Yellow-green algae include algae whose chloroplasts are colored light or dark yellow, very rarely green and only sometimes blue. The color of thalli is determined by the presence of the following pigments in the chloroplasts of cells - chlorophylls A And With, β -carotene and xanthophylls. The predominance of the latter determines the unique color of yellow-green algae. In addition, paramylon, oil droplets, and only in some species, lumps of leukosine and volutin accumulate in cells as the main assimilation product. Yellow-green algae do not produce starch. A distinctive feature of yellow-greens is the presence of a monadic structure in vegetative cells and two unequal flagella in zoospores. The cell wall contains cellulose, glucose and uronic acids. The cell wall often consists of two parts.
Reproduction is vegetative, asexual and sexual.
Widely distributed in fresh waters. Rarely found in sea, brackish waters and soil.
Previously, the class Yellow-green algae was called Tribophycean algae after the type genus Tribonema (from the Greek. tribe – skillful, cunning and nema – a thread). About 450 species are known.
Yellow-greens are characterized by significant morphological diversity. Among the numerous representatives of this department, almost all the main types of body structure are found: amoeboid, monadic, palmelloid, coccoid, filamentous, heterofilamentous, lamellar and siphonal (Fig. 44 – 46). Thallus unicellular,
Rice. 44. Appearance of yellow-green algae: 1, 2 – Charatiopsis, 3 – Centritractus, 4 – Ophiocytium
colonial, multicellular and noncellular. The cell membrane is dense, pectin and cellulose, consisting of parts tightly overlapping each other or of two leaves. Silica or lime is deposited in the shell. Mostly immobile forms. Among unicellular species there are mobile forms that lack a dense shell and are equipped with flagella, lobopodia and rhizopodia.
Rice. 45. Appearance of xanthococcal yellow-green algae: 1–3 – Botridiopsis, 4 – Tetrahedriella, 5 – Pseudostaurastrum, 6 – Goniochloris, 7, 8 – Bumilleriopsis
Most yellow-green – immobile organisms. In motile individuals, movement can be carried out using flagella or rhizopodia. Cells of various shapes: spherical, spindle-shaped, ellipsoidal, cylindrical, tetrahedral, sickle-shaped, pear-shaped, ovoid. Thalluses ranging in size from 0.5 – 1.5 µm ( Chloridella) up to several millimeters in diameter ( Botridiopsis) (Fig. 45, 1 – 3) and up to tens of centimeters in length ( Vaucheria) (Fig. 46, 3).
Rice. 46. Appearance of yellow-green algae: 1 – Tribonema, 2 – Heteropedia, 3 – Vaucheria, part of a filament with oogonium and antheridium
Most yellow-green species are phototrophs, but holozoic feeding by ingesting bacteria and small algae is also found. Yellow green algae are widespread in fresh waters. They are also common in soil, less common in marine and brackish water bodies. The class includes aerobiont, planktonic, benthic and periphytonic forms. Epiphytes, epizoites, as well as intracellular symbionts in protozoan cells.
Regardless of the external structure, the internal structure of the cell of yellow-green algae is the same. In the protoplast, several yellow-green chloroplasts are usually observed, having a disc-shaped, trough-shaped, lamellar, less often ribbon-shaped, stellate or cup-shaped with solid or lobed edges. The color is due to the lack of fucoxanthin, which is responsible for the golden and brown color in other ochrophytes. Among other pigments they have β -carotene, voucheriaxanthin, diatoxanthin, diadinoxanthin, heteroxanthin. In motile forms, a red eye, or stigma, is usually located at the anterior end of the chloroplast. Few species have semi-submerged pyrenoids. The nucleus in a cell is usually one, small in size, but there are species with multinucleated cells. In some species, there are one or two contractile (pulsating) vacuoles at the front of the cell.
Monad representatives and motile stages (zoospores and gametes) have two unequal flagella. The exception is synzoospores Vaucheria, in which numerous pairs of smooth flagella of slightly different lengths are located on the surface. The short flagellum ends with an acroneme. Flagella are attached subapically to the cell. In the sperm Vaucheria attachment is lateral.
Species with amoeboid, monadic and palmelloid organization lack a cell wall, they are covered only by a cytoplasmic membrane and can easily change shape. Sometimes “naked” cells are located inside houses, the walls of which can be painted brown with manganese and iron salts. The vast majority of forms have a cell wall consisting of two parts. The cell wall is dominated by cellulose and also contains polysaccharides, consisting mainly of glucose and uronic acids. Young cells have a thin membrane, but with age it thickens. Iron salts can be deposited in it, the compounds of which color it in various shades of brown and red. Most often, silica is present in the cell wall, giving it hardness and shine. It can also be encrusted with lime and be sculptured in various ways (spines, cells, warts, bristles, denticles, etc.) Attached forms can form an outgrowth of the shell – leg with attaching sole.
In filamentous forms of yellow-green algae with bivalve shells, when the filaments disintegrate, the cell membranes fall apart into H-shaped fragments. These fragments are tightly connected halves of the membranes of two neighboring cells (Fig. 47). As filaments grow, an H-shaped fragment of the cell wall of two adjacent daughter cells is inserted between the two halves of the mother cell wall. As a result, each of the daughter cells is half covered with the old membrane of the mother cell and half – newly formed membrane.
Rice. 47. Scheme of the formation of a transverse partition between two daughter cells in filamentous yellow-green algae (according to: A.A. Masyuk, 1993): A– fragment of thread; B– laying of the girdle ring and formation of a transverse septum between two cells; IN– layering of bicuspid cell membranes; G– disintegration of the shell into H-shaped sections
Contractile vacuoles are present in motile representatives. Usually there are 1-2 of them per cell. The Golgi apparatus has a unique structure. Dictyosomes are small, containing 3-7 cisternae. There is one core, less often there are many of them; In coenotic species, the cells are always multinucleated.
Reproduction. Most species of yellow-green algae are characterized by vegetative and asexual reproduction.
Vegetative propagation carried out in various ways: dividing cells in half, disintegrating colonies and multicellular thalli into parts. U Vaucheria Special brood buds are formed.
At asexual reproduction A variety of spores can be formed: amoeboids, zoospores, synzoospores, autospores, hemizoospores, hemiautospores, aplanospores. Zoospores are “naked” and usually pear-shaped.
Sexual process– isogamy, heterogamy and oogamy – described in a few representatives. U Tribonemes gametes are similar in size, but differ in behavior - this is isogamy. U Vaucheria Oogamy is observed: receptacles for female gametes are formed on the threads – oogonia and male – antheridia.
Under unfavorable conditions, the formation of cysts is observed. Cysts (statospores) are endogenous, mononuclear, less often multinucleate. Their wall often contains silica and consists of two unequal or, less commonly, equal parts.
Taxonomy.
At the end of the XIX – beginning of the 20th century various genera of yellow-green algae were classified as green algae, which was primarily due to the color and morphological similarity of the thalli. Currently, the yellow-greens are considered as a class within the ochrophyte division.
About 450 modern species of the class Yellow-green algae are known, which are grouped into four orders: Botridiaceae, Michococcaceae, Tribonemaceae and Vaucheriaceae. The identification of orders is based on the type of differentiation of the thallus and the characteristics of the life cycle.
