Haustorial Mother Cells Research Articles

Development of infection structures of the rust, Puccinia porri, on leek leaves

Light microscope and SEM techniques have been used to investigate the development on leek leaves of infection structures from urediniospores of the rust fungus Puccinia porri. Much of the volume of the appressorium develops within, and conforms to the shape of the chamber above the sunken stoma. During successive vacuolation of the appressorium, substomatal vesicle and haustorial mother cell that of the appressorium and haustorial mother cell is almost complete whereas that of the substomatal vesicle is partial.

Ultrastructural Observations on the Dikaryotic Haustorium ofCronartium Flaccidum(Alb. & Schw.) Wint. inVincetoxicum HirundinariaMedicus

SUMMARYThe haustorium of the uredial stage of Cronartium flaccidum in Vincetoxicum hirundinaria was studied with TEM. The observations concern the haustorial mother cell and its relation to the host cell wall, the penetration peg, the shape and the cytoplasm of the haustorium and some host cell organelles in relation to the haustorium. The presence of collars was noted. These features are similar to those described for host-dikaryotic haustorium relationship in other rusts. The extrahaustorial matrix however shows a unusual development. In fact, it wraps the whole length of haustorial neck although it is separated from the haustorial neck wall by the extrahaustorial membrane doubled in this region. The probable significance of this host-parasite interface, perhaps limited to the genus Cronartium, is discussed.

Lectin Binding Studies on the Cell Walls of Soybean Rust (Phakopsora pachyrhizi Syd.)

AbstractWalls of uredospores, infection structures, intercellular hyphae and haustoria of the soybean rust fungus (Phakopsora pachyrhizi) were studied by electron microscopy using gold‐labeled wheat germ lectin (WGL) and Concanavalin A (ConA) as cytochemical probes. Receptors for WGL (probably chitin) were detected in all fungal walls included in this study. WGL‐binding occurred throughout the entire walls (uredospores, appressorial cone, penetration hyphae, haustorial mother cells) or only to the inner wall layers (germ tubes, appressoria, intercellular hyphae).

Ultrastructural studies on fibrillar papillae formed in Welsh onion mesophyll cells infected by Puccinia allii.

Papillae containing ultrastructurally different components were observed in mesophyll cells of Welsh onion leaves inoculated with Puccinia allii. The components of the papillae observed in the mesophyll cells before penetration by the fungus were different from those formed after penetration. The papillae found before the fungal penetration were constituted only with fibrillar components, while the papillae formed after penetration contained non-fibrillar components in addition to the fibrillar components. The non-fibrillar components were primarily found around the haustorial necks, and sometimes around the haustorial bodies. Ultrastructural analysis of mesophyll cells of the leaves (cv. Ishikura-ippon-futonegi) before the papilla formation elucidated that the plasmalemma in mesophyll cells adjacent to the haustorial mother cells was retracted from the cell walls, and tubular or vesicular structures were observed in the paramural spaces. These structures appeared to be continuous with the plasmalemma or endoplasmic reticulum in the host cytoplasm. In addition to these structures, fibrillar materials were observed in the paramural spaces. The tubular or vesicular structures may play roles in the formation of the fibrillar papillae in Welsh onion-P. allii system.

Culturing Puccinia coronata on a Cell Monolayer of the Avena sativa Coleoptile

AbstractA culture of Puccinia coronata on an epidermal cell monolayer dissected from the Avena sativa caleoptile is described. To induce fungal development, infection structure formation had to be induced with a heat treatment. The host cells were fed with 1 % sucrose (or glucose or manitol) to sustain fungal growth. Under these conditions, normal development of hyphae, haustoria with haustorial mother cells and uredospores occurred. Uredospores had normal infectivity.

