Yellow green algae characteristics. Lecture: Department of yellow-green or heteroflagellate algae
These algae are characterized by the following pigments: chlorophylls a, c, e (chlorophyll b is absent), P-carotene, e-carotene, xanthophylls: antheraxanthin, lutein, zeaxanthin, neoxanthin, violaxanthin, voucheriaxanthin, heteroxanthin, diadinoxanthin, diatoxanthin. The cell usually contains two lamellar chromatophores, which lie in the endoplasmic reticulum tank, which is in direct connection with the nuclear membrane; trithylakoid lamellae are located in the chloroplast matrix; almost always (xanthophyceae) there is a girdle lamella (absent in eustigmatophyceae); the internal pyrenoids of xanthophyceae contain trithylakoid lamellae. The eye (stigma) is part of the plastid (xanthophyceae) or the stigma granules are located outside the plastid (eustigmatophyceae).
Reserve products: volutin, fat, often chrysolamine; starch is not formed. The longer flagellum bears mastigonemes, the shorter flagellum is smooth. Cell membranes often consist of two or more parts; cysts (statospores), like those of golden algae, are endoplasmic, their membranes are fossilized.
In Fig. Figure 22 shows diagrams of monad cells of yellow-green algae.
In most modern systems, two classes are distinguished: xanthophyceae and eustigmatophyceae.
This class includes algae at various stages of differentiation of the thallus: monadic, rhizopodial, lalmeloid, coccoid, filamentous, siphonous. In accordance with the types of organization of the thallus, orders are distinguished that are parallel to the orders of golden, dinophyte, and green algae. The order Heterochloridales unites monadic forms, the order Rhizochioridales includes rhizopodials, the order Helerogloeales - palmelloids, the order Mischococcales - coccoid, the order Tribonematales - filamentous, the order Bo(rydiales) - siphonous seaweed.
The last three orders are discussed below.
Order Mischococcales
The order includes numerous unicellular and colonial coccoid forms. Cells of various shapes are covered with a cell wall, often consisting of two parts. Reproduction by zoospores or aplanospores.
The genus Botrydiopsis (Botrydiop.sis) is widespread in freshwater bodies of water (ponds, ditches, etc.), represented by single spherical cells, covered with a cell membrane, under which there is a wall cytoplasm containing numerous disc-shaped chloroplasts, and in mature cells - many cell nuclei. The center of the cell is occupied by a large vacuole with cell sap, intersected by thin strands of cytoplasm. Drops of oil and clumps of chrysolaminarin are scattered in the cytoplasm. Reproduction by zoospores and autospores, which are formed in large quantities in the cell (up to 300). In B. arrhiza, during zoonospore formation, as in many other yellow-green algae (Characiopsis, Tribonema, Bothridium, etc.), along with typical zoospores, synzoospores are often observed (see also Chapter 4).
Order Tribonemales-Tribonematales
Unites filamentous forms. The genus Tribonema, widespread in fresh waters, can be considered as a representative. The thallus is represented by an unbranched filament composed of one row of cells.
Cylindrical, often slightly barrel-shaped cells, usually mononuclear, mostly contain several chloroplasts. In the cytoplasm there is fat, chrysolamine. The cell wall always consists of two halves, with their edges facing each other in the median plane of the cells. Each half of the shell is made up of a number of overlapping layers.
Even before the division of the cell nucleus (at the interphase stage), a new cylindrical piece of the membrane is laid in the equatorial region under the old cell membrane - an intermediate ring. At a later stage of mother cell division, during cytokinesis, a transverse septum is formed in the middle of this hollow cylinder. The new shell, which has an H-shape in its longitudinal optical section, when growing, pushes both older halves of the mother cell wall apart from each other, inserting itself between them. In this way, the membranes of neighboring cells are connected to each other; accordingly, each cell is surrounded by two halves of adjacent H-shaped figures. When reproductive cells are released or under the influence of certain agents (for example, strong chromic acid), the cell membrane disintegrates into H-shaped sections. Fragments of threads always end in empty halves of H-shaped figures, which in profile look like two points. Reproduction of filaments, continuously growing due to transverse cell divisions, is carried out vegetatively - by fragmentation and asexually - through zoospores, amoeboid cells, aplanospores, akinetes.
