BOTANY: Lecture Course for Bachelor Degree Students Specializing in Agronomy - 2016

LECTURE 8. Plant Kingdom. Algae. Phylum Lichenes

Chlorobionts: General characteristics. Structural and reproductive features. Gametophytic and sporophytic developmental lines.

Structural Features of Algae. Types of morphological Structure in algae. Ecological groups of algae. Classification. Subkingdom Red Algae (Rhodophyta): structural features, lifestyle, reproduction, main representatives, and their significance. Subkingdom True Algae. Main phyla of algae: Dinoflagellata, Chrysophyta, Bacillariophyta, Phaeophyta, Xanthophyta, Euglenophyta, Chlorophyta.

Features of structure, Nutrition, reproduction, and their distribution in Ukraine and worldwide. Significance of algae.

Lichens as complex (symbiotic) organisms. Classification based on thallus morphological structure: crustose, foliose, fruticose. Microscopic STRUCTURE OF THE thallus and its types: homoiomerous, heteromerous. Structure of the apothecium. Modes of reproduction. Soredia, isidia. Classification of lichens: Ascolichens and Basidiolichens. Significance of lichens.

Algae are annual or perennial, colonial or non-cellular autotrophic chlorophyll-bearing organisms inhabiting primarily aquatic environments. The Cell consists of a Cellulose-pectin or pectin membrane and a protoplast, which includes the Cytoplasm with all Organelles.

METABOLISM/14.html">Chloroplasts may be spherical, rod-shaped, granular, or ring-shaped. Chloroplasts bear protein bodies known as pyrenoids. The number of nuclei is one, two, or more. The vegetative body is a thallus.

Structural types of algae:

Monadoid structural type: presence of flagella in Cells for active locomotion. A stigma (photoreceptor) is present.

Amoeboid or rhizopodial structural type: lack of a rigid Cell wall, locomotion via rhizopodia (Chrysophyta, Xanthophyta).

Coccoid type: unicellular and colonial forms, non-motile in the vegetative state.

Sarcinoidean type: colloidal habit and vegetative Cell Division.

Trichal (filamentous) type: filamentous arrangement of cells, growing in a single direction.

Heterotrichous type: Differentiation of the filamentous structure.

Parenchymatous type: formation of cell complexes that perform specific Functions and resemble the Tissues of higher plants (Phaeophyta and Rhodophyta).

Siphonaceous type: absence of internal cell walls within the thallus in the presence of numerous organelles.

Charophyte type: large multicellular thallus with a linear-jointed structure, bearing rhizoids at the base.

Reproduction:

Vegetative: by cell division, repeated and multiple division, budding, fragmentation of the thallus via tubers, propagules, etc.

Asexual: via aplanospores or zoospores.

Sexual: via Gametes (hologamy - two motile vegetative cells), conjugation (non-flagellated cells), isogamy, heterogamy, and oogamy, which are formed in gametangia - antheridia and oogonia.

Alternation of sexual (gametophyte) and asexual (sporophyte) generations throughout The life cycle.

Ecological groups of algae:

Planktonic algae: microscopic algae inhabiting freshwater and marine Water bodies.

Benthic algae — growing attached to the bottom of water bodies (brown, red, and green algae).

Hot spring algae thriving at 35–52 °C (blue-green, diatom, and green algae).

Ice and snow algae (green and blue-green algae).

Saline water algae — single-celled, motile green algae.

Aerophytic algae — microscopic single-celled or colonial forms (found on rocks and tree bark).

Soil algae — single-celled or colonial blue-green, euglenoid, and golden algae.

Role of algae:

- producers of organic matter;

- the sole producers of free oxygen;

- utilization of Organic compounds and heavy metal salts;

- contribution to soil fertility;

- formation of mineral resources (sapropel, oil shale, petroleum);

- provision of building Materials, Pharmaceuticals, biologically active compounds, novel subjects for biotechnology, expansion of food resources, and space exploration.

Classification of Algae

Subkingdom Red Algae

Phylum Red Algae

Marine plants, comprising 4,000 species. Sizes range from a few centimeters to meters. Coloration varies from pink, red, bluish-purple, and nearly black to sometimes blue or yellow.

Pigments: chlorophylls a and d, carotenoids, phycobilins (phycoerythrin, phycocyanin, allophycocyanins). Reserve product: floridean starch. Flagellated stage is absent. Cells possess a wall composed of pectin and cellulose layers, secrete mucilage, and sometimes incorporate calcium carbonate. Nuclei: 1 to several. Chloroplasts are permanent, granular or plate-like, with stellate pyrenoids.

