As you know, a particular life cycle is one of characteristic features any species, including mushrooms. The concept of the life cycle in fungi includes both morphologically different types of sporulation replacing each other, and cytologically distinguishable changes in nuclear phases.
If we characterize the life cycle of any fungal organism that has both asexual and sexual reproduction, then it will be reduced to the following: in the spring and for a long summer period organs of asexual reproduction develop on the vegetative body of the fungus. Then, towards the end of the growing season, the organism proceeds to sexual reproduction. Asexual reproduction, often repeated many times during the growing season, performs the function of increasing the number of individuals and their resettlement, and the sexual process, which occurs at the end of the growing season and completes the development cycle, ensures the survival of unfavorable conditions and the preservation of individuals, and hence the species.
A successive change in the types of sporulation in fungi (fingerless and sexual) is called pleomorphism. The phenomenon of pleomorphism is very widely represented in fungi in different systematic groups, but it has received the greatest development in marsupials.
Consider the life cycle of Venturia inaequalis, the causative agent of apple scab. The development of apple scab begins in the spring, as soon as the first young, still very small leaves appear. Infection of these young apple leaves occurs with ascospores that develop in spring in bags inside the fruiting body. In spring, ascospores are actively ejected from the fruiting body and then spread by air currents. Once on the surface of young leaves of an apple tree, the spores germinate, and the resulting mycelium sprout is introduced into the tissues. The result of infection is the formation of very small, then gradually growing spots on the leaves, clearly visible from the upper side. On these spots, an olive-colored velvety coating is soon formed, which is the conidial stage of the fungus.
Looking through the section through the infected part of the leaf under a microscope, you can see the following picture. Simple, dark olive conidiophores protrude to the surface through ruptures in the integumentary tissues of the leaf, sitting next to each other. Each conidiophore develops a pear-shaped conidia with one transverse septum, also painted in a dark olive color. Ripening conidia soon fall off and, spreading by air currents, can get on the surface of new healthy leaves or fruits and cause infection of these plant organs.
During the growing season, conidial sporulation can be repeated approximately every 10-15 days, so during this period there may be 5-6, and sometimes more generations of conidia. Conidial sporulation on a haploid mycelium is called Fusicladium dendriticum. According to the marsupial stage, the fungus is called Venturia inaequalis.
In autumn, the leaves die and fall off the tree. The development of the fungus with the death of the leaves does not stop. Inside the dead leaves during the first half of autumn, when there is still enough heat favorable for the growth of fungi, the mycelium continues to grow inside the leaf tissue and forms a typical sclerotium in structure. The sclerocial stage here is the dormant stage. In this state, the fungus hibernates. Spring happens further development mushroom. Inner part sclerotia is used as a source of nutrition, and in place of the internal mycelial plexus, after the sexual process, bags develop inside the shell, i.e., a fruiting body is formed. At the top of such a fruiting body, a hole is formed, which opens outward through ruptures in the integumentary tissues of the leaf. Ascospores are ejected ("shoot") through the hole with force and serve as a source of infection for young leaves. The maturation of the fruiting body is timed to coincide with the time of ripening of the first leaves.
It should be noted that in the development cycle of fungi, asexual sporulation can be repeated many times during the vegetative period (in some cases, we can have up to a dozen or more generations of asexual spores); the sexual stage, as a rule, occurs only once during the growing season. In addition, asexual sporulation in fungi can not only be repeated, but also be different in the same species, while the sexual stages, in particular marsupial sporulation, in a particular species will always be of the same type.
For some marsupials, up to 3-4 different types conidial sporulation. A feature of fungi is the presence of another state of the body - the dikaryotic phase. Hence the great variety life cycles.
In most fungi, the development cycle is characterized by two nuclear phases - haploid and diploid, while the haploid phase predominates, diploid - only the zygote. This is the so-called haploid (haplophase) cycle. It is first noted in the most primitive lower fungi, in which the functions of asexual and sexual reproduction are performed by the same individual. Probably, the haplophase cycle should be considered the most primitive life cycle, characterized by zygotic reduction, which is also primary. So, development occurs in most Chytridiomycetes (in which the sexual process is known), in most Oomycetes, Zygomycetes, some primitive Ascomycetes. However, already here we encounter such cases when the zygote goes to rest not in the form of a diploid, but in the form of a dikaryotic cell (in some Chytridiales, for example, this is the cyst stage, in some representatives of Oomycetes it is the oospore stage, etc.).