Order botridial-Botrydiales
Unites xanthophycean algae, which have a siphon organization.
Representatives of the genus Botrydium live on damp soil. The thallus is siphonic, differentiated into an aerial part in the form of a spherical pear-shaped bladder with a diameter of 1-2 mm, and a rhizoidal part immersed in the substrate, usually branched. This normal form of the thallus can vary noticeably depending on external conditions. For example, when botrydium is cultivated immersed in water, thalli in the form of branched threads are observed. The wall is multilayered, with cellulose microfibrils differently oriented in each layer. The cytoplasm is concentrated in the wall layer and surrounds a continuous vacuole with cell sap. In the adult thallus, the cytoplasm contains numerous nuclei; in the aerial part, there are abundant disc-shaped chloroplasts with pyrenoids and other organelles. Reproduction is carried out by mononuclear zoospores with two heterokont and heteromorphic flagella, which appear when the bladder is immersed in water (after rain, etc.). Synzoospores were also observed. Then settling along the edge of the puddle, on the drying soil, the zoospores develop into new plants. In drier weather, aplanospores are formed instead of zoospores. Upon reaching a certain internal maturity, botridium enters the dormant stage. Russian researcher V.V. Miller, who studied the genus Botridium in detail in culture, described various methods for the formation of resting cysts. In some cases, the entire contents of the bladder give rise to one large cyst with a thick shell. V.V. Miller called such cysts “macrocysts” (B. walirothi, B. tuberosum, B. pachidermum). In other cases, the contents of the aerial part are divided to form many multinucleated sporocysts (B. walirothi). Finally, all or part of the contents of the bladder can pass into rhizoids and form rhizocysts there. The latter are either arranged in many rows, for example, in B. granulatum, or the contents pass into the swollen ends of rhizoids, in each of which a cyst is formed, for example in B. tuberosum. The same species may have different forms of cysts, which, under different external conditions, replace each other. All forms of cysts do not require a period of rest for their germination; they can germinate immediately after their appearance. Small cysts (rhizocysts, sporocysts arranged in a row) either directly germinate into new individuals or form zoospores. Large cysts (macrocysts, formed individually by rhizocysts of B. tuberosum) usually germinate with zoospores or aplanospores. In none of the studied species of Botridium B. V. Miller did not observe the sexual process. However, there is data from other authors about the existence of a sexual process in B. granulatum, which is iso- and heterogamous in different races. These data need confirmation
In the genus Vaucheria (both freshwater and marine and saltwater species are known), the thallus is in the form of branched siphon threads, forming cotton-like accumulations in the water or extensive dark green tufts on moist soil. The growth of filaments is apical. In the vegetative filaments of the voucheria, starting from the apex, three zones can be distinguished: apical, subapical and vacuolated. The apical segment is an actively growing part of the siphon thallus: there are numerous vesicles and mitochondria; chloroplasts and cell nuclei are absent. The vesicles contain fibrous material, possibly a precursor of the cell wall material (cellulose). In the subapical zone, the number of vesicles decreases, chloroplasts and cell nuclei appear. The chloroplasts are numerous, disc-shaped, and lack pyrenoids. The bud-shaped pyrenoid is observed only in Woucheria seedlings. Associated with each cell nucleus is a pair of centrioles, which during prophase of mitosis migrate to opposite poles of the elongating nuclei. The nuclear envelope remains intact during mitosis, an intranuclear spindle is formed inside it, and there are no centromeres; between diverging chromosomes, the nuclear envelope is laced and surrounds the telephase daughter nuclei. Normal mitosis occurring inside the shell of the maternal nucleus was observed by L. I. Kursanov (1911) in a number of Voucheria species. In all studied species, L.I. Kursanov noted an interesting distribution of nuclear divisions along the thread: having begun in one place, mitoses little by little spread to neighboring areas, etc. Thus, on a preparation that records a certain moment of this process, we get what can best be called a wave of divisions, where individual division phases, successive in time, along the thread are located in the correct sequence. In the apical and subapical zones there is still no central vacuole. Only in the older - vacuolated - part of the thread does a vacuole with cell sap appear (Fig. 23, A). Reproduction is asexual, through synzoospores and aplanospores.
