Lichens are a complex object for physiological studies, since they consist of two physiologically opposite components - a heterotrophic fungus and an autotrophic algae. Therefore, it is first necessary to separately study the vital activity of the myco- and phycobiont, which is done with the help of cultures, and then the life of the lichen as an integral organism. It is clear that such a “triple physiology” is a difficult path of research, and it is not surprising that there is still a lot of mystery in the life of lichens. However, the general patterns of their metabolism are still elucidated.
Quite a lot of research is devoted to the process of photosynthesis in lichens. Since only a small part of their thallus (5 - 10% of the volume) is formed by algae, which, nevertheless, is the only source of supply of organic substances, a significant question arises about the intensity of photosynthesis in lichens.
Measurements have shown that the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.
For normal photosynthetic activity, the thallus must contain a certain amount of water, depending on the anatomical and morphological type of lichen. In general, in thick thalli, the optimal water content for active photosynthesis is lower than in thin and loose thalli. At the same time, it is very significant that many species of lichens, especially in dry habitats, are generally rarely or at least very irregularly supplied with an optimal amount of intrathallus water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plants that have a special apparatus that can control the receipt and consumption of water. Lichens assimilate water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively with the entire surface of their body and partly with the rhizoids of the underside. This absorption of water by the thallus is a simple physical process, such as the absorption of water by filter paper. Lichens are able to absorb water in very large quantities, usually up to 100 - 300% of the dry mass of the thallus, and some slimy lichens (kollems, leptogiums, etc.) even up to 800 - 3900%.
The minimum water content in lichens in natural conditions is approximately 2 - 15% of the dry mass of the thallus.
The release of water by the thallus also occurs quite quickly. Lichens saturated with water in the sun after 30-60 minutes lose all their water and become brittle, i.e., the water content in the thallus becomes lower than the minimum required for active photosynthesis. From this follows a kind of “arrhythmia” of lichen photosynthesis - its productivity changes during the day, season, a number of years, depending on general environmental conditions, especially hydrological and temperature ones.
There are observations that many lichens photosynthesize more actively in the morning and evening hours and that photosynthesis continues in them in winter, and in ground forms even under a thin snow cover.
An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and most of them) perceive nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens also take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. Ecologically interesting group make up the so-called nitrophilic lichens growing in habitats rich in nitrogenous compounds - on "bird stones", where there is a lot of bird excrement, on tree trunks, etc. (types of xanthoria, fiscia, caloplaki, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are able to fix atmospheric nitrogen, since the algae contained in them have this ability. In experiments with such species (from the genera collema, leptogium, peltiger, lobaria, stikta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogenous compounds. Most of the nitrogen fixed by the algae goes to the mycobiont, and only a small part is used by the phycobiont itself. There is evidence that the mycobiont in the lichen thallus actively controls the assimilation and distribution of nitrogenous compounds fixed from the atmosphere by the phycobiont.
The rhythm of life described above is one of the reasons for the very slow growth of most lichens. Sometimes lichens grow only a few tenths of a millimeter per year, mostly less than one centimeter. Another reason for the slow growth is that the photobiont, often making up less than 10% of the lichen volume, takes over the supply of nutrients to the mycobiont. AT good conditions, with optimal humidity and temperature, for example in foggy or rainy tropical forests, lichens grow several centimeters per year.
The growth zone of lichens in scale forms is located along the edge of the lichen, in foliose and fruticose forms at each top.
Lichens are among the longest living organisms and can be several hundred years old, and in some cases over 4500 years old, such as Rhizocapron geographicum living in Greenland.
Lichen reproduction
Lichens reproduce either by spores, which are formed by the mycobiont sexually or asexually, or vegetatively - by fragments of the thallus, soredia and isidia.
During sexual reproduction on lichen thalli, as a result of the sexual process, sexual sporulation is formed in the form of fruiting bodies. Among the fruit bodies in lichens, apothecia, perithecia and gasterothecia are distinguished. Most lichens form open fruiting bodies in the form of apothecia - disc-shaped formations. Some have fruiting bodies in the form of perithecium - a closed fruiting body that looks like a small jug with a hole at the top. A small number of lichens form narrow elongated fruiting bodies, which are called gasterothecia.