In many fungi, their life cycle is characterized by a change in three nuclear phases: haploid, dikaryophytic (dikaryotic) and diploid. The dikaryotic phase occurs as a result of the association of nuclei into dikaryons or synkaryons without their fusion, while they behave as a single whole. And although for the first time the dikaryotic phase is noted already in lower fungi, then it is present in Ascomycetes, in ascogon, and then in ascogenous hyphae (and only in some marsupials we note dikaryotic mycelium, for example, at Taphrinales), but the dikaryotic phase reaches its greatest development. in representatives of the class Basidiomycetes, prevailing over the haploid and diploid stages.
In fungi, the diplophase development cycle, when the organism is always diploid, is quite rare; however, such cases are known, for example, in Saccharomycodes, and also in some forms of Pythium debaryanum. In the first case, a diploid vegetative cell is transformed as a result of meiosis into a bag with haploid ascospores, which copulate with each other while still in the bag and form diploid ascospores, which, leaving the bag, develop into a vegetative cell.
In the case of Pythium debaryanum, there is evidence that the reduction in the development cycle of one of the forms of this species is shifted to the period of gamete formation during the oogamous process (and does not occur during the germination of the zygote, as in most fungi of this group), hence the cycle becomes diplophase. Gametic reduction is clearly of secondary origin.
In fungi, cases are much more rare when some individuals of the same species begin to form only gametes, while other individuals of the same species specialize in the formation of only organs of asexual reproduction. In this case, we can talk about the alternation of generations in the development cycle - gametophyte and sporophyte. This type of life cycle is called haplodiplophase, it is characterized by the fact that one of the generations is diploid, and the other is haploid.
An example of a haplodiplophase cycle with an isomorphic change of generations is Allomyces javanicus, Allomyces arbuscula. Haploid zoospores of these species, developing on a diploid sporophyte, dress with a shell and germinate into a gametophyte (haploid generation), on which micro- and macrogametangia are formed. The sexual process here is heterogamous. The planosygote formed after copulation of gametes after some time is surrounded by a shell and without a dormant period develops into a diploid sporophyte. The sporophyte develops thin-walled zoosporangia, producing diploid zoospores (forming new diploid sporophytes) and thick-walled dormant cysts that usually germinate after a dormant period. In this case, the reduction division of the diploid nucleus occurs, resulting in the formation of haploid zoospores that develop into a haploid gametophyte. Other species of Allomyces (A. cystogenus, A. macrogynus) have a haplo-diplophase cycle with a heteromorphic alternation of generations. The diploid sporophyte predominates in the development cycle, while the haploid gametophyte is greatly reduced in them. Heteromorphic alternation of generations is observed in Physoderma, Spermophthora, Protomyces, etc.
In many fungi, the development cycle can be carried out as a haplo-dikaryotic, i.e., the organism has a more or less long haploid phase and exists as a dikaryophyte for a long period. The diploid stage in this cycle is very short, and meiosis occurs immediately after karyogamy. An example of such a life cycle is, in particular, Puccinia graminis. Its haploid phase begins with the stage of basidiospores, then it is represented by a haploid mycelium that develops in the intercellular spaces of barberry leaves. In the basal cells of the aecidia formed by the haploid mycelium, the first dikaryophyte cells are formed, which cut off the dikaryophyte aecidiospores. The dikaryophyte stage in the development of this fungus is very long. It is represented by dikaryophyte mycelium developing in the intercellular spaces of the second host - cereal (leaves, stems), as well as uredospores and telitospores.
During the germination of telitospores after wintering, two nuclei in each cell merge, forming a diploid nucleus, which immediately undergoes meiosis, and the basidiospores formed during the germination of telitospores on basidia begin again the haploid generation of the fungus. In this case, the haploid and dikaryophyte stages of this cycle exist independently and separately, each on its own host plant. The development of Puccinia coronifera, P. Poarum and others is carried out according to the same type.