The formation of synzoospores, their release, sedimentation and germination were traced in Vaucheria fontinalis at the electron microscopic level (Fig. 23.5 "-E). When a synzoospore is formed at the somewhat swollen end of the filament, the central vacuole disappears, and all organelles accumulate here. Associated with cell nuclei, pairs of centrioles form internal flagella. Cell nuclei and internal flagella are grouped around the emerging vesicles, into which the flagella protrude. The vesicles migrate to the surface of the protoplast and merge with the plasmalemma. Thus, the flagella reach the surface of the future synzoospore.
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.
The department of golden algae (Chrysophyta) includes about 400 species.
Set of photosynthetic pigments in golden algae almost the same as that of brown, diatoms and pyrophytic algae. Most golden algae have a monad shape, i.e. they are unicellular, motile and equipped with 1-2 flagella. Usually monads are naked (there is no cell wall), but many species carry calcareous bodies under the cell membrane - coccoliths or an internal skeleton of silica (Fig. 1). Reproduction is asexual (by division and zoospores). The sexual process is known only in a few species.
Habitats
Golden algae live mainly in clean fresh waters; characteristic of acidic waters of sphagnum bogs. Until recently, golden algae were considered primarily a freshwater group, but they have turned out to make a significant contribution to the productivity of marine phytoplankton. Distributed throughout the globe, but are more common in temperate latitudes.
It is not easy to study golden algae, since many representatives of the department, in particular coccolithophores (Fig. 1a), are very small organisms with a diameter of about 25-30 microns, so they are not captured by the usual planktonic network, and the structure of coccoliths can only be studied using an electron microscope.
Coccolithophores are important in the formation of bottom calcareous sediments (chalk consists of 50-75% of their skeletons - coccoliths). In addition, they prevent the greenhouse effect by binding excess carbon dioxide in the form of calcium carbonate when building “houses” from coccoliths.
Golden algae are one of the oldest groups of algae. Representatives of golden algae were found already in Cambrian sediments about 500-600 million years old. It is possible that golden algae are the ancestors of diatoms and brown algae.
Rice. 1. Golden algae: a-d) coccolithophores; d-g) silicoflagellates
Department of yellow-green algae
The department of yellow-green algae (Xanthophyta) includes about 500 species of unicellular, colonial, multicellular and noncellular algae. A set of photosynthetic pigments of yellow-green algae is represented by chlorophyll A, chlorophyll With and carotenoids, but unlike golden algae, representatives of this department do not have fucoxanthin.
Golden algae are found in reservoirs with fresh and salt water, as well as on land - in the soil, on stones; are an important component of both plankton and benthos.
The most famous representative of the department is voucheria, or water felt(Vaucheria), lives in fresh, brackish and sea waters. Has a noncellular thallus, i.e. It is one giant multinucleated cell. When reproducing asexually, Voucheria forms multiflagellate, multinucleated zoospores. The sexual process is pronounced oogamy (Fig. 2).
Rice. 2. Life cycle of Vaucheria: a) asexual reproduction; b) sexual reproduction; 1 - mother plant; 2 - zoosporangium; 3—zoospore release; 4 - zoospore; 5—zoospore germination; 6 - antheridium; 7 - oogonia; 8 - sperm; 9 - egg; 10 - zygote
9. Yellow-green algae. General characteristics. Orders.
Yellow-green algae can have unicellular flagellated, coccoid, filamentous and siphonal forms. Chloroplasts are disc-shaped. Contains chlorophyll a and c pigments, carotenoids. Reserve substances - glucan, fats. They reproduce by cell division or sexually (isogamy, oogamy).
