Quite detailed information about the organisms of interest to us is given by textbooks on the subject of "biology" (grade 6). The general characteristics of mushrooms, however, are 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 ecological 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 characteristics of mushrooms suggest that it is the osmotrophic way of nutrition that determines their morphological, physiological and biochemical features.
Vegetative body of mushrooms
The vegetative body of most fungi is a highly branched thread (hyphae) with unlimited growth, the totality of which is calledmycelium, or mycelium. Usually, the mycelium is completely immersed in the substrate (soil, plant tissue, animal droppings, plant residues, etc.), and such features of its structure allow the whole body to extract nutrients from it to the maximum using exoosmosis.
Organic substances in the listed substrates are mainly in the form of high-molecular polymers (proteins, polysaccharides, nucleic acids) that do not pass through the cell membranes. Therefore, fungi, the general characteristics of which we are interested in, secrete depolymerase enzymes into the substrate, which break down polymers to 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 outside, and then the fungal hyphae can be likened to an intestine turned inside out.
Mushroom reproduction
Complete immersion of the mycelium in the substrate limits the possibility of their settling in space. Therefore, their reproductive organs protrude to the surface of the substrate or rise above it in order to spread in the air or (if the substrate is in water) in the aquatic environment. In many mushrooms (macromycetes), the spore-bearing organs are large, clearly visible to the naked eye (cap mushrooms rising above the soil or tinder fungi growing on a tree). Other fungi (micromycetes) have small sporulation organs, their structure can only be seen under a microscope, but with mass development they form colored plaques in the form of molds on various substrates.
Two kingdoms of mushrooms
Phylogenetic constructions show that the "mushrooms" ecomorph is not a homogeneous monophyletic group, but is divided into two phyla (kingdoms). Most, called "true mushrooms" (eumycetes), are monophyletic and constitute the fungi kingdom itself (Fungi). A smaller part, called "mushroom-like organisms" (pseudomycetes), is included, along with some algae, into the kingdom Stramenopila, in which it is grouped into two divisions - Oomycota (oomycetes) and Labyrinthulomycota (netted slime molds). Based on this division, a general characteristic of mushrooms is built. Hat mushrooms, as you can see, are only a part of their variety.
Primary and secondary metabolites
All metabolites are conditionally divided into primary and secondary. Primary metabolites are necessary for the growth of the organism and are irreplaceable. These are nucleic acids, proteins, carbohydrates, coenzymes, lipids, etc. Cell organelles are built from them - nuclei, mitochondria, ribosomes, cell wall and membrane structures that fungi have. The general characteristic of primary metabolites is that their deposits are used by the cell as sources of nutrition and energy. Secondary metabolites are necessary for the adaptation of the organism to living conditions. They may be found in some species and absent in others. Unlike primary metabolites, secondary metabolites are usually low molecular weight compounds.
Proteins
Structural proteins are part of the cell wall, membrane structures,chromosomes, of which the elements of the cytoskeleton are built - microtubules and microfilaments. Enzymatic proteins provide all intracellular processes and interaction with the environment.
Carbohydrates
Structural polymeric carbohydrates are the basis of the cell wall that mushrooms have. The general characteristics 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 are attached (acetylated). Molecules "cross-linked" with each other by branched molecules of other polysaccharides make up a strong frame 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 true fungi lack it, but now its presence has been shown in the wall of some ascomycetes (genus Ophiostoma).
Polymers of other monosaccharides (mannose, galactose, etc.), called hemicellulose in higher plants, are not found in all groups of fungi. There are especially many mannose polymers - mannans - in the cell walls of yeast. Apparently, this composition of the wall provides budding better than glucan.
Finally, the general characteristics of mushrooms canbe supplemented by the fact that their cell walls, like plants, contain many polysaccharides associated with protein molecules - peptidoglucans, mannanoproteins, etc. They form the middle layer of a multilayer cell wall and play an important role both in maintaining the structural integrity of cells and in its exchange processes with the environment.
Reserve carbohydrates
This article provides a fairly detailed general description of mushrooms. Grade 6 of the school is the time when we first get to know these organisms in detail in biology lessons. We offer to deepen the knowledge and study them in more detail. Let's move on to the description of reserve carbohydrates.
Mushrooms have not found the main reserve polysaccharide inherent in higher plants and many algae - starch. Glucose in eumycetes is stored as a glucan, close to animal starch glycogen. In addition to glucans, mushrooms also have other storage carbohydrates, some of which are specific to the fungal kingdom. It is primarily the disaccharide trehalose. For a long time, trehalose was found only in mushrooms, which is why it received its 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. Mushroom cells also contain sugar alcohols - mannitol, sorbitol, xylitol, etc.
Lipids
Lipids (esters of glycerol with straight chain monocarboxylic acids) are importantreserve products, they are deposited in the cell in the form of droplets of fat. Mushrooms 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 (etherically linked to phosphoric acid), lipids are the main components of cell membranes. An important role in the creation of membrane structures is also played by sterol lipoids, which give the membrane strength. Unlike animal cholesterol, which has 27 carbon atoms in a molecule (C-27), and plant phytosterols (C-29), the main mushroom sterol is ergosterol (C-28).
Secondary metabolites: pigments
Mushrooms are devoid of photosynthetic pigments, but produce a large number of compounds that color the mycelium, propagative organs or substrate. By chemical nature, most pigments are classified as terpenoids (carotenoids) or aromatic compounds. They perform a variety of functions. So, orange derivatives of carotene induce the course of the sexual process in mucor fungi; dark green and black phenolic pigments of aspergillus are deposited only in the spore-bearing 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 cell walls, increasing their strength.
