SEPTAL PORES IN THE HETEROBASIDIOMYCETIDAE,PUCCINIA GRAMINIS AND P. RECONDITA

The septal pores in uredial mycelium of Puccinia graminis and P. recondita lack the septal swelling and septal pore cap (dolipore-parenthosome configuration) typically associated with the pores of previously investigated Homobasidiomycetidae and the Tremellales among the Heterobasidiomycetidae. The pores in young hyphae of these two species of Puccinia are characterized by the presence of a cytoplasmic matrix which apparently occludes the pore and acts as a plug, thus preventing the migration of organelles from cell to cell. Large vesicles are typically present at the periphery of the pore matrix and the matrix may be very incompletely bounded by a membrane. Nuclei and other cytoplasmic structures migrate from cell to cell through an opening in the septum lateral to the pore. The available evidence indicates that this peripheral gap in the septum results from a breakdown of a portion of an initially complete septum rather than from incomplete septum formation. In addition to the centripetally formed septa, the hyphae of P. graminis and P. recondita are further compartmentalized by shallow infoldings of the lateral wall and limited unilateral septum formation. There is apparent free passage of cellular material between adjacent compartments.     

Bipolar budding in yeasts — an electron microscope study

Bud formation in yeasts with bipolar budding was studied by electron microscopy of thin sections.Budding in yeasts of the speciesSaccharomycodes ludwigii, Hanseniaspora valbyensis andWickerhamia fluorescens resulted in concentric rings of scar ridges on the wall of the mother cell. The wall between the ridges consisted of the scar plug left by the former budding and opened up in the formation of the next bud. The wall of the bud arose from under the wall of the mother cell.In the yeasts of the speciesNadsonia elongata more than one bud might be formed from the same plug.InSchizoblastosporion starkeyi-henricii the scar ridges were close together and apparently not separated by the entire plug.In all species a cross wall was formed between mother cell and bud which consisted of an electron-light layer between two layers of more electron-dense material. The cells separated along the light layer.The authors wish to thank Dr J. A. Barnett for corrections of the English text, and Mr J. Cappon for drawing Fig. 1.     

Study on the cell cycle of Bacillus subtilis using temperature-sensitive mutants

Summary Among temperature-sensitive mutants which were defective in septum formation and formed nonseptate filaments at nonpermissive temperatures three (ts31, ts341, ts526) were identified among 434 temperature-sensitive mutants isolated at random from a mutagenized population of Bacillus subtilis 168. The results of morphological observations and characterization of these mutants showed that ts31 and ts341 were septum-initiation mutants and that ts526 was a DNA elongation mutant. The above mutations, and other mutations affecting septum initiation (div355 and tms12) were mapped by PBS1-mediated transduction on the chromosome in three separate regions as follows: pur A16-ts526-div355-cysA14; metC3-(ts31, tms12)-pyrD1-recA1; ebr-2-ts341-uvrA1-hisA1-cysB3. Our results suggest that the initiation process of septum formation requires at least four kinds of gene product. In addition, the sesult obtained with ts526 suggests an intimate connection between septum initiation and DNA replication.     

ULTRASTRUCTURE OF CYST FORMATION IN OCHROMONAS TUBERCULATA (CHRYSOPHYCEAE)1

The cysts (statospores) of Ochromonas tuberculata Hibberd are produced within a cytoplasmic silica deposition vesicle (SDV) whose membrane (silicalemma) appears to be formed by the coalescence of golgi vesicles. Silica is first deposited as small nodules and the collar and spines develop by centrifugal growth only after a complete but still thin wall has been laid down. Small vesicles appear to be attached to the SDV only in the region overlying the developing collar; a cap of radially arranged, moderately electron-dense material occurs at the tip of the growing spines. The cyst pore is formed at the anterior end of the flagellate cell, by lack of silica deposition over a small region of the SDV and rupture of the SDV and other membranes crossing this region. When the cyst wall is complete, an extracystic plug is formed in the pore, resulting in the loss of some extracystic cytoplasm and the plasmalemma, and the inner SDV membrane becomes the functional plasmalemma. The plug develops first by coalescence with the cell membrane of golgi-derived vesicles containing dense but apparently nonsiliceous spicules surrounded by amorphous material. During later stages of plug formation only fibrous material is deposited, some of which may be extruded through the pore forcing out some of the spiculate component. Scanning electron micrographs of the mature wall show it is smooth except for the concentrically wrinkled inner face of the flared collar and that the real pore diameter is only ca. half that of the collar. At germination the plug completely disappears in an unknown way and a single cell, similar to a normal vegetative cell emerges through the pore. Chrysophycean cyst formation generally resembles cell wall formation in diatoms, but differs in some details.     

