BOTANY: Lecture Course for Bachelor's Degree Students in Agronomy - 2016

LECTURE 7. Eukaryotes (Nucleated Organisms). Kingdom Fungi

Cytology/cytology/25.html">General characteristics and Structural Features of the vegetative body. Plasmodium. Rhizomyslium. Mycelium, hyphae. Structure OF THE fungal Cell. Plectenchyma. Fruiting bodies. Modes of Nutrition. Parasitic and saprophytic Fungi. Ecological groups of fungi. Classification of fungi. Phyla: Myxomycetes, Oomycetes, their characteristics, main representatives, and life cycles.

Fungi are a group of achlorophyllous heterotrophic organisms. The science that studies fungi is mycology. A separate kingdom with a polyphyletic origin.

Features shared with plants:

1. Indeterminate growth;

2. Absorptive nutrition;

3. Rigid Cell wall;

4. Forms that are largely sessile in the vegetative state.

Features shared with animals:

1. Heterotrophic organisms;

2. Presence of true urea in METABOLISM;

3. Chitin as a component of The Cell wall;

4. Glycogen as a storage product;

5. Lysine synthesis following the animal pathway.

The vegetative body of fungi—the mycelium or thallus—is a system of fine filaments (hyphae) that often intertwine to form plectenchyma. In lower fungi, the vegetative body is a small mass of Cytoplasm bounded by a Plasma Membrane or a rudimentary mycelium (rhizomycelium).

Fungal mycelium can develop exogenously on the substrate surface or endogenously within the substrate (in parasitic species). The fungal mycelium may be non-cellular (aseptate) or cellular (septate). Based on this feature, fungi are divided into lower fungi with an aseptate mycelium and higher fungi with a septate mycelium.

Many higher fungi form sclerotia, mycelial strands, and rhizomorphs.

Coloration is caused by pigments: carotene, monascoflavin, rubropunctatin, muscarufin, telephoric acid, citrinin, citromycetin, and xylindein.

Nutrition is heterotrophic, divided into obligate and facultative parasites and saprotrophs, with many symbiotic species among them. Facultative parasites feed saprotrophically, but under certain conditions can switch to parasitic nutrition (e.g., Saprolegnia).

Facultative saprotrophs, conversely, exist as parasites, but upon the death of the host, they switch to saprotrophic nutrition (e.g., bracket fungi). Symbiotic fungi are associated with other organisms, such as the roots of higher plants (e.g., aspen bolete, birch bolete), forming mycorrhiza.

Ecological groups:

Soil fungi; forest litter fungi; mycorrhizal fungi; carnivorous fungi; coprophilous fungi; parasitic fungi. Reproduction is vegetative, asexual, and sexual.

Life cycles involve the alternation of several types of sporulation, such as pleomorphism in rust fungi.

Significance of fungi:

Positive aspects:

1 - they participate in the biogeochemical cycling of matter and break down Organic compounds, converting them into minerals.

2 - they decompose Lignin and Cellulose, and form symbioses with higher plants;

3 - cap mushrooms are of nutritional value.

4 - In medicine - Antibiotics.

5. In the baking and brewing industries, fodder and food Yeasts are used, as well as brewer's Yeast in livestock farming.

Negative aspects:

1 - poisonous species,

2 - they spoil food supplies and destroy wood and buildings;

3 - they cause diseases in agricultural crops;

4 - they cause infectious diseases in animals and humans, such as scab, ringworm, etc.

Fungal Taxonomy:

Lower fungi:

1. Chytridiomycetes

2. Oomycetes

3. Zygomycetes

Higher fungi:

1. Ascomycetes

2. Basidiomycetes

3. Deuteromycetes

Phylum Chytridiomycota

Class Chytridiomycetes

The vegetative body is a plasmodium or a poorly developed mycelium (rhizomycelium). They are characterized by asexual reproduction via zoospores with a single posterior flagellum. The sexual process is diverse (isogamy, heterogamy, oogamy, hologamy). In the vegetative state, most chytridiomycetes are haploid, with only the zygote being diploid. Morphology/12.html">ALTERNATION OF GENERATIONS is known in some chytridiomycetes. The Cell walls contain chitin (up to 60%) and glucans. Most species inhabit Water and soil, including parasites of Algae, aquatic higher plants, and invertebrates, as well as saprotrophs on PLANT AND ANIMAL remains.

Order Chytridiales.

Cabbage blackleg (Olpidium brassicae) — the vegetative body is a plasmodium, a parasite of cabbage seedlings causing "blackleg." The mycelium is unicellular and haploid. The cell consists of a naked, uninucleate protoplast that parasitizes the Cells of the ROOT cortex, infecting the root collar of seedlings in greenhouses and causing it to blacken and die off.

Synchytrium endobioticum infects potato tubers, causing potato wart disease. Infection occurs in the spring in the soil in the Presence of water, through which zoospores move. Zoospores are uniflagellate.