Ultrastructural observations of the rust fungus Physopella zeae in Zea mays

Examination of sporulating uredia of the tropical corn rust fungus, Physopella zeae, with the transmission electron microscope revealed that this fungus possessed most of the distinguishing ultrastructural characteristics reported for temperate zone inhabiting members of the Uredinales. Physopella zeae differed from these latter fungi in the repeated production of urediospores from the same site on the sporogenous cell, and in the intracellular location of most of the mycelium. The intracellular mycelium was differentiated into structurally unspecialized hyphae and structurally distinct haustoria arising from differentiated haustorial mother cells which were located in the neighbouring host cell. Both types of intracellular structures were covered with a matrix, and that around the intracellular hyphae was continuous with similar material lining the plant cell wall. The matrix was thicker and more compact around intracellular hyphae than around the bodies of haustoria. The matrix lining the host walls was thinnest in sections of mesophyll cells containing a ratio of haustoria – intracellular hyphae profiles greater than one. These data suggest that the haustorium may actively inhibit matrix formation in invaded plant cells.

An ultrastructural comparison of monokaryotic and dikaryotic haustoria formed by the fusiform rust fungus Cronartium quercuum f.sp. fusiforme

Haustoria formed by the monokaryotic stage of Cronartium quercuum f. sp. fusiforme in Pinus taeda differed from those of the dikaryotic phase in Quercus rubra. Monokaryotic (M) haustorial walls were continuous with the walls of relatively undifferentiated haustorial mother cells. The septate M-haustorial neck and expanded M-haustorial body were separated from the invaginated host plasmalemma by a sheath which was continuous with the host cell wall. Collars encasing sheaths were infrequently observed. Dikaryotic (D) haustoria were morphologically similar to M-haustoria; however, they differed in several respects when examined with TEM. The D-haustorial mother cell wall was thickened at the penetration site but a reduction in the number of wall layers occurred between the thickened portion of the mother cell and the D-haustorium. A darkly staining neckband was present in the wall of the nonseptate D-haustorial neck but was lacking in the M-haustorium. An extensive sheath separated the invaginated host plasmalemma from the D-haustorial wall distally from the neckband. However, the sheath was separated from the D-haustorial wall and from the host cell wall by an invaginated host plasmalemma doubled in the haustorial neck region proximally from the neckband.

Early abortion of colonies of leaf rust, Puccinia hordei, in partially resistant barley seedlings

Partial resistance (PR) in barley to leaf rust is assumedly a case of durable resistance. PR is characterized by a reduced rate of epidemic development in spite of a susceptible infection type. One of the components of PR, low infectibility, was studied histologically by means of fluorescence microscopy. Quantitative analyses of the phases of the infection process beyond appressorium formation showed that the reduced infectibility of partially resistant barley seedlings rests on a significant "early abortion" of colonies. This type of abortion occurs at about the moment of the formation of the first haustoria, when the young colonies have formed up to five or six haustorial mother cells. Early abortion is only incidentally associated with the collapse of host cells. Not only the variation in infectibility among barley genotypes but also the variation in infectivity among leaf rust isolates is based mainly on differences in the degree of early abortion. The occurrence of a high degree of early abortion in several unrelated barley genotypes indicates that the PR genes are part of a generally occurring system.

Structure and Development of Mattirolella Crustosa (Termitariales, Deuteromycetes) on Panamanian Termites

