梨胶锈菌性孢子和锈孢子阶段吸器的超微结构研究

本文对梨胶锈菌性子期和锈子期菌丝吸器的形成方式、吸器及其与寄主细胞界面的超微结构进行了研究。观察结果表明：梨胶锈菌性子期和锈子期寄主胞间菌丝吸器的形成方式有两种：一种是由寄主胞间菌丝直接形成吸器;另一种是由寄主胞间菌丝先形成吸器母细胞,然后由吸器母细胞形成吸器。吸器在开始形成时只是一个乳头状的侵入楔,以后逐渐形成囊状、镰刀状、指状及其它不规则形状的吸器。多数吸器分化为颈和吸器主体两部分,在颈部及部分吸器主体外有一个由类似寄主细胞壁物质形成的领圈。吸器内部的超微结构与寄主胞间菌丝基本相同,但吸器壁比胞间菌丝或吸器母细胞的壁薄。吸器鞘的厚度随着吸器伸长膨大 而逐渐增厚。     

小麦条锈菌吸器母细胞超微结构的研究

本文利唱电镜技术研究了小麦条锈菌吸器母细胞的超微特征。观察发现,小麦条锈菌吸器母细胞大部位于胞间菌丝的顶部,但也可形成于两菌丝细胞间,同一菌丝细胞上可着生多个吸器母细胞,吸器母细胞的多核现象较为普遍。吸器母细胞壁由6层组成,而其隔膜可分辩为4层。细泡化学染色结果表明隔膜突中含有多糖类物质,吸器母细胞隔膜突的出现和消失与吸器的发育密切相关。本文结果表明小麦条锈菌吸器母细胞的一些超微特征明显不同于其它锈菌。     

Structure and Development of the Mature Secondary Haustorium in Alectra vogelii Benth

Anatomical investigations were carried out on the structureand development of the mature secondary haustorium in Alectravogelii growing on Arachis hypogaea or Vigna unguiculata. Followingthe formation of the young secondary haustorium, both the cambiumand pericycle of the host root directly opposite the young secondaryhaustorium are stimulated to divide and form new tissues andorgans including haustorial roots. Further proliferations ofthe host root pericycle and the haustorial cortex give riseto a large, tuberous and complex mature secondary haustoriumwithin which the tissues of the host and parasite remain inintimate contact forming a perfect graft union with a wide zoneof contact. Apart from the haustorial axial xylcm strand whichnormally connects the xylem of the parasite secondary root withthat of the host, direct xylary connections are also establishedbetween the axial xylem of the haustorium and the xylem of thehaustorial roots. The entire surface of the mature secondaryhaustorium of Alectrais covered with these haustorial rootsas was previously observed in its mature primary haustorium. Alectra vogelii Benth, secondary haustorium, haustorium, haustorial roots, root parasite, hemiparasitism, Arachis hypogaea, Vigna unguiculata     

Influence of carbohydrates on the induction of haustoria of the cowpea rust fungusin vitro

Rust fungi are obligate plant parasites whose successful parasitism appears to depend on the formation of haustoria within living plant cells. To test the hypothesis that the lack of haustorium formation in the absence of a living cell reflects a need for a simple “signal” released during attempted invasion, various carbohydrates were applied toin vitro-formed infection structures ofUromyces vignae just prior to haustorial mother cell (HMC) formation. Up to 6% of HMCs formed haustoria after treatment with arabinose, mannose, xylose, sucrose, or xylan. Other monosaccharides, oligosaccharides, and polysaccharides were less or not effective. Sugar mixtures induced haustorium frequencies of up to 10%. Timing of the application of inducing chemicals was critical. The data indicate that haustorium formation does not require the presence of a living plant cell and may be triggered by plant products at the time of penetration peg development.     

