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FEDERAL UNIVERSITY DUTSE
FACULTY OF SCIENCE
BIOLOGICAL SCIENCES DEPARTMENT
SEEDLESS PLANT LECTURE NOTES
THALLOPHYTA
1 (THE ALGAE)
1.1 WHAT ARE ALGAE?
Algae are any of many diverse aquatic photosynthetic organisms whose size ranges from unicellular to multicellular forms such as in giant kelps that grow to 65m in length. Like plants, most algae are photosynthetic and simple. They are simple because their tissues are not organized into the many distinct organs as found in land plants. The largest and most complex marine forms are called seaweeds. Algae were earlier classified with plants as they are photosynthetic, possessing chlorophyll and chloroplasts and superficially appear like plants. However, algae, particularly the prokaryotic forms are in modern science placed in kingdom protista along with protozoa because their gametes do not have protective cells around them and thus no longer classified with plants. 1.2 GENERAL CHARACTERISTICS OF ALGAE
- Most algae are photosynthetic and simple because their tissues are not organized into many distinct organs as are found in land plants. The largest and most complex marine forms are called seaweeds. However, l ike other green plants, algae also require good sources of Nitrogen, Phosphorus, potassium, e.t.c.
- Algae are mostly aquatic; both fresh water and marine, living entirely in the water or on wet substrates such as walls, soils, rocks, as well as in association with fungi and certain animals. Though the prokaryotic cyanobacteria (commonly referred to as blue-green algae) were traditionally included as "algae" in older textbooks, many modern sources regard this as outdated as they are now considered to be bacteria. The term algae is now restricted to eukaryotic thallophytes.
- All true algae therefore have a nucleus enclosed within a membrane and plastids bound in one or more membranes.
- Algae exhibit a wide range of reproductive strategies from simple asexual cell division to complex forms of sexual reproduction.
- Algae lack the various structures that characterize land plants, such as phyllids (leaves) and rhizoids in nonvascular plants or leaves, roots and other organs that are found in tracheophytes (vascular plants). Many are phototrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy or phagotrophy. However, some unicellular
species rely entirely on external energy sources and have limited or no photosynthetic apparatus.
- Nearly all algae have photosynthetic machinery ultimately derived from cyanobacteria and hence, produce oxygen as a by-product of photosynthesis. Three principal pigments are found in various marine and aquatic algae. They are: chlorophyll, carotenoids (sub-divided into carotenes, xanthophyll and carotenoid acids) and phycobilins (sub-divided into phycocyanins and phycoerythrins). 1.3 MORPHOLOGY OF ALGAE Although simple in structure and lacking differentiation, algae exhibit great diversity in size and appearance. Their size ranges from simple microsocpic to giant thallus extending several metres in length as in kelps. Therefore, algal morphology varies from simple unicellular form to complex thallus as found in seaweed. The body of an alga is called thallus. In unicellular algae it is simple consisting of a single cell. All multicellular organisms start their life as single cells. When a cell divides and the daughter cells form a packet enclosed in a mucilaginous mass, a colony is formed Morphologically, algae can be distinguished as unicellular, colonial, filamentous, heterotrichous, thalloid and polysiphonoid forms. 1.3.1 Unicellular Form Single cells, cylindrical, short or long; sometimes very long snake forms. Cells divide by constriction, the two daughter cell get separated and they rarely remain together to form a 2-celled filament. Typical unicellular form of algae can be seen in Anacystis and Clamydomonas 1.3.2 Colonial Form Here, when a cell divides and the daughter cells formed remain together within a common mucilage mass, it is known as a colony. A colony may contain large number of cells. Sometimes it may be so big that one can see it with unaided eyes. Example of colonial algae includes Microcystis and Volvox 1.3.3 Filamentous Form Filamentous form of algae can be generated when a cell divides always cross-wise and the daughter cells do not separate from each other, it results in a linear row of cells as in Nostoc , Ulothrix and Oedogonium. 1.3.4 Heterotrichous Form When some cells of a filament divide vertically it results in a branch. Many filamentous forms show extensive branching of the main filament giving it a bushy appearance. In some algae the branches at the base remain horizontal, attached to the substratum known as prostrate system from which erect system of vertical branched filaments arise. This type of body is known as heterotrichous habit. Heterotrichous
