Ultrastructure of the Wall of the Germinating Sporangiospore of Linderina pennispora (Mucorales)

Carbon replicas of germinating sporangiospores of Linderinapennispora show the outer wall complex to break open basally,during the phase of swelling, and the surface of the germ tubeto be smooth. Chemical treatment reveal the microfibrillar wallof the germ tube to be continuous with the microfibrillar innerwall complex of the spore. Microfibrils of the germ tube arerandornly arranged and appear to be finer than those of thespore wall. Ultra-thin sections reveal the wall of the germtube to consist of an outer electron-dense layer and an innermicrofibrillar electron-transparent layer and both layers originatein the basal region of the spore between the plasmalemma andthe inner wall complex of the spore.     

Formation of Aerial Hyphae in Candida albicans

Each of 22 isolates of Candida albicans was induced to produce aerial hyphae by culturing on a solid medium containing a peptone, acid-hydrolyzed casein, soluble starch, and agar in an atmosphere of 10% CO(2) at 37 C and room temperatures. Production of aerial hyphae is not diagnostic for C. albicans. Some of the other species of Candida may also produce such structures.     

Structural Proteins Involved in Emergence of Microbial Aerial Hyphae

Filamentous fungi and filamentous bacteria (i.e., the streptomycetes) belong to different kingdoms that diverged early in evolution. Yet, they adopted similar lifestyles. After a submerged feeding mycelium has been established, hyphae grow into the air and form aerial structures from which (a)sexual spores can develop. These spores are dispersed and can give rise to a new mycelium. Some of the key processes involved in the formation of aerial hyphae by these microbes appear to be very similar. In both cases molecules that lower the surface tension are secreted into the aqueous environment, thereby enabling hyphae to grow into the air. Aerial hyphae are then covered with a hydrophobic film. In fungi, this film is characterized by a mosaic of parallel rodlets, while similar rodlets have also been observed on aerial structures of filamentous bacteria. Although the erection of aerial hyphae in both filamentous fungi and filamentous bacteria is dependent upon (poly)peptides that are structurally unrelated, they can, at least partially, functionally substitute for each other.     

Cellulase Localization in Hyphae of Achlya ambisexualis

Cellulase (EC 3.2.1.4; beta-1, 4-glucan glucanohydrolase) was localized at the ultrastructural level and found to occur in dictyosomes and vesicles, around the periphery of unidentified storage bodies, between the plasmalemma and the cell wall, and on the outer surface of the cell wall in the male strain (E87) of Achlya ambisexualis after treatment with the sex hormone antheridiol.     

A Model for Growth of a Single Fungal Hypha Based on Well-Mixed Tanks in Series: Simulation of Nutrient and Vesicle Transport in Aerial Reproductive Hyphae

Current models that describe the extension of fungal hyphae and development of a mycelium either do not describe the role of vesicles in hyphal extension or do not correctly describe the experimentally observed profile for distribution of vesicles along the hypha. The present work uses the n-tanks-in-series approach to develop a model for hyphal extension that describes the intracellular transport of nutrient to a sub-apical zone where vesicles are formed and then transported to the tip, where tip extension occurs. The model was calibrated using experimental data from the literature for the extension of reproductive aerial hyphae of three different fungi, and was able to describe different profiles involving acceleration and deceleration of the extension rate. A sensitivity analysis showed that the supply of nutrient to the sub-apical vesicle-producing zone is a key factor influencing the rate of extension of the hypha. Although this model was used to describe the extension of a single reproductive aerial hypha, the use of the n-tanks-in-series approach to representing the hypha means that the model has the flexibility to be extended to describe the growth of other types of hyphae and the branching of hyphae to form a complete mycelium.     