In apothecia, perithecia and gasterothecia, spores develop inside bags - special sac-like formations. Lichens that form spores in bags are combined into large group marsupial lichens. They originated from fungi of the class Ascomycetes and represent the main evolutionary line of development of lichens.
In a small group of lichens, spores are formed not inside the bags, but exogenously, on top of elongated club-shaped hyphae - basidia, at the ends of which four spores develop. Lichens with such spore formation are combined into a group of basidial lichens.
The female genital organ of lichens - the archicarp - consists of two parts. The lower part is called askogon and is a spirally twisted hyphae, thicker than other hyphae and consisting of 10–12 one- or many nuclear cells. Trichogyne extends upward from the askogon - a thin, elongated hyphae that passes through the algae zone and the crustal layer and emerges on the surface of the thallus, towering above it with its sticky top.
The development and maturation of the fruit body in lichens is a very slow process that lasts 4 to 10 years. The formed fruiting body is also perennial, capable of producing spores for a number of years. How many spores are capable of producing lichen fruiting bodies? It has been calculated, for example, that in the lichen Solorin, 31 thousand bags are formed in an apothecia with a diameter of 5 mm, and 4 spores usually develop in each bag. Therefore, the total number of spores produced by one apothecia is 124,000. Within one day, from 1200 to 1700 spores are ejected from such an apothecia. Of course, not all spores thrown out of the fruiting body germinate. Many of them, once in adverse conditions, die. For spore germination, first of all, sufficient humidity and a certain temperature are necessary.
In lichens, asexual sporulation is also known - conidia, pycnoconidia and stylospores that occur exogenously on the surface of conidiophores. At the same time, conidia are formed on conidiophores that develop directly on the surface of the thallus, and pycnoconidia and stylospores in special receptacles - pycnidia.
From asexual sporulation, lichens most often form pycnidia with pycnoconidia. Pycnidia are often found on the thalli of many fruticose and leafy lichens, less often they can be observed in scale forms.
In each of the pycnidia, small unicellular spores, pycnoconidia, are formed in large numbers. The role of these widespread sporulation in the life of the lichen has not yet been elucidated. Some scientists, calling these spores spermatozoa, and pycnidia - spermagonia, consider them male germ cells, although there is still no experimental or cytological data proving that pycnoconidia are really involved in the sexual process of lichens.
vegetative reproduction. If scale lichens, as a rule, form fruiting bodies, then among the more highly organized leafy and bushy lichens there are many representatives that reproduce exclusively by vegetative means. In this case, such formations are more important for the reproduction of lichens, in which fungal hyphae and algae cells are simultaneously present. These are soredia and isidia. They serve to reproduce the lichen as a whole organism. Once in favorable conditions, they give rise directly to a new thallus. Soredia and isidia are more common in foliose and fruticose lichens.
Soredia are tiny formations in the form of dust particles, consisting of one or more algae cells surrounded by fungal hyphae. Their formation usually begins in the gonidial layer. Due to the mass formation of soredia, their number increases, they put pressure on the upper bark, tear it and end up on the surface of the thallus, from where they are easily blown away with any movement of air or washed off with water. Clusters of soredia are called sorals. The presence and absence of soredia and sorals, their location, shape and color are constant for certain lichens and serve as a defining feature.
Sometimes, when lichens die, their thallus turns into a powdery mass consisting of soredia. These are the so-called leprosy forms of lichens (from the Greek word "lepros" - "rough", "uneven"). In this case, it is almost impossible to determine the lichen.
Soredia, carried by wind and rainwater, once in favorable conditions, gradually form a new thallus. The renewal of a new thallus from the soredia is very slow. Thus, in species of the genus Cladonia, normal scales of the primary thallus develop from the soredia only after a period of 9 to 24 months. And for the development of a secondary thallus with apothecia, it takes from one to eight years, depending on the type of lichen and external conditions.
Isidia are found in a smaller number of lichen species than soredia and sorali. They are simple or coral-branched outgrowths, usually densely covering the upper side of the thallus (see figure). Unlike sorals, isidia are covered with bark on the outside, often darker than thallus. Inside, under the bark, they contain algae and fungal hyphae. Isidia easily break off from the surface of the thallus. Breaking off and spreading with the help of rain and wind, they, like soredia, can, under favorable conditions, form new lichen thalli.