Order Botridiaceae – Botrydiales. The order includes species with a siphonal type of differentiation of the thallus, in which there is no oogamous sexual process.
Genus Botridium lives on the soil and has the appearance of green bubbles several millimeters in size, attached with the help of colorless rhizoids. The thallus is siphonal, contains numerous nuclei and plastids. The shell is multi-layered and lime can be deposited on it. Reproduction is asexual with the help of biflagellate zoospores, and the entire contents of the bladder disintegrate into mononuclear fragments. When there is a lack of moisture, it reproduces using aplanospores or forms thick-walled cysts. In some cases, the entire contents of the bladder are used to form one large cyst. In other cases, cysts form in rhizoids, where the contents of the bladder first move. Cysts germinate either directly into a new thallus or form zoospores. The sexual process is iso- and heterogamy. The zygote germinates immediately, without a dormant period. Common and widespread species in terrestrial habitats, found along the banks of streams, ponds or on soils devoid of vegetation.
Order Mischococcaceae–Mishococcales. Unicellular or colonial representatives with a coccoid type of differentiation of the thallus.
Genus Charatiopsis includes unicellular attached forms. During reproduction, it forms zoospores, aplanospores and thick-walled cysts (Fig. 44, 1-2).
Genus Ophiocytium(Fig. 44, 4) has elongated cylindrical cells, which can be straight, bent or spirally twisted, and may bear a spike at the end. The cell wall consists of two unequal parts, most of which are involved in cell growth, the smaller part is permanent and has the shape of a lid. Unicellular and colonial species, free-living or attached to the substrate with a small stalk. They reproduce by zoospores and aplanospores, and cysts are also found. They live in fresh waters.
Genus Mischococcus forms tree-like attached colonies. Branching is dichotomous and tetrachotomous. The cells are located in groups of 2 or 4 at the tops of the mucous branches of the colony. The cells are spherical to oval, with a thin or thick cell wall. Sometimes the cell wall is shiny and brown due to its impregnation with iron salts. Young single-celled organisms with a slimy disc-shaped base that serves as a fulcrum for attachment. After the spores are released, the protoplast of the mother cell turns into jelly and stretches, the length becomes 6 times greater than the width, and thus a cylindrical leg appears. The empty cell wall of the mother cell always becomes the base of the stalk. Asexual reproduction by zoospores and autospores. Autospores are attached to the upper edge of the mucous stalk. Subsequent cell divisions repeat the process and produce a tree-like colony. Sexual process – isogamy. They live in small fresh water bodies as epiphytes of filamentous algae. Known in central Europe and Asia.
Order Tribonemales – Tribonematales. Representatives have filamentous, heterofilamentous, pseudotissue and tissue types of thallus differentiation. The cell walls are either with H-shaped overlapping parts or solid.
Genus Tribonema– non-branching threads (Fig. 46, 1). The cells are cylindrical or barrel-shaped. The cell wall consists of two halves, which end up facing each other in the middle of the cell. The shells are often layered. Fragments of threads always end in empty halves of H-shaped fragments of the shell, shaped like a fork. The cells contain several yellowish-green plastids and no pyrenoids. Reproduction is vegetative (by fragmentation of filaments), asexual (zoospores and aplanospores) and sexual (isogamy), with aplanospores being formed more often than zoospores. Can form akinetes. They live in fresh waters, where they develop especially abundantly in the cold season.
Order Vaucheriales. All representatives have a siphonal thallus, oogamous sexual process and synzoospores.
Genus Vaucheria(Fig. 46, 3) has a thallus of noncellular structure; its thallus reaches a length of several centimeters and is attached to the substrate with the help of a colorless rhizoid. There are no partitions in the filaments, most of the thallus is occupied by a vacuole, and numerous nuclei and plastids are located along the periphery in the cytoplasm. Filaments with apical growth and sparse lateral branching. The septa are formed when the thallus is damaged and to separate the reproductive organs. Asexual reproduction is carried out by aplanospores, synzoospores, and akinetes. Synzoospores are formed one at a time in the zoosporangium, which is separated from the vegetative cells by a septum at the end of the filament. Zoospores are multinucleate and multiflagellate. The sexual process is oogamy. The zygote becomes covered with a thick shell and, after a period of rest, grows into a new thallus.
Kinds Vaucheria widely distributed in fresh, brackish and marine waters, as well as in terrestrial habitats. They are found on all continents, including Antarctica. They form grassy-green or dark green tangled masses - so-called mats, smooth, creeping or cushion-shaped. Aquatic, semi-aquatic, terrestrial forms. They live in a variety of habitats: seas, estuaries, estuaries, salt marshes, mangroves, streams, canals, lakes, ponds, arable lands and swamps.
The importance of heterokont algae
From the Heterokont algae department, brown algae are of greatest importance for natural ecosystems and for humans.
Brown algae - main source of organic matter in the coastal zone of the seas. Their biomass in the seas of temperate and subpolar zones can reach several tens of kilograms per square meter. Thickets of brown algae create conditions for the feeding and reproduction of many coastal animals and other algae. Charles Darwin, who observed kelp forests off the coast of South America Macrocystis, wrote: “I can only compare these huge underwater forests of the Southern Hemisphere with the terrestrial forests of tropical regions. And yet, if a forest were destroyed in any country, I don’t think that at least approximately the same number of animal species would die as with the destruction of this algae.”
Thickets of brown algae serve feeding, sheltering and breeding place many animals. Figuratively speaking, brown algae provide other aquatic organisms with a “table, shelter and nursery.”
Brown algae is also widely used by humans. They are rich iodine and other microelements. The peoples of Southeast Asia traditionally use them for food, especially representatives of the order Laminariaceae, from which many different dishes are prepared. Feed meal, prepared from brown algae, increases livestock productivity; at the same time, the iodine content in eggs and milk increases.
From brown algae receive alginates– salts of alginic acid. Alginates are widely used in various industries. These are non-toxic compounds with colloidal properties, so they are widely used in the food and pharmaceutical industries. Alginic acid and its salts are capable of 200–300-fold absorption of water, forming gels that are characterized by high acid resistance. In the food industry they are used primarily as emulsifiers, stabilizers, gelling and moisture-retaining components. For example, dry powder sodium alginate is used in the production of powdered and briquetted soluble products (coffee, tea, milk powder, jelly, etc.) for their rapid dissolution. Aqueous solutions of alginates are used for freezing meat and fish products. In the world, up to 30% of the total volume of alginates produced goes to the food industry.
In the textile and pulp and paper industries, alginates are used to thicken paints and enhance the strength of their bond to the base. Impregnation of fabrics with some alginates gives them protective properties: waterproofness, acid resistance and increases mechanical strength. A number of salts of alginic acids are used to produce artificial silk. During World War II, a large amount of camouflage fabric and nets for residential and industrial buildings was produced from alginic acid and its salts in the USA and England.
