Fungi Lectures Bot 101 PDF

Dr. Suzan Abd-Elrazek rashed Lecturer of Algal Biotechnology-Phycology  KINGDOM No. Subject Prokaryotae Fungi Protista Plantae Amimalia Example 1. Chromosomes...

Dr. Suzan Abd-Elrazek rashed Lecturer of Algal Biotechnology-Phycology  KINGDOM No. Subject Prokaryotae Fungi Protista Plantae Amimalia Example 1. Chromosomes 1 >1 >1 >1 >1 Nuclear Absent Present Present Present Present 2. membrane (Prokaryotic) (Eukaryotic) (Eukaryotic) (Eukaryotic) (Eukaryotic) Present Present Present 3. Cell walls Present or absent Absent (peptidoglycan' (chitin) (mainly cellulose) Absorptive or Ingestive or 4. Nutrition Absorptive Photosynthetic Injective photosynthetic... photosynthetic Mobile or Mobile or 5. Mobility non-mobile Non-mobile Mobile non-mobile non-mobile Tissue Lack tissue Lack or Lack or 6. Well-organized Well-organized organization organization not well-organized not well-organized 2  Kingdom II: Fungi Division: Mycophyta General Features of Fungi 1. Mycology is the science that deals with the morphology, taxonomy, phylogeny, biology, and ecology of fungi. 2. Fungi are non-motile eukaryotic organisms. They possess cell walls and mitochondria but lack chloroplasts. 3. Fungal cell walls are typically made of chitin (a polymer also found in the shells of insects). 4. Like animals, fungi are heterotrophic; they obtain their nutrition from the environment by absorption. They can be categorized into: Parasitic (absorbs their nutrients from tissues of other organisms, usually harmful and causing diseases). Saprophytic (obtain nutrients from dead organic matter causing their decomposition). Symbiotic (exchange benefits). 3  Chitin ₙ is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature after cellulose. About 8–10 billion tons of chitin are produced by living organisms on an annual basis (2021). (a) Chemical structure of chitin. (b) Molecular models of the crystal structure of α-chitin and β-chitin showing the antiparallel and parallel chain directionality. 5. Structure: Most fungi consist of elongated unbranched or branched filaments. A single filament is termed a hypha, and a mass of hyphae is termed a mycelium. An individual hypha may be septate or non-septate (also known as aseptate or coenocytic). The body of some fungi consists of compact hyphae which form a false tissue (pseudoparenchymatous tissue). In a few cases, such as yeasts, the fungal body is reduced to a single cell. 5 Septate Hyphae Aseptate Hyphae 6. Fungi are sub-divided into: a. Myxomycota (slime molds which lack cell walls at some stages). b. Eumycota (true fungi) and Lichens (fungi living in a symbiotic relationship with some algae). The division Eumycota consists of simple bodies, which are, in most cases, filamentous. This division includes familiar organisms such as mushrooms and yeasts. Classification of true Fungi (Eumycota) They are divided into four classes according to: 1- The septation of their mycelium. 2- The types of spores. 3- The sexual reproductive methods. 7  1 2 Phycomycetes Ascomycetes Eumycota 3 4 Basidiomycetes Deuteromycetes 7-Reproduction Two main kinds of fungal spores are produced, asexual and sexual spores. Asexual spores are produced by mitotic divisions of Nuclei under favourable conditions. They produced within definite sporangia are known as sporangiospores, while those formed at the tip or sides of a hypha are called conidiospores or conidia. Other fungal spores are produced by sexual reproduction which occur under unfavourable conditions. These include zygospores, oospores, ascospores, and basidiospores. 9  According to motility, the asexual spores can be Zoospores Aplanospores Autospores Mobile (motile) spores that Immobile (nonmotile) spores Immobile (nonmotile) move by means of one or but can develop flagella latter. spores that cannot more flagella. develop flagella. According to the shape of gametes, there are three types of sexual reproduction: 1 –Isogamy: Is the fusion between two similar gametes (motile). 2-Anisogamy: Is the fusion between two dissimilar gametes (motile or non-motile). 3-Oogamy: This is the fusion between a small motile male gamete and a relatively large non-motile female gamete (egg). 1. Phycomycetes The mycelium is usually filamentous non- Gametangial Copulation septate, except during the formation of the reproductive unit. This class includes Fungal hyphae saprophytic and parasitic species. This group is divided into 2 subclasses according to the sexual reproduction: 1- Subclass Zygomycetes: Sexual reproduction takes place by gametangial copulation via isogamy fusion resulting in the formation of Zygospores, which can overcome unfavourable conditions. Zygospore 2- Subclass Oomycetes: in which sexual reproduction occurs by oogamy resulting in the formation of Oospores. Note: Oogamy means fusion between a motile male gamete (sperm) and a non-motile female gamete (egg).  