The relationship of echinate inclusions and coated vesicles on wound healing inNitella flexilis (Characeae)

Summary Wound healing in internodal cells of the freshwater algaNitella flexilis (Characeae) was studied in the light and electron microscope. Immediately after punctation of the cell wall a wound plug is formed which stops outflow of cytoplasm. The plug consists of echinate inclusions which are normally located in the central vacuole. A wound wall consisting of pectin and cellulose microfibrils is formed beneath the plug within one to several hours. During that time the wound shows intensive fluorescence when treated with chlorotetracycline indicating transmembrane Ca²⁺ fluxes. Numerous coated pits and vesicles are found at the plasmalemma. The glycosomes undergo pronounced structural changes. Neither plug nor wound wall formation depend on actin filaments or microtubules as shown by inhibitor experiments with cytochalasin and amiprophos-methyl. The function of the coated vesicles and their interrelationship with other cell organelles is discussed.     

GROWTH AND DIFFERENTIATION OF AXIAL AND LATERAL FILAMENTS IN BATRACHOSPERMUM SIRODOTII (RHODOPHYTA)1

Development of the vegetative gametophyte of Batrachospermum sirodotii Skuja was examined with light and both transmission and scanning electron microscopy. Patterns of wall growth were followed using the Calcofluor White ST pulse-chase method. Thallus structure was analysed in terms of the pattern of development of the apical, periaxial and pleuridial initials that generate the axial and whorled lateral filaments characteristic of Batrachospermum. Apical cells of axial filaments elongate initially by tip growth with the nucleus maintaining a distal position. Nuclear division is horizontal. One daughter nucleus migrates basipetally and a thin, convoluted annular septum and perforate-occluded pit connection are then formed. Elongating axial cells subsequently extend by wall deposition at the base of the cell. Periaxial cells are initiated laterally and elongate primarily by tip growth while the nucleus remains within the axial cell. The nucleus then migrates to the boundary between the initial and the axial cell, divides, and one daughter nucleus moves into the initial and the other back into the axial cell. A slightly irregular annular septum and simple-occluded pit connection are then formed. Pleuridial cell initials begin as terminal to subterminal protuberances on periaxial or pleuridial cells. They first extend by tip growth and later by bipolar band growth. The nucleus remains within the parent cell as the pleuridial initial expands and a narrow septal ring is formed between the two cells. It then migrates through the septal ring into the initial and divides transversely. One nucleus passes back into the parent cell and a thick, flat septum and perforate-occluded pit connection are formed. It is concluded that the potentially indeterminate axial filaments and the determinate lateral pleuridia represent distinct developmental types in Batrachospermum.     

Discharge papilla development in the phycomycete Allomyces

The process of discharge papilla (DP) formation in Allomyces macrogynus was studied by light and electron microscopy. The plug of the DP was first deposited between the plasmalemma and the wall of the zoosporangium (ZS). The wall above the plug subsequently was eroded away. Deposition of a new inner wall layer in the sporangium held the plug in place and thickening of the layer formed a collar around the plug. Further deposition of material after this stage resulted in the characteristic pulley-shape. The plug material appeared homogeneous in electron micrographs but there was evidence of an outer layer. Digestion of the plug at the time of spore release was from within.Abbreviations DP discharge papilla - ZS zoosporangium     

Sporogenesis in Streptomyces melanochromogenes

The mode of spore differentiation in a strain of Streptomyces melanochromogenes was followed by analysis of ultrathin sections of sporulating aerial hyphae at various stages of sporogenesis. A special accent was laid on the formation of the sporulation septum and its alterations in the course of spore delimitation and separation. Distinct differences in formation and substructure have been observed between the cross walls of vegetative hyphae and the sporulation septa.Cross walls of vegetative hyphae are formed in a way typical for Gram-positive bacteria by a centripetal annular ingrowth of cytoplasmic membrane, on which wall material immediately is deposited. The development of the sporulation septa is characterized by the accumulation of amorphous material in addition to the newly synthesized wall layer inside the invaginating cytoplasmic membrane. This amorphous septal material will later be decomposed presumably by two lytic systems which cause the separation of the spores. The central region of the finished sporulation septum is perforated by microplasmodesmata. Spores are released by a break down of the surface sheath. The complete spores are enveloped by a twolayered cell wall and the spiny surface sheath.     

