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

6. VEGETATIVE
• Fragmentation
• Akinate
• U. idiospora
ASEXUAL
 zoospores,
Akinetes
Hypnospore
and palmella stage.

7. 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.

8. • 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

9. • 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

12. 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.

13. 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.

14. 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.

15. 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.

17. 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

19. LIFE CYCLE ?