Main representatives: Rhizochloris, Chlorothetium, Tribonema, Botrydium.
10. Brown algae. Structure, reproduction, classes, main representatives, distribution, significance
The department of brown algae (about 1,500 species) includes numerous macroscopic algae, the common external feature of which is the yellowish-brown color of their thalli, due to the presence of yellow and brown pigments. Mostly disc-shaped chloroplasts contain chlorophylls a and c, carotenes and xanthophylls. The pyrenoids are very small. Spare nutrients - laminarin, mannitol (sugar alcohol), and in small quantities - fat. In addition to the usual organelles, the cells contain physodes, structures containing tannins. The cell membranes on the outside are mucilaginous - pectin, the inner layer is cellulose.
The type of structure of the thallus of brown algae is predominantly lamellar, often very complexly organized, and rarely multi-filamentous. The vast majority of representatives of this group are marine forms.
Thallus of brown algae range in size from several tens of micrometers to tens of meters (macrocystis - up to 50 m). In highly organized forms, the thalli are differentiated and resemble flowering plants. Some large representatives have air bubbles. All brown algae grow attached to soil or other algae. For attachment, they form rhizoids or a basal disk. In a cross section of large thalli of brown algae, zones are distinguished, occupied by cells of different structures, specialized to perform individual functions.
The cells are mononuclear, covered with thick membranes with large pores. The shell consists of an inner cellulose and outer layer, the basis of which is proteins combined with alginic acid and its salts. Algulose. Physodes. Chloroplasts are usually small, disc-shaped, less often ribbon-shaped and lamellar. A number of taxa have a pyrenoid in their chloroplasts. In chloroplasts, thylakoids are grouped into lamellae of 3. Pigments: chlorophyll a, c, carotenoids. Reserve nutrients in cells outside chloroplasts are laminarin (a polysaccharide) and mannitol (six-hydroxy alcohol), and lipids in small quantities.
Reproduction. At B.V. All main types of reproduction are found - vegetative, asexual and sexual. Vegetative propagation occurs when branches are accidentally separated from the thallus; these branches do not form organs of attachment and do not form organs of asexual and sexual reproduction. Reproductive organs are formed on them if their development has already begun by the time the thallus is detached from the ground. Asexual reproduction is carried out by zoospores (there are species that reproduce by mono- or tetraspores). The structure of zoospores. Pear-shaped zoospores have two unequal flagella on the side: the anterior one is long, the posterior one is short. The formation of zoospores and gametes in brown algae occurs in containers of two main types: single-locular and multilocular. Meiosis occurs when spores form in single-locular sporangia. The sexual process is isogamous, heterogamous and oogamous. All brown algae, with the exception of Fucus, have alternating generations; in the asexual generation (sporophyte) in zoosporangia (or tetrasporangia), after reduction division, zoospores (or tetraspores) are formed; from them grow haploid sexual plants (gametophytes), dioecious or bisexual. After fertilization, the zygote develops into a new asexual diploid plant (sporophyte) without a dormant period. In Fucus, the entire life of algae occurs in the diploid phase; only sperm and eggs are haploid, before the formation of which reduction division occurs.
Depending on the nature of the alternation of generations and the change of nuclear phases, brown algae are divided into 3 classes.
Class Isogeneratae
In most algae of this class, the sporophyte and gametophyte are the same in shape and size or do not differ very sharply in size. The sexual process is iso-, hetero- or oogamous. Representatives of the genus Ectocarpus are widespread in the seas; There are especially many of them in cold seas. They grow in the littoral and sublittoral zones. They participate in the fouling of ships and buoys. They look like small bushes or tufts, consisting of abundantly branching single-row filaments, often ending in colorless multicellular hairs. The growth of filaments is intercalary. Single-celled zoosporangia form on the sides of the branches. In them, reduction division and a number of divisions of the cell nucleus occur and the formation
many zoospores that emerge from the zoosporangium, after swimming for a short time, germinate into a plant of the same appearance, but haploid. On it, on short lateral branches, multicellular gametangia are formed, in which gametes that are identical in shape and size, but differ in behavior (+ and -) develop. The zygote, without a dormant period, grows into a new diploid thread with a zoosporangium. Ectocarpus is characterized by an isomorphic change of generations. The sexual process is isogamy.
