Ulothrix

Ulothrix thallus organisation, structure, sexual and asexual reproduction

1. Chlorophyceae Ulothricales Ulothricaceae ULOTHRIX

2. Occurrence Gr. oulos , woolly; thrix , hair About 30 sps Fresh water, ( U. aequalis , U. zonata ) saline ( U. flacca , U. pseudoflacca ) Lithophytes ( U. implexa ) Prefer cold water- rainy season to spring U.variabilis , U. oscillarina U. zonata , U.tennerima ,

3. Thallus Filamentous Unbranched Uniseriate Attached Basal, middle, apical cell Broader than its length Rectangular/ quadrangular/

4. Cell structure Outer pectin, inner cellulose Cytoplasm produce lining layer- primordial utricle Single nucleus, vacuole, single girdle shaped chloroplast or C- shaped, collar-shaped or ring-shaped . One (U. rorida ) or more ( U. zonata ) pyrinoids

5. VEGETATIVE Fragmentation Akinate U. idiospora Asexual zoospores, Akinetes Hypnospore and palmella stage.

6. Types of zoospore The protoplast either develops into single zoospore ( U. fimbriata ) or undergoes division and form 2, 4, 8, 16 or 32 units. Each unit contains single nucleus and cytoplasm i . Quadriflagellate macrozoospores - usually 4 per cell, ii. Quadriflagellate microzoospores - usually 8 per cell, and iii. Biflagellate micro- zoospores- usually 16-32 per cell.

7. Cell contents get enriched with food Two division- right angles Inner wall of cell develops into vesicle Macrozoospore swim in vesicle for some time. Spore releases after vesicle dissolved swim for few to 24 hours Each spore has Band like chloroplast Pyrinoid Anterior stigma Pointed posterior end Anterior flagella Macrozoospore

8. Protoplast divides and produce 8,16 or 32 cells can swim for 2-6 days Each spore has Chloroplast Pyrinoids Stigma Pointed anterior end and round posterior Quadri or biflagellate Microzoospore

9. APLANOSPORE With the sudden change of environment towards unfavourable condition during zoospore formation the protoplast units do not form flagella and remain inside the mother cell as non-motile units. These unicellular; uni­nucleate , thin walled non-motile units are called aplanospores During favourable condition they germinate after or before liberation from parent cell.

10. Hypnospores During drought, some­times the entire protoplast of a cell may round up and forms a single thick walled structure, the hypnospore . During favourable condition it ger­minates and develops into a new filament.

11. AKINATES During extreme unfavourable condition Cell becomes enlarged, protoplast accumulates food material. Forms thick wall around itself. This thick walled resting vegetative cell is called akinetes It is found in U. zonata , U.acrorhiza , U. oscillarina etc.

12. PALMELLA STAGE Forms during drier condition Protoplasts divides and produce many aplanospores The wall of the aplanospore mother cell becomes mucilaginous. Consequently the wall of aplanospores also gets enveloped by mucilaginous substance. These coverings protect the aplanospores against desiccation. In this way -many green round bodies become enclosed in a mucilaginous mass, called palmella stage. During favourable condition these green bodies come out by the dissolution of the mucilage covering and germinate into new plants.

13. Sexual reproduction Isogamy During End of the season Heterothallic Homothallic (U. rorida ) Gametangium - zoogamete = microzoospore Number of gametes may be 8, 16, 32 or 64.  Gametes are morphologically similar, they are physiologically different and designated as + and – strains. Zygote spindle shaped. Round off Resting period 5-8 months Meiosis – 4 meiospore (2+ and 2-) Parthenogenesis- parthenospore - azygospore

14. LIFE CYCLE ?