Brown algae are predominantly marine multicellular plants, very large, complexly dissected, attached to the substrate. Currently, about 1500 species of brown algae belonging to 240 genera are known. In the fresh, mostly cold running waters of temperate latitudes, 5 species of brown algae have so far been found. Due to the small size of their thalli and rare occurrence, they remain a poorly studied group of plants, both biologically and ecologically.
A common external sign of brown algae individuals is the yellowish-brown color of their thalli, due to the presence of a large amount of yellow and brown pigments. Thalluses can be microscopic (several tens of micrometers) and gigantic (30-50 m; in some species of the genera Laminaria Lamour., Macrocystis Ag., Sargassum Ag.). The shape of the thalli is very diverse: filiform, corky, saccular, lamellar (solid or with ruptures, outgrowths and numerous holes, smooth or with longitudinal folds and ribs), as well as bushy.
The thalli of brown algae of the order Ectocarpales are most simply organized. In primitive organisms (Bodanella Zimmerm.), the thallus is represented by single-row randomly branching filaments in one plane, tightly adjacent to the substrate. Species of the genus Ectocarpus Lyngb. have bushy thalli formed by single-row ascending, abundantly branching threads, the base of which are creeping rhizoids (Fig. 18.1).
In some representatives of the order Chordariales, the ascending filaments are connected into bundles enclosed in mucus. At the same time, a single-axis type of structure of the thallus is distinguished, in which one thread rises from the base, and other threads branch off from it, running next to it, and a multi-axial type of structure, when a bundle of single-row threads immediately rises from the base. In highly organized brown algae (Laminaria, Fucus Tourn., Sargassum), the thalli are differentiated and resemble flowering plants. They have stem, leaf and root parts, some large representatives have air bubbles that hold the branches in an upright position.
The growth of brown algae is intercalary or apical. In the most primitive forms, intercalary diffuse growth occurs, in more evolutionarily advanced algae, an intercalary growth zone is already outlined. It is usually located in the basal part of multicellular hairs and causes the trichothal growth characteristic of brown algae.
On the surface of single-row thalli of brown algae, multicellular filamentous hairs are formed. At the same time, real and false hairs are distinguished. Real hairs have an intercalary growth zone at the base, where the cells divide frequently and therefore they are smaller, short-cylindrical or disc-shaped. False hairs do not have such a special growth zone and are a continuation of vegetative single-row filaments with strongly elongated cells devoid of chloroplasts.
In the multi-row thalli of brown algae, specialization of cells with the formation of tissues is observed - a parenchymal type of body structure. In the simplest case, a cortex is distinguished from intensely colored cells containing a large number of chloroplasts and special vacuoles - physodes, and a core consisting of colorless, often larger cells of the same shape. In more complexly organized brown algae (Laminariaceae, Fucaceae), the crustal layer reaches a considerable thickness and consists of intensely colored cells of various sizes and shapes (Fig. 18.2). The surface four layers of the cortex are formed by small cells, elongated towards the surface. These upper layers are called meristoderm - dividing integumentary tissue. They are able to actively divide and produce hairs and reproductive organs. Real hairs are located on the surface of the meristoderm scattered or in bundles and are often immersed with their bases in special depressions - cryptostomes. Deeper under the meristoderm lies a cortex of larger stained cells. In the central colorless part of the thallus, two groups of cells can be distinguished. In the center there are loosely or densely arranged threads with strongly elongated cells - the core, large colorless cells - the intermediate layer lie between the core and the bark. The core of brown algae serves not only to transport the products of photosynthesis, but also performs a mechanical function; it often contains thin filaments with thick longitudinal sheaths. Representatives of the order Laminariales differ in the most complex anatomical structure, in which mucous channels develop in the core with special secretory cells for transporting photosynthesis products - sieve tubes and tubular filaments.
The thalli of brown algae are attached to the ground or other substrates and only occasionally, due to mechanical damage, break off and float freely. Attachment organs are usually long outgrowths - rhizoids, in large forms they are massive and are short root-like outgrowths covering the substrate like bird claws. In representatives of the order Fucales and some other algae, the attachment organ is a disc-shaped growth at the base of the thallus - a basal disc, flattened or conical, tightly adhering to the ground.
Branching of brown algae is monopodial. Lateral branches alternate, scattered or opposite. With their rapid growth to the size of the main thread (mother cells), dichotomous branching occurs. Quite often, alternate and opposite branches are located in the same plane and the algae acquire a peculiar pinnate appearance. The correct placement of branches is often masked by secondary branches.
