Vegetative Structure - Chlorophyceae.pptx

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1. Vegetative Structure Chlorophyceae (Green Algae)   Dr.Mansi Pandey Dr.Mansi Pandey Dr.Mansi Pandey 1

2.   Green algae or Chlorophyceae , Division Chlorophyta Comprises almost 9,000 to 12,000 species. Most green algae occur in fresh water, usually attached to submerged rocks and wood or as scum on stagnant water; there are also terrestrial and marine species. Free-floating microscopic species serve as food and oxygen sources for aquatic organisms. Green algae are also important in the evolutionary study of plants; the single-celled Chlamydomonas is considered similar to the ancestral form that probably gave rise to land plants.   The photosynthetic pigments (chlorophylls a and b, carotene, and xanthophyll) are in the same proportions as those in higher plants.     Dr.Mansi Pandey 2

3. Common chlorophytes : (A)  Chlamydomonas  sp., (B)  Volvox  sp., (C)  Pandorina  sp., (D)  Hydrodictyon ,  (E)  Microspora  sp., (F)  Entoderma  sp., (G)  Coleochaete  sp., (H)  Oedogonium  sp., (K)  Struvea  sp., and (L)  Caulerpa  sp. Green algae, varies in size and shape, include single-celled ( Chlamydomonas , desmids), colonial ( Hydrodictyon , Volvox ), filamentous (Spirogyra, Cladophora ), and tubular ( Actebularia , Caulerpa ) forms. Sexual reproduction is common, with gametes that have two or four flagella. Dr.Mansi Pandey 3

4. Structure : Exhibit a wide range of variations in their thallus structures- Like unicellular motile ( Chlamydomonas ), and unicellular non-motile (Chlorella) ( Ulva ) ), unbranched (Spirogyra), heterotrichous ( Coleochaete ), siphonaceous ( Vaucheria ), palmelloid ( Tetraspora ), dendroid ( Ecballocystis The typical green algal cell- Can be motile or non-motile. Flagella are inserted either apically or subapically , are one in number, and are of equal size. The anterior portion of the flagellate cells has an eye spot or stigma that is still inserted on one side of the chloroplast. Eukaryotic cells make up the organism. In most cells, there is only one nucleus, but the coenocytic bodies of Siphonales and Cladophorales have many nuclei. In contrast to the normal rule of one nucleolus per nucleus, Conjugales members have several nucleoli with a central vacuole. The protoplast is surrounded by a semipermeable cell membrane that is found inside the cell wall. Numerous tiny vacuoles in the cytoplasm push the nucleus and surrounding cytoplasm outward and are known as primordial utricles. Dr.Mansi Pandey 4

5. The chloroplast is where the pigments are found - pigments contained in plastids that vary in shape in different species like discoid, plate-like, reticulate, cup-molded, winding, or lace formed in various species, and a two-layered cellulose and pectin cell wall. Pyrenoids : Pyrenoid is typically present in chloroplast (s). The greater part of the individuals has at least one storing body called pyrenoids situated in the chloroplast where food is stored in the form of starch ( proteinaceous cores within the plastids) also contain proteins other than starch.. Some green growth might store food as oil drops. They generally have a cell wall comprised of an inward layer of cellulose and an external layer of pectose . Cellulose, which is primarily composed of xylans and mannans and hydroxyproline glycosides, makes up the majority of the cell wall. In Chara , calcium and magnesium carbonate are embedded in the cell wall.   Dr.Mansi Pandey 5

6. Vegetative Structure of Chlorophyceae :- Green algae, shows a great variety in their vegetative organization and also in their life cycle as well as in habitat. Organization of thallus ranges from simple, primitive motile unicells , to complex and highly evolved multicellular forms. They are few microns to several feet in dimension. Habitat Like : Green macroalgae of Ulvophyceous green algae exist in marine and brackish coastal ecosystems. Ulva mutabilis ( Foliaceous plantbody ) Dr.Mansi Pandey 6

