Mushrooms: general characteristics and meaning

Quite detailed information about organisms of interest to us is given by textbooks on the subject "biology" (grade 6). The general characteristic of mushrooms, however, is a topic for whole books and scientific works. And it's not surprising - to study them is very interesting.

Mushrooms, the general characteristic of which is presented in this article, are ecological and trophic indicators - heterotrophic eukaryotes with exclusively over-vision type of nutrition. This definition clearly delimits them from other organisms in the space occupied by the biota. The general characteristic of fungi suggests that it is the over-vision method of nutrition that determines the morphological, physiological and biochemical characteristics of these fungi.

Vegetative body of fungi

The vegetative body of most fungi is a highly branched filament (hyphae) with unlimited growth, the totality of which is called mycelium, or mycelium. Typically, the mycelium is completely immersed in the substrate (soil, plant tissue, animal droppings, plant remains, etc.), and such features of its structure allow maximum extraction of nutrients from it by the whole body with the help of exosmosis.

The organic substances in these substrates are mainly in the form of high-molecular polymers (proteins, polysaccharides, nucleic acids) that do not pass through the cell walls. Therefore, fungi, the general characteristic of which we are interested in, secrete depolymerase enzymes into the substrate, splitting the polymers to oligo- and monomers that can be transported to the cells. If the animals digestive enzymes are secreted into the intestine, then in the fungi they are released to the outside, and then the fungal hypha can be likened to the intestine turned inside out.

Reproduction of mushrooms

Complete immersion of the mycelium in the substrate limits the possibility of their dispersal in space. Therefore, their reproductive organs extend to the surface of the substrate or rise above it to spread in the air or (if the substrate is in the water) aquatic environment. In many fungi (macromycetes), sporiferous organs are large, well visible to the naked eye (hula mushrooms rising up above the soil or growing on the trunks tree). Other fungi (micromycetes) have small organs of sporulation, their structure can be considered only under a microscope, but with mass development they form colored raids in the form of molds on various substrates.

Two kingdoms of mushrooms

Phylogenetic constructions show that the ecomorph "fungi" is not a homogeneous monophyletic group, but is divided into two phyla (kingdoms). The most part, called "true fungi" (eumycete), is monophyletic and constitutes the actual kingdom of fungi (Fungi). The smaller part, called "mushroom-like organisms" (pseudomycetes), is included along with some algae in the kingdom of Stramenopila, in which it is grouped into two divisions - Oomycota (oomycetes) and Labyrinthulomycota (reticulum mucus). Based on this division, a general characteristic of the fungi is built up . Hats, as you can see, are only a part of their diversity.

Primary and secondary metabolites

All metabolites are conditionally divided into primary and secondary. Primary metabolites are essential for the growth of the body and are indispensable. These are nucleic acids, proteins, carbohydrates, coenzymes, lipids, etc. Of these, cellular organelles are built-nuclei, mitochondria, ribosomes, cell walls and membrane structures that have fungi. The general characteristic of primary metabolites is that their cells are used as sources of nutrition and energy. Secondary metabolites are necessary for the adaptation of the organism to the conditions of life. They can be found in some species and absent from others. Unlike primary, secondary metabolites are, as a rule, low-molecular compounds.

Proteins

Structural proteins are part of the cell wall, membrane structures, chromosomes, of which elements of the cytoskeleton are built - microtubules and microfilaments. Enzyme proteins provide all intracellular processes and interaction with the environment.

Carbohydrates

Structural polymeric carbohydrates are the basis of the cell wall, which fungi have. The general characteristics of these carbohydrates in terms of chemical composition allows them to be divided into three groups: glucose, other monosaccharides and carbohydrates covalently bound to peptides (glycoproteins).

Glucose polymers are glucans, chitins and cellulose. Glucans are linear or branched chains of glucose molecules. They make up the outer layer of the cell wall of most fungi. In chitin molecules, glucose residues are linked to amino groups (aminated), to which, in turn, acetic acid residues (acetylated) are attached. Molecules, "crosslinked" with each other by branched molecules of other polysaccharides, constitute a strong framework of the cell wall. Cellulose was found in all investigated oomycetes, in which it is about 10% of the mass of the cell wall. For a long time it was believed that it lacks true fungi, but now its presence in the wall of some Ascomycetes (genus Ophiostoma) is shown.

Polymers of other monosaccharides (mannose, galactose, etc.), called hemicellulose in higher plants , are not found in all groups of fungi. Especially a lot of mannose polymers - mannans - in the cell walls of yeast. Apparently, this wall composition provides better budding than glucan.