The dikaryophase cycle is characterized by the fact that the fungus, as a rule, exists in the dikaryotic stage, while both haploid and diploid states in this cycle are reduced to a minimum and are very short-lived. Thus, in the majority of Tilletia, Ustilago tritici, and others, we meet with just such a case. Mycelium and chlamydospores represent the dikaryotic phase; for example, in Tilletia caries, the filamentous hyploid basidiospores anastomose immediately after their formation, resulting in the formation of a dikaryotic phase. The haploid phase in the case of Uslilago tritici is even more reduced, since even basidiospores are not formed here, and the promycelial cell immediately forms clasps (anastomoses) that transfer nuclei from one cell to another, forming the first dikaryotic cell developing dikaryotic mycelium. The diploid phase here is also short-lived, since the diploid nucleus immediately after its formation undergoes meiosis.
Thus, when considering the developmental cycles in fungi, one can see all types of reduction - zygotic, spore, gametic and somatic. The movement of the reduction division of the diploid nucleus from the zygote to other stages led to the emergence various types life cycles of fungi. When reduction division occurs during the formation of gametes, the zygote germinates into a diploid plant, only gametes will be haploid. The elongation of the diploid phase and the division between individuals of the functions of sexual and asexual reproduction led to the emergence of the haplo-diplophase type of the life cycle, and the separation in time of the two stages of the sexual process - plasmo- and karyogamy - led to the emergence of a long dikaryophytic phase, which led to the emergence of the haplo-dikaryophytic, dikaryophyte and haplo-dikario-diplo-phase cycle.
After studying the features of the organization of the thallus of fungi and their reproduction in the life cycle of fungi, it is logical to distinguish two main phases of ontogenetic development:
Vegetative phase: Immediately after germination, a vegetative body (thallus, colony) of the fungus or fungus-like protist is formed. In the vegetative phase, the fungus masters the substrate, grows, accumulates biomass and energy, and after a certain time passes into the reproductive phase.
In the vegetative phase, set systematic position fungus is possible only up to the level of higher taxa - classes or orders. Certain features of the strain, race and species are noticeable in the vegetative phase only in exceptional cases.
Reproductive phase: The functional differentiation of the thallus begins - one part of it continues to perform its trophic functions, while the other develops specific organs of reproduction, or sporulation. At this time, most of the taxonomically significant characters appear. . Fruiting bodies appear, which make it possible to identify the fungus.
According to the predominance of the haploid or diploid phase in the life cycle, they distinguish:
1. Haploid mushrooms. Ascomycetes, zygomycetes, many chytridiomycetes.
2. Haploid dikaryotic mushrooms. Basidiomycetes, Taphrinomycetes.
3. Haplo-diploid fungi. Some yeast. The phases alternate.
4. Diploid mushrooms. Oomycetes, many myxomycetes (like some algae and protozoa, as well as plants and animals).
In macromycetes, fruiting bodies are often formed once a year (for example, in morels and lines in spring, in purple rowing in late autumn) or in several waves during summer and autumn (for example, in porcini mushrooms). Often, under adverse conditions, fruiting does not occur, although the mycelium retains its viability. Everyone knows that it is not every year that you can find mushrooms in places well known to mushroom pickers. In his book, specially dedicated to the porcini mushroom, the famous Soviet mycologist B.P. Vasilkov notes that this mushroom mass fruiting occurs in 2-4 years.
In most macromycetes, fruiting bodies develop quite quickly: in cap mushrooms, for example, 10-15 days pass from the appearance of the rudiment of the fruiting body to the end of growth, and spore maturation begins already on the 5-7th day. Such a fruiting body does not last long after ripening - from several hours in small dung beetles to several days. Unlike cap mushrooms, tinder fungi often form perennial fruiting bodies. Their development is very slow, growth is observed only in warm, humid periods, and slows down the rest of the time. Therefore, layering is often noticeable on the hymenophore of these fruiting bodies.
Often the same fungus forms in the cycle of its development not one, but several sporulations. They alternate, following one after another, and each time the mushroom changes shape. In some fungi, the vegetative body can also change throughout life, passing, depending on environmental conditions, from mycelial growth to yeast-like growth and vice versa. Such changes in the shape of mushrooms during life are called polymorphism. Polymorphism associated with the change of yeast and mycelial growth forms during the vegetative development of the fungus is usually called dimorphism, and with the change of different types of sporulation - pleomorphism. The phenomenon of fungal pleomorphism causes great difficulties in the work of mycologists. Indeed, if one does not investigate the connections between individual sporulations, each of them can be mistaken for an independent fungus. Recall that even the connection of the fruiting bodies of macromycetes with their mycelium was proved only in the 30s of the 19th century, while the study of development cycles in micromycetes is much more complicated and requires special methods for growing mushrooms in pure culture, artificial infection of plants, etc. Mycologists have long described asexual and sexual sporulation of the fungus as different species. This is how the gray aspergillus and the herbarium eurocium were described, and only in 1854 the famous German mycologist A. de Bari proved that these are the conidial and marsupial stages of the same species.