Among brown algae there are species with ephemeral, annual and perennial thalli. The duration of the existence of thalli is greatly influenced by environmental conditions. Perennial thalli of brown algae are of several types. In some algae, the thallus is perennial, every year only the shoots on which the reproductive organs (Fucales) developed, while in others (Laminariales) the trunk and attachment organs are perennial, the lamellar part is annual. In some tropical species of Sargasso algae, only a disk is perennial, which serves to attach the thallus.
Brown algae cells are mononuclear, spherical, ellipsoid, barrel-shaped, mostly cylindrical, elongated or short-cylindrical, disc-shaped, sometimes polygonal or indefinite. They also vary in size. The nucleus is of the usual type for eukaryotes.
The cell wall is bilayered. The inner layer is cellulose, but the cellulose of brown algae differs in its properties from the cellulose of flowering plants and therefore it is sometimes called algulose. The outer layer of the shell is pectin, usually consisting of protein compounds of alginic acid and its salts. Due to this structure, the shell of brown algae can swell strongly, turning into a mucous mass, sometimes of a significant volume. In most brown pectin, the basis of pectin is a gum-like substance - algin (soluble sodium salt of alginic acid), in some - fucoidin.
The contents of neighboring cells of brown algae are communicated through plasmodesmata. In cells with thick membranes (in large thalli), pores are well defined.
Brown algae cells have one large or several small vacuoles. In addition, there are physodes - very small vacuoles (up to 4 microns in diameter) filled with fucosan - a compound similar to tannin. In young cells, the physodes are colorless, in old cells they are colored yellow or brown.
Chloroplasts are parietal, mostly numerous, small, disc-shaped, less often ribbon-like or lamellar. However, as cells age, the shape of chloroplasts may change, and instead of narrow ribbon-like curved cells, numerous disc-shaped chloroplasts may appear. Pyrenoids are present either in the chloroplasts of vegetative cells or only in the chloroplasts of gametes; in a number of species, pyrenoids are absent or rare.
Brown algae are distinguished by a peculiar complex set of pigments. In chloroplasts, chlorophylls a, c (chlorophyll b is absent), β- and ε-carotenes, as well as several xanthophylls - fucoxanthin, violaxanthin, antheraxanthin, zeaxanthin, etc. were found. Fucoxanthin of intense brown color is especially specific among them. Different ratios of these pigments determine the color of brown algae from olive-yellowish to dark brown, almost black.
The assimilation products of brown algae are various carbohydrates soluble in cell sap - kelp (polysaccharide), mannitol (a six-hydric alcohol that plays a significant role in metabolism), as well as oil.
Brown algae have asexual and sexual forms of reproduction. However, vegetative propagation by fragmentation of the thallus cannot be considered unconditional. It is observed only when the torn thalli fall into more or less protected places and continue their vegetation there. At the same time, their lower older parts die off, collapse, and young branches develop into independent plants, which, however, are not attached to the ground. Such plants, floating or lying on the ground, never form organs of sexual and asexual reproduction.
Special buds for vegetative reproduction are found only in species of the genus Sphacelaria Lyngb. (Fig. 18.3).
Asexual reproduction is carried out by mobile zoospores, which are formed in large quantities in one-celled sporangia. In the most simply organized marine and freshwater brown algae (Ectocarpus, Sphacelaria, Pleurocladia A. Br., etc.), single-celled sporangia are spherical or ellipsoid cells that are located as lateral outgrowths of branches (Fig. 18.4, 1). In sporangia, a reduction division of the nucleus occurs, followed by multiple mitotic divisions; chloroplasts divide simultaneously with the nuclei. As a result, a large number of zoospores are formed, which are released through a rupture of the membrane at the top of the sporangium and, after swimming for a short time, germinate into a new, similar in appearance, but already haploid plant. In species of the genus Laminaria, zoosporangia form sori on the surface of the leaf-shaped plate. The sorus consists of paraphyses and zoosporangia (see Fig. 18.4, 2, 5). Paraphyses are elongated cells, with chloroplasts at the upper expanded end, developing on the surface of the thallus between the reproductive organs and serving to protect them. The shell of the paraphysis at the top is strongly mucilaginous, forming a kind of thick mucous cap. Mucous caps of adjacent paraphyses close, resulting in a continuous thick layer of mucus that protects the sorus. Zoosporangia are elongated ellipsoid, with a mucoid membrane at the top. Depending on the species, it develops in zoosporangia by 16-128 zoospores. The first division of the nucleus is reduction. Some brown algae reproduce by immobile, devoid of flagella, spores - aplanospores. Monospores are observed only in species of the order Tilopteridales, tetraspores - in species of the order Dictyotales (Dictyota dichotoma (Huds.) Lamour., see Fig. 18.4, 4).
