BOTANY VOLUME 3 - EVOLUTION AND SYSTEMATICS - 2007

11. SYSTEMATICS AND PHYLOGENY

11.2. Bacteria, Fungi, Plants

Sixth Subkingdom: Rhodobionta

Members of this subkingdom possess Plastids that resemble those of Glaucobionta. However, the chloroplast envelope no longer contains peptidoglycan. Flagellated Cells are completely absent.

The sole division: red Algae (Rhodophyta)

Red algae, which inhabit predominantly marine environments, range in color from light red to violet, occasionally from dark purple, brownish-red to almost black, or even from blue- to olive-green. Flagellated forms or stages, such as monadoid species, zoospores, or spermatozoa, are absent. Unicellular representatives occur only in the rather distinct subclass Bangiophycidae. Both in this small group and among other red algae, representatives with thalli in the form of individual filaments and interweaved filaments predominate; other forms have a pseudoparenchymatous (false-tissue) Structure. True Tissues are completely absent. Interweaved filaments and pseudoparenchyma (= plectenchyma) of red algae are formed According to the uniaxial (central-filament) or multiaxial (fountain) type (see 5.3.1; Figs. 5.6, 5.7). The cells, which are almost without exception uninucleate, usually contain numerous discoid, oval, or lobed chromatophores (plastids), which, however, are never cup-shaped.

Plastids. In them, chlorophyll a (chlorophylls b and c are absent; the presence of chlorophyll d was long considered controversial) and accompanying carotenoids are masked by red, strongly fluorescent pigments located in so-called phycobilisomes. Phycobilisomes (which also occur in prokaryotic cyanobacteria) are discoid or spherical bodies 30 — 540 nm in size. They are located on thylakoids within chromatophores and contain Water-soluble phycobiliproteins with prosthetic phycobilins that determine The Nature of the coloration. In red algae, it is primarily due to red phycoerythrin; phycobilisomes also contain phycocyanin (see Fig. 2.89, B, C).

Box 11.5. Organizational Types of Eukaryotic Algae

Species of Glaucophyta, Rhodobionta and adjacent groups (e.g., Heterokontophyta), as well as primitively organized representatives of Chlorobionta (Chlorophyta, Streptophytina), are treated as algae. Eukaryotic algae (i.e., Algae in the narrow sense, excluding prokaryotic blue-green algae) are unicellular or multicellular, variously colored, primarily photoautotrophic plants, usually having a thalloid Organization and mostly living in water. Their METABOLISM/14.html">Chloroplasts contain Photosynthetic Pigments along with accessory pigments. Plastids of all eukaryotic algae contain chlorophyll a and, for the most part, Other forms of chlorophyll as well (Table 11.3). For oxygenic Photosynthesis, water serves as the electron donor, releasing oxygen. Accessory pigments refer to various carotenoids (as well as phycobilins found in a few groups, see 6.4.2). Pyrenoids are often present inside or outside the chloroplasts (see 2.2.9.1). Chloroplasts are bounded either by two membranes—simple plastids, or by 3 — 4 membranes—complex plastids. In representatives of some algal groups (Cryptophyta, Chlorarachniophyta), complex plastids contain a nucleomorph, which is considered a reduced nucleus of a eukaryotic endosymbiont. According to the endosymbiotic theory (see 2.4.2), this process accounts for the appearance of plastids in the host Cell. It is assumed that simple plastids (in Glaucophyta, Rhodophyta, Chlorophyta) arose As a result of a single primary endocytobiosis from prokaryotic algae, a role attributed to Cyanophyta. Primary endocytobiosis was, perhaps, a unique evolutionary event.

Complex plastids (all other divisions of eukaryotic algae), by contrast, indicate that they arose as a result of two stages of endosymbiosis (see 2.4). After primary endosymbiosis, further independent endosymbiotic events occurred (secondary endocytobiosis): already eukaryotic algae were incorporated into host cells. For algae with a nucleomorph in their plastids, such secondary endocytobiosis is considered proven. Thus, eukaryotic algae are polyphyletic both with respect to the host cell and with respect to the acquisition of plastids as a result of primary or secondary endosymbiosis.

The relationship between the plastids of eukaryotic algae and the photosynthetic apparatus of prokaryotic algae has been confirmed by sequence analysis of small subunit rRNAs (SSU).

Gamete- and spore-forming Organs lack multicellular coverings and, in most cases, also lack postgenital, i.e., later-developing, coverings. Spore-producing organs (sporangia) are always unicellular, and gametangia are most often unicellular. Naked gametangia of algae, in contrast to the multicellular-walled and therefore protected antheridia and archegonia of mosses and ferns (see Box 11.8), are called spermogonia (♂: with flagellated spermatozoa; see Fig. 11.73, E: s) or spermatangia (♂: with non-flagellated spermatia; see Fig. 11.67, D) and oogonia (♀: with an egg cell; see Fig. 11.73: o) or carpogonia (♀: with special post-Fertilization development; see Fig. 11.67, F — I).

Zygotes never develop inside FEMALE REPRODUCTIVE ORGANS into multicellular embryos. In most groups of algae, reproductive cells (Gametes, spores) possess flagella, although in some more highly developed groups, flagella are present only in male gametes; in only a few groups of algae do no flagellated stages form at all (Pennales, Rhodophyta, Zygnematophyceae). Flagella have the 9 + 2 structure characteristic of eukaryotes (see Fig. 2.16). They are usually paired, with one directed forward along the path of motion and the second backward. The two flagella can be of equal or different length, both smooth or different: one smooth and the other equipped with pinnately arranged hairs (tinsel flagellum).

