Fungi Reproduction

8 Key excerpts on "Fungi Reproduction"

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  Fungal Diversity, Ecology and Metabolites

  • Nwosu, Obasi(Authors)
  • 2018(Publication Date)
  • Agri Horti Press

    (Publisher)

  Reproduction Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this diverse kingdom of organisms. It is estimated that a third of all fungi reproduce using more than one method of propagation; for example, reproduction may occur in two well- differentiated stages within the life cycle of a species, the teleomorph and the anamorph. Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containing propagules. Asexual Reproduction Asexual reproduction occurs via vegetative spores (conidia) or through mycelial fragmentation. Mycelial fragmentation occurs when a fungal mycelium separates into pieces, and each component grows into a separate mycelium. Mycelial fragmentation and vegatative spores maintain clonal populations adapted to a specific niche, and allow more rapid dispersal than sexual reproduction. The “Fungi imperfecti” (fungi lacking the perfect or sexual stage) or Deuteromycota comprise all the species that lack an observable sexual cycle. Sexual Reproduction Sexual reproduction with meiosis exists in all fungal phyla (with the exception of the Glomeromycota). It differs in many aspects from sexual reproduction in animals or plants. Differences also exist between fungal groups and can be used to discriminate species by morphological differences in sexual structures and reproductive strategies. Mating experiments between fungal isolates may identify Polyporus squamosus This ebook is exclusively for this university only. Cannot be resold/distributed. 82 Fungal Diversity, Ecology and Metabolites species on the basis of biological species concepts.

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  Fungi, Algae, and Protists

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  CHAPTER 2Life Cycle and Ecology of Fungi and Lichens

  T he abundance and wide distribution of fungi in nature are a reflection of reproductive success and adaptation to various ecological niches. Reproduction may be either asexual or sexual. In asexual life cycles, fungi are haploid (containing one set of chromosomes), and they may use fragmentation, budding, fission, or spores to produce offspring. In sexually reproducing forms, a diploid stage occurs, in which the nuclei of the haploid sex cells fuse together, facilitating the recombination of genetic material. This provides an opportunity for the emergence of genetic variation between individuals of the same species, thereby improving species adaptation to the immediate environment. Certain species of fungi are very highly adapted to their habitats, requiring specific nutrients or temperature ranges for growth. Other species, however, are less tailored to their surroundings. These fungi often are able to assimilate a wide variety of organic substances and are relatively indifferent to other ecological factors such as temperature.

  REPRODUCTIVE PROCESSES OF FUNGI

  Following a period of intensive growth, fungi enter a reproductive phase by forming and releasing vast quantities of spores. Spores are usually single cells produced by fragmentation of the mycelium or within specialized structures (sporangia, gametangia, sporophores, etc.). Spores may be produced either directly by asexual methods or indirectly by sexual reproduction. Sexual reproduction in fungi, as in other living organisms, involves the fusion of two nuclei that are brought together when two sex cells (gametes) unite. Asexual reproduction, which is simpler and more direct, may be accomplished by various methods.

  Sir Alexander Fleming (b. Aug. 6, 1881, Lochfield Farm, Darvel, Ayrshire, Scot.—d. March 11,1955, London, Eng.)

  Scottish bacteriologist Sir Alexander Fleming was best known for his discovery of penicillin. Fleming had a genius for technical ingenuity and original observation. His work on wound infection and lysozyme, an antibacterial enzyme found in tears and saliva, guaranteed him a place in the history of bacteriology. But it was his discovery of penicillin in 1928, which started the antibiotic revolution, that sealed his lasting reputation. Fleming was recognized for this achievement in 1945, when he received the Nobel Prize for Physiology or Medicine, along with Australian pathologist Howard Walter Florey and British biochemist Ernst Boris Chain, both of whom isolated and purified penicillin.

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  Fungi

  Biology and Applications

  • Kevin Kavanagh(Author)
  • 2005(Publication Date)
  • Wiley

    (Publisher)