An even more complex development cycle is found in many rust fungi. In puccinia cereal - the causative agent dangerous disease stem rust of many cereals, which causes large yield losses during its mass development, five different in appearance and functions of the stages of development. This fungus develops not on one host plant, but on two, and each of them goes through strictly defined stages of the life cycle. In spring, orange spots appear on the leaves of the barberry. On the upper side of the leaf, dark dots are visible on these spots - these are holes in the so-called spermogonia, one of the sporulation of the fungus. On the lower surface of the leaf, on the same spots, rounded or oblong cups are formed - aecidia, in which spherical bright yellow or orange spores - aecidiospores are formed. They infect young plants of cereals - the main hosts of the fungus (wheat, rye, etc.), on the stems and leaves of which the next stage develops - ovoid, orange summer spores or uredospores with colorless legs; this sporulation is clearly visible on rust-affected plants as rusty-orange pads or stripes.
3. MUSHROOMS: A SPECIAL FORM OF LIFE, Marsupials and Basidial Fungi MUSHROOMS. CYCLES OF DEVELOPMENT. SIGNIFICANCE IN HUMAN LIFE.
Mushrooms(lat. Fungi or Mycota) - a separate kingdom of wildlife, uniting eukaryotic organisms that combine some features, such as plants, and animals.
Animal signs:
Inability to carry out photosynthesis
Heterotrophic mode of nutrition
The presence in the metabolism of urea,
Glycogen is used as a reserve nutrient
Plant features:
Well defined cell wall
Absorption nutrients from solutions
In a vegetative state, they are immobile.
Mushrooms are studied by science mycology , which is considered a branch of botany, since mushrooms were previously assigned to the plant kingdom.
The biological and ecological diversity of fungi is very high. This is one of the largest and most diverse groups of living organisms, which has become an integral part of all aquatic and terrestrial ecosystems. According to modern estimates, there are from 100 to 250 thousand, and according to some estimates, up to 1.5 million species of mushrooms on Earth. As of 2008 in the kingdom Fungi 36 classes, 140 orders, 560 families, 97,861 species are described.
!!! But on this moment The taxonomy is still being actively reviewed and developed.
The fungus has a vegetative body mycelium , it can be unicellular or multicellular. Depending on this, fungi are divided into higher (multicellular) and lower (unicellular).
Higher mushrooms are divided into ascomicota (marsupials) and basidiomycota (basidial). In marsupials, spores are located in specialized formations - bags, that is, endogenous. In the basidial, basidia are formed, on their processes - sterigma are located basidiospores- exogenous.
Characteristic features of mushrooms:
*Form a well-defined cell wall.
* Reproduce by spores and vegetatively.
* Capable of unlimited growth.
* Primarily heterotrophic mode of nutrition. The type of nutrition is osmotrophic (absorption by the entire surface of the body). Digestion is external (excreted during external environment enzymes).
* Forms glycogen as a reserve nutrient.
Mycelium consists of branching filaments - gif (with apical growth) and lateral branching. The mycelium penetrates the substrate and absorbs nutrients from it with its entire surface, and is also located on the surface of the substrate (surface and aerial mycelium). Reproductive organs are formed on aerial mycelium. Distinguish non-cellular mycelium - devoid of partitions, representing one giant cell with a large number of nuclei, as well as cellular or septate mycelium, divided by partitions - septa into separate cells containing from one to several nuclei. All higher fungi have cellular mycelium, with true septa.
Motile cells of fungi - zoospores and gametes - have flagella. Fungi reproduce vegetatively, asexually and sexually.
At vegetative during reproduction, unspecialized parts of it are separated from the mycelium, which give rise to a new mycelium. One of the forms of vegetative propagation can be considered the formation of chlamydospores - thick-walled cells designed to endure adverse conditions. In yeast, vegetative reproduction occurs by cell budding.
- asexual reproduction occurs with the help of specialized cells - spores. Spores in fungi develop endogenously (inside the sporangia) and exogenously (on specialized mycelium branches). In some (oomycetes, hyphochitriomycetes, chytridiomycetes), spores are mobile - zoospores, in others (zygomycetes) spores are motionless - sporangiospores (passively carried by air currents, raindrops, insects).