In the course of evolution, algae have undergone progressive development from unicellular forms to complex pseudoparenchymatous or tissue thalli (see Chapter 5). Forms at the level of thallophytes do not yet show Differentiation of the vegetative body into "true" leaves, stems, and roots. Somewhat similar structures in some highly developed algae lack conducting structures that could be compared to the vascular bundles of vascular plants (for example, brown algae have only individual conducting elements resembling sieve tubes). For the most part, structures vaguely resembling the Morphology/4.html">MAIN ORGANS OF higher plants lack anatomical differentiation, which is why they are referred to as phylloids, cauloids, and rhizoids (see 5.3.2).

The following morphological groups of different Levels of organization (organizational levels) can be distinguished.

• Amoeboid (= rhizopodial) level. Unicellular naked algae form pseudopadia, with which they capture solid food particles. If these appendages are thin and thread-like, they are called rhizopodia (see Fig. 11.74, C). Associations of such cells also occur.

• Monadoid level. Unicellular flagellated algae, usually equipped with eyespots and contractile vacuoles ("flagellates"; see Fig. 11.103). After cell divisions, they can form colonies consisting of several (up to very many) cells (see Fig. 11.95, B; 11.74, F). The palmelloid stage (palmella stage) represents the palmelloid (capsal) level: Cell Division does not produce new flagella, and the daughter cells are embedded in a common mucilage (see Fig. 11.75, C).

• Capsal (= tetrasporal) level. Various Features of the monadoid level are still preserved in a rudimentary form. Thus, flagella, if still present, are rigid or reduced and in any case incapable of active movement, and may occur only in reproductive cells. Since the cells are embedded in a common mucilage after division, colonies arise that can even be elongated into thread-like structures (see Fig. 11.75, D). The Cell wall is thin or absent.

• Coccoid level. Vegetative cells lack flagella and are covered by a cell wall. They do not possess even any remnants of monadoid organization. These can be unicellular forms, coenobia, or colonies in the narrower sense (see Fig. 11.76; 11.97, A; 11.98, A).

• Filamentous (= trichal) level. Unicellular (monoergid) cells form branched or unbranched filaments growing intercalarily or apically (see Fig. 11.89, A).

• Siphonocladous level. Cells forming the filaments contain several nuclei; multinucleate cells are called polyergids.

• Siphonal level. The macroscopic thallus is represented by a single large multinucleate cell—filamentous or of another appearance. The size of the thallus can be quite large (see Fig. 11.73, O; 11.91; 11.92, D).

Pseudoparenchymatous thallus. Lateral axes (filaments) interweave with each other. Cells often adhere or even fuse together (see 5.3.1; Fig. 5.7, A).

Parenchymatous thallus. Cells dividing in different directions remain connected to each other, forming a tissue (see 5.3.2; Fig. 5.4, G).

The levels of organization briefly characterized here were achieved independently in different evolutionary lineages of algae, and their development proceeded in diverse ways. A parenchymatous (tissue) thallus, for example, appeared in a primitive form in Ulvophyceae and in a highly developed form in Phaeophyceae, while a pseudoparenchymatous form arose in Phaeophyceae and Rhodophyceae.

Both pigments have several variants, which differ, in particular, in their Absorption Spectra and their occurrence in specific groups (cyanobacteria or red algae). Phycobilisomes in cyanobacteria and red algae harvest light and transfer excitation energy to the actual photosynthetic pigment. The stratification of phycobilins within phycobilisomes (phycocyanins inside, phycoerythrins outside) directs the energy transfer. In Cryptophyta, which also possess phycobilins, phycobilisomes are absent.

In chloroplasts, thylakoids are not grouped but are spaced evenly apart (as in cyanobacteria and glaucophytes). A double membrane separates the chromatophores from the rest of The Cell; The Endoplasmic reticulum is not involved in this.

As a storage product, floridean starch is primarily deposited in the form of rounded, water-insoluble, often stratified granules that stain reddish with iodine. This is a polysaccharide whose properties are intermediate between Glycogen and starch. Unlike starch in green algae, these granules are deposited not inside the chloroplasts, but on their surface and in the Cytoplasm. Some other substances unique to red algae also occur ("floridosides"—compounds of galactose and glycerol), as well as oil droplets.

The fibrillar component of the cell wall consists mainly of Cellulose, whose microfibrils are composed of chains that are not arranged parallel to each other (as in Higher Plants and some green algae), but are interwoven like felt.

The amorphous part often contains mucilaginous galactans (e.g., Agar; carrageenan = galactan sulfate; galactans are polymers of galactose).

Life cycle. Red algae are characterized by an alternation of three generations, in which the haploid gametophyte is followed by a diploid carposporophyte and another

one diploid sporophytic generation (predominantly a tetrasporophyte).

In the diplobiontic type (three generations represented by two individuals, e.g., Polysiphonia, Fig. 11.65, A), the gametophyte is an independent haploid plant. It develops a ♀ gametangium—the carpogonium. In many red algae (e.g., all Florideae), its swollen lower part (base) extends into a trichogyne—a long, usually slender receptive organ (Fig. 11.66, F: t; 11.67, F: t). On other parts or other gametophyte individuals, non-flagellated male (♂) gametes—spermatia—arise in spermatangia (= male gametangia). They are uninucleate, passively carried by water currents, then adhere to the trichogyne and discharge their ♂ male nucleus into it, after which this nucleus migrates to the Nucleus of the carpogonium and fuses with it (gameto-gametangiogamy, or atypical oogamy).