Alginates are used in metallurgy: in foundries they improve the quality of molding earth. Alginic acid salts are used in the production of electrodes for electric welding, which make it possible to obtain higher-quality welds. Alginates are also used in the production of plastics, synthetic fibers, paints and weather-resistant building materials. They are used in the manufacture of high-quality lubricants for machines. In radio electronics, alginates act as a binding agent in the production of high-quality ferrites.
The most widely used is water-soluble sodium alginate, which is capable of forming viscous solutions. It is widely used to stabilize a variety of solutions and suspensions. Adding a small amount of sodium alginate to food products - canned food, ice cream - improves their quality. It is also used to make decorative cosmetics, creams and masks in the perfume industry.
In the pharmaceutical industry, alginates are used to coat tablets, pills, as component bases for various ointments and pastes, as gel carriers for drugs, in the production of soluble surgical sutures. In medicine, calcium alginate is used as a hemostatic agent and as a sorbent that removes radionuclides (for example, strontium). The annual production of alginates in the world exceeds 20 thousand tons.
Another important substance obtained from brown algae is the hexahydric alcohol mannitol. Mannitol is used as a sugar substitute for diabetics. In addition, it can be used as a plasma substitute for blood conservation. It is used to make tablets in the pharmaceutical industry. Mannitol is also used in production of synthetic resins, paints, paper, explosives, and leather tanning.
Fucoidans, obtained from brown algae are effective anticoagulants, even more active than heparin. Their use for the production of antitumor drugs and antiviral compounds is considered promising. Indeed, even at the lowest concentrations, fucoidans can inhibit the attachment of viruses to the cell surface. Fucoidans also have the ability to form extremely strong and viscous mucilages, which are used in the preparation of stable emulsions and suspensions.
The energy crisis, which has engulfed many countries around the world in recent years, has led to the need to search for new non-traditional energy sources. Thus, in the USA, the possibility of breeding giant kelp algae is being studied for this purpose. Macrocystis with subsequent processing into methane. It is estimated that from an area of 400 km 2 occupied by this algae, 620 million m 3 of methane can be obtained.
Heterocont algae from the classes Golden, Yellow-green, Sinuraceae, Raphidophyta and Eustigma algae, represented mainly by microscopic organisms, are widespread in fresh water bodies of all climatic zones of the globe, but are more often found in temperate latitudes. Among golden algae, there are species that live in seas and salt lakes, and very few live in polluted waters. Golden algae reach their maximum development in the cold season: they dominate plankton in early spring, late autumn and winter. At this time, they play a significant role as producers of primary production and serve as food for zooplankton organisms.
Some golden algae, e.g. Uroglen And Dinobryon, developing in mass quantities, they can cause algal blooms. They produce aldehydes and ketones, which can give water an unpleasant odor and taste, a Uroglen– fatty acids toxic to fish.
Raphid algae are widely represented in the plankton of fresh water bodies, mainly with an acidic pH, especially in sphagnum bogs, and less often in large lakes. In fresh water bodies, local “blooms” can form Goniostomum. Raphid algae are also found in desalinated sea bays and puddles on the seashore, as well as in the open sea. When they develop en masse in coastal sea waters, they cause toxic “blooming” of water. Thus, off the coast of Canada during a “bloom”, the concentration of cells of the raphid algae Heterosigma can reach 30 million per 1 liter. Outbreaks of raphid algae often lead to the development of “red tides,” which are associated with fish kills. The cause of such “red tides” may be the types of births Hattonella, Olistodiscus, Heterosigma and Fibrocapsa.
Sinur algae, when developed en masse in fresh water bodies, can give the water an unpleasant odor ( Sinura). Pheotamnia algae are found in standing and slowly flowing fresh water bodies, where they settle epiphytically on filamentous algae.
Eustigma algae are found only in fresh water bodies or in soil.
Yellow-green algae are common on all continents, living primarily in fresh water and soil, as well as in terrestrial, brackish and marine habitats. Yellow-green algae inhabit clean and polluted waters, with different pH values: they can live in both acidic and alkaline waters. They are found mainly in clean freshwater reservoirs, less often in seas and brackish waters, preferring moderate temperatures, most often developing in spring and autumn, although there are species found throughout all periods of the year, including winter. Most often they can be found in accumulations of filamentous plants and among thickets of higher aquatic plants in the coastal zone of rivers, ponds, lakes and reservoirs.
The vast majority of yellow-greens are free-living forms, but intracellular symbionts – zooxanthels – are also found in protozoan cells. Marine chloroplasts form an interesting intracellular symbiosis Vaucheria with clam Elision. For nine months, this mollusk is capable of photoautotrophic carbon dioxide fixation in culture. This is the longest symbiosis of this type, when the symbiotic plastid is in direct contact with the cytoplasm of the animal. In nature, mollusk larvae feed on threads Vaucheria. As a result of phagocytosis, algae chloroplasts enter the cytoplasm of the mollusk epithelial cells. During this process, the chloroplast membrane becomes three-layered, and one outer membrane of the chloroplast endoplasmic reticulum (chloroplast endoplasmic reticulum) is lost. This phenomenon provides good evidence that during evolution, as a result of secondary symbiogenesis due to the loss of membranes, chloroplasts with three membranes could arise.
Yellow-green, golden and other heterokont algae are producers of oxygen and organic substances; they are part of food chains. Heterocontophytes participate in the self-purification of polluted waters and soils, the formation of sapropel, and in the process of accumulation of organic substances in the soil, affecting its fertility. They are used as indicator organisms in determining the status of water pollution; yellow-green algae are part of a complex of microorganisms used for wastewater treatment.
Control questions
- Name the characteristic structural features of brown algae.
- Features of the structure of brown algae thalli.
- How do brown algae reproduce? What are monospores, tetraspores and zoospores, isogamy, heterogamy and oogamy?
- What are the life cycles of brown algae? Reproduction of fucus and kelp algae.
- Name the characteristic features and typical representatives of the orders of brown algae.
- In what habitats are brown algae found? What is their significance in nature?
- Economic importance of brown algae.
- Name the characteristic structural features and typical representatives of golden algae.
- What pigments and nutritional types are known in golden algae?
- Reproduction and ecology of golden algae.
- Name the characteristic features and typical representatives of yellow-green algae.
- What pigments and nutritional types are known in yellow-green algae?
- How do yellow-greens reproduce? Types of sexual reproduction: isogamy, heterogamy and oogamy?
- Name the characteristic structural features and typical representatives of sinuric algae.
- Reproduction and ecology of sinur algae.
- Name the characteristic structural features and typical representatives of pheotamnia algae.
- Reproduction and ecology of pheotamnia algae.
- Name the general structural features and typical representatives of raphidophyte algae.
- Reproduction and ecology of raphidophyte algae.
- Name the general structural features and typical representatives of eustigma algae.
- Reproduction and ecology of eustigma algae.
- The importance of heterokont algae in natural ecosystems.
5.2.4. Division Haptophytes - Haptophyta (Prymnesiophyta)
Unicellular, monadic, motile, or, rarely, colonial, filamentous, attached organisms. Haptophytes are similar to heterokont algae in a number of characteristics. There is a cellulose cell wall, sometimes with organic or calcified scales. All representatives of prymnesiophytes have a characteristic organelle - haptonema, or "accessory flagellum".