7. From simple to complicated forms, various types of thallus evolved in green algae along different lines or according to their habitat. These are grouped as follows: Unicellular (Motile or non-motile) Aggregates ( Palmelloid or Dendroid) Colonial (Motile or Non-motile) Filamentous ( Unbranched or Branched) [Branched filaments may be simple, heterotrichous or pseudoparenchymatous .] Siphonaceous , Foliaceous , and Parenchymatous Dr.Mansi Pandey 7

8. UNICELLULAR: Chlorella: Unicellular non-motile green alga, a genus of about thirteen species of single-celled green algae of the division Chlorophyta . It is spherical in shape, about 2 to 10 μm in diameter, and is without flagella. Their chloroplasts contain the green photosynthetic pigments chlorophyll-a and -b. In ideal conditions cells of Chlorella multiply rapidly, requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. Example of motile unicellular green alga is Chlamydomonas . Dr.Mansi Pandey 8

9. In another Chlorophyceae , flagella are whiplash type being two in number or in multiples of two, all being equal in size and attached at the anterior end e.g. Chlamydomonas or single e.g. Euglena . Euglena is of green algal origin with several chloroplasts surrounded by three membranes and phoreceptor pyrenoid . Dr.Mansi Pandey 9

10. Green algae mostly being aquatic and fresh water forms show great variety in thallus organization along with the life cycle and habitat, than any other group of algae. From simple to complicated forms, various types of thallus evolved in different groups of algae along different lines such as those known as Volvocine , Coccoid , Siphonaceous or Coenocytic , Tetrasporine , filamentous (branched and unbranched ), Heterotrichy , Uniaxial / Multiaxial filaments and Parenchymatous tissue formation. Dr.Mansi Pandey 10

11. The most primitive order of Chlorophyceae is Volvocales . In this group, the simplest and most primitive thallus is represented by the motile unicells . Such unicells could give rise to all other forms of thalli . If the motile unicells loose flagella, the Chlorella type of thalli could form. If the unicells could adhere together loosely, a colony of simple, similar and unspecialized or specialized cells could form. The colony could be motile or non-motile . Dr.Mansi Pandey 11

12. Definite number of flagellated unicells could unite together to form a motile colony. A simple motile colony may have 4,8,16 or more flagellated unicells , held by mucilage. All the cells of such a colony are physiologically independent and each of them resembles the unicell of Chlamydomonas . The colony, however, behaves as one unit. Gonium has colonies of 4-8-16 cells arranged in a flat quadrangular plate in a common gelatinous matrix. Cells are ovoid to pyriform with a single cup-shaped chloroplast and a pyrenoid . Dr.Mansi Pandey 12

13. Each cell of Gonium comprises two equal flagella with contractile vacuoles at their base and an eyespot. Four and eight-celled colonies have the flagella on the same side. Sixteen-celled colonies have four central cells with their flagella on the same side with twelve marginal cells with radially arranged flagella. 16-celled Gonium colony Dr.Mansi Pandey 13

14. First line of evolution of green algae into motile colonies is called the volvocine line . It culminates in Volvox . If the cells in a colony are definite in number, arrangement and having an anterior, posterior polarity, the colony is called coenobium, e.g. Gonium, Volvox and Pandorina - Is like Gonium. It is slightly advanced. It shows differentiation of cells in anterior end from posterior end. Dr.Mansi Pandey 14

15. A coenobium often gives rise to internal daughter colonies. In Volvox , the coenobium is spherical and consist of about 50,000 Chalamydomonas type biflagellate cells. On maturity, it shows 95% Chalamydomanas type cells towards the anterior end, and 10% gonidial cells towards the posterior end of the colony Dr.Mansi Pandey 15

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17. Hydrodictyon sp. Chlorococcum sp Non-motile colonies: The motile cells losing their flagella and associating together result into non- motile colonies. This line of evolution is called Chloro-coccine line. A mature colony of the waternet Hydrodictyon consists of non-motile elongated cells make polygonal shapes. These cells are coenocytic and contain many nuclei. Dr.Mansi Pandey 17