The sexual process is iso-, hetero- and oogamous. Gametes are usually produced in multilocular gametangia, one in each chamber. Motile cells of brown algae - zoospores into gametes - have a similar structure - they are pear-shaped, with one chloroplast and two flagella attached to the side. One flagellum is longer, pinnate, directed forward, the other is shorter, smooth, flagellate, directed backward. Stigma in motile cells is not always noticeable. The chloroplast of male gametes in oogamy may be colorless.
In the development cycle of most brown algae of the Phaeozoosporophyceae class, there is a change in development forms and alternation of sexual and asexual generations, i.e. gametophyte (sometimes also gametosporophyte, if the same organism can give rise to zoospores and gametes) and sporophyte.
These processes are detailed in Section 3.2.3. Here we dwell only on some features of the development cycles of brown algae. In the most primitive marine brown algae of the order Ectocarpales, an isomorphic change in developmental forms is observed, but there is still no strict alternation of generations. The spores produced by the sporophyte can develop into both gametophytes and sporophytes.
The correct isomorphic change of forms of development is observed in representatives of the order Dictyotales. The most widespread of these is Dictyota dichotoma (Huds.) Lam., which has a forked thallus with flat, usually in the same plane branches without a longitudinal rib (Fig. 18.5).
Algae of the order Laminariales have a heteromorphic change in developmental forms with the obligatory alternation of sporophytes and gametophytes. Their development cycle is characterized by the correct change of a powerful sporophyte and a microscopic, simply arranged gametophyte.
Brown algae that do not have a change in development forms, but only a change in nuclear phases, include representatives of the families Fucaceae, Cystoseiraceae and Sargassaceae. Their normal reproduction is possible only sexually. The sexual process is a typical oogamy. Sexual organs develop in conceptacles (Fig. 18.6). Long hairs grow from the wall of the conceptula - paraphyses, filling almost its entire cavity. Particularly long hairs develop in female conceptacles, where they protrude in the form of a bundle from the opening of the conceptacle. Among these hairs, oogonia and antheridia develop (Fig. 18.7, 1-5). Antheridia are formed in large numbers at the ends of special single-row branched branches growing from the wall of the conceptacle. Two layers are distinguishable in their shell. When the antheridium matures, its outer shell bursts and the antherozoids come out in the form of a package surrounded by an inner shell. In sea water, the inner shell is torn and pear-shaped antherozoids with a large nucleus and orange stigma are released. The oogonia are spherical or ellipsoid, equipped with a three-layered membrane, located in conceptacles on a short unicellular stalk. In the oogonium, 8 eggs are formed, they enter the water, surrounded by two inner layers of the oogonium membrane. When the eggs are completely freed from the shells of the oogonium, fertilization occurs. A fertilized egg develops its own thick shell and immediately begins to germinate, forming a new fucus thallus.
In freshwater brown algae, developmental cycles have not been studied.
There are some differences in views on the classification of brown algae. According to a number of researchers, the Phaeophyta division is divided into 2 classes: Phaeozoosporophyceae and Cyclosporophyceae. Brown algae belong to the Cyclosporaceae, in which the reproductive organs develop in conceptacles and are large in size, allowing them to be seen on preparations with the naked eye. All other brown algae are classified as pheozoospores, many of which reproduce by zoospores. Since the 1930s, there has been a tendency to classify brown algae depending on the characteristics of development cycles. At the same time, it was proposed to divide brown algae into 3 classes: Isogenerate, Heterogenerate, Cyclosporae. The proposed classification has received a very wide distribution. However, the division of brown algae into isogenerate and heterogeneous is rather arbitrary, since in both classes, in separate orders, there are representatives with the opposite type of change in developmental forms. Adhering to the views of domestic algologists, we adopt a classification scheme for dividing brown algae into 2 classes - Phaeozoosporophyceae and Cyclosporophyceae.
The question of the origin of brown algae is still poorly developed. A. Sherfell associated their origin with golden (Chrysophyta). According to A. Pasher, there is a phylogenetic relationship between brown and cryptophytic (Cryptophyta). The peculiar structure of the flagella, together with the brown coloration, allowed M. Shadefoe to unite such large taxa as Pyrrhophyta (where, in addition to peridines, he included cryptophyte and euglena algae), Chrysophyta (to which he included, in addition to golden, yellow-green and diatoms) into one large division of Chromophycophyta algae) and Phaeophyta. According to biochemical properties, of all brown-colored organisms, diatoms are closest to brown algae. It is diatoms and brown algae that are characterized by such common pigments as chlorophyll (also characteristic of peridineans), fucoxanthin (also found in golden algae) and neofucoxanthins A and B. Taking into account the presence of a number of similarities between diatoms, golden algae and brown algae, we join the thought expressed by a number of scientists about the possibility of their origin from close, if not common, monadic ancestors.