- sexual reproduction was noted in all groups of fungi, except for deuteromycetes (imperfect fungi). The forms of the sexual process are different:
* Gametogamy - fusion of gametes (in lower ones).
*Somatogami- fusion of ordinary somatic cells of the mycelium (in basidiomycetes).
*Chologamia- one of the forms of the somatogamous process, since unicellular thalli of fungi merge (in unicellular).
*Zygogamy fusion of two multinucleated gametogangia. A zygospore develops from a zygote (in zygomycetes).
DEVELOPMENT CYCLES:
Development cycles differ and depend on the lifestyle of the fungus.
Symbiotrophic fungi (mycorrhiza-forming - boletus)
Saprotrophic fungi (tinder fungi, chanterelles)
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Development cyclesaprotrophic mushroom (hat - on the example of a chanterelle). |
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SPRING On the barberry SUMMER On cereals AUTUMN WINTER On cereals SPRINGGerminate on cereals fly on barberry Top of the sheet From the bottom of the sheet infectious stage |
Very false cycle of development (with a change of owner). There is a main host on which telia(in winter) - CEREALS. There is an intermediate host - BARBERIS. There is a change in sporulation - different plants have different formations. |
ROLE OF MUSHROOMS IN HUMAN LIFE.
Many types of fungi are actively used by humans in food, household and medical purposes. Edible mushroom dishes are traditionally included in national cuisines many peoples of the world. Many countries have developed industrial cultivation edible mushrooms, production of materials for amateur mushroom growers. Microscopic fungi are used in Food Industry for preparation of drinks by way of fermentation, fermentation of various food products. Mushrooms are one of the most important objects of biotechnology used for the production of antibiotics and other medicines, some chemical substances used in the food industry and for technical purposes.
On the other hand, mushrooms can also cause significant harm. Phytopathogenic fungi, which usually do not cause harm in undisturbed natural ecosystems, can cause epiphytoties in agricultural plantations (agrocenoses), tree plantations and in forests where economic activities are carried out. In animals and humans, fungi cause skin diseases(dermatomycosis), and sometimes lesions internal organs(deep mycoses). Very dangerous and can lead to lethal outcome poisoning with poisonous mushrooms, as well as mycotoxicosis - poisoning food products contaminated with microscopic fungal toxins. Significant damage is caused by spoilage of various products and materials (biocorrosion) caused by fungi. There are also hallucinogenic mushrooms.
The development cycle, or life cycle, is the development of fungi from any one stage to its repetition (usually considered from zygote to zygote).
The life cycles of fungi, even belonging to the same division, are diverse and specific. Therefore, let us consider the main development cycles of fungi, which can be divided into two groups depending on the number of nuclear states.
1. In the development cycle - two nuclear states (n, 2n). Haplonts, the haploid stage predominates (chytridiomycota, zygomycota).
The whole life of an organism proceeds in a haploid state. Only the zygote is diploid. Meiosis is zygotic.
Example: development cycle of Mucor (mukor), department of Zygomycota (zygomycota).
Asexual reproduction is carried out by immobile endogenous sporangiospores formed in sporangia.
Sexual reproduction (zygogamy) begins when the hyphae of heterothallic mycelia collide. The ends of the hyphae swell, the apical parts are separated by a septum from the non-segmented mycelium and function as gametangia. Their contents are merged. The zygote is dressed in a dense shell (zygospore) and in this form is at rest long time. Remains of hyphae (suspensors) hold the zygospore on the surface of the substrate. After the fusion of the cytoplasm, karyogamy is possible in one or more pairs of nuclei. By the time of germination, only one diploid nucleus usually remains.
After a period of rest in the zygote, a reduction division occurs, as a result of which 4 haploid nuclei with different sex signs are formed. Before germination, 3 nuclei die off, and the remaining one begins to divide by mitosis with the formation of a primary sporangium, all spores in which have the same sex sign "+" or "-".
2. In development cycles - three nuclear states (n, 2n, n + n).
1) Development cycles with a predominance of the haploid stage (marsupials).
Most of the life cycle of an organism occurs in the haploid state. Only the zygote is diploid. The dikaryotic stage is short-lived. Meiosis is zygotic.
Example: Sphaerotheca development cycle (spheroteca, powdery mildew gooseberry), department Ascomycota (ascomycota, marsupial mushrooms).
