Fungi PDF

 Fungi General characters of fungi 1. Nutrition. Heterotrophic (lacking photosynthesis), feeding by absorption rather than ingestion. 2. Vegetative state. On or in the substratum, typically as a non-motile mycelium of hyphae. Motile reproductive states may o...

 Fungi General characters of fungi 1. Nutrition. Heterotrophic (lacking photosynthesis), feeding by absorption rather than ingestion. 2. Vegetative state. On or in the substratum, typically as a non-motile mycelium of hyphae. Motile reproductive states may occur. 3. Cell wall. present, usually based on glucans and chitin, rarely on glucans and cellulose (Oomycetes). 4. Nuclear status. Eukaryotic, uni- or multinucleate, the thallus being homo- or heterokaryotic, haploid, dikaryotic or diploid, the latter usually of short duration (but exceptions are known from several taxonomic groups). 5. Life cycle. Simple or, more usually, complex. 6. Reproduction. The following reproductive events may occur: sexual (i.e. nuclear fusion and meiosis) and/or parasexual (i.e. involving nuclear fusion followed by gradual de- diploidization) and/or asexual (i.e. purely mitotic nuclear division). 7. Propagules. small spores produced in high numbers 8. Sporocarps. Microscopic or macroscopic and showing characteristic shapes but only limited tissue differentiation. 9. Habitat. terrestrial and freshwater habitats, less in the marine environment. 10. Ecology. saprotrophs, mutualistic symbionts, parasites. 11. Distribution. Cosmopolitan Reproduction in Fungi Many, but not all, fungi reproduce both sexually and asexually. Some reproduce only sexually, others only asexually. a) Asexual Reproduction Fungi commonly reproduce asexual reproductive spores). These include the following, Zoospores (motile), Sporangiospores (non-motile) within sporangia or conidia on sterigmata of conidiophores and by budding which is common in unicellular fungi (yeast). b) Sexual Reproduction Sexual reproduction is by isogamy (gametes are indistinguishable morphologically), anisogamy or oogamy and different types of spores are produced including zygospores, oospores, ascospores and basidiospores. Beneficial Effects of Fungi: 1. Decomposition - nutrient and carbon recycling. 2. Biosynthetic factories. The fermentation property is used for the industrial production of alcohols, fats, citric, oxalic and gluconic acids. 3. Important sources of antibiotics, such as Penicillin. 4. Model organisms for biochemical and genetic studies. e.g., Saccharomyces cerviciae is extensively used in recombinant DNA technology, which includes the Hepatitis B Vaccine. 5. Some fungi are edible (mushrooms). 6. Yeasts provide nutritional supplements such as vitamins and cofactors. 7. Penicillium is used to flavour Roquefort and Camembert cheeses. 8. Ergot produced by Claviceps purpurea contains medically important alkaloids that help in inducing uterine contractions, controlling bleeding and treating migraine. 9. Fungi (Leptolegnia caudate and Aphanomyces laevis) are used to trap mosquito larvae and thus help in malaria control. Harmful Effects of Fungi: 1. Destruction of food, lumber, paper, and cloth. 2. Animal and human diseases, including allergies. 3. Toxins produced by poisonous mushrooms and within food (Mycetism and Mycotoxicosis). 4. Plant diseases. 5. Spoilage of agriculture produce such as vegetables and cereals. 6. Damage the products such as magnetic tapes and disks, glass lenses, marble statues, bones and wax. Classification of Fungi: Some mycologists are of opinion that the fungi have evolved from algae by loss of chlorophyll. If this is true, the fungi are plants and are properly placed in the ‘plant kingdom’. Mycologists of other school of thought, however, believe that the fungi had a common ancestry, with the protozoa but split off at a very early stage. If this is true, the fungi are neither plants nor animals - they are fungi. Ainsworth (1971) treated the fungi as a separate and independent kingdom. Based on the presence or absence of Plasmodium and pseudoplasmodium; the kingdom Mycota is further divided into two divisions: Myxomycota i.e., slime molds and Eumycota or true fungi. Classification of Fungi Fungi are classified to two main divisions: Division Myxomycota: fungal-like members of the kingdom Protozoa. Their body is a plasmodium, i.e., an amoeboid mass of protoplasm that has many nuclei and no definite cell wall. Division Eumycota: True fungi, all with cell wall. It is divided to four classes according to their method of sexual reproduction, types of spores and according to the septation of their mycelium. Mastigomycotina: Oomycetes Some members grow as sac-like or branched thalli, Most of them Produce hyphae forming a mycelium. Oomycetes