c) Planktophytes : - algae which float on the surface of the water. Examples are Volvox and Microspora. d) Halophytes : - are algae found to occur in saline waters. The most striking examples are Chlamydomonas and Oscillatoria. e) Epizoophytes : - many algae found on living aquatic animals such as mollusc shell and fishes. Species of Cladophora are found growing upon mollusc shells. f) Thermophytes : - these are aquatic algae that can tolerate the temperature of up to 70˚C or more than that. Examples of thermophytes algae are Oscillatoria and sompe species of Myxophyceae. g) Epiphytes : - many algae found upon other living plants and bigger species of algae. Aphanochaete and Oedogonium are found as epiphytes upon larger species of Cladophora and Vaucheria. h) Fluviatile algae : - these are algae found in rapidly flowing waters. Ulothrix occurs in mountain falls. 1.4.2 Edaphophytes : - these are also called terrestrial algae. They are found upon or inside the surface of the earth. Edaphophytes can be either: a) Saphophytes : - soil surface algae like Botrydium and Vaucheria. b) Cryptophytes : - algae which are subterranean in habit and occur inside the soil. Species of Nostoc, Anabaena and Euglena are reported to have been found inside the soil. 1.4.3 Aerophytes : - these algae are aerial in habitat. They are found upon the trunk of trees, walls, fencing wires, rocks and so many other aerial substrata. Some are found in mixture with some mosses and liverworts on the bark of trees called the Epiphloephytes , some are epiphytic upon leaves of trees called Epiphyllophytes , others are found growing on the rocks and walls called Lithophytes while others are found on the bodies of land animals called the Epizoophytes. 1.4.4 Cryophytes : - Many algae are found to grow on ice or snow which normally causes red, yellow, green, yellowish green and violet snows. Classical example of cryophytes is Clamydomonas which causes the green snow. 1.4.5 Symbionts or endophytes : - Many algae are found to grow in symbiotic association with other plants. The most striking example of symbiosis is lichens. Here, Nostoc and Anabaena are separated from the association. 1.4.6 Endozoophytes : - these are algae, which occur inside the body animals. Examples of endozoophytes are Zooxanthella found inside fresh sponges and Zoochlorella in Hydra viridis. 1.4.7 Parasite : - certain algae are parasite upon other plants. The most striking example is Cephaleurosvirescens which causes the hovoc of tea foliage called “red rust of tea”.
1.5 ECONOMIC IMPORTANCE OF ALGAE
The economic importance of algae cannot be much realized without deep study of it. The following are some economic importance of algae realized: 1.5.1 Destructive aspect
- Algae are very harmful to living stock by changing the colour and nature of water thereby blocking the gills of fishes and subsequently perish by suffocation.
- Some species like Cephaleurosvirescens are parasite causing various degrees of diseases.
- Blue-green algae deteriorate exposed fabrics, particularly during the rainy season to make the cloth black spotted and weak.
- Giant algae retard the speed of ship called fouling of ship. Ships therefore, have to constantly be cleaned and painted.
- Filamentous algae form a net-like structure in the water which causes mechanical injury to aquatic animals.
- Algae contaminate water by developing foul odour through their secretions and subsequently making it unhygienic. 1.5.2 Useful aspect
- Algae being the photosynthetic organisms are therefore, the primary producers in ecosystem.
- Several seaweeds are eaten rough by man particularly in Japan and some species of Spirogyra and Oedogonium in South India.
- Vitamin A, B and E are abundantly found in seaweed.
- Algae can be used as a source of agar which is used in the preparation of ice- cream, jellies, cosmetics e.t.c.
- Diseases caused by vitamin deficiency as vitex asthma and tooth decay can be cured by many species of algae.
- Algae are also found to be very useful in the manufacture of iodine.
- By burning seaweed on the sea coast, the alkalies are prepared from seaweed ash which is employed in the manufacture of soap and alums.
- Some species of algae like Botrydium and spirogyra are grown in the garden and ponds for good looking habitat.
- The oxygen given out by algae as a by-product of photosynthesis can be used by animals for respiration. 1.5 LIFE-CYCLE PATTERNS IN ALGAE Life cycle in biology refers to a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction. Most algae have two recognisable phases in their life-cycle (when it include sexual reproduction) alternating with one another. Each of these two phases, sporophyte (diploid) and gametophyte (haploid) can be regarded as plant.
plant by mitotic divisions. Laminaria, Urospora, and some members of chlorophyceae are some algal examples exhibiting this pattern of life-cycle.