Class Bangiophyceae

Porphyra in the Black Sea, used for human consumption.

Class Florideophyceae

Subkingdom True Algae

1,000 species of euglenoid algae found in freshwater bodies, including parasites of fish and frogs. The cell is covered with a pellicle. Reproduction occurs via cell division. The protoplast contains a stigma, nucleus, chloroplast, and Mitochondria. Assimilation product: paramylon; inclusions: volutin.

Phylum Diatoms

10,000 species of unicellular and colonial forms. Protoplast consists of cytoplasm, nucleus, plate-like or granular chloroplasts, pigments a and c, and carotenoids (fucoxanthin). Assimilation products: oil, volutin, chrysolaminarin.

Reproduction includes cell division and sexual reproduction.

They play a crucial role in trophic webs, and dead organisms form sedimentary rocks (diatomaceous earth). Modern species are responsible for water blooms.

Division Phaeophyta (Brown Algae)

Marine multicellular plants with a differentiated thallus attached to the bottom of water bodies. There are 1,500 species, 5 of which are freshwater.

The cells are uninucleate, cylindrical, or spherical. The cell wall is

two-layered, consisting of cellulose and pectin with pores. The protoplast contains numerous vacuoles; chloroplasts are numerous, discoid, ribbon-like, or plate-like. The pigments include chlorophylls a and c, carotenes, and xanthophylls (fucoxanthin). Assimilation products are CARBOHYDRATES (laminarin, mannitol) and oils. The thallus ranges from a few millimeters to 50 meters in length. They attach to the substrate via rhizoidal cells. In highly organized forms, the thallus resembles HIGHER SPORE PLANTS (stem-, leaf-, and ROOT-like parts). Growth is intercalary and apical. All types of reproduction are present.

Genus Laminaria comprises marine species up to 50 m long, which are valuable food and industrial plants.

Genus Sargassum

Genus Fucus

Producers of organic substances (alginates), mannitol (synthetic resins, paper, explosives), meal, iodine, fertilizers, and Trace Elements. In medicine, they are used as radioprotectants and iodine preparations.

Division Chlorophyta (Green Algae)

20,000 species of micro- and macroalgae distributed in fresh and saltwater habitats. They can be unicellular, colonial, multicellular, or non-cellular, exhibiting all types of organizational structure except amoeboid.

The cell wall is composed of cellulose or other Polysaccharides, encrusted with iron or calcium salts, and features pores. Cells contain one or several hundred nuclei. Chloroplasts vary in shape and number (1–100) and contain chlorophylls a and b along with carotenoids. They reproduce vegetatively, asexually, and sexually.

Genus Volvox

Representatives of this genus form spherical colonies (coenobia) of ball-like or spherical shape, up to 2 mm in size. Each colony consists of numerous biflagellate cells located at the periphery beneath a mucous involucre. Each cell is covered by its own wall, which fuses with the walls of neighboring cells to form a polygonal structure. The apical side of the cell wall presses against and tightly connects with the involucre. As a result, a peripheral layer of wall-chambers forms beneath the involucre, in which the cell protoplasts lie freely, as if suspended by their flagella. The flagella emerge outward through channels in the involucre. The space between the protoplasts and the walls is filled with mucus. In some species of the genus, the protoplasts of adjacent cells are interconnected by plasmodesmata passing through the lateral pores of the cell walls. The protoplast contains a parietal chloroplast with a pyrenoid and stigma, a single nucleus, and two contractile vacuoles. Representatives of the genus are widespread in the plankton of lakes, rivers, bogs, and puddles.

Genus Chlorococcum.

The cells have a rounded, spherical shape and resemble Chlamydomonas in structure, but lack flagella and contractile vacuoles. They occur singly or aggregated in clusters. They consist of a thin cell wall enclosing green contents, occasionally accompanied by orange or red pigments. They can be found as a green coating on tree bark and wooden structures. They reproduce via zoospores during asexual reproduction, and through isogamy during sexual reproduction. In asexual reproduction, the cell contents undergo repeated division, breaking down into several oval zoospores, each bearing two cilia.

Genus Ulothrix

Encompasses about 40 species. Ulothrix is common in rivers, living attached to submerged objects and forming bright green fouling mats. The filaments of Ulothrix consist of unbranched threads of varying lengths, which at the early stage of growth attach to the substrate by a colorless, elongated cell known as a rhizoid. The filament cells are short, cylindrical, or barrel-shaped. Each cell contains a nucleus, a parietal chloroplast shaped like an incomplete ring, and one or more pyrenoids. Reproduction is vegetative, asexual, and sexual. During Vegetative Reproduction, the Ulothrix filament breaks down into short segments, each of which grows to form a new filament.