Cutleria- distributed along the European shores of the Atlantic Ocean and the Mediterranean Sea. It has the appearance of dichotonically branched multilayered ribbons up to 20 cm in length, ending in hairs. Externally, cutleriaceae differ from other algae by the presence of a fringe of delicate hairs at the top or along the edge of the thallus. At the base of the hairs, on some specimens large-celled macrogametangia develop, producing biflagellate macrogametes; on other specimens, small-celled microgametangia develop, yielding microgametes. After fertilization, the zygote develops without a rest period into a new diploid plant - a sporophyte, which has the shape of a multilayer plate or crust, tightly pressed to the substrate. It is so unlike a gametophyte that it has been described under the new generic name Aglaozonia. On its upper side, unicellular zoosporangia develop, in which zoospores are formed after reduction division. Zoospores germinate into a ribbon-shaped bushy gametophyte. The genus Cutlaria is the most famous. She serves as an example of a heteromorphic change of generation; her sexual process is heterogamy.
Dictyota grows mainly in tropical and subtropical seas, and is also found in the Black Sea. It is characterized by a forked-branched thallus with branches located in the same plane. The height of the plant is about 20 cm, the width of the branches is 4-8 mm. Dictyota has an isomorphic alternation of generations. On the sporophyte, large spherical tetrasporangia develop from the surface cells, in which, after reduction division, 4 haploid, immobile, naked tetraspores are formed. From tetraspores, male (with numerous antheridia, producing up to 30,000 sperm) and female (with oogonia, producing one egg) gametophytes develop. Mature eggs fall out of the oogonia. After fertilization, the zygote develops into a new sporophyte. Dictyota is an example of the development of algae with an isomorphic change of generations, in which the sexual process is oogamy.
Class Heterogeneratae
In the development cycle of algae of this class, a macroscopic (in many powerfully developed) sporophyte and a microscopic small gametophyte alternate, which is often called a prothallus by analogy with ferns. The sexual process is isogamous or oogamous. Sporophytes of different genera differ sharply and are the largest lower plants, reaching a length of 60-100 m with significant morphological division and a complex anatomical structure. Sporophytes are divided into leaf blade, petiole and rhizoids or basal disc. At the junction of the plate and petiole there is an intercalary meristem. The sporophyte is perennial, with the exception of the plate, which dies off annually and is replaced by a new one. In the meristoderm of the plate, before its destruction, unicellular zoosporangia are formed. In each zoosporangium, after preliminary reduction division, from 16 to 64 (sometimes 128) zoospores are formed. Billions of zoospores are formed on one algae specimen. After a short period of movement, the zoospores germinate into microscopically small filamentous male and female gametophytes (prothallus). Antheridia produce one sperm, and oogonia produce one egg. After fertilization, a new powerful sporophyte gradually develops from the zygote.
So, heteromorphic alternation of generations is characteristic of heterogenate algae. The sexual process is oogamy.
Laminaria, species of the genus are widespread in the northern seas. The thallus is divided into leaf blade, trunk and rhizoids. It is found vertically from the sea surface to a depth of 200 m.
Macrocystis, growing at a depth of 10-20 m, has a multi-branched trunk up to 50-60 m long. In front of each plate, the branch is usually expanded into a pear-shaped air bubble. Thanks to air bubbles and long branches, the main part of the macrocystis thallus floats at the surface of the sea. It is mined throughout the world and processed into alginates and other chemical products.
Nereocystis It is represented by a long trunk (petiole) up to 15-25 m, which gradually expands upward, carries at the end a bubble with a diameter of 12-20 cm, from which narrow plates extend (up to 9 m).