  1.6.2 Cellular reproduction Fungal growth involves transport and assimilation of nutrients, followed by their integration into cellular components, followed by biomass increase and eventual cell division. The physiology of vegetative reproduction and its control in fungi has been most widely studied in two model eukaryotes, the budding yeast, Saccharomyces cerevisiae, and the fission yeast, Schizosaccharomyces pombe. Budding is the most common mode of vegetative reproduction in yeasts and multilateral budding is typical in ascomycetous yeasts (see Table 1.11). In S. cerevisiae, buds are initiated when mother cells attain a critical cell size and this coincides with the onset of DNA synthesis. The budding processes results from localized weakening of the cell wall and this, together with tension exerted by turgor pressure, allows extrusion of cytoplasm in an area bounded by a new cell wall. Cell wall polysaccharides are mainly synthesized by glucan and chitin synthetases. Chitin is a polymer of N-acetylglucosamine and this material forms a ring between the mother cell and the bud that will eventually form the characteristic bud scar after cell division. Fission yeasts, typified by Schizosaccharomyces spp., divide exclusively by forming a cell septum, which constricts the cell into two equal-sized daughters. In Schiz. pombe, newly divided daughter cells grow in length until mitosis is initiated when cells reach a constant cell length (about 14 mm). The cell septum in Schiz. pombe forms by lateral growth of the inner cell wall (the primary septum) and proceeds inwardly followed by deposition of secondary septa. Cellular fission, or transverse cleavage, is completed in a manner resembling the closure of an iris diaphragm. In certain yeast species, the presence or absence of pseudohyphae and true hyphae can be used as taxonomic criteria (e.g. the ultrastructure of hyphal septa may discriminate between certain ascomycetous yeasts).

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  Essential Microbiology

  • Stuart Hogg(Author)
  • 2013(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Figure 8.3 ). The conidia may be naked or protected by a flask-like structure called the pycnidium. Asexual reproduction by conidia formation is a means of rapid propagation for the fungus in favourable conditions. The characteristic green, pink or brown colour of many moulds is due to the pigmentation of the conidia, which are produced in huge numbers and dispersed by air or water currents. The conidia germinate to form another haploid mycelium.

  Figure 8.3 Asexual reproduction in the Ascomycota. Chains of conidia develop at the end of specialised hyphae called conidiophores.

  Figure 8.4 Budding in yeasts. Yeast cells in various stages of budding. A protuberance or bud develops on the parent yeast; the nucleus undergoes division and one copy passes into the bud. Eventually the bud is walled off and separated to form a new cell.

  In the case of the unicellular yeasts, asexual reproduction occurs as the result of budding , a pinching off of a protuberance from the cell, which eventually grows to full size (Figure 8.4 ).

  Plasmogamy is the fusion of the cytoplasmic content of two cells. Karyogamy is the fusion of nuclei from two different cells.

  Although some ascomycetes are self-fertile, sexual reproduction often involves separate ‘plus’ and ‘minus’ mating strains. Reproductively distinct, these two types are, however, morphologically identical, so it is not appropriate to refer to them as ‘male’ and ‘female’. The hyphae involved in reproduction are termed the antheridium (+ strain) and ascogonium (− strain). Hyphae from the different strains grow together and there is a fusion of their cytoplasm (Figure 8.5

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  Ecology of Saprotrophic Basidiomycetes

  • Lynne Boddy, Juliet Frankland, Pieter van West(Authors)
  • 2007(Publication Date)
  • Academic Press

    (Publisher)

  However, not all fungi possess mating type factors, and, indeed, even in species that have a well-developed mating type system apparently normal fruit bodies can be formed by haploid cultures, and fruit body formation can usually be separated from other parts of the sexual pathway by mutation (see Chapter 5 in Moore, 1998a). Generally, vegetative compatibility genes define the individuals of fungal populations, while mating type factors are usually interpreted as favouring the outbreeding of a fungal population (Chiu and Moore, 1999). Consequently, mating type genes contribute to management of the genetics of the population as Table 1. ( Continued ) to distribute viable spores, and poorly (or wrongly) differentiated cells still serving a useful function Principle 11 Mechanical interactions influence the form and shape of the whole fruit body as it inflates and matures, and often generate the shape with which we are most familiar Source : From Moore (2005). David Moore et al. 84 well as to the sexual development of the individual. Sexual reproduction generates genetic variation, offers an escape from DNA parasites and provides a means to repair DNA damage (Bernstein et al. , 1985). 1.3 Importance of Sexual Reproduction The crucial step in sexual reproduction, which provides the contrast with asexual reproduction, is the fusion of nuclei derived from different individuals. If the individuals involved in a mating have different genotypes, the fusion nucleus will be heterozygous and the products of the meiotic division can be recombinant genotypes. Thus, in one sexual cycle, new combinations of characters can be created in the next generation for selection. Consequently, the most common ‘explanation’ for sex is that it promotes genetic variability through out-crossing and that variability is needed for the species to evolve to deal with competitors and environmental changes.