水霉Saprolegnia菌丝内细胞颗粒运动的特征

水霉菌丝内细胞颗粒的运动有布朗运动和跳跃运动两种形式,跳跃运动的速度在０．０９至４μｍ／ｓ之间。细胞颗粒运动的速度时制改变．不是匀速运动。在同一根菌丝内细胞颗粒运动的速度与颗粒大小无明显相关性;在不同的菌丝内细胞颗粒运动的速度差异明显。细胞颗粒有共同的运动轨道,运动轨道弯曲,并与细胞长轴基本平行。在同一运动轨道上,不同细胞颗粒的运动速度不同。     

The Ascogenous Hyphae of Pyronema confluens

The ascogenous hyphae arise from the oogonium, opposite groupsof nuclei, as minute, enucleate papillae. Nuclei pass into themsingly, rarely two at a time, and a knob-like swelling is formed,containing several nuclei and later growing out into one ormore branches. The nuclei are in single file in the branchesand irregularly arranged in the bulbous base. There are frequentlytwo nuclei in a leading position at the tip of the young branch,but the nuclei may become more evenly spaced as the hypha elongates.The nuclei undergo a simultaneous mitosis. The spindles of thedividing nuclei in the branches are not parallel and this is,therefore, not a conjugate division. Walls are formed as ingrowingrings across the spindles so that the ascogenous hypha, whenseptate, has a uninucleate end cell followed by one, or usuallymore, binucleate cells and a basal bulb containing a variablenumber of nuclei. Croziers are formed as lateral, hooked outgrowths from the binucleatecells. After a simultaneous mitosis of the two nuclei a uninucleateend cell, a binucleate penultimate cell, and a uninucleate stalkcell are formed. Thus, the division in the crozier and thatin the ascogenous hypha are alike. The binucleate cell of the crozier may proliferate to form anothercrozier, or it may form an ascus after the fusion of its twonuclei. The stalk and terminal cell of the crozier may anastomoseand grow out to form a lateral crozier. The chromosome number in the mitosis in the ascogenous hyphais twelve and there are twelve bivalents at the first divisionof meiosis in the ascus. The effect of increasing the illumination of the cultures withan electric lamp in addition to diffuse daylight is to ensurethe further development of all early formed sexual organs, tomake the ascogenous hyphae develop rapidly, to make the lattershort and curved in form with few binucleate cells, and to increasethe tendency towards a period of erect proliferation beforethe formation of the asci and lateral proliferation begin. The bearing of the results on current theories of sexualityin the Ascomycetes is discussed.     

Fine-structural Correlates of Growth in Hyphae of Ascodesmis sphaerospora

Mycelial mats of Ascodesmis sphaerospora were fixed and embedded for electron microscopy, and thin sections of 1-mm blocks, taken from the 1st to the 7th mm behind the hyphal tips, were cut parallel to the long axis of the hyphae. The hyphal tip region is characterized by an outer zone of electron-transparent vesicles, 500 to 1,000 A in diameter, and is apparently associated with wall elaboration. Immediately behind this region, dense granules become evident along convoluted membrane systems and along the plasma membrane; in the same region are numerous small lomasomes in the lateral wall. As the hypha grows, septa are laid down at 3- to 7-min intervals at a distance of 200 to 250 μ behind the hyphal tip. A cylinder of endoplasmic reticulum is intimately involved in cross-wall deposition from its earliest stages; as the wall grows in, it becomes increasingly constricted in the pore region, finally assuming a torus-like configuration. Woronin bodies are shown to have a crystalline substructure and to originate in pouch-like membrane systems. Cross-walls from a 7- to 13-hr-old mycelium frequently show highly ordered structures in the vicinity of the pore. These structures may appear either as laminar stacks of discs to one side of the pore or as series of stubby concentric rings within the pore area itself. In the latter case, a mass of granular material is frequently seen plugging the pore. Other unusual organelles and inclusions in 7- to 13-hr hyphae are vesicles containing swirls of beaded or dilated membrane, membrane-enclosed rods, and stacks of unit membranes associated with spherical, electron-transparent vesicles.     