According to G. Papenfuss, the original order of brown algae is Ectocarpales. The parenchymal structure of the thallus, apical growth, the oogamous sexual process, and the heteromorphic change in development forms in different groups of brown algae developed independently of each other.
Marine brown algae are widespread in all seas of the globe. Their thickets are common in the coastal waters of Antarctica and the northern islands of the Canadian Arctic Archipelago. They reach their greatest development in the seas of temperate and subpolar latitudes, where, due to the low temperature and high concentration of nutrients, the most favorable conditions for their vegetation are created. Brown algae populate vertically all horizons of the shelf. Their thickets are found from the littoral zone, where they are out of the water for hours at low tide, to a depth of 40-100 (200) m. And yet, the most dense and extensive thickets of brown algae are formed in the upper part of the sublittoral to a depth of 6-15 m. In these places, with sufficient illumination, there is a constant movement of water caused by surf and surface currents, which, on the one hand, ensures an intensive supply of biogenic substances to the thalli, and, on the other hand, limits the settlement of herbivorous animals.
Usually brown algae live on rocky or rocky soils, and only in calm places near the coast or at great depths can they stay on the valves of large mollusk shells or on gravel. Torn off thalli are carried by the current to calm places with a muddy or sandy bottom, where they continue to vegetate under sufficient illumination. Species with air bubbles on the thallus, when separated from the ground, float to the surface of the water, forming large clusters (Sargasso Sea). Among marine brown algae, there are a significant number of epiphytic and endophytic forms.
In the seas of temperate and subpolar latitudes, brown algae reach their maximum development in the summer months, although the rapid growth of their thalli begins in early spring, when the water temperature approaches 0°C. In tropical seas, the mass development of brown is confined to the winter months, when the water temperature drops slightly. Some types of marine brown algae can be found in heavily desalinated areas of the seas with a salinity of less than 5‰.
The role of brown algae in nature is extremely large. They are one of the main sources of organic matter in the coastal zone, especially in the seas of temperate and subpolar latitudes, where their biomass can reach tens of kilograms per 1 m2. In addition, thickets of brown algae serve as breeding, sheltering and feeding grounds for many coastal animals; they also create conditions for the settlement of microscopic and macroscopic algae of other systematic groups.
The economic importance of brown algae is also great, especially as a raw material for obtaining various kinds of substances (for example, alginates - salts of alginic acid, in particular sodium alginate). This substance is widely used to stabilize various solutions and suspensions. The addition of a small amount of sodium alginate improves the quality of food products (canned food, ice cream, fruit juices, etc.), various coloring and adhesive substances. Alginates are used in book printing, in the production of plastics, synthetic fibers and plasticizers, to obtain weather-resistant coatings and building materials. They are found in high quality machine lubricants, dissolvable surgical sutures, ointments and pastes in the pharmaceutical and perfume industries. In the foundry, alginates are used to improve the quality of foundry earth. Alginates are used in the production of electrodes for electric welding, which make it possible to obtain higher quality seams. Brown algae is also used as a raw material for the production of mannitol, which is used in the pharmaceutical industry, in the food industry - for the manufacture of diabetic foods, and in the chemical industry - in the production of synthetic resins, paints, paper, explosives, and leather dressing. Brown algae contain a large amount of iodine and other trace elements, so they are used in the preparation of fodder meal. In fresh and processed form, they are used as fertilizers.
Brown algae have been used in medicine since ancient times. Now more and more new areas of their application are being identified, for example, for the manufacture of blood substitutes, for the preparation of drugs that prevent blood clotting and promote the removal of radioactive substances from the body. Since ancient times, brown algae (mainly representatives of the order Laminariales) have been eaten by humans.
The negative properties of brown algae include their participation, together with other organisms, in the fouling of ships, buoys, and various hydraulic structures submerged in water, which worsens their performance.
The intensive use of wild-growing marine macrophytes, in particular brown algae, has led to the depletion of their natural reserves and has confronted mankind with the need for their artificial cultivation. Therefore, in the last 30 years, aquaculture of algae has developed significantly. In Norway and the UK, not only are species of the genus Laminaria successfully cultivated, but the technology of their production is also being improved. In France, work is underway to acclimatize representatives of the genus Macrocystis. Seaweed aquaculture is intensively developing in the USA. In this case, special attention is paid to Macrocystis pyrifera. In the USSR, research is being carried out on the artificial breeding of Laminaria saccharina (L.) Lam. in the White Sea. Thus, the cultivation of seaweed is becoming industrial in nature and is becoming an increasingly profitable branch of crop production, despite some economic and environmental difficulties.