Many lichens do not form apothecia, soredia and isidia and multiply in thallus areas that are easily broken off from lichens that are fragile in dry weather by wind or animals and are also carried by them. Particularly widespread is the reproduction of lichens by thallus sites in the Arctic regions, representatives of the genera Cetraria and Cladonia, many of which almost never form fruiting bodies.
Lichen is a single organism that contains unicellular algae and a fungus. This symbiosis is exceptionally useful for the existence of the whole organism as a whole. After all, while the fungus absorbs water and dissolved mineral salts, the algae produces organic substances from carbon dioxide and water in the process of photosynthesis under the action of sunlight. Lichen- unpretentious organism. This gives lichens the opportunity to settle first in places where there is no other vegetation. After them, humus appears, on which other plants can live.
Lichens found in nature are extremely diverse in appearance and coloration. On old fir trees, you can often see hanging, disheveled beards of lichens, which are called vislyanka, or bearded man. And on the bark of some trees, in particular, aspen, orange plates of a round-shaped lichen of the wall goldfish are sometimes attached. Deer lichen is a grayish whitish small bushes. This plant grows in dry pine forests, and in dry weather makes a characteristic crunch if you walk on it.
Lichens are widespread. They are unpretentious, therefore they live in various, sometimes harsh conditions. Lichens can be found on bare rocks and stones, on the bark of trees, on fences, sometimes even on the soil. In the northern regions, and more specifically, in the tundra, lichens inhabit huge areas, for example, deer lichen. You can also often find lichens in the mountains.
In the structure of lichens there are features that allow them to be combined into a separate group. If we examine a thin section of a lichen under a microscope, it is noticeable that its structural elements are transparent threads, between which there are rounded green cells. Scientists have found that the colorless filaments are the mycelium of the fungus, and the green cells are nothing but unicellular algae. Thus, one lichen organism combines two different organisms - an algae and a fungus, which interact so closely that they form an integral organism.
The relationship of two organisms in the body of a lichen allows it to adapt favorably to conditions. environment. Thanks to the mycelium, water and carbon dioxide are absorbed, and organic substances are formed in the body of the algae. In some cases, the fungus can feed on algae that are in the body of the lichen. The lichen absorbs liquid from the entire surface of the body, mainly after rains, as well as from dew and fog. And nutrients are absorbed from everywhere - from the air, soil and even from the settling dust. All types of lichen do not need to create special favorable conditions for life. They are unpretentious and hardy. During the drought period, the lichen dries up to such an extent that it breaks at the slightest touch, and comes to life again after the rain. It is in connection with such features of life that lichens are found in such barren areas where other plants are not able to survive.
Lichens play an important role in nature and human economy. Since lichens are unpretentious, they are the first to settle in areas where there is no other vegetation. Having finished my life cycle on bare rocks and stones, lichens die off, leaving behind humus, on which other representatives of the plant kingdom can develop. Thus, in this case, the significance of lichens is that they create the soil for the vital activity of other plants. Deer lichen is of the greatest importance in the human economy. This lichen, which grows in the tundra over a vast territory, is the main food for reindeer.
Lichens
(lower plants)
Structure
This is a kind of group of lower plants, which consist of two different organisms- fungus (representatives of ascomycetes, basidiomycetes, phycomycetes) and algae (green - cystococcus, chlorococcus, chlorella, cladophora, palmella is found; blue-green - nostoc, gleocapsa, chroococcus), forming a symbiotic cohabitation, characterized by special morphological types and special physiological and biochemical processes. Some lichens were thought to contain bacteria (Azotobacter). However, later studies did not confirm their presence in lichens.
Lichens differ from other plants in the following ways:
1. Symbiotic cohabitation of two different organisms - a heterotrophic fungus (mycobiont) and an autotrophic algae (phycobiont). Lichen cohabitation is constantly and historically determined, and not by chance, for a short time. In a real lichen, the fungus and algae come into close contact, the fungal component surrounds the algae and can even penetrate into its cells.
2. Specific morphological forms of external and internal structure.
3. The physiology of the fungus and algae in the lichen thallus differs in many respects from the physiology of free-living fungi and algae.
