BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VI. PLANT SYSTEMATICS

LOWER SPORE PLANTS

GENERAL CHARACTERISTICS AND FEATURES

Division Green Algae - Chlorophyta

Eukaryotic, free-floating or attached, unicellular, colonial, and multicellular, micro- and macroscopic (over 8 m long) freshwater, hyperhaline, marine, soil, aerophytic, cryophilic, and thermophilic Algae. They exhibit monad, coccoid, sarcinoid, filamentous, and heterotrichous structural types of the thallus, sometimes parenchymatous-lamellar with leaf-, stem-, and rhizoid-like structures, as well as non-cellular siphonous and siphonocladous thallus Organization.

One of the most diverse groups of algae (over 20,000 species), represented in the flora of Ukraine by more than 1,300 species belonging to about 1,500 taxa of species and infraspecific ranks.

The photosynthetic apparatus is compositionally similar to that of vascular plants, containing chlorophylls a and b (and exceptionally a precursor of chlorophyll c), carotenes (α-, β-, γ-, and ε-carotene), and xanthophylls of the lutein series (lutein, zeaxanthin, neoxanthin, violaxanthin, antheraxanthin). At the same time, specific xanthophylls—prasinoxanthin, siphonein, siphonoxanthin, and loroxanthin—are characteristic of certain groups (classes).

The green coloration is typical due to the predominance of chlorophylls. However, under certain conditions (age, growth stage, physiological state such as resting Cells, or hyperhaline environments), the accumulation of carotene, oil pigmented by carotenoids and xanthophylls (hematochrome), leads to The Development of a yellow-orange or red coloration.

METABOLISM/14.html">Chloroplasts vary in shape, ranging from single to numerous, parietal or central-axial, primarily symbiotic, and possess a typical plant Structure similar to that of vascular plants. They are enclosed by a double-membrane envelope, and thylakoids are grouped into lamellae of 2–6 or form grana; girdle thylakoids are absent.

Often, the chloroplast contains a pyrenoid with or without a starch sheath ("naked"), though sometimes it is absent altogether. The assimilation product is starch, which is deposited in the chloroplast stroma and around the pyrenoid, while outside the Plastids, oil, leucosin, and occasionally inulin can be found. The cells of many representatives are characterized by the presence of a vacuole with Cell sap (Fig. 24).

Class="center">Water/water.files/image024.jpg" width="280"/>

Fig. 24. Schematic diagram of green algal Cell Structure:

1 - flagellum, 2 - contractile vacuole, 3 - Cell wall, 4 - Plasmalemma,

5 - chloroplast, 6 - Endoplasmic reticulum, 7 - vacuole, 8 - eyespot (stigma), 9 - nucleus, 10 - nucleolus,

11 - oil droplet, 12 - thylakoids assembled into grana, 13 - starch sheath (starch grains) of the pyrenoid, 14 - pyrenoid, 15 - Golgi apparatus, 16 - mitochondrion, 17 - Cytoplasm, 18 - flagellar microtubular roots, 19 - flagellar basal body,

20 - papilla, 21 - fibrillar connective fiber of basal bodies (after EM, 1976, 1983)

Most monadoid algae possess a photoreceptor complex consisting of a stigma—a shading organelle and light regulator formed by carotenoid-containing globules—and a specialized layer of the plasmalemma (the photoreceptor proper) located directly beneath the chloroplast envelope.

Monadoid forms possess 2–4 flagella, occasionally one or numerous (up to 120), equal in length (isokont) and identical in structure (isomorphic), most commonly smooth, rarely with mastigonemes, and sometimes bearing organic submicroscopic scales. In the region where the flagella emerge from The Cell (the so-called "transition zone"), a specific stellate structure is present, which is characteristic of these algae and vascular plants. The arrangement pattern of the "flagellar roots" and the Structural Features of the flagellar ROOT system vary and serve as diagnostic characters at the class level. The flagella are oriented opposite each other in a single line ("12/6" configuration), clockwise ("1/7" configuration), or counterclockwise ("11/5" configuration) (Fig. 23). The cells of most green algae have a cellulosic-pectic cell wall (Fig. 24), though some lack it and possess only a thickened layer of the plasmalemma, occasionally covered with submicroscopic organic scales.

The cell wall in most species is continuous, while in certain representatives it is composed of separate plates (2–9), being either smooth or ornamented with various structures such as warts, Ribs, Teeth, spinules, spines, bristles, or hairs. The cells contain true vacuoles with cell sap, while some possess 2 or sometimes several contractile vacuoles.

Fig. 25. Schematic diagram of the arrangement of flagellar microtubular roots in green algae:

1 - cruciate, symmetrical, in a single plane ("12/6" configuration); 2 - 3 - asymmetrical arrangement:

2 - "1/7" configuration (clockwise) and 3 - "11/5" configuration (counterclockwise)

Mitochondria have lamellar cristae. The nuclear complex has a typically eukaryotic structure. The nuclear envelope persists throughout mitotic division in some representatives, whereas in others it breaks down very early, and in Trebouxiophyceae it persists during division but disintegrates at the poles. The nucleolus disappears during mitotic division. The type of mitosis—closed, semi-closed, or open—is characteristic of representatives of a specific class. Centrioles are present in non-motile forms and absent in cells of monadoid representatives.

