Geosiphon pyriforme,an Endosymbiotic Consortium of a Fungus and a Cyanobacterium (Nostoc), Fixes Nitrogen

The bladders of Geosiphon pyriforme, an endosymbiotic consortium of a fungus and the cyanobacterium Nostoc punctiforme, show nitrogenase activity. This suggests that the organism is capable of nitrogen fixation.     

Characterization of theGeosiphon pyriforme symbiosome by affinity techniques: confocal laser scanning microscopy (CLSM) and electron microscopy

Summary Geosiphon pyriforme represents a photoautotrophic endosymbiosis of aGlomus-like fungus with the cyanobacteriumNostoc punctiforme. The fungus forms unicellular bladders of up to 2 mm in length and 0.5 mm in diameter growing on the soil surface and harboring the endosymbioticNostoc filaments. The cyanobacteria are located in a compartment (the symbiosome) bordered by a host membrane. The space between this symbiosome membrane (SM) and theNostoc cell wall is filled with an about 30–40 nm thick layer of amorphous material, which is present also in the regions of the symbiosome where noNostoc filaments are located. At these sites the amorphous material consists of a 20–30 nm thick layer separating the SM. The region between the SM and the cyanobacterium is defined as symbiosome space (SS). Fungal bladders, hyphae and free livingNostoc were analyzed by affinity techniques as well as the material occurring in the SS. FITC-coupled lectins with sugar specificity to -D-mannosyl/-D-glucosyl (Con A), N-acetyl--D-glucosamine oligomers (WGA), -L-fucosyl (UEA-I), -D-galactosyl (RCA-120), -D-galactosyl (BS-I-B₄), N-acetyl--D-galactosamine (HPA), and sialic acid (EBL) residues were tested. WGA binding and calcofluor white staining demonstrated that the bladder wall as well as the SS contain fibrillar chitin. Of the other lectins only Con A clearly labeled the symbiosome. On the contrary, the lectin binding properties of the slime produced by free livingNostoc-colonies indicate the presence of mannose, fucose, GalNAc, sialic acid, and galactose, while chitin or GlucNAc-oligomers could not be detected. The symbiosome was also investigated electron microscopically. WGA-gold binding confirmed the presence of chitin, while a slight PATAg reaction indicated some polysaccharidic molecules within the SS. Our results show that the amorphous material within the SS contains molecules typical of the fungal cell wall and suggest that the SM is related to the fungal plasma membrane. The applied lectins all bind to the hyphal surface, indicating a high molecular complexity. Mannosyl, -galactosyl, and sialic acid residues are strongly exposed at the outer cell wall layer, whereas GlucNAc, GalNAc, and -galactosyl residues seem to be present in smaller amounts. The symbiotic interface established between the fungus andNostoc inGeosiphon shows many similarities to that occurring between fungi and root cells in arbuscular mycorrhizas.Abbreviations AM arbuscular mycorrhiza - BS-I-B₄ Bandeiraea simplicifolia lectin I isolectin B₄ - CLSM confocal laser scanning microscopy - Con A Concanavalin A - EBL elderberry bark lectin I - FITC fluorescein isothiocyanate - HPA Helix pomatia agglutinin - PATAg periodic acid-thiocarbohydrazide-Ag proteinate - SM symbiosome membrane - SS symbiosome space - RCA-120 Ricinus communis agglutinin 120 - UEA-I Ulex europaeus agglutinin I - WGA wheat germ agglutinin Dedicated to Professor Dr. Peter Sitte at the occasion of his 65th birthday     

The Resorption of Cilia in Cyathodinium piriforme*

SYNOPSIS. The fine structure of the cilium, kinetosome, kinetodesmal fiber, and basal microtubules has been described in Cyathodinium piriforme. The ciliary axoneme is encased in an electron-dense jacket termed the axonemal jacket. This jacket surrounds the axoneme and is found midway between the axoneme and the ciliary membrane when viewed in cross section. Before division or reorganization the cilia are withdrawn into the cell. Intact cilia surrounded by their jackets are found in the cytoplasm during the early phases of retraction. Degradation of the axonemal microtubules precedes the dissolution of the axonemal jacket. Profiles of the jackets are observed after the microtubules have been resorbed. The cilia appear to detach from the kinetosomes. Barren kinetosomes are seen below the cell surface frequently with kinetodesmal fibers still attached. Whether all or some of these barren kinetosomes contribute to the formation of the new ciliary anlage cannot be ascertained.     

