Department Golden algae (photos, characteristics and descriptions of individual species you will find in this article) is known, perhaps, mainly only to biologists. Nevertheless, its representatives play a very important role in nature. Golden algae is one of the ancient groups of algae. Their ancestors were primary amoeboid organisms. Golden algae are similar to yellow-green, diatoms and partially brown algae in terms of a set of pigments, the presence of silicon in cell membranes, and the composition of reserve substances. There is reason to believe that they are the ancestors of diatoms. However, this assumption cannot be considered fully proven.
Department Golden algae: general characteristics
The plants we are interested in are distinguished by significant morphological diversity. Golden algae (their photo is presented above) are both unicellular and multicellular, colonial. In addition, among the golden algae there is a very peculiar representative. Its multinucleated thallus is a naked plasmodium. Thus, golden algae are very diverse.
The structure of the cells of these organisms is characterized by the presence of a different number of flagella. Their number depends on the species. Usually there are two, but it should be noted that some types of golden algae have three flagella. The third, motionless, is located between two mobile ones. It is called a gantonema and is characterized by an extension at the end. The function of the gantonema is that with its help the cell is attached to the substrate.
Coloring
Golden algae is a department that includes predominantly microscopic species. Their chloroplasts are usually golden yellow in color. Of the pigments, chlorophyll A should be noted. In addition, chlorophyll E was found, as well as many carotenoids, including carotene and a number of xanthophylls, mainly golden fucoxanthin. The color of the representatives of the department of interest to us may have different shades, depending on the predominance of one or another of these pigments. It can be from greenish-brown and greenish-yellow to pure golden yellow.
Meaning and reproduction
Golden algae, whose species are numerous, are phototrophic organisms. Their significance lies mainly in the creation of primary production in reservoirs. In addition, they are involved in the food chain of various hydrobionts, including fish, golden algae. Their species improve the gas regime of various reservoirs where they grow. They also form sapropel deposits.
Department Golden algae is characterized by the reproduction of its representatives with the help of simple cell division, as well as with the help of decaymulticellular thallus or colonies into separate parts. Scientists also know the sexual process, which is a typical autogamy, hologamy or isogamy. As a result of the reproduction process, endogenous siliceous cysts appear, differing in such a basis as the nature of the sculpture of their shell. These cysts perform an important function - they help algae survive adverse conditions.
Proliferation of golden algae
Golden algae are distributed throughout the world. However, most often they grow in temperate latitudes. These plants live mainly in clean fresh waters. Golden algae are especially characteristic of sphagnum bogs with acidic waters. A small number of these organisms live in s alt lakes and seas. They are much less common in polluted waters. As for soils, only a few of their species live in them.
The department Golden algae includes representatives of several classes. Below we briefly describe some of them.
Class Chrysocapsaceae
Its representatives are distinguished by the presence of a complex thallus, which is represented by a mucous structure. Chrysocapsaceae include colonial forms, non-motile, passively floating or attached. The cells of these organisms have neither flagella nor superficial protrusions. They are united into a single whole by the common mucus of the colonies, usually located in its peripheral layers, but can also be located in the central part.
Class Chrysotricaceae
This class includesgolden algae having a lamellar, filamentous and multifilamentous structure. All these organisms are multicellular, typically benthic, attached. Their thallus is represented by branched or simple, single or multi-row filaments, disc-shaped parenchymal plates or bushes. They are not immersed in common mucus.
This class combines freshwater forms, less often marine and brackish water. Chrysotrichaceae are the most highly organized group of organisms among all golden algae. Its representatives are similar in appearance to the ulothrix, belonging to the department of Green algae, as well as to the heterotrix, belonging to the department of Yellow-green algae. Some of the Chrysotriaceae resemble some of the simplest brown algae.
Chrysosphere class
This class includes golden algae, whose body structure is coccoid. The cells of these organisms are covered with a cellulose membrane. Tourniquets and rhizopodia are completely absent in representatives of this class. These plants are unicellular, non-motile. Less common are colonial forms, which are clusters of cells that are loosely connected to each other and not immersed in a common mucus. They do not form plates or filaments when they reproduce.
Class Chrysophycea
This class combines golden algae with different types of thallus organization. It is his device that is the basis on which the following orders are distinguished in this class:rhizochrysidal (having a rhizopodial structure), chrysomonadal (modal forms), chrysocapsal (palmelloid forms), feotamnial (filamentous), and also chrysosphere (coccoid forms). We invite you to get acquainted with the individual orders of this class.
