Quite detailed information about the organisms that interest us is provided by textbooks on the subject of "biology" (Grade 6). The general characterization of mushrooms, however, is a topic for entire books and scientific papers. And this is not surprising - it is very interesting to study them.
Mushrooms, the general characteristics of which are presented in this article, according to environmental and trophic indicators are heterotrophic eukaryotes with an exclusively osmotrophic type of nutrition. This definition clearly distinguishes them from other organisms in the space occupied by the biota. The general characteristic of fungi suggests that it is the osmotrophic way of feeding that determines their morphological, physiological and biochemical characteristics.
Vegetative body of mushrooms
The vegetative body of most fungi is a highly branched thread (hyphae) with unlimited growth, the totality of which is called mycelium, or mycelium. Usually, the mycelium is completely immersed in the substrate (soil, plant tissue, animal droppings, plant debris, etc.), and such features of its structure allow maximum extraction of nutrients from it with the whole body using exosmosis.
Organic substances in these substrates are mainly in the form of high molecular weight polymers (proteins, polysaccharides, nucleic acids) that do not pass through the cell walls. Therefore, fungi, the general characteristics of which we are interested in, secrete depolymerase enzymes into the substrate, which break down the polymers into oligo- and monomers that can be transported into cells. If in animals digestive enzymes are secreted inside the intestine, then in fungi they are secreted out, and then the fungal hypha can be likened to an inside-out gut.
Mushroom propagation
Complete immersion of the mycelium in the substrate limits the possibility of their dispersal in space. Therefore, their reproductive organs extend to or rise above the surface of the substrate in order to spread in the air or (if the substrate is in water) an aqueous medium. In many fungi (macromycetes), spore-bearing organs are large, clearly visible to the naked eye (hat mushrooms rising above the soil or polypore growing on a tree). Other fungi (micromycetes) have small sporulation organs, their structure can be examined only under a microscope, but with mass development they form colored deposits in the form of molds on various substrates.
Two kingdoms of mushrooms
Phylogenetic constructions show that the ecomorph “mushrooms” is not a homogeneous monophyletic group, but is divided into two phyla (kingdoms). Most, called "true mushrooms" (eumitsets), are monophyletic and constitute the realm of mushrooms (Fungi). The smaller part, called "mushroom-like organisms" (pseudomycetes), is included, along with some algae, in the kingdom of Stramenopila, which is grouped into two departments - Oomycota (oomycetes) and Labyrinthulomycota (reticulum mucus). On the basis of this division the general characteristic of mushrooms is built. Hat mushrooms, as you can see, are only part of their diversity.
Primary and secondary metabolites
All metabolites are conditionally divided into primary and secondary. Primary metabolites are necessary for the growth of the body and are indispensable. These are nucleic acids, proteins, carbohydrates, coenzymes, lipids, etc. Cell organelles are built from them - nuclei, mitochondria, ribosomes, cell wall and membrane structures that have fungi. The general characteristic of primary metabolites is that the cell uses their deposits as sources of nutrition and energy. Secondary metabolites are necessary for the adaptation of the body to living conditions. They can be found in some species and absent in others. Unlike primary, secondary metabolites are usually low molecular weight compounds.
Squirrels
Structural proteins are part of the cell wall, membrane structures, chromosomes, the elements of the cytoskeleton — microtubules and microfilaments — are built from them. Enzyme proteins provide all intracellular processes and interaction with the environment.
Carbohydrates
Structural polymer carbohydrates are the basis of the cell wall that fungi have. The general characteristic of such carbohydrates in terms of chemical composition allows us to divide them into three groups: glucose, other monosaccharides and carbohydrates covalently linked 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 connected 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 form a strong framework of the cell wall. Cellulose was found in all studied oomycetes, in which it makes up about 10% of the cell wall mass. For a long time, it was believed that it was absent in true fungi, but now its presence in the wall of some ascomycetes (genus Ophiostoma) has been shown.
Polymers of other monosugars (mannose, galactose, etc.), called hemicellulose in higher plants , are not found in all fungi groups. Especially many polymers of mannose - 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 their cell walls, like plants, contain many polysaccharides connected to protein molecules - peptidoglucans, mannanoproteins, etc. They form the middle layer of the multilayer cell wall and play an important role in both maintaining structural integrity of cells, and in its metabolic processes with the environment.
Spare Carbohydrates
This article provides a fairly detailed general description of mushrooms. Grade 6 of the school is the time when we first thoroughly get acquainted with these organisms in biology classes. We offer to deepen knowledge and study them in more detail. We turn to the description of spare carbohydrates.
In fungi, the main reserve polysaccharide inherent in higher plants and many algae, starch, was not found. Glucose in eumitsets is stored as glucan, which is close to animal starch glycogen. In addition to glucans, mushrooms also have other spare carbohydrates, some of which are characteristic only of the mushroom kingdom. This is primarily disaccharide trehalose. For a long time, trehalose was found only in mushrooms, which is why it received the second name - mycosis. Now it is 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. Mushroom cells also contain sugar alcohols - mannitol, sorbitol, xylitol, etc.
Lipids
Lipids (glycerol esters with monocarboxylic acids having an unbranched aliphatic chain) are important spare products; they are deposited in the cell as droplets of fat. Fungi are 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 (linked by an ether bond to phosphoric acid), lipids are the main components of cell membranes. Steroid lipoids also play an important role in creating membrane structures, which give membranes strength. Unlike animal cholesterol, which has 27 carbon atoms in the molecule (C-27), and plant phytosterols (C-29), the main fungal sterol is ergosterol (C-28).
