of the hair zone could be correlated to the elongation rate of the primary root. Under the growth conditions used, the emergence of root hairs always took place in the extending zone. In more basal regions, rhizodermal cells could not give rise to root hairs. Results were similar for roots preincubated in a buffer solution.     

低磷供应对拟南芥根系构型的影响

在人工气候箱中,采用Johnson培养基对拟南芥在低磷供应条件下根系构型的变化进行了研究,结果表明：拟南芥在磷饥饿诱导下,主根缩短,侧根密度、根毛的数量和长度显著增加,并且,根尖到第一侧根和第一根毛的距离也大大缩短。这些改变增加了根系比表面积,并且使得根系分布更加靠近土壤表层,有利于提高植物吸收土壤中有机磷的效率。低磷胁迫还导致拟南芥根系分生组织区细胞形状变异,柱细胞数量减少;主根生长和细胞伸长的动力学分析显示,磷饥饿促使拟南芥主根生长变缓,细胞长度随磷饥饿程度的加深迅速缩小。CycB1;1:GUS染色分析结果表明,低磷破坏拟南芥根系分生组织细胞分裂能力,这些结果说明磷胁迫同时抑制了细胞的伸长和分裂,从而引起拟南芥主根的缩短。