A Novel Apical Corpuscle in Hyphae of Mucor rouxii

Median longitudinal sections of germ tube apices of Mucor rouxii revealed the presence of a single, roughly hemispherical, electron-dense organelle, in intimate contact with the apical cell wall. Conceivably, this "apical corpuscle" may be responsible for the emission of the germ tube and its continued apical growth.     

Age-Dependent Metabolic Differences in Peripheral Hyphae of Rhizoctonia solani

Peripheral hyphae were separated from the remaining thallus of Rhizoctonia solani in exponential and stationary phases of growth. The QO(2) in whole cells of peripheral hyphae from young fungal colonies was on the average 2.6 times and the protein content 1.6 times greater than in peripheral hyphae from old fungal colonies. The overall rate of amino acid uptake was less in old than in young fungal colonies. In a polyuridylic acid-polyphenylalanine incorporating system, the two kinds of peripheral hyphae required ribosomes, supernatant fraction, polyuridylic acid, soluble ribonucleic acid, adenosine triphosphate, and pyruvate kinase. The rate of polyphenylalanine synthesis in old fungal colonies was slower than in the young fungal colonies. The ribosomes and supernatant fraction of the young and old fungal colonies were interchangeable and active. The factor responsible for deficient protein synthesis in old fungal colonies appears to be in the soluble fraction of the mycelium.     

A Method for Staining Infection Hyphae in Pine Leaves

Fungus-inoculated Pinus radiata leaves were fixed and then stained with periodic acid-Schiff reagent. Pieces of leaf with fungal material on the surface were removed. These pieces were stained in lactophenol cotton blue for a few minutes and then mounted in dilute lactophenol cotton blue. Microscopic examination of fungal material inside and outside the mounted leaf pieces revealed the following: conidia and germ tubes on the leaf surface were red, appressoria remained unstained, and infection hyphae within the leaf were stained blue. This differential staining method was particularly useful for distinguishing germ tubes from infection hyphae arising from appressoria.     

猪苓菌丝形成菌核结构的特点(英文)

对猪苓(Grifolaumbellata(Pers.)Pilat)菌丝在人工条件下形成菌核及繁殖过程、人工菌核与野生菌核及培养基上未形成菌核的猪苓菌丝的显微结构进行了系统研究。研究证明人工菌核的结构与野生菌核的结构相似,均具有菌髓和皮层结构。人工菌核中的菌丝与培养基表面未形成菌核的猪苓菌丝存在着显著的差异,人工菌核是由培养基上纯培养的菌丝分化为膨大菌丝再由此形成有高度组织分化的猪苓菌核。     