5. Haplobiontic pattern : - unlike in isomorphic and heteromorphic patterns where they have two phases each, there are three phases (triphasic) in haplobionticlife- cycle. Two of these three phases are haploid (n) and the remaining phase is diploid (2n). In this case, a haploid gametophytic phase produces gametes which on fusion form a zygote (2n). This zygote is the only diploid phase which divides meiotically to form haploid asexual phase called carposporophyte (n). The carposporophyte also reproduces asexually to form haploid carpospores which again develop into gametophyte (haploid plant). Therefore, carposporophyte and gametophyte alternate with zygote in this life-cycle pattern. Some members of chlorophyceae and rhodophyceae are found to exhibit this life-cycle pattern. 6. Diplobiontic pattern : - this is a reverse of haplobionticlife-cycle. It is also triphasic but differs with latter in having two diploid (2n) phases called carposporophyte (2n) and tetrasporophyte (2n) alternating with one haploid (n) or gametophyte phase. In this case, the gametophyte (n) produces gametes which unite to from zygote (2n) and the zygote divide mitotically to form a carposporophyte (2n) bearing carpospores (2n). These carpospores germinate to form another diploid plant called tetrasporophyte (2n). The tetrasporophyte undergo reduction division (meiosis) to form haploid (n) tetraspores which later germinate to give rise to haploid gametophytic plant. 1.6 REPRODUCTION IN ALGAE The act of producing new biological generation in algae is achieved by three common methods. These are: a) Vegetative b) Sexual and c) Asexual However, under adverse conditions, several perrennating bodies also develop in addition to these three common methods. 1.7.1 Vegetative reproduction : - It is a process by which new individuals arise without production of seeds or spores. Vegetative reproduction in algae is of several types. Among which are:
i. Cell division : - in this method, the mother cells divides to produce the daughter cells which grow into new plants. Some examples of algae undergoing this mode of reproduction are: diatoms, desmids, Euglenae.t.c. ii. Fragmentation : - the algal body here breaks into several parts or fragments and each of the fragments formed develops into an individual. Examples of algae undergoing this mode of vegetative reproduction are mostly filamentous like Ulothrix, Spirogyra, e.t.c. iii. Hormogone formation : - the hair like structures called the trichomes breaks into small pieces of two or more cells. These pieces are called hormogone and each hormogone develops into a new plant. Example is seen in Oscillatoria, Nostoc, e.t.c. iv. Hormospores or hormocysts: - these are very thick-walled hormogones normally produced in a drier condition. Examples of algae producing hormospores are Oscillatoria, Nostoc, e.t.c. v. Tubers: - these are usually fleshy, thickened and rounded bodies filled up with abundance of starch. Each body may give rise to a new plant. Example of algae showing this mode of vegetative reproduction is Chara. vi. Bulbils: - these are usually small bud-like structures often develop from the rhizoids of Chara. They may develop into new plant. Other types of vegetative reproduction in algae include: akinetes, starch or amylum star, primary and secondary protonema and adventitious thalli formation. 1.6.2 Sexual reproduction : - the process that creates a new organism by combining the genetic material of two organisms in algae is momentously progressive and yet found unknown in some group of algae like Myxophyceae. There are two general types of sexual reproduction in algae. These are: i. Isogamy : - this is a form of sexual reproduction involving gametes of similar morphology. Fusion of similar motile gametes of algae is found in many species and the gametes taking part in the fusion are usually from different individuals or filaments or from different cells of the same filament. ii. Heterogamy : - this involves union of dissimilar gametes in terms of size, structure and function. They can be: a. Anisogamy : it is a form of sexual bonding involving partners of unusually widely differing ages. However, the motile gametes taking part in fusion may either differ in size or physiological behaviour. b. Oogamy : - a form of anisogamy in which the female gamete (egg) is significantly larger than the male gamete (antherozoid) and is non-motile. The fusion may be of primitive type as in Cylindrocapsa or advanced type as found in Oedogonium, Vaucheria, Chara, e.t.c.
Pigmentation: pigments are just like in higher green plants. i.e. chlorophyll a, chlorophyll b, Xanthophyll and Carotenes and are localized in definite plastids or chromatophores. Assimilatory food products: is starch, rarely oil as in Vaucheria. The pyrenoids are usually present in the chromatophores. Type of flagella: is isokonate type. i.e. both the flagella are equal in length.