4. The biochemistry of lichens is specific: they form secondary metabolic products that are not found in other groups of organisms.
5. Method of reproduction.
6. Attitude to environmental conditions.
Morphology. Lichens do not have a typical green color, they do not have a stem, leaves (this is how they differ from mosses), their body consists of a thallus. The color of lichens is grayish, greenish-gray, light or dark brown, less often yellow, orange, white, black. The color is due to pigments that are in the shells of the hyphae of the fungus, less often in the protoplasm. There are five groups of pigments: green, blue, purple, red, brown. The color of lichens may also depend on the color of lichen acids, which are deposited in the form of crystals or grains on the surface of the hyphae.
There are lichens scale, or cortical, leafy and bushy.
At scale thallus has the appearance of a powdery, tuberculate or smooth skin, which is tightly fused with the substrate; about 80% of all lichens belong to them. Depending on the substrate on which scale lichens grow, there are:
epilithic, developing on the surface of rocks;
epifleodnye - on the bark of trees and shrubs;
epigeic - on the surface of the soil,
epixile - on rotting wood.
The lichen thallus can develop inside the substrate (stone, tree bark). There are scale lichens with a spherical shape of the thallus (the so-called nomadic lichens).
At leaf lichens thallus has the appearance of scales or rather large plates that are attached to the substrate in several places with the help of bundles of fungal hyphae. The simplest thallus of leaf lichens has the form of one large rounded leaf-shaped plate, reaching a diameter of 10-20 cm. Such a thallus is called monophyllic. It is attached to the substrate in its central part with the help of a thick short leg called gomf. If the thallus consists of several leaf-shaped plates, it is called polyphilic. characteristic feature leaf lichen thallus is that its upper surface differs in structure and color from the lower. Among leaf lichens, loose, nomadic forms are also found.
At fruticose lichens thallus consists of branched filaments or stems, grows together with the substrate only at the base; grow up, sideways, or hang down - "bearded" lichens. The thallus of fruticose lichens has the appearance of an upright or hanging bush, less often unbranched upright outgrowths. This is the highest stage in the development of the thallus. The height of the smallest is only a few millimeters, the largest - 30-50 cm (sometimes 7-8 m - a long usnea, hanging in the form of a beard from the branches of larch and cedar in taiga forests). Thalluses come with flat and rounded lobes. Sometimes large bushy lichens in tundra and high mountains develop additional attachment organs (hapters), with the help of which they grow to the leaves of sedges, grasses, and shrubs. In this way, lichens protect themselves from separation strong winds and storms.
The internal structure of lichens. According to the anatomical structure, lichens are of two types.
In one of them, algae are scattered throughout the entire thickness of the thallus and are immersed in the mucus secreted by the algae (homeomeric type). This is the most primitive type. Such a structure is typical for those lichens whose phycobiont are blue-green algae - nostoc, gleokapsa, etc. They form a group of slimy lichens.
In another (heteromeric type), several layers can be distinguished under a microscope on a cross section. Above is the upper bark, which looks like intertwined, tightly closed fungal hyphae. Under it, the hyphae lie more loosely, algae are located between them - this is the gonidial layer. Below, the fungal hyphae are located even more loosely, large gaps between them are filled with air - this is the core. The core is followed by the lower crust, which is similar in structure to the upper. Bundles of hyphae pass through the lower cortex from the core, which attach the lichen to the substrate.
Crustose lichens do not have a lower bark and the fungal hyphae of the hearts fuse directly with the substrate.
Bushy radially built lichens have a bark on the periphery of the transverse section, a gonidial layer under it, and a core inside. The bark performs protective and strengthening functions. Attachment organs usually form on the lower crustal layer of lichens. Sometimes they look like thin threads, consisting of one row of cells. They are called rhizoids. Rhizoids can join to form rhizoidal bands.
In some foliose lichens, the thallus is attached with a short stalk (gomfa) located in the central part of the thallus.
The algae zone performs the function of photosynthesis and accumulation organic matter. The main function of the core is to conduct air to algae cells containing chlorophyll. In some bushy lichens, the core also performs a strengthening function.