An ultrastructural study of septal development in hyphae of Polyporus biennis

A method was developed which allowed the ultrastructural study of septal formation in the basidiomycete Polyporus biennis. The method involved fixing and embedding single clamp connections. Clamp connections with septa at desired developmental stages were located by light microscopy. The septum grew by the incorporation of vesicles of wall material precursors. The rim of the developing septum was drawn centripetally inwards by a contracting collar of microfilaments within a darkly staining matrix. The inflation of the central pore swelling was governed by realigned microfilaments. The parenthesomes were formed, starting at the apex, by the utilization of the microfilament/matrix material lying along the septum. On completion of the parenthesomes a transient striated structure, governed by microfilaments, was formed in the pore channel and the areas enclosed by the parenthesomes. The maturation of the septum involved the laying down of ER along the septum and the occlusion of each end of the pore channel.     

MoCDC14 is important for septation during conidiation and appressorium formation in Magnaporthe oryzae

As a typical foliar pathogen, appressorium formation and penetration are critical steps in the infection cycle of Magnaporthe oryzae. Because appressorium formation and penetration are closely co‐regulated with the cell cycle, and Cdc14 phosphatases have an antagonistic relationship with cyclin‐dependent kinases (CDKs) on proteins related to mitotic exit and cytokinesis, in this study, we functionally characterized the MoCDC14 gene in M. oryzae. The Mocdc14 deletion mutant showed significantly reduced growth rate and conidiation. It was also defective in septum formation and nuclear distribution. Septation was irregular in Mocdc14 hyphae and hyphal compartments became multi‐nucleate. Mutant conidia often showed incomplete septa or lacked any septum. During appressorium formation, the septum delimiting appressoria from the rest of the germ tubes was often formed far away from the neck of the appressoria or not formed at all. Unlike the wild‐type, some mutant appressoria had more than one nucleus at 24 h. In addition to appressoria, melanization occurred on parts of the germ tubes and conidia, depending on the irregular position of the appressorium‐delimiting septum. The Mocdc14 mutant was also defective in glycogen degradation during appressorium formation and appressorial penetration of intact plant cells. Similar defects in septum formation, melanization and penetration were observed with appressorium‐like structures formed at hyphal tips in the Mocdc14 mutant. Often a long fragment of mutant hyphae was melanized, together with the apical appressorium‐like structures. These results indicate that MoCDC14 plays a critical role in septation, nuclear distribution and pathogenesis in M. oryzae, and correct septum formation during conidiogenesis and appressorium formation requires the MoCdc14 phosphatase.     

Ultrastructure and cell wall composition in cell division cycle mutants ofSchizosaccharomyces pombe deficient in septum formation

A number of temperature-sensitive cdc^- mutants ofSchizosaccharomyces pombe that are affected in septum formation were analyzed with respect to their ultrastructure and the composition of their cell wall polymers. One mutant strain, cdc 16–116, has a cell wall composition similar to the wild type (strain 972 h^-). However two other mutants, cdc 4 and cdc 7, show a higher galactomannan content and a lower -glucan content. In all the mutants tested, total glucose incorporation, protein, RNA and DNA synthesis increased similarly to wild type over 3 1/2 h. After 2–3 h of incubation at the non permissive temperature-35°C-, cell numbers remained constant although, increases in optical densities at 600 nm were observed. According to scanning electron microscopy, the mutants had aberrant shapes after 5h of incubation at 35°C. Transmission electron microscopy showed that cdc 3 is unable to complete septum formation. cdc 4 showed the most varied morphological shapes and aberrant depositions of cell wall material. cdc 8 exhibited a deranged plasma membrane and cell wall regions near of cell poles; an abnormal septum and several nuclei. cdc 7 showed elongated cells with several nuclei and with an apparently normal cell wall completely lacking in septum and septal material. cdc 16 showed more than one septum per cell.     

Wall structure and bud formation in Rhodotorula glutinis

Summary The first stage in the formation of a bud in Rhodotorula glutinis is the production of a tapered plate of new wall material between the existing wall and the plasmalemma. The parent cell wall is lysed, allowing the bud to emerge enveloped in this new wall. Mucilage is synthesised to surround the developing bud. As the bud grows a septum forms centripetally dividing the two cells. When the daughter cell reaches maximum size the septum cleaves along its axis, producing the bud scar on the parent cell and the birth scar on the daughter cell. The birth scar is obliterated later as the wall of the young cell grows. A system of endoplasmic reticulum and vesicles is found in young buds and is thought to be responsible for the transport of wall material precursors.     