There are 24-40 such plates in total. Nereocystis grows at depths of up to 20 m, while the upper part of the trunk with a bladder floats near the surface.
The life cycles of the above representatives are similar. Zoosporangia form on leaf blades.
Class Cyclosporeae
This class includes brown algae, which do not have an alternation of generations, but only a change in nuclear phases: the entire algae is diploid, only the gametes are haploid. There is no asexual reproduction. The class contains only one order - Fucus.
Fucuses have leathery, olive- or yellow-brown, dichotonically branched, belt-like thalli 0.5-1 m long, 1-5 cm wide; some have swellings filled with air. Apical growth.
By the time of sexual reproduction, bean-shaped yellowish swellings are formed at the ends of the branches - receptacles, on which the genital organs are located. Gametophytes develop on the receptacles in the form of a layer lining the depressions (conceptacles or scaphidia). Gametangia form in depressions in a layer of cells that arises from a single cell called the conceptaculum initial cell or prospore. The lining layer of the conceptaculum developing from the prospore is the gametophyte. Fucus gametophytes form vertical branched and simple mononuclear multicellular filaments, some of them bear gametangia, and the rest serve as paraphyses.
Oogonia in Fucus sit directly on the surface of the gametophyte. Antheridia are formed at the ends of branched branches. Developing oogonia (8 eggs) and antheridia (64 sperm) are excreted with mucus
they shoot outward from the concentaculum, here the germ cells are released from them. Fertilization occurs in the surrounding water. The fertilized egg grows into a new plant without a dormant period.
Genus fucus (Fucus) distributed in the northern seas, it is the main inhabitant of the coastal zone.
Sargassum - “leaves” are lamellar or subulate. The trunk is short, long branches carrying receptacles extend from its upper part; these branches die off annually. Representatives are distributed mainly in tropical and subtropical seas. Sargassum is used to produce alginates; some species with non-rigid leaves are used as food. In the Sargasso Sea on an area of 4.4 million square meters. km swim two species of sargassum, which reproduce vegetatively and do not have organs of attachment.
Isomorphic or heteromorphic variants of the haploid-diploid life cycle or isomorphic and heteromorphic change of generations. Life cycles of the genera Ectocarpus, Laminaria, Fucus, Conceptacula, Receptacula or Scaphidia.
Distribution and ecology of B.V. Almost exclusively marine plants. They are distributed everywhere from the Arctic to the Antarctic. But the largest species grow mainly in temperate and subpolar latitudes. Representatives of the department grow mainly in shallow water and predominate on rocky coastal substrates in cold regions of the globe. but they are also found at depths of up to 200 m. Species that have air bubbles become free-floating when separated from the ground and sometimes (for example, in the Sargasso Sea) form large accumulations on the surface of the water. The most powerful thickets of B.V. form in waters rich in nutrients. Many large algae are widely used as livestock feed and to fertilize fields (rich in potassium). Some types of kelp are used as food; in addition to food, they also have dietary value, because rich in iodine and useful for atherosclerosis. Previously, iodine was extracted from kelp. Brown algae is used in significant quantities to produce algin, which has great adhesive ability and is used in the production of paper, cardboard, and printing inks. Algae is collected with special harvesting machines, and those thrown ashore are also used.
Yellow-green algae are widespread throughout the globe, especially in clean fresh water bodies. But they are also found in brackish, acidic and alkaline waters, and are also common in soil. Most yellow-green algae are planktonic organisms. They can often be found in accumulations of filamentous algae and among thickets of higher aquatic plants near the banks of rivers, ponds, and lakes.
Many of the yellow-green algae were at one time classified as green because of some similarities with them. However, yellow-green algae differ from green algae in important ways: their mobile forms have flagella of different lengths and structures. The main flagellum consists of an axis and pinnately located ciliated hairs, and the lateral flagellum is short and smooth. It is because of this feature that yellow-green algae are also called heteroflagellates. In motile forms, there is a red eye at the anterior end of the chromatophore.
