BIO102: Plant Diversity DIVERSITY OF FUNGI

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1 DIVERSITY OF FUNGI ~ 1 ~ Department of Plant Science

2 Contents Topic: Diversity of Fungi...3 Objectives...3 Reading Assignment...3 Lecture...3 Introduction...4 Main Content...4 Background of Fungi...4 Reproduction in Fungi...5 Classification of Fungi...7 Characteristics of Fungi...8 Diversity of Forms in Fungi...9 Habitats of Fungi Ecology of Fungi Economic uses of Fungi Conclusion Summary References/Further readings/links Test Yourself Questions (TYQ) ~ 2 ~ Department of Plant Science

3 Topic: Diversity of Fungi Objectives In this lecture we will learn the followings: Awareness and knowledge of the fungi diversity Acquired skills to identify poisonous members of the Fungi ecological functions of fungi Economic values of fungi to our lives Reading Assignment In addition to the discussion in this lecture read current textbooks in the main library of OOU and visit: ilearn.bupoyesiku.net and for the online lecture. Lecture Fungi are majorly land plants, and equally important in many different ecosystems as bacteria. Activities of fungi and bacteria make possible the recycling of dead organisms in the ecosystems. They are the decomposers of any given ecosystem, without them there may be no ecosystem. In today s lecture, we shall be discussing the kingdom Fungi, which consists of mainly non-photosynthetic organisms. For students aspiring to major in Mycology, Plant Pathology, as well as those that need the knowledge in various fields of study, you will gain more knowledge about the unusual diversity of fungi and their contributions to our ecosystems, particularly their importance to our life. ~ 3 ~ Department of Plant Science

4 Introduction Fungi belong to the Kingdom Fungi. Mycology (Gr. Mykes = mushroom) is the study of fungi. A scientist who studies fungi is called mycologist. It is important you know that fungi contain some fascinating and unusual species. They are neither green plants nor animals. But share certain characteristics of both plant and animal. The important facts that made them stand in-between plants and animals are given to their shared characters. Rigid cell walls made of mixture of polysaccharides (cellulose) as in plants and chitin similar to exoskeleton of insect. Aside from shared characters with other organisms, fungi relationship with the environment is very different from that of any given organism. They are discussed in this lecture because they have traditionally been grouped with plants. Although no direct evolutionary connection with plants, but fungi share filamentous multicellular growth forms, except for the yeast that exists in a unicellular form. Fungi form the decomposers (saprobic fungi) of terrestrial food web in a typical ecosystem. It is also important for you to note that continued existence of the whole world rest solely on activities of fungi and bacteria as the only heterotrophic organisms of the universe. Another fact is that fungi are equipped with a powerful arsenal of enzymes that break organic products. Fungi activities (decomposition) like bacteria also consume oxygen, releases carbon dioxide into the atmosphere and nitrogenous compounds into the soil that are in turn recycled by plant and humans. The importance of fungi as commercial pests cannot be overemphasized by their ability to grow under a wide range of conditions. Main Content Background of Fungi Fungi are primarily terrestrial with only few examples of aquatic members. Traditionally, the fungi have been observed to include heterotrophic protists. For clarity protists will be discussed in another lecture because there are few evidences as regard their connection ~ 4 ~ Department of Plant Science

5 with fungi and it seems not to be a likely ancestor of fungi. About 100,000 species of fungi have been so far discovered and described, while double these numbers of species are out there in the soils waiting to be discovered. Reproduction in Fungi The three most important and common modes of reproduction in fungi are as follows: Vegetative strategy Asexual strategy Sexual strategy Vegetative strategy Almost all fungi reproduce majorly by vegetative strategies. In fragmentation method the mycelium breaks up into small fragments. Each fragment in turn develops into a new mycelium. Other strategies include fission, budding, sclerotia and rhizomorphs (Fig 1.1). Fission Budding Sclerotia Rhizomorphs Fragmentation Figure1.1 Diversity of fungi vegetative reproduction ~ 5 ~ Department of Plant Science

6 Asexual strategy Asexual reproduction takes place in fungi by production of asexual or sexual spores. hey Spores may be produced singly or on a special structure/stalks known as sporangia or conidia. (Fig1.2). Conidia Conidia Conidiophore Hypha A B Hypha C Figure 1.2 Diversity of fungi asexual spores. Conidia of Aspergillus (A), Clamydospores of Ustilago spp., Conidiophore and conidia of Penicillium(C) Sexual strategy A large number of fungi reproduce sexually except for the members of Deuteromycetes (Imperfecti). Sexual reproduction in fungi involved alternation of generations of haploid (n) and diploid (2n) phases. The gametes are always haploids and through process of fusion a diploid sexual spores (zygospores, oospores) are produced. It is important to note here that gametes taking part in sexual fusion may be morphologically or physiologically different. Any two gametes taking part in fusion are of opposite sexes (male and female sex organs) or plus and minus strains. Gametes that are involved in fusion are found inside a special sac called sporangium. If participating gametes are equal in size and shape the resulting gametes are therefore isogametes. The morphologically dissimilar male and female gametes are called the heterogametes. To further enhance your understanding, sexual reproduction in fungi involves the union of two compatible nuclei, which takes place once in a life cycle. Fungi are remarkable for ~ 6 ~ Department of Plant Science