Mattirolella crustosa is a peculiar entomogenous fungus that forms a discoid to hysterecioid pycnidial lesion on termites. Three species of termites, Nasutitermes corniger, N. ephratae, and N. columbicus, from Panama were found infected with several developmental stages of M. crustosa. Various aspects of primary infection and pycnidial development are discussed, including lesion spread, formation of haustorial mother cells, phialides, and conidia, spore release, and ostiole structure. Mattirolella is morphologically similar to species of Termitaria and Termitariopsis, but differing largely in its chambered, beaked pycnidium. Mattirolella was first described by Colla (1929) parasitizing the integument of the termite Rhinotermes marginales (L.) in British Guiana. She described a single species, M. sylvestrii Colla, noting the similarity to Termitaria, another genus with termite-inhabiting species described by Thaxter (1920). Mattirolella differed, however, in having its hymenium of sporogenous cells covered by a stromatic tissue and separated into chambers by rows of sterile cells. In their study of Termitaria, Khan and Kimbrough (1974a) found among the Thaxter collections at Harvard's Farlow Herbarium a slide labelled T. crustosa. From excellent sections on this slide they were able to determine that the collection represented not a species of Termitaria, but a Mattirolella. They proposed for this species the name M. crustosa, placing it in the newly created form-order Termitariales. They were also able to clarify many of the observations made by Colla (1929) in her study of M. sylvestrii. The sporogenous cells of the basal stratum were shown to be haustorial mother cells, and penetration pegs were noted in the termite exoskeleton. The hymenium of phialides was separated into chambers by rows of sterile cells and overlaid by a stromatic layer. The phialides broke at their apices and released small rectangular spores into an epihymenial cavity. Termitaria differed from Mattirolella in having an undivided hymenium of phialides without an epihymenial stromatic layer. The black-bordered, discoid lesion, phialidic hymenium, and basal layer of haustorial mother cells confirmed a relationship of the two genera. During a study of termites in Panama (BLT), colonies of Nasutitermes corniger (Motschulsky), N. ephratae (Holmgren), and N. columbicus (Holmgren)

Ultrastructural Observations on the Host-Pathogen Interface in Infections ofCronartium Flaccidumon Pine

SUMMARYHyphae and haustoria of the pycnio-aecial stage of Cronartium flaccidum in Pinus pinea and P. pinaster were observed with a TEM. This characteristically systemic and long-lasting monokaryotic mycelium was examined in primary needles of young seedlings with the first symptoms of infection, in the stem of the same seedlings just invaded by the rust and in cortical tissues of infected internodes of older plants. The described ultrastructural features, generally referable to all examined materials, regarded: the wall, capsular sheath and contents of the intercellular hyphae; the haustorial mother cell and the penetration peg; the general morphology, wall, extrahaustorial matrix, collar and encasement of the haustorium; the close proximity to the extrahaustorial membrane of the host cell endoplasmic reticulum and Golgi apparatus. Some aspects of C. flaccidum monokaryotic haustorium and related structures are discussed and compared to those reported for monokaryotic and dikaryotic haustoria of other rusts.

Development of Puccinia striiformis in a susceptible winter wheat variety

Development of Puccinia striiformis in leaves of seedlings and adult plants of a yellow rust-susceptible winter wheat variety was studied using a fluorescent staining technique. Penetration of the host and formation of sub-stomatal vesicles by the fungus was similar in seedlings and adult plants except that, in the latter, most infections were concentrated in the distal one-third of the lamina. Two infection hyphae usually develop from the side of the vesicle nearest to the base of the leaf. In seedlings these hyphae branch frequently and grow in all directions, often crossing the vascular bundles. In adults, one infection hypha grows directly into the mesophyll and the other develops at right angles to the axis of the leaf blade. From this ‘initial transverse runner hypha’ develop many branched hyphae, which ramify through the mesophyll producing haustorial mother cells and haustoria and establishing a pustule bed from which a uredinium develops. A broad longitudinal runner hypha, which grows alongside the veins towards the base of the leaf, originates from the edge of the primary pustule bed and gives rise to secondary infection hyphae, pustule beds and stripes of uredinia between the veins.

Ultrastructure of haustorium development in Puccinia coronata avenae. I. Cytochemistry and electron probe X-ray analysis of the haustorial neck ring

The structure and composition of the haustorial neck ring in Puccinia coronata avenae was determined by histochemical methods and by electron-probe X-ray analysis (EDX). In mature haustoria, the neck ring structure was composed of two cylindrical bands. A broad band, nearer to the haustorial mother cell, was designated as the α (alpha) band and a narrower band, nearer to the haustorial body, the β (beta) band. The chemical composition of the two bands was different. The results of EDX analysis showed silicon as the major element present in the α band, and iron and phosphorus (possibly in the form of ferric pyrophosphate), the major elements of the β band. Digestion with protease or treatment with the organic solvents chloroform–methanol, ether–ethanol, or acetone failed to extract either band, indicating the presence of little, if any, protein or lipid materials.