In most green algae (Chlorophyta), cytokinesis occurs via a Cleavage furrow. However, in algae with a well-developed cell wall, The formation of a cell plate has also been observed (cytotomy involving both a cleavage furrow and a cell plate, which consistently drives the growth of the thallus), a feature characteristic of this phylum.

Green algae exhibit a variety of reproduction types: vegetative, asexual, and sexual. Vegetative Reproduction in unicellular forms occurs through simple Cell Division into two (schizotomy), whereas in coenocytic, colonial, and multicellular forms, it happens via thallus fragmentation (schizogony, leading to sporulation or the formation and growth of multicellular sarcina-like aggregates, or driving thallus growth in filamentous and heterotrichous forms) and akinete formation. They display the main modes of asexual reproduction (via zoospores—either walled or wall-less, aplanospores, autospores, hypnospores, hemizoospores, and hemiautospores) and sexual processes (holo-, iso-, hetero-, and oogamy) known in eukaryotic algae, accompanied by a progressive reduction of motile reproductive stages. Vegetative and sexual reproduction are playing an increasingly important role.

The life cycles of green algae are diverse. Most representatives (eughamous) are characterized by haplo-, haplodiplo-, and diplophasic cycles featuring zygotic, gametic, sporic, and somatic reduction, with isomorphic and heteromorphic Morphology/12.html">ALTERNATION OF GENERATIONS. Meanwhile, among agamous or apogamous forms, life cycles follow a cyclomorphosis pattern.

The taxonomic Classification of this phylum is still a work in progress. In the 1970s and 1980s, classical morphological approaches (based on thallus organization type and sexual process characteristics) were superseded by ultrastructural criteria (The structure of the flagellar apparatus, flagellar Symmetry, the type of organization and structure of flagellar roots, cell and nuclear division features, fine Structure of Cell coverings, etc.), which subsequently guided a new subdivision of the phylum into classes.

Later on, molecular phylogenetic research—based on nucleotide sequence analyses of the nuclear genes encoding the 5S, 18S, and 26S ribosomal RNA subunits, as well as various chloroplast and Mitochondrial Genes (such as those for tubulin elongation factor, cytochrome c, Actin, RUBISCO, etc.)—confirmed the validity and reliability of these classification changes. This data facilitated the establishment of new classes and the redistribution of green algal taxonomic groups, a refinement process that continues to this day.

The most prominent and well-supported division of the phylum Chlorophyta, backed by a combination of classical and recent molecular biology findings, recognizes the following classes: Prasinophyceae, Chlorophyceae, Oedogoniophyceae, Trebouxiophyceae, Ulvophyceae, and Siphonophyceae (Bryopsidophyceae). We will examine the main characteristics and representative organisms of several of these classes (as outlined in the standard curriculum).

Green algae are a widespread group of plants that have colonized diverse habitats, ranging from ephemeral water bodies and marine environments to soils, ice, thermal springs, and aerophytic zones. Specific groups (classes) are adapted to distinct ecological conditions. Chlorophyceae and (partially) Trebouxiophyceae are most diverse in freshwaters, Ulvophyceae and Siphonophyceae in marine environments, and Trebouxiophyceae and (partially) Chlorophyceae in aerophytic and soil habitats.

Mass proliferation of certain species causes water "blooms" and biomass accumulation of up to several kilograms per cubic meter (e.g., Dunaliella salina). In soils, or during soil "blooms," their biomass can reach up to 50 kg/ha, occasionally hitting 200 kg/ha. Green algae are frequently the agents behind green or red "blooms" of snow (Volvocales and Chlorococcales), tree bark, and various natural or industrial surfaces (Chlorellales, Trebouxiales). Symbiotic species are also well known, forming relationships with other plants (algae and vascular forms), Fungi and fungus-like organisms (Lichens), and animals (Cnidaria, Ciliates). Furthermore, some species act as parasites on macroalgal hosts, vascular plants, and vertebrates.

Their acknowledged significance spans biotechnology, industrial production, and aquaculture; they serve as bioindicators of environmental and aquatic health, air pollution test organisms, and producers of ^-carotene (Dunaliella salina, Haematococcus pluvialis) and lipid complexes for biodiesel (Botryococcus braunii), as well as glycerin and hydrocarbon compounds (Dunaliella). They are also utilized as feed supplements for livestock and poultry and as human food sources (Chlorella vulgaris, Scenedesmus sp., Ulva sp., Enteromorpha sp., Monostroma sp.). Additionally, their role as soil-stabilizing and water-retaining agents in soils (Chlamydomonas) has been widely noted.