The organs of gas exchange are pseudocyfellae (ruptures of the cortex, visible to the naked eye as white spots are not correct form). On the lower surface of leaf lichens there are round, regular white depressions - these are cyphella, also gas exchange organs. Gas exchange is also carried out through perforations (dead areas of the crustal layer), cracks and breaks in the crustal layer.
Nutrition
Hyphae play the role of roots: they absorb water and mineral salts dissolved in it. Algae cells form organic substances, perform the function of leaves. Lichens can absorb water with the entire surface of the body (they use rainwater, fog moisture). An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont receive nitrogen compounds from aqueous solutions when their thallus is saturated with water, partly directly from the substrate. Lichens that have blue-green algae (especially nostocs) as a phycobiont are able to fix atmospheric nitrogen.
reproduction
Lichens reproduce either by spores, which are formed by the mycobiont sexually or asexually, or vegetatively - by fragments of the thallus, soredia and isidia.
During sexual reproduction, sexual sporulation in the form of fruiting bodies is formed on the thalli of lichens. Among the fruit bodies in lichens, apothecia are distinguished (open fruit bodies in the form of disc-shaped formations); perithecia (closed fruiting bodies that look like a small jug with a hole at the top); gasterothecia (narrow fruiting bodies of an elongated shape). Most lichens (over 250 genera) form apothecia. In these fruiting bodies, spores develop inside bags (sac-like formations) or exogenous, on top of elongated club-shaped hyphae - basidia. The development and maturation of the fruiting body lasts 4-10 years, and then for a number of years the fruiting body is able to produce spores. A lot of spores are formed: for example, one apothecia can produce 124,000 spores. They don't all grow. For germination, conditions are needed, primarily certain temperature and humidity.
Asexual sporulation of lichens - conidia, pycnoconidins and stylospores that occur exogenously on the surface of conidiophores. Conidia are formed on conidiophores that develop directly on the surface of the thallus, and pycnoconidia and stylospores - in special receptacles - pycnidia.
Vegetative reproduction is carried out by thallus bushes, as well as special vegetative formations - soredia (dust particles - microscopic glomeruli, consisting of one or more algae cells surrounded by fungal hyphae, form a fine-grained or powdery whitish, yellowish mass) and isidia (small, variously shaped outgrowths of the upper surface of the thallus , the same color as it, they look like warts, grains, club-shaped outgrowths, sometimes small leaves).
Lichens are peculiar complex organisms, the thallus of which is a combination of fungus and algae, which are in complex relationships with each other, more often in symbiosis. More than 20 thousand species of lichens are known.
From other organisms, including free-living fungi and algae, they differ in shape, structure, nature of metabolism, special lichen substances, methods of reproduction, and slow growth (from 1 to 8 mm per year).
Structural features
lichen thallus consists of intertwined fungal threads - hyphae, and algae cells (or threads) located between them.
There are two main types of microscopic structure of the thallus:
- Homeomeric;
- heteromeric.
On a cross section of a lichen homeomeric type there is an upper and lower bark, which consists of one layer of fungal cells. The entire inner part is filled with loosely arranged fungal filaments, between which algae cells are located without any order.
in lichen heteromeric type of algae cells are concentrated in one layer, which is called gonidial layer. Below it is the core, consisting of loosely arranged filaments of the fungus.
The outer layers of the lichen are dense layers of fungal filaments called cortical layers. With the help of fungal filaments extending from the lower cortical layer, the lichen is attached to the substrate on which it grows. In some species, the lower bark is absent and it is attached to the substrate by the threads of the core.
The algal component of the lichen consists of species belonging to the blue-green, green, yellow-green and brown divisions. Representatives of 28 genera of them enter into symbiosis with fungi.
Most of these algae may be free-living, but some are found only in lichens and have not yet been found in a free state in nature. Being in the thallus, algae change greatly in appearance, and also become more resistant to high temperatures, and can tolerate prolonged drying. When cultivated on artificial media (separate from fungi), they acquire a form characteristic of free-living forms.
The lichen thallus is diverse in shape, size, structure, painted in various colors. The color of the thallus is due to the presence of pigments in the shells of hyphae and fruiting bodies of lichens. There are five groups of pigments: green, blue, purple, red and brown. A prerequisite for the formation of pigments is light. The brighter the lighting in the places where lichens grow, the brighter they are colored.