The chloroplasts of yellow-green algae contain chlorophylls a And c, a- and b-carotene and three types of xanthophyll pigment: lutein, violaxanthin and neoxanthin. Depending on the combinations of these pigments, the cells are colored light or dark yellow, less often green, and in some cases blue. Starch is not formed in the cells of yellow-green algae. Instead, oil accumulates, and in some species, the carbohydrates chrysolaminerin and volutin. The cell walls of these algae are varied - from thin, allowing the cell to form pseudopodia, to dense cellulose, whole or bivalve, often encrusted with lime, silica or iron salts.
Vegetative reproduction in yellow-green algae is carried out by longitudinal cell division, while asexual reproduction is carried out by zoospores and aplanospores. The sexual process - iso- or oogamy - is known in few species.
1 – botridium; 2 – peridinium; 3 – ceratium
Botridiopsis eriensis(Botrydiopsis eriensis) is a representative of yellow-green algae, a unicellular organism widely distributed throughout the globe. It lives in the soil, at the bottom of the coastal zone of water bodies, among thickets, in the biological film of biofilters of treatment plants. It is usually found in small quantities, but sometimes, when developed en masse, it gives the water or the surface of the substrate a delicate yellow-green color.
Botridiopsis can be easily detected by taking a pinch of any soil during an excursion to the forest, meadow, or river. It must be placed in a Petri dish, moistened and sterile cover slips placed on its surface, on which algae grow well. The dishes are kept in the light at room temperature and, as the algae grows on the slides, they are examined under a microscope. Botridiopsis cells that can be seen on glass can be young, small, about 6 µm in diameter, with two chloroplasts, or adult, large, up to 18 µm in diameter, with a double-circuited, sometimes yellowish shell and with many chloroplasts. You can also see cells filled with autospores and covered with a swollen mucus membrane.
Myxochloris(Myxochloris) is a yellow-green algae that lives in the cells of the leaves of sphagnum mosses. Its body is a large multinucleate plasmodium. In the fall, myxochloris forms cysts, from which in the spring zoospores or amoebas emerge, penetrating the empty cells of moss leaves and merging there into plasmodium.
Tribonema green(Tribonema viride) is a filamentous yellow-green algae, widespread in various bodies of water. Its threads, collected in cotton wool-like tufts, form yellow-green clusters in the coastal strip, soft to the touch, but not slimy. Young tribonema filaments remain attached to the substrate for a long time with the help of a basal cell, but later it dies; the threads break off and form clusters that float on the surface of the water or sink to the bottom of reservoirs.
Under a microscope, Tribonema can be easily distinguished from other filamentous algae by the characteristic outline of the ends of its filaments. Since the Tribonema cell wall is strong and bicuspid, the rupture of the filaments during asexual reproduction occurs in the middle of the cells. In this case, the zoospores come out, and the remaining shell takes the form of two horns on each marginal cell. When unfavorable conditions occur, aplanospores with a thick bivalve shell, filled with drops of oil and fat, are formed in the tribonema filaments.
Botridium(Botrydium). In summer, on the damp soil of the banks of reservoirs, along the ruts of forest roads, along the edges of drying puddles, you can see many dark green shiny bubbles 1–2 mm in diameter, reminiscent of scattered beads. Each such bubble is a cell of the yellow-green algae botridium. Downwards, the cell gradually narrows and turns into branching colorless rhizoids, immersed in the soil. There is a vacuole in the center of the cell; in the near-wall layer of the cytoplasm there are small nuclei, numerous chromatophores and oil droplets. It is believed that this type of organization of the thallus is siphonal, or non-cellular.
During rain, when the botrydium is filled with water, numerous zoospores are formed inside the bubble, emerging from the hole in the upper part. It's like a volcanic eruption. Zoospores settle in water, settle on moist soil and develop into new plants. When there is no rainfall for a long time and the soil dries out, the contents of the aerial part of the botridium form aplanospores or flow into rhizoids and there disintegrate into cysts. When moistened, the cysts either germinate into new individuals or form zoospores.