A) Subclass: Zygomyceteae Genus: Rhizopus It is commonly known as black bread mold. It grows as a saprophyte on moist bread and other foodstuffs. The coenocytic hyphae are differentiated into horizontally growing stolons from which descending rhizoids and ascending sporangiophores arise. Each sporangiophore is terminated by one sporangium with many dark- coloured, non-motile spores. Asexual Reproduction of Rhizopus The sporangium is separated from the rest of the sporangiophore by a dome- shaped septum called columella. The sporangium ruptures to release the mature multinucleated spores. The released spores are dispersed and carried by air to a suitable substrate, where they germinate and grow into new Reproduction Cycle of Rhizopus sp. organisms. 15  Sexual Reproduction of Rhizopus Sexual reproduction ensures the genetic variety and ability to endure harsh environmental conditions. The compatible hyphae come together, and a small outgrowth develops. It is known as progametangia. Nuclei and cytoplasm move towards the apical region and progametangia make contact. The apical region is separated from the rest of the hyphae by septa formation. This is known as gametangia which are multinucleate. It takes place by fusion between similar gametangia produced by two different mating types (+ & - strains), i.e. heterothallic or between gametangia produced by one mating type, i.e. homothallic. The resulting zygospore has a thick and dark wall. Meiosis takes place during the germination of a zygospore into a new sporangiophore, which is terminated by a sporangium with many spores. Dispersed spores germinate into new individuals. 16 Rhizopus’ sexual reproduction 17  Subclass: Oomyceteae Albugo Candida It is a parasitic fungus on some plants of the family Cruciferae, causing the white rust disease. Infected plants show white pustules on their stems and leaves. The non-septate hyphae of the fungus grow in the intercellular spaces of the host tissues where they send haustoria into the host cells to absorb food materials. 18  a b Albugo conidial chains on the surface of plant leaf a. diagram, b. SEM image. 19 Asexual reproduction of Albugo The coenocytic hyphae, growing between the cells of the mesophyll tissue of the host, produce club-shaped structures known as conidiophores. Chains of multinucleate conidia are cut off from the tips of each conidiophore. After the separation, the dispersion of the conidia occurs by winds to infect new host plants. Under moist conditions, each conidium behaves as a sporangium where it produces several multinucleate, biflagellate and kidney-shaped zoospores. These motile spores when set free, they Asexual reproduction of Albugo candida infect new host plants. 20 Sexual reproduction of Albugo It takes place through the formation of antheridia and oogonia, i.e. oogamous sexual reproduction. At fertilization, a fertilization tube is developed between the antheridium and oogonium through which only one of the male nuclei passes into the oogonium and fuses with the egg nucleus. The zygote develops into a thick-walled, dark-coloured oospore. After a period of dormancy, the diploid oospore divides meiotically and then mitotically to produce a large number of flagellated haploid zoospores which infect new host plants. 21 2. Ascomycetes Mycelium is formed of septate hyphae except unicellular yeasts. The male ascomycete produces antheridium, and the female ascomycete produces an ascogonium. The fertilization process forms the Zygote which divides then into many ascospores enclosed inside sac-like structures called asci, which are formed after sexual reproduction. Usually, each ascus contains eight ascospores. ascospores Ascomycetes do not have any flagellated stages in their life cycles. 22 Sexual reproduction and ascus formation: The sexual organs are the antheridium and the ascogonium. Both are multinucleate, but the ascogonium is distinguished by its prolonged apex (trichogyne). At fusion, male nuclei are transferred to the ascogonium through the trichogyne. Many filaments called ascogenous hyphae are produced from the ascogonium. Pairs of male and female nuclei migrate to the ascogenous hyphae, which bend downwards at their tips. Each nucleus is divided mitotically into two nuclei. Transverse septa are formed to cut a terminal uninucleate cell, a sub-terminal bi- nucleate cell and a stalk uninucleate cell. The two nuclei of the sub-terminal cell fuse to form a diploid ascus mother cell. The latter is elongated while the diploid nucleus divides meiotically followed by mitotic division to form an ascus with eight haploid oospores. In most ascomycetes the asci are surrounded by sterile hyphae in a compact structure called ascocarp or fruit body.  Ascus with 8 ascospores Development of Ascus Mitosis Meiosis Ascogenous Fusion hypha  In most ascomycetes the asci are surrounded by sterile hyphae in a compact structure called ascocarp or fruit body. Three types of ascocarps are known: 1) Cleistothecium: globular and closed. 2) Perithecium: flask-shaped with a narrow opening or ostiole. 3) Apothecium: cup-shaped and opened. In some ascomycetes asci are not contained in ascocarp, i.e. asci are naked. 25 Genus 1: Saccharomyces (Yeast) Unicellular organism with spherical or oval- shaped cells. The protoplast includes a distinct nucleus, a vacuole and many granules of reserve food in the form of volutin, glycogen and fat droplets. Yeasts are widely distributed in nature. They live as saprophytes and multiply easily. A few species of yeast are parasites and cause diseases in plants and animals. Yeasts are of great economic importance to man due to their content of amino acids, elements and vitamins (especially vitamin B complex). They are also used in baking and in fermenting sugars due to the enzymes they produce. 