A fine-structural study of the infection of leaves of Phaseolus vulgaris by uredospores of Uromyces phaseoli

The infection of leaves of Phaseolus vulgaris by uredospores of Urornyces phaseoli followed the normal sequence for rust fungi. After germination the tip of the germ tube formed an appres-sorium over a stoma, through which an infection peg then penetrated the leaf. The stomata were unaffected by the fungus. Cell penetration followed the formation of a haustorial mother cell and its adhesion to a plant cell. The staining characteristics of the host wall were affected, and wall apposition formed inside the infected cell at the point of penetration. A fungal haustorium formed within the plant cell, and following tannic acid treatment during fixation, the extrahaustorial complex surrounding the haustorial wall was shown to consist of 2 layers. The surface spines of uredospores were formed in pockets of wall material below the surface of the immature spore, and consisted of fibrillar material aligned towards the tip of the spine.

Electron microscopy of susceptible and resistant near-isogenic (sr6/Sr6) lines of wheat infected by Puccinia graminis tritici. III. Ultrastructure of incompatible interact

The interaction between avirulent wheat stem rust and wheat mesophyll cells containing the temperature-sensitive Sr6 gene for stem rust resistance was studied by electron microscopy. Mesophyll cells that were invaded at 26 °C (conditioning compatibility) did not develop any signs of incompatibility after they were transferred to 19 °C, at which temperature incompatibility is normally expressed. In host tissue that appeared to be invaded after the change from 26 to 19 °C, the early ultrastructural symptoms of incompatibility were a more electron-dense and often perforated invaginated host plasmalemma, disruptions of the noninvaginated host plasmalemma, vacuolation of the cytoplasm, and accumulations of electron-dense material along the membranes of the vacuoles. At later stages in the development of incompatible interactions, the electron-dense accumulations along the vacuole membranes increased in size and occurred along chloroplast and mitochondrial membranes. Eventually, the entire protoplasts were electron dense and collapsed. In haustoria and haustorial mother cells, incompatibility was usually expressed by a uniform increase in electron density of the cytoplasm. In the Sr6/P6 interaction at 19 °C, host cell necrosis was not always accompanied by fungal necrosis or vice versa. In Sr5/P5 interactions, which were examined for comparison, the intracellular symptoms of incompatibility were similar to those of the Sr6/P6 interactions.

Effects of heat shock, actinomycin D, cycloheximide and blasticidin S on nonhost interactions with rust fungi

The effect of treating the nonhost plant with heat shock, actinomycin D, cycloheximide or blasticidin S before inoculation was examined for four angiosperm-rust combinations. In cabbage infected with cowpea rust and in French bean infected with sunflower rust, preinoculation treatments with heat shock and at least one of the protein synthesis inhibitors resulted in increased growth of the infection hypha and an increase in the number of infection sites at which haustoria developed. However, intercellular growth still ceased at about 24 h after inoculation in spite of evidence from delayed inoculation experiments that, in cabbage, the effects of the blasticidin S treatment lasted for at least 48 h. In pea leaves infected with cowpea rust, all treatments resulted in increased growth of the infection hypha, but they had no similar effect on this same rust in French bean. All treatments, except actinomycin D in pea, also increased the frequency of haustoria formed in these two nonhost plants and, in contrast to their effects on the other plant-rust combinations, also allowed fungal colonies to develop which continued to grow for at least 4 days. In French bean infected with cowpea rust, delayed inoculation experiments suggested that such growth continued long after the plant had recovered from the pre-inoculation treatments. Such growth did not depend on the development of a haustorium from the first-formed haustorial mother cell or on the absence of necrosis of the invaded cells. None of the treatments had any observable effect on the compatible interaction of bean rust in French bean. The significance of these observations is discussed.