In fresh waters of temperate latitudes, 5 species of brown algae from the Phaeozoosporophyceae class were found: Bodanella lauterbornii Zimmerm. (order Ectocarpales, family Ectocarpaceae) (Fig. 18.8, 1), Pleurocladia lacustris A. Br. (order Chordariales, family Myrionemataceae) (Fig. 18.8, 2). Heribaudiella fluviatilis (Aresch.) Sved. (order Chordariales, family Lithodermataceae (Fig. 18.8, 3)), Streblonema longiseta Arnoldi (order Chordariales, family Streblonemataceae) (Fig. 18.8, 4). Sphacelaria fluviatilis Jao (order Sphacelariales, family Sphacelariaceae) (Fig. 18.8, 5).
The department of brown algae (Phaeophyta) has about 1500 species.
Brown algae live almost exclusively in the seas(only a few species are found in fresh water bodies). Relatively shallow depth, for most species - 5-15 m, but some species are common to a depth of 40-100 m and even 200 m. Brown algae are included in ecological group of benthic(bottom) organisms.
The precursors of brown algae chloroplasts are bacteria close to Heliobacterium chlorum. The main photosynthetic pigment is chlorophyll a, the auxiliary ones are carotenoids, including brown fucoxanthin and yellow xanthophylls. Auxiliary pigments of brown algae expand the spectrum of light absorbed by them in the blue-green region.
Spare material - starch-like soluble carbohydrate kelp.
Thallus (thallus) - only multicellular. Large, sometimes multi-meter thalli of brown algae are kept afloat thanks to air bubbles located in the thallus. In many representatives of brown algae, tissue differentiation has been outlined. Inside the thallus pass vascular bundles resembling the phloem of higher plants. The appearance of the vascular system is associated with the need to transport nutrients to a multi-meter thallus - from the upper, photosynthetic, parts of the plant to the lower, in which the conditions for photosynthesis are worse.
Rice. The structure of brown algae
In brown algae, there are all forms of sexual reproduction - isogamy, heterogamy and oogamy. There is an alternation of generations, usually heteromorphic. Asexual reproduction - zoospores and pieces of thallus (vegetative reproduction).
Brown algae form entire "underwater forests" at a relatively shallow depth, the coasts of all the seas and oceans of both hemispheres surrounding with a solid wall. These "underwater forests" provide food, shelter, and breeding grounds for a vast array of marine life, including many game fish. After dying, the algae form detritus, which is food for planktonic organisms.
Brown algae are ubiquitous, but the largest species are found in the seas of temperate and northern latitudes.
Rice. 1. Brown algae: a) macrocystis (Macrocystus); c) sargassum (Sargassum); c) fucus (Fucus); d) kelp (Laminaria)
Brown algae is widespread in the Far Eastern seas. kelp (seaweed), the length of the thallus is 5-6 m. Laminaria is used as food by the peoples of Southeast Asia.
Giant brown algae found on the Pacific coast of South America macrocystis. Its huge thallus reaches a length of 50-60 m. It is interesting that it grows in just one season.
On the littoral (exposed at low tide part of the bottom) of the northern seas, extensive thickets form fucus(thallus length up to 2 m).
The South Atlantic (Sargasso Sea) is characterized by huge accumulations of brown algae sargassum."Sargasso" in Spanish means "grapes", and indeed, the groups of air bubbles that keep the thallus of these algae afloat resemble bunches of grapes. Sargassum species living in the Sargasso Sea are the only brown algae that float on the surface of the water, and are not attached to the bottom.
Brown algae cells are covered over a cellulose shell with a layer of a special carbohydrate - pectin, consisting of alginic acid or its salts (alginates). When mixed with water (at a ratio of 1:300), alginates form a viscous solution.
Alginates are used extremely widely:
Hexahydric alcohol is obtained from brown algae mannitol, used as a blood substitute, as a medicine in the treatment of diabetes, as well as in light and chemical industries (in the production of paper, varnishes, paints, explosives and leather dressing).
Brown seaweed kelp (seaweed) is consumed into food.
Brown algae are used and how medicine: as a mild laxative, in the treatment of vascular diseases, as well as a source of iodine and trace elements in diseases of the thyroid gland. Iodine was first obtained from brown algae, and in the past they were the main raw material for its production. Currently, the scale of this production has declined sharply due to the emergence of more cost-effective sources of iodine.
Brown algae can be used as indicators of gold deposits, because they are able to accumulate it in the cells of the thallus.
Brown algae are also used in agriculture - as fertilizer and for livestock feed.
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The thalli of kelp and fucus are the most complex. Their thalli show signs of tissue differentiation with cell specialization. In their thallus, one can distinguish: a bark consisting of several layers of intensely stained cells; core, consisting of colorless cells, often collected in filaments. In kelp, sieve tubes and tubular filaments form in the core. The core performs not only a transport function, but also a mechanical one, since it contains threads with thick longitudinal walls. Between the bark and the core of many brown algae, there may be an intermediate layer of large colorless cells.