Phylum Oomycota

Class OOMYCETES

The mycelium is well-developed, unicellular, and aseptate. The sexual process is oogamous. The zoospore has two flagella: one tinsel and one whiplash. They are parasites and Saprophytes. The cell wall lacks chitin. The content of the antheridium is not differentiated into Gametes.

Family Pythiaceae occurs in marine and fresh water, in various types of soils, and on higher plants.

The infection is known as root rot, affecting beets, alfalfa, cotton, and trees.

Genus Phytophthora includes 70 species. The mycelium is white and cobweb-like. Phytophthora infestans causes late blight in solanaceous crops.

Control measures: treating plants with Bordeaux mixture or fungicides, breeding resistant varieties, and utilizing Mexican species in breeding programs.

Family Peronosporaceae — Plasmopara viticola causes downy mildew of grapevine; the fungus affects leaves, tendrils, pedicels, and berries.

Class ZYGOMYCETES

Unites over 500 species of fungi, including saprophytic and parasitic species of higher plants, insects, other animals, and humans. They lead a predominantly terrestrial lifestyle.

The mycelium is well-developed, aseptate in the order Mucorales and septate in Entomophthorales. The sexual process is zygogamous (the contents of two heterothallic mycelia fuse). Cells separate from the main mycelium. Gametes are not formed. A resting zygospore develops at the site of fusion of cells that function as multinucleate gametangia. Asexual reproduction occurs via sporangiospores or conidia. The cell wall contains chitin and chitosan.

Mucor or pin mold (Mucor mucedo). The mycelium is well-developed, predominantly coenocytic. The Organs of asexual reproduction are sporangia containing sporangiospores. The sexual process is zygogamy (the contents of two identical non-motile multinucleate cells fuse). There are about 350 species (44 genera) grouped into 8 families. Mucoralean fungi are very common in nature, particularly in the soil, and play an active role in the decomposition and Mineralization of organic residues. They develop as saprophytes on foodstuffs, livestock feed, vegetables, and fruits during storage, causing their spoilage.

Known pathogens of Human and Animal mycoses, as well as diseases of higher plants, including agricultural crops.

Phylum True Fungi (Eumycota): Chytridiomycetes, Zygomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes. Their characteristics, main representatives, and life cycles. The Role of fungi in nature and the national economy. Fungal parasites of agricultural crops.

Phylum Ascomycota

- formation during Sexual reproduction of asci (sing. ascus) — unicellular structures containing 8 ascospores. The vegetative body is a branched, multicellular, haploid mycelium composed of multi- or uninucleate cells connected by a pore. It may break down into individual cells or bud; the vegetative body consisted of individual cells capable of budding.

Asexual reproduction occurs via spores (conidia) produced exogenously on conidiophores on the haploid mycelium.

The sexual process is gametangiogamy.

Widespread across the globe; they include saprophytes, mycorrhizal symbionts, and parasites. They are producers of antibiotics, Alkaloids, phytoncides, Vitamins (riboflavin), Enzymes, Single-Cell Protein, and the agents of Alcoholic Fermentation, as well as objects of biochemical and genetic research.

Class Saccharomycetes — asci are solitary, formed from a zygote without the participation of ascogenous hyphae. Sometimes by budding. The majority are saprophytes developing on sugar-containing media. The yeast cell has a wall, cytoplasm with all Organelles, and reproduces by budding.

Schizosaccharomyces — the cell reproduces not by budding, but by amitosis; it is used for alcoholic fermentation and is widespread in Jamaica, Africa, and Java.

The fungus Candida albicans causes candidiasis (oral thrush and infections of other mucous membranes).

Class Taphrinomycetes — a monotypic class comprising 100 species of parasitic fungi. The dikaryotic annual or perennial mycelium predominates in The life cycle. It affects stone fruit crops.

Taphrina deformans is the CAUSATIVE AGENT OF peach leaf curl; the leaf blade thickens, and the Stomata become dysfunctional. The mycelium persists in the wood and bark.

Class Ascomycetes - asci are formed within fruit bodies known as ascomycetes, which can be open (apothecia), closed (cleistothecia), or semi-open (perithecia).

Order Aspergillales - possess a well-developed mycelium and microscopic cleistothecia; they are saprotrophs developing on various plant and animal substrates, in soil, forest litter, foodstuffs, fodder, and industrial Materials. These include keratinophilic fungi (growing on feathers, horns, and hooves) and dermatophytic fungi (affecting the Hair, Skin, and Nails of mammals).

Genus Penicillium - features a multicellular mycelium with branched, brush-like conidiophores at the tips. The mycelium forms blue or green Molds on organic substrates. They produce antibiotics (such as penicillin, biomycin, tetracycline, and vitacin) and are used in cheese production (e.g., Roquefort).