Asexual reproduction is carried out via zoospores formed within the cells. Zoospores are egg- or pear-shaped cells with four flagella at the anterior end, a red eyespot, and two contractile vacuoles. Upon release, each zoospore attaches to the substrate after a short time and grows into an adult Organism.

During sexual reproduction, gametes similar to zoospores—though possessing only two flagella—are formed within the filament cells. There are more gametes per cell than zoospores. Fusing in pairs, gametes from the same filament or, more commonly, from different filaments form a zygote. It remains motile for a short time before settling to the bottom of the water body, losing its flagella, and becoming enveloped in a thick protective wall that shields it from adverse conditions. Upon zygote germination, reduction division (Meiosis) occurs, resulting in The formation of 4–16 haploid individuals.

Genus Spirogyra

A genus of filamentous macroscopic green algae that some researchers classify under the division Streptophyta. The filaments are unbranched, solitary or aggregated in clusters, ranging from a few millimeters to 10 m in length. The cells are short or elongated, cylindrical, with lens-shaped cross-walls. The cell wall is cellulosic, exteriorly covered with a layer of mucus. Each cell contains one to several parietal, ribbon-like, spiral chloroplasts with numerous pyrenoids. The pyrenoids feature a starch sheath. A large central vacuole is located in the center. A single large nucleus with a prominent nucleolus lies in the center of the vacuole within a cytoplasmic pocket, from which cytoplasmic strands radiate toward the periphery. The reserve nutrient is starch. The genus includes over 300 species. It reproduces both vegetatively and sexually. Vegetative reproduction occurs through filament fragmentation (accidental breakage of filaments or their dissolution into individual cells under unfavorable conditions, for example). New filaments develop from each filament segment or individual cell via division.

Sexual reproduction is accomplished through conjugation, which can be lateral or scalariform. In lateral conjugation, specialized outgrowths called conjugation tubes form between adjacent Cells of the same filament; these tubes fuse, after which the separating wall dissolves, the protoplasts and nuclei merge, and a zygote is formed. In scalariform conjugation, which is more common, conjugation tubes form between cells of two separate filaments. The behavior of the cells during this process differs: the receiving cell is termed the female cell, and the cell transferring its protoplast is termed the male cell.

As noted, conjugation results in the formation of a zygote, which becomes enveloped in a thick three-layered wall and germinates after a resting period. During germination, it undergoes meiotic division, producing four haploid nuclei. Three small ones degenerate, while the remaining large one—along with the zygote contents—forms the germling of a new individual, which gives rise to a new filament.

Species of this genus are widely distributed in freshwater and brackish basins, particularly in stagnant or slow-flowing waters. They can either float freely, forming slippery-to-the-Touch, bright green or emerald algal mats (commonly known as pond scum), or attach themselves to a substrate using rhizoids.

Charophytes (Chara)

One of the most highly evolved genera of algae, closely related to higher plants. The name originates from the Greek word *chara*, meaning joy or beauty. Over 400 species of charophytes are known, with 38 species recorded in the flora of Ukraine.

These are macroscopic algae that superficially resemble certain terrestrial plants, such as horsetails and hornworts. Their thallus typically reaches a height of 20–30 cm, though it can grow up to 1–2 m; lateral branches have limited growth. Green chloroplasts contain chlorophylls $a$ and $b$, as well as lycopene. They accumulate starch as a reserve nutrient.

Both vegetative and sexual reproduction are characteristic of this group. Vegetative reproduction occurs via specific bulbils on the rhizoids or star-shaped cell clusters at the lower stem nodes, which give rise to a new thallus. Asexual reproduction is absent. The sex Organs reach the highest level of development among all algae. The archegonia (female sex organs) and antheridia (male sex organs) are multicellular and, in most species, develop on the same plant (although dioecious species are also known). The antheridium appears as a small sphere up to 0.5 mm in diameter, initially green, but turning orange or red upon maturation. It sits on a short unicellular stalk and consists of 8 flat shield cells that tightly adjoin each other along their serrated edges. From the center of each shield cell, a cylindrical cell known as the "manubrium" extends inward into the antheridium, terminating in a rounded HEAD cell. This cell bears 6 smaller cells, each of which gives rise to 4 spermatogenous filaments. These filaments consist of 200–300 cells, with each cell producing a single biflagellate spermatozoid (antherozoid).

LICHENS

The branch of science that studies lichens is known as lichenology. The term was coined by Theophrastus (371–286 BC).

These are symbiotic organisms comprising Fungi—the heterotrophic component (mycobiont)—and algae—the autotrophic component (phycobiont).