The growth of the thallus in brown algae is most often intercalary and apical, less often basal. Intercalary growth may be diffuse or have a growth zone. In large representatives, the intercalary meristem is located at the transition point of the petiole to the leaf blade. Large algae also have a meristematic zone on the surface of the thallus, the so-called meristoderm (a kind of analogue of the cambium of higher plants).
An unusual type of meristem, which is found only in some brown algae, is the trichothallic meristem, the development of cells of which occurs at the base of true hairs. Real hairs are located on the surface of the meristoderm scattered or in bundles and are often immersed at their base in special depressions - cryptosomes.
The flagellar stages in the life cycle of brown algae are represented only by gametes and zoospores. Two unequal flagella attached laterally (spermatozoa Dictyota have only one flagellum). Usually, a long pinnate flagellum is directed forward in brown algae, and a smooth flagellum is directed sideways and backward, but in spermatozoa of Laminaria, Sporochnalia and Desmarestia, on the contrary, a long pinnate flagellum is directed backward, and a short smooth flagellum is directed forward. In addition to three-part mastigonemes, scales and spines are present on a long flagellum; its tip may be spirally twisted. At the base of the smooth flagellum is a basal swelling. Fucus spermatozoa around the flagellum have a peculiar funnel-shaped structure - the proboscis, supported by microtubules of the first root.
The basal bodies of the flagella are located at an angle of almost 110 degrees and are connected by three striated bands. A typical configuration for brown algae is the presence of four microtubule roots. One root consists of 7-5 microtubules, directed towards the anterior end of the cell, where it folds and goes back; the other root consists of 5-4 microtubules and is directed in two directions from the basal body - to the anterior and posterior ends of the cell; two more roots are short, each consisting of one microtubule. There is no rhizoplast in the radicular system. In a number of brown algae, the structure of the radicular system differs from that described.
Soluble alginates are part of the cell wall matrix; sometimes they account for up to 40% of the dry weight of the thallus.
Fucans (fucoidans or ascophyllans) are polymers of L-fucose and sulfated sugars. Their function has not been fully elucidated. They are believed to play an important role in zygote attachment and germination in fucus algae.
Some dictyotes, such as Padina, lime is deposited in the cell walls in the form of aragonite.
In the cells of brown algae, one to many plastids are found. More often chloroplasts are small, discoid, parietal. Their shape can be stellate, ribbon-like or lamellar; the shape of chloroplasts can change with cell age. The chloroplast envelope consists of four membranes; where the chloroplast is located near the nucleus, the outer membrane of the chloroplast endoplasmic reticulum passes into the outer membrane of the nucleus. Periplastid space is well developed. Lamellae trithylakoid; there is a girdle lamella; chloroplast DNA is assembled into a ring.
Only 8 species belonging to the genera are found in fresh waters Heribaudiella, ectocarpus, Sphacelaria, Pseudobodanella, Lithoderma, Pleurocladia and porterinema. Maybe, H. fluviatilis- a common component of river flora, but due to ignorance of this group, it often goes unnoticed in samples.
The role of brown algae in nature is extremely large. This is one of the main sources of organic matter in the coastal zone, especially in the seas of temperate and subpolar latitudes; their thickets serve as food, shelter and breeding grounds for many animals.
Brown algae are used for food, for livestock feed, as fertilizers, for the production of alginates and mannitol. Annual Fee laminaria and close to it algae reaches 2 million tons of wet weight, more than a million tons is produced by the production of its mariculture in China.
Alginates are non-toxic compounds with colloidal properties, which is why they are widely used in the food and pharmaceutical industries. Alginic acid and its salts are capable of 200-300-fold water absorption, forming gels, which are characterized by high acid resistance. In the food industry, they are used as emulsifiers, stabilizers, gelling and water-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, about 30% of the alginates obtained are used in the food industry.
In the textile and pulp and paper industries, alginates are used to thicken paints and increase the strength of their bond with the base. Impregnation of fabrics with some salts of alginic acid gives them water resistance, acid resistance and increases mechanical strength. A number of salts of alginic acids are used to obtain artificial silk. During the Second World War in the USA and England, a large amount of camouflage fabric and nets for residential and industrial buildings was produced from alginic acid and its salts. Alginates are used in metallurgy as a component of molding earth, in radio electronics - as a binding agent in the manufacture of high-quality ferrites, as well as in mining, chemical and other industries.
In the pharmaceutical industry, alginates are used to coat tablets, pills, as component bases for various ointments and pastes, as drug carrier gels. In medicine, calcium alginate is used as a hemostatic agent, as a sorbent that promotes the excretion of radionuclides (including strontium).