Evolution of the secondary haustoria to a primary haustorium in the parasiticScrophulariaceae/Orobanchaceae

In the parasiticScrophulariaceae andOrobanchaceae, two types of contact organs exist: secondary and primary haustoria. Secondary haustoria are lateral organs, developing in large numbers and only when the seedling is fully established. In contrast, a primary haustorium represents the first developmental stage of the seedling itself. In the root system of the parasiticLesquereuxia syriaca (=Siphonostegia syriaca) there are only secondary haustoria, but a few of them apparently develop in a terminal position. This is achieved by transferring the haustorial initiation region closer to the root apex. One can interpret this as a transformation of the apical meristem into a meristematic haustorial tissue. On the condition that an extreme shortening (abbrevation) of the primary root could happen, we discuss the transformation of the terminal secondary into a primary haustorium.     

ELECTRON MICROSCOPY OF THE HOST-PARASITE RELATIONSHIPS IN STEM RUST OF WHEAT

Ehrlich , H. G., and Mary A. Ehrlich . (Duquesne U., Pittsburgh, Pa.) Electron microscopy of the host-parasite relationships in stem rust of wheat.—Amer. Jour. Bot. 50(2): 123–130. Illus. 1963.—A series of micrographs showing intercellular dikaryotic mycelium, haustorial mother cells, stages in haustorial formation, and haustoria within host cells are presented in the present report. Of special interest and potential significance in a study of obligate parasitism is an encapsulation ranging from 800 to 3400 A in thickness which surrounds the haustorium, but which is not present around the intercellular hyphae. The encapsulation completely encases the haustorium proper; it is bounded on the inside by the cell wall of the haustorium, and its thin membranous outer margin abuts directly on the protoplast of the host cell. The nature of the material composing the encapsulation is uncertain, but it appears to originate from the haustorial protoplast, and at least a portion of it may be fungal cytoplasm. This newly described structure represents the actual interface between the host and pathogen. Small vesicles which seem to originate from the outer margin of the encapsulation are sometimes found in the host cytoplasm surrounding apparently vigorous haustoria. The vesicles are bounded by a membrane and contain particulate material.     

Ultrastructure of intercellular hypha and haustorium of the rust fungus,Uromyces euphorbiae

The ultrastructure of intercellular hyphae and dikaryotic haustoria of Uromyces euphorbiae, and the host response to haustorial invasion was investigated. The intercellular hyphae share common characteristics with those of other uredinial stages of rust fungi. Three types of septa were recognized inside the intercellular hypha. This study showed that the extrahaustorial membrane was possibly formed before the development of the haustorium. The periodic acid-thiocharbohydrazide-silver proteinate technique showed that the haustorial mother cell wall at the penetration site, and the haustorial wall contained more carbohydrates than other fungal structures. In addition, the neckband, present around the haustorial neck, contains different material from those of the rest of the haustorial neck wall. The close associations of host organelles, such as the nucleus, chloroplasts, mitochondria, endoplasmic reticulum and microtubules, with the haustorium, is described.     

The Initiation of the Secondary Haustorium in Alectra vogelii Benth

Anatomical studies were carried out on initiation of the secondaryhaustorium in Alectra vogelii, a root parasite of leguminouscrops in Nigeria. In both the normal and self-haustorium, theformation of the haustorial initial on the parasite root soonafter initial contact between the host and parasite roots isfollowed by the penetration of the host root by the haustorium.Specialized penetrating cells (intrusive cells) at the haustorialfront prise apart and loosen the host root cortical cells, whichlater become digested. Through the same processes, a few ofthese columnar intrusive cells at the haustorial front piercethe endodermis to make contact with the xylem of the host root.Thereafter, a true conductive bridge consisting of short, isodiametric,reticulate vessel elements is established between the parasiteand host roots through the secondary haustorium. No pholem tissuewas observed in the connection. There is a close similaritybetween the mode of initiation of the secondary haustorium ofAlectra vogelii and that previously described for its primaryhaustorium. Alectra vogelii Benth, haustorium, self-haustorium, root parasite, hemiparasitism, Vigna unguiculata, Arachis hypogaea     