Cells with one nucleus containing the nucleolus and condensed sections of chromosomes. Chloroplasts, one or two per cell, are golden brown in color, surrounded by 4 membranes, 2 of which are their own. Thylakoids in groups of three. Pigments - chlorophylls A And With, carotenoids. Mitochondria with tubular cristae. The main reserve substance is β -glucan. They have a special organelle - a haptonema, located between the flagella (Fig. 48). The haptonema is a filament with a thickness close to the thickness of the flagella, and varying in length in different species: from 1 to 100 μm. It is based on 6-8 crescent-shaped microtubules surrounded by the EPS channel.
Rice. 48. Diagram of the structure of the flagellar apparatus of prymnesia algae Pleurochrisis(after: S. Hoek van den et al., 1995): 1 – first microtubular root; 2 – second microtubular root; 3 – third microtubular root; 4 – haptonema: 5 – additional microtubules extending from the first root; 6 – additional microtubules extending from the second root; 7 – basal body; 8 – connection between the basal bodies; 9 – connection between the basal body and the haptonema; 10 – connection between the basal body and the root
Apparently, the haptonema in some species of prymnesiophyte algae acts as an attachment apparatus.
Scales. Under the plasmalemma in prymnesiophytes there is a layer of endoplasmic reticulum cisterns, and above the plasmalemma the cells are covered with one or several rows of different scales (Fig. 49, A). Organic scales have a characteristic structure: radially arranged fibrils on the inner surface and concentrically located fibrils on the outer surface. The most primitive scales are considered to be thin disc-shaped or elliptical cellulose-containing plates. They are found in those representatives who do not have coccoliths.
Rice. 49. Prymnesiophyte scales (according to: Belyakova G.A. et al., 2006): A– organic scale; B-D– inorganic scales (coccoliths)
Coccoliths(Fig. 49, B-D)– calcined inorganic flakes; with their help, the buoyancy of cells is regulated and they perform protective functions. Based on the structure and location of formation, 2 types of coccoliths are distinguished: heterococcoliths, which form intracellularly (in the Golgi apparatus), and holococcoliths, which form extracellularly. Holococcoliths consist of regular rhomboid and hexagonal crystals, heterococcoliths have rhomboid crystals.
general characteristics
The cells are usually free-swimming, with two flagella. If the flagella are noticeably unequal, the shorter one is sometimes reduced. Sometimes a longer flagellum with thin non-tubular hairs. Equal flagella are usually smooth, never having tubular hairs - mastigonemes. If the flagella are equal, there are probably more than two. Their body sizes usually do not exceed 30 µm in length; non-motile colonies can reach 8 mm in diameter (for example, macroscopic colonies Theocystis). The shape of the cells varies from round to oval and flattened. In the life cycle of some representatives, filamentous, amoeboid, coccoid and palmelloid stages may be present.
Pigments - chlorophylls A And With, β -carotene.
Most species of prymnesiophytes are phototrophs. Prymnesiophytes are capable of absorbing bacteria and small algae. Phagotrophy is carried out as follows: a particle adheres to the haptonema due to a group of sugars on its surface and moves to its base, where the particle aggregation center is located. The formed large particle moves upward to the end of the haptonema, then the haptonema bends towards the posterior end of the cell, where a digestive vacuole is formed in which the food particle is digested. It is likely that the phosphorus content inside cells affects phagotrophy, and bacterial phospholipids are used as a source of phosphates for prymnesiophyte cells.
Spare assimilation products - paramylon, chrysolamine.
Asexual reproduction occurs through mitotic cell division. The sexual process is anisogamy.
The term algae covers a large group of organisms belonging to lower plants that contain chlorophyll and have a primitive body structure, not divided into stems, leaves and roots, like higher plants. Due to the presence of chlorophyll, a green pigment, they are colored green. But in some cases, this color is distorted by the presence of additional pigments in the cells, such as; phycocyan (blue), phycoerythria (red), carotene (orange), xanthophyll (yellow), etc. Depending on the amount of certain pigments, algae have different colors. [...]
Yellow-green algae are characterized by great morphological diversity.[...]
Yellow-green algae are mainly representatives of plankton, mainly passive plankters; they are less common in periphyton and benthos. Most often they can be found in accumulations of filamentous plants and among thickets of higher aquatic plants in the coastal zone of rivers, ponds, lakes and reservoirs, less often in clear water.[...]
Several types of spores can be found in algae. Many of the green and yellow-green chlorococci have spores that cover themselves with a membrane inside the mother cell. Such spores are called aplanospores. When a particularly thickened shell is formed, they are called hypnospores, since they are capable of remaining dormant for a long period of time. Hypnospores are formed one at a time per cell, but, unlike akinetes, the mother cell membrane does not participate in the formation of their shell. Sometimes aplanospores immediately in the mother cell acquire a shape similar to it. In such cases they talk about auto disputes.[...]
Vegetative cells in such a thallus are of two types: internal, irregularly polygonal in outline, and marginal, somewhat larger and rounded. Each heteropedia cell contains several disc-shaped chloroplasts (this is reflected in the species name). Reproduction is carried out by biflagellate zoospores, which are formed mainly from midline cells. In addition, autospores can also form. Heteropedia is found mainly in moist soil.[...]
Of the algae, the object of research was a marine monoculture from the algae collection created at the Institute of South Sea Biology - a representative of the yellow-green algae (Nephrochloris salina). Rotifers (Brachionus plicatilis plicatilis) were used for toxicological studies.[...]
Among the yellow-green algae there are representatives with a thallus of unicellular (Fig. 188, 1,2,5; 190, 191), colonial (Fig. 189), multicellular (Fig. 192, 1, 2) and noncellular structure (Fig. 192 , 3). In addition, very peculiar algae with a multinucleate thallus in the form of naked plasmodium are known here (Fig. 188, 3).[...]
Red algae also develop abundantly in the upper horizons of the sea, including in the littoral zone. Here they are exposed to strong lighting, and at low tide - to direct solar radiation. In conditions of strong lighting, the color of the purple flowers changes greatly. Brown, yellow, and green tones appear in their color. This is due to changes in the composition of pigments and an increase in the role of chlorophyll. Color change depending on light is a reversible process. Even dry specimens that had lain for some time in the herbarium acquired a more intense color in the absence of light. In the tropics, where insolation is so strong that it is sometimes destructive, many scarlet plants are no longer able to grow in the littoral zone and descend to the sublittoral zone.[...]
The yellow-green department includes algae whose chloroplasts are colored light or dark yellow, very rarely green and only sometimes blue. This color is determined by the presence of the main pigments in the chloroplasts - chlorophyll, carotenes and xanthophylls. However, in the chloroplasts of yellow-green algae, carotenes always predominate, which determines the originality of their color. In addition, their cells lack starch, and droplets of oil accumulate as the main assimilation product, and only in some, in addition, lumps of leukosin and volutin.[...]
Type III. Blue-green algae (Cyanophyceae) include unicellular, colonial and filamentous forms. A distinctive feature of these algae is a peculiar blue-green color, due to the presence of four pigments in their cells: green, blue, red and yellow. Depending on the quantitative ratios of pigments, the color of algae also changes.[...]