They encompass 26,000 species distributed globally, including both cosmopolitan and endemic forms. Species diversity is particularly high in the temperate zone.

Mycobionts—the fungal component of lichens—may belong to the classes Basidiomycetes, Ascomycetes, or Phycomycetes. Mycobionts do not occur in nature in a free-living state, and when cultured in a laboratory, they grow very slowly and fail to form fruiting bodies.

Phycobionts. The algal component is represented by blue-green, green, yellow-green, and brown algae. Representatives of 28 genera from these algal divisions enter into Symbiosis with fungi. The most common lichen phycobiont is the green alga *Trebouxia*, alongside other green algae such as *Chlorella* and *Chlorococcum*. Among blue-green algae, *Nostoc* and *Gloeocapsa* are most frequently found within the lichen thallus.

While most of these algae exist as free-living organisms, some are found exclusively within lichens (*Trebouxia*, *Coccomyxa*, etc.) and have not yet been discovered in a free state. Within the lichen thallus, the algae undergo dramatic morphological changes. This is especially true for filamentous algae, which break down into individual cells inside the lichen and become completely unrecognizable. Inside the lichen, algae develop a higher resistance to elevated temperatures and can withstand prolonged desiccation. When cultivated on artificial media (separated from the fungi), they revert to the Morphology typical of free-living forms.

While the algae and cyanobacteria that make up lichens are represented by free-living species, lichen-forming fungi exist exclusively in symbiosis with them.

The partnership in a lichen is arguably more akin to a controlled parasitism of the autotroph by the fungus than a mutualistic symbiosis. The fungus and alga establish a close, long-term relationship, forming distinct morphological structures and metabolic pathways. The fungus acts as an obligate parasite. It develops specialized hyphae called haustoria, which penetrate the algal cells to facilitate nutrient exchange. The fungus gradually consumes the algal cell contents while maintaining a reserve, as destroying the entire alga would lead to its own demise. In return, the alga receives water and mineral nutrients from the fungus.

Nutrition is mixed—autotrophic-heterotrophic. Lichen nutrition is driven by Photosynthesis within the algal cells, and the resulting organic compounds are utilized by the fungus. Respiration, as well as the absorption of water and mineral salts, is managed by the fungal component (mycobiont) of the lichen thallus. The rates of photosynthesis, respiration, water uptake, and mineral absorption depend on light, Temperature, and humidity. Although the photosynthetic rate in lichens under optimal conditions is significantly lower than that of independent autotrophic plants, it produces sufficient organic matter to sustain normal metabolic activity.

Lichens are undemanding regarding environmental conditions and exhibit high resistance to adverse factors. They can thrive in A wide variety of light and moisture regimes, easily withstanding prolonged water shortages and drastic temperature fluctuations, though they react differently to air pollution.

Distribution: ranging from arid deserts to the Arctic (found on bare soil, tree bark, rocks, fences, and alpine peaks).

Coloration: ranging from white to black through various shades of red, orange, brown, yellow, and green. The color of the thallus is determined by pigments located in the hyphal walls and lichen fruiting bodies. Five pigment groups are distinguished: green, blue, violet, red, and brown. Pigments are synthesized only in the presence of light; therefore, the more light the lichen receives in its habitat, the brighter its coloration.

Morphology and Anatomical Structure of Lichens

Form:

- Crustose (crust-like) lichens feature thalli that resemble powdery, granular, or smooth coatings, or crusts tightly fused to the substrate. The thickness of these crusts varies from a barely perceptible film or powdery deposit to 0.5 cm, with diameters ranging from a few millimeters to 20–30 cm. Crustose lichens grow on soil surfaces, rock outcrops, tree and shrub bark, and decaying exposed wood. This group comprises the largest number of species (about 80%), which inhabit diverse environments;

- Foliose (leaf-like) lichens appear as dorsiventral flattened thalli attached to the substrate only at the center, typically via rhizines. These lobes are generally circular and 10–20 cm in diameter. A characteristic feature of foliose lichens is the distinct coloration and structure of the upper and lower surfaces of the thallus. Most species develop attachment organs on their lower surface—rhizoids consisting of bundled hyphae. They grow on soil surfaces and among mosses. Compared to crustose forms, foliose lichens represent a more advanced evolutionary stage.

- Fruticose lichens appear as branched shrubby clumps or ribbons attached to the substrate solely by their base. In terms of organizational complexity, fruticose lichens represent the peak of thallus evolution. Their size varies widely, from a few millimeters to 30–50 cm, while pendulous ("bearded") lichens like *Usnea* can reach lengths of 7–8 m. This group includes genera such as *Cetraria*, *Alectoria*, *Neuropogon*, and *Evernia*.