At the end of the growing season, gametangia are formed on the mycelium: male antheridia and female ascogones. First, the cytoplasm of the gametangia fuses (plasmogamy), but the nuclei do not fuse. The dikaryotic stage is short-lived. This is followed by karyogamy with the formation of a diploid zygote. After reduction division, a bag (ascus) with haploid ascospores is formed. In parallel, the formation of shells (peridium) of the fruiting body - cleistothecia. The bag is inside it. Ascospores fall on plant organs and germinate as haploid mycelium.
2) Cycles of development with a predominance of the dikaryotic stage (basidiomycetes).
This life cycle is typical for most basidiomycetes. The developmental cycle is dominated by the dikaryotic stage. Only the zygote is diploid, while the basidiospores and the primary mycelium developing from them are haploid. Gametes and gametangia are not formed, the sexual process in many representatives is somatogamy. Plasmogamy is significantly distant in time from karyogamy.
Example: the development cycle of a cap fungus, the division of Basidiomycota (basidiomycota).
Cap mushrooms have large fruiting bodies, consisting of a cap and a stem. On the underside of the cap there are plates or tubes, where there are basidia with basidiospores, which fall on the substrate and germinate with haploid primary mycelium.
Hyphae with different sexual signs collide, while the cytoplasm merges (plasmogamy!), And the nuclei are connected in pairs (n + n). This is how the secondary mycelium is formed, on which fruiting bodies subsequently develop.
On the plates, unicellular club-shaped basidia are formed, in which the nuclei merge (karyogamy!). Then comes the reduction division, as a result of which haploid basidiospores are formed.
Apressoria- specialized organs of attachment such as suckers. They form as short lateral outgrowths of germ tubes or long hyphae on the host cuticle (in nature) and in the laboratory sometimes on glass or other artificial substrates. They mechanically hold the fungus on the surface of the plant while it breaks through its cuticle and cell wall, and also overcomes the osmotic pressure of the cellular contents. Apressoria prevent the fungus from being blown away by the wind and washed away by rain.
Stolons - horizontal hyphae that branch at the points of contact with the substrate, forming haustoria or rhizoids that go into the substrate. In fungi of the genus RhizoRus (Mucoraceae), several sporangiophores and new stolons grow upward from the rhizoids (Fig. 2). Many fungi populate the substrate in this way: first, individual hyphae spread over the surface for considerable distances, and then, due to their lateral branching, a denser mycelium develops, absorbing nutrients more intensively.
Trapping hyphae- these are loops formed by special hyphae of some predatory fungi, covered with a sticky secretion and instantly contracting in response to touch. The victims of these fungi are mainly nematodes and protozoa.
rhizomorphs- these are bundles of hyphae of considerable diameter with pronounced internal differentiation; their more durable outer layers of cells protect the internal hyphae of the usual structure, which serve for the accumulation and transport of substances.
resting structures - structures necessary to tolerate adverse conditions. Many fungi tolerate adverse conditions in the form chlamydospores. These are cells separated from the mycelium, covered with a thickened, often melanized membrane. In zygomycetes, the resting stage is represented by a zygote covered with a thick membrane - zygospore. Often meets - sclerotium, which is a dense plexus of hyphae. Hyphae cells are often differentiated: the outer cells are thick-walled and pigmented, isodiametric, densely packed, while the inner cells are looser, light-colored, elongated with thin membranes and numerous drops of fat. In some fungi, the tissue of the host plant, penetrated by mycelium, can also take part in the formation of sclerotia. So, apples infected with the causative agent of fruit rot turn black and mummify, turning into sclerotium.
4. Reproduction of mushrooms
Fungi have three types of reproduction: vegetative, asexual and sexual. In many species, they successively replace each other in the development cycle. The structures formed during asexual and sexual reproduction are often complex in structure and morphologically differ significantly from each other. Sometimes in the development cycle of one or another fungus there are two or more different types of sporulation. This phenomenon is called pleomorphism. This is especially true for marsupials. For example, in the ergot development cycle (Claviceps purpurea) two morphologically very different stages are replaced: asexual - sphacelia; and sexual - capitate strictma with fruit bodies. Different stages of development of ergot and some other fungi were often taken as independent species, which were given their own specific names.