Secondary metabolites: pigments
Mushrooms lack photosynthetic pigments, but produce a large number of compounds staining mycelium, propagative organs, or substrate. By chemical nature, most pigments are terpenoids (carotenoids) or aromatic compounds. They perform a variety of functions. So, orange derivatives of carotene induce the course of the sexual process in mushroom fungi; dark green and black phenolic aspergillus pigments are deposited only in the spore-forming apparatus, which, unlike the substrate mycelium, is formed in the air and in spores to protect against 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 description of fungi is compiled (grade 6 textbook or textbook for the university). 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 fungi living 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 secreted 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 the enzymatic processes in the cells of infected plants (for example, Alternaria fungus tentoxin inhibits photosynthetic phosphorylation), have a strong membrane-stimulating effect and affect the transport of substances through membranes, transmembrane ion transfer (fusaric acid, fusicoccin, etc.).
Mycotoxins are divided into two groups - toxins of microscopic fungi (micromycetes) and toxins of fungi of macromycetes with large fruiting bodies. The former are especially dangerous in fungi that infect plant products that are used in food. For example, alkaloids (heterocycles containing nitrogen), which are nerve agents, accumulate in ergot sclerotia. They are not destroyed by baking, so bread baked from flour mixed with ground sclerotia is extremely dangerous. Its use can cause serious poisoning, often fatal. Another cereal parasite is the causative agent of fusarium spike. This is the Fusarium fungus , which releases terpenoid toxins into the grain, which also cause serious poisoning (bread baked from flour infected with fusarium is popularly called "drunk bread" because it caused dizziness, vomiting and other symptoms resembling severe alcohol poisoning).
Mushroom nutrition
Currently, quite a lot of information about their nutrition has accumulated biology science. The general characteristic of fungi from this point of view is as follows. Most fungi are nourished by plants, so they have active enzymes that decompose structural and storage polysaccharides in living plants and plant debris. These are pectinases that destroy polygalacturonic acid (pectin) into low molecular weight oligogalacturonides, xylanases, cellobiase and cellulose, which destroy cellulose and hemicellulose — the main carbohydrate components of the plant cell wall, amylase, which decomposes starch, and others. The second component after cellulose is cellulose — by mass of cellulose which is a three-dimensional polymer of aromatic rings. Especially a lot of it in lignified cells. Lignin is the most persistent plant polymer, and only fungi (mainly wood-destroying tinder fungi) have lignase enzymes that destroy it. Parasitic fungi affecting the integument of animals and humans (skin, hair, feathers) secrete enzymes that destroy the protein keratin from which they are built.
For the purpose of energy saving, most of these enzymes are not synthesized by cells continuously, but only if the corresponding substance is present in the medium (for example, if there is no pectin in the environment, then pectinase is not synthesized). They are not constitutive, but subject to substrate induction. In addition, they do not form if the medium contains a mixture of nutrients with more favorable compounds of energy metabolism (catabolites). For example, the end product of the destruction of most polysaccharides is glucose; therefore, in an environment in which glucose is contained in addition to pectin or cellulose, pectinases and cellulases are not produced. It is hardly advisable to carry out complex chemical processes to produce glucose, if it is already present in the growth medium. This regulation is called catabolite repression.
Asexual reproduction
Continuing to uncover such a topic as “General characteristics of mushrooms,” we briefly describe the features of reproduction. Asexual reproduction in these organisms can be carried out by mobile and motionless spores. Zoospores form a small number of fungi, aquatic and terrestrial, in which genetic links with aquatic are clearly traced. The structure of flagella in zoospores of oomycetes and hyphychitria is similar to that described for ochrophyte algae, and in chitridiomycetes it will be considered in the description of this group. Most species of fungi reproduce 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 sporangium, which usually happens when it gets wet. Usually, a large number (thousands) of spores are formed in sporangia, but some species form small sporangia (sporangioli), in which only a few spores (sometimes one) are found. In the latter case, the shells of sporangioli and spores can grow together, and then the endogenous spore functions as exogenous. This indicates the primary occurrence of endogenous spores, which were the precursors of exogenous.
Sexual reproduction
The most common type of sexual process, the simplest one, is the fusion of two vegetative cells that are not differentiated into gametes, called somatogamy. A similar type of reproductive process is characteristic of ascomycetic yeast, many basidiomycetes, and other fungi. Sometimes it proceeds even without cell fusion, by a simple fusion of nuclei inside the cell. A more complex sexual process is preceded by the isolation of the mycelial sites of the partners (gametangia), which then merge. This sexual process, gametangiogamy, is characteristic of many zygos and ascomycetes. Finally, in fungi, gametogamy is also common 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 is absent in mushrooms at all. Even oomycetes, so named because of the presence of oogamy, do not have male gametes (sperm or sperm), and the oocytes in oogony lack their own cell wall and are called oospheres. Some species of marsupials mushrooms have oogonium (but without female egg gametes, i.e., which is a gametangium), but there is no anteridium, so fertilization occurs by vegetative hyphae. Other ascomycegs and basidiomycete rust fungi have male gametes - spermatozoa, but there are no female gametes, and sometimes gametangia (spermatogamy). Some sperm species have dual functions - male gametes and asexual reproduction spores (conidia).
Conclusion
General characteristics of mushrooms: nutrition and respiration, spore reproduction - all this causes great interest among nature lovers. After all, these are unique organisms that do not apply to plants or animals. Having opened the topic "General characteristics of mushrooms" (Grade 7) in the textbook, you will learn that they constitute a separate kingdom. Other kingdoms are animals, plants, viruses, and bacteria. The topic "General Description and Importance of Mushrooms" set out in school textbooks and in this article is just basic information about them. Entire books have been written about them, so 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 oldest 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, “The Kingdom of Mushrooms. General Description” (Grade 6), and you will find more information about it.