In North America, alginates are harvested macrocystis and Nereocystis, species are used on the European coast laminaria and Ascophyllum. By the end of the twentieth century, the annual production of alginates in the world reached 21,500 tons: 12,800 tons in Europe, 6,700 in North America, 1,900 in Japan and Korea, 100 in Latin America. In Russia in 1990, only 32 tons of food sodium alginate were obtained.
Fucoidans are effective anticoagulants, even more active than heparin. Their use for the production of anticancer drugs and antiviral compounds is considered promising. Even at very low concentrations, they can inhibit the attachment of viruses to cell surfaces. Fucoidans are able to form extremely strong and viscous mucus, which is used in obtaining stable emulsions and suspensions.
Mannitol is used as a sugar substitute for diabetics. In addition, it can be used as a plasma substitute for blood conservation.
The cells of many brown algae accumulate iodine. Its content can reach 0.03%-0.3% of the fresh mass of algae, while its content in sea water reaches only 0.000005% (0.05 mg per liter of water). Until the 40s. 20th century brown algae were used to extract iodine.
The energy crisis that has engulfed many countries of the world in recent years has led to the need to search for new non-traditional energy sources. So, in the USA, for this purpose, the possibility of breeding algae is being studied. Macrocystis pyrifera with subsequent processing into methane. It is estimated that from an area of 400 square kilometers occupied by this algae, 620 million cubic meters of methane can be obtained.
In recent years, brown algae have attracted attention due to their ability to release organic bromides (bromoform, dibromochloromethane and dibromomethane) into the atmosphere. The annual release of organic bromides by algae reaches 10,000 tons, which is comparable to the formation of these substances by industry. There is an opinion about the relationship between the release of organic bromides and the destruction of ozone in the atmosphere of the Arctic.
Fossils that may be related to brown algae date back to the late Ordovician (about 450 Ma) and are known as Winnipegia and Tallocystis from the Middle Silurian (425 Ma). But these findings cannot be accurately attributed only to brown algae, since they are also similar to some modern green and red algae. Fossil finds that can definitely be associated with modern brown algae date back to the Miocene (5-25 Ma). it Zonarites and Limnophycus reminiscent of modern Dictyota and others. Molecular methods determine the age of brown algae as 155-200 million years.
Browns are a monophyletic group, but the relationships within it are not fully understood. To date, data on the analysis of the nucleotide sequences of a number of genes, due to their paucity, do not yet reflect the complete picture in the phylogeny of brown algae. Traditionally, the most primitive brown algae were classified as ectocarpus, but the analysis of gene sequences rbc L psa A, psa B and their combinations shows that they are not. In the trees obtained in these studies, ectocarpus are located at the top, and at the base - representatives of the order Ishigeales, which separated early from the common kelp tree.
There is no doubt that brown algae are classified as ochrophytes. Within this division, for a number of features, they have long been considered the closest to golden algae. This view is currently being contested. According to ultrastructural, biochemical features and comparison of the nucleotide sequences of the 16S rRNA gene, brown algae are closest to tribophytic ones. After describing the new class Schizocladiophyceae, a number of studies have shown that it is a sister group to brown algae.
The class contains about 265 genera and 1500-2000 species. The type of thallus organization, the presence or absence of a pyrenoid, the growth method, the type of sexual reproduction (isogamy, heterogamy, oogamy) and the life cycle are used to distinguish brown algae orders. In recent years, in connection with the use of data on the comparison of the nucleotide sequences of a number of genes, the system of brown algae has been actively revised. In different systems, from 7 or more orders are distinguished, differently understanding the volume of orders of Ectocarpales and Fucales. In 1999, F. Rousseau and B. Reviers proposed a broad concept of the order Ectocarpales s.l., which included the orders Chordariales, Dictyosiphonales, Punctariales, Scytosiphonales. At the same time, Ralfsiales and 2004 Ischigeales were excluded from it (this order was described for the genus ischige, previously attributed to the family Chordariaceae). In one order Fucales s.l. it is proposed to combine the orders Fucales and Durvillaeales. In 1998, a new order of brown algae, the Scytothamnales, was described based on plastid features (centrally located stellate cells with pyrenoid) and SSU rDNA data. This new order includes three genera: Scytothamnus, Splachnidium(derived from dictyosiphon) and stereocladon(derived from Chordariaceae).
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Brown algae are representatives of lower plants. The body of a sea vegetable is usually called a thallus, or a thallus. Tissues and organs are absent. Only in some species there is a division of the body into organs. In these plants, scientists isolate various tissues. The multicellular thallus keeps afloat with the help of air bubbles located in the body of the plant. Inside the thallus are vascular bundles. They provide transport of nutrients to all parts of the plant. Among sea vegetables there are champions - the largest algae. Thus, organisms are known whose thallus length exceeds 10 m. Laminaria is attached to various surfaces with the help of rhizoids, or basal discs.