Intermediate and transitional forms also exist.

Anatomical Structure of Lichens

The lichen thallus consists of intertwined fungal hyphae and algal cells or filaments distributed among them. There are two MAIN TYPES OF microscopic thallus structure in lichens: homoiomerous and heteromerous:

- homoiomerous - a more primitive type in which the phycobiont cells are evenly distributed throughout the thallus thickness, with fungal hyphae running between them. When dry, they appear as black, brittle crusts or wrinkled cushions that swell upon wetting. These lichens form a group known as gelatinous lichens, as the algae secrete a mucilage in which both fungal and algal cells are embedded.;

- heteromerous type, in which a cross-section reveals several distinct layers: the upper surface of the thallus is covered by an upper cortex formed by densely intertwined fungal hyphae (plectenchyma), the next layer is an accumulation of phycobiont cells (gonidial layer), followed by the medulla, which consists of loosely interwoven fungal hyphae with large air-filled spaces between them. The underside of the thallus is covered by a lower cortex similar to the upper one. Fungal hyphae—rhizines—extend from the medulla into the lower cortex, anchoring the lichen to the substrate.

Reproduction of lichens

All types of reproduction occur, most frequently vegetative (via soredia and isidia).

Soredia are minute propagules consisting of one or a few algal cells surrounded by fungal hyphae. An accumulation of soredia is called a soralium. Soredia form inside the thallus within the gonidial layer of foliose and fruticose lichens. Once formed, the soredia are pushed out of the thallus, caught by the wind, and dispersed. Under favorable conditions, they germinate in new locations to form new lichens. About 30% of lichens reproduce via soredia.

Isidia are outgrowths On the surface of the lichen thallus consisting of both the phycobiont and mycobiont, but covered with a cortex. They appear as granules—cylindrical or coral-like outgrowths, or tiny leaf-like structures. Unlike soredia, isidia are not shed onto the thallus surface; instead, together with fragments of the thallus, they are broken off by animals or humans and, under favorable conditions, develop into a new lichen. Reproduction by isidia occurs in 15% of lichens.

Asexual reproduction involves pycnoconidia, which produce pycnospores of various SHAPES AND SIZES.

A sexual process is characteristic of lichens containing ascomycetous fungi, resulting in the formation of open or semi-open fruiting bodies containing asci and ascospores.

A characteristic biological feature of lichens is The production of lichen acids, which deposit on The surface of hyphae as crystals, rods, granules, etc. These acids determine the color of lichens. Up to 150 lichen acids are known. Their biological significance is not yet fully understood; however, some exhibit antibiotic or toxic properties and presumably serve a protective function.

Ecological groups of lichens

They colonize soil, trees, rocks, and various other substrates.

Epiphytic lichens grow on the trunks and leaves of trees and shrubs.

Epixylous species colonize decaying wood.

Epilithic lichens inhabit rocky substrates.

Taxonomy is based on the mycobiont composition within the thallus. They are divided into three classes: Ascomycetes (Ascomycota), Basidiomycetes (Basidiomycota), and Mitosporic lichens (Mitolichenes).

Ecological and Economic Importance of Lichens

- They accumulate solar energy and break down organic and mineral compounds. Being pioneer organisms, they are the first to colonize substrates unsuitable for other life forms. In the tundra, they act as key ecosystem engineers, serve as bioindicators of air purity, and provide vital forage for reindeer.

- They yield gelatinous substances used in the confectionery

industry, and serve as a source of glucose and Vitamin C. In Japan, the edible lichen Umbilicaria esculenta is consumed as a delicacy; in the deserts of the Middle East, Aspicilia esculenta is known as "manna from heaven"; and in Egypt, Evernia species are used to flavor bread. They are used to produce litmus paper and Dyes (e.g., Lecanora esculenta, Roccella), as well as fixatives in the perfume industry to stabilize fragrances (e.g., Parmelia, Ramalina, Evernia prunastri), along with various dyes (Ochrolechia, certain Roccella species). Alcohol is also extracted from lichens (such as Cetraria islandica and some Cladonia species).

In medicine, about 40 lichen species are utilized (including Cetraria, Lecanora, and Lobaria). In Egypt, they are used to treat Liver disorders; Cetraria islandica (Iceland moss) exhibits tonic and antibiotic properties effective against staphylococci, streptococci, and other pathogens.

Given their slow growth rate, the harvesting of lichens must be carefully managed and regulated to prevent irreversible environmental damage.