Diatoms as a division are not directly related to other divisions of algae. Some individual characteristics, such as the commonality of pigments, the similarity of assimilation products, the presence of a silica shell and resting spores, reveal a distant relationship with the divisions of golden algae (Crybolya) and yellow-green algae. Some algologists even now unite them as classes in the general department Chryvoryla.[...]
Golden algae are a very ancient group of algae that arose from some primary amoeboid organisms. In terms of the set of pigments, the composition of reserve substances and the presence of silicon in the membranes of vegetative cells and cysts, golden algae show similarities with diatoms, yellow-green and partly brown algae. There is reason to believe that it was golden algae that at one time gave rise to diatoms.[...]
Of the soil algae, the most sensitive to oil pollution are yellow-green and diatoms, less so are blue-green algae, especially nitrogen fixers. Oil pollution of soils leads to a sharp reduction in the species composition and number of algae in general and the active part of algal flora in particular. The sterilizing effect of oils on algae is especially pronounced at a depth of 10 - 20 cm. The toxicity of oil and its penetration deep into the soil depends on the type of economic use of the soil and is less pronounced in a meadow than in arable land; with increasing humidity, toxicity decreases.[...]
Yellow-green algae reproduce by simple cell division or the disintegration of colonies and multicellular thalli into separate parts. The sexual process is known in few species and is represented by iso- and oogamy. In some species, in the development cycle, exo- and endogenous cysts with a bivalve, often silicified shell are known (Fig. 189, 3).[...]
Yellow-green algae are distributed throughout the globe. They are found mainly in clean freshwater bodies of water, less often in seas and brackish waters, they are also common in soil; can live in both acidic and alkaline waters; preferring moderate temperatures, they often develop in spring and autumn, although there are species found throughout all periods of the year, including winter.[...]
In the second group of algae, along with chlorophyll a, there is a second chlorophyll, but different from that of green algae, chlorophyll c. There are also carotenoids, including specific ones that are not found in green ones. Carotenoids in the pigment complex of algae of these groups are involved in photosynthesis, thanks to them their color is golden, yellow, brown and brownish-green. Starch in these plants is replaced by other carbohydrates. These include the following departments: golden algae, diatoms, brown algae (Fig. 5). [...]
Therefore, in relation to such algae, it is customary to talk about cyclomorphosis. It can cover several generations or be limited to the period of growth and development of one individual.[...]
In some cases (in green, woolly, brown, and some yellow-green algae) the stigma is located in the chloroplast (Fig. 11, 1, 2), and in others (in euglena, oribatid flagellates) - outside it, in the immediate vicinity from the motor apparatus of the cell (Fig. 11, 3, 4, 5).[...]
They are close to the pigments of blue-green algae, but are not identical to them, as they differ in chemical composition. As has been shown in numerous experiments, the number of pigments in scarlet mushrooms increases with depth; in this case, the amount of phycoerythrin increases to a greater extent than the amount of chlorophyll. Anyone who has collected these algae in nature knows that red-colored algae grow at depth and that in shallow water they change color. As the amount of light increases, they become pale red, then yellow-green, straw-colored, and finally completely discolored.[...]
This class includes yellow-green algae with a siphonal structure, i.e., a non-cellular structure of the thallus. Xanthosiphonova may have a complex shape in appearance, but according to the structure of the protoplast, they all represent one giant multinucleated cell, most often of macroscopic size, visible to the naked eye. As a rule, the xanthosiphon thallus is terrestrial, attached, differentiated into a colored aboveground and colorless underground part. [...]
The distribution pattern of algae changes when moving from one soil-vegetation zone to another. In areas with sparse vegetation cover, algae occupy the free surface of the soil, where they grow quickly and intensively during periods of temporary moisture and favorable temperature. In the Arctic desert and tundra, such films are formed by green, yellow-green and blue-green algae. In the thickness of tundra soils, algae (mainly single-celled green) develop only in the uppermost layers.[...]
Two species from the department of yellow-green algae belonging to the order Heterococcales were discovered: Ellipsoidion solitäre, Pleurochloris magna.[...]
In the vast majority of algae, the shells are solid, although, as in yellow-green, desmidia and diatoms, there are also composite shells made up of two or more parts.[...]
A distinctive feature of yellow-green algae is the presence of two unequal flagella in vegetative cells of a monadic structure and zoospores. It was this feature that at one time served as the basis for calling this group of algae heteroflagellates, or heterokonts (Heterocontae). In addition to differences in length, the flagella here also differ morphologically: the main flagella consists of an axis and ciliated hairs pinnately located on it, the lateral flagella is whip-shaped.[...]
For the germination of algae spores and zygotes, a set of conditions is required, including certain values of temperature, light, and the content of nutrients and biologically active substances. Otherwise they will not germinate. At the same time, the zygotes of some algae, for example fucus, which do not belong to hypnozygotes, remain viable for three to four months. The reproduction and preservation of some algae in unfavorable conditions is facilitated by the formation of cysts. They are known from golden, yellow-green, diatoms and dinophyte algae. One cyst is formed in each cell. The cell contents become rounded and a hard shell containing silica is developed around it. When cysts germinate, one individual is formed, rarely several. [...]
The presence of plasmodial forms in yellow-green algae to a certain extent confirms the family ties of this department with golden algae, since only in these two departments there are representatives with a similar body structure (cf. Myxochrysis paradoxa from the department Chrysophyta).[...]
Visual changes in filamentous algae in a toxic environment can be expressed in a change in their color (chlorosis) with a gradual transition from green to yellow, brown, brown or complete discoloration (albinization). A decrease in cell turgor and the rupture of connections between them under the influence of a toxicant is externally expressed in the softening of filamentous algae, a decrease in their resistance to rupture, homogenization of the plant mass and its transformation into an amorphous pulp. If a substance tends to inhibit (inhibit) the photosynthesis of algae, then oxygen bubbles disappear in the test culture (especially when exposed to bright sunlight), and a lump of algae settles to the bottom. This is clearly visible against the background of the control experiment, in which the algae float up, lifted by bubbles of released oxygen. Substances that stimulate photosynthesis cause the formation of a large number of bubbles (merging into large bubbles) and the floating of a lump of algae. Excess oxygen and corresponding alkalization of the medium lead to chlorosis and destruction of the test culture. Stimulants can also cause rapid growth of the crop and its intensive greening. The final stage of destruction of the test culture is its lysis (the organic mass disappears, and the water turns yellow, brown or brown with secreted pigments). Lysis accelerates when the temperature rises to 25° C and above. [...]
This type includes yellow-green algae, similar in structure to green algae, but without starch.[...]
Less noticeable in the forest are the growths of algae among mosses - on their leaves and stems.[...]
The color of chloroplasts in diatoms has different shades of yellow-brown color depending on the set of pigments, among which brown pigments predominate - carotene, xanthophyll and diatomine, which mask chlorophylls a and c in a living cell. After the cell dies, the brown pigments dissolve in water and the green chlorophyll becomes clearly visible.[...]