Class="center">Fig. 11.65. Rhodobionta, Rhodophyceae. ALTERNATION OF GENERATIONS and nuclear phases. Three-phase diplobiontic cycle of Polysiphonia (A); three-phase haplobiontic cycle of Batrachospermum (B). Light lines—haplophase; dark lines—diplophase; R!—reduction division

From the fertilized egg cell, the carposporophyte arises in the form of diploid, cellular filaments that grow out of the carpogonium, while remaining, however, attached to the haploid gametophyte. Accordingly, the alternation of the first two generations, separated by a change of nuclear phases, occurs on the very same plant. Following exclusively mitotic divisions, the carposporophyte produces diploid carpospores, which are thus mitospores.

Tetrasporophyte. In the vast majority of red algae, a carpospore gives rise to a new plant, which is usually morphologically similar to the gametophyte but diploid. On this plant, after reduction division, four haploid tetrameiospores are formed from each spore mother cell (see Fig. 11.65; 11.66, B); this generation is called the tetrasporophyte. In the transition from the carposporophyte to the tetrasporophyte, the alternation of the 2nd and 3rd generations of The life cycle occurs accordingly without A change in the nuclear phase. The Development of three generations is thus carried out on two vegetative bodies (diplobiontic development); most red algae (except for Nemalionales) belong to this type.

Fig. 11.66. Rhodophyceae: A, B—Callithamnion corymbosum, tetraspore formation (300x): A—closed, B—released sporangium with 4 meiospores; C, D—Bonnemaisonia hamifera, gametophyte and tetrasporophyte (5x), C—gametophyte and cystocarp primordia, D—sporophyte, also known as Trailiella intricata; E—Ceramiales, Platysiphonia miniata, cystocarp with carposporophytes visible inside by transmitted light (100x); F, G—Cryptonemiales, Dudresnaya; F—fertilized carpogonium, with several more spermatia (s) adhering to its trichogyne (t), giving rise to branched sporogenous filaments (sf) that connect with six auxiliary cells (a1–a6), cells a1–a6 are part of the branches arising from the axis ha (250x), G—mature cluster of carpospores

The gametophyte and tetrasporophyte usually have the same appearance, but they can also be dissimilar (see Fig. 11.66, C, D), which is why they were previously assigned not only to different genera, but even to widely separated orders. Likewise, the carposporophyte parasitizing the gametophyte in some cases looks so foreign that it was considered an actual foreign parasite and given a special name. Gametophytes can be monoecious or dioecious. In the latter case, differences in The structure of ♂ and ♀ plants sometimes occur. Often, the carposporophyte (= gonimocarp) is enveloped by special sterile filaments of the gametophyte, resulting in a so-called fruiting body—the cystocarp (see Fig. 11.66, E). If the protective envelope is initiated before fertilization of the carpogonium, it is referred to as a procarp.

Often, the carposporophyte is supported by accessory, or auxiliary cells, which apparently play a role in nutritional physiology. These are cytoplasm-rich cells located near the carpogonium, which receive the zygote nucleus (or a diploid nucleus resulting from subsequent divisions) from the carpogonium, undergo subsequent mitotic divisions, and finally initiate the Development of the carposporophyte. Connecting filaments (see Fig. 11.66, E: sf) growing out of the carpogonium can reach many auxiliary cells. In this process, diploid nuclei multiply and spread throughout the gametophyte, so that following a single fertilization event, numerous carposporophytes arise from the gametophyte and can draw Nutrition from it.

The sequence of different generations on a single Organism (haplobiontic type of development) can be traced in freshwater species of the genus Batrachospermum (see Fig. 11.65, B). Here, too, a three-part, heteromorphic, and heterophasic alternation of generations occurs, the three members of which, however, remain linked to one another, namely: 1) the diploid “Chantransia-sporophyte” (protonema); 2) the whorled-branched haploid gametophyte; 3) the diploid carposporophyte.

Gametophyte. The monoecious thallus consists of haploid, whorled-branched filaments (see Fig. 11.67, A). Numerous spermatangia usually arise in pairs from the terminal Cells of the whorled lateral branches (Fig. 11.67, A). Each spermatangium consists of only a single cell, the entire contents of which are used to form a single, rounded, colorless spermatium with a large nucleus and a very delicate wall (D). The female organs—carpogonia—are situated between the spermatangia-bearing branches, also at the tips of the branches, and consist of a long cell that is flask-shaped at its base and elongated into a club-shaped trichogyne at its apex (E, F). The carpogonium with its trichogyne is deeply embedded in mucilage. The spermatium, passively carried by water currents, can actively penetrate this mucilage (the mechanism is unknown); in doing so, it reaches the trichogyne, into which it discharges all its contents. The spermatium nucleus migrates into the carpogonium and fuses with the female nucleus located there. Afterwards, the basal part of the carpogonium, containing the newly formed diploid nucleus, is separated from the trichogyne by a mucilaginous plug (G).