Vegetative reproduction carried out by non-specialized parts of the mycelium, which give rise to a new mycelium. The basis of this method of reproduction is the high ability of the mycelium to regenerate. Vegetative propagation is widely used in the preparation of mycelium for artificial cultivation. edible mushrooms(champignon, oyster mushroom), upon receipt of the biomass of fungi in food and forage purposes.
The specialized structures of vegetative reproduction include oidia- thin-walled cells chlamydospores - thick-walled cells into which the mycelium breaks down and which give rise to a new mycelium. Chlamydospores also perform the function of transferring adverse conditions. Most yeasts reproduce vegetatively by cell budding.
asexual reproduction carried out using a variety of specialized cells or multicellular structures, dispute. Fungi are known endogenous and exogenous asexual spores. endogenous motile spores zoospores develop in zoosporangia different shape. Zoospores are equipped with flagella; the number, location and structure of which is different in different systematic groups of fungi. Zoospores of different structure are characteristic of representatives of the departments oomycote, hyphochytridiomycote, and chytridiomycote; those. for aquatic and rarely terrestrial fungi. Endogenous immobile spores - sporangiospores- dressed in a shell and formed inside sporangiev, developing on specialized hyphae - sporangiophores- usually rising above the substrate. Sporangiospores reproduce asexually in zygomycotes. Exogenous spores of asexual reproduction of fungi - conidia- immobile, formed on specialized, usually morphologically different from the vegetative mycelium, differentiated sporophores - conidiophores. Typical conidia are characteristic of marsupials, basidiomycetes, and imperfect fungi.
The spread of immobile spores of asexual reproduction (sporangiospores and conidia) is carried out mainly passively by currents of air or water. Sometimes the spread of spores can be carried out with the help of animals, for example, when eating the fruiting bodies of cap mushrooms.
The specialized structures associated with vegetative and asexual reproduction in fungi are called anamorphs.
sexual reproduction in fungi and the process of changing nuclear phases associated with it, the structure of the genital organs differs in different groups mushrooms. The most important moments of the sexual process in fungi: plasmogamy(fusion of the cytoplasm), curryogamia(nuclear fusion) and meiosis. Accordingly, the fungus can be in the haploid or diploid stages. Plasmogamy and karyogamy in marsupials and basidiomycetes do not coincide in time, as a result of which, after plasmogamy, they have a special stage dikaryotic mycelium, when the haploid nuclei are brought together in pairs, but not merged and form dikarion. Dikaryon nuclei usually divide synchronously. At a certain point in the development cycle, they merge, forming a diploid nucleus, which then divides by reduction.
As a result of the sexual process, haploid, genetically heterogeneous spores are formed, which fundamentally distinguishes them from the spores of asexual reproduction of fungi. These haploid spores are located either on the mycelium or, more often, on the surface or inside the fruiting bodies of various structures, which are called teleomorphs. Thus, reproduction with the help of spores that have arisen sexually gives rise to forms with a new combination of genetic material, which is the basis for the further evolution of forms, and reproduction by spores that have arisen asexually contributes to the spread and preservation of this form.
Types of sexual process in fungi. Sexual reproduction in fungi is known in all groups, with the exception of anamorphic or imperfect fungi, for which they received their name. The sexual process in fungi is diverse and its features underlie the allocation of classes. In fungi, three main types of sexual process are known: gametogamy, gametangiogamy, and somatogamy.
Gametogamy - fusion of gametes formed in gametangia. Distinguish isogamy- fusion of motile morphologically similar gametes and heterogamy- the fusion of mobile, differing in size and often in the degree of mobility of gametes. These two types of gametogamy are characteristic of chytrid and hyphochytrid fungi.
At oogamy large immobile eggs that form in special oogonia are fertilized by small mobile spermatozoa that develop in specialized antheridia. In many fungi with this type of sexual process, spermatozoa are not formed, and the egg is fertilized by the contents of the outgrowths of the multinuclear antheridium, undifferentiated into spermatozoa. This type of oogamy is characteristic of all representatives of the oomycot department.