Structural studies of the development of infection structures of cowpea rust, Uromyces phaseoli var. vignae. II. Vacuoles.

During development of infection structures of cowpea rust, Uromyces phaseoli var. vignae, migration of cytoplasm from one structure to the next is accompanied by production of vacuoles. The developmental pathway of these vacuoles appears to differ in different sites of production. In germinating uredospores, appressoria, and substomatal vesicles, their development includes the formation and enlargement of electron-opaque globule-containing vesicles, termed vacuole precursor vesicles (VPVs). In contrast, in the elongating germ tubes and vacuolating haustorial mother cells, VPVs do not appear during vacuolation. During development of VPVs into vacuoles there seems to be a control system which selectively activates only a portion of the VPV population.

A histological study of interactions between avirulent races of stem rust and wheat containing resistance genes Sr5, Sr6, Sr8, or Sr22

Primary leaves of wheat (Triticum aestivum L.) with and without resistance genes Sr5, Sr6, Sr8, or Sr22 were inoculated with avirulent races of stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn.) and examined by fluorescence microscopy. In leaves containing the Sr5 gene for resistance, both epidermal and mesophyll cells fluoresced when interacting with the fungus, indicating incompatibility. In leaves containing the Sr6 gene, interacting epidermal cells did not fluoresce and incompatibility was expressed only in mesophyll cells.When the effect of the Sr5 gene was studied in leaves with different genetic backgrounds, it was found that most colonies developed only one or two haustorial mother cells in leaves containing this gene in Prelude, Marquis, or Reliance backgrounds, when examined up to 72 h after incubation. Conversely, in leaves with the Chinese Spring background, one-third of the colonies continued to grow and they produced macroscopically visible lesions. Our observations indicated that the Chinese Spring genotype partially altered the expression of the Sr5 gene in mesophyll but not in epidermal cells. In contrast, the Sr6 gene was more effective in the Chinese Spring background than in the Prelude background.Rust development in leaves with or without the Sr8 gene was the same up to 60 h after incubation, when incompatibility in resistant plants was first detected by the appearance of fluorescing host cells. By 72 h, mean colony size in resistant leaves was smaller than that in susceptible leaves, evidently because growth of runner hyphae was inhibited. Apparently, the P8 gene for avirulence was not expressed until colonies had reached considerable size. In leaves containing the Sr22 gene for resistance, the sequence of histological events was similar to that in leaves containing Sr8, but fluorescing host cells appeared later (72 h) and colony growth was inhibited only at 96 h after incubation. In both of these interactions, fluorescing host cells developed at the periphery of colonies when incompatibility was expressed. The host-parasite interaction in cells invaded before that time remained compatible even at later stages of colony development. In leaves containing the Sr5 or the Sr8 gene, but not in those with the Sr6 gene, the growth of some colonies was inhibited although they were not associated with fluorescing host cells. Evidently, host-cell necrosis was closely associated with reduced fungal growth in interactions involving Sr6, but not in interactions involving the resistance genes Sr5 and Sr8.

Structural studies of the development of infection structures of cowpea rust, Uromyces phaseoli var. vignae. I. Nucleoli and nuclei

Light microscopical observations of living germ tubes and infection structures of cowpea rust were combined with an ultrastructural study to show that a nucleolus was present in the interphase nucleus at all stages of development from uredospore germination through to new uredospore formation. Vacuolate nucleoli were common in germ tubes but only nonvacuolate nucleoli were observed at other stages of fungal development. When grown on oil-containing collodion membranes, germinating uredospores, germ tubes, appressoria, and infection hyphae without haustorial mother cells all contained nucleoli composed primarily of nongranular material. Predominantly granular nucleoli were observed in developing uredospores and all parasitic stages in the leaf after the formation of the first haustorial mother cell. However, the fact that granular nucleoli were also seen in a membrane-grown infection hypha after haustorial mother cell formation suggested that the host was not required to stimulate the resumption of nucleolar activity. Electron-opaque patches, presumed to be condensed chromatin, were most prominent in the nucleoplasm of haustorial mother cells and virtually absent in germinating uredospores and germ tubes. The significance of this observation is discussed. A reduction in nuclear volume was observed in living material prior to cytokinesis in the appressorium and the substomatal vesicle. Evidence suggested that this reduction was produced by the expulsion of part of the nucleoplasm, plus the nucleolus, during mitosis rather than before as suggested for other rusts. Nuclei of haustorial mother cells and haustoria were also smaller than those in intercellular hyphae but the mechanism by which this was achieved could not be determined.