Carposporophyte. It consists of branched, cellular filaments that grow out of the zygote but remain connected to the gametophyte (Fig. 11.67, H). In the swollen terminal cells, the carposporophyte forms a single rounded mitospore containing a nucleus and a chloroplast—the diploid carpospore. Carpospores are released from the remaining walls of the terminal cells (Ik1, k2) as rounded, non-flagellated structures. They grow into the Chantransia-stage (Chantransia-sporophyte). These are branched diploid filaments that adhere closely to the substrate and represent a protonema for the gametophytes that later arise from them. The Chantransia-stage is thus still diploid, but the gametophyte proper is haploid. Meiosis occurs without The formation of meiospores in individual cells of the Chantransia filaments. The haploid cells then develop into whorled-branched gametophytes (C).

У некоторых видов в качестве 2-го спорофита образуется маленькое, мутовчато разветвленное растение, которое в определенных местах (после мейоза) непосредственно дает начало гаметофитам; это сближает Сhantransia-стадию со спорофитным поколением.

Fig. 11.67. Rhodophyceae, Nemalionales. Batrachospermum moniliforme:

A—habit (3x); B—part of the gametophyte thallus with a whorl of branches (20x); C—diploid sporophyte (Chantransia) with two gametophytes sitting on it (100x); D—part of a gametophyte branch with 4 spermatangia, with a released spermatium on the left (540x); E—carpogonium primordium; F—mature carpogonium; G—carpogonium after fertilization by a spermatium (s), with fusion of gametic nuclei (o) at its base; H—diploid carposporophyte (g) with haploid sterile filaments (h); I—mature carposporophyte with carposporangia (k); k1, k2—released carposporangia; t—trichogyne

DISTRIBUTION AND LIFESTYLE. Red algae are represented by approximately 4,000 species in more than 500 genera. With few exceptions (e.g., Batrachospermum, Lemanea), they inhabit the coastal zones of seas, especially warmer ones; many species are highly sensitive to Temperature fluctuations. Red algae often grow much deeper (up to a maximum of 180 m), where only weak short-wave light penetrates. Here, they can not only survive as shade-tolerant algae, but, thanks to the presence of accessory pigments (phycobiliproteins), they can optimally utilize the short-wave light prevailing at depth, which is complementary to the color of these pigments (see 6.4.3). Red algae are members of the benthos. They are always firmly attached by special filaments or rhizoids, usually to a rocky substrate, while some grow as epiphytes on larger algae. Such epiphytes can be strictly associated with a specific genus of host plant (phorophyte) (e.g., species of the genus Polysiphonia on Ascophyllum). Red algae are autotrophic; some of them are colorless parasites, of which several dozen are highly reduced forms living on other, closely related species of red algae (“adelphoparasites”).

Systematics. The only class of red algae is Rhodophyceae. It is subdivided into the subclasses Bangiophycidae and Florideophycidae.

1. Subclass: Bangiophycidae

These are very simply organized unicellular, filamentous, or foliose algae with intercalary growth. Pit connections are usually absent. Chloroplasts are stellate, with a pyrenoid.

1. Order: Porphyridiales. It comprises unicellular, partly colonial forms. Sexual reproduction is unknown. In the common terrestrial alga Porphyridium purpureum, numerous individual cells are embedded in mucilage.

2. Order: Bangiales. This order includes filamentous (e.g., Bangia) or foliose (e.g., Porphyra) forms. Erythrotrichia forms unbranched filaments in which vegetative monosporangia can arise, each containing a single monospore. Initially, monospores are naked and exhibit amoeboid movement. They grow into new filaments of Erythrotrichia. In Porphyra (purple laver), carpogonia are usually indistinguishable from vegetative cells. The diploid zygote, fertilized by spermatia, directly divides after several mitoses into A number of diploid carpospores; thus, the carposporophyte generation is either absent or highly reduced. The carpospore germinates into a filamentous, apparently also diploid structure that penetrates the calcareous shells of bivalve Mollusks and barnacles. This initiates the development of the so-called Conchocelis phase, which represents the sporophyte generation. It ends with the formation of conchospores (homologous to tetraspores), after which, in all probability, reduction division occurs. The Conchocelis phase is widespread along the marine coasts of Europe. Cyanidium caldarium, a species whose relationship to blue-green algae (cyanobacteria) is debated, possibly belongs to this order as well¹.

¹ In virtually all modern systems, Cyanidium caldarium and some species related to it are placed in a separate class, Cyanidiophyceae, which is sometimes classified as an independent division Prerhodophyta. — Translator's Note.

2. Subclass: Florideophycidae

Representatives of this subclass have a more complex thallus structure, based on branched filaments with apical growth. Unicellular representatives do not occur. Even the simplest Florideophycidae already have a heterotrichous structure (i.e., they are differentiated into a basal disc and vertical filaments); however, even the most highly developed representatives, in contrast to brown algae, are never parenchymatous (see 5.3.1), but form their thallus according to the uniaxial or multiaxial (fountain) type (see Figs. 5.6; 5.7). Cells are often connected to each other by "pores" (pit connections). These are openings or channels containing plug-like structures (pit plugs); their function has not been clearly established.

1. Order: Nemalionales¹. Auxiliary cells are absent. In Central Europe, this order is represented by species of the genus Batrachospermum, which grow mainly in fast-flowing, shaded streams as mucilaginous, frogspawn-like masses ranging from brownish to olive-green. Batrachospermum exhibits a haplobiontic life cycle that deviates from the normal type. It also clearly differs from most other red algae in that it inhabits fresh water, most commonly in fast-flowing streams with high water purity.

¹ It is more correct to call this order Nemaliales. — Translator's note.