Geosiphon pyriforme,an Endosymbiotic Association of Fungus and Cyanobacteria: the Spore Structure Resembles that of Arbuscular Mycorrhizal (AM) Fungi

The zygomycete Geosiphon pyriforme is the only known endocyanosis of a fungus. The Nostoc spp. filaments are included in photosynthetically active and nitrogen fixing, multinucleated bladders, which grow on the soil surface. The spores of the fungus are white or slightly brownish. They are about 250 μm in diameter and develop singly on hyphal ends or, less frequently, intercalarly. The wall of the spores consists of a thin innermost layer, a laminated inner layer with a thickness of about 10–13 μm, and an evanescent outer layer. The laminated layer is composed of helicoidally arranged microfibrils, and is separated from the evanescent outer layer by a thin electron-dense sublayer. Polarisation microscopy indicates the occurrence of chitin. Shape and wall ultrastructure of the Geosiphon spores and their cytoplasm resemble that of Glomus spores, but are different from that of other genera of the Glomales and Endogonales. Germination occurs by a single thick hyphal outgrowth directly through the spore wall. Like various AM forming fungi, Geosiphon pyriforme contains endocytic bacteria-like organisms, which are not surrounded by a host membrane. Our observations indicate that Geosiphon is a potential AM fungus.     

中国和西方化石人头骨面部三项非测量性状的比较

采用传统的人类学观察方法,对一些中国和西方的化石人头骨模型的犬齿窝、颧骨缘结节和梨状孔上外侧部的膨隆情况进行观察比较,希望为研究头骨形态的发展变化及现代人起源问题,特别是中国现代人的起源提供一些值得参考的信息。得到如下提示：（1）在欧洲犬齿窝似乎是随着人类的进化逐渐出现的,（2）在化石人头骨上,颧骨缘结节的出现似看不出明显的地域差异,（3）梨状孔上外侧部的膨隆这一性状似乎在大荔头骨与其他中国化石人“不融洽”,而与欧洲尼人接近,这一现象可能反映了某种程度的基因交流。     

现代人头骨面部几项非测量性状的观察

用人类学观察法比较了中国云南、华北和欧洲现代人头骨的犬齿窝、颧骨缘突和梨状孔上外侧部膨隆的出现情况,以探讨其在人种、群体区分上是否有意义。结果：（1）在云南头骨,犬齿窝、颧骨缘突的出现率无性别差异,梨状孔上外侧部骨表面膨隆的出现率男性明显高于女性,而在欧洲头骨,这3项非测量必状的出现率男女间无差异。（2）上述3项性状,在中国云南和华北头骨（男性）的出现率无差异。（3）犬齿窝、梨状孔上外侧部骨表面膨隆的出现率,在现代欧洲人头骨明显高于现代中国人头骨。颧骨缘突的出现率在欧洲与中国现代人头骨上无差异。     

PHOTOSYNTHETIC ACTIVITY OF TWO DEVELOPMENTAL STAGES OF A NOSTOC STRAIN (CYANOBACTERIA) ISOLATED FROM GEOSIPHON PYRIFORME (MYCOTA)1

Sessile colonies and motile hormogonia, the two main developmental stages in the life cycle of a Nostoc strain isolated from the endocytobiosis with Geosiphon pyriforme (Kützing) F. v. Wettstein, were investigated for their photosynthetic competence. Large-scale fractionation of the two stages is presented. Photosynthetic parameters were assessed by measurement of chlorophyll fluorescence and oxygen evolution. Hormogonia were as photosynthetically competent as the colonial stage. In addition, hormogonia showed an enhanced capability for nonradiative dissipation of absorbed light energy, a feature that might be important for their function as propagula. Data for the quantum yield of photosystem II of the isolated Nostoc strain were compared to the values determined in situ in G. pyriforme and indicated the possibility of a higher photosynthetic capacity of the endosymbiotic as compared to the isolated cyanobacterium.     