Chrysomonadal (otherwise - chromulinal)
This is the most extensive order, uniting golden algae with a monadic structure, both colonial and unicellular. The taxonomy of chrysomonads is based on the structure and number of flagella. Of particular importance is the nature of their cell covers. There are single and double flagella forms. Previously, it was believed that the first ones are the most primitive, the initial ones. However, the electron microscope helped scientists to discover that the supposedly single-flagellar forms have a second lateral flagellum of a small size. The researchers suggested that biflagellated chrysomonads with heteromorphic and heterocont flagella could have been the source, and single-flagellated forms appeared as a result of the subsequent reduction of a short flagellum.
As for the cell covers of representatives of chrysomonadal, they are different. There are naked forms, dressed exclusively with plasmalemma. Cells of other species are enclosed in special cellulose houses. On top of the plasmalemma of the third is a cover consisting of silicified scales.
With the help of cell division, the process of reproduction of chrysomonads is carried out. Some species also have a sexual process.
It should be noted that chrysomonads are mostly freshwater organisms. Most often they live in clear waters. chrysomonadsare usually found in the cold season, in late autumn and early spring. Some organisms live under the ice in winter. However, as scientists have found out, the temperature of the water is not so important for them. It has only an indirect meaning. The chemistry of the water is the decisive factor. It changes throughout the year: in the cold season, the water contains more nitrogen and iron as a result of the absence of other vegetation. Most chrysomonads live in plankton. They have special adaptations for leading a planktonic lifestyle. Some representatives of chrysomonads color the water brown, causing it to "bloom".
We invite you to get acquainted with the Ochromonas family, which belongs to this class.
Ochromonas family
We continue to consider the department of Golden algae. Representatives of the Ochromonas family - various naked forms. Their cells are covered only by a cytoplasmic membrane that has one or two flagella (unequal).
Chode Ochromonas
Algae of this genus usually live in neuston or freshwater plankton. They are rarely found in brackish waters. This genus is represented by solitary golden cells with two heteromorphic and heterocont flagella. Ochromonas is a naked cell, dressed on the outside only with a cytoplasmic membrane. The cytoskeleton, consisting of microtubules located peripherally, maintains its teardrop shape. In the center of such a cell there is a cell nucleus. It is surrounded by a nuclear membrane consisting of two membranes.
Lamellar chromatophores (there are two of them) are enclosed in an extension that exists between the membranes of the nuclear envelope. Their ultrastructure is typical of the department to which they belong. A large vacuole, together with chrysolaminarin, is located in the back of this cell. Mitochondria are scattered in the cytoplasm, the Golgi apparatus is located in front of such a cell. Flagella extend from its anterior end. There are two of them, they are not the same in length.
G. Buck studied the origin of mastigonemes and the fine structure of Ochromonas danica (golden algae). Photos with names help to visualize certain types of organisms. In the photo above - Ochromonas danica algae. This species is convenient for determining the dynamics of development of mastigonemes. The fact is that its cells have one interesting feature - they easily lose their flagella, after which they form them again. This makes it possible to examine the material at various stages of regeneration of their flagellar apparatus.
Rod Mallomonas
Its representatives usually live in freshwater plankton. This genus is the richest in terms of species. The cells of its representatives are different in shape. They are covered with scales with bristles or silicified scales. Mallomonas caudata (pictured above) is one of the largest species in this genus. The ultrastructure of the contents of setae, scales, and cell contents, as well as the mechanism of their formation, release, and subsequent deposition on the cell surface, is described in detail for it. However, research of this kind is stillrelatively few.
Let's briefly talk about the flagella of such a representative of the Mallomonas genus as M. caudata. He has two of them, but one is distinguishable only in an optical microscope. This flagellum has a normal structure. It bears 2 rows of hairy mastigonemes. In a light microscope, the second flagellum is indistinguishable, which protrudes a short distance from the cell. A cover of scales hides it.
Rod Sinura
This genus is characterized by ellipsoidal or spherical colonies consisting of pear-shaped cells. In the center of the colony, they are connected by their posterior ends, sometimes very long. From the cytoplasmic membrane outside the cells are dressed with silicified scales. These scales are spirally arranged, they overlap each other in a tiled pattern. The ultrastructure and shape of these scales, like those of Mallomonas, are of great taxonomic significance. For example, in a representative such as S. sphagnicola (pictured above), the basal plate examined in a transverse section is flat, that is, it has the same thickness. Small perforations permeate it. The apical thickened edge is present at the anterior margin. The basal margin is curved. It surrounds the basal plate, forming something like a staple in this golden algae. Its representatives have a hollow spike, bent outwards. It is attached at some distance from the front edge of the plate. The time is at its base.