The xanthococcal class includes yellow-green algae with a coccoid body structure. Their cells have a real dense shell, consisting of two parts, or a solid one, often sculptured or inlaid. These are unicellular, less often colonial forms, and the latter have the appearance of clusters of cells that are not immersed in mucus and are weakly connected to each other. During vegetative propagation, such colonies do not form threads and plates. Among the xanthococcals there are both free-floating and attached forms.[...]
The total number of algae species found in the soil is already approaching 2000. About 1,400 species, varieties and forms have been found in the soils of the USSR to date, relating mainly to blue-green (438), green (473), yellow-green (146) and diatoms (324) algae (Fig. 39).[...]
In July 2003, the total number of soil algae species in the study area decreased. We identified 19 species: among them there are approximately equal numbers of green and blue-green - 8 (42%) and 9 (48%) and one species each of diatoms (5%) and yellow-green (5%).[...]
The xanthomonad class includes representatives of yellow-green algae with a monad body structure. Their characteristic feature is the presence of two unequal bundles, allowing them to move in the water column. Like the xanthopods, the xanthomonas include a small number of mostly monotypic genera.[...]
The monad structure is very widespread in the world of algae - it is characteristic of many representatives in the divisions of pyrophytic, golden, yellow-green, yellow-green and green algae, and in the first three it is predominant. [...]
In contrast to the internal contents of the cell, its shell in yellow-green algae shows significant diversity. In the simplest representatives, the cell is surrounded only by a thin and delicate periplast, allowing it to produce protrusions in the form of pseudo- and rhizopodia (Fig. 188.2 - 4). But in most species the cell is covered with a real dense membrane, which determines the constant shape of the body. This shell can be solid or bicuspid, with valves of equal or unequal size. In most representatives, the valves are usually difficult to distinguish; they become clearly visible only under the influence of a 60% solution of caustic potassium or when stained.[...]
Under forest vegetation in podzolic and gray forest soils, algae develop mainly in the top layer of soil, as well as in litter. Algal groups of forest soils are uniform throughout the entire zone. They are dominated by green and yellow-green algae, the number of which reaches 30-85 thousand cells per 1 g, and the biomass does not exceed 20 kg/ha. [...]
The most numerous group consists of endosymbioses of unicellular green and yellow-green algae with unicellular animals (Fig. 48, 1). These algae are called zoochlorella and zooxanthellae, respectively. Among multicellular animals, green and yellow-green algae form endosymbioses with freshwater sponges, hydra, etc. (Fig. 48, 2). Blue-green algae form with protozoa and some other organisms a unique group of endosymbioses called syncyanoses; the resulting morphological complex of two organisms is called c and a n o-m, and blue-green algae in it are called c and a-nells (Fig. 48, 3).[...]
In soil samples from the areas of phosphogypsum dumps in May 2004, as well as during the same period in 2003, blue-green and yellow-green algae were absent. In July 2004, Cyanophyta and Xanthophyta were absent. The specific species of this algocenosis were Chloronomala palmelloides Mitra, Scendesmus acutus Meyen.[...]
The phytoplankton of the Nizhny pond was characterized by low species diversity. Representatives of 5 divisions of algae, 14 families and 17 genera were discovered. In total, 20 species of algae were identified: green - 10, euglenophytes - 4, blue-green - 3, diatoms - 2 and yellow-green - 1. The dominant species was Stephanodiscus hantzschii, its biomass varied from 10.32 to 14.60 mg/l.[...]
Approximately the same number of species were identified in air and snow (35 and 39, respectively). In terms of ecobiomorphs, Ch-form algae clearly predominated. These are single-celled representatives of green and yellow-green algae, species of the genera Chlorella, Chlorococcum, Myrmecia, Pleurochloris that tolerate extreme conditions well. Often these species are found on soil lumps or surface deposits (Shtina et al., 1981). Therefore, it is quite possible for these algae to get into the air along with soil particles that are lifted by strong gusts of wind. A pairwise comparison of the snow algal flora of the studied areas of the city using the Sørensen coefficient shows that, unlike soil samples, the snow samples showed great similarity. This pattern appeared regardless of the distance between sampling points.[...]
The Chrysotrichaceae class combines freshwater, less often brackish-water and marine forms. This is the most highly organized group of golden algae, whose representatives are similar in appearance to the ulothrixaceae from the department of green algae and the heterothrixaceae from the department of yellow-green algae. Some of them are similar to the most simply structured representatives of brown algae.[...]
Seedlings grown in the absence of light are called etiolated. Such seedlings, as a rule, are characterized by a changed shape (elongated stems, rotten leaves) and a weak yellow color (there is no chlorophyll in them). At the same time, it has been known since the time of Sachs (1864) that in some cases chlorophyll is formed in the absence of light. The ability to form chlorophyll in the dark is characteristic of plants at the lower stage of the evolutionary process. Thus, under favorable nutritional conditions, pepotry bacteria can synthesize a yellow-green pigment in the dark - bacteriochlorophyll. Blue-green algae, when supplied with sufficient organic matter, grow and form pigments in the dark.[...]
Soil samples from May - July 2004 from the plant territory were characterized by a general decrease in species composition: a total of 12 species and intraspecific taxa were identified, which may be due to an increase in production capacity. In May, there were no yellow-green algae, blue-green algae were represented by 2 species (17%), diatoms - 3 species (25%), green - 7 species (58%). In July, the picture remained virtually unchanged: we identified one species of yellow-green algae (9%), one species of diatoms (9%), 2 species of blue-green algae (18%) and 7 (64%) species of green algae.[ .. .]
Only two species of lichens, representatives of the genus Verrucaria, have the yellow-green algae Heterococcus as their phycobiont. Brown algae are also rare in lichen thalli. The brown algae Petroderma was found in the thallus of one of the species of the same genus Verrucaria.
According to their characteristics (color, structure, methods of reproduction, etc.), algae are divided into several types (divisions): green, blue-green, golden, diatoms, yellow-green, pyrrophytic, euglenic, red and brown algae.
Let's give a brief description of the types.
Green algae - Chlorophyta
Unicellular, colonial, multicellular and noncellular forms. Multicellular forms are represented mainly by filamentous algae. Some are distinguished by a complex internal structure, reminiscent of higher plants in appearance.
Algae are purely green in color, however, in addition to green chlorophyll, the chromatophores contain yellow pigments - carotene and xanthophyll. The cell membrane consists of fiber. Chromatophores with pyrenoids.
Reproduction is carried out by vegetative, asexual and sexual means. Vegetative propagation occurs by dividing the organism into parts. Asexual reproduction is carried out by motile zoospores with flagella of equal size (usually 2-4 of them) or aplaiospores - immobile spores.
With the help of zoospores, green algae not only reproduce, but also disperse. The sexual process of reproduction is varied. Representatives of green algae are Chlamydomonas, Spirogyra, Chlorella, Ulothrpx, Cladophora, Closterium, etc.
Blue-green algae - Cyanophyta
Unicellular, colonial and filamentous forms. Algae have blue-green, yellow-green, olive green and other types of colors. The color is explained by the presence of four pigments in blue-green algae: green chlorophyll, blue phycocyan, red phycoerythryp-pa and yellow carotene. These algae do not have a formed chromatophore and nucleus, flagellar stages and the sexual process are absent. Blue-green algae include: oscillatoria, nostoc, gleotrichia, anabena, etc.