Finally, the general characteristics of fungi can be supplemented by the fact that in their cell walls, like in plants, there are many polysaccharides connected with protein molecules - peptidoglucans, mannanoproteins, etc. They form the middle layer of the multilayered cell wall and play an important role both in maintaining Structural integrity of cells, and in its metabolic processes with the environment.

Spare carbohydrates

This article presents a rather detailed general description of fungi. 6th grade of the school is the time when we first become thoroughly acquainted with these organisms in the lessons of biology. We suggest deepening our knowledge and studying them in more detail. We now turn to the description of spare carbohydrates.

The main reserve polysaccharide inherent in higher plants and many algae - starch - is not found in fungi. Glucose in eumycetes is stored as a glucan, close to animal starch glycogen. In addition to glucans in mushrooms, there are other reserve carbohydrates, and some are characteristic only of the kingdom of mushrooms. This is primarily a trehalose disaccharide. For a long time, trehalose was found only in mushrooms, making it the second name - mycosis. Now it is also found in some higher plants as a minor compound. Trehalose plays an important role in the adaptation of fungal cells to stress and the regulation of osmotic processes. Fungal cells also contain sugar alcohols - mannitol, sorbitol, xylitol, and others.

Lipids

Lipids (glycerol esters with monocarboxylic acids having an unbranched aliphatic chain) are important reserve products, they are deposited in the cell in the form of droplets of fat. For fungi is characterized by a high content of polyunsaturated (having several double bonds in the aliphatic chain) fatty acids, such as linolenic - with three, and arachidonic - with four double bonds. In the form of phospholipids (connected by ether linkage with phosphoric acid), lipids are the main components of cell membranes. A great role in the creation of membrane structures is also played by the steroid lipids, which impart strength to the membranes. Unlike animal cholesterol, which has 27 carbon atoms in the molecule (C-27), and phytosterols (C-29) plants, the main fungal sterol is ergosterol (C-28).

Secondary metabolites: pigments

Fungi lack photosynthetic pigments, but produce a large number of compounds staining the mycelium, propagating organs or substrate. By chemical nature, most pigments refer to terpenoids (carotenoids) or to aromatic compounds. They perform a variety of functions. Thus, orange derivatives of carotene induce the course of the sexual process in mucoral fungi; Dark green and black phenolic pigments of aspergillas are deposited only in the sporiferous apparatus, which, unlike the substrate mycelium, is formed in the air, and in spores for protection from ultraviolet light; Dark-colored melanin is deposited in the cell walls, increasing their strength.

Toxins and antibiotics

Many fungi produce compounds that are toxic to other organisms, which is often noted when a general characteristic of fungi (a 6th grade textbook or manual for a university) is compiled. Substances toxic to microorganisms are called antibiotics, toxic to plants - phytotoxins, toxic to animals and humans - mycotoxins. Some metabolites of fungi, being toxic to different groups of organisms (microorganisms and plants, plants and animals), have a complex effect. Antibiotics are synthesized by many mushrooms that live in the soil, which have to compete for nutrient substrates with other microorganisms. Their chemical nature and mechanism of action are diverse. So, antibiotics-penicillins and cephalosporins inhibit the synthesis of the cell wall in bacteria, trichothecins - protein synthesis in eukaryotic microorganisms, griseofulvin-mitosis.

Phytotoxins and mitotoxins

Phytotoxins released by fungi into the tissue of an infected plant cause the death of plant cells, which then become easy prey for the parasite. Toxins inhibit enzymatic processes in cells of infected plants (for example, the toxin of the fungus Alternaria inhibits photosynthetic phosphorylation), have a strong membranotropic effect and affect the transport of substances through membranes, transmembrane transfer of ions (fusaric acid, fusicocin, etc.).

Mycotoxins are divided into two groups - toxins of microscopic fungi (micromycetes) and toxins of fungi of macromycetes, which have large fruiting bodies. The first are particularly dangerous in fungi that infect plant products that are used for food. For example, in alkaline sclerotia, alkaloids accumulate (heterocycles containing nitrogen), which are nerve agents. They do not collapse when baked, so bread, baked from flour with a mixture of ground sclerotia, is extremely dangerous. Its use can cause serious poisoning, often with a fatal outcome. Another parasite of cereals is the causative agent of fusariosis of the ear. It is a fungus of Fusarium, which releases into the grain terpenoid toxins, also causing serious poisoning (the bread baked from fusariosis-infected flour was popularly called "drunk bread" because it caused dizziness, vomiting and other symptoms resembling strong alcohol poisoning).