Toxins and antibiotics
Many fungi produce compounds that are toxic to other organisms, whichit is often noted when a general description of mushrooms is compiled (a 6th grade textbook or a textbook for a university). Substances toxic to microorganisms are called antibiotics, toxic to plants - phytotoxins, toxic to animals and humans - mycotoxins. Some fungal metabolites, 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. Thus, antibiotics penicillins and cephalosporins inhibit cell wall synthesis 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 enzymatic processes in the cells of infected plants (for example, tentoxin of the fungus Alternaria inhibits photosynthetic phosphorylation), have a strong membranotropic effect and affect the transport of substances through membranes, transmembrane transport of ions (fusaric acid, fusicoccin, etc.).
Mycotoxins are divided into two groups - toxins of microscopic fungi (micromycetes) and toxins of macromycete fungi with large fruiting bodies. The former are especially dangerous in fungi that infect plantproducts used for food. For example, ergot sclerotia accumulate alkaloids (heterocycles containing nitrogen), which are nerve poisons. They are not destroyed during baking, so bread baked from flour with an admixture of ground sclerotia is extremely dangerous. Its use can cause serious poisoning, often fatal. Another cereal parasite is the causative agent of ear fusarium. This is a Fusarium fungus that releases terpenoid toxins into the grain, which also cause serious poisoning (bread baked from Fusarium-infected flour was popularly called "drunken bread" because it caused dizziness, vomiting and other symptoms resembling severe alcohol poisoning).
Food mushrooms
Currently, quite a lot of information about their nutrition has been accumulated by the science of biology. The general characteristics of mushrooms from this point of view are as follows. The nutrition of most fungi occurs at the expense of plants, therefore they have active enzymes that decompose structural and storage polysaccharides in living plants and plant debris. These are pectinases that break down polygalacturonic acid (pectin) into low molecular weight oligogalacturonides, xylanases, cellobiases and celluloses that break down cellulose and hemicellulose - the main carbohydrate components of the plant cell wall, amylase, which decomposes starch, etc. The second component of plant cells after cellulose by weight is lignin, 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 break it down. Parasitic fungi that affect the integument of animals and humans (skin, hair, feathers), secrete enzymes that destroy the keratin protein from which they are built.
Most of the enumerated enzymes are synthesized by cells not constantly for the purpose of energy saving, but only in the presence of the corresponding substance in the environment (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 are not formed if the medium contains a mixture of nutrients with more favorable energy metabolism compounds (catabolites). For example, the end product of the destruction of most polysaccharides is glucose, therefore, in an environment that contains glucose in addition to pectin or cellulose, pectinases and cellulases are not produced. It is hardly advisable to carry out complex chemical processes to obtain glucose if it is already present in the growth medium. This regulation is called catabolite repression.
Asexual reproduction
Continuing to reveal such a topic as "General characteristics of mushrooms", we will 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, in which genetic relationships with aquatic are clearly traced. The structure of flagella in zoospores of oomycetes and hyphychytria is similar to that described for ochrophytes.algae, and in chytridiomycetes will be considered in the description of this group. Most fungal species reproduce by immobile spores, indicating their very long landfall. Spores can form endogenously in sporangia (sporangiospores) or exogenously (conidia). Endogenous spores are released only after the destruction of the sporangium, which usually occurs when it gets wet. Usually, a large number (thousands) of spores are formed in sporangia, however, some species form small sporangia (sporangioles), in which there are only a few spores (sometimes one). In the latter case, the sporangioli membranes and spores can coalesce, and then the endogenous spore functions as an exogenous one. This indicates the primary occurrence of endogenous spores, which were the precursors of exogenous ones.
Sexual reproduction
The most common type of sexual process, and the simplest, is the fusion of two vegetative cells that are not differentiated into gametes, called somatogamy. A similar type of sexual process is characteristic of ascomycete yeasts, many basidiomycetes and other fungi. Sometimes it proceeds even without cell fusion, a simple fusion of nuclei inside the cell. A more complex sexual process is preceded by the separation of partner mycelial sites (gametangia), which then merge. Such a sexual process, gametangiogamy, is characteristic of many zygo- and ascomycetes. Finally, fungi also have gametogamy common to other eukaryotic organisms, i.e. fusion of specialized gametes.
Classic iso- and heterogamy characteristic of algae,are found only in lower fungi - chytridiomycetes. There is no classical oogamy in fungi at all. Even oomycetes, so named because of their oogamy, do not have male gametes (spermatozoa or spermatozoa), and the eggs in the oogonium lack their own cell wall and are called oospheres. Some species of marsupials have an oogonium (but without the female egg gametes, i.e., representing a gametangia), but no antheridium, so that fertilization occurs by a vegetative hypha. Other ascomycetes and basidiomycete rust fungi have male gametes - spermatozoa, but lack female gametes, and sometimes gametangia (spermatogamy). In some species, spermatozoa have dual functions - male gametes and asexual spores (conidia).
Conclusion
General characteristics of mushrooms: nutrition and respiration, spore reproduction - all this is of great interest to nature lovers. After all, these are unique organisms that do not belong to either plants or animals. Having opened the topic "General characteristics of mushrooms" (Grade 7) in the textbook, you will find out that they constitute a separate kingdom. The other kingdoms are animals, plants, viruses and bacteria. The topic "General characteristics and significance of mushrooms", set out in school textbooks and in this article, is only 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 characteristics of mold fungi. Mold is one ofthe 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 "The kingdom of mushrooms. General characteristics" (Grade 6), and you will find more detailed information about it.