A comparative study of non-host interactions with rust fungi

The interactions of non-host plants with sunflower, corn and cowpea rusts were compared with those described previously for other cowpea rust-non-host combinations. Compared with the situation on the respective host plant, all three rusts made fewer attempts at penetration into the leaf on half or more of the non-hosts examined. Nevertheless, in no case could such surface behavior completely account for non-host resistance since at least a few attempts at penetration were observed for all the non-host-rust combinations. In only one non-host, cabbage, was linear growth inside the leaf significantly less than that in the respective susceptible plant during the first 24 h after inoculation. Since, for cowpea and sunflower rusts at least, growth in this non-host was also less than that achieved on artificial membranes, it was concluded that non-host resistance of cabbage leaves involved an inhibition of fungal growth. In contrast, a detailed study using cowpea rust showed that the extent and pattern of growth in most of the other non-hosts was similar, apart from a greater frequency of haustorial mother cells, to that on the membranes. Thus it seemed that these non-hosts had little influence on the development of the fungus except in the induction of the haustorial mother cell septum. Susceptible plants, however, appeared to stimulate the formation of secondary hyphae, and it is postulated that the resistance of many non-hosts to this rust, and others, may be due to the absence of any similar stimulation by the plant. The importance of the haustorium in this stimulation could not be clearly determined. The possibility that the non-host plant may actively inhibit haustorium formation, however, was suggested by the fact that their absence in many non-host-rust combinations could be correlated with the darkening of the plant wall adjacent to the haustorial mother cell. The general lack of specificity of non-host responses to rust fungi was indicated by the observation that where a given non-host-rust combination was characterized by a particular feature, such as the presence of wall darkening or the relatively high frequency of haustoria, then a similar feature was often seen following infection of the same non-host with the other two rusts. The observation of a few instances where this was not the case, however, suggested that the nature of the fungus may have a modifying effect on the plant response.

Ultrastructural changes associated with the haustorial mother cell septum during haustorium formation inUromyces phaseoli var.vignae

The ultrastructural features of developing haustoria and associated haustorial mother cell septa were examined in the cowpea rust fungus,Uromyces phaseoli var.vignae. Significant changes occurred in the septal pore apparatus, and in structures associated with the septum, during the formation of a haustorium. The originally open septal pore became plugged with osmiophilic material and, on both sides of the septum, elaborations of the plasmalemma developed whose maximum growth coincided with the close association of numerous mitochondria. Those elaborations on the haustorial mother cell side consisted of irregular whorls and tangles of membranes and disappeared prior to the formation of the penetration peg. In contrast, the more tubular protrusions on the hyphal side of the septum reached their maximum length of about 900 nm during the breaching of the host cell wall but subsequently shrank rapidly until, by the time the haustorium was mature, they and their osmiophilic matrix adjacent to the septal wall had usually disappeared. By this time, the osmiophilic plug had also disappeared and the pore now resembled that most commonly seen in other portions of the vegetative mycelium in being covered on either side by a thin layer of osmiophilic material and in being surrounded by a region of differentiated cytoplasm bordered with microbodies. Little change in this septal pore apparatus was observed as the haustorium aged until the tonoplast of the haustorial mother cell broke down. At this time the differentiated regions of the cytoplasm, and the associated microbodies, disappeared from the haustorial mother cell side of the septum.