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  Plant Bacteriology

  • Wezelman, T(Authors)
  • 2018(Publication Date)
  • Agri Horti Press

    (Publisher)

  For example, the separate dispersal of fungal and algal ( Trebouxia ) spores might be the major means of dispersal for the common lichen Xanthoria parietina and for Buellia species because these lichens do not seem to have soredia. In these cases there is immunological evidence to suggest that lichens are synthesised in nature from free-living Trebouxia and fungal spores on rock surfaces. FUNGAL GENETICS Fungi possess strikingly different morphologies. They include large, fleshy, and often colorful mushrooms or toadstools, filamentous organisms only just visible to the naked eye, and single-celled organisms such as yeasts. Molds are important agents of decay. They also produce a large number of industrially important compounds like antibiotics (penicillin , griseofulvin, etc.), organic acids (citric acid, gluconic acid, etc.), enzymes (alpha-amylases, lipase, etc.), traditional foods (softening and flavoring of cheese, shoyu soy sauce, etc.), and a number of other miscellaneous products (gibberellins, ergot alkaloids, steroid bioconversions). As late as 1974 the only widely applicable techniques for strain improvement were mutation, screening, and selection . While these techniques proved dramatically successful in improving penicillin production, they deflected attempts to employ a more sophisticated approach to genetic manipulation. The study of fungal genetics has recently changed beyond all recognition. The natural genetic variation present in fungal species has been characterized using molecular methods such as electrophoretic karyotyping, restriction fragment length polymorphism, DNA finger printing, and DNA sequence comparisons. The causes for the variation include chromosomal polymorphism, changes in repetitive DNA, transposons , virus-like elements, and mitochondrialplasmids . Genetic recombination occurs naturally in many fungi.

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  Survey of Biological Progress

  Volume 2

  • George S. Avery, E. C. Auchter, G. W. Beadle, George S. Avery, E. C. Auchter, G. W. Beadle(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  It is, to cite one example only, clear that respiration is essentially the same whether the organism be a bacterium, yeast, tree, elephant, or man. Another basic process, that of reproduction, may well be studied with a view to determining if there are essentially similar steps among different organisms. To that end it is instructive to draw together for com- parison the essential information available concerning the physiology of reproduction among fungi, algae, bryophytes, ferns, and seed plants. In general investigations concerned with reproduction among plants, whether they be fungi, algae, ferns, or seed plants, have been searchingly directed toward an understanding of the effects of various environmental PHYSIOLOGY OF REPRODUCTION IN PLANTS 2 6 1 factors upon this phase of the life cycle. Light, temperature, and nutri- tional factors have received the greatest attention. Though it is fully recog- nized that these are extremely important, emphasis in recent research has shifted because it is clear other factors are involved as correlating agents. The hypothesis that the differentiation, development, and proper func- tioning of vegetative and sexual organs of plants depend upon the activity of specific chemical substances is an old one. Within a few years after Sachs formulated it (1865), on the basis of his observations on higher plants, sev- eral students of the fungi were led by deductive reasoning to postulate chemical correlative mechanisms to account for reproductive phenomena such as antheridial production (de Bary, 1881), conjugation (Brefeld, 1883), and hyphal fusion (Ward, 1888). It was much later, however, before the hypothesis proposed by Sachs was used in accounting for the initiation of sexual structures in other plants. The following discussion is to be concerned chiefly with what is known about the factors of the environment and changes in physiology which can be associated with the production of sex structures of all kinds of plants.

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  Food Mycology

  A Multifaceted Approach to Fungi and Food

  • Jan Dijksterhuis, Robert A. Samson, Jan Dijksterhuis, Robert A. Samson(Authors)
  • 2007(Publication Date)
  • CRC Press

    (Publisher)

  53 Chapter 3 Spore formation in food-relevant fungi Unai Ugalde 1 and Luis M. Corrochano 2 1 Unidad de Bioquímica II, Facultad de Química, Universidad del País Vasco, Apartado 1072, 20080 San Sebastian, Spain; 2 Departamento de GenØtica, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain. INTRODUCTION A large number of filamentous fungi are noto-riously familiar to most people for their dash-ing colonisation of foods, often resulting in spoilage, even under cold storage (Fisher, 2002). They also share the ability of producing large numbers of asexual spores. This appar-ently harmless feature renders them ubiquitous in natural and human environments, including thoroughly sanitised food storage and process-ing facilities. Indeed, prolific spore production and dispersal is at the very heart of their un-welcome success. This chapter aims to provide an overview of spore production as well as the stimuli which are involved in triggering this important biological phenomenon. Given the fundamen-tal differences at the phylogenetic, cellular and developmental level between the Zygomycetes, which produce sporangiospores, and other fungal groups, which normally form conidia (Deuteromycetes and Ascomycetes), sporula-tion in these two groups of organisms will be presented separately. CONIDIAL FUNGI The Process of Conidiation Conidia are cellular propagules which com-monly emerge from aerial hyphae at zones which lie behind the growing colony edge, and therefore, no longer participate in vegetative growth. Their purpose is to provide the fungal colony with a means of dispersal in a rapidly changing environment. Hence, conidial pro-duction (conidiation) typically relies on rela-tively simple cellular transformations which can be completed relatively swiftly in every aerial hypha, resulting in a concerted and mas-sive production of spores.

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