小麦条锈菌吸器超微结构和细胞化学的研究

本文应用电镜技术和细胞化学方法,对小麦条锈菌吸器和入侵点的超微结构进行了研究。小麦条锈菌吸器由呈管状的颈部和顶端膨大的吸器体组成,颈部壁和吸器体壁相互连贯,均为两层,并且含有多糖物质。在颈部中段存在有一染色较深的颈环结构。观察发现吸器中的多核现象极为普遍。细胞化学染色结果表明:在吸器外间质内分布有多糖物质;经蛋白消酶解处理后,吸器外间质中可观察到染色较深的纤丝状物质。在入侵点部位,吸器母细胞壁因局部增厚而呈凸镜状,入侵栓壁由内、外两层构成,这两层分别与吸器母细胞壁的第六层和第五层相连接。本研究还观察到同一入侵点产生两个入侵栓的现象。     

马铃薯对晚疫病水平抗性的组织细胞学观察

以马铃薯晚疫病水平抗性品种LBr-12和感病品种费乌瑞它为材料,采用普通光学和电子显微镜技术,系统研究了马铃薯与晚疫病菌(致病疫霉)互作的组织细胞学反应特征。观察结果显示:(1)接种后,水平抗性材料LBr-12出现过敏反应,病菌被限制在侵染点的几个细胞中,菌丝产生较少的分支和吸器。(2)感病品种费乌瑞它被侵染细胞呈蔓延趋势,菌丝产生较多的分支和吸器。(3)电镜观察发现,抗病品种上病菌的胞间菌丝、吸器母细胞、吸器在细胞和亚细胞水平均发生了一系列异常变化,包括原生质的电子致密度加深、液泡增多变大、菌丝细胞壁不规则增厚、细胞器排列紊乱及解体、吸器母细胞及吸器形态异常、病菌最终畸形坏死,同时发现抗病品种受病菌侵染时可迅速产生结构防卫反应,形成的细胞壁沉积物使胞壁极度增厚或细胞膜上产生乳突状结构。     

Anatomy of the endophyte of Viscum album L. (Loranthaceae)

Anatomy of the endophyte of Viscum album L. (Loranthaceae). An anatomical investigation into the nature of the host-parasite interaction of V. album and several of its phanerogamic hosts using SEM and light microscopy was conducted. Three kinds of parasite cell (haustorial parenchyma cells, cells resembling transfer cells and haustorial tracheids) were identified at the host-parasite interface. The terms haustorial parenchyma and haustorial tracheid are defined. Haustorial tracheids were seen to have penetrated the walls of host vessel elements and it is suggested that V. album is able to establish on a wide range of hosts because of the anatomically plastic nature of its haustorium. The development of the haustorium depends to a large extent on the nature of the surrounding host tissues. Parasite-induced host abnormalities including hypertrophy, distorted xylem elements, vessel-wall penetration and tylosis-occluded vessels were observed. The macroanatomical features observed are discussed and interpreted by-proposing a new theory for the ontogenesis of the V. album haustorium. Cortical strands with 'chisel' and 'pencil' shaped apices were both found to be present at the same time on one plant and thus were not seasonally separated.     

Ultrastructural specialization at the host-pathogen interface in rust-infected flax