Rhodochorton investiens—a red alga living as an epiphyte on Batrachospermum—has, by contrast, a normal diplobiontic life cycle; in this case, the gametophyte and tetrasporophyte are highly similar to each other. The closely related marine species Rhodochorton purpureum is a haplobiont with a two-phase alternation of generations: the carposporophyte generation is omitted, and the fertilized carpogonium grows directly into a tetrasporophyte, which remains attached to the morphologically identical gametophyte.

Другой род пресноводных водорослей из этого порядка — Lemanea, тогда как виды родов Nemalion, Bonnemaisonia (см. рис. 11.66, С, D) и Gelidium живут в морях. Систематическое положение последнего рода спорное, так как здесь встречаются Клетки, трактуемые как ауксилярные².

² Currently, the genera Batrachospermum, Lemanea, and several others characterized by a similar life cycle (without the formation of meiospores), freshwater habitat, and lack of red coloration are usually separated into a distinct order, Batrachospermales; the genus Gelidium is placed in the order Gelidiales. — Translator's note.

2. Order: Cryptonemiales. Auxiliary cells are formed before fertilization on specialized branch clusters. In Corallinaceae¹ (Corallina, Lithothamnion, Lithophyllum), cell walls are encrusted with calcite crystals (coral reef formation); fossil representatives are important as rock-forming organisms. This order also includes Melobesia (see Fig. 5.7, B) with a thallus developing according to the "multiaxial (fountain) type".

¹ In most modern systems, this is a separate order, Corallinales. — Translator's note.

3. Order Gigartinales. A normal intercalary cell of the thallus differentiates into an auxiliary cell. This order includes the pectinate-pinnate Plocamium, Furcellaria (see Fig. 5.7, A) with a multiaxial (fountain) structure, and the flat-dichotomous Chondrus.

4. Order: Rhodymeniales. Before fertilization, the supporting cell of the carpogonium cuts off a daughter cell, which in turn cuts off an auxiliary cell. The carpogonium arises from a procarp (consisting of the supporting cell, daughter cell, auxiliary cell, and carpogonial branch), which becomes a cystocarp after fertilization. This includes Rhodymenia, which is common in the Atlantic and has a foliose thallus.

5. Order: Ceramiales. The auxiliary cell is cut off from the supporting cell of the carpogonial branch after fertilization of the carpogonium. A procarp (here consisting of the supporting cell, auxiliary cell, and carpogonial branch) and a cystocarp are present, as in the previous order. The life cycle corresponds to the basic scheme presented at the beginning (see Fig. 11.65, A). The thallus is uniaxial and consists of profusely branched filaments, which often form a cortex.

The thallus of the alga Delesseria sanguinea, which lives in the Atlantic Ocean, is particularly complexly differentiated. Its blade-like lobes, arising from a basal disc, have a midrib and lateral Veins; in autumn, the blades die off, but the main axes persist and develop new blades the following spring. The Ceramiales include Grinnellia (see Fig. 5.8, A), Platysiphonia (see Fig. 11.66, E), as well as the genera Polysiphonia, Ceramium, and Plumaria, which are represented in the North and Baltic Seas.

In the past, a relationship between red algae and ascomycetes (Mycobionta) was sometimes suggested. This assumption has not been supported by DNA analysis data. Indeed, the similarity of the following features is particularly striking: the ♀ gametangium (here, the carpogonium; there, the ascogonium, sometimes with a trichogyne; here, carposporophyte filaments; there, ascogenous hyphae); the close relationship between the gametophyte and sporophyte generations; the absence of flagellated reproductive cells; fertilization by spermatia (as in some ascomycetes); lichen thalli with septal pores and The ability to form anastomoses; the similarity in the Chemical Structure of fungal glycogen and floridean starch; and trehalose as a storage product. However, The chemical composition of the cell wall is different: cellulose here, Chitin there.

In the fossil record, red algae occur in all formations from the Permian onward; the assignment of Solenopora from the Ordovician to the red algae is controversial.

• Algal divisions with complex plastids lacking chlorophyll b. The following algal divisions possess complex plastids that arose through secondary endosymbiosis. Since these plastids do not contain chlorophyll b, phycobilins are very often present as accessory pigments. Their origin from ancestors close to those of the Rhodobionta is assumed, which is supported by the similarity in plastid DNA composition.

1. Appendix to Rhodobionta: division Cryptophyta (Cryptophytes)

Representatives of this division, with few exceptions (palmelloid and filamentous forms), are flagellated organisms (monadoid level of organization). The genus Biornbergiella is distinguished by a filamentous thallus. The flagellated asymmetric cells characteristic of the vast majority of species lack a cell wall and are covered only by a periplast, which consists of rectangular or polygonal proteinaceous plates. Two flagella, slightly differing in length, emerge at the anterior end. Both flagella bear pinnate hairs: the longer one in two rows, the shorter one in a single row.

The flagella are usually directed forward, less frequently backward along the body (Fig. 11.68, C). They emerge together above a deep gullet lined with highly refractive ejectosomes—bodies that discharge upon irritation. The variously colored (e.g., blue, blue-green, reddish) chloroplasts contain chlorophylls a and c, α- and β-carotene, and the xanthophyll diatoxanthin, as well as the phycobilins phycoerythrin and phycocyanin. Unlike in red algae and cyanobacteria, these pigments are not localized in phycobilisomes here. An important storage product is starch, which is deposited around the pyrenoids. The latter, however, are located within a fold of the endoplasmic reticulum (= chloroplast envelope) but outside the chloroplast membrane.