are now known to be the result of convergent evolution with the true fungi (Eumycota), Hyphae of Oomycetes display the following: Apical growth and enzyme secretion, Form a mycelium, Show morphogenetic plasticity by differentiation into specialized structures such as appressoria or haustoria. Are coenocytic, i.e., they generally do not form cross-walls (septa) except in old compartments or at the base of reproductive structures. The cytoplasm is granular and contains vacuoles, Golgi stacks, mitochondria and diploid nuclei. Peronosporales Albuginaceae Albugo sp. Family Albuginaceae, has only a single genus, Albugo, with about 40_50 species of biotrophic parasites of flowering plants. cause diseases known as white blisters or white rusts. The commonest species is A. candida causing white blisters of crucifers such as cabbage, turnip. In Albugo, The mycelium in the host tissues is intercellular with only small spherical haustoria They are spherical or flattened 4 mm in diameter, connected to the intercellular mycelium by a narrow stalk about 0.5 mm wide.  The base of the haustorium of A. candida is surrounded by a collar-like sheath which is an extension of the host cell wall Host cytoplasm reacts to infection by an increase in the number of ribosomes and Golgi complexes. In the vicinity of the haustorium the host cytoplasm contains numerous vesicular and tubular elements not found in uninfected cells. Zygomycetes Mucorales Mucoraceae Mucor and Rhizopus Rhizopus is saprophytic and parasitic fungi. They are found in moist or damp places ,on organic substances like vegetables, fruits, bread, jellies, etc. The vegetative structure is made up of coenocytic (multinucleated) and branched hyphae. They are used to produce various chemicals and alcoholic products. Some species of Rhizopus cause plant diseases and may cause infection in humans too, known as mucormycosis. 1. They are fast-growing fungi and have a cottony appearance. 2. The body of Rhizopus consists of branched mycelium. 3. The mycelium is coenocytic and composed of three types of hyphae; stolon, rhizoids and sporangiophores. 4. Stolon is the internodal region, it is aerial, forms an arch and touches the substratum forming nodal region. 5. Rhizoids are formed where the stolon touches the substratum at nodes. They are branched, anchor the mycelium to the substratum and absorb food. 6. Sporangiophores are the aerial and reproductive mycelia. They are branched and consist of sporangiospores terminally. Life Cycle of Rhizopus Rhizopus reproduce by three processes, i.e. vegetative, asexual and sexual Vegetative reproduction is by fragmentation and each of the fragments of a stolon develops separately making a complete mycelium Asexual reproduction is by the formation of sporangiospores and chlamydospores 1. Formation of Sporangiospores: Sporangiospores are formed terminally in sporangia of aerial mycelium called sporangiophores. They are formed under favorable conditions. The apical part swells up forming sporangium, as nuclei and cytoplasm move apically.  The cytoplasm of sporangium differentiates into the denser peripheral region with more nuclei and the central columella region with fewer nuclei and more vacuoles. **The wall of sporangium ruptures after maturation and sporangiospores come out as a powdery mass. After getting suitable condition and substratum, each spore germinates into a new mycelium. 2. Formation of Chlamydospores: Chlamydospores are formed during unfavourable conditions. An intercalary segment of mycelium develops due to the formation of septae and accumulation of protoplasm. It is thick-walled and detaches from the mycelium once it dries. They remain dormant until the favorable conditions return and then germinate to form a new mycelium. Sexual reproduction Sexual reproduction is by fusion of two compatible hyphae. Most of the Rhizopus species (R. stolonifer) are heterothallic, i.e. having different mycelium for + and – mating strains. R. sexualis is homothallic. In both the mycelia, 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 septae formation. This is known as gametangia. Gametangia conjugate to form a multinucleated structure. Plasmogamy is followed by karyogamy and diploid (2n) zygote is formed(zygospore). Rest of the unpaired nuclei degenerate.  Zygospores enlarge and become thick-walled and resistant to adverse environmental conditions. On getting favorable conditions, zygospores germinate. The inner wall of zygospore develops into promycelium forming germ sporangiophore, with germ sporangium formed apically. Meiosis occurs and haploid meiospores are formed. They come out after rupture of the germ sporangium wall and develop into new mycelia. Life cycle of Rhizopus nigricans