Summary Ultrastructure of the association between the rust fungus, Melampsora lini, and a compatible variety of flax, Linum usitatissimum, was studied to clarify the structural relationships and interactions at the site of host penetration and at the host-parasite interface. Results of freeze-etching as well as a special section-staining procedure consisting of periodate-chromate-phosphotungstate (PACP) are shown with a host-parasite combination for the first time. The host plasma membrane is invaginated by the fungus and forms a continuous boundary around the fungal haustoria which penetrate the host cells. No morphological continuities are observed linking the protoplasts of host and fungus. With both freeze-etching and the PACP stain, the invaginated portion of the host plasma membrane at the host-parasite interface shows distinctive features that are not characteristic of the non-invaginated portion of the membrane. This localized specialization of host plasma membrane in response to the fungus appears as a significant and consistent feature of the host-parasite interaction. The host plasma membrane is separated from the haustorial wall by an amorphous layer of sheath material which covers the body but not the neck of the haustorium. This sheath provides the environment in which the haustorium exists and functions during the course of the host-parasite association. Occasionally, a collar of wall-like material derived from the host cell forms around the haustorial neck. The collar is continuous with the host wall and is distinct and discontinuous from the haustorial sheath. In fewer than 5% of the infected cells this wall material encases entire haustoria. The fungal wall is structurally specialized around the site of host penetration, and it becomes intimately associated with the host wall where the fungus penetrates into the lumen of the host cell. During penetration, the host and fungal walls appear to be fused so that the interface between them is not clearly delineated. The haustorial wall is continuous, via the haustorial neck, with the wall of the haustorial mother cell which lies outside the host cell. Different staining properties reveal this wall continuum to consist of several well-defined regions having different structure or composition. A ring of fungal wall material midway along the haustorial neck stains densely with lead citrate, but is preferentially etched away by periodic acid. The neck ring denotes a transition in the staining reaction of the fungal wall, from that present in the region of host penetration to that of the wall surrounding the haustorium. The findings demonstrate specialization of the fungal wall in the area of host penetration as well as specialization of the host plasma membrane at the host-parasite interface to a degree not previously realized from ultrastructural information.     

Structure and development of the upper haustorium in the parasitic flowering plant Cuscuta japonica (Convolvulaceae)

The anatomical and ultrastructural development of the haustorium of the Cuscuta japonica, a holoparasitic angiosperm, growing on the host plant Impatiens balsamina was studied. After the shoot tips of light-grown parasite seedlings contacted the host, the upper haustorium (external to the host organ) developed through three main successive stages of the haustorial initials, the meristem, and the endophyte primoridium (EP) within the middle layer of the cortex of the parasite stem. The haustorial initial cells were characterized by abundant starch-bearing amyloplasts and mitochondria with an expanded intermembrane space. The meristem cells had numerous large chloroplasts with well-developed thylakoids, reflecting the capability for photosynthesis. Commonly, all three stages of haustorial cells contained conspicuous, large nuclei with enlarged nucleoli and dense cytoplasm including many other organelles, indicating a very active metabolism. In the final stage of upper haustorium development, the meristem cells differentiated into the EP, a host-penetrating tissue. The primordium had smaller file cells at the proximal end and elongate digitate cells at the distal end. The file cells divided actively, while the digitate cells contained abundant chloroplasts, dictyosomes, rough endoplasmic reticulum, and other organelles, suggesting that the EP was cytohistologically well organized for penetration into the host tissue.     

Comparative ultrastructure of aecial and telial infections of the autoecious rust fungus Puccinia tuyutensis

This study demonstrates morphological differences between aecial and telial stages of the autoecious rust Puccinia tuyutensis. The aeciospores possess verrucose ornamentation while the teliospores have smooth surfaces. The aecial and telial haustoria of this rust produced in the mesophyll of Cressa cretica differ morphologically in the following respects:(1) the haustorial mother cell of telial haustorium is more differentiated than that of aecial haustorium and its wall at the penetration site is composed of 4 layers; (2) the aecial haustorium is filamentous in appearance and slightly constricted at the point of entry into the host cell, while the telial haustorium is clavate and possesses a narrow neck with a densely staining neckband and swollen body; (3) the neck of the telial haustorium is always associated with numerous vesicles while that of the aecial haustorium is not. Vascular tissue of host leaves is heavily invaded by aecial haustoria but not by telial haustoria.     