Meals of mushrooms

At the present time quite a lot of information about their nutrition has accumulated the science of biology. From this point of view, the following is the general description of fungi. Most fungi are fed by plants, so they have active enzymes that decompose structural and reserve polysaccharides in living plants and plant residues. These are pectinases that destroy polygalacturonic acid (pectin) into low-molecular oligogalacturonides, xylanases, cellobiases and celluloses, which destroy cellulose and hemicellulose, the basic carbohydrate components of the plant cell wall, amylase, starch degrading, etc. The second component of plant cells, after cellulose, is lignin, Which is a three-dimensional polymer of aromatic rings. Especially a lot of it in lignified cells. Lignin is the most persistent vegetable polymer, and only fungi (mainly wood-pulverising tinder) have lignase enzymes that destroy it. Mushrooms-parasites, affecting the covers of animals and humans (skin, hair, feathers), secrete enzymes that destroy the protein keratin from which they are built.

Most of these enzymes are not permanently synthesized by the cells for energy saving purposes, but only if there is a corresponding substance in the medium (for example, if there is no pectin in the environment, then pectinase is not synthesized). They are not constitutive, but are subject to substrate induction. In addition, they are not formed if there is a mixture of nutrients with more favorable energy metabolites (catabolites) in the medium. For example, the final product of destruction of most polysaccharides is glucose, therefore, in an environment in which glucose is not contained in pectin or cellulose, pectinases and cellulases are not produced. It is hardly advisable to produce complex chemical processes for the production of glucose, if it already exists in the growth medium. This regulation is called catabolic repression.

Asexual reproduction

Continuing to disclose a topic such as "General characteristics of fungi," we briefly describe the features of reproduction. Asexual reproduction in these organisms can be carried out by mobile and immobile spores. Zoospores form a small number of fungi, aquatic and terrestrial, which clearly traces their genetic connections to aquatic fungi. The structure of the flagella in zoospores of oomycetes and hyphychitriae is similar to that described for ochrofitic algae, and in chitridiomycetes it will be considered in the description of this group. Most species of fungi multiply by immovable spores, which indicates their very long-term access to land. Spores can form endogenously in sporangia (sporangiospores) or exogenously (conidia). Endogenous spores are released only after the destruction of sporangia, which occurs usually when it is wet. Typically, sporangia form a large number (thousands) of spores, but some species form small sporangia (sporangioli), in which there are only a few spores (sometimes one). In the latter case, the sporangiola shells and spores can fuse, and then the endogenous spore functions as exogenous. This indicates the primary occurrence of endogenous spores, which were precursors of exogenous.

Sexual reproduction

The most common type of sexual process, the simplest, is the fusion of two non-differentiated vegetative cells into gametes, called somatogamy. A similar type of sexual process is characteristic of ascomycete yeast, many basidiomycetes and other fungi. Sometimes it occurs even without the fusion of cells, a simple fusion of nuclei within the cell. A more complex sexual process is preceded by the isolation of the partners' mycelium sites (gametangia), which then merge. Such a sexual process, gametangiogamy, is characteristic of many zygo- and ascomycetes. Finally, in mushrooms there is also common gametogamy for other eukaryotic organisms, i.e. Fusion of specialized gametes.

Classical iso- and heterogamy, characteristic of algae, are found only in lower fungi - chitridiomycetes. Classical oogamy in mushrooms is absent altogether. Even oomycetes, so named because of their oogamy, do not have male gametes (spermatozoa or spermatozoa), and oocytes in oogonia are devoid of their own cell wall and are called osospheres. Some species of marsupials have oogonia (but without female gametes of eggs, that is, it is gametangia), but there is no antheridium, so that fertilization takes place by vegetative hyphae. Other Ascomyche and basidiomycete rust fungi have male gametes - spermatozoa, but there are no female gametes, and sometimes gametangia (spermatogamy). In some species, spermatozoa carry dual functions-male gametes and asexual multiplication (conidia).

Conclusion

General characteristics of fungi: nutrition and respiration, spore reproduction - all this is of great interest among nature lovers. After all, these are unique organisms that do not belong either to plants or to animals. Having opened in the textbook the topic "General characteristics of fungi" (Grade 7), you will learn that they constitute a separate kingdom. Other kingdoms are animals, plants, viruses and bacteria. The topic "General characteristics and significance of fungi", set forth in school textbooks and in this article, is only basic information about them. About them written whole books, so that you can study them for a very long time. One of the most interesting topics, in our opinion, is the general characteristic of mold fungi. Mold is one of the most ancient species of living organisms on Earth. It appeared 200 million years ago and feels great in modern conditions. Open the section of any school textbook "Kingdom of Mushrooms. General Characteristics" (Grade 6), and you will find more information about it.