Development of the discharge apparatus in the fungus Entophlyctis

Correlative light and electron microscopic observations were used to reconstruct the morphological events involved in the development of the discharge apparatus of Entophlyctis zoosporangia. A discharge plug formed as vesicles containing fibrillar material fused with the plasma membrane and deposited their matrices between the plasma membrane and zoosporangial wall. At the apex of the enlarging plug, the zoosporangial wall lost its microfibrillar appearance, became diffuse, and left an inoperculate discharge pore. The discharge plug exuded through this pore and then expanded into a sphere which rested at the tip of the discharge papilla or tube. After the release of the discharge plug, the number of fibrilla containing vesicles decreased and abundant endoplasmic reticulum appeared in the cytoplasm below the plug. Granular material then accumulated at the interface of the discharge plug and the plasma membrane. This was the endo-operculum. A single layer of endoplasmic reticulum subtended the area of plasma membrane which the endo-operculum covered. Later, dictyosomes appeared in the cytoplasm below the endo-operculum. Fusion of Golgi vesicles with the plasma membrane below the endo-operculum coincided with the initiation of cytoplasmic cleavage. This sequence of events indicates that, unlike the discharge plug, the endo-operculum does not originate by vesicular addition of preformed material.     

Ultrastructure of Aerial Hyphae in Linderina pennispora

Ultrathin sections of the aerial hyphae of Linderina pennispora,fixed in glutaraldehyde, show the wall to be composed of anouter electron-dense layer and an inner less-dense one. Thefully developed septum is plugged by electrondense material.A similar septum exists at the base of the pseudophialide. Cytoplasmiccontinuity on both sides of the septum is maintained by theplasmalemma which passes through the septal pore around theperiphery of the plug. Membrane-lined vesicles may occur inthe wall, between the wall and the plasmalemma and internalto the plasmalemma. Ribosome-like particles are numerous inthe cytoplasm and endoplasmic reticulum is virtually absent.     

Don't pull the plug! the Drosophila mating plug preserves fertility

ABSTRACT

Mating plugs are hardened structures—typically a coagulation of seminal fluid components—that are transferred to, or formed within, the female reproductive tract of numerous animal species (both mammals and insects). Analysis of the role(s) of the mating plug in reproduction has been conducted in a wide array of diverse species. These structures have been proposed to have a multitude of functions, which include altering female re-mating rate, acting as a barrier to re-mating and being required for sperm storage or sperm movement to occur in mated females. A recent analysis of the Drosophila melanogaster mating plug has shown that proper formation of the structure is required for optimal fertility in flies: the Drosophila mating plug is required to retain the ejaculate within the female reproductive tract once mating has terminated. Here, we discuss the possible implications of the Drosophila mating plug in the fertility of this species in light of these new results.     

PHIALIDE AND CONIDIUM DEVELOPMENT IN ASPERGILLUS CLAVATUS

Phialide formation in Aspergillus clavatus begins with the formation of thin areas in the vesicle wall. These thin-walled regions and adjacent cytoplasm then push out synchronously to produce the phialides. Mature phialides are broadly oval with an attenuated base and tapered apex. A secondary wall forms inside the phialide apex. The entire phialide apex pushes out to form the first conidium which is delimited by formation of a septum inside the mouth of the phialide. No collarette is present as the first conidium forms, but as the second conidium begins to develop, the outer wall breaks at the mouth of the phialide, leaving a collarette. The walls of the second and subsequent conidia are continuous with the inner wall of the phialide apex, from which they form. Conidia are held in chains by a connective which is a greatly thickened septum.     

The influence of tetrad shape and intersporal callose wall formation on pollen aperture pattern ontogeny in two eudicot species

Background and Aims

In flowering plants, microsporogenesis is accompanied by various types of cytoplasmic partitioning (cytokinesis). Patterns of male cytokinesis are suspected to play a role in the diversity of aperture patterns found in pollen grains of angiosperms. The relationships between intersporal wall formation, tetrad shape and pollen aperture pattern ontogeny are studied.