2. Xanthophyceae Pigmentation: the chromatophores are yellow green, containing chlorophyll a, carotenes (ß carotene) and xanthophyll in them. Assimilatory food products: the starch is not found and the pyrenoids are absent. The chief food products are oils. Type of flagella: is heterokonate type. i.e. one flagellum is short and other long. 3. Baccillariophyceae Pigmentation: the chromatophores are golden brown or yellow due to the presence of pigment called diatomin. Other pigments present are chlorophyll a, carotenes (ß carotene) and xanthophyll. Assimilatory food products: are fats and volutin. Type of flagella: flagellate bodies are 1 to 2 flagellate. 4. Phaephyceae Pigmentation: the chromatophores are yellowish brown, possessing xanthophyll in abundance in them. Chlorophyll a, carotenes (ß carotene) are also found. Assimilatory food products: are alcohols, mannitol and laminarin. Type of flagella: motile cells are pyriform with two laterally inserted flagella, one of which is of tinsel type and mostly the anterior flagellum is longer. 5. Rhodophyceae Pigmentation: the chromatophores possess r-phycoerythrin and c-phycocyanin pigments. Chlorophyll a, carotenes (ß carotene) and xanthophyll are other pigments found in them. The plant looks reddish in colour Assimilatory food products: are polysaccharides, floridean starch and a soluble sugar called floridoside. Type of flagella: flagellation is completely absent. 6. Myxophyceae Pigmentation: pigments are not localized in definite chromatophores, but in the peripheral portion of the protoplast. The main figments are chlorophyll a, carotenes (ß carotene) and xanthophyll. r-phycoerithrin and c-phycocyanin pigments are responsible for red and blue pigmentation. Assimilatory food products: are sugars and glycogen-like compound called cyanophycean starch Type of flagella: flagellation is completely absent.
CHLOROPHYTA:
The division is considered as the most important group of algae and is commonly considered as the group in which higher plants emerged. They have the following characteristics: They are the ancestors of angiosperms and gymnosperms. The division chlorophyta is composed of plants which posses the grass-green chromatophore. There is presence of starch grain which acts as a reserved food material. The vegetative plant body varies from a motile unicellular to a complex filament of many cells. They are commonly found in ponds and other water bodies which are mostly turbin. They can also be founon a free-living plants as epiphyte or a parasite. Several genera of chlorophyta are known to exist. Among which are: Chlamydomonas The Genus chlamydomonas consists of over 500 species and they are commonly found in stagnant water like ditches, ponds, pools and other stagnant waters. They are also found in fresh water habitat, moist and dump areas. Structure Chlamydomonas is unicellular and motile due to the presence of a pair of flagella at the anterior end of the cell. The cell is oval in shape and has a cell wall made up of cellulose. It contains a cup-shaped chloroplast which is usually green in colour due to the possession of chlorophyll. The chloroplast occupied about ½ - ⅔ of the cell. At the basal portion of the chloroplast is the pyrenoid and functioned as the site of starch synthesis. There is a reddish spot knwon as an eye-spot or stigma spot. This organ is useful in photoreception. There are two contractile vacoules used to accumulate excess water and passed it out (osmoregulation). Nucleus is present and is located within the cytoplasm, i.e. within the cup-shaped chloroplast.
In Bryophytes, plant body is parenchymatous(soft plant tissue made up of thin- walled cells) with cells arranged in several layers. Branching of thalli is dichotomous. Tissues show no distinct differentiation; however they are modified for specialized functions. Tissue shows distinct division of labor. There are many chloroplasts present. Stomata / pores are present. Rhizoids and scales are present. Rhizoids may be smooth-walled or tuberculated. Growth and development is restricted to specialized cells. Reproduction In Thallophytes, reproduction is mainly asexual. When sexual, reproduction is isogamous, anisogamous or oogamous. Sex organs are single celled. Oogonium, the female sex organ is single celled which is typical of aquatic plants. Jacket and sterile vegetative cells are absent in the sex organs. In Bryophytes, asexual reproduction is absent. Vegetative reproduction may be observed. Reproduction is predominantly sexual in nature. Jacket cells are vegetative and sterile around the sex organs, which are multi-celled. The female sex organ is the Archegonium, which is characteristic of land plants. It consists of jacket cells, neck canal cells, and an egg cell. The Sporophyte: In Thallophytes, the parent plant releases the zygospore. The zygospore goes through a resting phase before it germinates. It then goes through a phase of meiotic divisions to produce spores. The sporophyte constitute the independent stage in the life cycle. Plant exhibits ill-defined homogamous(having same type of sex chromosomes: producing gametes that have the same type of sex chromosome) alternation of generation. With regard to Bryophytes, soon after fertilization, the zygote germinates into the sporophyte while still in the parent plant. There is no resting phase. Plant exhibits heterogamous alternation of generation. Meiosis occurs later during the growth of the embryo. The sporophyte, once formed, is still dependent on the mother plant. In most cases, it is released on the death of the parent plant.