The shape of the thallus can also be varied. By external structure thallus lichens are divided into:
- scale;
- leafy;
- bushy.
At scale lichens the thallus has the appearance of a crust, tightly fused with the substrate. The thickness of the crusts is different - from a barely noticeable scale or powdery coating to 0.5 cm, the diameter - from a few millimeters to 20-30 cm. Scale species grow on the surface of soils, rocks, bark of trees and shrubs, and exposed decaying wood.
foliose lichens have the form of a leaf-shaped plate, horizontally located on the substrate (parmelia, wall goldfish). Usually the plates are rounded, 10-20 cm in diameter. A characteristic feature of leafy species is the unequal color and structure of the upper and lower surfaces of the thallus. In most of them, on the underside of the thallus, organs of attachment to the substrate are formed - rhizoids, consisting of hyphae collected in strands. They grow on the surface of the soil, among mosses. Leafy lichens are more highly organized forms compared to scale ones.
fruticose lichens have the form of an upright or hanging bush and are attached to the substrate in small areas of the lower part of the thallus (cladonia, Icelandic lichen). According to the level of organization, bushy species are the highest stage in the development of the thallus. Their thalli are of different sizes: from a few millimeters to 30-50cm. Hanging thalli of fruticose lichens can reach 7-8m. An example is a lichen hanging in the form of a beard from the branches of larches and cedars in taiga forests (bearded lichen).
reproduction
Lichens reproduce mainly vegetatively. At the same time, pieces are separated from the thallus, carried by wind, water or animals, and in favorable conditions give new thalli.
In foliose and bushy lichens, for vegetative propagation in the surface or deeper layers, special vegetative formations are formed: soredia and isidia.
Soredia have the appearance of microscopic glomeruli, each of which contains one or more algae cells surrounded by fungal hyphae. Soredia are formed inside the thallus in the gonidial layer of leafy and fruticose lichens. Formed soredia are pushed out of the thallus, picked up and carried by the wind. Under favorable conditions, they germinate in new places and form thalli. About 30% of lichens reproduce by soredia.
Nutrition
The nutritional characteristics of lichens are associated with the complex structure of these organisms, consisting of two components that receive nutrients. different ways. Mushrooms are heterotrophs and algae are autotrophs.
The algae in the lichen provides it organic matter produced by photosynthesis. The lichen fungus receives high-energy products from the algae: ATP and NADP. The fungus, in turn, with the help of filamentous processes (hyphae) acts as a root system. So the lichen gets water and minerals that are adsorbed from the soil.
Also, lichens are able to absorb water from the environment with their whole body, during fogs and rains. To survive they need nitrogen compounds. If the algal component of the thallus is represented by green algae, then nitrogen comes from aqueous solutions. When blue-green algae act as a phycobiont, nitrogen fixation from atmospheric air is possible.
For the normal existence of lichens are necessary in sufficient quantities light and moisture. Insufficient illumination prevents their development, as photosynthetic processes slow down and lichens receive less nutrients.
Light pine forests have become the best place for their life. Although lichens are among the most drought-resistant species, they still need water. Only in a humid environment are respiratory and metabolic processes carried out.
The value of lichens in nature and human life
Lichens are very sensitive to harmful substances, so they do not grow in places with high dust and gas content in the air. So, they are used as indicators of pollution.
They take part in the cycle of substances in nature. Their photosynthetic part is capable of producing organic matter in places where other plants cannot survive. An important role of lichens in soil formation, they settle on a lifeless rocky surface and, after dying off, form humus. This creates favorable conditions for plant growth.
Forage lichens are an important link in the food chain. For example, deer, roe deer, moose feed on deer moss or reindeer moss. They serve as material for bird nests. Lichen manna or Aspicilia edible is used in cooking.
The perfume industry uses them to give durability to perfumes, and the textile industry uses them to dye fabrics. Species with antibacterial properties are also known, which are used in the manufacture of medicines to combat tuberculosis and furunculosis.
Lichens are organisms whose body is formed as a result of the symbiosis of a fungus and an algae. The body of a lichen is called a thallus (thallus). The photosynthetic component of the lichen is an algae or cyanobacteria, and the fungus ensures the absorption of water and mineral salts.