18. Siphonaceous or coenocytic thallus : Some single celled algae elongate to form a nonseptate , multinucleate, tubular structure. It is called coenocytic condition. It results from karyokinesis without cytokinesis, e.g. Codium and Vaucheria . Vaucheria has a long and branched, coenocytic and siphonaceous thallus and the septa are formed only at the time of reproduction or at the site of injury. Dr.Mansi Pandey 18

19. Acetabularia is a siphonaceous alga, which consists of a stalk ending in an umbrella shaped cap. The stalk bears the only nucleus present in thallus . In Caulerpa , a large coenocytic thallus consists of a branched creeping rhizome and erect assimilatory shoots of various shapes. Dr.Mansi Pandey 19

20. Filamentous Thallus : It is formed when the cells are held together by the production of the middle lamellae after multiple transverse divisions. Such cases develop when a unicell divides several times in a single plane. When the cells undergo longitudinal divisions, the filament branches. Thus filamentous forms are of two types: Simple And Branched Examples: Spirogyra , Ulothrix and Oedogonium . Spirogyra filaments Ulothrix filament Apical Cell Hold Fast Oedogonium filaments Dr.Mansi Pandey 20

21. Simple filamentous type of thallus consists of a single row of cells. Spirogyra has the cells arranged from end to end in a single row or file. It is unbranched with all cells similar. In Ulotrix , the cells are arranged in a single row like Spirogyra , but it has a rhizoidal cell at the base to get it attached to the substratum. It has an apical cell too for division and growth. Oedogonium shows higher degree of division of labour. It has a rhizoidal cell for attachment, green vegetative cells for photosynthesis, cap cells for cell division, and specialized antheridia and oogonia for reproduction. Dr.Mansi Pandey 21

22. Branched filament: When a few specialized cells in a filament divide in a second plane but longitudinally, branched filament is formed. Such branches arise from the main axis as lateral outgrowths. In Cladophora , bush like thallus is formed that attaches to a substratum by rhizoidal outgrowths arising from the base of the plant body. Dr.Mansi Pandey 22

23. Foliaceous Thallus : A membranous or foliaceous plant body results if the cells of a filament divide in two planes simultaneously i.e. transversely and longitudinally e.g. Ulva . Heterotrichous filament: Heterotrichy is presence of two types of branching. The filament has a prostrate system and an erect system of branches. It is the most highly evolved type of thallus organization in green algae found in the Chaetophorales . The prostrate system creeps along the substratum and sends rhizoids to fix the thallus . From it arise the upright filaments at certain points. Dr.Mansi Pandey 23

24. In some genera, both the prostrate and the upright systems are well developed e.g. Stigeoclonium and Fritschiella . In Coloeochaete , the erect system is reduced to a few hairs. In Chaetophora , the erect system is more developed Coloeochaete Stigeoclonium   Chaetophora Dr.Mansi Pandey 24

25. In Fritschiella , the erect system consists of a lower primary projecting system and an upper secondary projecting system. In Draparnaldia , the prostrate system is reduced to the hold fast. In Draparnaldiopsis , the main branches bear short and long cells with nodes and internodes Draparnaldiopsis Dr.Mansi Pandey 25

26. Large parenchymatous thallus : If the cell divisions in the plant body do occur regularly in all the 3 planes, a bulky three dimensional parenchymatous body is formed. The sea weed Enteromorpha is a common example. Enteromorpha sp. Dr.Mansi Pandey 26

27. Zygnematales was earlier kept in Chlorophyceae as an order but now it belongs to the Zygnematophyceae of Charophyta . Sexual reproduction is by conjugation such as in Spirogyra but it represents the most species-rich algal lineage within the Streptophyta . Studies using various molecular markers have placed Charophyta as one of the crown groups in Streptophyta having a close relationship with land plants. The Charophytes (including Charales and Zygnematales ) are now kept with the Embryophytes in Streptophyta of Viridiplantae . Dr.Mansi Pandey 27