Vegetative Reproduction occurs by longitudinal division; sexual reproduction has not been reliably established.

The 120 species, living in marine and fresh waters (roughly equally), are distributed among 12 genera.

Chloroplasts can be viewed as highly reduced eukaryotic endosymbionts (related to red algae) based on the presence of a remnant, vestigial Cell Nucleus — the nucleomorph. It occurs singly within the pyrenoid or near the chloroplast surface.

It can be assumed that cryptophytes originally possessed primary plastids of the cyanelle type (see Glaucobionta), which, however, were replaced during subsequent evolution by invading unicellular red algae (via secondary endocytobiosis).

The division contains a single class with a single order — Cryptomonadales. Numerous species of the genus Cryptomonas (Fig. 11.68, A) inhabit predominantly mesotrophic water bodies.

Fig. 11.68. Cryptophyta: A — Cryptomonas sp.; B — Chilomonas paramaecium; C — Katablepharis phoenicoston with one flagellum directed forward and another flagellum directed backward (A — C — 1,200x); c — chloroplast with several pyrenoids (indicated by dots); k — nucleus; s — gullet; v — vacuole

Saprotrophic Representatives of the genus Chilomonas (B) are colorless, but still contain a single leucoplast. The phagotroph Katablepharis (C) is also colorless. One species is a highly reduced form living as an endosymbiont in the Ciliate Mesodinium rubrum, which has thus acquired the capacity for photosynthesis. This symbiotic alga contains only a single chloroplast and a few Mitochondria.

2. Appendix to Rhodobionta: division Dinophytes (Dinophyta, Pyrrhophyta, Dinoflagellata)

Mostly unicellular forms bearing two flagella with fine mastigonemes; only a few coccoid and filamentous forms are known. Along with vegetative reproduction, sexual reproduction also occurs.

Chloroplasts contain chlorophyll a; in some species, the presence of chlorophyll c has also been established. Cell coloration ranges from yellow-brown to reddish due to the presence of accessory pigments such as β-carotene and various xanthophylls, of which peridinin is the most important. The chloroplast envelope usually consists of three membranes that are not connected to the nuclear endoplasmic reticulum. Thylakoids are arranged in lamellae of three and do not form a peripheral girdle lamella (thus, the pattern is different from that in Fig. 11.72, G). The primary assimilation product is starch, which accumulates as grains outside the chlo

roblasts. Along with it, lipid-like substances also occur. For some representatives, there is evidence that the originally present simple plastid was significantly reduced, even to the point where only an eyespot remained; it became photosynthetically inactive and, as a result of secondary endosymbiosis, was functionally replaced by a complex plastid.

Fig. 11.69. Dinophyta. Zooxanthellae in a radiolarian (Eucoronis challengerr, 260x)

Dinophytes may represent a heterogeneous group of eukaryotic algae. They contain plastids of very different types. This is correlated with their capacity for phagotrophy, which is retained even in autotrophic species. In some species, plastids are not permanent cell components — these are kleptochloroplasts. There are species that may possess a nucleomorph. Molecular Phylogenetic Analysis of the nuclear genome suggests a close relationship between dinophytes and animal-associated Protozoans (Ciliata, Sporozoa, or Apicomplexa). In the heterotrophically living malaria parasite Plasmodium falciparum, active remnants of complex plastids that would confirm a relationship with dinophytes are no longer detectable.

The cell wall often has fine pores that open into sac-like trichocysts. Upon stimulation, trichocysts discharge proteinaceous threads. The cell wall in many dinophytes is constructed in a highly characteristic manner from polygonal cellulose plates that form an armor (theca) with transverse and longitudinal grooves. The thecal plates (like the Valves in diatoms) are formed within flat vesicles inside the Plasmalemma; The Plasma Membrane is retained over the armor.

At the intersection of the longitudinal and transverse grooves, two flagella arise, each situated in one of the grooves (see Fig. 11.70, A). The transverse flagellum bears a single row of somewhat longer hairs, while the longitudinal flagellum bears two rows of shorter hairs. The lateral hairs are significantly thinner than those in Heterokontophyta and Cryptophyta. The flagellum beating in the transverse groove causes rotational movement of the cell around its longitudinal axis, whereas the flagellum in the longitudinal groove drives the cell forward. For example, a Peridinium cell, moving along a helical path, covers a distance several times its own length in one second.

Chromosomes in most dinophytes (as in euglenoids) are distinguishable even in the interphase nucleus, as they remain in a condensed state during interphase (cf. other eukaryotes; see Fig. 2.27).

Under Electron Microscopy, the chromosomes appear as compactly folded fibrils ("wreaths"). The fibrils have a diameter of 2.5 nm, which corresponds to the diameter of the DNA double helix (see Fig. 1.5). Chromosomes of other eukaryotes, by contrast, possess submicroscopic fibrils with a diameter about 10 times larger — 25 to 30 nm (see Fig. 2.21). These thicker Chromatin coils of the DNA double helix with a central nucleohistone core are absent in dinophyte chromosomes. In this respect, there is some resemblance to the nucleoplasm of prokaryotic Bacteria and blue-green algae.