As for the other members of the department like the Goldenalgae, the structure of their scales is somewhat more complicated. This applies in particular to S. petersonii. On top of the finely perforated basal plate, this species has a medial crest (hollow). It is apical, obtuse or pointed. Its end may extend beyond the frontal edge of the scale, thus imitating a spike. A large pore is located in the medial crest, in its anterior part. The basal end of this scale is curved in a horseshoe shape. It hangs over her body. The posterior and anterior scales that cover the cell body have transverse ribs that radiate from the medial crest. In addition to the transverse ones, the median ones also have longitudinal ribs. On the cell, the scale does not lie flat, but is apparently attached only by the end opposite to the spine. In S. sphagnicola (pictured above), body scale profiles can also be found in cytoplasmic vesicles, mostly located near the outer surface of the chloroplast, although they can also be observed between it and vesicles with chrysolaminarin.
Coc-colitophorid group
Golden algae, the species and names of which we study, are numerous. Among them, a special group stands out - coc-colitophorid. Its representatives have their own characteristics. Their pellicle is surrounded on the outside by an additional layer of coccoliths (the so-called rounded calcareous bodies). They are in the mucus secreted by the protoplast.
Class Haptophyceous
This class is distinguished primarily by the structure of monad cells, which have a haptonema, in addition to flagella. This class includes three orders. Consider one of them.
Primiesial order
It is usually characterized by two isomorphic and isocont flagella, as well as a long haptoneme. The cell surface outside the plasmalemma is covered with non-mineralized organic scales or coccolith (calcareous) bodies, which together form a coccosphere around the cell.
One of the families of this order is Prymnesiaceae. Both in fresh waters and in the seas, the genus Chrysochromulin related to it is represented. Oval or spherical cells with two smooth flagella of equal length, as well as a haptonema, are covered outside the cytoplasmic membrane with non-mineralized organic scales. The latter are usually of two types. They differ either in shape or size.
For example, Chrysochromulina birgeri has two types of scales that cover its body. They differ only in size. These scales consist of oval plates, the pattern of which is represented by radial ridges. There are also two central protrusions, presented in the form of horns. The cell surface in other species is covered with scales, which differ more or less sharply morphologically. For example, flat, rounded inner scales in Ch. cyanophora have thin concentric ridges. They overlap each other, forming a sheath around the cell. Usually they are hidden by numerous cylindrical scales located on the outside.
Ch. megacyiindra are cylinders and plates. The cylinders are distributed quite evenly over the cage. Each of them is attached to its basal plate at the lower end. Lateral sides of these cylinders almost touch each other. Beneath them are flat scales with rims, forming many layers.
Three types of scales are observed in Ch. chiton. Their location is characteristic: six large ones without a rim are located around one large one with a rim. The gaps between them are filled with the smallest scales.
In conclusion, let's briefly consider one more family.
Family Coccolithophoridae
It mainly includes marine species. An exception is hymenomonas, a freshwater genus. The monad cells of this family have two identical flagella. Their haptonema is usually quite noticeable. Nevertheless, in a number of coccolithophorids, it is apparently reduced. For example, it is not observed in H. coronate.
The cells of representatives of this family do not differ in their structure from the cells of other haptophytes. They have a nucleus, as well as chloroplasts, which are surrounded by an endoplasmic reticulum. They contain three-thylakoid lamellae, while there is no encircling lamella. The cell also contains a pyrenoid. Paired thylakoids cross it. There are also mitochondria, the Golgi apparatus, etc. As for the cell cover, it is located outside the cytoplasmic membrane. Coccoliths are scales impregnated with carbonate, of which it is composed. The coccoliths together form a coccosphere around the cell. Some forms have organic non-mineralized scales in addition to them.
Coccoliths and chalk
The origin of writing chalk, familiar to all of us, is very interesting. When considered underunder a microscope, if the image is not greatly enlarged, the shells of foraminifers are usually striking to researchers. However, at a higher magnification, many transparent plates of a different origin are found. Their value does not exceed 10 µm. It is these plates that are coccoliths, which are particles of the shell of coccolithophorid algae. The use of an electron microscope allowed scientists to establish that coccoliths and their fragments make up 95% of the Cretaceous rock. These interesting formations are currently studied from the point of view of ultrastructure. In addition, scientists have considered their genesis.
So, we briefly reviewed the department of Golden algae. Classes and individual representatives of it were characterized by us. Of course, we have only talked about some of the species, but this is enough to get a general idea of the department of interest to us. Now you can answer the question: "Golden algae - what is it?"