In ponds, rivers, and lakes you can also find planktonic yellow-green algae, which have cells of various shapes, and various outgrowths and decorations of the shells.
Diatoms
Diatom pinnularia: view from the girdle side (1), from the suture side (2), opened cell (3), cross section through the cell (4), 5 – cyclotella; a – hypotheca, b – epitheca, c – suture, d – nodule, e – chromoplast, f – pyrenoids, g – cytoplasm, h – nucleus, i – vacuole
The diatom division includes more than 10,000 species of algae, represented exclusively by unicellular or colonial forms. Diatoms are distributed throughout the globe and are widely represented in the plankton and benthos of the seas and oceans, as well as various fresh water bodies, even hot springs with water temperatures above 50 °C. These algae can also be found in high bogs, on mosses, on stones and rocks, and in the soil. Sometimes they can develop en masse on the surface of snow and ice, turning them brown. F. Nansen, while sailing on the Fram, observed the appearance of brown spots (accumulations of diatoms) on the ice, under which the ice quickly melted.
Most of the diatom cell is filled with a vacuole, and the cytoplasm is located in a thin layer along the walls. But the nucleus is usually located in the center of the cell, in a special cytoplasmic bridge. The cytoplasm contains lamellar or granular chloroplasts, which contain chlorophylls A And With, as well as carotenoids and xanthophylls, which give the algae a yellow or yellow-brown color. But after dying, the diatom cells turn green, because... chlorophyll breaks down later than other pigments. The reserve nutrients of diatoms are oils deposited in the cell in the form of droplets, as well as volutin and chrysolamine.
Diatoms differ sharply from other unicellular algae in that a silica shell, consisting of two halves that fit on top of each other like a lid on a box, is tightly adjacent to the plasmalemma of the cell on the outside. Each such half consists of a flap (“bottom”) and a belt ring welded to it. If you look at a diatom cell in profile, you can see that the belts are on top of each other.
Cells of various diatoms can have (when viewed from the bottom) either radial or bilateral symmetry. This feature is systematic - the first are classified into the Centric class, and the second are classified into the Cirrus, or Pennate class.
Many planktonic forms of diatoms also have various projections on their shells, which increase the surface area and facilitate soaring in the water column. Cells of a number of species can connect with each other using these outgrowths, forming colonies.
Diatoms reproduce by vegetative cell division, which occurs especially intensively in the spring. During division, the mass of the protoplast increases, and both halves of the shell move away from each other. The nucleus divides mitotically, then the protoplast splits in half in a plane parallel to the valves. After this, the daughter cells of unicellular diatoms disperse, but in colonial ones they remain connected by their valves.
Each new protoplast inherits half of the shell from the mother cell, and the second is formed anew. It is interesting that in both daughter cells this new half will be smaller (“box”), while the old one in any case becomes a “lid”. As a result of a series of successive divisions, the size of the cells in the population progressively decreases.
Diatoms are diploid organisms; only the gametes formed immediately before the sexual process, which can occur in the form of iso-, hetero-, or oogamy, are haploid. The resulting zygote immediately, without a rest period, sharply increases in size and forms auxospore– “growing spore” (from the Greek “auxo” - increasing, growing). After the completion of growth and maturation of the auxospore, a new cell develops in it, which first forms a large (outer) and then a smaller (inner) half of the shell. The size of such cells is significantly larger than the parent ones - thus, the sexual process leads to the restoration of the size of cells that were crushed as a result of vegetative propagation.
Diatoms play a large role in the silicon cycle in nature: as already mentioned, in the World Ocean they annually extract from the water and use up to 150-109 tons of silica to build their shells, and when they die, they form special geological rocks - diatomites. Having high porosity and low specific gravity, diatomites are widely used in various industries - they are used to make lightweight bricks and are used as an additive to various types of cement. The dome of Hagia Sophia in Istanbul is covered with diatomite tiles. Diatomites have found wide application as a filter material in the production of various oils, fats, in the sugar and chemical industries.
To be continued