26 Reproduction a) Vegetative Under favourable conditions, yeasts grow and flourish on media-rich in carbohydrates. They multiply by budding. Buds may separate from the mother cell, or re-budding may occur to form a chain or cluster of cells (pseudomycelium). a) Sexual reproduction: Haploid vegetative (somatic) cells, under certain conditions, may act as gametes. Two cells of different strains (+ve and -ve) conjugate, and the resulting zygote acts functionally as a vegetative diploid cell. Or the zygote itself becomes an ascus and undergoes meiosis, in which the diploid cells produce four haploid ascopores within an ascus. Ascospores, after being set free, grow into haploid vegetative cells. 27  Life cycle of Saccharomyces 29 Genus 2: Penicillium and Genus 3: Aspergillus The two genera are commonly known as black, blue, or green molds. Sometimes, they have blue, green, yellow, or brown colours. They are saprophytes, growing on all kinds of food stuffs, stored fruits and vegetables causing their decay. Penicillium and Aspergillus have the following common characteristics: 1. Their mycelia are formed of septate and branched hyphae. 2. Both reproduce asexually by conidia carried on conidiophores. 3. Both reproduce sexually by fusion between antheridia and ascogonia. The resulting asci with ascospores are enclosed within cleistotheium (closed ascocarp). The released ascospores germinate into new mycelia. On the other hand, both genera can be distinguished on the following bases: 1. The conidiophores of Penicillium are septate and branched. The last branches terminate with sterigmata (phialides), which carry conidia chains. 2. The conidiophores of Aspergillus are unbranched, non-septate, and terminate with swollen heads. Each carries radiating sterigmata with chains of conidia. 30 31 3. Class Basidiomycetes Members of this class have septate hyphae and non-motile spores (basidiospores) carried externally on club-shaped structures called basidia(single: Basidium), in which the sexual reproduction takes place by fusion of nuclei (Karyogamy, fusion of two nuclei), and then meiosis occurs. The spores of the perfect stage are known as basidiospores, which are borne externally on the basidia. Basidia and Basidiospore formation Basidia are either unicellular or filamentous (formed of four cells). Young basidium is binucleate; it increased in size. The two nuclei fuse to form a diploid nucleus (karyogamy), followed by meiosis and as a result, four haploid basidiospores are developed and are carried externally on each basidium. In many basidiomycetes, the basidia are formed in a fruiting body called basidiocarp 36 Genus: Agaricus (Mushroom) Agaricus is a saprophytic fungus that grows on rotten wood logs and decaying organic matter. Edible species are called mushrooms, while poisonous species are known as toadstools. Fruiting bodies (basidiocarp) are formed when sufficient food materials are accumulated within the mycelium. In wet conditions, young basidiocarps appear as round, small bodies known as buttons. The latter develop rapidly under warm and moist conditions into fully mature fruiting bodies with their characteristic umbrella-like forms. Each basidiocarp is formed of a stipe, pileus, and gills. 37  In a vertical section, the gill shows three distinct zones: the trama, the sub-hymenium, and the hymenium. The hymenium consists of basidia and paraphyses. Mature basidium carries four haploid basidiospores borne on sterigmata. Out of the four basidiospores two are of (+) strain and the other two of (-) strain. Gills of Agaricus  Lichens Lichens are composite organisms formed of an algal partner (Phycobiont) and a fungal partner (Mycobiont) living together in symbiosis. The algal partner belongs to chlorophyceae or cyanophyceae. The fungal partner belongs to Ascomyceteae or Basidiomyceteae. The fungus provides the alga with water, minerals, and protection against drought, while the alga can carry out photosynthesis and share its products with the fungus. Lichens are widely distributed everywhere and in different habitats. They can survive under very dry conditions and extremes of hot and cold. 40 Three forms of thalli can be distinguished in lichens: a) Crustose lichens They are in the form of a thin crust closely adhering to the substratum. b) Foliose lichens The thallus is leaf-like, lobed and attached to the substratum by rhizoid-like hyphae called rhizine. c) Fruticose lichens The thallus is shrub-like and attached to the substratum by its basal portion. 41 Crustose lichens Foliose Lichens Fruticose Lichens Reproduction 1) Asexual a. by fragmentation: Detached fragments are dispersed and grow into new thalli. b. by soredia: These are bud-like outgrowths composed of the two partners. Soredia are carried by winds to a suitable area where they grow into new thalli. 2) Sexual It is restricted to the fungal partner. 45 Importance of Fungi and Lichens