Methods

A comparative analysis of meiosis and aperture distribution was performed within tetrads in two triporate eudicot species with contrasting aperture arrangements within their tetrads [Epilobium roseum (Onagraceae) and Paranomus reflexus (Proteaceae)].

Key Results and Conclusions

Intersporal wall formation is a two-step process in both species. Cytokinesis is first achieved by the formation of naked centripetal cell plates. These naked cell plates are then covered by additional thick, localized callose deposits that differ in location between the two species. Apertures are finally formed in areas in which additional callose is deposited on the cell plates. The recorded variation in tetrad shape is correlated with variations in aperture pattern, demonstrating the role of cell partitioning in aperture pattern ontogeny.     

The morphology of mating plugs and its formation in scorpions: Implications for intersexual participation

Mating plugs have been proposed as a mechanism that has evolved to avoid sperm competition. Their structure and composition vary across taxa and are related to the effectiveness of its function. This effectiveness could be related to different evolutionary interests of the sexes. Urophonius brachycentrus and Urophonius achalensis (Scorpiones, Bothriuridae) are highly suitable species to study mating plugs because both are monandrous species with specific morphological and physiological responses in the female's genitalia. Here, we analyze (a) the morphology and fine structure of the mating plugs of both species, (b) the site of production in males and the formation process of the mating plug, and (c) the changes that it undergoes over time in the female's reproductive tract. In both species, a complex mating plug obliterates the female's genital aperture and fills the genital atrium. We observed considerable interspecific variation in the mating plug morphology. A mating hemi-plug was found surrounding the capsular lobes of the hemispermatophore, which could have a mixed composition (involving portions of the hemispermatophore and glandular products). The glandular portion was transferred in a semi-solid state filling the female's genital atrium and then hardening. Changes that the plug undergoes in the female's genitalia (darkening and increase of the “distal” area of the plug) indicate a participation of the female to the formation of this type of plug. Our study provides new insights into the plugging phenomenon in scorpions, and we discussed the adaptive significance as a post-copulatory mechanism to avoid sperm competition.     

STRUCTURE AND DEVELOPMENT OF HYPHAL SEPTA IN ALLOMYCES

Development of hyphal septa (pseudosepta) in Allomyces macrogynus begins with the formation of five or more discontinuous pieces of wall material that project inward from the hyphal wall. Lateral fusion of these projections leaves a central pore in the septum that is later filled in by centripetal deposition of wall material. However, lateral fusion of the projections is not complete; peripheral pores remain in the rim of the mature septum. The position of cytoplasmic microtubules corresponds to the position of actively moving cellular particles and organelles. Allomyces reticulatus and A. arbuscula have similar septa.     

RAPID ASSEMBLY OF A WOUND PLUG: STAGE ONE OF A TWO‐STAGE WOUND REPAIR MECHANISM IN THE GIANT UNICELLULAR CHLOROPHYTE DASYCLADUS VERMICULARIS (CHLOROPHYCEAE)1

Upon injury, selected coenocytic algae are capable of forming temporary wound plugs to prevent detrimental cytoplasmic loss. Wound plugs of Dasycladus vermicularis ([Scropoli] Krasser) were harvested 5 min post‐injury and dried. The plug material contained 94% water and can be considered a hydrogel. The gel plug extended several millimeters from the cut end and filled the space inside the cell wall, which resulted from cytoplasmic retraction. Total organic carbon included 55% sugars, 5%–15% protein, and 0.18% lipids. The major sugars were glucose, galactose, mannose, and galacturonic acid. Fluorescein isothiocyanate‐lectins specific for these sugars were localized around the plug matrix. Sulfur content calculated as sulfate corresponded to 17% of the carbohydrate by weight, and sulfated material was detected in plugs by Alcian Blue staining. Formation of the initial plug occurred within 1 min of injury and was not significantly perturbed by the addition of ionic, antioxidant, or chelating agents to the seawater medium. However, addition of exogenous d (+)‐galactose and d (+)‐glucose prevented formation of the nascent gel plug. Wound plugs that were allowed to form from 10 min up until 24 h post‐injury were isolated and incubated with selected biochemical probes to identify the biochemical processes involved in plug formation. The operative strategy in Dasycladus to prevent “cytoplasmic hemorrhage” required availability of sequestered carbohydrate and lectin precursor components throughout the thallus for plug assembly. Once the initial assembly had commenced, additional biochemical interactions were initiated (as a function of time) to promote structural integrity.