Structure and Development of the Primary Haustorium in Alectra vogelii Benth. (Scrophulariaceae)

Anatomical observations were made on the structure and developmentof the primary haustorium of Alectra vogelii. Its developmentinvolves a mutual aggressive growth of both the host and parasitetissues resulting in the formation of a very large and complextuberous organ. One of the host tissues whose growth is stimulatedby parasite infection is the pericycle whose cells divide repeatedlyand grow around and within the parasite haustorial cortex. Fromvarious points of the proliferating host pericycle, roots becomeinitiated and eventually the entire surface of the haustoriumbecomes covered with these roots. We have referred to them as‘haustorial roots’, a term which we have re-examinedand redefined. True xylary connections are established not onlybetween the parasite and the host root but also between theparasite and these ‘haustorial roots’. The uniquedevelopment of primary haustorium and ‘haustorial roots’in A. vogelii is discussed in relation to the development ofprimary haustoria in other root parasites.     

Surface carbohydrates and cell wall structure of in vitro-induced uredospore infection structures ofUromyces viciae-fabae before and after treatment with enzymes and alkali

Summary Uredospores ofUromyces viciae-fabae differentiate to form germ tubes, appressoria, infection hyphae and haustorial mother cells on oil-containing collodion membranes. The cell walls of these infection structures were studied with the electron microscope and with FITC-labeled lectins before and after treatment with enzymes and inorganic solvents. Binding of the FITC-labeled lectins was measured with a microscope photometer. The enzymes pronase E, laminarinase, chitinase and lipase had different effects on each infection structure. Pronase treatment uncovered the chitin of germ tubes, appressoria and haustorial mother cells, but not of substomatal vesicles and infection hyphae. A mixture of - and -1,3-glucanase which also contained chitinase activity dissolved germ tubes and appressoria completely, but not infection pegs, substomatal vesicles, infection hyphae and haustorial mother cells. After treatment with laminarinase or lipase, an additional layer, which is especially obvious over the substomatal vesicle, infection hypha and haustorial mother cell, bound to LCA-FITC. In the wall of the haustorial mother cell, a ring, which surrounds the presumed infection peg, had strong affinity for WGA after protease and sodium hydroxide treatment. The infection structures have a fibrillar skeleton. The main constituent seems to be chitin. This skeleton is more dense or has a higher chitin content in the walls of appressoria and haustorial mother cells. The fibrils of the skeleton extend throughout the cell wall of the germ tube and appressorium. They are embedded within amorphous material of complex chemical composition (-1,3-glucan, -1,3-glucan, glycoprotein). The chitin of the infection peg, substomatal vesicle, infection hypha and haustorial mother cell is covered completely with this amorphous material. These results show, that each infection structure has distinct surface and wall characteristics. They may reflect the different tasks of the infection structures during host recognition and leaf penetration.Abbreviations AP appressorium - FITC fluorescein isothiocyanate - GT germ tube - HC haustorial mother cell - IH infection hypha - IP infection peg - LCA Lens culinaris agglutinin - n nucleus - neu neuramic acid - p pyranoside - R ring - s septum - SV substomatal vesicle - WGA wheat germ agglutinin     

EXPERIMENTAL STUDIES OF HAUSTORIUM INITIATION AND EARLY DEVELOPMENT IN AGALINIS PURPUREA (L.) RAF. (SCROPHULARIACEAE)

In parasitic angiosperms the haustorium, an organ specialized for attachment and penetration of host tissue, functions in the transport of water and nutrients from the host to the parasite. In Agalinis purpurea (L.) Raf. (Scrophulariaceae) these organs are initiated laterally along its roots, opposite a primary xylem pole. Analyses of haustoria distribution and cellular root profiles show that the portion of the root which is most sensitive to haustorial elicitor molecules is the area distal to the zone of elongation and near the root meristem. Sectioned material supports this finding and, further, indicates that the cells which are the first to respond to haustorial elicitors are located in the inner cortex. Haustoria develop rapidly in response to a host root or to isolated chemical elicitors (xenognosins) normally contained in host root exudate. By 6 hr, vacuolation and radial cellular enlargement are observed in the cortex, and a lateral swelling along the root is visible. By 12 hr, cells of the epidermis divide anticlinally to establish a group of densely cytoplasmic cells at the apex of the haustorial swelling. Accompanying these divisions is the differentiation of specialized hair cells which elongate from epidermal cells flanking the presumptive haustorial apex. Next, the internal, radially enlarged cortical cells divide periclinally. Periclinal divisions are subsequently initiated in the pericycle as early as 18 hr post-induction. Cellular division and enlargement continue so that by 24–36 hr a mature pre-contact haustorium is formed. There is a reduction in root elongation concomitant with haustorial initiation. Depending upon the number of haustoria produced, elongation typically returns to the preinduction level within 2 or 3 days.     