7 their diversity of sexual process. For your knowledge, basically, sexual reproduction involves a cycle of plasmogamy, karyogamy and meiosis, which happens in sequence; first the fusion of the plasma (plasmogamy) of the gametes followed by the fusion of nuclei (karyogamy) and finally the meiotic division. It is beginning to be clear why fungi should have a separate kingdom; they have a different mechanism of sexual reproduction compare to other plants and animals. Classification of Fungi Traditionally in the past fungi membership includes protists (molds) but now treated as separate group (Fig 1.3). Protista (molds) including three divisions, Myxomycota, Oomycota and Acrasiomycota, which have been separated from fungi; because unlike fungi they are known to produce motile cells (swarm cells and zoospores) during certain stage of their life cycles. This attribute of motile cells is never found in most fungi, this attribute supported the recent separation from fungi. However, fungi are classified by their reproductive structures. There are three divisions of fungi, distinguished by reproductive structures. Division Zygomycota - fusion of plus and minus hyphae lead directly to the formation of a zygote Division Ascomycota - fusion of plus and minus strains leads to massive hyphae that form zygotes in a sac-like structure (ascus). Yeast, a unicellular fungus is mostly Ascomycetes that play many important commercial and medicinal roles. Division Basidiomycota - zygotes are produced within reproductive structures called basidia Fungi imperfecti have not been observed to reproduce sexually so they have not been classified into any one of the three divisions. However they have a separate division, Deuteromycota. Besides the macroscopic fungi division outlined above there are few microscopic members belonging to the division Phycomycota. Members in this group include fungi with coenocytic hyphae. ~ 7 ~ Department of Plant Science

8 Motile Slime molds Water molds Cellular molds A FUNGI Ascomycetes Non-motile Basidiomycetes Deuteromycetes B Phycomycetes Zygomycetes Fig Classification of protista (A) and fungi (B) Characteristics of Fungi Fossil records have shown that the first fungi were believed to be unicellular eukaryotic organisms with no living copies. The oldest fossils with a resemblance of fungi exist 900 Million Years Ago (MYA). Other characteristics of fungi include the followings: All fungi have cell walls with cellulose, hemicellulose and chitin(as in animals) Almost all fungi have glycogen as the basic storage polysaccharide (as in animals) ~ 8 ~ Department of Plant Science

9 Almost all fungi produce spores as in bryophytes and pteridophytes (cryptogams) All fungi are non-motile throughout their life cycle (unlike Protista) Almost all fungi spores are dispersed by wind All fungi are non-photosynthetic Modes of feeding in fungi include biotrophic, necrophytic, saprophytic and symbiotic Diversity of Forms in Fungi Fungi are traditionally divided into two groups based on absence or presence of cross walls (septate) partitions. The two groups are coenocytic; filament with no partitions and non-coenocytic, filament with partitions. In coenocytic hypha filament many nuclei are contained in an extensive cytoplasm while in non-coenocytic hypha filament nuclei are in compartments created by the cross walls, which may or may not be perforated (Fig 1.4). The divisions include Zygomycota, Ascomycota and Basidiomycota). Of the three divisions only members of Ascomycetes have coenocytic hyphae (or mycelia). A B Figure1.4 Typical hyphae filaments in fungi. A=Coenocytic, B=Non-coenocytic. ~ 9 ~ Department of Plant Science

