Classification of plant groups

PLANT GROUPS
(2)

The characteristic of algal forms basic to a classification system are:
1 Pigments Chemical composition and relative amounts
2 Food Reserves Products of photosynthesis and their chemistry
3 Flagellation The type and number or flagella morphology
4 Cell wall Chemistry, physical features
5 Nucleus Presence or absence of a true nucleus (Eukaryotic or Akaryotic)
6 Life history and reproduction Reproductive organ and methods


Bold and Wyne (1978) Classified Algae into Ten Groups
1. Division Cyanophyta
2. Division Prochlorophyta
3. Division Chlorophyta
4. Division Euglenophyta
5. Division Phaeophyta
6. Division Chrysophyta
7. Division Pyrrophyta
8. Division Rhodophyta
9. Division Cryptophyta
10. Division Charophyta

Kumar and Singh Classified Algae into two Sub kingdoms
A. Sub Kingdom Procaryota
1 Division Cyanophyta
B. Sub Kingdom Eucaryota
2 Division Chlorophyta
3 Division Xanthophyta
4 Division Chrysophyta
5 Division Bacillariophyta
6 Division Pyrrophyta
7 Division Cryptophyta
8 Division Euglenophyta
9 Division Phaeophyta
10 Division Rhodophyta

Round (1973) divided Algae into two major groups
Major Group Phylum
Procaryota Cyanophyta

Eucaryota

Euglenophyta
Chlorophyta
Charophyta
Parsinophyta
Xanthophyta
Haptophyta
Dinophyta
Bacillriophyta
Crysophyta
Phaeophta
Rhodophyta
Cryptophyta

The Procaryotic Algae
The Cyanophyta (Blue green algae) are representative of the simplest photoautotrophic. The algae may occur in unicellular, aggregates or arranged linearly in a filament.
General characteristic of the Cyanophyta
1 Habitat Water, Swaps, Soil, occasionally Endolithic
2 Pigments Chlorophyll a, ?-carotene, myxo-xanthin, biliprotein (phycoerythrin & phycocyanin)
3 Food Reserves Cyanophycean starch(similar to glycogen),polyphosphate granules (volutin), cyanophycin (a Protein)
4 Cell wall component Murein, Hemicelloses
5 Reproduction Vegetative, Asexual, Genetic recombination observed but mechanism unknown
6 Growth forms Unicellular, Aggregates, Filamentous

The cells rarely exceeding 10µm in diameter are less differentiated than those of any other algal division. The nuclear material is not enclosed in an envelope. The Cyanophyta are thus Procaryotic. All blue-green algae and prochlorophytes are non-motile Gram-negative eubacteria. And in many features resemble the bacteria. They are indeed often classified with bacteria rather than with algae. The resemblance is enhanced by many being
1) Attacked by viruses similar the bacteriophage
2) Some species bearing filamentous appendages (Fimbriae) found only in gram negative bacteria.
Some marine species also contain gas vesicles used for buoyancy regulation. In many filamentous species the chains of cells are interrupted by conspicuously large cells called Heterocysts. The heterocysts contain chlorophyll a & some other pigments but altogether pale. Heterocysts are the site of the fixation of atmospheric nitrogen & the enzyme responsible for this is Nitrogenase. The cell wall of the Cyanophyta contains a layer of peptidoglucan & Murein adjacent to Plasmalemma. The walls are thus chemically & structurally similar to gram negative bacteria & their formation is disorganized by penicillin.


Reproduction in Cyanophyta
1) Sexual Reproduction: Genetic recombination observed but mechanisms unknown
2) Vegetative Reproduction:
a. Cell division in some species mainly those that are unicellular
b. Fragmentation in colonies and filamentous forms
c. Hormogonium a short thread (2-3 or more of cells) there are no flagella or cilia the Hormogonium eventually settle and give rise to filaments
d. Homospore or Homocyst found in branched filament
3) Asexual Reproduction
a. Heterocysts serve as reproductive organs
b. Akinetes thick walled resting spore are very resistant to desiccation and extreme of temperature
c. Endospores the cell enlarges and the protoplast meanwhile divides to many naked daughter cells termed endospore
d. Exospore separated of outer part of protoplast and enclosed with wall to form spore termed exospore.