There are several types of growth in algae. Either the plant increases in size due to the top, or all the cells of the body divide in it. In some species, only superficial cells or special zones on the body have the ability to divide. Cell membranes consist of two layers: cellulose and gelatinous. It is the gelatinous layer that includes useful substances, such as carbohydrates, proteins and salts. The cells contain a nucleus, disc-shaped chloroplasts and vacuoles.
Sea vegetables can reproduce in two ways: sexually and asexually. Some species carry out fragmentation of their thallus, others form buds. Spores in brown algae have flagella, that is, they are mobile. They give rise to a gametophyte, which, in turn, forms germ cells, resulting in the formation of a sporophyte. An interesting feature of these plants is the ability to produce pheromones that stimulate the activity of spermatozoa.
Red and brown algae are most often found in salt water bodies, namely in the seas and oceans. They grow at a depth of up to 20 m. Individual species can live at a depth of 100 m. As a rule, they grow in clusters that form a kind of thicket. For the most part, algae live in temperate and subpolar latitudes, but there are species that are found in warm waters. Very rarely, these plants grow in fresh water. Representatives of this department are classified as benthic, or bottom organisms.
Green and brown algae are capable of photosynthesis. Their cells contain chlorophyll - a green pigment, with the help of which the process of absorbing carbon dioxide and releasing oxygen is carried out. In the cells of sea vegetables there is not only chlorophyll, but also yellow, green, brown pigment. It "covers" the green hue of the algae and gives them a brown color. In addition, "color" pigments increase the spectrum of light absorbed by the plant.
One of the most famous representatives of sea vegetables is kelp. It is familiar to every person as seaweed. This plant is used by people for food. Laminaria has a cylindrical stem, or stem. Its length does not exceed half a meter. Leaf plates depart from the stem, the dimensions of which are several meters.
Macrocystis, a giant brown algae, lives on the Pacific coast of Latin America. The length of its thallus is from 50 to 60 meters, and this is not the limit. In the northern seas, you can observe the littoral. This is the part of the bottom that is exposed at low tide. It is here that you can find thickets of fucus. Sargassum lives in the South Atlantic, resembling grapes in appearance. Only this type of algae floats freely on the water surface. All other species are firmly attached to the bottom.
Brown algae form the so-called underwater forests. They resemble a wall built along the coast of all seas and oceans. Such formations play a very important role in the life of many marine life, including commercial fish. In the "forests" of algae, it searches for food, hides from predators, and a large number of organisms reproduce. After the life cycle of the algae ends, the dead plant cells that form detritus serve as food for plankton.
Algae cell walls contain salts of alginic acid. They are widely used in the food industry, in the production of juices, marshmallows, marmalades. Alginates are used in perfumery and medicine. With their help, ointments, creams, pastes and gels are made. In the chemical industry, these substances are used in the synthesis of various fibers, the production of adhesives, paints and varnishes. In addition, with the help of alginic acid salts, print quality is improved. In some cases, sea vegetables serve as indicators of gold deposits, since this substance accumulates in the cells of the plant thallus.
The value of brown algae is great for humans, because these plants can be used as medicines. They are part of mild laxatives, as well as drugs for the treatment of diseases of the cardiovascular system. Algae are an indispensable source of iodine for people suffering from thyroid diseases. An interesting fact is that for the first time iodine was obtained from sea vegetables.
There is another group of brown algae. These plants belong to the order of diatoms. They can take the form of colonies or exist unicellularly. The structure of brown algae is quite interesting. Their body is divided into two halves: epithecus and hypothecus. They are united in a hard shell, with the help of which metabolism is carried out. The shell has silica impregnation. This means that its dimensions are fixed. Due to the inability of the shell to grow, new generations of algae are smaller than their predecessors. Plants reproduce by division.
Most often, diatoms exist in the form of tubular colonies. They take the form of brown bushes and grow up to 20 cm in height. Brown algae live in dark corners, located close to organic matter. That is why they often settle in aquariums, occupying all the free space.
Diatoms appear in new reservoirs. If you find brown spots on the walls of the aquarium after one or two weeks after purchasing it, this is normal. The fact is that the habitat has not yet been inhabited: the water contains a large amount of carbon and organic matter.
If algae settled in an old aquarium, it is worth fighting them. It is necessary to understand what exactly was wrong. First, the aquarium may not be well lit. Secondly, the appearance of diatoms contributes to the increased content of iodine. Thirdly, brown algae are fed from the sand at the bottom of the aquarium, as well as from substrates with silicon. It is necessary to solve the above problems in order to prevent the growth of algae.
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