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CHAPTER 2 IMAGES: THE DIVERSITY OF FUNGI AND FUNGUS-LIKE ORGANISMS
Fig 2.1 Chytridiomycota. (a) Life-cycle of Allomyces, which alternates between haploid (n) and diploid (2n) generations. The haploid thallus produces male and female gametangia that release motile gametes. These fuse in pairs and encyst to produce 2n zygotes, which germinate to produce a 2n thallus. The 2n sporangia release zoospores for recycling of the 2n phase. Thick-walled resting sporangia (rs) are formed in adverse conditions; after meiosis these germinate to release n zoospores. (b) Rhizophyctis rosea, a common cellulolytic fungus in soil. It grows as a single large cell, up to 200 µm diameter, with tapering rhizoids. At maturity, the large, inflated cell converts into a sporangium, where the cytoplasm is cleaved around the individual haploid nuclei, and large numbers of zoospores are released through the exit papillae. (c) Olpidium brassicae grows as naked protoplasts in root cells of cabbages. At maturity, the protoplasts convert to sporangia, which release zoospores into the soil. These spores encyst on a host root, germinate and release a protoplast into the host. Thick-walled resting spores are produced in adverse conditions and can persist in soil for many years (see Fig. 2.3). [© Jim Deacon]
Fig 2.2 Catenaria anguillulae, a facultative parasite of nematodes and some fungal spores. a-c: Three zoospores showing amoeboid crawling in a water film on a glass slide (note the single posterior flagellum and the pseudopodium-like extensions at the front of the cells). d: Zoospores crawling on the surface of a nematode and (e) encysting over the nematode’s heart region. f: Encysted zoospores (s) germinate and penetrate the nematode then produce a swollen vesicle (v). g: A catenulate (beaded) chain of cells growing from a killed nematode. h: Zoospore cysts (C) of C. anguillulae that germinated to produce germ-tubes then produced swollen vesicles (V) and rhizoids (R). Two cells of Bacillus (B), about 3 µm long, are indicated. i: Part of a catenulate chain of cells with rhizoids. [© Jim Deacon]
Fig 2.3 Olpidium brassicae, a biotrophic (obligate) parasite commonly found in cabbage roots. The root cell contents were destroyed by treatment with hot KOH, then rinsed, acidified and stained with trypan blue to reveal fungal structures within the roots. Left: Two sporangia (sp) about 30 µm long, with exit tubes (et) and many germinating zoospore cysts (cy). Right: Two thick-walled resting spores of O. brassicae about 25 µm diameter, within a root cell. [© Jim Deacon]
Fig 2.5 Vesicles (v) and arbuscules (a) of arbuscular mycorrhizal fungi in clover roots. [© Jim Deacon]
Fig 2.6 A and B: Fossil hyphae and spores from the Ordovician, about 460 MYA, compared with a spore (C) of a present-day Glomus species (an arbuscular mycorrhizal fungus). All bars 50 µm. [Images courtesy of Dirk Redecker; see Redecker et al., 2000]
Fig. 2.7. A phylogenetic tree based on small subunit ribosomal RNA gene sequences (Courtesy of Redecker et al., 2000). Triangle ‘a’ indicates fossil spores of the Ordovician (460 million years ago). Triangle ‘b’ indicates fossil spores of presumed arbuscular mycorrhizal (AM) from the Rhynie chert (400 MYA). Triangle ‘c’ indicates a fossil clamp connection (see Chapter 4) – the earliest evidence of Basidiomycota (290 MYA). Triangle ‘d’ indicates Ascomycota from the Rhynie chert (400 MYA). Triangle ‘e’ indicates a gilled mushroom in amber (90 MYA). Triangle ‘f’ indicates AM fungi of the Gigaspora type in the Triassic (about 240 MYA). As reference points, the ‘outgroups’ are Diphanoeca (a choanoflagellate from which fungi are thought to have arisen), and two early divergent forms of animals, Ichthyophanus and Dermocystis.
Fig. 2.8 General life cycle of Mucorales. Asexual reproduction occurs by production of sporangia which release haploid spores. Sexual reproduction occurs by fusion of gametangia at the tips of zygophores, leading to a diploid zygospore that undergoes meiosis to release haploid spores. [© Jim Deacon]
Fig. 2.9. Left: the characteristically unbranched sporangiophores of most Mucor species. The sporangia are still intact and contain many darkly pigmented spores with melanised walls. Right: Thamnidium elegans, showing one of several variations in the production of sporangiospores by Zygomycota. This fungus produces typical sporangia on long sporangiophores, but complex branching structures arise from the sporangiophore and terminate in small, few-spored sporangioles. [© Jim Deacon]
Fig 2.10. Left: A 2-day-old colony of Thermomucor pusillus (previously called Mucor pusillus), a thermophilic species common in composts. Right: the characteristic branched sporangiophores of this fungus; the spores have been shed but the sporangiophores and columellae remain, like drumsticks. [© Jim Deacon]
Fig. 2.11. (a): Sporangia of insect-pathogenic members of the Entomophthorales (e.g. Entomophthora, Pandora spp.) are released and function like spores. (b) Pilobolus, a common fungus on herbivore dung, has a sporangium containing many spores. It is mounted on a vesicle, which ruptures at maturity to shoot the sporangium onto surrounding vegetation (see Chapter 10). (c) Piptocephalis is a parasite of other Zygomycota. It produces branched sporangiophores with merosporangia (each containing a few linearly arranged spores) at the branch tips. [© Jim Deacon]
Fig. 2.12 A mature, thick-walled, warty zygospore (sexual spore) of Rhizopus sexualis, produced by the fusion of two gametangia. The bulbous swellings on either side are termed suspensors. [© Jim Deacon] |
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