Genus Aspergillus - form conidial stages consisting of a single, unbranched conidiophore bearing sterigmata with chains of unicellular conidia. They occur in the soil as bluish-green or yellow molds. Some species are pathogenic, causing aspergillosis in animals and humans. They are also sources of antibiotics and citric acid, and frequently appear on bread, footwear, and cooked vegetables.

Order Erysiphales (Powdery Mildews) - characterized by cleistothecia as fruit bodies. They are obligate parasites of Higher Plants and the causative agents of powdery mildew. The mycelium develops On the surface of the substrate, reproducing asexually via conidia. Infected plant organs appear dusted with a powdery layer of conidia.

Erysiphe - pathogens of powdery mildew that destroy the chlorenchyma of leaves and stems, reducing crop yields by up to 30%.

Family Clavicipitaceae - feature perithecia embedded in well-developed stromae composed of fungal hyphae. These are primarily parasites of fungi, plants, and insects.

Ergot fungi parasitize cereals. They contain toxic alkaloids (such as ergotine and ergotamine, which are derivatives of lysergic acid). Ergotism manifests in gangrenous and neuro-paralytic forms.

Subclass Pezizomycetidae - predominantly saprotrophic fungi. Order Pezizales includes edible fungi such as the common morel (Morchella esculenta) and steppe morel, conditionally edible species (which can cause Blood hemolysis), and the false morel (Gyromitra esculenta), which is deadly poisonous.

Order Tuberales (Truffles) - includes the edible or summer truffle (growing up to 1 kg), the autumn truffle, and the true black truffle.

Division Basidiomycota - comprises 30,000 species possessing a multicellular mycelium. They function as saprotrophs, mycorrhiza formers, and parasites of plants and animals.

Sexual reproduction occurs via basidiospores. The sexual process involves the fusion of two vegetative cells from either a heterothallic or homothallic mycelium developing from a haploid basidiospore.

During the sexual process, cell cytoplasms fuse while the nuclei form a dikaryon, which then divides synchronously to produce a secondary dikaryotic mycelium that serves as The basis of the fungus vegetative body. At the onset of sexual reproduction, the nuclei of the dikaryotic hyphae fuse at their tips, and the resulting diploid cells form basidia. The diploid Nucleus of the basidium undergoes Meiosis, and two or four basidiospores are formed on outgrowths of the basidium.

Class Basidiomycetes

Subclass Agaricomycetidae - characterized by the presence of a hymenial layer within the fruit bodies. The hymenium is the fertile part of the fruit body bearing basidia, basidioles, cystidia, sterigmata, paraphyses (sterile cells), and basidiospores. Fruit bodies exhibit high morphological diversity and bear a hymenophore—a specialized layer supporting the hymenium, which may be lamellate (gilled), tubular, folded, or smooth.

Order Boletales - fungi that form annual, open fruit bodies consisting of a stipe and a cap (e.g., the penny bun or porcini, with a cap diameter of 57 cm, stipe of 52 cm, and mass of 2.72 kg); they are important mycorrhiza formers.

Order Agaricales - fungi with either closed or open fruit bodies, including the common cultivated mushroom (Agaricus bisporus).

Class Urediniomycetes (Rust Fungi) - characterized by a four-celled basidium developing from a thick-walled resting cell known as a teliospore. The overwintering stage is the diploid teliospore.

Order Uredinales - parasitic fungi causing spots or stripes on photosynthetic organs. Their life cycle typically involves two different hosts (a primary and an alternate host).

Cereal stem rust (Puccinia graminis). Brown spots—representing the fungal fruiting bodies originating from a mycelium that developed from a haploid basidiospore within the leaf mesophyll—appear on the upper epidermis of barberry leaves (the alternate host).

Features 5 developmental stages: 1) pycnia with pycniospores, 2) aecia with aeciospores, 3) urediniospores, 4) teliospores, and 5) basidiospores. The phenomenon where multiple types of spore-producing stages alternate within the fungal life cycle is known as pleomorphism.

Class Ustilaginomycetes (Smut Fungi) - parasitic fungi. The "smut" represents aggregations of chlamydospores. The spore germinates to produce a germ tube or promycelium.

Representatives of the order Ustilaginales are parasites that infect buds, leaves, flowers, fruits, herbaceous plants, and cereals. Their chlamydospores are thick-walled and binucleate. Infection occurs when spores adhere to grain kernels during threshing. The fungus overwinters as chlamydospores. Under favorable conditions, karyogamy occurs (nuclear fusion → diploid state). Meiosis follows, producing a basidium with 4 haploid basidiospores that germinate into a primary mycelium. Haploid cells or basidiospores subsequently fuse (plasmogamy → dikaryotic mycelium, which penetrates the seedling and spreads through plant Tissues). As the crop matures, the dikaryotic mycelium breaks apart into dikaryotic chlamydospores, forming the characteristic "smut" sori.