Cytoplasmic Bulk Flow Propels Nuclei in Mature Hyphae of Neurospora crassa

We used confocal microscopy to evaluate nuclear dynamics in mature, growing hyphae of Neurospora crassa whose nuclei expressed histone H1-tagged green fluorescent protein (GFP). In addition to the H1-GFP wild-type (WT) strain, we examined nuclear displacement (passive transport) in four mutants deficient in microtubule-related motor proteins (ro-1, ro-3, kin-1, and a ro-1 kin-1 double mutant). We also treated the WT strain with benomyl and cytochalasin A to disrupt microtubules and actin microfilaments, respectively. We found that the degree of nuclear displacement in the subapical regions of all strains correlated with hyphal elongation rate. The WT strain and that the ro-1 kin-1 double mutant showed the highest correlation between nuclear movement and hyphal elongation. Although most nuclei seemed to move forward passively, presumably carried by the cytoplasmic bulk flow, a small proportion of the movement detected was either retrograde or accelerated anterograde. The absence of a specific microtubule motor in the mutants ro-1, ro-3, or kin-1 did not prevent the anterograde and retrograde migration of nuclei; however, in the ro-1 kin-1 double mutant retrograde migration was absent. In the WT strain, almost all nuclei were elongated, whereas in all other strains a majority of nuclei were nearly spherical. With only one exception, a sizable exclusion zone was maintained between the apex and the leading nucleus. The ro-1 mutant showed the largest nucleus exclusion zone; only the treatment with cytochalasin A abolished the exclusion zone. In conclusion, the movement and distribution of nuclei in mature hyphae appear to be determined by a combination of forces, with cytoplasmic bulk flow being a major determinant. Motor proteins probably play an active role in powering the retrograde or accelerated anterograde migrations of nuclei and may also contribute to passive anterograde displacement by binding nuclei to microtubules.Organelle movement and positioning are important aspects of cell growth and differentiation (19, 20, 27, 35). Movement and positioning of nuclei are especially important because of their implications in mitotic divisions during hyphal growth and asexual sporulation (conidiation), as well as fertilization events leading to meiosis and ascospore formation during sexual development (1, 3, 33). In yeast, nuclei move comparatively short distances (20, 32), whereas in filamentous fungi nuclei are typically transported over long distances within hyphae (1, 34, 35).Movement of nuclei in fungal cells may be either an active or a passive process. Early studies of filamentous fungi showed nuclei uniformly distributed along the entire hypha; they appeared to move with the growing hyphal apex, keeping a more or less constant distance from the cell tip. Such evidence pointed to passive displacement of nuclei by cytoplasmic bulk flow (10-12, 24), a role confirmed in our recent study on the dynamics of the microtubular cytoskeleton (28) and supported by studies with injected lipid droplets (17). Upon the discovery of motor proteins and their role in nuclear migration and positioning in filamentous fungi, attention was primarily focused on the participation of motors in nuclear events, including the movement of nuclei during hyphal extension (15, 25, 26, 29, 37), while the role of cytoplasmic bulk flow was largely discounted or disregarded.Whereas much effort has been directed toward the characterization of the components involved in motor-driven nuclear transport, the relative importance of passive nuclear propulsion has remained an open question. For the purpose of distinguishing clearly between active migration and passive displacement, we will consider “migration” to mean an active, motor-dependent process, while “displacement” will refer to passive transport of nuclei within the hypha. “Movement” refers either to active or passive transport of nuclei through hyphae. Here, we used strains of Neurospora crassa whose nuclei were tagged with green fluorescent protein (GFP) to examine the dynamics and distribution of nuclei in growing hyphae. In addition to evaluating nuclear movement in a wild-type (WT) strain, we examined the dynamics of nuclear movement in mutants defective in microtubule-related motor proteins: a ro-1 mutant for its deficiency in the heavy chain of dynein, a ro-3 mutant deficient in the dynactin p150^glued subunit, a kin-1 mutant deficient in conventional kinesin, and a ro-1 kin-1 a dynein-kinesin double mutant. We also tested the effect of drugs that inhibit specifically microtubules and actin microfilaments. Our study demonstrates that passive displacement plays a major role in nuclear dynamics in growing hyphae of N. crassa.     

Nonrandom Sister Chromatid Segregation and Nuclear Migration in Hyphae of Aspergillus nidulans

Radioactive conidiospores of Aspergillus nidulans were prepared by growing a purine-requiring mutant with tritiated adenine. When these spores germinated in a nonradioactive medium, the dispersion of the original chromosome set could be followed by treating the hyphae with ribonuclease and preparing radioautograms. Germinating spores with four or eight nuclei contained two highly labeled nuclei and two or six nuclei with much less or no radioactivity. Successive mitotic divisions thus distributed the deoxyribonucleic acid (DNA) of the eight spore chromosomes among only two of the progeny nuclei. The two nuclei containing the original chromosome set were not dispersed at random along the linear hypha but were usually located near the growing tip. These results are compatible with the view that chromatids containing DNA strands of identical age segregate as a unit during mitosis. They further indicate that the mechanism which disperses newly formed nuclei in the growing hypha can distinguish between nuclei containing DNA strands of different ages.