Gametangiogamy – the fusion of two usually multinucleated specialized structures, the contents of which are not differentiated into gametes. Gametangiogamy is characteristic of zygo- and ascomycota. Gametangiogamy in zygomycotes is called zygogamy. It consists in the fusion of mostly multinucleated gametangia, well distinguishable from the vegetative mycelium on which they form, but not morphologically differentiated into male and female. From the zygote formed as a result of their fusion, a thick-walled colored shell is formed. zygospore, which germinates after a dormant period into a special germinal sporangium. In ascomycota, during gametangiogamy, two multinuclear gametangia also merge, but in them, unlike zygomycota, the genital organs are differentiated into female – ascogon and male – antheridium. Askogon consists of two cells: a large multinucleated, or askogon proper, and a thin filamentous – trichogynes, located on its top, through which the contents of the multinuclear antheridium pour into the askogon. In this case, only plasmogamy occurs, and the nuclei associate in pairs, forming dikarion. From a fertilized ascogon without a dormant period grow ascogenous dikaryotic hyphae. In their cells, the nuclei of the dikaryon merge and form a diploid nucleus, which then divides meiotically. As a result of this process, special formations are formed on ascogenous hyphae in a rather complicated way. – asci (bags); within which, after mitotic division of postmeiotic nuclei, eight endogenous haploid nuclei are formed ascospore.
Somatogamy- a sexual process in which ordinary somatic or vegetative cells of the mycelium merge. Sex organs and gametes are absent. Somatogamy is characteristic of some representatives of the divisions of chytridiomycosis and hyphochytridymycosis, which have a unicellular thallus. In this case, two single-celled individuals completely merge. This type of somatogamy is called hologamy. Somatogamy in basidiomycota consists in the fusion of two vegetative cells of the haploid mycelium. In this case, as in ascomycots, at first only plasmogamy takes place, as a result of which dikaryons are formed and a dikaryotic (consisting of binuclear cells) mycelium is formed. This is the longest stage in the development cycle of basidiomycetes. Then special cells are formed on this dikaryotic mycelium - basidia, in which the nuclei of the dikaryon merge and the meiotic division of the diploid nucleus occurs, after which exogenous haploid basidiospores.
Endogenous ascospores of marsupial fungi and exogenous basidiospores of basidiomycetes are formed as a result of the sexual process. The sexual process of marsupial and basidial fungi has two characteristic common features: firstly, a temporary gap by plasmogamy and karyogamy and the appearance of a dikaryotic phase and, secondly, the absence of a state of rest in the zygote: the meiotic division of the diploid nucleus occurs immediately after the fusion of the haploid nuclei of the dicarion.
According to the nature of sexual differentiation in fungi, homothallic(bisexual) and heterothallic(separate) forms. In homothallic fungi, cells of the same mycelium are capable of fusion. On the same mycelium, both male and female reproductive organs are formed (for example, oogonia and antheridia in oomycots). In heterothallic fungi, on the mycelium grown from one spore, the genital organs are not laid and, accordingly, zygotes are not formed. They develop only when two mycelia meet, differing from each other in terms of gender (+ and -, or male and female).
In imperfect (anamorphic) fungi, there is no sexual process, and these fungi spend their life cycle in a haploid state. To a certain extent, the absence of the sexual process in this group is compensated by heterocariosis and the parasexual process that occurs on its basis. Heterokaryosis- the presence of genetically different nuclei in mycelial cells. Heterokaryosis is characteristic of many groups of fungi and ensures the adaptation of fungi to changing environmental conditions. In such a mycelium, the nuclei can sometimes merge, forming a diploid heterozygous nucleus. Such a nucleus divides mitotically, with mitotic recombination and then vegetative haploidization of these diploid nuclei by losing some of their chromosomes. This complex process, which includes mitotic recombination as the most important moment, is called parasexual process. It is known in various groups of fungi, and is of particular importance for imperfect fungi that lack a true sexual process.
Development cyclesmushrooms
haploid life cycle.
Ascomycota, zygomycota and most chytridiomycota grow in the haplophase ending at full development plasmogamy, karyogamy and reduction division. Most imperfect mushrooms, as well as slime molds without teleomorphs, exist as asexual organisms in the haplophase.
Haplo-diploid fungi. Some yeasts (ascomycota) bud in a diploid and haploid state.
diploid mushrooms. In oomycots, only the contents of the gametangia of antheridia and oogonia are haploid. The oosphere, which later develops into a dormant oospore, begins the diploid phase of the fungus, in which it reproduces vegetatively. Diploid fungi include myxomycota and some ascomycot yeasts.
Lecture 3. Mushroom-like organisms
1. Department of Myxomycota
2. Department of Plasmodiophoromycota
3. Department of Oomycota
4. Features of the biology of Phytophthora infestans