Among the algae, green and yellow-green algae are most common, there are about 100 species in total. In modern flora, there are about 13,500 species of lichens.
Lichens are found in a variety of habitats from the North to the South Pole. They grow on stones and rocks, tree bark and plant leaves, soil, artificial substrates. Some lichens live in water.
According to the shape of the thallus, lichens are divided into three types: scale, leafy and bushy. The scale ones have the appearance of crusts and are tightly fused with the substrate. Leafy have a flattened shape, parts of the thallus rise above the substrate and resemble leaves. They are attached to the substrate by bundles of hyphae and can be separated from the substrate without damaging the thallus. Bushy lichens look like hanging or erect bushes, which are attached to the substrate only by the base of the thallus.
By internal structure Lichens are of two types. In some, the algae are evenly distributed among the hyphae of the fungus throughout the entire thickness of the thallus. The space between hyphae and algae is filled with mucus. This is a homeomeric type of structure. In other lichens, a dense interlacing of hyphae forms the upper bark, under which
there is a layer of loosely arranged hyphae with algae cells between them. Under this layer are loosely arranged hyphae that form the core. The core is underlain by the lower cortex, formed by closely woven hyphae. Bundles of hyphae emerge from the core, with the help of which the lichen is attached to the substrate.
Most often, lichens reproduce vegetatively: by parts of the thallus; algae cells braided with fungal hyphae; specialized outgrowths of the thallus containing phyco- and mycobionts. After separation of these structures under favorable conditions, they begin to develop into a new lichen thallus. Lichens can reproduce both asexually and sexually, but this reproduction is associated with mycobiont. Lichens grow very slowly: in a year their thallus grows from a few hundredths of a millimeter to several centimeters.
Lichens are able to accumulate solar energy and create organic compounds from inorganic ones. On the other hand, the lichen mycobiont is a heterotroph. Lichens are the pioneers of vegetation, they are the first to master lifeless substrates, making them suitable for other organisms over time. Lichens are indicators of air pollution, especially sensitive to the content of sulfur dioxide in the atmosphere. They are used in archeology and geomorphology to determine the age of the substrate.
Lichens serve as food for animals, especially in winter in the northern regions (for example, reindeer moss, or reindeer moss). Birds can use lichen thalli as building material for their nests.
Some lichens are also edible for humans. A number of substances used in the perfume industry are obtained from lichens. Some lichens are used in traditional medicine in the treatment of a number of diseases.
Choose one correct answer.
1. Mushrooms are
1) a separate group of plants
2) symbiosis of plants and bacteria
3) a special group of animals
4) a special group of living beings
2. Lower plants include
1) mushrooms 3) mosses
2) algae 4) lichens
3. A sign common to fungi and animals is *
1) lack of plastids
2) method of reproduction
3) the presence of an internal skeleton
4) inspection type of food
| 4. | The cell wall of fungi contains | ||
| 1) murein | 3) | cellulose | |
| 2) pectin | 4) | chitin | |
| 5. | The mycelium of the fungus is formed | ||
| 1) chitin fibers | 3) | disputes | |
| 2) hyphae | 4) | rhizoids | |
| 6. | Reproduces by budding | ||
| 1) mukor | 3) | penicillium | |
| 2) smut | 4) | yeast | |
| 7. | The agaric fungi include | ||
1) russula
2) butter
3) flywheels
4) boletus
8. Mycorrhiza is
1) fungal disease of rye
2) symbiosis of the fungus with the roots of higher plants
3) the reproductive organ of mold fungi
4) one of the most poisonous mushrooms
9. Mycorrhiza forms
1) mukor 3) boletus
2) champignon 4) ergot
10. Mycelium is represented by one cell in
1) smut 3) penicilla
2) tinder fungus 4) mucor
11. Mukor spores ripen
1) in special balls at the ends of vertical hyphae
2) throughout the mycelium
3) in racemes
1) water and organic matter
2) water and minerals
3) exclusively with water
4) oxygen and carbon dioxide
Choose three correct answers.