Vegetative reproduction occurs by oblique division. In armored forms (e.g., Ceratium), the theca usually ruptures at an angle to the transverse groove, and the new cells regenerate the missing halves of the armor (see Fig. 2.83, D). However, in species of some genera (e.g., Peridinium), the entire armor is shed before division, so that each of the resulting daughter cells completely rebuilds its own armor from scratch. After several such divisions, two cells, initially naked, develop inside the armor; they leave the maternal envelope and become covered with new armor. Under unfavorable conditions, thick-walled cysts develop within the armor, capable of remaining viable for a long time.

Sexual reproduction has so far been established in only a few dinophytes. In Ceratium, it is anisogamous, with zygotic meiosis (meiosis occurring upon zygote germination); in Glenodinium, isogametes have been described, which arise within cells (gametangia), are released, and fuse with each other.

Distribution. Most of the approximately 1,000 species (120 genera) of dinophytes inhabit the seas, where, together with diatoms (division Heterokontophyta), they constitute the bulk of the phytoplankton (important primary producers in the oceans). The greatest diversity of forms is achieved in warmer waters, whereas the most massive development occurs in colder waters. Only a few Peridiniales inhabit fresh waters, though sometimes in large numbers; in high-altitude lakes, they can constitute up to 50% of the biomass. Many species possess characteristic appendages that serve for flotation in water (Fig. 11.70, C, F — J). Noctiluca miliaris (a heterotrophic species with naked cells!), as well as species of Ceratium, Gonyaulax, and Peridinium, cause Bioluminescence of seawater. Massive blooms of dinophytes ("red tides") can cause fish mortality¹. Round endosymbionts of various marine animals are commonly known as "zooxanthellae" (Fig. 11.69). All reef-building corals live in Symbiosis with such dinophytes. Without endosymbionts, corals survive but lose the ability to form a calcareous Skeleton. Some species of dinophytes live as parasites On the surface and inside the bodies of marine animals. Among such heterotrophic forms, phagotrophy ("ingestion" of bacteria and planktonic algae) occurs.

¹ Not only fish but also many invertebrates suffer from "red tides"; eating any of these animals can cause human poisoning. — Translator's note.

Fig. 11.70. Dinophyta (Pyrrhophyceae): A — Peridinium tabulatum (600x); B — Gymnodinium aeruginosum (300x); C — Ornithocercus splendidus (125x); D₁, D₂ — Ceratium hirundinella after division (350x); E — Ceratium cornutum, cyst (150x); F — Ceratium tripos (125x); G — C. palmatum (125x); H — C. reticulatum (65x); J — C. fusus (50x)

Systematics. The sole class Dinophyceae is subdivided into 4 orders. Members of Dinophysiales (1) have a wall whose two halves (epicone and hypocone) are further subdivided by a longitudinal groove; the longitudinal and transverse grooves are often bordered by prominent, wing-like projections (Ornithocercus, Fig. 11.70, C). In Peridiniales (2), the cell either has a simple covering (Gymnodiniaceae, B) or is armored with cellulose plates (Peridiniaceae, with the genera Peridinium and Ceratium, A, D–J). Marine species possess sac-like "pusules" that open via a narrow canal into the groove where the flagellum is located; their function is not yet fully understood. The coccoid level of organization corresponds to the order Dinococcales (3), and the filamentous level to Dinotrichales (4), each containing only a few genera.

As fossils, dinophytes are known since the Jurassic and are represented by a great diversity of forms; in the Cretaceous, numerous excellently preserved representatives of various taxa are found. Furthermore, the so-called hystrichospheres in deposits ranging from the Precambrian to the Holocene have been identified as reproductive cells belonging to dinophytes. They play an important role as index microfossils.

3. Appendix to Rhodobionta: Division Haptophyta

This division (also called Prymnesiophyta) includes forms representing monadoid, palmelloid, coccoid, and filamentous levels of organization. Unicellular monadoid forms predominate. Most species inhabit marine plankton. Monadoid cells have two flagella, usually of equal length, which bear not stiff hairs but submicroscopic scales or nodules of organic material. In addition to these flagella, each cell has an extra thread-like appendage — the haptonema. It serves not for locomotion, but for attachment. Its submicroscopic structure is clearly distinct from that of flagella. In cross-section, the haptonema reveals 6 or 7 crescentically arranged microtubules (the 9 + 2 structure is absent!). In some forms, this haptonema is reduced to a short stump. The outer surface of the cell bears scales of various sizes or nodules, which are formed in Golgi vesicles and then deposited externally. The Golgi cisternae are inflated like vesicles in the middle. Yellow, yellow-brown, or brown chloroplasts contain chlorophylls a and c, β-carotene, and xanthophylls; chrysolaminarin, oil, and paramylon are deposited as storage substances. The chloroplasts are surrounded by a fold of the endoplasmic reticulum; the girdle lamella (see Fig. 11.72, G) is absent. Thylakoids are grouped in threes. The eyespot, consisting of globules, is located in the chloroplast close to its membrane. The basal Swelling of the flagellum is absent.

Systematics. In this division, about 250 species belonging to approximately 45 genera are known. Only a few species have been found in fresh waters; Haptophyceae is the sole class of this division.