Golden algae - Chrysophyta
Single-celled and colonial forms. They contain chlorophyll and phycochrysipus, which is why the color of representatives of this group of algae is golden or brownish-yellow. The cells are in some cases naked or covered with a poorly differentiated protoplasmic membrane; golden algae are found, the body of which is dressed in a shell or enclosed in a house.
Some forms are mobile and move with the help of flagella, while other forms are immobile in a vegetative state. They reproduce by division or zoospores.
Capable of forming cysts to withstand unfavorable conditions. The sexual process is very rare. Representatives of this type of algae are mallomonas, dinobrion, chrysameba, etc.
Diatoms - Bacillariophyta
Unicellular and colonial organisms with a silicified shell consisting of two halves called valves. Chromatophore I<ел-того или светло-бурого цвета от наличия в нем, кроме хлорофилла, бурого пигмента диатомина. Размножение осуществляется путем деления клеток на две, у некоторых диатомовых наблюдается образование двужгутиковых зооспор. Известен половой процесс. К диатомовым водорослям относятся пинну л я р ия, навикула, плевросигма, гомфонема, сиредра, мелозира и др.
Yellow-green, or heteroflagellate, algae - Xanthophyta, or Heterocontae
These include unicellular, colonial, filamentous and noncellular forms. These algae contain, in addition to chlorophyll, yellow pigments - xanthophyll and carotene; their color varies from light to dark yellow-green. Reproduction occurs by longitudinal cell division, zoospores (they are characterized by the presence of two flagella of unequal size and unequal structure), and autospores. The sexual process is known. Representative: botridium.
Pyrrophyte algae - Pyrrophyta
Unicellular and colonial forms. In addition to chlorophyll, algae contain the pigment pyrrophyll, which gives the algae a brown and brownish-yellow color. The cells are naked or covered with armored membranes. They reproduce by division, zoosiors, autosiors. They form cysts. Sexual reproduction is rare. Pyrrophyte algae include: peridinium, ceracium, etc.
Euglenophyta - Euglenophyta
Unicellular motile forms with one or two flagella, sometimes without them; the cells are bare, the role of the shell is played by the outer layer of protoplasm, sometimes the cell is located in the house. Most algae are green in color, sometimes light green due to the presence of xaptophylla. Reproduction occurs by longitudinal division, the sexual process is unknown. Representatives of euglena algae are euglena and facus.
Red algae, or purple algae, Rhodophyta
They live mainly in the seas, only a few live in fresh waters. These are multicellular algae, colored red.
(with different shades). The color of algae is associated with the presence in them, in addition to chlorophyll, of other pigments - phycoerythrin and phycocyan.
Asexual reproduction is carried out by aplano-spores. The sexual process is very complex and is characterized by the presence of male organs - antheridia and female organs - oogonia, or carpogones.
The representative is batrachospermum.
Brown algae, Phaeophyta
The name was given due to the yellow-brown color of the thallus, caused by the presence, in addition to green chlorophylls, of a large number of brown carotenoid pigments. Multicellular, predominantly macroscopic algae (the largest organism living in water is the brown algae macrocystis, which reaches a length of 60 m, growing by 45 cm per day).
Reproduction is vegetative, asexual and sexual. Gametes and zoospores bear two flagella on the side, different in length and morphology. Brown algae are widespread in all seas of the planet; they often form underwater forests, reaching their greatest development in the seas of temperate and subpolar latitudes, where they are the main source of organic matter in the coastal zone. In tropical latitudes, the largest accumulation of brown algae is in the Sargasso Sea. Representatives of only a few genera live in desalinated and fresh waters, for example, Pleurocladia, Streblonema, Lithoderma.
Yellow-green algae
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Xanthophyceae P.Allorge ex Fritsch, 1935 |
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Yellow-green algae(lat. Xanthophyceae, or Xanthophyta), or Multiflagellate algae(lat. Heterocontae), or Tribophyceae(lat. Tribophyceae) - a class of lower plants, including algae, the chloroplasts of which are colored yellow-green or yellow. Representatives are unicellular, colonial and multicellular, mainly freshwater organisms. Similar to golden algae, the division of yellow-green algae into classes is based on the variety of morphological organization of the thallus. Class named after type genus Tribonema(from Greek tribe- experienced, skillful, nema- a thread).
Cell structure
Flagella
Monadic representatives (zoospores and gametes) have two flagella of unequal length and morphology: the main flagellum has feathery ciliated hairs, the lateral flagellum is whip-shaped. The exception is synzoospores Vaucheria, in which numerous pairs of smooth flagella of slightly different lengths are located on the surface. Flagella are attached subapically to the cell (in sperm Vaucheria lateral attachment). Mastigonemes are synthesized in cisterns of the endoplasmic reticulum. The short flagellum ends with an acroneme.
The basal bodies of tribophycean flagella have a typical structure, located at right angles to each other. The radicular system is represented by a cross-striated root - rhizoplast and three microtubular roots, each of which consists of 3-4 microtubules.
Chloroplast
The chloroplast has a structure typical of ochrophytes. Typically, a cell contains several green or yellow-green disc-shaped plastids. Their color is due to the absence of fucoxanthin, which is responsible for the golden and brown color of other ochrophytes. Among the carotenoids in Tribophyceae there are α- and β-carotenes (predominant), vocheriaxanthin, diatoxanthin, diadinoxanthin, heteroxanthin, lutein, violaxanthin, neoxanthin, etc. Chlorophylls - a And c. In the cells of Tribophyceae, in addition to disc-shaped ones, there are plastids of other forms: lamellar, trough-shaped, ribbon-shaped, cup-shaped, stellate, etc. In a few species, pyrenoids of the semi-constricted type were found. The ocellus consists of a number of lipid globules, located at the anterior end of the body in the chloroplast, oriented towards the basal swelling of the flagellum.
Cell wall
Species with amoeboid, monadic and palmelloid organization lack a cell wall, they are covered only by a cytoplasmic membrane and can easily change shape. Sometimes “naked” cells are found inside houses, the walls of which can be painted brown with manganese and iron salts. The vast majority of tribophyceae have a cell wall that is solid or consisting of two parts. In its composition, studied by Tribonema And Vaucheria, cellulose predominates and contains polysaccharides, consisting mainly of glucose and uronic acids. Young cells have a thin membrane, but with age it thickens. Iron salts can be deposited in it, the compounds of which color it in various shades of brown and red. Most often, silica is present in the cell wall, giving it hardness and shine. It can also be inlaid with lime and be sculptured in various ways (spines, cells, warts, bristles, denticles, etc.). In attached forms, an outgrowth of the shell may form - a leg with an attaching sole.
In filamentous algae with bivalve membranes, when the filaments disintegrate, the cell membranes fall apart into H-shaped fragments, which are tightly connected halves of the membranes of two neighboring cells. As filaments grow, an H-shaped fragment of the cell wall of two adjacent daughter cells is inserted between the two halves of the mother cell wall. As a result, each of the daughter cells is half covered with the old membrane of the mother cell and half with the newly formed membrane.