16. A sign common to fungi and plants is
1) immobility
2) the presence of rigid cell walls
3) constant growth
4) storage of carbohydrates in the form of glycogen
5) the presence of mycelium
Lichens obtain organic matter through photosynthesis. It is carried out in a temperature optimum from +10 to +25 o. Maximum productivity is observed at illumination from 4000 to 25000 lux. Epigean withstand up to 40 thousand lux; below 4 thousand - lepraria, condellaria. Lichens can carry out photosynthesis processes at both +35 o and -10 o. High temperature stops photosynthesis, if + high humidity is fatal, it falls into a latent state, parts of the thallus die off. For normal photosynthetic activity, the lichen thallus must contain a sufficient amount of water (65-90%). Organic substances synthesized in the thallus by the photobiont are actively used by the photobiont. During photosynthesis, glucose is produced in the cells of the photobiont. It is absorbed by hyphae and turns into polyhydric alcohols (erythritol, valinite, beckons - if cyanobacteria are in the thallus)
An important component of lichen nutrition is nitrogen (especially if there are blue-green algae). Lichens receive a certain part of nitrogenous compounds from the substrate on which they grow, from rain in the form of dissolved compounds, nitrophilic leaves on the rocks of bird colonies - their droppings, from exhaust gases in the form of oxides. Most of the nitrogen is used by the mycobiont, the smaller part is used by the photobiont.
Lichens are not capable of regulating water balance, since they do not have true roots to actively absorb water and protect against evaporation. The surface of the lichen can hold water for a short time in the form of liquid or vapor. In dry conditions, water is quickly lost to maintain metabolism and the lichen passes into a photosynthetically inactive state, in which water can be 2-15% of the mass. Unlike the mycobiont, the photobiont cannot be without water for a long time. The sugar trehalose plays an important role in protecting vital macromolecules such as enzymes, membrane elements and DNA. But lichens have found ways to prevent complete moisture loss. Many species show bark thickening to allow for less water loss; sliming of the thallus (absorption of water 100-3900%). Fast return of water at high insolation. The ability to keep water in a liquid state is very important in cold areas, because frozen water is not usable by the body.
The rhythm of life described above is one of the reasons for the very slow growth of most lichens. Sometimes lichens grow only a few tenths of a millimeter per year, mostly less than one centimeter. Another reason for slow growth is that the photobiont, often making up less than 10% of the lichen volume, takes over the supply of nutrients to the mycobiont. In good conditions, with optimal humidity and temperature, such as in cloudy or rainy tropical forests, lichens grow several centimeters per year. The growth zone of lichens in scale forms is located along the edge of the lichen, in foliose and fruticose forms - at each top.
8. Chemical composition of lichens.
Primary Substances- those substances that are directly involved in cellular metabolism and the body of the lichen is built from them (shells of fungal hyphae, carbohydrate often contain chitin, hyphae contain lichin and its isomer (isoloquinine), sucrose, trihalose, umbilicin, polysaccharide, erythrin, lures, contain pectin substances, enzymes: emilase, catalose, lichenase; nitrogen-containing substances-amino acids: alanine, astoraginic acid, lysine, valine, tryptadine, tryptophan; mycobiont produces vitamins, radioactive: cesium and strontium, and other heavy metals; various substances accumulate in Umbilicaria ( zinc, cadmium, tin, lead).
secondary connections. There are a large number, about 3000. Almost 80 compounds are specific: atranorine, gyrophoric acid, salocic and usnic acid. Most have antibacterial, antitumor properties: drugs: evosine (a mixture of evernive and usnic acid) is used against streptococci, with mastitis; paramycin (evosin 2), (consisting of: atramarin, isodic, caperic and usnic acids) in the treatment of an open form of tuberculosis in humans; sodium salt of usnic acid (binam) is active against streptococci, pneumococci, tuberculosis bacillus; It is used in surgery for the treatment of suppuration of wounds, in plastic surgery, burns of 2-3 degrees, in gynecology.
Most intracellular products, both photo-(phyco-) and mycobionts, are not specific to lichens. Unique substances (extracellular), the so-called lichens, are formed exclusively by the mycobiont and accumulate in its hyphae. Today, more than 600 such substances are known, for example, usnic acid, mevalonic acid. Often, it is these substances that are decisive in the formation of the color of the lichen. Lichen acids play an important role in weathering by destroying the substrate.