The Cyanophyta contain two principal orders
1) Chroococcales mainly single or aggregated spherical cells
2) Hormogonales: Filament forms
Chroococcales
Containing the simplest blue green algae are colonies forms with a regular and conspicuous symmetry. In Chroococcus single cells are occasionally seen. But, more usually and always similar to Gloeocapsa the cells remain held together after division in mucilage matrix. These aggregate of indefinite size and shape are referred to as Palmelloid forms. The sheath of Gloeocapsa maybe colored in the living cells and usually is thicker and more prominent than in Chroococcus. The colonies of Gloeocapsa are more complex than those of Chroococcus being composed of more individual and in Gloeocapsa each cell has an individual sheath. In Gloeocapsa the cell rounded or rounded in pole but in Chroococcus half circle.






Chamaesiphon is epiphytic on other algae and aquatic flowering plants. The cells of Chamaesiphon are attached to their hosts by holdfasts. The cells are enlarged distally from a tapering base.
Division of one cell into two equal daughters don’t occur in Chamaesiphon Instead a series of small walled cells are delimited from the distal portion of the individual and these are gradually discharged through a terminal opening in the cell wall. These small cells are called exospore and presumably float to suitable substrata where they germinate into new individual.










Microcystis
The cells are surrounded by a common sheath the densely cellular colonies vary in shape from spherical to irregular. M. aeroginosa frequently is a component of water blooms. The individual cells are minute and spherical and usually contain refractive pseudo vacuoles which are filled with gas, a common attribute of plankton.







Merismopedia
The cells are arranged in regular rows to form a plate. The ellipsoidal cells are arrangement in flat colonies this regularity of arrangement arises from the limitation of cell division to two directions.









Hormogonales
Oscillatoria
It’s occurring floating in aquatic habitats or on damp soil. This genus contains many species. In some of them the cells are broader than long, whereas in others reverse is true. In Oscillatoria there is no differentiation among component cells of a trichome, except that apical cell may differ in shape from the other vegetative cells, and its wall thickens sheath usually are not demonstrable around the trichome of Oscillatoria













Lyngbya
It’s occurs in both fresh and salt water, differs from Oscillatoria in that trichomes are surrounded by rather firm clearly visible sheath.











In both Oscillatoria and Lyngbya multiplication of the filament takes place by type of fragmentation called Hormogonium formation in this process either because of the death of one or more cells in the trichome or because of weakness at one point. The chains of cells break up into multicellular fragment (Hormogonia). These are motile and capable of forming a new trichome. In Oscillatoria and Lyngbya the rapture is evoked by the death of cells.

Anabaena and Nostoc
They are unbranched filamentous, Anabaena a genus that contains both planktonic species and some forms coatings on other vegetation.

Nostoc includes a member of both aquatic and terrestrial or rock inhabiting species.
In Anabaena and Nostoc the filaments differentiated into three types of cells Vegetative cells, Heterocysts and Akinetes.









Function of Heterocysts
1) Maybe the agent of nitrogen fixation
2) Transfer of combined nitrogen to the vegetative cells
3) They may evoke the transformation of vegetative cell adjacent to them into Akinetes
4) Maybe germinate to filament (Asexual reproduction)

Akinetes are highly resistant to environment adverities and have germinated after 87 years of air dry storage.
Anabaena and Nostoc use in Rices field because of nitrogen fixation.
Anabaena differ from Nostoc in vegetative cells are being dram or cylindrical shape while in Nostoc are being small spherical shape and Nostoc forms colonies but Anabaena lives in aggregates or alone.




Rivularia and Gloeotrichia
They are taper forms basal to apex almost colorless hair like cells. The basal vegetative cell of each filament becomes transformed in to heterocyst. In Gloeotrichia one or more enlarged Akinetes usually are developed from vegetative cells in the vicinity of Heterocysts. Akinetes are lacking in Rivularia





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