Other structures
Contractile vacuoles are present in motile representatives. Usually there are 1-2 of them per cell, sometimes more. The Golgi apparatus has a unique structure. Dictyosomes are small, containing 3-7 cisternae.
Reserve nutrients are oils, some have volutin, chrysolamine and leukosin.
Core
There is one nucleus, less often there are many nuclei; in coenotic representatives the cells are always multinucleated. The details of mitosis have been studied in detail only in Vaucheria. Its mitosis is closed, with centrioles located at the poles outside the nucleus. No kinetochores were found. During anaphase, the interpolar microtubules of the spindle greatly elongate, which leads to a significant distance between the daughter nuclei and each other. The nuclear membrane is preserved, so in telophase the daughter nuclei have the shape of a dumbbell. It is believed that such mitosis is not typical for the entire group of Tribophyceae.
Reproduction
Most yellow-greens have vegetative and asexual reproduction. Vegetative propagation is carried out by dividing cells in half, disintegrating colonies and multicellular thalli into parts. During asexual reproduction, amoeboids, zoospores, synzoospores, hemizoospores, hemiautospores, autospores, and aplanospores can be formed. Zoospores are “naked” and usually pear-shaped with two flagella. The sexual process (iso-, hetero- and oogamous) is described in a few representatives.
When unfavorable conditions occur, the formation of cysts is observed. Cysts (statospores) are endogenous, mononuclear, less often multinucleate. Their wall often contains silica and consists of two unequal, or less often, equal parts.
Ecology
Tribophyceae are found on all continents, including Antarctica. They live mainly in fresh waters of temperate latitudes, are also common in soil, and are less common in terrestrial, brackish-water and marine habitats. They inhabit both clean and polluted waters, with varying pH values, but are rarely found in abundance. Tribofyceous algae are significantly more diverse and abundant in soils, where, developing in masses, they can cause a “blooming” of its surface. Aerophytic representatives are found on tree trunks, rocks, and walls of houses, sometimes causing them to turn green. They often live in accumulations of filamentous algae and aquatic higher plants along the banks of rivers, ponds, lakes and reservoirs.
Yellow-green algae are included in various ecological groups - plankton, less often periphyton and benthos. The vast majority of them are free-living forms, but intracellular symbionts - zooxanthellae - are also found in protozoan cells. Seaweed chloroplasts form an interesting intracellular symbiosis V. litorea with clam Elysia chlorotica. For 9 months, this mollusk is capable of photoautotrophic carbon dioxide fixation in culture. This is the longest symbiosis of this type, when the symbiotic plastid is in direct contact with the cytoplasm of the animal. In nature, mollusk larvae feed on threads Vaucheria. As a result of phagocytosis, algae chloroplasts enter the cytoplasm of the mollusk epithelial cells. During this process, the chloroplast envelope becomes three-layered, and the outer membrane of the chloroplast endoplasmic reticulum is lost. This phenomenon can serve as evidence that in the process of evolution, as a result of secondary symbiogenesis due to the loss of membranes, chloroplasts with three membranes could arise.
Meaning
Tribophycean algae are producers of oxygen and organic substances and are part of trophic chains. They participate in the self-purification of polluted waters and soils, the formation of silts and sapropels, and in the process of accumulation of organic substances in the soil, affecting its fertility. Their economic importance comes down to their use as indicator organisms in determining the state of water pollution; they are part of a complex of microorganisms used for wastewater treatment.
Phylogeny
At the end of the 19th - beginning of the 20th centuries. various genera of Tribophyceae were classified as green algae, which was primarily due to the color and morphological similarity of the thalli. But A. Pascher already included this group in the same evolutionary series with golden algae and diatoms. This point of view was subsequently confirmed in studies at the cytological, biochemical and molecular level. Currently, Tribophyceae are considered as a class within the Ochrophytae division. From tribophyceae, eustigmatophyceae were isolated in the rank of the same class, but, as it turned out, in evolutionary terms they are far from each other. In phylogenetic trees built on the analysis of nucleotide sequences of a number of genes, tribophyceae among ochrophytes are much closer to brown algae than to golden algae, diatoms, sinuraceae and eustigmatophyceae.
Diversity and systematics
About 90 genera and more than 600 species have been described, which are grouped into 6-7 orders (H. Ettl, 1978). The identification of orders is based on the type of differentiation of the thallus and the characteristics of the life cycle. The number of orders depends on the point of view on coenotic tribophycean algae: whether they are classified as one or two orders.
These algae contain, in addition to chlorophyll, yellow pigments - xanthophyll and carotene; their color varies from light to dark yellow-green. less often green and for some – blue. Representative: botridium.
Yellow-green algae are organisms at different stages of morphological differentiation of the thallus, – unicellular, colonial and multicellular. Among them there are predominantly coccoid, palmelloid or filamentous structures, less often – amoeboid, monadic, siphonal, heterofilamentous and lamellar.
Motile forms of yellow-green algae (including zoospores) are characterized by the presence of two flagella of unequal size (lateral – short, flagellated and anterior – long with mastigonemes) and yellow-green color of chromatophores. Spare products – volutin, fat, often chrysolamine. In primitive forms, the cell contents are surrounded by a thin periplast, while in more highly organized representatives there is a pectin or cellulose shell (solid or bicuspid). The cell membrane is often impregnated with iron salts, silica, lime, and has various “sculptural decorations”.
The protoplast of a cell contains several chromatophores, which can be disc-shaped, plate-shaped, ribbon- or cup-shaped or star-shaped. One or many cores. Some species have pyrenoids. Stigma is noted in mobile forms.
Yellow-green algae can reproduce by longitudinal cell division, the disintegration of colonies or filaments into separate sections, and also by zoo- or aplanospores. The sexual process (iso- or oogamy) is known to few. To withstand unfavorable conditions, some species form cysts with a slightly silicified bivalve shell.
Yellow-green algae are distributed throughout the globe. They are found mainly in clean freshwater bodies of water, less often in seas and brackish waters, they are also common in soil; can live in both acidic and alkaline waters; preferring moderate temperatures, they most often develop in spring and autumn, although there are species found throughout all periods of the year, including winter.
Yellow-green algae are mainly representatives of plankton, mainly passive plankters; they are less common in the periphytope and benthos. Most often they can be found in accumulations of filamentous plants and among thickets of higher aquatic plants in the coastal zone of rivers, ponds, lakes and reservoirs, less often in clear water.
The importance of yellow-green algae as phototrophic organisms lies primarily in the creation of primary production in water bodies and their participation in the food chain of aquatic organisms. Yellow-green algae, along with many others, form sapropel (silt). Living in bodies of water rich in organic residues, they can serve as indicative forms in determining the degree of water pollution. In soils, they actively participate in the accumulation of organic matter, helping to increase fertility.
Yellow-green algae are a group that has not yet been sufficiently studied. Its origin has not been reliably determined. At present, the prevailing opinion is that they are an independent department, since they show a clearly defined parallelism of forms with golden and green algae, the separation of which into independent departments no one doubts. Undoubtedly, yellow-green algae are related to golden algae and diatoms.