Initiation, Development and Structure of the Primary Haustorim in Striga gesnerioides (Scrophulariaceae)

A light-microscopic study is reported on the initiation, establishmentand structure of the primary haustorium of Striga gesnerioideson the host, cowpea (Vigna unguiculata). The radicular apexof the germinated parasite seed dissolves its way through thehost root cortex to the stele. Thus, it is converted into aprimary haustorium. Some of the haustorial front-line cellsin contact with the host endodermis penetrate into the steleand make contact with the xylem vessels. Differentiation ofthese haustorial cells into xylem vessels occurs and extendsbackwards through the median axial region of the haustorialtract in the host cortex to connect with the conductive xylemof the radicle outside the host root. Subsequently the parasite'splumule develops into a leafy shoot. On penetrating the steleof the host, the haustorium stimulates cell division in thehost pericycle whose triggered proliferation together with expansionof the parasite haustorial tissues result in the formation ofa large, tuberous primary haustorium. At various points of thehost-parasite interface, differentiation of xylem elements occurs,presumably maximizing nutrient transfer from host to parasite.In spite of this, many proliferated host cells at the interfaceremain apparently meristematic showing densely-stained cytoplasmand prominent nuclei.     

THE HOST-PARASITE INTERFACE OF ALBUGO CANDIDA ON RAPHANUS SATIVUS

The fine structure of the intercellular hyphae of the obligate parasite Albugo candida infecting radish does not differ markedly from that described previously for cells of Peronospora manshurica. The stalked, capitate haustoria do not contain nuclei and are packed with mitochondria and lomasomes. The fungal plasma membrane and cell wall are continuous from the intercellular hypha throughout the haustorium except that there is no evidence of fungal cell wall around a portion of the haustorial stalk proximal to the haustorial head. Within the vacuolate host mesophyll cell, the haustorium is always surrounded by host plasma membrane and with at least a thin layer of host cytoplasm. The host cell wall invaginates at the point of haustorial penetration to form a short sheath around the region of penetration, but normally there is no host cell wall around the balance of the haustorium. About 1% of the haustoria observed were necrotic, and these were invariably walled-off completely from host cytoplasm by host cell wall. An amorphous, moderately electron-dense encapsulation lies between the haustorium proper and the host plasma membrane and extends into the penetration region between the sheath and the fungal cell wall. Invaded host cells contain more ribosomal-rich ground cytoplasm than uninfected cells. Glandular-like systems of tubules and connecting vesicles are often numerous in host cytoplasm in the vicinity of haustorial heads. These tubules open into the encapsulation, their limiting unit membranes being continuous with the host plasma membrane. We suggest that these represent a secretory mechanism of the host specifically induced by the parasite.     

Effects of host resistance on the development of haustoria and colonies of oat mildew

Colony development of Erysiphe graminis f.sp. avenae race 2 was studied on detached leaf segments of a range of Avena hosts with different levels of resistance, none of which possesses known specific gene resistance to this race. Resistance affected the length attained by mature primary haustoria, and also colony size as assessed by numbers of haustoria and conidiophores produced per colony 5 days after inoculation. A more accurate assessment of the size of mature haustoria was provided by the total length of their digitate processes. At the primary haustorium stage resistance affected not only haustorial size, but also haustorial efficiency measured as colony growth per unit size. Adult plant resistance of some hosts decreased haustorial size and/or efficiency in colonies on the fifth in comparison with the first formed leaf.