1. Order: Prymnesiales. Members of this order are usually characterized by a very long haptonema. The cells are covered with two layers of polysaccharide scales, visible only under electron microscopy (Fig. 11.71, A). The scales are distinguished by their radial, spoke-like structure; the scales of the outer layer are additionally characterized by an upturned rim. Chrysochromulina has a very long haptonema, which is approximately 5 times longer than the flagella. Along with autotrophic nutrition, phagotrophic nutrition is also possible, in which, for example, entire Chlorella cells can be ingested. The cells can transition into an amoeboid phase. Reproduction occurs by longitudinal division of flagellated or amoeboid cells into several daughter cells. Species of the genus Prymnesium have a short haptonema, while species of the genus Chrysochromulina have a longer one. Prymnesium parvum attaches with its haptonema to fish gills and, during algal blooms in saltwater ponds, causes fish kills due to toxin release (as does Chrysochromulina polylepis).

Fig. 11.71. Haptophyta: A — Prymnesiales, Chrysochromulina chiton, shell plates (10,000x); B, C — Coccolithophorales: B — Syracosphaera pulchra, reduced haptonema between the flagella (1,500x); C — fossil coccolith (Deflandrius sp.), constructed of calcite rhombohedra; Lower Cretaceous (700x)

2. Order: Coccolithophorales. The haptonema is short or completely absent (see Fig. 11.71, B). The cells bear two layers of thin polysaccharide scales on top of the plasmalemma. Another outer layer features highly diverse scales, plates, or rods ("coccoliths"). The latter are also initiated in the Golgi vesicles, initially as cellulose plates, upon which remarkable calcite deposits are subsequently laid down; these are species-specific and therefore extremely diverse. The extruded coccoliths form a regular armor around the cell. In this order, species are also known that have become non-motile as a result of flagellar loss (Coccolithus pelagicus) or exhibit an alternation between flagellated and attached stages (Syracosphaera). In Hymenomonas carterae, a heteromorphic alternation of generations occurs, where the gametophyte, which is more developed than the sporophyte, has the form of branched filaments. Coccolithophorales (or their coccoliths), known as fossils since the Jurassic (Fig. 11.71, C), comprise characteristic fossil species of microorganisms (128 genera). They make up a significant proportion of certain limestone deposits, where they are present in quantities of up to 800 million coccoliths per 1 cm³ of rock (Application — see Box 11.6).

4. Appendix to Rhodobionta: Division Heterokontophyta (= Chrysophyta, Chromophyta)¹

¹ Currently, the most commonly used name for this division is ochrophytes (Ochrophyta). — Translator's note.

Despite significant differences in thallus forms, this division is characterized by the uniformity of its ultramicroscopic structures (for example, heterokont motile cells).

All morphological levels are represented here — from monadoid to siphonous organization; the highest level of organization in Heterokontophyta is represented by morphologically complex and anatomically differentiated parenchymatous thalli.

The relationship between autotrophic Heterokontophyta and heterotrophic, fungus-like Labyrinthulomycota and Oomycota has been convincingly proven. The Structural Features of their cells, despite the presence of plastids acquired via secondary endosymbiosis, coincide to such an extent that Heterokontophyta and Oomycota should be combined into a common subkingdom Heterokontobionta (see Oomycota). Only the STRUCTURE OF THE plastids justifies considering Heterokontophyta as an appendix to Rhodobionta, since the plastids of Heterokontophyta and Rhodobionta share a common origin.

Plastids. Sometimes green, but more often yellow, yellow-brown to brown due to the presence of accessory pigments, the chloroplasts contain chlorophylls a and c, β-carotene, and various xanthophylls (see Table 11.3). In addition to the two chloroplast membranes, the plastids are surrounded by an extra fold of the endoplasmic reticulum (Fig. 11.72, G).

Fig. 11.72. Xanthophyceae: A — C — Mischococcales, Capitulariella radians (500x): A — zoospore, B — detached zoosporangium, C — thallus with zoosporangial initials located at the ends of the filaments; D — Chloramoebales, Ankylonoton pyreniger in The process of division (1,000x); E — G — Tribonematales: E — fragment of a Tribonema filament with characteristic H-shaped cell wall structures overlapping in pairs (600x), F — heterokont zoospore of Tribonema (2,300x), G — chloroplast of Bumilleria (30,000x); a — eyespot; c — chloroplast; e — envelope formed by a fold of the endoplasmic reticulum; g — girdle lamella of three peripheral thylakoids; m — the two chloroplast membranes proper; p — contractile vacuole; t — stack (lamella) of three thylakoids

In chloroplasts, thylakoids are grouped in stacks of three (see Fig. 2.88) — an arrangement also observed, for example, in Dinophyta and Euglenophyta. Directly beneath the chloroplast envelope, parallel to its inner surface, lie the thylakoids that make up the girdle lamella, which is highly characteristic here (cf., for example, representatives of Haptophyta and Heterokontophyta, which share many similar substances, with Chlorophyta). Eyespots, if present, are located near the Base of the flagella, but inside the chloroplast.

Chrysolaminarin, and sometimes also laminarin and the sugar alcohol mannitol, are formed as Storage Polysaccharides. They are located outside the chloroplasts, but mainly near the pyrenoids. Oil often accumulates, appearing near the pyrenoids, but it is predominantly found secondarily in vacuoles.

Cell walls are reinforced with additional protective layers in very diverse ways.

Flagella. Flagellated cells are heterokont. They bear one long, forward-directed tinsel flagellum and one backward-directed smooth flagellum. The tinsel flagellum has two rows of hairs, which are formed in the cisternae of the endoplasmic reticulum. The smooth flagellum (sometimes reduced) often has a swelling at its base.

The division is subdivided into five classes. In the first two classes, the chloroplasts, which range in color from green to yellow-green, do not contain fucoxanthin.