10 Habitats of Fungi Fungi grow by mean of filaments called hyphae (singular=hypha) which tangle together to form a network called mycelia (singular=mycelium) that make up the body of most fungi. It is important we should know that hyphae of some species of fungi can spread more than 30 acres in forest soil and may be one of the world's longest length living organisms. Fungi occupy habitats with large quantity of decaying organic matter. They obtain their food either by living off dead organic materials as saprobes or feed on living materials as parasites. Saprobic fungi are equipped with modified hyphae called rhizoids, for attachment to their habitats (substrates). Parasitic fungi have specialized hyphae called haustoria for absorbing nutrients from the living cells of their host organisms. Others are pathogenic fungi and mostly the phycomycetes group, which will be discussed in another lecture. Ecology of Fungi Fungi are important key-species in the world ecosystems, occupying the basal portion of ecological food chain (or web) as decomposers of organic products. Almost all living plants directly or indirectly depend fungi and bacteria for their nutritional needs. It is important for you to know that all fungi are heterotrophic except lichenized fungi. Fungi are mostly in relationship with other organisms. For example in nature, certain vascular plants form associations called Mycorrhiza between their roots and fungi; these associations are responsible for production and distribution of the plants nutrients. You will recollect a similar association between bacteria and the root nodules of vascular plants, legumes; this alliance fixes nitrogen in nodules of legume roots and enhances soil fertility balance. Another example is lichens, a symbiotic associations of fungi and algal or cyanobacteria cells. It is important to know that lichen occupies all inhospitable environments as you will learn in another lecture. Like bacteria, fungi are known to cause biodeterioration of synthetic materials. Such as cloths, paper, leather, optical lenses and almost any materials you can possibly imagine. Nevertheless, it has not been established anywhere that fungi are effective biomonitor of environmental pollution. But fungi are specially known for binding soil particles together by their mycelia. ~ 10 ~ Department of Plant Science

11 Economic uses of Fungi From historical stand point, fungi have a great economic value to humans, animals and plants. It will also be interesting to you to know that the qualities that make fungi important pests also make them commercially valuable. However, almost all fungi reduce the nutritional values and palatability of foodstuffs. Current trend in the use of fungi have step up the interest in the field of pharmaceuticals. New unknown compounds extracted from soil dwelling fungus Cyclosporine; wonder drug suppresses immune reactions that could arise following organ transplantation. It will be of utmost interest to you that the discovery of this novel drug makes organ transplantation successful today. Because it does not have any side effect of the other drugs used in the past, which often kill bone marrows and cause leukemia. Androstenol extracted from truffles and added to certain cosmetics designed to attract potential opposite sex. Yeasts (unicellular organisms) are used in production of ethanol and carbon dioxide by fermentation process; play a key role in baking and brewery industries. You should not be surprised to know that fungi are singularly responsible for the majority of plants diseases. Of the world s Basidiomycetes (mushrooms) 95% are deadly to higher organisms. Learn to distinguish the edible fungi from the poisonous ones before deciding to pick mushrooms for consumption. Poisonous mushrooms are roughly identified on the field by presence of a number of characters (Fig. 1.5). Fragments of the veil net on the mushroom cap Cap (yellowish green, brownish or white) with shiny radiating stripes White or greenish gills with white spores Larger annular ring (white) compared with that of edible mushrooms White long stem (with or without) green patches white cuplike or sheath (volva) surrounding the stem and partially underground Let these characteristics remain engraved in your mind. ~ 11 ~ Department of Plant Science

12 A B C D E F Figure1.5 Field diagnostic characters of poisonous mushrooms. A=Veil, B=Cap, C=Ring, D=Stem, E=Volva, F=Substrate. We should be careful because some of these characters are unstable and quickly fade away from sight. They are not always reliable characters to identify poisonous fungi. A traditional method of placing a silver spoon in a pan containing cooked mushrooms to see if it turns black is also not a reliable method of testing poisonous mushrooms. The only reliable and safe method is the use of Taxonomic key by the experts. Conclusion You must have learnt how to recognize fungi in the wild, and their diverse divisions. Habitats and niches of many of the fungi as emphasized here. Absolute dependence of natural ecosystems upon the fungi; a need for further research as to discover more commercial and ecological uses of fungi cannot be overemphasized. ~ 12 ~ Department of Plant Science

13 Summary Having study this lecture, students should: Have some understanding of types of Fungi Have a better idea of the characters that separate the fungi from other organisms Be ready to look around the environment for the common members of mushrooms Develop skills to identify the poisonous fungi in the wild Know ecological and economic benefits of fungi References/Further readings/links ~ 13 ~ Department of Plant Science

14 Test Yourself Questions (TYQ) Matric No Department Attendance Code Session/Student s Level AC Question TRUE FALSE 1. Fungi are mostly aquatic and terrestrial in nature X 2. All Fungi are non-photosynthetic organisms X 3. Protists are true fungi X 4. Fusion of two nuclear is term karyogamy X 5. Association of vascular plant root with a fungus is Mycorrhiza X 6. Fungi mycelium length is one of the longest living world s organism X 7. Fungi are good indicator of pollution X 8. Sexual reproduction in fungi involve plus and minus hyphae X 9. Existence of the universe only rest upon fungi X 10. Soil fungus that suppresses immune reactions is Androstenol X Comment: ~ 14 ~ Department of Plant Science