Molecular phylogeny,taxonomy, and evolution of Geosiphon pyriformis and arbuscular mycorrhizal fungi

Geosiphon pyriformis(Kütz.) v. Wettstein is the only known example of a fungus living in endocytobiotic association with a cyanobacterium. The close phylogenetic relationship of Geosiphonwith some arbuscular mycorrhizal fungi (AMF) and the phylogenetic position of Geosiphonare shown in detail. Comprehensive small subunit (SSU) rRNA sequence analyses allow the erection of a new, molecular phylogeny-based taxonomic system for the AMF, including Geosiphon (Geosiphonaceae). Within the recently described phylum Glomeromycota (with one class, Glomeromycetes), a system including four orders was proposed. The erection of several new families will also be necessary. Evolutionary implications are discussed, referring to different possibilities of the influence of AMF on the colonization of the terrestrial habitat by plants.     

Geosiphon pyriforme,a fungus forming endocytobiosis withNostoc (Cyanobacteria), is an ancestral member of the glomales: Evidence by SSU rRNA Analysis

Geosiphon pyriforme inhabiting the surface of humid soils represents the only known example of endocytobiosis between a fungus (Zygomycotina; macrosymbiont) and cyanobacteria (Nostoc; endosymbiont). In order to elucidate the taxonomical and evolutionary relationship ofGeosiphon pyriforme to fungi forming arbuscular mycorrhiza (AM fungi), the small-subunit (SSU) ribosomal RNA genes ofGeosiphon pyriforme andGlomus versiforme (Glomales; a typical AM fungus) were analyzed and aligned with SSU rRNA sequences of several Basidiomycetes, Ascomycetes, Chytridiomycetes, and Zygomycetes, together with all AM-fungal (Glomales) sequences published yet. The distinct group of the order Glomales, which includesGeosiphon, does not form a clade with any other group of Zygomycetes. Within the Glomales, two main lineages exist. One includes the families Gigasporaceae and Acaulosporaceae; the other one is represented by the genusGlomus, the members of which are very divergent.Glomus etunicatum andGeosiphon pyriforme both form independent lineages ancestral to the Glomales. The data provided by the present paper confirm clearly thatGeosiphon represents a fungus belonging to the Glomales. The question remains still open as to whether or notGeosiphon is to be placed within or outside the genusGlomus, since this genus is probably polyphyletic and not well defined yet.Geosiphon shows the ability of aGlomus-like fungus to form a “primitive” symbiosis with a unicellular photcautotrophic organism, in this case a cyanobacterium, leading to the conclusion that a hypothetical association of aGlomus-like fungus with a green alga as a step during the evolution of the land plants appears probable. Correspondence to: H. Gehrig     

Symptomatic Evidence for Differential Root Invasion by Fusarium Crown and Root Rot Pathogens Between Common Tomato Lycopersicon esculentum and Its Varieties

The pathogenic isolates (Kin2001a, Kin2001b and Kin2003) of Fusarium oxysporum f. sp. radicis‐lycopersici were obtained from hydroponically cultured seedlings of pear tomato (Lycopersicon esculentum var. pyriforme) infected at different times and their pathogenicity examined in an in vitro assay system on cotyledonal seedlings of pear tomato, cherry tomato (L. esculentum var. cerasiforme) and common tomato (L. esculentum). With the in vitro assay, infection and subsequent disease progress could be microscopically observed. Pear and cherry tomatoes suppressed invasion by all isolates at the junctions of epidermal cells along the root, comparable with the resistant cultivars of common tomato. The pathogen entered pear and cherry tomatoes at the tips of lateral roots and tap roots, in contrast to infection of susceptible cultivars of common tomato. In Kin2003‐inoculated roots, the top of the lateral rootlets first became discoloured, followed by the cortical parenchyma, central xylem vessel and finally the crown. This dark‐brown discolouration expanded rapidly and severe rot developed in the discoloured regions. In contrast, the dark‐brown discolouration in Kin2001b‐infected roots expanded into the cortical parenchyma cells abutting the originally infected lateral rootlets and at a much slower rate. Kin2001a was in a new group that entered via the cortical cleavage formed by the emergence of lateral rootlets, in addition to the tips of taproots and lateral roots. In this in vitro assay system, the Japanese pathogenic isolates collected from different districts of Japan were characterized and classified by the mode of host invasion. Of 13 isolates, four were placed with Kin2003, six with Kin2001a and three with Kin2001b.